Are individual NOEC levels safe for mixtures? A study on mixture toxicity of brominated flame-retardants in the copepod Nitocra spinipes

MRA Toolbox v. 1.0: a web-based toolbox for predicting mixture toxicity of chemical substances in chemical products

The chemical risk assessment paradigm is shifting from “substance-based” to “product/mixture-based” and from “animal testing” to “alternative testing” under chemical regulations. Organisms and the environment may be exposed to mixtures rather than a single substance. Conducting toxicity tests for all possible combinations is impractical due to the enormous combinatorial complexity. This study highlights the development and application case studies of Mixture Risk Assessment Toolbox, a novel web-based platform that supports mixture risk assessment through the use of different prediction models and public databases. This integrated framework provides new functional values for assessors to easily screen and compare the toxicity of mixture products using different computational techniques and find strategic solutions to reduce the mixture toxicity in the product development process. The toolbox (https://www.mratoolbox.org) includes four additive toxicity models: two conventional (Concentration Addition; and Independent Action) and two advanced (Generalized Concentration Addition; and Quantitative Structure–Activity Relationship-based Two-Stage Prediction) models. We demonstrated the multiple functions of the toolbox using three cases: (i) how it can be used to calculate the mixture toxicity, (ii) those for which safety data sheet (SDS) only indicating representative toxicity values (EC₅₀; and LC₅₀), and (iii) those comprising chemicals with low toxic effects.

Neonicotinoid Insecticides from a Marine Perspective: Acute and Chronic Copepod Testing and Derivation of Environmental Quality Standards

Neonicotinoid insecticides have become of global concern for the aquatic environment. Harpacticoid copepods are among the organisms most sensitive to neonicotinoids. We exposed the brackish copepod Nitocra spinipes to 4 neonicotinoid insecticides (clothianidin, imidacloprid, thiacloprid, and thiamethoxam) to investigate acute toxicity on adults (96-h exposure) and effects on larval development (7-d exposure). We used these results in combination with publicly available ecotoxicity data to derive environmental quality standards (EQS). These EQS were ultimately used in a single-substance and mixture risk assessment for the Belgian part of the North Sea. Acute toxicity testing revealed that immobilization is a more sensitive endpoint than mortality, with 96-h median effect concentration (EC50) values of 6.9, 7.2, 25, and 120 µg L^-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. In addition, the larval development tests resulted in 7-d no-observed-effect concentrations (NOECs) of 2.5, 2.7, 4.2, and >99 µg L^-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. The derived saltwater annual average (AA-)EQS were 0.05, 0.0048, 0.002, and 0.016 µg L^-1 for clothianidin, thiacloprid, imidacloprid, and thiamethoxam, respectively. Finally, the risk characterization revealed some exceedances of the AA-EQS in Belgian harbors for imidacloprid (number of exceedances, n = 2/4), for thiacloprid (n = 1/4), for thiamethoxam (n = 1/4), and for the mixture of the 4 neonicotinoids (n = 4/4), but not at the open sea. At the open sea site, the toxic unit sums relative to the AA-EQS were 0.72 and 0.22, suggesting no mixture risk, albeit with a relatively small margin of safety. Including short-term EC10 (96-h) values of N. spinipes for the AA-EQS derivation led to a refinement of the AA-EQS for clothianidin and thiamethoxam, suggesting their use for the AA-EQS derivation because one of the overarching goals of the definition of EQS is to protect species at the population level. Environ Toxicol Chem 2021;40:1353-1367. © 2021 SETAC.

