Effects of binary mixtures on the life traits of Daphnia magna

Effects of Cadmium and Nickel Mixtures on Multiple Endpoints of the Microalga Raphidocelis subcapitata

It is crucial to investigate the effects of mixtures of contaminants on aquatic organisms, because they reflect what occurs in the environment. Cadmium (Cd) and nickel (Ni) are metals that co-occur in aquatic ecosystems, and information is scarce on their joint toxicity to Chlorophyceae using multiple endpoints. We evaluated the effects of isolated and combined Cd and Ni metals on multiple endpoints of the chlorophycean Raphidocelis subcapitata. The results showed that Cd inhibited cell density, increased reactive oxygen species (ROS) production (up to 308% at 0.075 mg L-1 of Cd), chlorophyll a (Chl a) fluorescence (0.050-0.100 mg L-1 of Cd), cell size (0.025-0.100 mg L-1 of Cd), and cell complexity in all concentrations evaluated. Nickel exposure decreased ROS production by up to 25% at 0.25 mg L-1 of Ni and Chl a fluorescence in all concentrations assessed. Cell density and oxygen-evolving complex (initial fluorescence/variable fluorescence [F0/Fv]) were only affected at 0.5 mg L-1 of Ni. In terms of algal growth, mixture toxicity showed antagonism at low doses and synergism at high doses, with a dose level change greater than the median inhibitory concentration. The independent action model and dose-level-dependent deviation best fit our data. Cadmium and Ni mixtures resulted in a significant increase in cell size and cell complexity, as well as changes in ROS production and Chl a fluorescence, and they did not affect the photosynthetic parameters. Environ Toxicol Chem 2024;43:1855-1869. © 2024 SETAC.

Chronic toxicity of three formulations of neonicotinoid insecticides and their mixture on two daphniid species: Daphnia magna and Ceriodaphnia dubia

Neonicotinoid insecticides represent nearly a quarter of the global insecticide market and are widely used in agriculture but also for lawn, garden care, and pest control. They are highly water-soluble, persistent in soil, may enter the aquatic compartment via spray drift, runoff, or leaching, and contribute to downstream aquatic toxicity. Although insects appear to be the most sensitive group to neonicotinoids, other groups, such as crustaceans, may also be affected. Furthermore, most studies focus on single-insecticide exposure and very little is known concerning the impact of neonicotinoid mixtures on aquatic invertebrates. The present study was designed to test potential toxicological effects of an environmentally relevant mixture of imidacloprid, clothianidin, and thiamethoxam on populations of Ceriodaphnia dubia and Daphnia magna under controlled conditions. Chronic toxicity tests were conducted in the laboratory, and survival and reproduction were measured for both species under environmentally relevant, 'worst-case' concentrations for each compound separately and in combination as pesticides are often detected as mixtures in aquatic environments. The neonicotinoids did not appear to affect the survival of C. dubia and D. magna. Reproduction of C. dubia was affected by the mixture whereas all three individual insecticides as well as the mixture caused a significant reduction in the reproduction of D. magna. Our results highlight the complexity of pesticide toxicity and show that traditional toxicological approaches such as, acute mortality studies and tests with single compounds can underestimate negative impacts that occur in the environment.

Microbiota-Derived Short-Chain Fatty Acids: New Road in Colorectal Cancer Therapy

The colon microbiota is an important player in colorectal cancer (CRC) development, which is responsible for most of the cancer-related deaths worldwide. During carcinogenesis, the colon microbiota composition changes from a normobiosis profile to dysbiosis, interfering with the production of short-chain fatty acids (SCFAs). Each SCFA is known to play a role in several biological processes but, despite their reported individual effects, colon cells are exposed to these compounds simultaneously and the combined effect of SCFAs in colon cells is still unknown. Our aim was to explore the effects of SCFAs, alone or in combination, unveiling their biological impact on CRC cell phenotypes. We used a mathematical model for the prediction of the expected SCFA mixture effects and found that, when in mixture, SCFAs exhibit a concentration addition behavior. All SCFAs, alone or combined at the physiological proportions founded in the human colon, revealed to have a selective and anticancer effect by inhibiting colony formation and cell proliferation, increasing apoptosis, disturbing the energetic metabolism, inducing lysosomal membrane permeabilization, and decreasing cytosolic pH. We showed for the first time that SCFAs are specific towards colon cancer cells, showing promising therapeutic effects. These findings open a new road for the development of alternatives for CRC therapy based on the increase in SCFA levels through the modulation of the colon microbiota composition.

The impact of imidacloprid and thiacloprid on the mean species abundance in aquatic ecosystems

Neonicotinoids are currently the most widely used and sold insecticides in the world, providing effective pest control. Risk assessment of these and other pesticides by lab-based indicators is common. Yet, empirically and theoretically underpinning of extrapolation to indicators used in field surveys is severely limited. Consequently, the aim of our study was to quantify the toxicological and ecological impact of the neonicotinoids imidacloprid and thiacloprid to aquatic invertebrates. We derived Species Sensitivity Distributions (SSDs) based on chronic LC₅₀ data and Mean Species Abundance Relationships (MSARs), comparing these lab-based approaches to field data as well. MSARs are changes in mean species abundance (MSA) as a function of chemical exposure, providing insight into the overall decline of a community. The MSA expresses the mean abundance of species in disturbed conditions relative to their abundance in undisturbed habitat. The medians of the SSD of imidacloprid and thiacloprid for the different species were 16.45 μg/L and 26.40 μg/L, respectively. HC₅₀s of the MSAR of imidacloprid and thiacloprid were 4.25 μg/L and 5.12 μg/L, respectively. The three taxonomic groups tested (insects, crustaceans and mollusks) did not differ significantly in sensitivity for imidacloprid and thiacloprid, both according to the SSDs and MSARs derived. Quantile exposure-response curves (99%-tile) were plotted showing the relative abundance (RA) of aquatic invertebrate species at increasing imidacloprid levels. The 99%-tile of the Relative Abundances (RA₉₉) of species and corresponding imidacloprid concentrations monitored in field surveys in the Netherlands was significantly lower than the Potentially Affected Fraction (PAF) calculated from the SSD. Yet, the MSA was similar to the RA₉₉, suggesting that MSAR is an ecologically meaningful relationship for toxic stress estimated from lab data. Future efforts should be directed to additional empirical underpinning as well as determining the relationship of PAF to other metrics for ecosystem diversity and productivity.

Urinary neonicotinoid concentrations and pubertal development in Chinese adolescents: A cross-sectional study

BACKGROUND

Animal studies suggest that exposure to certain neonicotinoids may interfere with the normal function of endocrine system in mammals. However, evidence from human studies is limited.

OBJECTIVES

This study conducted a cross-sectional analysis to examine urinary neonicotinoids concentrations in Chinese adolescents and its association with pubertal development.

METHODS

774 urine samples from 439 boys (median age: 13.7 years; 25th-75th percentile: 12.7-14.5 years) and 335 girls (median age: 13.7 years; 25th-75th percentile: 12.7-14.5 years) were collected for determination of ten neonicotinoids (imidacloprid, nitenpyram, acetamiprid, thiacloprid, imidaclothiz, thiamethoxam, clothianidin, dinotefuran, flonicamid, sulfoxaflor) and one metabolite (N-desmethyl-acetamiprid). Urinary creatinine was detected for concentration adjustment. Pubertal development including pubic hair, axillary hair, genitalia (boys), testicular volume (boys) and breast (girls) assessed by Tanner stages and others (spermarche, facial hair for boys and menarche for girls) were obtained by physical examination and questionnaire. Logistic and bayesian kernel machine regression were used to investigate the association between neonicotinoids concentrations and pubertal developments.

RESULTS

High detection rates ranged from 72.0% to 100.0% for all neonicotinoids. Boys and girls with thiacloprid concentration at the >75th percentile had lower stage of genitalia development (OR: 0.83, 95% CI: 0.33-0.93) and higher stage of axillary hair development (OR: 1.46, 95% CI: 1.12-3.41), respectively, compared with those at the <25th percentile. The estimate change in genitalia stage was significantly different at or above the 75th percentile concentration of neonicotinoids mixture compared to the 50th percentile concentration. No associations were found between other urinary neonicotinoids and other indicators of puberty.

CONCLUSIONS

Higher thiacloprid concentration was associated with delayed genitalia development in boys and early axillary hair development in girls. Neonicotinoids mixture was negatively associated with genitalia stage in the joint effect. Given the characteristic of the cross-sectional study, our results need further confirmation of the causal relationship.

