Ten years of research on synergisms and antagonisms in chemical mixtures: A systematic review and quantitative reappraisal of mixture studies

Machine learning-derived dose-response relationships considering interactions in mixtures: Applications to the oxidative potential of particulate matter

Conventional environmental health research is primarily focused on isolated chemical exposures, neglecting the complex interactions between multiple pollutants that may synergistically or antagonistically influence toxicity, thereby posing unexpected health risks. In this study, we address this knowledge gap by introducing an explainable machine learning (ML) approach with Feature Localized Intercept Transformed-Shapley Additive Explanations (FLIT-SHAP) designed to extract the dose-response relationships of specific pollutants in mixtures. In contrast to traditional SHAP, FLIT-SHAP can localize the global intercept to elucidate mixture effects, which is crucial for understanding the oxidative potential (OP) of ambient particulate matter (PM). Assessing multi-pollutant OP using FLIT-SHAP revealed both synergistic (55-63 %) and antagonistic (25-42 %) effects in laboratory-controlled OP data, but an antagonistic (33-66 %; lower OP) effect in ambient PM. Notably, the FLIT-SHAP approach demonstrated higher prediction accuracy (R2 = 0.99) compared to the additive model (R2 = 0.89) when evaluated against real-world PM samples. Quinones, such as phenanthrenequinone, play a more significant role in PM2.5 than previously recognized. Through this study, we highlighted the potential of FLIT-SHAP to enhance toxicity predictions and aid decision-making in the field of environmental health.

Toxicity of individual and mixture of organic compounds to P. Phosphoreum and S. Capricornutum using interpretable simple structural parameters

Human and environmental ecosystem beings are exposed to multicomponent compound mixtures but the toxicity nature of compound mixtures is not alike to the individual chemicals. This work introduces four models for the prediction of the negative logarithm of median effective concentration (pEC50) of individual chemicals to marine bacteria Photobacterium Phosphoreum (P. Phosphoreum) and algal test species Selenastrum Capricornutum (S. Capricornutum) as well as their mixtures to P. Phosphoreum, and S. Capricornutum. These models provide the simplest approaches for the forecast of pEC50 of some classes of organic compounds from their interpretable structural parameters. Due to the lack of adequate toxicity data for chemical mixtures, the largest available experimental data of individual chemicals (55 data) and their mixtures (99 data) are used to derive the new correlations. The models of individual chemicals are based on two simple structural parameters but chemical mixture models require further interaction terms. The new model's results are compared with the outputs of the best accessible quantitative structure-activity relationships (QSARs) models. Various statistical parameters are done on the new and comparative complex QSAR models, which confirm the higher reliability and simplicity of the new correlations.

Retinal toxicity of heavy metals and its involvement in retinal pathology

The objective of the present review is to discuss epidemiological evidence demonstrating the association between toxic metal (Cd, Pb, Hg, As, Sn, Ti, Tl) exposure and retinal pathology, along with the potential underlying molecular mechanisms. Epidemiological studies demonstrate that Cd, and to a lesser extent Pb exposure, are associated with age-related macular degeneration (AMD), while the existing evidence on the levels of these metals in patients with diabetic retinopathy is scarce. Epidemiological data on the association between other toxic metals and metalloids including mercury (Hg) and arsenic (As), are limited. Clinical reports and laboratory in vivo studies have shown structural alterations in different layers of retina following metal exposure. Examination of retina samples demonstrate that toxic metals can accumulate in the retina, and the rate of accumulation appears to increase with age. Experimental studies in vivo and in vitro studies in APRE-19 and D407 cells demonstrate that toxic metal exposure may cause retinal damage through oxidative stress, apoptosis, DNA damage, mitochondrial dysfunction, endoplasmic reticulum stress, impaired retinogenesis, and retinal inflammation. However, further epidemiological as well as laboratory studies are required for understanding the underlying molecular mechanisms and identifying of the potential therapeutic targets and estimation of the dose-response effects.

Antagonistic effects of a COX1/2 inhibitor drug in human HepG2 cells exposed to an environmental carcinogen

Understanding interactions between legacy and emerging environmental contaminants has important implications for risk assessment, especially when mutagens and carcinogens are involved, whose critical effects are chronic and therefore difficult to predict. The current work aimed to investigate potential interactions between benzo[a]pyrene (B[a]P), a carcinogenic polycyclic aromatic hydrocarbon and legacy pollutant, and diclofenac (DFC), a non-steroidal anti-inflammatory drug and pollutant of emerging concern, and how DFC affects B[a]P toxicity. Exposure to binary mixtures of these chemicals resulted in substantially reduced cytotoxicity in human HepG2 cells compared to single-chemical exposures. Significant antagonistic effects were observed in response to high concentrations of B[a]P in combination with DFC at IC50 and ⅕ IC50. While additive effects were found for levels of intracellular reactive oxygen species, antagonistic mixture effects were observed for genotoxicity. B[a]P induced DNA strand breaks, γH2AX activation, and micronuclei formation at ½ IC50 concentrations or lower, whereas DFC induced only low levels of DNA strand breaks. Their mixture caused significantly lower levels of genotoxicity by all three endpoints compared to those expected based on concentration additivity. In addition, antagonistic mixture effects on CYP1 enzyme activity suggested that the observed reduced genotoxicity of B[a]P was due to its reduced metabolic activation as a result of enzymatic inhibition by DFC. Overall, the findings further support the growing concern that co-exposure to environmental toxicants and their non-additive interactions may be a confounding factor that should not be neglected in environmental and human health risk assessment.

Towards a more effective REACH legislation in protecting human health

There is growing evidence indicating the substantial contribution of man-made products to an increase in the risk of diseases of civilization. In this article, the Belgian Scientific Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) Committee gives a critical view on the working of REACH. The current regulatory framework needs to further evolve taking into account data generated using modern science and technology. There is a need for improved assessment process not only before but also after entering the market. Objectivity, transparency, and the follow-up after market access can be optimized. Additionally, no guidance documents exist for regulation of mixture effects. Further, the lengthiness before regulatory action is a big concern. Decision-making often takes several years leading to uncertainties for both producers and end users. A first proposed improvement is the implementation of independent toxicity testing, to assure objectivity, transparency, and check and improve compliance. A "no data, no market" principle could prevent access of hazardous chemicals to the market. Additionally, the introduction of novel testing could improve information on endpoints such as endocrine disrupting abilities, neurotoxicity, and immunotoxicity. An adapted regulatory framework that integrates data from different sources and comparing the outputs with estimates of exposure is required. Fast toxicology battery testing and toxicokinetic testing could improve speed of decision-making. Hereby, several improvements have been proposed that could improve the current REACH legislation.

Time-dependent hormesis transfer from five high-frequency personal care product components to mixtures

There is potential for personal care products (PCPs) components and mixtures to induce hormesis. How hormesis is related to time and transmitted from components to mixtures are not clear. In this paper, we conducted determination of components in 16 PCP products and then ran frequent itemset mining on the component data. Five high-frequency components (HFCs), betaine (BET), 1,3-butanediol (BUT), ethylenediaminetetraacetic acid disodium salt (EDTA), glycerol (GLO), and phenoxyethanol (POE), and 14 mixtures were identified. For each mixture system, one mixture ray with the actual mixture ratios in the products was selected. Time-dependent microplate toxicity analysis was used to test the luminescence inhibition toxicity of five HFCs and 14 mixture rays to Vibrio qinghaiensis sp.-Q67 at 12 concentration gradients and eight exposure times. It is showed that BET, EDTA, POE, and 13 mixture rays containing at least one J-type component showed time-dependent hormesis. Characteristic parameters used to describe hormesis revealed that the absolute value of the maximum stimulatory effect (|Emin|) generally increased with time. Notably, mixtures composed of POE and S-type components showed greater |Emin| than POE alone at the same time. Importantly, the maximum stimulatory effective concentration, NOEC/the zero effective concentration point, and EC50 remained relatively stable. Nine hormesis transmission phenomena were observed in different mixture rays. While all mixtures primarily exhibited additive action, varying degrees of synergism and antagonism were noted in binary mixtures, with no strong synergism or antagonism observed in ternary and quaternary mixtures. These findings offer valuable insights for the screening of HFCs and their mixtures, as well as the study of hormesis transmission in personal care products.

Association of Combined PFOA, PFOS, Metals and Allostatic Load on Hepatic Disease Risk

This study utilizes the National Health and Nutrition Examination Survey (NHANES) 2017-2018 data to explore the relationship between exposure to perfluoroalkyl substances (specifically perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS), metals lead (Pb), mercury (Hg), and cadmium (Cd), allostatic load, and hepatic disease markers, including the fatty liver index a measure of the likelihood of non-alcoholic fatty liver disease, aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), and total bilirubin. The paper identified significant associations and interaction effects by employing descriptive statistics, Spearman's correlation analysis, linear regression, and Bayesian kernel machine regression (BKMR). Descriptive statistics highlight sex-specific differences in contaminant levels. Spearman's analysis underscores strong correlations among metals and per- and polyfluoroalkyl substances (PFAS). Linear regression reveals significant impacts of specific contaminants on AST, ALT, ALP, and bilirubin levels, adjusting for age and alcohol consumption. BKMR results further elucidate the complex, potentially synergistic relationships between these environmental exposures and the likelihood of non-alcoholic fatty liver disease, offering nuanced insights into their combined effects on liver health. The findings emphasize the intricate dynamics of environmental exposures on hepatic function, advocating for targeted public health interventions.