A review of 1,2-dibromo-4-(1,2-dibromoethyl)cyclohexane in the environment and assessment of its persistence, bioaccumulation and toxicity

Following the ban of many historically-used flame retardants (FRs), numerous replacement chemicals have been produced and used in products, with some being identified as environmental contaminants. One of these replacement flame retardants is 1,2-dibromo-4-(1,2-dibromoethyl)-cyclohexane (DBE-DBCH; formerly abbreviated as TBECH), which to date has not been identified for risk assessment and potential regulation. DBE-DBCH technical mixtures consist largely of α- and β-diastereomers with trace amounts of γ- and δ-DBE-DBCH. The α- and β-isomers are known contaminants in various environmental media. While current global use and production volumes of DBE-DBCH are unknown, recent studies identified that DBE-DBCH concentrations were among the highest of the measured bromine-based FRs in indoor and urban air in Europe. Yet our mass balance fugacity model and modeling of the physical-chemical properties of DBE-DBCH estimated only 1% partitioning to air with a half-life of 2.2 d atmospherically. In contrast, our modeling characterized DBE-DBCH adsorbing strongly to suspended particulates in the water column (~12%), settling onto sediment (2.5%) with minimal volatilization, but with most partitioning and adsorbing strongly to soil (~85%) with negligible volatilization and slow biodegradation. Our modeling further predicted that organisms would be exposed to DBE-DBCH through partitioning from the dissolved aquatic phase, soil, and by diet, and given its estimated logKow (5.24) and a half-life of 1.7 d in fish, DBE-DBCH is expected to bioaccumulate into lipophilic tissues. Low concentrations of DBE-DBCH are commonly measured in biota and humans, possibly because evidence suggests rapid metabolism. Yet toxicological effects are evident at low exposure concentrations: DBE-DBCH is a proven endocrine disruptor of sex and thyroid hormone pathways, with in vivo toxic effects on reproductive, metabolic, and other endpoints. The objectives of this review are to identify the current state of knowledge concerning DBE-DBCH through an evaluation of its persistence, potential for bioaccumulation, and characterization of its toxicity, while identifying areas for future research.

Cytotoxicity of hexabromocyclododecane, 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane and 1,2,5,6-tetrabromocyclooctane in human SH-SY5Y neuroblastoma cells

With the listing of the of cycloaliphatic brominated flame retardants (CBFR) hexabromocyclododecane (HBCD) as a persistent organic pollutant (POP) by the Stockholm Convention, much attention has been paid to the environmental behaviors and biological effects of HBCD, as well as its potential alternatives, such as 1,2-dibromo-4-(1,2-dibromoethyl) cyclohexane (TBECH) and 1,2,5,6-tetrabromocyclooctane (TBCO). In this study, the neurotoxicity of HBCD, TBECH, and TBCO in human SH-SY5Y cells were compared. The results showed that HBCD, TBECH, and TBCO induced cytotoxicity, including dose-dependent cell viability decreases, cell membrane permeability increases, cytoskeleton development damage, and apoptosis induction, with the cytotoxicity in the order of HBCD > TBCO > TBECH. The expression levels of apoptotic proteins (caspase-3, Bax, caspase-9, Bcl-2, and cytochrome c (Cyt c)) followed the same order, which indicated that mitochondrial apoptotic pathway may be one of the mechanisms responsible for their neurotoxicity. In order to study the mechanisms of cytotoxicity, CBFRs-induced reactive oxygen species (ROS) and the intracellular calcium levels were determined. The ROS levels were significantly elevated for three CBFRs treatment, suggesting that oxidative stress contributes to their cytotoxicity. The intracellular calcium concentrations were significantly enhanced for HBCD and TBCO treatment, but not for TBECH, indicating that in addition to ROS, cytotoxicity of HBCD and TBCO may follow Ca²⁺-mediated apoptotic pathway. This study first compared the neurotoxicity of different CBFRs, providing valuable information for their risk assessment.

Growth, physiological function, and antioxidant defense system responses of Lemna minor L. to decabromodiphenyl ether (BDE-209) induced phytotoxicity