Physiological and metabolic alterations induced by commercial neonicotinoid formulations in Daphnia magna

Neonicotinoid insecticides are widely used agents in agriculture to control a broad range of insect pests. Although use of neonicotinoid pesticides has resulted in the widespread contamination of surface waters, sublethal toxicity data of these products in relation to non-target aquatic biota are still poor. Therefore, the objective of this study was to assess the effects of two neonicotinoid pesticides with widespread use on the basic physiological functions: the thoracic limb activity and heart rate of Daphnia magna, and to screen for their potential to affect the cytochrome P450 monooxygenase system (ECOD activity) of daphnids. The considered pesticides were the acetamiprid- and thiacloprid based products Mospilan 20 SG and Calypso 480 SC, respectively. The dose-dependent variation in the three biological endpoints considered were assessed following 24 h exposures. The two neonicotinoid formulations elicited significant depression on the thoracic limb activity and heart rate of daphnids at doses close to the immobility thresholds of formulations (48h-EC₅₀: Mospilan 20 SG = 190 mg L^-1; Calypso 480 SC = 120 mg L^-1), an effect mainly attributable to the overall drop in the general health status of the organisms. The alterations in the physiological traits were significant at exposures to 190 mg L^-1 for Mospilan 20 SG and 48 mg L^-1 for Calypso 480 SC. The dose related variation in the ECOD activity of daphnids exposed to the selected neonicotinoid formulations followed a biphasic pattern, with starting effective doses for Mospilan 20 SG of 6.3 mg L^-1 (=1/20 of 48h-EC₅₀ for Daphnia neonates), and for Calypso 480 SC of 0.034 mg L^-1 (=1/4000 of 48h-EC₅₀). Maximal ECOD activity (2.2 fold increase vs. controls) was induced by Mospilan 20 SG in daphnids exposed to 114 mg L^-1 product (=48 h-EC₂₀), and by Calypso 480 SC (1.8 fold increase) at 5.2 mg L^-1 dose (=1/20 of 48 h-EC₅₀). Our results outlined significant alterations in the physiological traits and ECOD activity in exposed daphnids at concentrations below the immobility thresholds (48 h-EC₅₀) of the products used as benchmarks to rate their toxicity risks to aquatic biota. Therefore, we think our findings might deserve consideration in the environmental risk evaluation of these products.

Individual and Combined Effects of Manganese and Chromium on a Freshwater Chlorophyceae

Manganese (Mn), an essential metal in trace amounts, and chromium (Cr), a nonessential metal to algae, are often found in effluent discharges and may co-occur in contaminated aquatic environments. Therefore, we investigated the effects of Mn and Cr, and their mixtures, on a freshwater Chlorophyceae, Raphidocelis subcapitata, using a multiple endpoint approach. Regarding the single exposure of metals, Mn was 4 times more toxic (median inhibitory concentration at 72 h [IC50_72 h ] = 4.02 ± 0.45 µM Mn) than Cr (IC50_72 h  = 16.42 ± 4.94 µM Cr) for microalgae, considering the effects on the relative growth rate. Moreover, this species was the most sensitive to Mn, according to the species sensitivity distribution curve. Overall, the tested metals did not lead to significant changes in reactive oxygen species production, cellular complexity, and cell relative size but significantly decreased the algal growth and the mean cell chlorophyll a (Chl a) fluorescence at the highest concentrations (3.64-14.56 µM of Mn and 15.36-19.2 µM of Cr). The decreased mean cell Chl a fluorescence indicates an impact on pigment synthesis, which may be related to the observed growth inhibition. In the mixture tests, the reference models concentration addition and independent action were used to analyze the data, and the independent action model was the best fit to describe our results. Therefore, the Mn and Cr mixture was noninteractive, showing additive effects. This is the first study to address the combined toxicity of Mn and Cr regarding freshwater Chlorophyceae. Environ Toxicol Chem 2022;41:1004-1015. © 2022 SETAC.

Toxicity and Risk Assessment of Zinc and Aluminum Mixtures to Ceriodaphnia silvestrii (Crustacea: Cladocera)

Despite the co-occurrence of metals in aquatic environments, their joint effects are generally not considered during risk assessments. Data on the combined effects of zinc (Zn) and aluminum (Al) on aquatic animals are extremely scarce in the literature, although these metals are commonly used in domestic and industrial activities. In the present study, we investigated the effects of mixtures of Zn and Al on the cladoceran Ceriodaphnia silvestrii. We evaluated immobility (at 48 h) and ingestion rates (at 24 h). We also performed chronic toxicity tests for single metals. The environmental risks of these substances for tropical freshwaters were estimated from the risk quotient (measured environmental concentration/predicted no-effect concentration). In immobility tests, our results showed a 48-h median effect concentration (EC50) of 0.22 mg Zn L^-1 and 0.52 mg Al L^-1 , and we observed synergistic effects of Zn and Al, following the independent action model. The ingestion rates of C. silvestrii were inhibited at 0.1, 0.4, and 0.5 mg Al L^-1 , and they were increased at 0.08 mg Zn L^-1 ; we observed antagonistic effects in all treatments combined with 0.5 mg Al L^-1 . In terms of chronic toxicity, a 7-d EC50 occurred at 0.11 mg Zn L^-1 and 0.37 mg Al L^-1 . The risk assessment suggests a potential risk of these metals at environmentally relevant concentrations, especially when in a mixture. Therefore, we recommend mixture toxicity tests during risk assessments to ensure that zooplankton are protected. Environ Toxicol Chem 2021;40:2912-2922. © 2021 SETAC.

Comparison of Multiple Linear Regression and Biotic Ligand Models to Predict the Toxicity of Nickel to Aquatic Freshwater Organisms

Toxicity-modifying factors can be modeled either empirically with linear regression models or mechanistically, such as with the biotic ligand model (BLM). The primary factors affecting the toxicity of nickel to aquatic organisms are hardness, dissolved organic carbon (DOC), and pH. Interactions between these terms were also considered. The present study develops multiple linear regressions (MLRs) with stepwise regression for 5 organisms in acute exposures, 4 organisms in chronic exposures, and pooled models for acute, chronic, and all data and compares the performance of the Pooled All MLR model to the performance of the BLM. Independent validation data were used for evaluating model performance, which for pooled models included data for organisms and endpoints not present in the calibration data set. Hardness and DOC were most often selected as the explanatory variables in the MLR models. An attempt was also made at evaluating the uncertainty of the predictions for each model; predictions that showed the most error tended to show the highest levels of uncertainty as well. The performances of the 2 models were largely equal, with differences becoming more apparent when looking at the performance within subsets of the data. Environ Toxicol Chem 2021;40:2189-2205. © 2021 SETAC.

Toxicity of fipronil and 2,4-D formulations (alone and in a mixture) to the tropical amphipod Hyalella meinerti

Conventional farming uses a large volume of pesticides that may reach aquatic ecosystems. This is also the case for the insecticide fipronil and the herbicide 2,4-D, which are widely used in many crops. This study aimed at evaluating the individual and mixture toxicity of these pesticides to the tropical amphipod Hyalella meinerti. To this end, acute toxicity tests (96 h) were conducted. Chronic bioassays (10 days) were also carried out, in which the body length and dry biomass were evaluated as endpoints. In addition, a complete factorial mixture chronic toxicity test was carried out. H. meinerti was sensitive to fipronil in the acute toxicity tests, with a LC₅₀-96-h of 0.86 μg L^-1 (95% CI 0.26-0.46), and no acute effects were observed after 2,4-D exposure even at the highest test concentration of 100 mg L^-1. In the chronic toxicity tests, all tested concentrations of both pesticides decreased the growth of H. meinerti, in which losses on biomass reached 45% and 65% for 2,4-D and fipronil, respectively. The pesticide mixture indicated antagonism although it still significantly decreased the body growth. The results obtained indicate a high sensitivity of H. meinerti exposed to environmentally realistic concentrations, demonstrating that there are risks for the species in real field conditions.

Comparisons of the Effect of Different Metal Oxide Nanoparticles on the Root and Shoot Growth under Shaking and Non-Shaking Incubation, Different Plants, and Binary Mixture Conditions

We evaluated the toxicity of five metal oxide nanoparticles (NPs) in single or binary mixtures based on root and shoot growth of two plant species under non-shaking and shaking conditions. The effects of NPs on root and shoot growth differed depending on the NP type, incubation condition, and plant type. The half maximal effective concentration (EC₅₀) of NPs based on root growth were significantly lower, by 2.6–9.8 times, under shaking than non-shaking conditions (p = 0.0138). The magnitude of the effects of NPs followed the order CuO > ZnO > NiO >> Al₂O₃, TiO₂. In addition, Lactuca sativa L. was more sensitive to the tested NPs than Raphanus sativus L., with an EC₅₀ 0.2–0.7 times lower (p = 0.0267). The observed effects of 12 combinations of binary NP mixtures were slightly, albeit non-significantly, lower than expected, indicative of an additive effect of the individual NPs in the mixtures. The results emphasize the importance of careful plant model selection, appropriate application of incubation conditions, and consideration of chemical mixtures rather than single compounds when evaluating the effects of metal oxide NPs.

Imidacloprid dominates the combined toxicities of neonicotinoid mixtures to stream mayfly nymphs

Contamination of the environment with toxic chemicals such as pesticides has become a global problem. Understanding the role of chemical contaminants as stressors in ecological systems is therefore an important research need in the 21st century. In surface freshwaters, mixtures of neonicotinoid insecticides are being detected around the world as more monitoring data become available. Combinations of imidacloprid, clothianidin and thiamethoxam are commonly found, but studies testing their combined toxicities to freshwater invertebrates are rare. Taking a multiple-stressor approach, we employed a full-factorial design to investigate the individual and combined chronic toxicities of these three neonicotinoids in a 28-day laboratory experiment using Deleatidium spp. mayfly nymphs. Imidacloprid (1.2 μg/L achieved concentration) reduced mayfly survival (by 50% on Day 28) and mobility (~100%) more than clothianidin (1.1 μg/L, affecting about 25% of individuals across the responses measured) and thiamethoxam (2.9 μg/L, affecting 12%). Imidacloprid interacted with the other two neonicotinoids to cause a greater-than-additive negative effect when combined until 25 days of exposure, after which the strong negative overall effects of imidacloprid prevented these interactions from being observed. Our findings represent a novel contribution to multiple-stressor research by demonstrating the combined effects of chronic exposure to environmentally relevant neonicotinoid concentrations on an ecologically important stream insect taxon. These results emphasise the higher toxicity of imidacloprid to non-target freshwater insects compared to clothianidin and thiamethoxam, implying that stricter regulation to control the use of imidacloprid may need to be prioritised to protect vulnerable aquatic insect populations that provide key links to terrestrial food webs. Finally, our study provides an ecological, multiple-stressor comparison for related ecotoxicological investigations indicating neonicotinoid mixtures can deviate from additive toxicity.

