Joint toxicity of a pyrethroid insecticide, cypermethrin, and a heavy metal, lead, to the benthic invertebrate Chironomus dilutus

The exposure risk of heavy metals to insect pests and their impact on pests occurrence and cross-tolerance to insecticides: A review

Heavy metal (HM) pollution is a severe global environmental issue. HMs in the environment can transfer along the food chain, which aggravates their ecotoxicological effect and exposes the insects to heavy metal stress. In addition to their growth-toxic effects, HMs have been reported as abiotic environmental factors that influence the implementation of integrated pest management strategies, including microbial control, enemy insect control, and chemical control. This will bring new challenges to pest control and further highlight the ecotoxicological impact of HM pollution. In this review, the relationship between HM pollution and insecticide tolerance in pests was analyzed. Our focus is on the risks of HM exposure to pests, pests tolerance to insecticides under HM exposure, and the mechanisms underlying the effect of HM exposure on pests tolerance to insecticides. We infer that HM exposure, as an initial stressor, induces cross-tolerance in pests to subsequent insecticide stress. Additionally, the priming effect of HM exposure on enzymes associated with insecticide metabolism underlies cross-tolerance formation. This is a new interdisciplinary field between pollution ecology and pest control, with an important guidance value for optimizing pest control strategies in HM polluted areas.

Heavy metals and metalloid in aquatic invertebrates: A review of single/mixed forms, combination with other pollutants, and environmental factors

Heavy metals (HMs) and metalloid occur naturally and are found throughout the Earth's crust but they are discharged into aquatic environments at high concentrations by human activities, increasing heavy metal pollution. HMs can bioaccumulate in higher organisms through the food web and consequently affect humans. In an aquatic environment, various HMs mixtures can be present. Furthermore, HMs adsorb on other environmental pollutants, such as microplastics and persistent organic pollutants, causing a synergistic or antagonistic effect on aquatic organisms. Therefore, to understand the biological and physiological effects of HMs on aquatic organisms, it is important to evaluate the effects of exposure to combinations of complex HM mixtures and/or pollutants and other environmental factors. Aquatic invertebrates occupy an important niche in the aquatic food chain as the main energy link between higher and lower organisms. The distribution of heavy metals and the resulting toxic effects in aquatic invertebrates have been extensively studied, but few reports have dealt with the relationship between HMs, pollutants, and environmental factors in biological systems with regard to biological availability and toxicity. This review describes the overall properties of individual HM and their effects on aquatic invertebrates and comprehensively reviews physiological and biochemical endpoints in aquatic invertebrates depending on interactions among HMs, other pollutants, and environmental factors.

Effects of Single and Combined Ciprofloxacin and Lead Treatments on Zebrafish Behavior, Oxidative Stress, and Elements Content

Even though the toxic effects of antibiotics and heavy metals have been extensively studied in the last decades, their combined adverse impact on aquatic organisms is poorly understood. Therefore, the objective of this study was to assess the acute effects of a ciprofloxacin (Cipro) and lead (Pb) mixture on the 3D swimming behavior, acetylcholinesterase (AChE) activity, lipid peroxidation level (MDA-malondialdehyde), activity of some oxidative stress markers (SOD-superoxide dismutase and GPx-glutathione peroxidase), and the essential elements content (Cu-copper, Zn-zinc, Fe-iron, Ca-calcium, Mg-magnesium, Na-sodium and K-potassium) in the body of zebrafish (Danio rerio). For this purpose, zebrafish were exposed to environmentally relevant concentrations of Cipro, Pb, and a mixture for 96 h. The results revealed that acute exposure to Pb alone and in mixture with Cipro impaired zebrafish exploratory behavior by decreasing swimming activity and elevating freezing duration. Moreover, significant deficiencies of Ca, K, Mg, and Na contents, as well as an excess of Zn level, were observed in fish tissues after exposure to the binary mixture. Likewise, the combined treatment with Pb and Cipro inhibited the activity of AChE and increased the GPx activity and MDA level. The mixture produced more damage in all studied endpoints, while Cipro had no significant effect. The findings highlight that the simultaneous presence of antibiotics and heavy metals in the environment can pose a threat to the health of living organisms.