Transcriptome analyses in juvenile yellow perch (Perca flavescens) exposed in vivo to clothianidin and chlorantraniliprole: Possible sampling bias

The St. Lawrence River is an important North American waterway that is subject to anthropogenic pressures including intensive urbanization, and agricultural development. Pesticides are widely used for agricultural activities in fields surrounding the yellow perch (Perca flavescens) habitat in Lake St. Pierre (Quebec, Canada), a fluvial lake of the river where the perch population has collapsed. Clothianidin and chlorantraniliprole were two of the most detected insecticides in surface waters near perch spawning areas. The objectives of the present study were to evaluate the transcriptional and biochemical effects of these two pesticides on juvenile yellow perch exposed for 28d to environmental doses of each compound alone and in a mixture under laboratory/aquaria conditions. Hepatic mRNA-sequencing revealed an effect of chlorantraniliprole alone (37 genes) and combined with clothianidin (251 genes), but no effects of clothianidin alone were observed in perch. Dysregulated genes were mostly related to circadian rhythms and to Ca2+ signaling, the latter effect has been previously associated with chlorantraniliprole mode of action in insects. Moreover, chronic exposure to clothianidin increased the activity of acetylcholinesterase in the brain of exposed fish, suggesting a potential non-target effect of this insecticide. Further analyses of three clock genes by qRT-PCR suggested that part of the observed effects of chlorantraniliprole on the circadian gene regulation of juvenile perch could be the result of time-of-day of sacrifice. These results provide insight into biological effects of insecticides in juvenile perch and highlight the importance of considering the circadian rhythm in experimental design and results analyses.

Spatial distributions and temporal trends (2009-2020) of chemical mixtures in streams and rivers across Lombardy region (Italy)

Chemical mixtures in the environment are of increasing concern in the scientific community and regulators. Indeed, evidence indicates that aquatic wildlife and humans can be simultaneously and successively exposed to multiple chemicals mainly originating from different anthropic sources by direct uptake from water and indirectly via eating aquatic organisms. This study analyses a large set of sampling data referring to the entire Lombardy region, the most industrialised and at the same time the most important agriculture area in Italy, investigating the presence and potential effects of chemical mixtures in surface water bodies. We enriched and further developed an approach based on a previous work, where the overall mixture toxicity was evaluated for three representative aquatic organisms (algae, Daphnia, fish) using the concentration addition model to combine exposure with ecotoxicological data. The calculation of the mixture toxicity has been realised for two scenarios, namely best- and worst-case scenarios. The former considered only quantified compounds in the monitoring campaign, while the latter also included substances with concentrations below the limit of quantification (LoQ). Differences between the two scenario results established the potential toxicity range. Our findings revealed that differences were minimal when the calculated toxicity in the best-case scenario indicated potential risk and, on the contrary, they suggest that the worst-case scenario is overly conservative; we could also state that including substances with concentrations below the LoQ when calculating the overall toxicity of the mixture is useless and then we focused solely on the best-case scenario. The analysis of spatial and temporal risk trends together with contaminant types and target organisms highlighted specific clusters of contamination. Finally, in several cases, our study found that only few compounds were responsible for the majority of mixture toxicity.

Modeling mixtures interactions in environmental toxicology

In the environment, organisms are exposed to mixtures of different toxicants, which may interact in ways that are difficult to predict when only considering each component individually. Adapting and expanding tools from pharmacology, the toxicology field uses analytical, graphical, and computational methods to identify and quantify interactions in multi-component mixtures. The two general frameworks are concentration addition, where components have similar modes of action and their effects sum together, or independent action, where components have dissimilar modes of action and do not interact. Other interaction behaviors include synergism and antagonism, where the combined effects are more or less than the additive sum of individual effects. This review covers foundational theory, methods, an in-depth survey of original research from the past 20 years, current trends, and future directions. As humans and ecosystems are exposed to increasingly complex mixtures of environmental contaminants, analyzing mixtures interactions will continue to become a more critical aspect of toxicological research.

Advantages of model averaging of species sensitivity distributions used for regulating produced water discharges

Produced water (PW) generated by Australian offshore oil and gas activities is typically discharged to the ocean after treatment. These complex mixtures of organic and inorganic compounds can pose significant environmental risk to receiving waters, if not managed appropriately. Oil and gas operators in Australia are required to demonstrate that environmental impacts of their activity are managed to levels that are as low as reasonably practicable, for example, through risk assessments comparing predicted no-effect concentrations (PNECs) with predicted environmental concentrations of PW. Probabilistic species sensitivity distribution (SSD) approaches are increasingly being used to derive PW PNECs and subsequently calculating dilutions of PW (termed "safe" dilutions) required to protect a nominated percentage of species in the receiving environment (e.g., 95% and 99% or PC95 and PC99, respectively). Limitations associated with SSDs include fitting a single model to small (six to eight species) data sets, resulting in large uncertainty (very wide 95% confidence limits) in the region associated with PC99 and PC95 results. Recent advances in SSD methodology, in the form of model averaging, claim to overcome some of these limitations by applying the average model fit of multiple models to a data set. We assessed the advantages and limitations of four different SSD software packages for determining PNECs for five PWs from a gas and condensate platform off the North West Shelf of Australia. Model averaging reduced occurrences of extreme uncertainty around PC95 and PC99 values compared with single model fitting and was less prone to the derivation of overly conservative PC99 and PC95 values that resulted from lack of fit to single models. Our results support the use of model averaging for improved robustness in derived PNEC and subsequent "safe" dilution values for PW discharge management and risk assessment. In addition, we present and discuss the toxicity of PW considering the paucity of such information in peer-reviewed literature. Integr Environ Assess Manag 2024;20:498-517. © 2023 Commonwealth Scientific and Industrial Research Organisation. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Environmental Risks of Pharmaceutical Mixtures in Aquatic Ecosystems: Reflections on a Decade of Research

Pharmaceuticals and personal care products (PPCPs) occur as variable mixtures in surface waters receiving discharges of human and animal wastes. A key question identified a decade ago is how to assess the effects of long-term exposures of these PPCP mixtures on nontarget organisms. We review the recent progress made on assessing the aquatic ecotoxicity of PPCP mixtures-with a focus on active pharmaceutical ingredients-and the challenges and research needs that remain. New knowledge has arisen from the use of whole-mixture testing combined with component-based approaches, and these studies show that mixtures often result in responses that meet the concentration addition model. However, such studies have mainly been done on individual species over shorter time periods, and longer-term, multispecies assessments remain limited. The recent use of targeted and nontargeted gene analyses has improved our understanding of the diverse pathways that are impacted, and there are promising new "read-across" methods that use mammalian data to predict toxicity in wildlife. Risk assessments remain challenging given the paucity of ecotoxicological and exposure data on PPCP mixtures. As such, the assessment of PPCP mixtures in aquatic environments should remain a priority given the potential for additive-as well as nontarget-effects in nontarget organisms. In addition, we need to improve our understanding of which species, life stages, and relevant endpoints are most sensitive to which types of PPCP mixtures and to expand our knowledge of environmental PPCP levels in regions of the globe that have been poorly studied to date. We recommend an increased use of new approach methodologies, in particular "omics," to advance our understanding of the molecular mechanics of mixture effects. Finally, we call for systematic research on the role of PPCP mixtures in the development of antimicrobial resistance. Environ Toxicol Chem 2024;43:549-558. © 2023 SETAC.

In Vitro Toxicity Screening of Fifty Complex Mixtures in HepG2 Cells

To develop the risk prediction technology for mixture toxicity, a reliable and extensive dataset of experimental results is required. However, most published literature only provides data on combinations containing two or three substances, resulting in a limited dataset for predicting the toxicity of complex mixtures. Complex mixtures may have different mode of actions (MoAs) due to their varied composition, posing difficulty in the prediction using conventional toxicity prediction models, such as the concentration addition (CA) and independent action (IA) models. The aim of this study was to generate an experimental dataset comprising complex mixtures. To identify the target complex mixtures, we referred to the findings of the HBM4EU project. We identified three groups of seven to ten components that were commonly detected together in human bodies, namely environmental phenols, perfluorinated compounds, and heavy metal compounds, assuming these chemicals to have different MoAs. In addition, a separate mixture was added consisting of seven organophosphate flame retardants (OPFRs), which may have similar chemical structures. All target substances were tested for cytotoxicity using HepG2 cell lines, and subsequently 50 different complex mixtures were randomly generated with equitoxic mixtures of EC10 levels. To determine the interaction effect, we calculated the model deviation ratio (MDR) by comparing the observed EC10 with the predicted EC10 from the CA model, then categorized three types of interactions: antagonism, additivity, and synergism. Dose-response curves and EC values were calculated for all complex mixtures. Out of 50 mixtures, none demonstrated synergism, while six mixtures exhibited an antagonistic effect. The remaining mixtures exhibited additivity with MDRs ranging from 0.50 to 1.34. Our experimental data have been formatted to and constructed for the database. They will be utilized for further research aimed at developing the combined CA/IA approaches to support mixture risk assessment.

