Synergistic effects caused by atrazine and terbuthylazine on chlorpyrifos toxicity to early-life stages of the zebrafish Danio rerio

This study examined the effects of three widely used pesticides that have been previously detected in aquatic systems neighbouring agricultural fields on the early-life stages of the zebrafish Danio rerio. Tests involving single exposures and binary combinations of the s-triazine herbicides (atrazine and terbuthylazine) and the organophosphate insecticide chlorpyrifos were performed. Several endpoints, such as swimming behaviour, morphological abnormalities and mortality, were studied. In addition, the inhibition of acetylcholinesterase (AChE) activity was investigated in order to evaluate the mode of action and toxicity of chlorpyrifos in the presence of these herbicides. Results indicate that both binary mixtures elicited synergistic responses on the swimming behaviour of zebrafish larvae. Moreover, although the herbicides were not effective inhibitors of the AChE on their own, a synergistic inhibition of the enzyme activity was obtained by exposure to mixtures with chlorpyrifos. We observed a correlation between impairment of swimming behaviour of the larvae and inhibition of AChE activity. This study supports previous studies concerning the risk assessment of mixtures since the toxicity may be underestimated when looking only at the single toxicants and not their mixtures.     

An overall risk probability-based method for quantification of synergistic and antagonistic effects in health risk assessment for mixtures: theoretical concepts

Purpose

In the assessment of health risks of environmental pollutants, the method of dose addition and the method of independent action are used to assess mixture effects when no synergistic and/or antagonistic effects are present. Currently, no method exists to quantify synergistic and/or antagonistic effects for mixtures. The purpose of this paper is to develop the theoretical concepts of an overall risk probability (ORP)-based method to quantify the synergistic and antagonistic effects in health risk assessment for mixtures.

Method

The ORP for health effects of environmental chemicals was determined from the cumulative probabilities of exposure and effects. This method was used to calculate the ORP for independent mixtures and for mixtures with synergistic and antagonistic effects.

Results

For the independent mixtures, a mixture ORP can be calculated from the product of the ORPs of individual components. For systems of interacting mixtures, a synergistic coefficient and an antagonistic coefficient were defined respectively to quantify the ORPs of each individual component in the mixture. The component ORPs with synergistic and/or antagonistic effects were then used to calculate the total ORP for the mixture.

Conclusions

An ORP-based method was developed to quantify synergistic and antagonistic effects in health risk assessment for mixtures. This represents a first method to generally quantify mixture effects of interacting toxicants.     

A comparison of mixture toxicity assessment: examining the chronic toxicity of atrazine, permethrin and chlorothalonil in mixtures to Ceriodaphnia cf. dubia

Pesticides predominantly occur in aquatic ecosystems as mixtures of varying complexity, yet relatively few studies have examined the toxicity of pesticide mixtures. Atrazine, chlorothalonil and permethrin are widely used pesticides that have different modes of action. This study examined the chronic toxicities (7-d reproductive impairment) of these pesticides in binary and ternary mixtures to the freshwater cladoceran Ceriodaphnia cf. dubia. The toxicity of the mixtures was compared to that predicted by the independent action (IA) model for mixtures, as this is the most appropriate model for chemicals with different modes of action. Following this they were compared to the toxicity predicted by the concentration addition (CA) model for mixtures. According to the IA model, the toxicity of the chlorothalonil plus atrazine mixture conformed to antagonism, while that of chlorothalonil and permethrin conformed to synergism. The toxicity of the atrazine and permethrin mixture as well as the ternary mixture conformed to IA implying there was either no interaction between the components of these mixtures and/or in the case of the ternary mixture the interactions cancelled each other out to result in IA. The synergistic and antagonistic mixtures deviated from IA by factors greater than 3 and less than 2.5, respectively. When the toxicity of the mixtures was compared to the predictions of the CA model, the binary mixture of chlorothalonil plus atrazine, permethrin plus atrazine and the ternary mixture all conformed to antagonism, while the binary mixture of chlorothalonil plus permethrin conformed to CA. Using the CA model provided estimates of mixture toxicity that did not markedly underestimate the measured toxicity, unlike the IA model, and therefore the CA model is the most suitable to use in ecological risk assessments of these pesticides.     