Effects of abamectin-based and difenoconazole-based formulations and their mixtures in Daphnia magna: a multiple endpoint approach

This study evaluated the toxicity of pesticide formulations Kraft® 36 EC (active ingredient-a.i. abamectin) and Score® 250 EC (a.i. difenoconazole), and their mixtures in Daphnia magna at different biological levels of organization. Survival, reproduction and biochemical markers (cholinesterase (ChE), catalase (CAT) and lipid peroxidation (LPO)) were some of the endpoints evaluated. Total proteins and lipids were also studied together with energy consumption (Ec). D. magna neonates were exposed for 96 h to Kraft (2, 4, and 6 ng a.i./L) and Score (12.5, 25, and 50 µg a.i./L) for the biochemical experiments, and for 15 days to abamectin (1-5 ng a.i./L) and to difenoconazole (3.12-50 µg a.i./L) to assess possible changes in reproduction. Exposures of organisms to both single compounds did not cause effects to antioxidant and detoxifying enzymes, except for LPO occurring at the highest concentration of difenoconazole tested. For ChE and CAT there was enzymatic induction in mixture treatments organisms, occurring at minor pesticides concentrations for CAT and at the two highest concentrations for ChE. There were no significant differences for total protein in D. magna but lipids showed an increase at the highest concentrations of pesticide mixture combinations. There was a significant increase of Ec in individuals of all treatments tested. In the chronic test, increased fecundity occurred for D. magna under difenoconazole exposures and mixtures. This study demonstrated that mixtures of these pesticides caused greater toxicity to D. magna than when tested individually, except for Ec. Therefore, effects of mixtures are very hard to predict only based on information from single compounds, which most possibly is the result of biological complexity and redundancy in response pathways, which need further experimentation to become better known.

Acute and chronic toxicity of 2,4-D and fipronil formulations (individually and in mixture) to the Neotropical cladoceran Ceriodaphnia silvestrii

Brazil is the largest producer of sugarcane and the world's top pesticide market. Therefore, environmental consequences are of concern. The aim of the present study was to evaluate the acute and chronic toxicity of pesticide formulations largely used in sugarcane crops: the herbicide DMA® 806 BR (a.i. 2,4-D) and the insecticide Regent® 800 WG (a.i. fipronil), isolated and in mixture, to the Neotropical cladoceran Ceriodaphnia silvestrii. Toxicity tests with the individual formulated products indicated 48h-EC₅₀ values of 169 ± 18 mg a.i./L for 2,4-D and 3.9 ± 0.50 µg a.i./L for fipronil. In the chronic tests, the 8d-EC₅₀ values for reproduction were 55 mg a.i./L (NOEC/LOEC: 50/60 mg a.i./L) and 1.6 µg a.i./L (NOEC/LOEC: 0.40/0.80 µg a.i./L) for 2,4-D and fipronil, respectively. A significant decrease in reproduction of C. silvestrii in all concentrations tested of fipronil, except at the lowest, was observed. Regarding 2,4-D, the organisms had total inhibition of reproduction in the two highest concentrations. Probably your energy reallocation was focused (trade-off) only on its survival. The acute pesticide mixture toxicity (immobility) revealed a dose level dependent deviation with antagonism at low and synergism at high concentrations. For chronic mixture (reproduction) toxicity, antagonism occurred as a result of the interaction of the pesticides. Based on our results and concentrations measured in Brazilian water bodies, fipronil represents ecological risks for causing direct toxic effects on C. silvestrii. These results are worrisome given that agricultural production is likely to increase in the coming years.

Quantification of metal uptake in Spinacia oleracea irrigated with water containing a mixture of CuO and ZnO nanoparticles

An extensive application and potential release of nanoparticles (NPs) through wastewater treatment plants to agricultural lands have created an urgent necessity to evaluate food safety. The study here grew Spinacia oleracea until maturity in the soil and irrigated with CuO and ZnO NPs (as single and as a binary mixture). The plants were grown in soil containing pots and were exposed to NPs (CuO and ZnO) and ions (Cu²⁺ and Zn²⁺) (concentration = 1.2 × 10^-4, 1.2 × 10^-3, 1.2 × 10^-2 mol/Kg of soil); a binary mixture (CuO + ZnO and Cu²⁺+Zn²⁺) concentration = 1.2 × 10^-4+1.2 × 10^-4 mol/Kg of soil, respectively. At maturity, plant fresh weight, root length, and elemental content (Cu and Zn) were quantified. Results showed significant adverse effects on plant biomass exposed at 1.2 × 10^-2 mol/Kg of soil (percentage reduction = 36%, 26% and 45% for CuO, ZnO, and CuO + ZnO NPs, respectively). The interaction of toxicity between two NPs and ions on reduction in fresh weight was observed to be additive. Desorption studies were performed for determining root-surface adsorbed CuO and ZnO NPs using three different concentrations of Na₄EDTA. The estimated internal uptake of Cu and Zn was found to be 0.4 mg Cu/g dry weight and 0.7 mg Zn/g dry weight in the shoot portion of the plant and 3.06 mg Cu/g dry weight and 3.4 mg Zn/g dry weight in the root portion of the plant, respectively. (at 1.2 × 10-2 mol/Kg of soil). Exposure of metal ions has shown a higher reduction in biomass and higher uptake in plants as compared to NPs. The projected hazard quotient values for the intake of NPs by children was found to be greater than 1 indicating risks to children. Given the importance of food safety, determination of the potential risk of consuming contaminated plants, irrigated using nanoparticles containing wastewater is advised.

Sensitivity of larval and juvenile freshwater mussels (unionidae) to ammonia, chloride, copper, potassium, and selected binary chemical mixtures

In aquatic environments, organisms such as freshwater mussels are likely exposed to complex contaminant mixtures related to industrial, agricultural, and urban activities. With growing interest in understanding the risk that chemical mixtures pose to mussels, this investigation focused on the effects of various waterborne contaminants (ammonia, chloride, copper, and potassium) and selected binary mixtures of these chemicals following a fixed-ratio design to Villosa iris glochidia and juvenile Lampsilis fasciola. In individual exposures, 48-h EC₅₀ values were determined for V. iris glochidia exposed to ammonia chloride (7.4 [95% confidence interval (CI) 6.6-8.2] mg N/L), ammonia sulfate (8.4 [7.6-9.1] mg N/L), copper sulfate (14.2 [12.9-15.4] μg Cu²⁺/L), potassium chloride (12.8 [11.9-13.7] mg K⁺/L), potassium sulfate (10.1 [8.9-11.2] mg K⁺/L), and sodium chloride (480.5 [435.5-525.5] mg Cl^-/L). The 7-d LC₅₀ values for juvenile L. fasciola were determined for potassium sulfate (45.0 [18.8-71.2] mg K⁺/L), and sodium chloride (1738.2 [1418.6-2057.8] mg Cl^-/L). In Ontario these waterborne contaminants have been reported to co-occur, with concentrations exceeding the EC₁₀ for both life stages at some locations. Data from binary mixture exposures for V. iris glochidia (chloride-ammonia, chloride-copper, and copper-ammonia) and juvenile L. fasciola (chloride-potassium) were analyzed using a regression-based, dose-response mixture analysis modeling framework. Results from the mixture analysis were used to determine if an additive model for mixture toxicity [concentration addition (CA) or independent action (IA)] best described the toxicity of each mixture and if deviation towards dose-ratio (DR) or dose-level (DL) synergism/antagonism (S/A) occurred. For all glochidia binary mixture exposures, CA was the best fit model with DL deviation reported for the chloride-copper mixture and DR deviation reported for the copper-ammonia mixture. Using the model deviation ratio (MDR), the observed toxicity in all three glochidia mixture exposures were adequately described by both CA (mean = 0.71) and IA (mean = 0.97) whereas the juvenile mixture exposure was only adequately described by CA (mean = 0.64; IA mean = 0.05).