Insecticides and Drought as a Fatal Combination for a Stream Macroinvertebrate Assemblage in a Catchment Area Exploited by Large-Scale Agriculture

This case study documents responses in a headwater macroinvertebrate assemblage to insecticide pollution and hydrological drought. In 2014, the Doubravka brook (Czech Republic) was damaged by a large overflow of a mixture of chlorpyrifos (CPS) and cypermethrin (CP). In 2016–2017, this brook was then affected by severe drought that sometimes led to an almost complete absence of surface water. We found significant relationships between the strength of both these disturbances and the deeper taxonomic levels of both the overall macroinvertebrate assemblage (classes) and the arthropod assemblage alone (orders and dipteran families), as well as the functional feeding groups (FFGs). The CPS-CP contamination was mostly negatively correlated to arthropod and non-arthropod taxa and was positively correlated only with FFG collector-gatherers; on the other hand, the drought was negatively correlated to Simuliidae, Ephemeroptera, Trichoptera, and the FFG of grazer-scrapers and passive filterers. Drought conditions correlated most positively with Isopoda, Ostracoda, Heteroptera, adult Coleoptera, and predator and active filterer FFGs. The chosen eco-indicators (SPEARpesticides, SPEARrefuge, BMWP, and EPT) used as support information reveal the poor ecological status of the whole assemblage, including the control site, the cause of which is most likely to be the exploitation of the adjacent catchment area by large-scale agriculture. This type of agricultural exploitation will undoubtedly affect macroinvertebrate assemblages as a result of agrochemical and soil inputs during run-off events and will also exacerbate the effect of droughts when precipitation levels drop.

Development of the transcriptome for a sediment ecotoxicological model species, Chironomus dilutus

Chironomus dilutus is a prominent model species in conventional sediment toxicity testing and sediment contamination diagnosis. However, lack of genomic data significantly limited its application in identifying toxicological mode of action (MOA) and molecular biomarkers of toxicants. Here the transcriptome of C. dilutus in full life span and both sexes (1st, 2nd, 3rd and 4th instar larvae, pupae, and adults) were developed and temporal gene expression across adjacent life stages were investigated to understand the regulation of development. Furthermore, transcriptional response of Midges (the 4th instar larvae) exposed to chemicals of different MOAs (CdCl₂, nonylphenol and triclosan) were profiled based on the reference transcriptome. Consequently, a complete transcriptome of 31132 unigenes with N50 of 3117bp, covering 98.8% of the arthropod single-copy orthologs were assembled. While 364 genes were differentially expressed among adjacent larval stages, 7142 and 2127 of transcripts were significantly changed for the transition of larvae-pupae and pupae-adults, respectively. Finally, chemical-specific gene expression profile were identified in the midges, showed its potential in classifying distinct contaminants. Overall, the comprehensive transcriptome of C. dilutus developed here could not only facilitate the mechanistic understanding of environmental toxicants during critical life stage of aquatic insects, but also provide molecular diagnostic tools in sediment ecotoxicology.

Antagonistic effects in zebrafish (Danio rerio) behavior and oxidative stress induced by toxic metals and deltamethrin acute exposure

In natural environments, the aquatic organisms are exposed to complex mixtures of chemicals which may originate from natural sources or from anthropogenic activities. In this context, the aim of the study was to assess the potential effects that might occur when aquatic organisms are simultaneously exposed to multiple chemicals. For that, we have studied the acute effects of cadmium (0.2 μg L^-1), nickel (10 μg L^-1) and deltamethrin (2 μg L^-1) as individual toxicants and as mixture on the behavioral responses, oxidative stress (SOD and GPx), body electrolytes and trace metals profiles of zebrafish (Danio rerio). So far the scientific literature did not report about the combined effects of pesticides and toxic metals on zebrafish behavior using a 3D tracking system. Compared with other studies, in the present paper we investigated the acute effects of two heavy metals associated with a pesticide on zebrafish, in the range of environmentally relevant concentrations. Thus, the environmental concentrations of cadmium and nickel in three rivers affected by urban activities and one river with protected areas as background control were measured. The observations that resulted in our study demonstrated that deltamethrin toxicity was significantly decreased in some of the behavioral variables and oxidative stress when combined with CdNi mixture. Consequently, our study supports previous works concerning the combined toxicity of environmental chemicals since their simultaneous presence in the aqueous environment may lead to higher or lower toxicological effects on biota than those reported from a single pollutant. Therefore, the evaluation of toxic effects of a single contaminant does not offer a realistic estimate of its impact against aqueous ecosystems. This study also supports the idea that the interactions between different chemical compounds which do not exceed the maximum permitted limits in environment may have benefits for aquatic life forms or be more toxic.