Total Effective Xenoestrogen Burden in Serum Samples and Risk of Endometrial Cancer in the Spanish Screenwide Case-Control Study

BACKGROUND

Endometrial cancer is a hormone-dependent cancer, and estrogens play a relevant role in its etiology. However, little is known about the effects of environmental pollutants that act as xenoestrogens or that influence estrogenic activity through different pathways.

OBJECTIVE

We aimed to assess the relationship between the combined estrogenic activity of mixtures of xenoestrogens present in serum samples and the risk of endometrial cancer in the Screenwide case-control study.

METHODS

The total effective xenoestrogen burden (TEXB) attributable to organohalogenated compounds (TEXB- α ) and to endogenous hormones and more polar xenoestrogens (TEXB- β ) was assessed in serum from 156 patients with endometrial cancer (cases) and 150 controls by combining chemical extraction and separation by high-performance liquid chromatography with the E-SCREEN bioassay for estrogenicity.

RESULTS

Median TEXB- α and TEXB- β levels for cases (0.30 and 1.25  Eeq pM / mL , respectively) and controls (0.42 and 1.28  Eeq pM / mL , respectively) did not significantly differ (p = 0.653 and 0.933, respectively). An inverted-U risk trend across serum TEXB- α and TEXB- β levels was observed in multivariate adjusted models: Positive associations were observed for the second category of exposure in comparison to the lowest category of exposure [odds ratio  ( OR ) = 2.11 (95% CI: 1.13, 3.94) for TEXB- α , and OR = 3.32 (95% CI: 1.62, 6.81) for TEXB- β ], whereas no significant associations were observed between the third category of exposure and the first [OR = 1.22 (95% CI: 0.64, 2.31) for TEXB- α , and OR = 1.58 (95% CI: 0.75, 3.33) for TEXB- β ]. In mutually adjusted models for TEXB- α and TEXB- β levels, the association of TEXB- α with endometrial cancer risk was attenuated [OR = 1.45 (95% CI: 0.61, 3.47) for the second category of exposure], as well as estimates for TEXB- β (OR = 2.68 ; 95% CI: 1.03, 6.99). Most of the individual halogenated contaminants showed no associations with both TEXB and endometrial cancer.

CONCLUSIONS

We evaluated serum total xenoestrogen burden in relation to endometrial cancer risk and found an inverted-U risk trend across increasing categories of exposure. The use of in vitro bioassays with human samples may lead to a paradigm shift in the way we understand the negative impact of chemical mixtures on human health effects. These results are relevant from a public health perspective and for decision-makers in charge of controlling the production and distribution of chemicals with xenoestrogenic activity. https://doi.org/10.1289/EHP13202.

Comparative deterministic and probabilistic approaches for assessing the aquatic ecological risk of pesticides in a mixed land use basin: A case study in Uruguay

Environmental concentrations of 25 pesticides in superficial water were employed to conduct an ecological risk assessment (ERA) in a mixed land-use basin utilized as a drinking water source. A deterministic risk assessment (RQ) was utilized to evaluate the chronic risk to aquatic biota, while a probabilistic risk assessment (PRA) approach was applied to assess the acute and chronic risk in the most sensitive species and at the community level. A high risk was identified for insecticides (pyrethroids, organophosphates and organochlorines). RQs ranged from 4.0e-4 (2,4-D) to 105.3 (ethion) considering median concentrations and from 8.0e-4 (2,4-D) to 230 (p,p'-DDT) considering extreme concentrations. Temporal variation in ΣRQs showed the highest risk during spring and summer months, which is related to the crop calendar and land use in the Laguna del Cisne basin. For PRA, the probability of exceeding the hazardous concentration HC5 (5th percentile) was higher for the most sensitive species in chronic exposure, especially for cypermethrin (38.9 %), permethrin (25.6 %), and chlorpyrifos (16.6 %). In the case of acute exposures, the probability of surpassing HC5 was higher for the entire freshwater biota, with the highest values observed for bifenthrin (28.3 %), cypermethrin (25.5 %), permethrin (11.75 %), and ethion (11.1 %). The advantages and disadvantages of PRA for assessing pesticide ecological risk were compared with the conventional deterministic RQs approach, highlighting that PRA offers improvements over the deterministic risk assessment, especially for organophosphate pesticides. Additionally, PRA provides a more comprehensive evaluation of risk for both short and long-term exposure, has the potential to incorporate others available toxicity data (e.g., LD50, Daily Intake), and utilizes different hazardous concentrations, such as HC5, HC10, and HC50. Our findings emphasize the urgent need to establish a national regulatory framework to evaluate and mitigate pesticide risks in aquatic ecosystems, especially in drinking water source like Laguna del Cisne.

Ancestors' Gift: Parental Early Exposure to the Environmentally Realistic Pesticide Mixture Drives Offspring Phenotype in a Larger Extent Than Direct Exposure in the Pacific Oyster, Crassostrea gigas

Marine organisms are threatened by the presence of pesticides in coastal waters. Among them, the Pacific oyster is one of the most studied invertebrates in marine ecotoxicology where numerous studies highlighted the multiscale impacts of pesticides. In the past few years, a growing body of literature has reported the epigenetic outcomes of xenobiotics. Because DNA methylation is an epigenetic mark implicated in organism development and is meiotically heritable, it raises the question of the multigenerational implications of xenobiotic-induced epigenetic alterations. Therefore, we performed a multigenerational exposure to an environmentally relevant mixture of 18 pesticides (nominal sum concentration: 2.85 μg·L-1) during embryo-larval stages (0-48 hpf) of a second generation (F1) for which parents where already exposed or not in F0. Gene expression, DNA methylation, and physiological end points were assessed throughout the life cycle of individuals. Overall, the multigenerational effect has a greater influence on the phenotype than the exposure itself. Thus, multigenerational phenotypic effects were observed: individuals descending from exposed parents exhibited lower epinephrine-induced metamorphosis and field survival rates. At the molecular level, RNA-seq and Methyl-seq data analyses performed in gastrula embryos and metamorphosis-competent pediveliger (MCP) larvae revealed a clear F0 treatment-dependent discrimination. Some genes implicated into shell secretion and immunity exhibited F1:F0 treatment interaction patterns (e.g., Calm and Myd88). Those results suggest that low chronic environmental pesticide contamination can alter organisms beyond the individual scale level and have long-term adaptive implications.

Disruption of the thyroid hormone system and patterns of altered thyroid hormones after gestational chemical exposures in rodents - a systematic review

We present a comprehensive overview of changes in thyroxine (T4) and thyroid stimulating hormone (TSH) serum concentrations after pre-gestational, gestational and/or lactation exposures of rodents to various chemicals that affect the thyroid hormone system. We show that T4 and TSH changes consistent with the idealized view of the hypothalamic-pituitary-thyroid (HPT) feedback loop (T4 decrements accompanied by TSH increases) are observed with only a relatively small set of chemicals. Most substances affect concentrations of various thyroid hormones without increasing TSH. Studies of altered T4 concentrations after gestational exposures are limited to a relatively small set of chemicals in which pesticides, pharmaceuticals and industrial chemicals are under-represented. Our risk-of-bias analysis exposed deficits in T4/TSH analytics as a problem area. By relating patterns of T4 - TSH changes to mode-of-action (MOA) information, we found that chemicals capable of disrupting the HPT feedback frequently affected thyroid hormone synthesis, while substances that produced T4 serum decrements without accompanying TSH increases lacked this ability, but often induced liver enzyme systems responsible for the elimination of TH by glucuronidation. Importantly, a multitude of MOA leads to decrements of serum T4. The current EU approaches for identifying thyroid hormone system-disrupting chemicals, with their reliance on altered TH serum levels as indicators of a hormonal mode of action and thyroid histopathological changes as indicators of adversity, will miss chemicals that produce T4/T3 serum decreases without accompanying TSH increases. This is of concern as it may lead to a disregard for chemicals that produce developmental neurotoxicity by disrupting adequate T4/T3 supply to the brain, but without increasing TSH.

Harm from Residential Indoor Air Contaminants

This study presents a health-centered approach to quantify and compare the chronic harm caused by indoor air contaminants using disability-adjusted life-year (DALY). The aim is to understand the chronic harm caused by airborne contaminants in dwellings and identify the most harmful. Epidemiological and toxicological evidence of population morbidity and mortality is used to determine harm intensities, a metric of chronic harm per unit of contaminant concentration. Uncertainty is evaluated in the concentrations of 45 indoor air contaminants commonly found in dwellings. Chronic harm is estimated from the harm intensities and the concentrations. The most harmful contaminants in dwellings are PM2.5, PM10-2.5, NO2, formaldehyde, radon, and O3, accounting for over 99% of total median harm of 2200 DALYs/105 person/year. The chronic harm caused by all airborne contaminants in dwellings accounts for 7% of the total global burden from all diseases.