Evaluating additive versus interactive effects of copper and cadmium on Daphnia pulex life history

A key challenge of standard ecotoxicological risk assessment is to predict the sub-lethal risk of multiple contaminants on aquatic organisms. Our study assessed the sub-lethal mixture toxicity of copper (Cu) and cadmium (Cd) on Daphnia pulex and included manipulations of food level and assessment of three genotypes. We investigated the interaction between essential (Cu) and non-essential (Cd) metals on ingestion rate, reproduction, maturation time, size at maturity and somatic growth rate of three D. pulex genotypes, over 21 days and under standard and high food conditions. We explored the potential interaction of the metals on ingestion and life history by implementing a response surface experimental design combining control and two levels of Cu and Cd and their combinations. Overall, both metals reduced ingestion rates, reduced reproduction, delayed maturation, reduced body size at maturity and lowered somatic growth rate. Our results further indicated pervasive interactions between the metals; numerous instances where the effects of each metal were non-linear; the effect of a metal varied by D. pulex food levels (ingestion rate and size at maturity), and the effect of a metal varied by genotypes (reproduction). Apart from the maturation time and somatic growth rate, our results suggest that life history traits are affected in non-additive ways by three factors that are often discussed and rarely estimated together: mixtures of metals, genotypes and resource levels. Our data that are derived from exposing daphnids to two metals highlight how metals interact with each other and the context of food resource and genetic variation. While interactions make it harder to generate predictions, and ultimately water quality regulations about the effects of metals, those detected in this study appear to be tractable.

Rapid screening for ecotoxicity of plating and semiconductor wastewater employing the heartbeat of Daphnia magna

Industrial wastewater discharge is one of major threats to the sustainability of aquatic environment. Rapid and sensitive detection of toxic wastewater discharge and appropriate control if necessary are therefore crucial. In the present study, a 1 h Daphnia magna exposure with heartbeat as an observation endpoint was developed and assessed for its utility as a rapid toxicity screening measure. Two types of metal-rich industrial wastewater, i.e., metal plating and the semiconductor industry were chosen as target samples, and the 1 h heartbeat assay was applied. Based on a literature search, four metals, i.e., Cu, Cr, Ni and Zn were identified as major chemicals of ecotoxicological concerns in these wastewaters. The effective concentrations determined for each metal from the D. magna 1 h heartbeat test were comparable to those derived from the conventional D. magna 48 h immobilization test. Copper sulfate (CuSO₄) was determined as the most toxic, followed by potassium dichromate (K₂Cr₂O₇), nickel sulfate (NiSO₄) and zinc sulfate (ZnSO₄). For ternary mixtures, the 1 h heartbeat test showed also comparable responses to those of the 48 h immobilization test, suggesting its utility for screening the toxicity of simple metal mixtures. For the site-sampled metal plating water, the rapid heartbeat assay showed similar responses to those of the 48 h immobilization assay. However, for the semiconductor industry wastewater, clearly different responses were observed in both the heartbeat and immobilization assays, probably due to the influence of other contaminants with different modes of action that are present in the wastewater. Our observations showed that the D. magna 1 h heartbeat test can be considered as a rapid ecotoxicity screening measure for certain wastewaters with simple metal mixtures.

Chronic Toxicities of Neonicotinoids to Nymphs of the Common New Zealand Mayfly Deleatidium spp

Neonicotinoid insecticides have been shown to have high chronic toxicity relative to acute toxicity, and therefore short-term toxicity tests ≤96 h in duration may underestimate their environmental risks. Among nontarget aquatic invertebrates, insects of the orders Diptera and Ephemeroptera have been found to be the most sensitive to neonicotinoids. To undertake a more accurate assessment of the risks posed by neonicotinoids to freshwater ecosystems, more data are needed from long-term tests employing the most sensitive taxa. Using nymphs of the common New Zealand mayfly genus Deleatidium spp., we performed 28-d static-renewal exposures with the widely used neonicotinoids imidacloprid, clothianidin, and thiamethoxam. We monitored survival, immobility, impairment, and mayfly moulting propensity at varying time points throughout the experiment. Imidacloprid and clothianidin exerted strong chronic toxicity effects on Deleatidium nymphs, with 28-d median lethal concentrations (LC50s) of 0.28 and 1.36 µg/L, respectively, whereas thiamethoxam was the least toxic, with a 28-d LC50 > 4 µg/L (highest concentration tested). Mayfly moulting propensity was also negatively affected by clothianidin (during 3 of 4 wk), imidacloprid (2 of 4 wk), and thiamethoxam (1 of 4 wk). Comparisons with published neonicotinoid chronic toxicity data for other mayfly taxa and larvae of the midge genus Chironomus showed similar sensitivities for mayflies and midges, suggesting that experiments using these taxa provide reliable assessments of the threats of neonicotinoids to the most vulnerable freshwater species. Environ Toxicol Chem 2019;38:2459-2471. © 2019 SETAC.

Acute Effects of Binary Mixtures of Imidacloprid and Tebuconazole on 4 Freshwater Invertebrates

Receiving waters from agricultural areas can contain multiple pesticides such as the neonicotinoid imidacloprid and the fungicide tebuconazole, leading to the potential for aquatic life to be exposed to such mixtures. In the present study, the effects of tebuconazole were tested alone and in binary mixtures with imidacloprid on 4 aquatic invertebrates: Chironomus dilutus, Hyalella azteca, Lumbriculus variegatus, and Neocloeon triangulifer. Acute (96-h) median lethal concentrations (LC50s) were derived for individual compounds and used to design a binary mixture study to determine cumulative effects. The LC50s showed that imidacloprid was more potent than tebuconazole by 1 to 3 orders of magnitude for the 4 species. Lethality data from mixture experiments were analyzed using MIXTOX to determine deviations from independent action, followed by the model deviation ratio (MDR) technique to determine the biological significance and reproducibility of observed mixture effects. MIXTOX showed that the cumulative toxicities of imidacloprid-tebuconazole differed between the species: for C. dilutus there was no deviation from independent action; however, for H. azteca the mixture was antagonistic (specifically dose ratio-dependent), and for N. triangulifer it was synergistic. The MDR method showed that only observations with H. azteca significantly deviated from independent action. Because of the lack of evidence of a clear deviation from independent action and the much greater potency of imidacloprid, the weight of evidence indicates that the presence of tebuconazole is unlikely to appreciably increase the hazard from imidacloprid exposure to aquatic invertebrates. Environ Toxicol Chem 2019;00:1-17. © 2019 SETAC.

A large-scale survey of house sparrows feathers reveals ubiquitous presence of neonicotinoids in farmlands

The massive use of neonicotinoid insecticides has been repeatedly incriminated for their impacts to avian populations. Some studies have reported contamination of granivorous birds by neonicotinoids but very little is known about exposure to neonicotinoids in other bird species. To fill this lack of knowledge, we trapped house sparrows Passer domesticus, an omnivorous bird whose diet is composed of both grains and insects, and we collected 617 feathers from individuals living on 47 conventional, integrated-production (IP-Suisse) and organic farms distributed all over the Swiss plateau, the country's main agricultural area. We then assessed the concentration of five neonicotinoids in 146 pools of feathers. We found that all feather samples were contaminated by at least one neonicotinoid at measurable concentration (>LOQ), with thiacloprid accounting for most of the prevalence (99%), while clothianidin was found at highest concentrations (with averages ranging from 1.68 to 9.2 ppb). Additionally, house sparrows living on conventional farms showed higher concentrations of neonicotinoids (15.26 ± 3.58 ppb) than individuals living on IP-Suisse (3.38 ± 0.86 ppb), and organic farms (2.59 ± 0.56 ppb). Our large-scale survey highlights how ubiquitous neonicotinoid insecticides have become in agricultural habitats, and reveals generalized exposure of house sparrows, and potentially other species inhabiting farmlands, to neonicotinoids.

The risk of neonicotinoid exposure to shrimp aquaculture

Widespread agricultural use of systemic neonicotinoid insecticides has resulted in the unintended contamination of aquatic environments. Water quality surveys regularly detect neonicotinoids in rivers and waterways at concentrations that could impact aquaculture stock. The toxicity of neonicotinoids to non-target aquatic insect and crustacean species has been recognised, however, there is a paucity of information on their effect on commercial shrimp aquaculture. Here, we show that commercially produced shrimp are likely to be exposed to dietary, sediment and waterborne sources of neonicotinoids; increasing the risks of disease and accidental human consumption. This review examines indicators of sublethal neonicotinoid exposure in non-target species and analyses their potential usefulness for ecotoxicology assessment in shrimp. The identification of rapid, reliable responses to neonicotinoid exposure in shrimp will result in better decision making in aquaculture management.

Neonicotinoid insecticide mixtures: Evaluation of laboratory-based toxicity predictions under semi-controlled field conditions

Neonicotinoid insecticide mixtures are frequently detected in aquatic environments in agricultural regions. Recent laboratory studies have indicated that neonicotinoid mixtures can elicit greater-than-additive toxicity in sensitive aquatic insects (e.g. Chironomus dilutus). However, this has yet to be validated under field conditions. In this study, we compared the chronic (28- and 56-day) toxicity of three neonicotinoids (imidacloprid, clothianidin, and thiamethoxam) and their mixtures to natural aquatic insect communities. Using experimental in-situ enclosures (limnocorrals), we exposed wetland insects to single-compounds and binary mixtures at equitoxic concentrations (1 toxic unit under the principle of Concentration Addition). We assessed the composition of all emerged insect taxa and the cumulative Chironomidae emergence and biomass over time. In treated limnocorrals, there were subtle shifts in community composition, with greater mean proportions of emergent Trichoptera and Odonata. Cumulative emergence and biomass increased over time and there was a significant interaction between time and treatment. At 28 days, cumulative Chironomidae emergence and biomass were not significantly different between neonicotinoid treatments and controls. However, cumulative emergence in the imidacloprid, clothianidin, and clothianidin-thiamethoxam treatments were 42%, 20%, and 44% lower than predicted from applied doses. At 56 days, effects on cumulative emergence and biomass were significant for imidacloprid, clothianidin, and the clothianidin-thiamethoxam mixture. Contrary to laboratory predictions, mixtures were not more toxic than single compounds under semi-controlled field settings. Furthermore, only clothianidin significantly shifted sex-ratios towards female-dominated populations. Results showed that the responses of natural Chironomidae populations to neonicotinoids and their mixtures cannot be adequately predicted from laboratory-derived single-species models, and although occasional overdosing may have influenced the magnitude of effects, reductions in Chironomidae emergence and biomass can occur at average neonicotinoid concentrations below some current water quality guidelines. Therefore, neonicotinoid guidelines should be revised to ensure that Chironomidae and other sensitive aquatic insects inhabiting agricultural wetlands are adequately protected.