Ecotoxicological and biochemical mixture effects of an herbicide and a metal at the marine primary producer diatom Thalassiosira weissflogii and the primary consumer copepod Acartia tonsa

Mixture effects of chemicals and their potential synergistic interactions are of great concern to the public and regulatory authorities worldwide. Intensive agricultural activities are leading to discharges of chemical mixtures to nearby estuarine and marine waters with possible adverse effects on the aquatic communities and for the trophic food web interlinking these communities. Further information about the impacts of these stressors on aquatic organisms is needed. This study addresses ecotoxicological and biochemical effects of single and mixtures of the metal copper and the herbicide Primextra® Gold TZ on the marine diatom Thalassiosira weissflogii and on the estuarine calanoid copepod Acartia tonsa by determining growth rate and survival, respectively, and changes on fatty acid(FA) profiles in both species. Mixture effects on diatom species revealed that copper and Primextra® acted most likely additively with respect to the concentration addition (CA) and independent action (IA) models with model deviation ratios (MDR), 0.752 and 1.063, respectively. For the copepod species, copper and Primextra® were most likely non-interactive with respect to the CA model (MDR = 1.521) but acted most likely synergistically with respect to the IA model (MDR = 2.026). A significant decline in the absolute FA concentration was observed for copepod species after mixture exposure including a considerable decrease of essential FAs that cannot be synthesized de novo by these grazers. We concluded that the mixture effects are more hazardous for primary consumer than for primary producer species in terms of both abundance and biomass quality, suggesting a potential for harmful effects for higher trophic levels and thus a decrease in energy flow through the ecosystem.

Effects of metals on enantioselective toxicity and biotransformation of cis-bifenthrin in zebrafish

Co-occurrence of pyrethroids and metals in watersheds previously has been reported to pose great risk to aquatic species. Pyrethroids are a class of chiral insecticides that have been shown to have enantioselective toxicity and biotransformation. However, the influence of metals on enantioselectivity of pyrethroids has not yet been evaluated. In the present study, the effects of cadmium (Cd), copper (Cu), and lead (Pb) on the enantioselective toxicity and metabolism of cis-bifenthrin (cis-BF) were investigated in zebrafish at environmentally relevant concentrations. The addition of Cd, Cu, or Pb significantly increased the mortality of zebrafish in racemate and R-enantiomer of cis-BF-treated groups. In rac-cis-BF- or 1R-cis-BF-treated groups, the addition of Cd, Cu, or Pb caused a decrease in enantiomeric fraction (EF) and an increased ratio of R-enantiomer residues in zebrafish. In 1S-cis-BF-treated groups, coexposure to Cd led to a lower EF and decreased residue levels of S-enantiomer. In addition, coexposure to the 3 metals resulted in different biodegradation characteristics of each enantiomer accompanied with differential changes in the expression of cytochrome P450 (CYP)1, CYP2, and CYP3 genes, which might be responsible for the enantioselective biodegradation of cis-BF in zebrafish. These results suggest that the influence of coexistent metals should be considered in the ecological risk assessment of chiral pyrethroids in aquatic environments. Environ Toxicol Chem 2017;36:2139-2146. © 2017 SETAC.