Polybrominated diphenyl ethers (PBDEs), represent one of the new types of persistent organic pollutants (POPs) that are currently found in ambient aquatic ecosystems. Lemna minor L. is a floating freshwater plant, which is widely employed for phytotoxicity studies of xenobiotic substances. For this study, we investigated the growth, physiological functions, and antioxidant capacities of L. minor, which were exposed to 0-20 mg L^-1 decabromodiphenyl ether (BDE-209) for 14 days. A logistic model was suitable for describing the growth of L. minor when the BDE-209 concentration was in the range of from 0 to 15 mg L^-1. When exposed to 5 and 10 mg L^-1 BDE-209, the growth of L. minor was significantly increased, where the intrinsic rate (r) and the maximum capacity of the environment (K) of L. minor were significantly higher than those of the control. In this case, the chlorophyll content and soluble proteins were also markedly increased. Moreover, the photosynthetic function (Fv/Fm, PI) was enhanced. However, for 15 mg L^-1 BDE-29 treated group, the growth of L. minor was significantly inhibited, with decreases in chlorophyll and the soluble protein content, until the L. minor yellowed and expired under a concentration of 20 mg L^-1. Photosynthetic functions were also negatively correlated with increasing increments of BDE-209 (15 and 20 mg L^-1). The malondialdehyde (MDA), superoxide anion radical (O₂^̄·) content, and permeability of the plasma membranes increased with higher BDE-209 concentrations (0-20 mg L^-1). The superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities of L. minor increased when the BDE-209 concentration ranged from 0 to 10 mg L^-1; however, the activities of SOD and POD were decreased. Only the CAT activity remained higher in contrast to the control group under 15-20 mg L^-1 BDE-209. These results demonstrated that 15 mg L^-1 BDE-209 imparted high toxicity to L. minor, which was a consequence of the overproduction of reactive oxygen species (ROS), which conveyed oxidative damage to plant cells. This study provided a theoretical understanding of BDE-209 induced toxicity as relates to the physiology and biochemistry of higher hydrophytes.

Risk assessment of an organochlorine pesticide mixture in the surface waters of Qingshitan Reservoir in Southwest China

Risk assessment of single pollutants has been extensively studied. However, the co-exposure of pollutants in a real environment may pose a greater risk than single chemicals. In this study, concentration addition-based risk quotients were applied to the risk assessment of the 15 organochlorine pesticides (OCPs) mixtures (α-hexachlorocyclohexane (HCH), β-HCH, γ-HCH, δ-HCH, heptachlor, aldrin, heptachlor epoxide, chlordane, α-endosulfan, p,p′-dichloro-diphenyl-dichloroethylene, endrin, β-endosulfan, p,p′-dichloro-diphenyl-dichloroethane, p,p′-dichloro-diphenyl-trichloroethane, and methoxychlor) detected in the surface water (reservoirs, ponds, and streams) of Qingshitan Reservoir in Southwest China from 2014 to 2016 by summing up the toxic units (RQ_STU) of the toxicity data from the individual chemicals. The RQ_STU of the OCPs mixture exceeded 1 in 45.23% of the 283 surface water samples based on acute data and an assessment factor of 100, indicating a potential risk for the aquatic environment (fish). Methoxychlor and γ-HCH contributed the most toxicities in the pesticide mixtures toward Daphnia and fish and provided at least 50% of the mixture toxicity in all samples with RQ_STU larger than 1. The most sensitive organism to realistic OCPs mixtures in the surface waters of Qingshitan Reservoir was fish, followed by Daphnia and algae. The values of the maximum cumulative ratio for all samples indicated that the risk assessment based on single chemicals underestimated the pesticide mixture toxicities, which shows that special consideration should be made for the ecological risk of pesticide mixtures in the aquatic environment.

Risk assessment of single pollutants has been extensively studied.

Acute mixture toxicity of halogenated chemicals and their next generation counterparts on zebrafish embryos

Perfluorinated chemicals and flame retardants are halogenated compounds commonly used in food packaging and in clothing and electronics, respectively. Due to the hazardous effects of many of these chemicals, manufacturers are developing next generation potential less toxic alternatives. The objective of this study was to assess the toxicity of potentially "safer" alternatives, singly and in mixtures, in relation to their first generation counterparts. We used zebrafish embryos as our model organism due to its high structural and functional homology to other vertebrates and its suitability for early developmental studies. We tested three well studied halogens, perfluorooctanoic acid (PFOA), tris (1,3-dichloro-2-propyl) phosphate (TDCPP) and tetrabromobisphenal A (TBBPA), and two less-studied next generation chemicals, 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO) and perfluorobutyric acid (PFBA). First, we identified their lethal concentration (LC₅₀) under 96 h exposures using zebrafish embryos; chemical LC50 values ranged from 1.3 to 13,795 ppm. Next, we tested the toxicity of tertiary mixtures containing the estimated LC₅₀ values for each chemical which ranged from 126 to 5,094 ppm. We found that chemicals within these mixtures displayed concentration addition suggesting a similar mode of toxic action. Importantly, next generation chemicals were less acutely toxic singly and in mixtures than their first generation counterpart.