Relative chronic sensitivity of neonicotinoid insecticides to Ceriodaphnia dubia and Daphnia magna

Neonicotinoid insecticides are a group of plant protectants frequently detected in surface waters at low concentrations. Aquatic invertebrates therefore have the potential to be exposed chronically to low concentrations of neonicotinoids. The cladocerans Daphnia magna and Ceriodaphnia dubia are among the most commonly used invertebrate test species in aquatic toxicology. Both species are known to be acutely insensitive to neonicotinoids, and while chronic toxicity has been characterized for D. magna, little research has been conducted with C. dubia. In the present study we conducted 7-d static-renewal life cycle tests for 6 neonicotinoids (acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam) with C. dubia, and a 21-d test with imidacloprid with D. magna. 7-d LC50s for C. dubia ranged from 8.42 mg L^-1 for imidacloprid to > 100 mg L^-1 for clothianidin; 7-d reproduction EC50s were 2.98 for thiacloprid, to > 67 mg L^-1 for dinotefuran. D. magna were less sensitive than C. dubia to imidacloprid, by 4-fold for lethality and 1.5-fold for reproduction; however, acute-to-chronic ratios (ACRs) were similar. ACRs, based on 48-h acute LC50s and 7- or 21-d chronic reproduction EC10s, ranged from 5.4 for acetamiprid to 53.0 for imidacloprid (mean 36.6, CV = 51%). Chronic toxicity values for both species were orders of magnitude greater than concentrations reported in the environment, and thus hazard to these cladocerans is negligible.

Effects of imidacloprid and a neonicotinoid mixture on aquatic invertebrate communities under Mediterranean conditions

Neonicotinoid insecticides are considered contaminants of concern due to their high toxicity potential to non-target terrestrial and aquatic organisms. In this study we evaluated the sensitivity of aquatic invertebrates to a single application of imidacloprid and an equimolar mixture of five neonicotinoids (imidacloprid, acetamiprid, thiacloprid, thiamethoxam, clothianidin) using mesocosms under Mediterranean conditions. Cyclopoida, Cloeon dipterum and Chironomini showed the highest sensitivity to neonicotinoids, with calculated NOECs below 0.2 μg/L. The sensitivity of these taxa was found to be higher than that reported in previous studies performed under less warm conditions, proving the high influence of temperature on neonicotinoid toxicity. The short-term responses of the zooplankton and the macroinvertebrate communities to similar imidacloprid and neonicotinoid mixture concentrations were very similar, suggesting that the concentration addition model can be used as a plausible hyphotesis to assess neonicotinoid mixture effects in aquatic ecosystems. Long-term mixture toxicity assessments, however, should consider the fate of the evaluated substances in the environment of concern. As part of this study, we also demonstrated that Species Sensitivity Distributions constructed with chronic laboratory toxicity data and calculated (multi-substance) Potentially Affected Fractions provide an accurate estimation to asssess the ecotoxicologial risks of imidacloprid and neonicotinoid mixtures to aquatic invertebrate species assemblages.

Can chronic exposure to imidacloprid, clothianidin, and thiamethoxam mixtures exert greater than additive toxicity in Chironomus dilutus?

Widespread agricultural use of neonicotinoid insecticides has resulted in frequent detection of mixtures of these compounds in global surface waters. Recent evidence suggests that neonicotinoid mixtures can elicit synergistic toxicity in aquatic insects under acute exposure conditions, however this has not been validated for longer exposures more commonly encountered in the environment. Therefore, we aimed to characterize the chronic (28-day) toxicity of imidacloprid, clothianidin, and thiamethoxam mixtures under different doses and mixture ratios to determine if the assumption of synergistic toxicity would hold under more environmentally realistic exposure settings. The sensitive aquatic insect Chironomus dilutus was used as a representative test species, and successful emergence was used as a chronic endpoint. Applying the MIXTOX modeling approach, predictive parametric models were fitted using single-compound toxicity data and statistically compared to observed toxicity in subsequent mixture tests. Imidacloprid-clothianidin, clothianidin-thiamethoxam and imidacloprid-clothianidin-thiamethoxam mixtures did not significantly deviate from concentration-additive toxicity. However, the cumulative toxicity of the imidacloprid-thiamethoxam mixture deviated from the concentration-additive reference model, displaying dose-ratio dependent synergism and resulting in up to a 10% greater reduction in emergence from that predicted by concentration addition. Furthermore, exposure to select neonicotinoid mixtures above 1.0 toxic unit tended to shift sex-ratios toward more male-dominated populations. Results indicate that, similar to acute exposures, the general assumption of joint additivity cannot adequately describe chronic cumulative toxicity of all neonicotinoid mixtures. Indeed, our observations of weak synergism and sex-ratio shifts elicited by some mixture combinations should be considered in water quality guideline development and environmental risk assessment practices for neonicotinoid insecticides, and explored in further investigations of the effects of neonicotinoid mixtures on aquatic communities.

Thiacloprid-induced toxicity influenced by nutrients: Evidence from in situ bioassays in experimental ditches

Many studies show that neonicotinoid insecticides cause toxicity to aquatic invertebrates. Some studies report that insecticide toxicity may differ in combination with other agrochemicals under realistic field conditions. To explore such altered toxicity further, we aimed to determine the single and combined effects of environmentally relevant levels of the neonicotinoid thiacloprid and nutrients on different endpoints of 4 aquatic invertebrate species. Animals were exposed to these agrochemicals using a caged experiment within experimental ditches. We observed thiacloprid-induced toxicity for 2 crustaceans, Daphnia magna and Asellus aquaticus, and for 1 out of 2 tested insect species, Cloeon dipterum. We observed no toxic effects for Chironomus riparius at the time-weighted average test concentration of 0.51 μg thiacloprid/L. For D. magna, the observed toxicity, expressed as the lowest-observed-effect concentration (LOEC), on growth and reproduction was present at thiacloprid concentrations that were 2456-fold lower than laboratory-derived LOEC values. This shows that these species, when exposed under natural conditions, may exhibit neonicotinoid-induced toxic stress. Contrary to the low nutrient treatment, such toxicity was often not observed under nutrient-enriched conditions. This was likely attributable to the increased primary production that allowed for compensatory feeding. These findings warrant the inclusion of different feeding regimes in laboratory experiments to retrieve the best estimates of neonicotinoid-induced toxicity in the natural environment. Environ Toxicol Chem 2018;37:1907-1915. © 2018 SETAC.

Neonicotinoid insecticides imidacloprid, guadipyr, and cycloxaprid induce acute oxidative stress in Daphnia magna

Cycloxaprid (CYC) and guadipyr (GUA) are two new and promising neonicotinoid insecticides whose effects on Daphnia magna are as yet unknown. In this study, the acute toxicities of CYC and GUA to D. magna, including immobilization and embryo-hatching inhibition, and their effects on antioxidant enzymes and related gene expression were determined after a 48-h exposure. Imidacloprid (IMI) was evaluated at the same time as a reference agent. The 48-h EC₅₀ values of IMI, GUA, and CYC for neonate immobilization were 13.0-16.5mg/L and for embryo hatching were 11.3-16.2mg/L. The specific activity of the enzymes superoxide dismutase (SOD) and catalase (CAT) were interfered by IMI, but not by GUA and CYC, while the activity of acetylcholinesterase (AChE) was significantly increased by IMI, but inhibited by GUA and CYC. The relative expressions of the Sod-Cu/Zn, Sod-Mn, Cat, and Ache genes were usually inhibited by IMI, GUA, and CYC, except for Cat by CYC, Ache by GUA, and Sods by IMI. For vitellogenin genes with a SOD-like domain (Vtg1/2-sod), relative expression was increased by IMI and inhibited by GUA and CYC, indicating that IMI, GUA, and CYC have potential toxicity toward reproduction. CYC and GUA are highly active against IMI-resistant pests, and considering the similar toxicity of IMI to D. magna, CYC and GUA are suitable for use in future integrated pest management systems.