Toxicant mixtures in sediment alter gene expression in the cysteine metabolism of Chironomus tepperi

Sediment contamination can pose risks to the environment, and sediment toxicity tests have been developed to isolate the impact of sediment from other factors. Mixtures of contaminants often occur in sediments, and traditional endpoints used in toxicity testing, such as growth, reproduction, and survival, cannot discern the cause of toxicity from chemical mixtures because of complex interactions. In urban waterways, the synthetic pyrethroid bifenthrin and the metal copper are commonly found in mixtures, so the present study was designed to investigate how these contaminants cause toxicity in mixtures. To investigate this, Chironomus tepperi was exposed to environmentally relevant concentrations of copper and bifenthrin-spiked sediments in a 2-way factorial mixture for 5 d. Growth and expression profiles of cysteine metabolism genes were measured after exposure. Growth increased at low copper concentrations, decreased at high copper concentrations, and was unaffected by bifenthrin exposures. Copper exposures induced possible cellular repair by upregulating S-adenosylmethionine synthetase expression and downregulating expression of S-adenosylhomocysteine hydrolase and cystathionine-β-synthase. Metallothionein upregulation was also observed. Bifenthrin exposure altered cysteine metabolism to a lesser extent, downregulating cystathionine-β-synthase and γ-glutamylcysteine synthase. Synergistic, antagonistic, and dose-dependent interactions were observed, and there was evidence of conflicting modes of action and limited substrate production. These findings demonstrate how contextual gene expression changes can be sensitive and specific identifiers of toxicant exposure in mixtures. Environ Toxicol Chem 2017;36:691-698. © 2016 SETAC.

Global occurrence of pyrethroid insecticides in sediment and the associated toxicological effects on benthic invertebrates: An overview

Pyrethroids are the third most applied group of insecticides worldwide and are extensively used in agricultural and non-agricultural applications. Pyrethroids exhibit low toxicity to mammals, but have extremely high toxicity to fish and non-target invertebrates. Their high hydrophobicity, along with pseudo-persistence due to continuous input, indicates that pyrethroids will accumulate in sediment, pose long-term exposure concerns to benthic invertebrates and ultimately cause significant risk to benthic communities and aquatic ecosystems. The current review synthesizes the reported sediment concentrations of pyrethroids and associated toxicity to benthic invertebrates on a global scale. Geographically, the most studied area was North America, followed by Asia, Europe, Australia and Africa. Pyrethroids were frequently detected in both agricultural and urban sediments, and bifenthrin and cypermethrin were identified as the main contributors to toxicity in benthic invertebrates. Simulated hazard quotients (HQ) for sediment-associated pyrethroids to benthic organisms ranged from 10.5±31.1 (bifenthrin) to 41.7±204 (cypermethrin), suggesting significant risk. The current study has provided evidence that pyrethroids are not only commonly detected in the aquatic environment, but also can cause toxic effects to benthic invertebrates, and calls for better development of accurate sediment quality criteria and effective ecological risk assessment methods for this emerging class of insecticides.

Pyrethroid insecticide lambda-cyhalothrin and its metabolites induce liver injury through the activation of oxidative stress and proinflammatory gene expression in rats following acute and subchronic exposure

Lambda-cyhalothrin (LTC) [α-cyano-3-phenoxybenzyl-3-(2-chloro-3,3,3-trifluoro-1-propenyl)-2,2-dimethylcyclo-propanecarboxylate] is a synthetic type II pyrethroid insecticide commonly used in residential and agricultural areas. The potential hepatotoxicity of pyrethroids remains unclear and could easily be assessed by measuring common clinical indicators of liver disease. To understand more about the potential risks for humans associated with LTC exposure, male adult rats were orally exposed to 6.2 and 31.1 mg/kg bw of LTC for 7, 30, 45, and 60 days. Histopathological changes and alterations of main parameters related to oxidative stress and inflammatory responses in the liver were evaluated. Further, lambda-cyhalothrin metabolites [3-(2-chloro-3,3,3-trifluoroprop-1-enyl)-2,2-dimethyl-cyclopropane carboxylic acid (CFMP), 4-hydroxyphenoxybenzoic acid (4-OH-3-PBA), and 3-phenoxybenzoic acid (3-PBA)] in the liver tissues were identified and quantified by ultra-high-performance liquid chromatography coupled to quadripole time-of-flight mass spectrometry (UHPLC-MS-Q-ToF). Results revealed that LTC exposure significantly increased markers of hepatic oxidative stress in a time-dependent and dose-dependent manner, and this was associated with an accumulation of CFMP and 3-PBA in the liver tissues. In addition, the levels of tumor necrosis factor-α (TNF-α) and interleukin (IL-6 and IL-1β) gene expressions were significantly increased in the liver of exposed rats compared to controls. Correlation analyses revealed that CFMP and 3-PBA metabolite levels in the liver tissues were significantly correlated with the indexes of oxidative stress, redox status, and inflammatory markers in rats exposed to lambda-cyhalothin. Overall, this study provided novel evidence that hepatic damage is likely due to increased oxidative stress and inflammation under the condition of acute and subchronic exposure to lambda-cyhalothrin and that LTC metabolites (CFMP and 3-PBA) could be used as potential biomarker in human biomonitoring studies.