Temperature and food quantity effects on the harpacticoid copepod Nitocra spinipes: Combining in vivo bioassays with population modeling

The harpacticoid copepod Nitocra spinipes has become a popular model species for toxicity testing over the past few decades. However, the combined influence of temperature and food shortage, two climate change-related stressors, has never been assessed in this species. Consequently, effects of three temperatures (15, 20 and 25°C) and six food regimes (between 0 and 5 × 10⁵ algal cells/mL) on the life cycle of N. spinipes were examined in this study. Similarly to other copepod species, development times and brood sizes decreased with rising temperatures. Mortality was lowest in the 20°C temperature setup, indicating a close-by temperature optimum for this species. Decreasing food concentrations led to increased development times, higher mortality and a reduction in brood size. A sex ratio shift toward more females per male was observed for increasing temperatures, while no significant relationship with food concentration was found. Temperature and food functions for each endpoint were integrated into an existing individual-based population model for N. spinipes which in the future may serve as an extrapolation tool in environmental risk assessment. The model was able to accurately reproduce the experimental data in subsequent verification simulations. We suggest that temperature, food shortage, and potentially other climate change-related stressors should be considered in environmental risk assessment of chemicals to account for non-optimal exposure conditions that may occur in the field. Furthermore, we advocate combining in vivo bioassays with population modeling as a cost effective higher tier approach to assess such considerations.

Potential of the small cyclopoid copepod Paracyclopina nana as an invertebrate model for ecotoxicity testing

Aquatic invertebrates contribute significantly to environmental impact assessment of contaminants in aquatic ecosystems. Much effort has been made to identify viable and ecologically relevant invertebrate test organisms to meet rigorous regulatory requirements. Copepods, which are ecologically important and widely distributed in aquatic organisms, offer a huge opportunity as test organisms for aquatic toxicity testing. They have a major role not only in the transfer of energy in aquatic food chains, but also as a medium of transfer of aquatic pollutants across the tropic levels. In this regard, a supratidal and benthic harpacticoid copepod Tigriopus japonicus Mori (order Harpacticoida) has shown promising characteristics as a test organism in the field of ecotoxicology. Because there is a need to standardize a battery of test organisms from species in different phylogenetic and critical ecosystem positions, it is important to identify another unrelated planktonic species for wider application and comparison. In this regard, the cyclopoid copepod Paracyclopina nana Smirnov (order Cyclopoida) has emerged as a potential test organism to meet such requirements. Like T. japonicus, it has a number of features that make it a candidate worth consideration in such efforts. Recently, the genomics of P. nana has been unraveled. Data on biochemical and molecular responses of P. nana against exposure to environmental chemicals and other stressors have been collected. Recently, sequences and expression profiles of a number of genes in P. nana encoding for heat shock proteins, xenobiotic-metabolizing enzymes, and antioxidants have been reported. These genes serve as potential biomarkers in biomonitoring of environmental pollutants. Moreover, the application of gene expression techniques and the use of its whole transcriptome have allowed evaluation of transcriptional changes in P. nana with the ultimate aim of understanding the mechanisms of action of environmental stressors. Whole-animal bioassays and gene expression studies indicate that P. nana may serve as an excellent tool to evaluate the impact of diverse disturbances in the marine environment. With a better understanding of toxicological mechanisms, ecotoxicologists will be able to understand defense mechanisms against toxicants in copepods. In this review, we illustrate the potential of P. nana as an alternative as well as a complementary invertebrate model organism for risk assessment of aquatic pollutants.