A novel mixture sampling strategy combining latin hypercube sampling with optimized one factor at a time method: A case study on mixtures of antibiotics and pesticides

Global sensitivity analysis in conjunction with quantitative high-throughput screening presents a novel technique for identifying the key components that induce the toxicities of mixtures. However, the mixtures currently designed with this method suffer from unequal frequency sampling, repeated mixtures, and only odd factor levels being considered. Accordingly, we use latin hypercube sampling to generate the starting points of the trajectories to achieve equal frequency sampling and non-repeated mixtures, as well as apply different one factor at a time methods for factors with odd and even levels to achieve suitability for factors with both odd and even levels. This method is called LHS-OAT. LHS-OAT was successfully applied to design 110 equal-frequency and non-repeated mixtures consisting of six antibiotics and four pesticides. It was found that four factors, roxithromycin (A5), tetracycline (A6), dichlorvos (P1), and demeton-S (P3), induce the toxicities of mixtures, and A5 and P1 in the Shaying River Basin have risk quotients ≥ 1. Additionally, we developed the toxicity deviation ratio to correct the risk quotients of interacting mixtures for effective risk assessments. This study provides a rational and effective method for mixture design that accurately identifies the important factors that induce the toxicities of mixtures.

Exploring the association between two groups of metals with potentially opposing renal effects and renal function in middle-aged and older adults: Evidence from an explainable machine learning method

BACKGROUND

Machine learning models have promising applications in capturing the complex relationship between mixtures of exposures and outcomes.

OBJECTIVE

Our study aimed at introducing an explainable machine learning (EML) model to assess the association between metal mixtures with potentially opposing renal effects and renal function in middle-aged and older adults.

METHODS

This study extracted data from two cycle years of the National Health and Nutrition Examination Survey (NHANES). Participants aged 45 years or older with complete data on six metals (lead, cadmium, manganese, mercury, and selenium) and related covariates were enrolled. The EML model was developed by the optimized machine learning model together with Shapley Additive exPlanations (SHAP) to assess the chronic kidney disease (CKD) risk with metal mixtures. The results from EML were further compared in detail with multiple logistic regression (MLR) and Bayesian kernel machine regression (BKMR).

RESULTS

After adjusting for included covariates, MLR pointed out the lead and arsenic were generally positively associated with CKD, but manganese had a negative association. In the BKMR analysis, each metal was found to have a non-linear association with the risk of CKD, and interactions can exist between metals, especially for arsenic and lead. The EML ranked the feature importance: lead, manganese, arsenic and selenium were close behind in importance after gender, age or BMI for participants with CKD. Strong interactions between mercury and lead, manganese and cadmium and arsenic and manganese were identified by partial dependence plot (PDP) of SHAP and bivariate exposure-response effect plots of BKMR. The EML model determined the "trigger point" at which the risk of CKD abruptly changed.

CONCLUSION

Co-exposure to metals with different nephrotoxicity could have different joint association with renal function, and EML can be a powerful method for studying complex exposure mixtures.

Dose Addition Models Accurately Predict the Subacute Effects of a Mixture of Perfluorooctane Sulfonate and Perfluorooctanoic Acid on Japanese Quail (Coturnix japonica) Chick Mortality

Biomonitoring data have consistently demonstrated that fish, wildlife, and humans are exposed to multiple per- and polyfluoroalkyl substances (PFAS) in drinking water and foods. Despite ubiquitous exposure to mixtures of PFAS, there is a lack of in vivo PFAS mixture research that addresses whether these chemicals act in a cumulative, dose-additive (DA) manner or whether they behave independently. For this reason, there is a critical need for mixtures studies designed to evaluate the cumulative toxicity and potential chemical interactions to support the assessment of human and ecological risks and also to define appropriate regulatory actions. Our primary objective was to evaluate the previously published Japanese quail chick mortality concentration-response data for perfluorooctane sulfonate (PFOS), perfluorooctanoic acid (PFOA), and the mixture of PFOS + PFOA and to use statistical modeling to determine whether the effects of the mixtures were accurately predicted by either DA or response addition modeling. In addition, we wanted to compare different DA models to determine whether one model produced more accurate predictions than the others. Our results support the hypothesis of cumulative effects on shared endpoints from PFOA and PFOS co-exposure and DA approaches for predictive estimates of cumulative effects. Given the limited number of in vivo studies that have been executed with enough individual PFAS and PFAS mixture concentration-response data to test the hypothesis of DA for PFAS mixtures, this re-analysis of the data is an important contribution to our understanding of how PFAS mixtures act. The analysis will provide support for regulatory agencies as they begin to implement PFAS cumulative hazard assessments in higher vertebrates. Environ Toxicol Chem 2024;43:97-104. © 2023 SETAC. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Assessing organism differences in mixed metal sensitivity

Metal contamination of aquatic environments remains a major concern and has received significant attention in recent years. The present study aimed to evaluate the effects of metal mixtures of varying concentrations over time in a lake receiving runoff water from a decommissioned mine. By subjecting several organisms to this water, we aimed to identify the most susceptible species, thus enabling a comprehensive evaluation of the risk posed by different toxins to the biotic environment. We have evaluated the effects of mixed metal exposure on survival and stress gene expression in selected invertebrate and vertebrate model species. Our observations revealed differences in sensitivity among the invertebrate models Caenorhabditis elegans, Daphnia magna, Ceriodaphnia dubia, and Heterocypris incongruens, as well as in the vertebrate model Zebrafish (Danio rerio) and two cell lines; a zebrafish liver cell line (ZFL) and a human hepatocellular carcinoma cell line (HepG2). While the sensitivity shows great variation among the tested species, the expression of metallothionein was consistent with the levels of metals found in the mixed exposure media. Despite differences in acute toxicity, the universal induction of mt1/A and mt2/B genes make them important biomarkers for assessing the environmental risk of metals.

Proteomic analysis of the hepatic response to a pollutant mixture in mice. The protective action of selenium

Metals and pharmaceuticals contaminate water and food worldwide, forming mixtures where they can interact to enhance their individual toxicity. Here we use a shotgun proteomic approach to evaluate the toxicity of a pollutant mixture (PM) of metals (As, Cd, Hg) and pharmaceuticals (diclofenac, flumequine) on mice liver proteostasis. These pollutants are abundant in the environment, accumulate in the food chain, and are toxic to humans primarily through oxidative damage. Thus, we also evaluated the putative antagonistic effect of low-dose dietary supplementation with the antioxidant trace element selenium. A total of 275 proteins were affected by PM treatment. Functional analyses revealed an increased abundance of proteins involved in the integrated stress response that promotes translation, the inflammatory response, carbohydrate and lipid metabolism, and the sustained expression of the antioxidative response mediated by NRF2. As a consequence, a reductive stress situation arises in the cell that inhibits the RICTOR pathway, thus activating the early stage of autophagy, impairing xenobiotic metabolism, and potentiating lipid biosynthesis and steatosis. PM exposure-induced hepato-proteostatic alterations were significantly reduced in Se supplemented mice, suggesting that the use of this trace element as a dietary supplement may at least partially ameliorate liver damage caused by exposure to environmental mixtures.

Prediction and assessment of xenoestrogens mixture effects using the in vitro ERα-CALUX assay

Introduction: Many natural or synthetic compounds used in foods, dietary supplements, and food contact materials (FCMs) are suspected endocrine disruptors (EDs). Currently, scientific evidence to predict the impacts on biological systems of ED mixtures is lacking. In this study, three classes of substances were considered: i) phytoestrogens, ii) plant protection products (PPP) and iii) substances related to FCMs. Fourteen compounds were selected based on their potential endocrine activity and their presence in food and FCMs. Methods: These compounds were evaluated using an in vitro gene expression assay, the ERα-CALUX, to characterize their responses on the estrogen receptor alpha. Cells were exposed to fixed ratio mixtures and non-equipotent mixtures of full and partial agonists. The concentration-response curves measured for the three classes of compounds were characterized by variable geometric parameters in terms of maximum response (efficacy), sensitivity (slope) and potency (median effective concentration EC50). To account for these variations, a generic response addition (GRA) model was derived from mass action kinetics. Results: Although GRA does not allow us to clearly separate the concentration addition (CA) and independent action (IA) models, it was possible to determine in a statistically robust way whether the combined action of the chemicals in the mixture acted by interaction (synergy and antagonism) or by additive behavior. This distinction is crucial for assessing the risks associated with exposure to xenoestrogens. A benchmark dose approach was used to compare the response of phytoestrogen blends in the presence and absence of the hormone estradiol (E2). At the same time, 12 mixtures of 2-5 constituents including phytoestrogens, phthalates and PPPs in proportions close to those found in food products were tested. In 95% of cases, the response pattern observed showed a joint and independent effect of the chemicals on ER. Discussion: Overall, these results validate a risk assessment approach based on an additive effects model modulated by intrinsic toxicity factors. Here, the CA and IA approaches cannot be distinguished solely based on the shape of the concentration response curves. However, the optimized GRA model is more robust than CA when the efficacy, potency, and sensitivity of individual chemical agonists show large variations.