Does cadmium affect the toxicokinetics of permethrin in Chironomus dilutus at sublethal level? Evidence of enzymatic activity and gene expression

Pyrethroids and metals were simultaneously detected in aquatic environment and showed antagonistic lethality to the benthic invertebrate, Chironomus dilutus. Accelerated biotransformation of pyrethroids in organism by the presence of metals was proposed as the likely reason for the antagonism. Mechanistic explanation for the role of toxicokinetics of pyrethroids in the antagonistic interaction would help better understanding the reasons for the joint toxicity. The goal was achieved in the current study by evaluating the impact of cadmium on toxicokinetic parameters of permethrin in C. dilutus, and by explaining the interaction through quantifying the activity and gene expression of biotransformation-related enzymes. Toxicokinetic parameters were simulated using a first-order kinetic model. Bioconcentration factors and uptake and elimination rate constants for permethrin were not significantly changed with the addition of cadmium at sublethal level, neither did the activity of enzymes, including glutathione S-transferase (GST), carboxylesterase (CarE), catalase and lipid peroxidation. Yet, the activities of metabolism-related enzymes (GST and CarE) showed an elevating tendency with adding cadmium. Furthermore, the expression of metabolism-related genes, including cytochrome P450 and glutathione S-transferase genes were significantly up-regulated in C. dilutus exposed to a mixture of permethrin and cadmium compared with permethrin only. Although co-exposure to cadmium did not induce toxicokinetic changes of permethrin in C. dilutus, it did enhance the activity of metabolic enzymes which were encoded by the metabolism-related genes, suggesting an acceleration of biotransformation of permethrin to less toxic metabolites in the midges. This possibly explained the antagonistic interaction for permethrin and cadmium.

Joint Toxicity of Two Phthalates with Waterborne Copper to Daphnia magna and Photobacterium phosphoreum

Di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) are two widely used phthalates, while Cu(II) is a common valence state of copper. They have been ubiquitously detected in the aquatic environment, but information on their joint toxicity to aquatic organisms is scarce. In this study, we evaluated the combined effects of copper and these two phthalates to Daphnia magna and Photobacterium phosphoreum by quantifying the acute toxicity expressed by the EC50 (the concentration causing 50 % of maximal effect) value. The toxicity order was DEHP + Cu(II) > DBP + Cu(II) > Cu(II) > DEHP > DBP for both test species. Antagonism effects were found in the joint toxicity of Cu(II) combined with DBP or DEHP using the toxic unit method. These findings have important implications in environmental risk assessment for phthalates in the aquatic environment in the presence of heavy metals.

Developmental toxicity and DNA damage to zebrafish induced by perfluorooctane sulfonate in the presence of ZnO nanoparticles