Temperature and food concentration have limited influence on the mixture toxicity of copper and Microcystis aeruginosa to Daphnia magna

Standard ecotoxicity tests are conducted under constant and favorable experimental conditions. In natural communities, however, the toxicity of chemicals may be influenced by abiotic and biotic environmental factors. Firstly, the authors examined the influence of temperature and total food concentration on the nature of the combined effects of copper (Cu) and the cyanobacterium Microcystis aeruginosa to Daphnia magna (i.e., whether the combined effects deviated from noninteraction). Secondly, the authors investigated the relative influence of the percentage of M. aeruginosa in the diet, temperature, and total food concentration on chronic Cu toxicity to D. magna. The nature of the combined effects between Cu and M. aeruginosa (i.e., synergism according to the independent action reference model and noninteraction according to concentration addition reference model) was not affected by temperature and total food concentration. In line with other studies, the concentration addition reference model gave rise to more protective predictions of mixture toxicity than the independent action reference model, thus confirming the former model's suitability as a conservative scenario for evaluating mixture toxicity of Cu and M. aeruginosa under the temperature and food concentrations tested. Further, the 21-d median effective concentration for Cu based on reproduction varied between 20 μg/L and 100 μg/L, and the results indicate that the percentage of M. aeruginosa explained 76% of the variance in the Cu median effective concentration for reproduction, whereas the effects of temperature and total food were limited (together explaining 11% of the variance). The present study suggests that environmental risk assessment of Cu should consider specific situations where harmful M. aeruginosa blooms can co-occur with elevated Cu exposure.

Dose-response behavior of the bacterium Vibrio fischeri exposed to pharmaceuticals and personal care products

The presence of pharmaceuticals and personal care products (PPCPs) in the environment has become a real and widespread concern in recent years. Therefore, the primary goal of this study was to investigate 20 common and widely used PPCPs to assess their individual and combined effect on an important species in one trophic level, i.e., bacteria. The ecotoxicological effects of PPCPs at two different concentration ranges were determined in the bacterium Vibrio fischeri using Microtox(®) and were statistically analyzed using three models in the GraphPad Prism 6 program for Windows, v.6.03. A four-parameter model best fit the majority of the compounds. The half maximal effective concentration (EC50) of each PPCP was estimated using the best-fitting model and was compared with the results from a recent study. Comparative analysis indicated that most compounds showed the same level of toxicity. Moreover, the stimulatory effects of PPCPs at environmental concentrations (low doses) were assessed. These results indicated that certain compounds have traditional inverted U- or J-shaped dose-response curves, and 55% of them presented a stimulatory effect below the zero effect-concentration point. Effective concentrations of 0 (EC0), 5 (EC5) and 50% (EC50) were calculated for each PPCP as the ecotoxicological points. All compounds that presented narcosis as a mode of toxic action at high doses also exhibited stimulation at low concentrations. The maximum stimulatory effect of a mixture was higher than the highest stimulatory effect of each individually tested compound. Moreover, when the exposure time was increased, the hormetic effect decreased. Hormesis is being increasingly included in dose-response studies because this may have a harmful, beneficial or indifferent effect in an environment. Despite the results obtained in this research, further investigations need to be conducted to elucidate the behavior of PPCPs in aquatic environments.

Ecotoxicity of neutral red (dye) and its environmental applications

Neutral red (NR) is a synthetic phenazine with promising prospect in environmental biotechnology as an electron shuttle. Recently, NR injections into coal seam associated groundwater in Australia (final dissolved NR concentration: 8 µM ± 0.2) were shown to increase methanogenesis up to ten-fold. However, information about NR toxicity to ecological receptors is sorely lacking. The main aim of this study was to investigate the concentration dependent toxicity of NR in microorganisms and plants. Acute toxicity of NR was determined by the modified Microtox™ assay. Microbial viability was determined using Escherichia coli and Bacillus subtilis. Germination and early growth of plants was studied using Lactuca sativa, Daucus carota, Allium cepa and an Australian native Themeda triandra. Lastly, mutagenicity of the coal seam associated groundwater was assessed using the Ames test. The EC50 of acute NR toxicity was determined to be 0.11 mM. The EC50 of microbial viability was between 1 and 7.1mM NR. Among the concentrations tested, only 0.01, 0.10 and 100mM of NR significantly affected (p<0.001) germination of L. sativa. The EC50 for root elongation in seeds was between 1.2 and 35.5mM NR. Interestingly, root elongation in seeds was significantly stimulated (p<0.001) between 0.25 and 10mM NR, showing a hormetic effect. A significant increase in mutagenicity was only observed in one of the three wells tested. The results suggest that the average dissolved NR concentration (8 µM ± 0.2) deployed in the field trial at Lithgow State Coal Mine, Australia, appears not to negatively impact the ecological receptors tested in this study.