Toxicity Evaluation of Individual and Mixtures of Nanoparticles Based on Algal Chlorophyll Content and Cell Count

The toxic effects of individual and binary mixtures of five metal oxide nanoparticles (NPs) were evaluated based on changes in two endpoints of algal growth: the cell count and chlorophyll content. Various effects were observed according to the concentration tested and type of NPs, and there were no significant differences in findings for the two endpoints. In general, ZnO NPs caused the greatest inhibition of algal growth, and Fe₂O₃ NPs the least. The EC50 for ZnO was 2.0 mg/L for the cell count and 2.6 mg/L for the chlorophyll content, and it was 76 and 90 mg/L, respectively, for Fe₂O₃. The EC50 values were in the order ZnO > NiO > CuO > TiO₂ > Fe₂O₃. Subsequently, the effects of 30 binary mixture combinations on the chlorophyll content were evaluated. Comparisons were made between the observed and the expected toxicities calculated based on the individual NP toxicities. Overall, additive action (67%) was mainly observed, followed by antagonistic (16.5%) and synergistic (16.5%) actions. These results suggest that environmental exposure to NP mixtures may cause toxicity levels similar to the sum of those of the constituent NPs.

Investigating long-term effect of nanoparticles on growth of Raphanus sativus plants: a trans-generational study

In the past decade, there has been an unprecedented growth in the application of nanoparticles (NPs) worldwide. Even though the acute toxicity of CuO and ZnO NPs to plants has been investigated in past, the trans-generational effects of these NPs in the environment are still unknown. In this study, we investigated whether the treatment of radish plants with CuO and ZnO NPs as single compound and as a binary mixture (10, 100 and 1000 mg/Kg soil) through their lifecycle would affect the seed quality and the development of second-generation seedlings or not. Results showed reduced root length, shoot length and biomass in F1 seedlings of NPs treated plants. The treated F1 seeds had smaller seed weight with accumulated Cu and Zn. The effect of toxic interaction between CuO and ZnO on plant growth was antagonistic in nature. Evaluation of the trans-generational impact is important to understand the long-term effect of NPs on the environment.

Mixture toxicity in the marine environment: Model development and evidence for synergism at environmental concentrations

Little is known about the effect of metal mixtures on marine organisms, especially after exposure to environmentally realistic concentrations. This information is, however, required to evaluate the need to include mixtures in future environmental risk assessment procedures. We assessed the effect of copper (Cu)-Nickel (Ni) binary mixtures on Mytilus edulis larval development using a full factorial design that included environmentally relevant metal concentrations and ratios. The reproducibility of the results was assessed by repeating this experiment 5 times. The observed mixture effects were compared with the effects predicted with the concentration addition model. Deviations from the concentration addition model were estimated using a Markov chain Monte-Carlo algorithm. This enabled the accurate estimation of the deviations and their uncertainty. The results demonstrated reproducibly that the type of interaction-synergism or antagonism-mainly depended on the Ni concentration. Antagonism was observed at high Ni concentrations, whereas synergism occurred at Ni concentrations as low as 4.9 μg Ni/L. This low (and realistic) Ni concentration was 1% of the median effective concentration (EC50) of Ni or 57% of the Ni predicted-no-effect concentration (PNEC) in the European Union environmental risk assessment. It is concluded that results from mixture studies should not be extrapolated to concentrations or ratios other than those investigated and that significant mixture interactions can occur at environmentally realistic concentrations. This should be accounted for in (marine) environmental risk assessment of metals. Environ Toxicol Chem 2017;36:3471-3479. © 2017 SETAC.

Evaluation of the Effects of Nanoparticle Mixtures on Brassica Seed Germination and Bacterial Bioluminescence Activity Based on the Theory of Probability

Effects of binary mixtures of six metal oxide nanoparticles (NPs; 54 combinations) on the activities of seed germination and bacterial bioluminescence were investigated using the theory of probability. The observed toxicities of various NPs combinations were compared with the theoretically expected toxicities, calculated based on individual NPs toxicities. Different sensitivities were observed depending on the concentrations and the types of NPs. The synergistic mode (67%; observed toxicity greater than expected toxicity) was predominantly observed in the bioluminescence test, whereas both synergistic (47%) and additive (50%) modes were prevalent in the activity of seed germination. With regard to overall analysis, a slightly high percentage (56%) of the synergistic mode of action was (30 out of 54 binary mixture combinations; p < 0.0392) observed. These results suggest that the exposure of an NPs mixture in the environment may lead to a similar or higher toxicity level than the sum of its constituent NPs would suggest. In addition, one organism for assessment did not always show same results as those from a different assessment. Therefore, combining results of different organisms exposed to a wide range of concentrations of binary mixture will more properly predict and evaluate the expected ecotoxicity of pollutants on environments.

Planting of neonicotinoid-coated corn raises honey bee mortality and sets back colony development

Worldwide occurrences of honey bee colony losses have raised concerns about bee health and the sustainability of pollination-dependent crops. While multiple causal factors have been identified, seed coating with insecticides of the neonicotinoid family has been the focus of much discussion and research. Nonetheless, few studies have investigated the impacts of these insecticides under field conditions or in commercial beekeeping operations. Given that corn-seed coating constitutes the largest single use of neonicotinoid, our study compared honey bee mortality from commercial apiaries located in two different agricultural settings, i.e. corn-dominated areas and corn-free environments, during the corn planting season. Data was collected in 2012 and 2013 from 26 bee yards. Dead honey bees from five hives in each apiary were counted and collected, and samples were analyzed using a multi-residue LC-MS/MS method. Long-term effects on colony development were simulated based on a honey bee population dynamic model. Mortality survey showed that colonies located in a corn-dominated area had daily mortality counts 3.51 times those of colonies from corn crop-free sites. Chemical analyses revealed that honey bees were exposed to various agricultural pesticides during the corn planting season, but were primarily subjected to neonicotinoid compounds (54% of analysed samples contained clothianidin, and 31% contained both clothianidin and thiamethoxam). Performance development simulations performed on hive populations' show that increased mortality during the corn planting season sets back colony development and bears contributions to collapse risk but, most of all, reduces the effectiveness and value of colonies for pollination services. Our results also have implications for the numerous large-scale and worldwide-cultivated crops that currently rely on pre-emptive use of neonicotinoid seed treatments.

Effects of diuron and carbofuran and their mixtures on the microalgae Raphidocelis subcapitata

In aquatic environments, organisms are often exposed to mixtures of several pesticides. In this study, the effects of carbofuran and diuron and their mixtures on the microalgae Raphidocelis subcapitata were investigated. For this purpose, toxicity tests were performed with the single compounds (active ingredients and commercial formulations) and their combinations (only active ingredients). According to the results, the toxicity of active ingredients and their commercial formulations to R. subcapitata was similar. In the single exposures, both carbofuran and diuron inhibited significantly the R. subcapitata growth and caused physiological (chlorophyll a content) and morphological (complexity and cell size) changes in cells, as captured by flow cytometry single-cell properties. Regarding the mixture toxicity tests, data fitted to both reference models, concentration addition (CA) and independent action (IA), and evidenced significant deviations. After the CA fitting, dose-ratio dependent deviation had the best fit to the data, demonstrating synergism caused mainly by diuron and antagonism caused mainly by carbofuran. After fitting the IA model, a synergistic deviation represented the best fit for the diuron and carbofuran mixtures. In general, the two reference models indicated the occurrence of synergism in the mixtures of these compounds, especially when diuron was the dominant chemical in the combinations. The increased toxicity caused by the mixture of these pesticides could pose a greater environmental risk for phytoplankton. Thus, exposure to diuron and carbofuran mixtures must also be considered in risk assessments, since the combination of these compounds may result in more severe effects on algae population growth than single exposures.

Prediction of toxicity of zinc and nickel mixtures to Artemia sp. at various salinities: From additivity to antagonism

Few studies have examined the toxicity of metal mixtures to marine organisms exposed to different salinities. The aim of the present study was to investigate the acute toxicity of zinc and nickel exposures singly and in combination to Artemia sp. under salinities of 10, 17, and 35 psu. The mixture concentrations were determined according to individual toxic units (TUs) to follow a fixed ratio design. Zinc was more toxic than nickel, and both their individual toxicities were higher at lower salinities. These changes in toxicity can be attributed to the Biotic Ligand Model (BLM) rather than to metal speciation. To analyze the mixture effect, the observed data were compared with the expected mixture effects predicted by the concentration addition (CA) model and by deviations for synergistic/antagonistic interactions and dose-level and dose-ratio dependencies. For a salinity of 35 psu, the mixture had no deviations; therefore, the effects were additive. After decreasing the salinity to 17 psu, the toxicity pattern changed to antagonism at low concentrations and synergism at higher equivalent LC₅₀ levels. For the lowest salinity tested (10 psu), antagonism was observed. The speciations of both metals were similar when in a mixture and when isolated, and changes in toxicity patterns are more related to the organism's physiology than metal speciation. Therefore, besides considering chemical interactions in real-world scenarios, where several chemicals can be present, the influence of abiotic factors, such as salinity, should also be considered.