Biochemical and gene expression alterations due to individual exposure of atrazine, dichlorvos, and imidacloprid and their combination in zebrafish

In environmental toxicology, combined toxicity has emerged as an important concern. Atrazine (ATZ), dichlorvos (DIC), and imidacloprid (IMD) are the major pesticides, extensively used to control insect, flies, mosquitoes, and weed. Here, we investigate whether the exposure to three different types of pesticides individually and in combination for 24 h alters antioxidant enzyme responses in zebrafish (Danio rerio). Oxidative stress parameters (biochemical and mRNA expression), acetylcholinesterase (AChE) activity, and Metallothionein-II (MT-II) mRNA expression levels were measured. Present work includes toxicological assessment of individual and combined (CMD) exposure of ATZ (185.4 µM), DIC (181 µM), IMD (97.8 µ), and CMD (ATZ 92.7 µM + DIC 90.5 µM + IMD 48.9 µM), in the liver, kidney, and brain of adult zebrafish. Lipid peroxidation (LPO), glutathione (GSH) content, AChE, superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) activity along with mRNA expression of SOD, CAT, GPx, and MT-II were evaluated. Briefly, LPO, GSH content, the activity of AChE, and all antioxidant enzymes enhanced significantly in individual exposure, which was further altered in the CMD group. The mRNA expression of SOD, CAT, GPx, and MT-II in the liver and kidney showed significant down-regulation in all exposed groups. In the brain, significant upregulation in mRNA expression of SOD, CAT, GPx, and MT-II was observed in DIC and IMD groups, while ATZ and CMD showed significant downregulation except for GPx. Findings postulate that the CMD group exhibits synergistic toxic manifestation. The present study provides the baseline data on the combined toxic effects of pesticides and suggests regulating the use of pesticides.

Differences in MCF-7 response to endocrine disruptors in waste, superficial, and treated water from Southern Brazil

The aim of this study was to evaluate the effect of possible endocrine disruptors in surface and wastewater using a cell proliferation assay in an estrogen-responsive cell line (MCF-7). This study was conducted in the Sinos River (Brazil). The residual water was collected from a Pilot Treatment Plant (using Typha domingensis) and surface waters of the Luis Rau stream, the Sinos River, and the Water Treatment Station (WTS). After exposures (24-120 h), a Sulforhodamine B assay was performed to determine the proliferation rate. The higher increase in proliferation rate was observed with the Luiz Rau stream and the sewage treated by macrophytes in a flotation filter. The results from WTS water remained with a proliferation rate similar to the negative control at all times, suggesting that the conventional treatment is partially effective for the withdrawal of endocrine-disrupting agents. The study demonstrated the efficiency of the MCF-7 line in assessing endocrine disruption caused by wastewater and surface water samples. Our results indicate that conventional water treatment can partially remove the polluting load of endocrine disruptors, minimizing their environmental and public health impacts. Besides, it demonstrates the need to expand sanitary services to improve the population's quality of life.

Developmental programming: Impact of preconceptional and gestational exposure to a real-life environmental chemical mixture on maternal steroid, cytokine and oxidative stress milieus in sheep

BACKGROUND

Gestational exposure to environmental chemicals (ECs) is associated with adverse, sex-specific offspring health effects of global concern. As the maternal steroid, cytokine and oxidative stress milieus can have critical effects on pregnancy outcomes and the programming of diseases in offspring, it is important to study the impact of real-life EC exposure, i.e., chronic low levels of mixtures of ECs on these milieus. Sheep exposed to biosolids, derived from human waste, is an impactful model representing the ECs humans are exposed to in real-life. Offspring of sheep grazed on biosolids-treated pasture are characterized by reproductive and metabolic disruptions.

OBJECTIVE

To determine if biosolids exposure disrupts the maternal steroid, cytokine and oxidative stress milieus, in a fetal sex-specific manner.

METHODS

Ewes were maintained before mating and through gestation on pastures fertilized with biosolids (BTP), or inorganic fertilizer (Control). From maternal plasma collected mid-gestation, 19 steroids, 14 cytokines, 6 oxidative stress markers were quantified. Unpaired t-test and ANOVA were used to test for differences between control and BTP groups (n = 15/group) and between groups based on fetal sex, respectively. Correlation between the different markers was assessed by Spearman correlation.

RESULTS

Concentrations of the mineralocorticoids - deoxycorticosterone, corticosterone, the glucocorticoids - deoxycortisol, cortisol, cortisone, the sex steroids - androstenedione, dehydroepiandrosterone, 16-OH-progesterone and reactive oxygen metabolites were higher in the BTP ewes compared to Controls, while the proinflammatory cytokines IL-1β and IL-17A and anti-inflammatory IL-36RA were decreased in the BTP group. BTP ewes with a female fetus had lower levels of IP-10.

DISCUSSION

These findings suggest that pre-conceptional and gestational exposure to ECs in biosolids increases steroids, reactive oxygen metabolites and disrupts cytokines in maternal circulation, likely contributors to the aberrant phenotypic outcomes seen in offspring of BTP sheep - a translationally relevant precocial model.

Environmental neurology: Concepts and short history of an interdisciplinary approach to etiology, treatment and prevention

Environmental Neurology (EN), a sub-discipline of Neurology and Neurological Sciences, favors an interdisciplinary collaboration allowing a holistic approach to understanding the impact of environmental factors on the nervous system and their relationship with neurological diseases. Several examples of diseases and conditions show the large scope of subjects addressed by EN. The EN sub-discipline focuses on both individual and population issues thus joining patient care and public health, respectively. Neuropathogenesis is addressed by several major questions: How do the environment and nervous system interact? Which exogenous factors can trigger neurological disease? When, where and how do they act? What are the therapeutic implications, and how can these disorders be controlled or prevented. To answer such questions, we address the incentive for, philosophy of and methods developed by EN, which seeks to safeguard Brain Health and, thus, the quality of life.

Evaluation of mixture toxicity literature and chemical space: a data centric approach

Using the Abstract Sifter tool to analyse PubMed, we reveal published mixture related research most commonly relates to water pollutants, pesticides, environmental pollutants, insecticides, soil pollutants, and chemicals described as persistent, bioaccumulative, and toxic. Furthermore, we discern individual chemicals that also identify as priority chemicals in biomonitoring initiatives and using an ontology-based chemical classification, at the level of the chemical subclass, found these priority chemicals overlap with just 9% of the REACH chemical space.

Association between environmental cadmium exposure and increased mortality in the U.S. National Health and Nutrition Examination Survey (1999-2018)

BACKGROUND

Cadmium (Cd) is toxic to human health and increases overall mortality. In this study, we investigated the association between Cd exposure and all-cause, cardiovascular (CVD), and cancer mortality in the general population and the mediating effect of smoking on these association.

METHODS

We used data from U.S. National Health and Nutrition Examination Survey for 1999-2018. To evaluate the hazard ratio (HR) for mortality, a multiple Cox regression analysis was conducted by adjusting for age, sex, race/ethnicity, body mass index, smoking, alcohol, hypertension, diabetes, hyperlipidemia, and history of CVD and cancer. A causal mediation analysis was performed to estimate the effects of smoking.

RESULTS

Among the 31,637 subjects, 5452 (12.3%) died. Blood Cd concentrations were significantly associated with all-cause (HR 1.473, 95% confidence interval [CI] 1.403-1.546, p < 0.001), CVD (HR 1.445, 95% CI 1.344-1.554, p < 0.001), and cancer (HR 1.496, 95% CI 1.406-1.592, p < 0.001) mortality. Urinary Cd concentrations were also significantly associated with them. Using feature selection via machine learning, the importance of Cd in all-cause and cancer mortality was second only to age. The association between Cd concentrations and all-cause mortality was significant in both ever-smokers and never-smokers. The mediating effect of smoking was estimated at 32%, whereas a large proportion (68%) remained a direct effect of Cd. In a subgroup analysis of subjects with cancer history, blood Cd concentrations were significantly associated with cancer-related deaths in those with a history of breast, gastrointestinal, and skin cancers.

CONCLUSION

High Cd exposure is an important risk factor for all-cause, CVD, and cancer mortality among the general population. Cd exposure increased the risk of death even in never-smokers, and its effects unrelated to smoking were substantial, suggesting the importance of regulating other sources of Cd exposure such as food and water.

IMPACT STATEMENT

Using national large-scale data, we found that low-level environmental exposure to cadmium significantly increased the risk of all-cause, cardiovascular, and cancer mortality in the general population even after adjusting for several risk factors. Although smoking is a major source of cadmium exposure, cadmium was nevertheless significantly associated with all-cause mortality in never-smokers, and the mediating effect of smoking on this association was only 32%. Hence, other sources of cadmium exposure such as food and water may be important.

Anti-androgenic activity of novel flame retardants in mixtures: Newly identified contribution from tris(2,3-dibromopropyl) isocyanurate (TDBP-TAZTO)

In recent decades, male infertility has been on the rise, largely attributed to exposure to chemicals with endocrine-disrupting properties. The adverse effects of disrupting androgen actions on the development and reproductive health of children and adolescents have been extensively studied. Flame retardants (FRs), used in consumer products to delay flammability, have been identified as antagonists of the androgen receptor (AR), potentially leading to adverse outcomes in male reproductive health later in life. This study examined the interaction of eight novel FRs with the AR, employing an in vitro AR-dependent luciferase reporter gene assay utilizing MDA-kb2 cells. The investigation revealed the anti-androgenic activity of tris(2,3-dibromopropyl) isocyanurate (TDBP-TAZTO), a frequently detected FR in the environment. Furthermore, TDBP-TAZTO contributed to anti-androgenic activity when combined with six other anti-androgenic FRs. The mixture effects were predicted by three commonly employed models: concentration addition (CA), generalized CA, and independent action, with the CA model showcasing the highest accuracy. This suggests that all FRs act through a similar mechanism, as further confirmed by in silico molecular docking, indicating limited synergy or antagonism. Importantly, in the mixtures, each FR contributed to the induction of anti-androgenic effects at concentrations below their individual effective concentrations in single exposures. This raises concern for public health, especially considering the co-detection of these FRs and their potential co-occurrence with other anti-androgenic chemicals like bisphenols. Therefore, our findings, along with previous research, strongly support the incorporation of combined effects of mixtures in risk assessment to efficiently safeguard population health.