Effects of two polybrominated diphenyl ethers (BDE-47, BDE-209) on the swimming behavior, population growth and reproduction of the rotifer Brachionus plicatilis

Polybrominated diphenyl ethers (PBDEs) are new kinds of persistent organic pollutants (POPs) and their potential threats to the equilibrium and sustainability of marine ecosystems have raised worldwide concerns. Here, two kinds of PBDEs, tetra-BDE (BDE-47) and deca-BDE (BDE-209) were applied, and their toxic effects on the swimming behavior, population growth and reproduction of Brachionus plicatilis were investigated. The results showed that: (1) The actual concentrations of BDE-47 and -209 in the seawater phase measured by GC-MS (Gas Chromatography-Mass Spectrometer) were much lower than their nominal concentrations. (2) In accordance with the 24-hr acute tests, BDE-209 did not show any obvious swimming inhibition to rotifers, but a good correlation did exist between the swimming inhibition rate and BDE-47 concentration suggesting that BDE-47 is more toxic than BDE-209. (3) Both BDE-47 and -209 had a significant influence on the population growth and reproduction parameters of B. plicatilis including the population growth rate, the ratio of ovigerous females/non-ovigerous females (OF/NOF), the ratio of mictic females/amictic females (MF/AF), resting egg production and the mictic rate, which indicate that these parameters in B. plicatilis population were suitable for monitoring and assessing PBDEs. Our results suggest that BDE-47 and -209 are not acute lethal toxicants and may pose a low risk to marine rotifers at environmental concentrations for short-term exposure. They also accumulate differently into rotifers. Further research data are needed to understand the mechanisms responsible for the effects caused by PBDEs and to assess their risks accurately.

Mixture genotoxicity of 2,4-dichlorophenoxyacetic acid, acrylamide, and maleic hydrazide on human Caco-2 cells assessed with comet assay

Assessment of genotoxic properties of chemicals is mainly conducted only for single chemicals, without taking mixture genotoxic effects into consideration. The current study assessed mixture effects of the three known genotoxic chemicals, 2,4-dichlorophenoxyacetic acid (2,4-D), acrylamide (AA), and maleic hydrazide (MH), in an experiment with a fixed ratio design setup. The genotoxic effects were assessed with the single-cell gel electrophoresis assay (comet assay) for both single chemicals and the ternary mixture. The concentration ranges used were 0-1.4, 0-20, and 0-37.7 mM for 2,4-D, AA, and MH, respectively. Mixture toxicity was tested with a fixed ratio design at a 10:23:77% ratio for 2.4-D:AA:MH. Results indicated that the three chemicals yielded a synergistic mixture effect. It is not clear which mechanisms are responsible for this interaction. A few possible interactions are discussed, but further investigations including in vivo studies are needed to clarify how important these more-than-additive effects are for risk assessment.