Toxic potential of the emerging contaminant nicotine to the aquatic ecosystem

Nicotine is a "life-style compound" widely consumed by human populations and, consequently, often found in surface waters. This fact presents a concern for possible effects in the aquatic ecosystems. The objective of this study was to assess the potential lethal and sublethal toxicity of nicotine in aquatic organisms from different trophic levels (Vibrio fischeri, Pseudokirchneriella subcapitata, Thamnocephalus platyurus, and Daphnia magna). The bioassays were performed by exposing the organisms to concentrations of nicotine in a range of 0.5-1000 μg/L. Results showed that nicotine, at tested concentration, was not acutely toxic to V. fischeri and T. platyurus. On the contrary, this substance exhibited toxicity to P. subcapitata and Daphnia magna. Thus, concentrations of nicotine of 100 and 200 μg/L promoted an inhibition in the growth of P. subcapitata. In addition, a concentration of 100 μg/L nicotine acted on the reproduction of the crustacean D. magna, by decreasing the number of juveniles produced by female. On the other hand, the results showed that concentrations equal to or greater than 10 μg/L induced the production of daphnids male offspring, which may indicate that nicotine is a weak juvenoid compound of the D. magna endocrine system. Furthermore, the result showed that concentrations tested of this chemical have the capacity to revert the effect of fenoxycarb, a strong juvenoid chemical insecticide. The results of the study revealed that nicotine can induce several changes in some of the most important key groups of the aquatic compartment, which can compromise, in a short time, the balance of aquatic ecosystem. Finally, a preliminary environmental risk assessment of this stimulant was performed from the highest measured concentration in surface water and the no observable effect concentration value in the most sensitive species, i.e., D. magna. This process revealed that nicotine can produce an important risk to aquatic organisms.

Ecological risk assessment for aquatic invertebrate communities exposed to imidacloprid as a result of labeled agricultural and nonagricultural uses in the United States

A probabilistic ecological risk assessment (ERA) was conducted to determine the potential effects of acute and chronic exposure of aquatic invertebrate communities to imidacloprid arising from labeled agricultural and nonagricultural uses in the United States. Aquatic exposure estimates were derived using a higher-tier refined modeling approach that accounts for realistic variability in environmental and agronomic factors. Toxicity was assessed using refined acute and chronic community-level effect metrics for aquatic invertebrates (i.e., species or taxon sensitivity distributions) developed using the best available data. Acute and chronic probabilistic risk estimates were derived by integrating the exposure distributions for different use patterns with the applicable species or taxon sensitivity distributions to generate risk curves, which plot cumulative probability of exceedance versus the magnitude of effect. Overall, the results of this assessment indicated that the aquatic invertebrate community is unlikely to be adversely affected by acute or chronic exposure to imidacloprid resulting from currently registered uses of imidacloprid in the United States. Environ Toxicol Chem 2017;36:1375-1388. © 2016 SETAC.

The influence of thiacloprid on the feeding behaviour of the copepod, Diacyclops bicuspidatus, preying on nematodes

Nowadays, neonicotinoids are the most widespread insecticides. As neurotoxins with high toxicity to many arthropods, they provide effective pest control, but it also became apparent that they are impacting non-target organisms in freshwater habitats. This study investigated the influence of the neonicotinoid thiacloprid on the behaviour of the copepod, Diacyclops bicuspidatus, feeding on different nematode species (Caenorhabditis elegans, Plectus aquatilis, Panagrolaimus sp.) and on a natural nematode community. All experiments demonstrated that thiacloprid led to decreased feeding of D. bicuspidatus (EC50 values 116-158 μg l−1). In addition, in the experiment where nematodes from a natural sediment were offered as prey, copepod feeding was significantly reduced. The copepod feeding response was a more sensitive endpoint than acute and chronic toxicity tests with daphnids that are routinely used for regulatory risk assessment. An impact on feeding is also a parameter with immediate relevance for the copepod population (reduced fitness) and the associated ecosystem.

Joint toxicity prediction of nanoparticles and ionic counterparts: Simulating toxicity under a fate scenario

The joint effects of NPs with other chemicals is not fully yet understood along with the joint effects of the particulate and dissolved forms/fractions. The predictability of joint effects is of great importance for environmental risk assessment. Therefore this study aimed at inferring on the predictability of NPs binary mixture toxicity based on their ionic counterparts' mixtures, and evaluating if the joint toxicity of two forms of the same element (NP and ion) acts as dilution of each other. Effects of individual and mixtures of ZnO and Ag NPs and their respective salts (AgNO₃ and ZnCl₂) were studied in immobilization and feeding tests using Daphnia magna. NPs mixture toxicity patterns did not mirror their ionic counterparts' mixture toxicity responses and therefore their prediction should not rely on the available knowledge for regular chemicals. Regarding mixtures from the same element with different forms (NP and ions), both Zn and Ag mixtures showed a deviation from additivity, relying on the interaction between NP and ions. A synergistic effect was depicted when the concentrations of Ag ions increased, while antagonism was observed with AgNP increase in suspension. This is an expected pattern in long term studies due to dissolution, relating fate and toxicity.

Hydractinia echinata test-system. IV. Toxic synergism of human pharmaceuticals in mixtures with iodoform

The structure-toxicity relationships for a series of singular human stomatological pharmaceuticals preparations and in mixture with Iodoform on Hydractinia echinata were obtained and their synergism was analyzed through the Metamorphosis Reduction Concentration (MRC50) within the "Köln model". The differences manifested between the total and individual components of the samples and mixtures, associated with toxic versus non-toxic synergism, are dependent on three essential factors of synthesis (the nature, the concentration and the number) besides manifested isotoxicity of the given components. The method represents a practical alternative useful for the reduction of experimental tests on animal to the lowest possible level, in accordance to the '3Rs' (reduce, reuse and recycle) integrative concept.

Effects of properties of metal-contaminated soils on bacterial bioluminescence activity, seed germination, and root and shoot growth

This study examined the effects of several factors (metal contents and soil properties) on bacterial bioluminescence activity, seed germination and root/shoot growth of Lactuca in metal-contaminated soils. Each bioassay showed different sensitivities to extractants of soil samples. Average sensitivities of the bioassay were in the following order: root growth > bioluminescence ≥ shoot growth ≥ seed germination. Both total and weak acid-extracted metal contents showed no observable correlations with the activity of any bioassays (r(2) < 0.279). However, reasonable correlations were observed between the bioluminescence activity and organics (r(2) = 0.7198) as well as between root growth and CEC (r(2) = 0.6676). Effects of soils were difficult to generalize since they were dependent on many factors, such as soil properties, metal contents, and the organism used in each test. Nonetheless, these results indicated that a battery of bioassays is an effective strategy for assessment of contaminated soils. Furthermore, specific soil factors were shown to more influence on soil toxicity, depending on the type of bioassay.

Combination effects of pyrethroids and neonicotinoids on development and survival of Chironomus riparius

Standard ecotoxicological risk assessments are conducted on individual substances, however monitoring of streams in agricultural areas has shown that pesticides are rarely present alone. In fact, brief but intense pulse events such as storm water runoff and spray drift during application subject freshwater environments to complex mixtures of pesticides at high concentrations. This study investigates the potential risks to non-target aquatic organisms exposed to a brief but intense mixture of the neonicotinoid pesticides imidacloprid and thiacloprid and the pyrethroid pesticides deltamethrin and esfenvalerate, compared to single substance exposure. All four of these pesticides have been detected in surface waters at concentrations higher than benchmark values and both classes of pesticides are known to exert adverse effects on non-target aquatic organisms under single substance exposure scenarios. First instar midge larvae of the non-target aquatic organism, Chironomus riparius, were exposed to combinations of these four pesticides at 50% of their LC50 (96 h) values in a 1h pulse. They were then reared to adulthood in uncontaminated conditions and assessed for survival, development time and fecundity. Our results show that the risk of disruption to survival and development of non-target aquatic organisms under this scenario is not negligible on account of the significant increases in mortality of C. riparius found in the majority of the pesticide exposures and the delays in development after pyrethroid exposure. While none of the deleterious effects appear to be amplified by combination of the pesticides, there is some evidence for antagonism. No effects on fecundity by any of the pesticide treatments were observed.

Effects of Monotypic and Binary Mixtures of Metal Oxide Nanoparticles on Microbial Growth in Sandy Soil Collected from Artificial Recharge Sites

The potential effects of monotypic and binary metal oxide nanoparticles (NPs, ZnO, NiO, Co₃O₄ and TiO₂) on microbial growth were evaluated in sandy soil collected from artificial recharge sites. Microbial growth was assessed based on adenosine triphosphate (ATP) content, dehydrogenase activity (DHA), and viable cell counts (VCC). Microbial growth based on ATP content and VCC showed considerable differences depending on NP type and concentration, whereas DHA did not significantly change. In general, ZnO NPs showed the strongest effect on microbial growth in all measurements, showing an EC50 value of 10.9 mg/L for ATP content. The ranking (EC50) of NPs based on their effect on microbial growth assessed by ATP content and VCC was ZnO > Co₃O₄ > NiO > TiO₂. Upon exposure to binary NP mixtures, synergistic and additive modes of action were observed for ATP content and VCC, respectively. The ranges of observed (P(O)) and expected (P(E)) activity were 83%-92% and 78%-82% of the control (p-value 0.0010) based on ATP content and 78%-95% and 72%-94% of the control (p-value 0.8813) based on VCC under the tested conditions, respectively. The results indicate that the effects of NP mixtures on microbial growth in the sandy soil matrix were as great, or greater, than those of single NPs. Therefore, understanding the effects of single NPs and NP mixtures is essential for proper ecological risk assessment. Additionally, these findings demonstrate that the evaluation of NP effects may be profoundly influenced by the method of microbial growth measurement.