Bee Pollinator Mortality Due to Pesticide-Laden Particulate Matter from Beef Cattle Feedyards

Wild and managed bees are critical for the stability of trophic webs, angiosperm reproduction, and agricultural productivity. Unfortunately, as many as 40% of crop pollinators are in a steep decline due to habitat loss and exposure to agrochemicals. Pyrethroids, neonicotinoids, and macrocyclic lactones are among the many agrochemicals toxic to pollinating insects that are used extensively in industrial beef cattle feeding operations throughout the world. Fugitive feedyard particulate matter (PM) transports agrochemicals into the surrounding environs. To determine the impact of agrochemical-laden feedyard particulate matter on bee pollinators, we conducted in situ experiments wherein honeybees and mason bees were placed downwind and upwind of feedyards (N = 40). Concurrent, colocated total suspended particulate matter samples contained multiple insecticides and parasiticides including pyrethroids, neonicotinoids, and macrocyclic lactones, in significantly higher concentrations downwind of feedyards (bifenthrin, 8.45 ± 4.92; permethrin, 1032.34 ± 740.76; clothianidin, 3.61 ± 1.48; imidacloprid, 73.32 ± 47.52; thiamethoxam, 5.81 ± 3.16; abamectin, 0.45 ± 0.29; ivermectin, 8.88 ± 5.06 ng/g). Honeybees and mason bees sited downwind of feedyards always experienced higher mortality than those correspondingly sited upwind, and male mason bees experienced significantly higher mortality compared to females when both were sited downwind. Bees occurring downwind of beef cattle feedyards for 1 h are 232-260% more likely to die than those occurring upwind. Thus, agrochemicals used on and emitted from beef cattle feedyards are significant threats to bee pollinators.

Nickel and aluminium mixture elicit memory impairment by activation of oxidative stress, COX-2, and diminution of AChE, BDNF and NGF levels in cerebral cortex and hippocampus of male albino rats

This study evaluated nickel and aluminium-induced neurotoxicity, as a binary metal mixture. Twenty-eight male Sprague Dawley albino rats were weight-matched and divided into four groups. Group 1 (control) received deionized water. Group 2 and 3 received Aluminium (1 mg/kg) and Nickel (0.2 mg/kg) respectively, while Group 4 received Ni and Al mixture HMM three times a week orally for 90 days. Barnes maze tests was performed. Rats were sacrificed under pentobarbital anaesthesia, cerebral cortex and hippocampus were separated, and metal levels were measured using Atomic Absorption Spectroscopy (AAS). Malondialdehyde (MDA), catalase (CAT), glutathione content (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), Brain Derived Neurotrophic Factor (BDNF), Nerve growth factor NGF, cyclo-oxygenase COX-2 and Acetylcholinesterase (AChE) were assayed using ELISA kits. Ni/Al binary mixture exposed rats showed a shorter latency period (though not significant) of 3.21 ± 1.40 s in comparison to 3.77 ± 1.11 (Ni only) and 3.99 ± 1.16(Al only). Ni/Al mixture gp had the lowest levels of Mg in both the hippocampus and frontal cortex when compared with the individual metals. In the hippocampus Al only exposed rats significantly showed p < 0.05 higher iron and Ca levels in comparison to Ni/Al mixture. Al alone significantly showed p < 0.05 lower levels of Fe but higher Ca than the Ni/Al mixture group. Exposure to Al only showed lower levels of BDNF in comparison to Ni/Al combination, whereas Ni/Al mixture gp had lower levels of NGF in comparison to the individual metals in the hippocampus. In the frontal cortex Ni only, group showed significantly lower BDNF in comparison to Ni/Al mixture whereas the mixture showed significantly lower NGF when compared with Al only group. There were higher levels of COX-2 in the Ni/Al mixture than individual metal treated rats in both hippocampus and frontal cortex. AChE levels in the Ni/Al mixture group was higher than Ni or Al only gps in the hippocampus whereas in the frontal cortex, Ni/Al exposed rats showed significantly lower AChE levels in comparison to Al only group. Ni, Al and Ni/Al mixture exhibited memory impairment by activation of oxidative stress, COX-2, and diminution of AChE, BDNF and NGF levels in cerebral cortex and hippocampus. The BDNF-COX-2 AChE signalling pathway may be involved in the neurotoxicity of Ni and Al.

The regulation of endocrine-disrupting chemicals to minimize their impact on health

Endocrine-disrupting chemicals (EDCs) are substances generated by human industrial activities that are detrimental to human health through their effects on the endocrine system. The global societal and economic burden posed by EDCs is substantial. Poorly defined or unenforced policies can increase human exposure to EDCs, thereby contributing to human disease, disability and economic damage. Researchers have shown that policies and interventions implemented at both individual and government levels have the potential to reduce exposure to EDCs. This Review describes a set of evidence-based policy actions to manage, minimize or even eliminate the widespread use of these chemicals and better protect human health and society. A number of specific challenges exist: defining, identifying and prioritizing EDCs; considering the non-linear or non-monotonic properties of EDCs; accounting for EDC exposure effects that are latent and do not appear until later in life; and updating testing paradigms to reflect 'real-world' mixtures of chemicals and cumulative exposure. A sound strategy also requires partnering with health-care providers to integrate strategies to prevent EDC exposure in clinical care. Critical next steps include addressing EDCs within global policy frameworks by integrating EDC exposure prevention into emerging climate policy.

Environmental metabolomics uncovers oxidative stress, amino acid dysregulation, and energy impairment in Daphnia magna with exposure to industrial effluents

Anthropogenic activities are regarded as point sources of pollution entering freshwater bodies worldwide. With over 350,000 chemicals used in manufacturing, wastewater treatment and industrial effluents are comprised of complex mixtures of organic and inorganic pollutants of known and unknown origins. Consequently, their combined toxicity and mode of action are not well understood in aquatic organisms such as Daphnia magna. In this study, effluent samples from wastewater treatment and industrial sectors were used to examine molecular-level perturbations to the polar metabolic profile of D. magna. To determine if the industrial sector and/or the effluent chemistries played a role in the observed biochemical responses, Daphnia were acutely (48 h) exposed to undiluted (100%) and diluted (10, 25, and 50%) effluent samples. Endogenous metabolites were extracted from single daphnids and analyzed using targeted mass spectrometry-based metabolomics. The metabolic profile of Daphnia exposed to effluent samples resulted in significant separation compared to the unexposed controls. Linear regression analysis determined that no single pollutant detected in the effluents was significantly correlated with the responses of metabolites. Significant perturbations were uncovered across many classes of metabolites (amino acids, nucleosides, nucleotides, polyamines, and their derivatives) which serve as intermediates in keystone biochemical processes. The combined metabolic responses are consistent with oxidative stress, disruptions to energy metabolism, and protein dysregulation which were identified through biochemical pathway analysis. These results provide insight into the molecular processes driving stress responses in D. magna. Overall, we determined that the metabolic profile of Daphnia could not be predicted by the chemical composition of environmentally relevant mixtures. The findings of this study demonstrate the advantage of metabolomics in conjunction with chemical analyses to assess the interactions of industrial effluents. This work further demonstrates the ability of environmental metabolomics to characterize molecular-level perturbations in aquatic organisms exposed to complex chemical mixtures directly.

The association between urinary metals/metalloids and chronic kidney disease among general adults in Wuhan, China

The relation between exposure to single metal/metalloid and the risk of chronic kidney disease (CKD) remains unclear. We aimed to determine the single and mixed associations of 21 heavy metals/metalloids exposure and the risk of CKD. We performed a cross-sectional study that recruited 4055 participants. Multivariate logistic regression, linear regression and weighted quantile sum (WQS) regression were conducted to explore the possible effects of single and mixed metals/metalloids exposure on the risk of CKD, the risk of albuminuria and changes in the estimated glomerular filtration rate (eGFR). In single-metal models, Cu, Fe, and Zn were positively associated with increased risks of CKD (P-trend < 0.05). Compared to the lowest level, the highest quartiles of Cu (OR = 2.94; 95% CI: 1.70, 5.11; P-trend < 0.05), Fe (OR = 2.39; 95% CI: 1.42, 4.02; P-trend < 0.05), and Zn (OR = 2.35; 95% CI: 1.31, 4.24; P-trend < 0.05) were associated with an increased risk of CKD. After multi-metal adjustment, the association with the risk of CKD remained robust for Cu (P < 0.05). Weighted quantile sum regression revealed a positive association between mixed metals/metalloids and the risk of CKD, and the association was largely driven by Cu (43.7%). Specifically, the mixture of urinary metals/metalloids was positively associated with the risk of albuminuria and negatively associated with eGFR.