Ecotoxicity and biodegradability of new brominated flame retardants: a review

Brominated flame retardants (BFRs) have been routinely used as additives in a number of consumer products for several decades in order to reduce the risk of fire accidents. Concerns about the massive use of these substances have increased due to their possible toxicity, endocrine disrupting properties and occurrence in almost all the environmental compartments, including humans and wildlife organisms. Several conventional BFRs (e.g. polybrominated diphenylethers (PBDE)) have been included in the list of Persistent Organic Pollutants and their use has been restricted because of their established toxicity and environmental persistence. Over the past few years, these compounds have been replaced with "new" BFRs (NBFRs). Despite the fact that NBFRs are different chemical molecules than traditional BFRs, most of physical-chemical properties (e.g. aromatic moiety, halogen substitution, lipophilic character) are common to both groups; therefore, their fate in the environment is potentially similar to the banned BFRs. Therefore, this article has been compiled to summarize the published scientific data regarding the biodegradability of the most widely used NBFRs, a key factor in their potential persistency in the environment, and their ecotoxicological effects on humans and test organisms. The data reviewed here document that the mechanisms through NBFRs exibit their ecotoxicity and the processes leading to their biotransformation in the environment are still poorly understood. Thus emphasis is placed on the need for further research in these areas is therefore emphasized, in order to avoid the massive use of further potentially harmful and recalcitrant substances of anthropogenic origin.

AQUATOX coupled foodweb model for ecosystem risk assessment of Polybrominated diphenyl ethers (PBDEs) in lake ecosystems

The AQUATOX model considers the direct toxic effects of chemicals and their indirect effects through foodwebs. For this study, the AQUATOX model was applied to evaluating the ecological risk of Polybrominated diphenyl ethers (PBDEs) in a highly anthropogenically disturbed lake-Baiyangdian Lake. Calibration and validation results indicated that the model can adequately describe the dynamics of 18 biological populations. Sensitivity analysis results suggested that the model is highly sensitive to temperature limitation. PBDEs risk estimate results demonstrate that estimated risk for natural ecosystems cannot be fully explained by single species toxicity data alone. The AQUATOX model could provide a good basis in ascertaining ecological protection levels of "chemicals of concern" for aquatic ecosystems. Therefore, AQUATOX can potentially be used to provide necessary information corresponding to early warning and rapid forecasting of pollutant transport and fate in the management of chemicals that put aquatic ecosystems at risk.

Monitoring micropollutants in marine waters, can quality standards be met?

The environmental risks of 33 micropollutants occurring in Belgian coastal zone were assessed as single-substances and as mixtures. Water and sediment samples were taken in harbors, coastal waters and the Scheldt estuary during 2007-2009. Measured environmental concentrations were compared to quality standards such as Predicted No Effect Concentrations (PNECs), Environmental Quality Standards (EQSs), and Ecotoxicological Assessment Criteria (EAC). Out of a total of 2547 samples analyzed, 232 and 126 samples exceeded the EQS and EAC, respectively. Highest risks were observed for TBT, PBDEs, PCBs and the PAHs anthracene, indeno(1,2,3-cd)pyrene, benzo(g,h,i)perylene, benzo(k)fluoranthene, and benzo(b)fluoranthene in the water compartment and for TBT and PCBs in the sediment compartment. Samples taken at all stations during the April 2008 campaign indicate a potential risk of the contaminant mixtures to the aquatic environment (except W06 station). This study argues the need to revise quality standards when appropriate and hence the overall regulatory implication of these standards.

Effects of decabromodiphenyl ether (BDE-209) on the avoidance response, survival, growth and reproduction of earthworms (Eisenia fetida)

The effects of decabromodiphenyl ether (BDE-209) on avoidance response, survival, growth, and reproduction of earthworms (Eisenia fetida) were investigated under laboratory conditions using natural and artificial soils as substrate. Results showed that no significant avoidance response was observed when earthworms were exposed to 0.1-1000 mg/kg of BDE-209 for 48 h. After 28-days exposure, no significant effects on survival and growth of adult earthworms was induced by 0.1-1000 mg/kg of BDE-209 indicating the Lowest Observed Effect Level (LOEL) of BDE-209 on their survival and body weight was more than 1000 mg/kg. Except for a significant decrease in the number of juveniles per hatched cocoon in artificial soils at 1000 mg/kg of BDE-209, no significant effects on reproductive parameters (e.g. cocoon production per earthworms, weight per cocoon and cocoon hatchability) were observed. These results suggest that adult earthworms have a strong tolerance for BDE-209 exposure in soils, but a potential toxicity does exist for earthworm embryos or juveniles.