Perfluorooctane sulfonate (PFOS) and ZnO nanoparticles (ZnO-NPs) are frequently detected in the environment, but few studies have assessed their joint toxicity. In this study, the acute toxicity and chronic toxicity to zebrafish (Danio rerio) induced by PFOS in the presence of ZnO-NPs were investigated, including developmental toxicity and DNA damage. The embryos were exposed to PFOS (only) (0.4, 0.8, and 1.6 mg/L) and PFOS plus ZnO-NPs (0.4 + 50, 0.8 + 50, and 1.6 + 50 mg/L) solutions to evaluate mortality (96 h), body length (96 h), hatch rate (72 h), heart rate (48 h),and malformation rate (96 h). The results revealed that the co-treatment could cause more severe developmental toxicity compared with the control and single-treatments, and the toxic effects generally increased in a dose-response manner. In addition, adult zebrafish were exposed to single and mixed solutions of PFOS and ZnO-NPs (at the concentrations mentioned above) for 30 days. DNA damage to zebrafish was evaluated by the comet assay and micronucleus test. We found that the PFOS single-treatment at all doses (0.4, 0.8, and 1.6 mg/L) could strongly induce DNA damage to peripheral blood cells and that ZnO-NPs could aggravate the formation of DNA damage in co-treatments. Histological examination of liver, testicle, and ovary showed that the presence of ZnO-NPs (50 mg/L) could also cause more serious histological damage to adult zebrafish than PFOS alone. As a result, the synergistic effects played an important role during joint exposure. Our observations provide a basic understanding of the joint toxicity of PFOS and ZnO-NPs to aquatic organisms.

Joint toxicity of sediment-associated permethrin and cadmium to Chironomus dilutus: The role of bioavailability and enzymatic activities

Pyrethroid insecticides and metals commonly co-occurred in sediment and caused toxicity to benthic organisms jointly. To improve accuracy in assessing risk of the sediments contaminated by insecticides and metals, it is of great importance to understand interaction between the contaminants and reasons for the interaction. In the current study, permethrin and cadmium were chosen as representative contaminants to study joint toxicity of pyrethroids and metals to a benthic invertebrate Chironomus dilutus. A median effect/combination index-isobologram was applied to evaluate the interaction between sediment-bound permethrin and cadmium at three dose ratios. Antagonistic interaction was observed in the midges for all treatments. Comparatively, cadmium-dominated group (the ratio of toxicity contribution from permethrin and cadmium was 1:3) showed stronger antagonism than equitoxicity (1:1) and permethrin-dominated groups (3:1). The reasons for the observed antagonism were elucidated from two aspects, including bioavailability and enzymatic activity. The bioavailability of permethrin, expressed as the freely dissolved concentrations in sediment porewater and measured by solid phase microextraction, was not altered by the addition of cadmium, suggesting the change in permethrin bioavailability was not the reason for the antagonism. On the other hand, the activities of metabolic enzymes, glutathione S-transferase and carboxylesterase in the midges which were exposed to mixtures of permethrin and cadmium were significantly higher than those in the midges exposed to permethrin solely. Cadmium considerably enhanced the detoxifying processes of permethrin in the midges, which largely explained the observed antagonistic interaction between permethrin and cadmium.

Acute tier-1 and tier-2 effect assessment approaches in the EFSA Aquatic Guidance Document: are they sufficiently protective for insecticides?

BACKGROUND

The objective of this paper is to evaluate whether the acute tier-1 and tier-2 methods as proposed by the Aquatic Guidance Document recently published by the European Food Safety Authority (EFSA) are appropriate for deriving regulatory acceptable concentrations (RACs) for insecticides. The tier-1 and tier-2 RACs were compared with RACs based on threshold concentrations from micro/mesocosm studies (ETO-RAC). A lower-tier RAC was considered as sufficiently protective, if less than the corresponding ETO-RAC.

RESULTS

ETO-RACs were calculated for repeated (n = 13) and/or single pulsed applications (n = 17) of 26 insecticides to micro/mesocosms, giving a maximum of 30 insecticide × application combinations (i.e. cases) for comparison. Acute tier-1 RACs (for 24 insecticides) were lower than the corresponding ETO-RACs in 27 out of 29 cases, while tier-2 Geom-RACs (for 23 insecticides) were lower in 24 out of 26 cases. The tier-2 SSD-RAC (for 21 insecticides) using HC5 /3 was lower than the ETO-RAC in 23 out of 27 cases, whereas the tier-2 SSD-RAC using HC5 /6 was protective in 25 out of 27 cases.

CONCLUSION

The tier-1 and tier-2 approaches proposed by EFSA for acute effect assessment are sufficiently protective for the majority of insecticides evaluated. Further evaluation may be needed for insecticides with more novel chemistries (neonicotinoids, biopesticides) and compounds that show delayed effects (insect growth regulators).