Multiomics reveals new biomarkers and mechanistic insights into the combined toxicity effects of 2,2',4,4',5,5'-hexachlorobiphenyl and atrazine exposures in MCF-7 cells

Humans are constantly exposed to complicated chemical mixtures from the environment and food rather than being exposed to a single pollutant. The underlying mechanisms of the complicated combined toxicity of endocrine disrupting chemicals (EDCs) are still mainly unexplored. In this study, two representative EDCs, 2,2',4,4',5,5'-hexachlorobiphenyl (PCB153) and atrazine (ATZ), were selected to explore their combined effects on MCF-7 cell proliferation at environmental exposure concentrations by an integrated analysis of metabolomics and transcriptomics. The results showed that 1 μM ATZ and PCB153 combined exposure significantly accelerated MCF-7 cell growth by 18.2%. More than 400 metabolites detected by UHPLC-QTOF/MS were used to observe metabolism differences induced by binary mixtures. Metabolomics analysis verified that ATZ and PCB153 exposure alone or in combination could have an additive effect on metabolism and induce significant disruption to glycolysis, purine metabolism and the TCA cycle, which provide energy demand and biosynthetic substrates for cell proliferation. Compared to PCB153 and ATZ exposure alone, a combined effect was observed in purine and pyrimidine metabolic pathways. Hexokinase 3 (HK3) and cytochrome P450 19 subfamily A1 (CYP19A1) were identified as differentially expressed genes based on transcriptomic analysis. By integrating metabolome and transcriptome analysis, the proliferation effects of ATZ and PCB153 were induced at low doses in MCF-7 cells through potential interference with the downstream transcription signaling of CYP19A1. Furthermore, molecular docking indicated that PCB153 and ATZ directly affected CYP19A1. Altogether, the regulation of pivotal metabolites and differentially expressed genes could provide helpful information to reveal the mechanism by which PCB153 and ATZ affect MCF-7 cell proliferation.

Toxicity of benzethonium chloride and polyhexamethylene guanidine hydrochloride mixtures on Daphnia carinata: synergistic and antagonistic effects at specific ratios

Throughout the coronavirus (COVID-19) pandemic, the sanitizing products benzethonium chloride (BEC) and polyhexamethylene guanidine hydrochloride (PHMG-H) were widely used; however, few studies have investigated their combined toxicity to organisms. In the present study, acute toxicity and genotoxicity of BEC, PHMG-H, and the combination of the two were investigated as endpoints using Daphnia carinata as the model organism. For individual reagents, PHMG-H was found to be more toxic than BEC in terms of both mortality and genotoxicity. DNA damage and survival rate were used as toxicity endpoints. The interaction was evaluated with the concentration addition (CA) model via toxic unit (TU) approach and additive index (AI) method in mixtures at different ratios in TU. Only the binary mixture BEC + PHMG-H at the ratio 1:9 in TU was regarded as synergistic, while all others indicated increased antagonistic effects as the proportion of BEC increased over the PHMG-H concentration. The findings here benefit understanding surrounding precisely how BEC and PHMG-H interact at different mixing ratios, and can assist with the evaluation of risk assessments for binary mixtures in aquatic ecosystems.

Analysis and management of herbicidal mixtures in a high-intensity agricultural landscape in Belgium

Water bodies located in anthropogenically influenced environments, such as agricultural landscapes, may be exposed to different chemicals simultaneously or sequentially. Yet, current environmental risk assessments focus on single active substances for unintended mixtures. For 3.5 years, the present study monitored the mixture of herbicides, within an intensively managed agricultural catchment, accompanied by a stewardship program. Twelve herbicides and one metabolite were monitored on a daily to sub-daily basis, generating a unique, high temporal resolution data set, enabling an assessment of cumulative exposure in a worst-case scenario. Analyses focused on the number of events at which the herbicide mixture concentration exceeded the regulatory accepted concentration for algae and macrophytes, based on concentration addition, and the potential factors influencing the frequency of these events are considered. A low number of individual herbicides drove the toxicity and only two of these overlapped for the two organism groups, algae and macrophytes. The observed exceedance events coincided with seasonal influences, and low rainfall during the 2011 season correlated with a highly reduced number of these events. The major influence was found to be the implementation of the stewardship program, which directed farmers to use more advanced farming techniques, avoid spillages, and other point sources. The number of exceedance events was reduced by more than half for algae (9% of the daily mean samples in 2010 and 4% in 2013) and by approximately 10 times for macrophytes (36% in 2010 to 3% in 2013). This high-resolution monitoring data set illustrates how knowledge of the influencing factors can help reduce unintended exposure to chemicals and achieve real-world improvements. Overall, a single-substance assessment is protective of mixture effects. Where mixture effects do play a role, local measures to manage point sources are more effective than changes to the desk-based environmental risk assessments that focus on diffuse sources. Integr Environ Assess Manag 2023;19:1297-1306. © 2022 Cambridge Environmental Assessments RSK ADAS Ltd and Bayer AG. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Chemical Mixtures and Multiple Stressors: Same but Different?

Ecosystems are strongly influenced by multiple anthropogenic stressors, including a wide range of chemicals and their mixtures. Studies on the effects of multiple stressors have largely focussed on nonchemical stressors, whereas studies on chemical mixtures have largely ignored other stressors. However, both research areas face similar challenges and require similar tools and methods to predict the joint effects of chemicals or nonchemical stressors, and frameworks to integrate multiple chemical and nonchemical stressors are missing. We provide an overview of the research paradigms, tools, and methods commonly used in multiple stressor and chemical mixture research and discuss potential domains of cross-fertilization and joint challenges. First, we compare the general paradigms of ecotoxicology and (applied) ecology to explain the historical divide. Subsequently, we compare methods and approaches for the identification of interactions, stressor characterization, and designing experiments. We suggest that both multiple stressor and chemical mixture research are too focused on interactions and would benefit from integration regarding null model selection. Stressor characterization is typically more costly for chemical mixtures. While for chemical mixtures comprehensive classification systems at suborganismal level have been developed, recent classification systems for multiple stressors account for environmental context. Both research areas suffer from rather simplified experimental designs that focus on only a limited number of stressors, chemicals, and treatments. We discuss concepts that can guide more realistic designs capturing spatiotemporal stressor dynamics. We suggest that process-based and data-driven models are particularly promising to tackle the challenge of prediction of effects of chemical mixtures and nonchemical stressors on (meta-)communities and (meta-)food webs. We propose a framework to integrate the assessment of effects for multiple stressors and chemical mixtures. Environ Toxicol Chem 2023;42:1915-1936. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Sexually dimorphic impact of preconceptional and gestational exposure to a real-life environmental chemical mixture (biosolids) on offspring growth dynamics and puberty in sheep

Humans are ubiquitously exposed to complex mixtures of environmental chemicals (ECs). This study characterised changes in post-natal and peripubertal growth, and the activation of the reproductive axis, in male and female offspring of sheep exposed to a translationally relevant EC mixture (in biosolids), during pregnancy. Birthweight in both sexes was unaffected by gestational biosolids exposure. In contrast to females (unaffected), bodyweight in biosolids males was significantly lower than controls across the peripubertal period, however, they exhibited catch-up growth eventually surpassing controls. Despite weighing less, testosterone concentrations were elevated earlier, indicative of early puberty in the biosolids males. This contrasted with females in which the mean date of puberty (first progesterone cycle) was delayed. These results demonstrate that developmental EC-mixture exposure has sexually dimorphic effects on growth, puberty and the relationship between body size and puberty. Such programmed metabolic/reproductive effects could have significant impacts on human health and wellbeing.

Xeno-estrogenic activity of real-life mixtures of perfluoroalkylated substances in human placenta homogenates

Humans are simultaneously exposed to complex chemical mixtures, and its combined effect can affect human health. As part of the HBM4EU project, the actual mixture of perfluoroalkylated substances (PFAS) in 25 human placenta samples was extracted by chromatographic methods and assessed for xeno-estrogenic activity using two in-vitro bioassays: the estrogen receptor transactivity and the E-Screen assay. Most of the PFAS extracts displayed xeno-estrogenic activity, in one or both assays. The xeno-estrogenic activities in the two bioassays were not correlated, but both assays showed an overall negative correlation with placenta concentrations of single PFAS. Xeno-estrogenic activities were significantly related to maternal characteristics; being higher in young, smokers and primiparous women, but not with fetal growth (birth weight, birth length, head circumference, gestational age, placenta weight). The presented extraction method can be used to study the combined effect of real-life mixtures of PFAS in relation to health outcomes in large-scale human biomonitoring studies.

Quantifying synergistic interactions: a meta-analysis of joint effects of chemical and parasitic stressors

The global biodiversity crisis emphasizes our need to understand how different stressors (climatic, chemical, parasitic, etc.) interact and affect biological communities. We provide a comprehensive meta-analysis investigating joint effects of chemical and parasitic stressors for 1064 chemical-parasitic combinations using the Multiplicative model on mortality of arthropods. We tested both features of the experimental setup (control mortality, stressor effect level) and the chemical mode of action, host and parasite phylogeny, and parasite-host interaction traits as explanatory factors for deviations from the reference model. Synergistic interactions, defined as higher mortality than predicted, were significantly more frequent than no interactions or antagony. Experimental setup significantly affected the results, with studies reporting high (> 10%) control mortality or using low stressor effects (< 20%) being more synergistic. Chemical mode of action played a significant role for synergy, but there was no effects of host and parasite phylogeny, or parasite-host interaction traits. The finding that experimental design played a greater role in finding synergy than biological factors, emphasize the need to standardize the design of mixed stressor studies across scientific disciplines. In addition, combinations testing more biological traits e.g. avoidance, coping, and repair processes are needed to test biology-based hypotheses for synergistic interactions.