Interactive Effects of Metal Mixtures on Seed Germination and Bioluminescence Activities based on the Theory of Probabilities

The interactive effects of metal mixtures on seed germination (36 combinations) and bacterial bioluminescence (60 combinations) activities were investigated based on the theory of probabilities. Observed effects were compared with expected effects, which were calculated based on single metal activities. Different responses and sensitivities were observed depending on the types and concentrations of mixture metals as well as the organisms tested. In general, an additive mode of action (observed and expected effects are nearly same) was mostly common in the bioluminescence assay, whereas synergistic and additive inhibition modes were mostly observed in seed germination. Therefore, the mixture effects of the different bioassays could not be generalized because they were dependent on the types and concentrations of chemicals and organisms used. The results indicated that mixture, rather than single, effects by various bioassays and wide ranges of concentration combinations may comprise a better strategy for the bioassessment of contaminated environments.

Toxic effects of combined stressors on Daphnia pulex: Interactions between diazinon, 4-nonylphenol, and wastewater effluent

Contaminant exposure in aqueous systems typically involves complex chemical mixtures. Given the large number of compounds present in the environment, it is critical to identify hazardous chemical interactions rapidly. The present study utilized a prototype for a novel high-throughput assay to quantify behavioral changes over time to identify chemical interactions that affect toxicity. The independent and combined effects of 2 chemicals, diazinon (an insecticide) and 4-nonylphenol (a detergent metabolite), on the swimming behavior of the freshwater crustacean Daphnia pulex were examined. Cumulative distance and change in direction were measured repeatedly via optical tracking over 90 min. Exposure to low concentrations of diazinon (0.125-2 µM) or 4-nonylphenol (0.25-4 µM) elicited significant concentration- and time-dependent effects on swimming behavior. Exposure to 0.5 µM 4-nonylphenol alone did not significantly alter mean cumulative distance but did elicit a small, significant increase in mean angle, the measure of change in direction. When 0.5 µM 4-nonylphenol was used in combination with diazinon (0.125-0.5 µM), it augmented the adverse impact of diazinon on the swimming behavior of Daphnia. Additionally, enhanced sensitivity to diazinon was observed in animals exposed to treated wastewater effluent for 24 h prior to a diazinon challenge. The present experiments demonstrate that exposure to 4-nonylphenol and complex chemical mixtures (e.g., treated wastewater) can enhance the toxicity of exposure to the insecticide diazinon.

Ecotoxicity and genotoxicity of a binary combination of triclosan and carbendazim to Daphnia magna

In the environment, chemical substances appear as complex mixtures and consequently organisms are exposed to a variety of chemicals from different sources (e.g. wastewater treatment plants, agriculture runoffs). When studying chemical mixtures, there are two conceptual models usually used to predict toxicity: the Independent Action (IA) and Concentration Addition (CA) models. However, deviations from these reference models can occur as synergism or antagonism, dose ratio or dose level dependency. The aim of the present study was to investigate the effects of triclosan and carbendazim, and their binary mixture to Daphnia magna. With this purpose, immobilisation, feeding inhibition, and reproduction were assessed as main ecotoxicity endpoints. In addition, in vivo genotoxicity of both chemicals was investigated using the comet assay. In the single exposure, carbendazim was more toxic to D. magna than triclosan. When daphnids were exposed to both single compounds, DNA damage was observed. Concerning mixture exposures, different endpoints followed different patterns of response, from additivity: IA model (feeding inhibition and reproduction data), to deviations that indicate interaction between chemicals inside the organism: dose level dependency (immobilisation data) and dose ratio dependency (DNA damage). This study showed that additivity does not rule the dose-effect relation in chemical mixtures of carbendazim and triclosan and interactions between both chemicals might induce generally higher toxicity than predicted based on single chemical exposures.

Daphnid life cycle responses to the insecticide chlorantraniliprole and its transformation products

Chlorantraniliprole (CAP) is a newly developed, widely applied insecticide. In the aquatic environment, several transformation products are formed under natural conditions, one by dehydration and others by photoinduced degradation. Data on aquatic ecotoxicity of CAP can mainly be found in registration and regulatory evaluation reports. Moreover, the toxicity of its transformation products and especially effects upon chronic exposure remain completely unknown. Hence, our aim was to investigate the acute and chronic toxicity of CAP and its transformation products to the daphnid Daphnia magna. The results showed that CAP is extremely toxic to D. magna, with an acute and chronic LC50 of 9.4 and 3.7 μg/L, respectively. No effects on daphnid reproduction were observed, but the impact on daphnid survival also affected population growth rate, with an EC50 of 3.5 μg/L. In contrast, no negative effects of the two main degradation products were observed. The present study demonstrated a high sensitivity of nontarget microcrustaceans to CAP. However, the actual risk of CAP in water diminishes with its spontaneous or light-induced degradation into two transformation products, showing no toxicity to the daphnids in the present study.

Neonicotinoids in the Canadian aquatic environment: a literature review on current use products with a focus on fate, exposure, and biological effects

Developed to replace organophosphate and carbamate insecticides, neonicotinoids are structurally similar to nicotine. The three main neonicotinoid insecticides, imidacloprid, clothianidin, and thiamethoxam, are being re-evaluated by Health Canada's Pest Management Regulatory Agency (PMRA). An important aspect of the re-evaluation is the potential for effects in non-target organisms, including aquatic organisms. Leaching into surface waters is one of the major concerns surrounding extensive use of neonicotinoids, especially in close proximity to water bodies. The PMRA has classified IMI as 'persistent' with a 'high' leaching potential. Globally, neonicotinoids have been detected in a variety of water bodies, typically at concentrations in the low μg/L range. While IMI has been included in some monitoring exercises, there are currently very few published data for the presence of CLO and THM in Canadian water bodies. The majority of neonicotinoid toxicity studies have been conducted with IMI due to its longer presence on the market and high prevalence of use. Aquatic insects are particularly vulnerable to neonicotinoids and chronic toxicity has been observed at concentrations of IMI below 1 μg/L. Acute toxicity has been reported at concentrations below 20 μg/L for the most sensitive species, including Hyalella azteca, ostracods, and Chironomus riparius. Fish, algae, amphibians, and molluscs are relatively insensitive to IMI. However, the biological effects of THM and CLO have not been as well explored. The Canadian interim water quality guideline for IMI is 0.23 μg/L, but there is currently insufficient use, fate, and toxicological information available to establish guidelines for CLO and THM. Based on concentrations of neonicotinoids reported in surface waters in Canada and globally, there is potential for aquatic invertebrates to be negatively impacted by neonicotinoids. Therefore, it is necessary to address knowledge gaps to inform decisions around guidelines and registration status for neonicotinoid insecticides in Canada to protect our aquatic ecosystems.

Neonicotinoid contamination of global surface waters and associated risk to aquatic invertebrates: a review

Neonicotinoids, broad-spectrum systemic insecticides, are the fastest growing class of insecticides worldwide and are now registered for use on hundreds of field crops in over 120 different countries. The environmental profile of this class of pesticides indicate that they are persistent, have high leaching and runoff potential, and are highly toxic to a wide range of invertebrates. Therefore, neonicotinoids represent a significant risk to surface waters and the diverse aquatic and terrestrial fauna that these ecosystems support. This review synthesizes the current state of knowledge on the reported concentrations of neonicotinoids in surface waters from 29 studies in 9 countries world-wide in tandem with published data on their acute and chronic toxicity to 49 species of aquatic insects and crustaceans spanning 12 invertebrate orders. Strong evidence exists that water-borne neonicotinoid exposures are frequent, long-term and at levels (geometric means=0.13μg/L (averages) and 0.63μg/L (maxima)) which commonly exceed several existing water quality guidelines. Imidacloprid is by far the most widely studied neonicotinoid (66% of the 214 toxicity tests reviewed) with differences in sensitivity among aquatic invertebrate species ranging several orders of magnitude; other neonicotinoids display analogous modes of action and similar toxicities, although comparative data are limited. Of the species evaluated, insects belonging to the orders Ephemeroptera, Trichoptera and Diptera appear to be the most sensitive, while those of Crustacea (although not universally so) are less sensitive. In particular, the standard test species Daphnia magna appears to be very tolerant, with 24-96hour LC50 values exceeding 100,000μg/L (geometric mean>44,000μg/L), which is at least 2-3 orders of magnitude higher than the geometric mean of all other invertebrate species tested. Overall, neonicotinoids can exert adverse effects on survival, growth, emergence, mobility, and behavior of many sensitive aquatic invertebrate taxa at concentrations at or below 1μg/L under acute exposure and 0.1μg/L for chronic exposure. Using probabilistic approaches (species sensitivity distributions), we recommend here that ecological thresholds for neonicotinoid water concentrations need to be below 0.2μg/L (short-term acute) or 0.035μg/L (long-term chronic) to avoid lasting effects on aquatic invertebrate communities. The application of safety factors may still be warranted considering potential issues of slow recovery, additive or synergistic effects and multiple stressors that can occur in the field. Our analysis revealed that 81% (22/27) and 74% (14/19) of global surface water studies reporting maximum and average individual neonicotinoid concentrations respectively, exceeded these thresholds of 0.2 and 0.035μg/L. Therefore, it appears that environmentally relevant concentrations of neonicotinoids in surface waters worldwide are well within the range where both short- and long-term impacts on aquatic invertebrate species are possible over broad spatial scales.