The synergistic toxicity of the multiple chemical mixtures: implications for risk assessment in the terrestrial environment

The combined toxicity of five insecticides (chlorpyrifos, avermectin, imidacloprid, λ-cyhalothrin, and phoxim), two herbicides (atrazine and butachlor) and a heavy metal (cadmium) has been examined with the earthworm acute toxicity test. Toxicological interactions of these chemicals in four, five, six, seven, and eight-component mixtures were studied using the combination-index (CI) equation method. In four-component and five-component mixtures, the synergistic effects predominated at lower effect levels, while the patterns of interactions found in six, seven, and eight-component mixtures displayed synergism. The λ-CY+IMI+BUT+ATR+CPF+PHO combination displayed the most strongly synergistic interaction, with CI values ranging from 0.09 to 0.15. The nature of the interaction changes with the effect level and the relevance of synergistic effects increase with the complexity of the mixture. The CI method was compared with the classical models of concentration addition (CA) and independent action (IA) and we found that the CI method could accurately predict the combined toxicity. The predicted synergism resulted from co-existence of the pesticides and the heavy metal especially at low effect levels may have important implications in risk assessment for the real terrestrial environment.

Ternary toxicological interactions of insecticides, herbicides, and a heavy metal on the earthworm Eisenia fetida

The combined toxicities of five insecticides (chlorpyrifos, avermectin, imidacloprid, λ-cyhalothrin, and phoxim), two herbicides (atrazine and butachlor), and a heavy metal (cadmium) have been examined using the acute toxicity test on the earthworm. With a concentration of 2.75 mg/kg being lethal for 50% of the organisms, imidacloprid exhibited the highest acute toxicity toward the earthworm Eisenia fetida. Toxicological interactions of these chemicals in ternary mixtures were studied using the combination-index (CI) equation method. Twenty-one ternary mixtures exhibited various interactive effects, in which 11 combinations showed synergistic effects, four led to dual synergistic/additive behaviors, one exhibited an additive effect, and five showed increasing antagonism within the entire range of effects. The CI method was compared with the classical models of concentration addition and independent action, and it was found that the CI method could accurately predict combined toxicity of the chemicals studied. The predicted synergism in the majority of the mixtures, especially at low-effect levels, might have implications in the real terrestrial environment.

Joint toxicity of sediment-associated DDT and copper to a polychaete, Nereis succinea

As major components in antifouling paints, both dichlorodiphenyltrichloroethane (DDT) and copper are ubiquitous in estuarine sediment and have been detected at high concentrations in the harbors in South China. In the present study joint toxicity between DDT and copper to an estuarine polychaete, Nereis succinea, was examined using bioaccumulation potential, growth impairment and change in lipid peroxidation contents as sub-lethal endpoints. In general, the toxicity of DDXs (DDT and its metabolites) and copper acted independently and copper was more toxic to the lugworms at environmentally relevant concentrations. Nevertheless, co-exposure to copper led to a significant reduction in the bioaccumulation of DDXs when the concentrations of DDXs in sediment were high. The inhibition of DDX bioaccumulation by copper may be partially explained by the decrease in the bioavailability of sediment-associated DDXs which were estimated by biomimetic gut fluid extraction. The saturation of the solubilization agents or the inhibition of protease activity in gut fluid of N. succinea by copper limited the DDX bioavailability and the subsequent bioaccumulation.

Joint toxicity of heavy metals and chlorobenzenes to pyriformis Tetrahymena

Chlorobenzens and heavy metals are frequently detected in the environment, but few studies have assessed the joint toxicity of organic and inorganic contaminants. The joint toxicity of heavy metals and chlorobenzenes was evaluated in the present study. Growth metabolism of the joint toxicity was studied by microcalorimetry at 28°C, the growth constant (k) and inhibitory ratio (I) were calculated. Toxic unit (TU) and additional index (AI) were introduced to determine the outcome in combined tests, and the coexistence of Cu, Cd, Cr(III) and p-chlorobenzene was antagonism, and the effect of Cu, Cd, Cr(III) and o-chlorobenzene, Cu and 1,2,4-trichlorobenzene were synergism. In addition, micro-situation of the cell membrane surface of pyriformis Tetrahymena was observed by SEM. The cells suffered serious damage after sufficient acting time. ATR-FTIR spectra revealed that amide groups and PO2(-) of the phospholipid phospho-diester, both in the hydrophobic end exposed to the outer layer, were the easiest to be damaged.