Estrogenic potency of endocrine disrupting chemicals and their mixtures detected in environmental waters and wastewaters

Endocrine disrupting chemicals such as natural and synthetic steroid hormones and bisphenols are among the most important pollutants in the aquatic environment. We performed an environmental chemical analysis of five Slovenian water samples, two rivers, one groundwater, and the influent and effluent of wastewater treatment plants, with a highly sensitive analysis of twenty-five endocrine-disrupting compounds belonging to the groups of natural hormones, synthetic hormones, and bisphenols. Since these compounds are simultaneously present in the environment, it is important to study their individual effects as well as the effects of mixtures. We investigated in vitro the estrogenic potency of selected natural and synthetic steroid hormones and bisphenols detected in surface, ground and waste water in Slovenia using the OECD-validated transactivation assay on the cell line Hela9903. We predicted their mixture effects using the concentration addition model and compared them with experimentally determined values. Two mixing designs were used: a balanced design in which chemicals were combined in proportion to their individual EC₅₀ values, and an unbalanced design with compounds in proportion to their measured concentrations in the environmental samples. The estrogenic effects of the experimental mixtures followed the concentration addition model. Real water samples exhibited weaker estrogenic effects, showing the great heterogeneity of the real water samples.

Evaluation of perinatal exposure of glyphosate and its mixture with 2,4-D and dicamba οn liver redox status in Wistar rats

Wide-scale emergence of glyphosate-resistant weeds has led to an increase in the simultaneous application of herbicide mixtures exacerbated by the introduction of crops tolerant to glyphosate plus dicamba or glyphosate plus 2,4-D. This raises serious concerns regarding the environmental and health risks resulting from increased exposure to a mixture of herbicide active ingredients. We evaluated hepatotoxic effects following perinatal exposure to glyphosate alone or in combination with 2,4-D and dicamba from gestational day-6 until adulthood in Wistar rats. Animals were administered with glyphosate at the European Union (EU) acceptable daily intake (ADI; 0.5 mg/kg bw/day) and no-observed-adverse-effect level (NOAEL; 50 mg/kg bw/day). A mixture of glyphosate with 2,4-D (0.3 mg/kg bw/day) and dicamba (0.02 mg/kg bw/day) with each at their EU ADI was evaluated. Redox status was determined by measuring levels of reduced glutathione, decomposition rate of Η₂Ο₂, glutathione reductase, glutathione peroxidase, total antioxidant capacity, thiobarbituric reactive substances, and protein carbonyls. Gene expression analysis of Nr1d1, Nr1d2, Clec2g, Ier3, and Gadd45g associated with oxidative damage to DNA, was also performed. Analysis of liver samples showed that exposure to the mixture of the three herbicides induced a marked increase in the concentration of glutathione and malondialdehyde indicative of a disturbance in redox balance. Nevertheless, the effect of increased lipid peroxidation was not discernible following a 3-month recuperation period where animals were withdrawn from pesticide exposure post-weaning. Interestingly, toxic effects caused by prenatal exposure to the glyphosate NOAEL were present after the same 3-month recovery period. No statistically significant changes in the expression of genes linked with genotoxicity were observed. Our findings reinforce the importance of assessing the combined effects of chemical pollutants at doses that are asserted by regulatory agencies to be safe individually.

Adipogenic and endocrine disrupting mixture effects of organic and inorganic pollutant mixtures

Chronic health conditions are rapidly increasing in prevalence and cost to society worldwide: in the US, >42 % of adults aged 20 and older are currently classified as obese. Exposure to endocrine disrupting chemicals (EDCs) has been implicated as a causal factor; some EDCs, termed "obesogens", can increase weight and lipid accumulation and/or perturb metabolic homeostasis. This project aimed to assess the potential combination effects of diverse inorganic and organic contaminant mixtures, which more closely reflect environmentally realistic exposures, on nuclear receptor activation/inhibition and adipocyte differentiation. Herein, we focused on two polychlorinated biphenyls (PCB-77 and 153), two perfluoroalkyl substances (PFOA and PFOS), two brominated flame retardants (PBB-153 and BDE-47), and three inorganic contaminants (lead, arsenic, and cadmium). We examined adipogenesis using human mesenchymal stem cells and receptor bioactivities using luciferase reporter gene assays in human cell lines. We observed significantly greater effects for several receptor bioactivities by various contaminant mixtures relative to individual components. All nine contaminants promoted triglyceride accumulation and/or pre-adipocyte proliferation in human mesenchymal stem cells. Comparing simple component mixtures to individual components at 10 % and 50 % effect levels revealed putative synergistic effects for each of the mixtures for at least one of the concentrations relative to the individual component chemicals, some of which also exhibited significantly greater effects than the component contaminants. Our results support further testing of more realistic and complex contaminant mixtures that better reflect environmental exposures, in order to more conclusively define mixture responses both in vitro and in vivo.

Exposure of Swedish adolescents to elements, persistent organic pollutants (POPs), and rapidly excreted substances - The Riksmaten adolescents 2016-17 national survey

Adolescence is a period of significant physiological changes, and likely a sensitive window to chemical exposure. Few nation-wide population-based studies of chemical body burdens in adolescents have been published. In the national dietary survey Riksmaten Adolescents (RMA) 2016-17, over 13 chemical substance groups, including elements, chlorinated/brominated/fluorinated persistent organic pollutants (POPs) were analysed in blood, and in urine metabolites of phthalates/phthalate alternatives, phosphorous flame retardants, polycyclic aromatic hydrocarbons (PAHs), and pesticides, along with bisphenols and biocide/preservative/antioxidant/UV filter substances (N = 1082, ages 11-21). The aim was to characterize the body burdens in a representative population of adolescents in Sweden, and to compare results with human biomonitoring guidance values (HBM-GVs). Cluster analyses and Spearman's rank order correlations suggested that concentrations of substances with known common exposure sources and similar toxicokinetics formed obvious clusters and showed moderate to very strong correlations (r ≥ 0.4). No clusters were formed between substances from different matrices. Geometric mean (GM) concentrations of the substances were generally less than 3-fold different from those observed among adolescents in NHANES (USA 2015-16) and GerES V (Germany 2014-17). Notable exceptions were brominated diphenyl ethers (PBDEs) with >20-fold lower GM concentrations, and the biocide triclosan and ultraviolet (UV) filter benzophenone-3 with >15-fold lower mean concentrations in RMA compared to NHANES. Exceedance of the most conservative HBM-GVs were observed for aluminium (Al, 26% of subjects), perfluorooctanesulfonic acid (PFOS, 19%), perfluorooctanoic acid (PFOA, 12%), lead (Pb, 12%), MBP (dibutyl phthalate metabolite, 4.8%), hexachlorobenzene (HCB, 3.1%) and 3-phenoxybenzoic acid (PBA, pyrethroid metabolite, 2.2%). Males showed a higher proportion of exceedances than females for Pb, HCB and PFOS; otherwise no gender-related differences in exceedances were observed. A higher proportion of males than females had a Hazard Index (HI) of substances with liver and kidney toxicity and neurotoxicity >1. Industrialized countries with similarly high standards of living, with some exceptions, show comparable average body burdens of a variety of toxic chemicals among adolescents from the general population. The exceedances of HBM-GVs and HIs strongly suggests that further efforts to limit chemical exposure are warranted.

Molecular and phenotypic effects of early exposure to an environmentally relevant pesticide mixture in the Pacific oyster, Crassostrea gigas

Early life stages are crucial for organism development, especially for those displaying external fertilization, whose gametes and early stages face environmental stressors such as xenobiotics. The pacific oyster, Crassostrea gigas, is considered a model species in ecotoxicology because of its ecological characteristics (benthic, sessile, filter feeding). So far studies have investigated the impact of xenobiotics at embryotoxic, genotoxic and physiological endpoints, sometimes at the multigenerational scale, highlighting the role of epigenetic mechanisms in transmitting alterations induced by exposure to single xenobiotics. However, to date, little is known about the impact of environmentally-mimicking contaminants cocktails. Thus, we examined the impact of an early exposure to environmentally relevant mixture on the Pacific oyster life history. We studied transcriptomic, epigenetic and physiological alterations induced in oysters exposed to 18 pesticides and metals at environmental concentration (nominal sum concentration: 2.85 μg.L-1, measured sum concentration: 3.74 ± 0.013 μg.L-1) during embryo-larval stage (0-48 h post fertilization, hpf). No significant differences in embryo-larval abnormalities at 24 hpf were observed during larval and spat rearing; the swimming behaviour of exposed individuals was disturbed, while they were longer and heavier at specific time points, and exhibited a lower epinephrine-induced metamorphosis rate as well as a higher survival rate in the field. In addition, RNA-seq analyses of gastrula embryos revealed the differential expression of development-related genes (e.g. Hox orthologues and cell cycle regulators) between control and exposed oysters. Whole-genome DNA methylation analyses demonstrated a significant modification of DNA methylation in exposed larvae marked by a demethylation trend. Those findings suggest that early exposure to an environmentally relevant pesticide mixture induces multi-scale latent effects possibly affecting life history traits in the Pacific oyster.

Complex Mixtures and Multiple Stressors: Evaluating Combined Chemical Exposures and Cumulative Toxicity

The problem of chemical mixtures in the environment encompasses biological, analytical, logistical, and regulatory challenges, among others [...].