Toxic effects of two brominated flame retardants BDE-47 and BDE-183 on the survival and protein expression of the tubificid Monopylephorus limosus

The toxic effects of two brominated diphenyl ethers (BDE), BDE-47, and BDE-183, on a benthic oligochaete tubificid, Monopylephorus limosus were studied under laboratory conditions. Investigated responses included survival, growth, and protein expression profiles, at BDE concentrations of 1, 10, 100, and 700 ng/g on a dry soil weight basis, with isooctane as the carrier solvent. Body weight losses among treatments were insignificant after 8 weeks of exposure. The 8-wk LC(50) of BDE-47 and -183 were 2311 and 169 ng/g, respectively. By applying multivariate analysis techniques, protein expression patterns were compared and correlated with stressful sources of long-term culture, carrier solvent, BDE-47 and -183. The treatment of 8-wk 100 ng/g BDE-47 was most closely clustered to the 10 ng/g BDE-183 treatment, based on the 40 examined protein spots. This indicated that BDE-183 was more potent to M. limosus, than was BDE-47. The 2-wk and 8-wk controls clustered into different groups indicating the occurrence of physiological changes due to long-term laboratory culture. Additionally, solvent effect was shown by grouping the isooctane carrier to different clusters. With further characterization by principle component analysis, it was found that the separation was mainly contributed by the 2nd principal-component. And, the primarily inhibitory variation was at spots 2 (UMP-CMP kinase) and 40 (plasma retinol-binding protein precursor) in the 8-wk groups. On the contrary, protein spots 16 (cell division control protein 2 homolog) and 24 (mitochondrial DNA mismatch repair protein) showed stimulatory variation. In all, the observed proteomic responses suggest that BDEs disrupted metabolic function in M. limosus and multivariate analysis tool offers significant potential for the assessment of various stress sources at biochemical level.

Predicting mixture toxicity of seven phenolic compounds with similar and dissimilar action mechanisms to Vibrio qinghaiensis sp.nov.Q67

The predictions of mixture toxicity for chemicals are commonly based on two models: concentration addition (CA) and independent action (IA). Whether the CA and IA can predict mixture toxicity of phenolic compounds with similar and dissimilar action mechanisms was studied. The mixture toxicity was predicted on the basis of the concentration-response data of individual compounds. Test mixtures at different concentration ratios and concentration levels were designed using two methods. The results showed that the Weibull function fit well with the concentration-response data of all the components and their mixtures, with all relative coefficients (Rs) greater than 0.99 and root mean squared errors (RMSEs) less than 0.04. The predicted values from CA and IA models conformed to observed values of the mixtures. Therefore, it can be concluded that both CA and IA can predict reliable results for the mixture toxicity of the phenolic compounds with similar and dissimilar action mechanisms.

An ecotoxicological approach for hazard identification of energy ash

Within the EU, ash should be classified by its inherent hazardous effects under criterion H-14 (ecotoxic) in the Directive on waste (2008/98/EC). Today, however, there are no harmonized quantitative criterions for such a classification, but it is stated that biological test systems can be used. In this study seven ash materials were leached and characterized, both biologically and chemically. The objectives were to evaluate if (a) clear concentration-response relationships could be achieved for the selected toxicity tests (bacteria, algae, crustacean and fish), (b) some test(s) are generally more sensitive and (c) the toxic responses were consistent with the chemical analyzes. Interestingly, our results indicate that high concentrations of non-hazardous components (Ca, K) influenced the toxicity of almost all ash eluates, whereas hazardous components (e.g. Zn, Pb) only influenced the toxicity of the eluates ranked as most hazardous. If considering both hazardous and non-hazardous substances, the observed toxic responses were relatively consistent with the chemical analyzes. Our results further showed that the (sub)chronic tests were much more sensitive than the acute tests. However, the use of extrapolation factors to compensate for using the less sensitive acute tests will likely lead to either over- or underestimations of toxicity. Our recommendation is therefore that classification of waste according to H-14 should be based on (sub)chronic test data. Finally, given that treatment of the eluates prior to toxicity testing has a major significance on the concentration and speciation of released substances, further studies are needed in order to propose a relevant testing scheme.