Addition of contaminant bioavailability and species susceptibility to a sediment toxicity assessment: application in an urban stream in China

Sediments collected from an urban creek in China exhibited high acute toxicity to Hyalella azteca with 81.3% of sediments being toxic. A toxic unit (TU) estimation demonstrated that the pyrethroid, cypermethrin, was the major contributor to toxicity. The traditional TU approach, however, overestimated the toxicity. Reduced bioavailability of sediment-associated cypermethrin due to sequestration explained the overestimation. Additionally, antagonism among multiple contaminants and species susceptibility to various contaminants also contributed to the unexpectedly low toxicity to H. azteca. Bioavailable TUs derived from the bioavailability-based approaches, Tenax extraction and matrix-solid phase microextraction (matrix-SPME), showed better correlations with the noted toxicity compared to traditional TUs. As the first successful attempt to use matrix-SPME for estimating toxicity caused by emerging insecticides in field sediment, the present study found freely dissolved cypermethrin concentrations significantly improved the prediction of sediment toxicity to H. azteca compared to organic carbon normalized and Tenax extractable concentrations.

Differential protein profile in zebrafish (Danio rerio) brain under the joint exposure of methyl parathion and cadmium

As different chemicals, methyl parathion (MP) and cadmium (Cd) can induce neurotoxicity on the brain of aquatic ecosystems. This study aims to explore the differential expression proteins in the brain induced by their joint stress and their joint effects, which are poorly reported, and devotes finding novel biomarkers for monitoring their contamination in water and assessing their neurological effects. The bioaccumulation of MP and Cd in tissues after 96 h of exposure was first analyzed by GC and inductively coupled plasma-MS to provide insights into the interaction. Protein profile changes in the brains of the zebrafish (Danio rerio) exposed to MP and Cd were further investigated using the proteomic approach. The correlation of gene expression on the transcription level of mRNA and the translation level of protein was examined by real-time quantitative PCR and Western blotting analysis. It showed that Cd and MP have an interaction on their bioaccumulation, which suggests that their joint effect over 96 h might be antagonistic. Proteomics revealed that 22 protein spots changed their expression levels under stress, of which 16 proteins were identified using MS. These proteins were involved in oxidation/reduction, metabolism, energy production, receptor activity, and cytoskeleton assembly. Among them, five proteins with a remarkable abundance change are significantly suggested to play important roles in the joint effect. This work demonstrates that there exists an interaction between MP and Cd toxicities, which may aid in our understanding of the mechanism of neurotoxicity induced by joint stress. The results may also provide the possibility of the establishment of candidate biomarkers for monitoring MP and Cd contamination in water.

Influence of bioturbation on bioavailability and toxicity of PAHs in sediment from an electronic waste recycling site in South China

The present study examined the effects of bioturbation by the oligochaete Lumbriculus variegatus on bioavailability and toxicity of sediment-associated polycyclic aromatic hydrocarbons (PAHs) to the oligochaete and the epi-benthic amphipod Hyalella azteca. Various densities of L. variegatus in sediment were used to represent different levels of bioturbation. Total sediment concentration declined with increasing worm density, but bioavailability of PAHs estimated using the biomimetic extractions showed no significant difference among treatments with different worm densities. Alternatively, PAH bioaccumulation by L. variegatus decreased and the growth of the worms was reduced at the highest worm density, which was probably due to overcrowding of organisms, food competition and increasing release of PAHs by bioturbation. Additionally, co-exposure with high density of L. variegatus to contaminated sediment significantly increased PAH accumulation and mortality of H. azteca. The increased toxicity was probably because of the transport of sediment-associated contaminants to sediment surface and water column by the bioturbation by L. variegatus. Overall, the present study showed that bioturbation may alter the toxicity of contaminants in sediment to other organisms, thus the presence of benthic invertebrates and their interactions with the sediment should be considered in future sediment risk assessment.