Discrepancies in the acute versus chronic toxicity of compounds with a designated narcotic mechanism

In this study, it was illustrated that even for certain simple organic compounds with a designated mode of action (MOA) (i.e. narcotic toxicity) unexpected differences in acute and chronic toxicity can be observed. In a first part of the study, species sensitivity distributions (SSDs) based on either acute or chronic toxicity data of three narcotic test compounds (methanol, ethanol and 2-propanol) were constructed. The results of the acute SSDs were as expected for narcotic compounds: rather similar sensitivity and small differences in toxicity were observed among different species. On the contrary, the chronic SSDs of methanol and ethanol indicated larger interspecies variation in sensitivity. Furthermore, the chronic toxicity trend (ethanol > methanol > 2-propanol) was unexpectedly different from the acute toxicity trend (2-propanol > ethanol > methanol) and acute versus chronic extrapolation could not be successfully described for methanol and ethanol using an ACR of 10 (as suggested for narcotic compounds). In contrast to the interspecies approach in the first part of this study, the second part of the study was focused on the assessment of acute and chronic toxicity of the three test compounds in Daphnia magna, which was identified as one of the most sensitive organisms to methanol and ethanol. Here, the differences in acute and chronic toxicity trend were in accordance to the results of the SSDs. The enhancement of membrane penetration due to the small molecular size of methanol and ethanol, in combination with the higher toxicity of their respective biotransformation products were suggested as potential causes of the increased chronic toxicity. Furthermore, it was stressed that larger awareness of these irregularities in acute to chronic extrapolations of narcotic compounds is required and should receive additional attention in further environmental risk assessment procedure.     

Effects of pharmaceuticals on Daphnia survival, growth, and reproduction

Pharmaceuticals have been globally detected in surface waters, and the ecological impacts of these biologically-active, ubiquitous chemicals are largely unknown. To evaluate the aquatic toxicity of individual pharmaceuticals and mixtures, we performed single species laboratory toxicity tests with Daphnia magna, a common freshwater zooplankton. We conducted acute (6-day) and chronic (30-day) exposure pharmaceutical bioassays and evaluated survivorship and morphology of adults and neonates, adult length, resting egg production, brood size (fecundity), and the proportion of male broods produced (sex ratio). In general, exposure to a single pharmaceutical in the 1-100 microg/l range yielded no apparent effects on the normal life processes of Daphnia. However, chronic fluoxetine exposure (36 microg/l) significantly increased Daphnia fecundity, and acute clofibric acid exposure (10 microg/l) significantly increased sex ratio. A mixture of fluoxetine (36 microg/l) and clofibric acid (100 microg/l) caused significant mortality; the same fluoxetine concentration mixed with 10 microg/l clofibric acid resulted in significant deformities, including malformed carapaces and swimming setae. Mixtures of three to five antibiotics (total antibiotic concentration 30-500 microg/l) elicited changes in Daphnia sex ratio. We conclude: (1) individual and mixtures of pharmaceuticals affect normal development and reproduction of Daphnia magna, (2) aquatic toxicity of pharmaceutical mixtures can be unpredictable and complex compared to individual pharmaceutical effects, and (3) timing and duration of pharmaceutical exposure influence aquatic toxicity.     

Tumor promoting effects of cyanobacterial extracts are potentiated by anthropogenic contaminants--evidence from in vitro study

Inhibition of gap junctional intercellular communication (GJIC) is affiliated with tumor promotion process and it has been employed as an in vitro biomarker for evaluation of tumor promoting effects of chemicals. In the present study we investigated combined effects of anthropogenic environmental contaminants 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) and fluoranthene, cyanotoxins microcystin-LR and cylindrospermopsin, and extracts of laboratory cultures of cyanobacteria Aphanizomenon gracile and Cylindrospermopsis raciborskii, on GJIC in the rat liver epithelial cell line WB-F344. Binary mixtures of PCB 153 with fluoranthene and the mixtures of the two cyanobacterial strains elicited simple additive effects on GJIC after 30 min exposure, whereas microcystin-LR and cylindrospermopsin neither inhibited GJIC nor altered effects of PCB 153 or fluoranthene. However, synergistic effects were observed in the cells exposed to binary mixtures of anthropogenic contaminants (PCB 153 or fluoranthene) and cyanobacterial extracts. The synergistic effects were especially pronounced after prolonged (6-24 h) co-exposure to fluoranthene and A. gracile extract, when mixture caused nearly complete GJIC inhibition, while none of the individual components caused any downregulation of GJIC at the same concentration and exposure time. The effects of cyanobacterial extracts were independent of microcystin-LR or cylindrospermopsin, which were not detected in cyanobacterial biomass. It provides further evidence on the presence of unknown tumor promoting metabolites in cyanobacteria. Clear potentiation of the GJIC inhibition observed in the mixtures of two anthropogenic contaminants and cyanobacteria highlight the importance of combined toxic effects of chemicals in complex environmental mixtures.     

Derivation of predicted no effect concentrations (PNEC) for 2,4,6-trichlorophenol based on Chinese resident species

2,4,6-Trichlorophenol (2,4,6-TCP) is a common chemical intermediate and a by-product of water chlorination and combustion processes, and is a priority pollutant of the aquatic environment in many countries. Although information on the toxicity of 2,4,6-TCP is available, there is a lack of information on the predicted no-effect concentration (PNEC) of 2,4,6-TCP, mainly due to the shortage of chronic and site-specific toxicity data. In the present study, acute and sub-chronic toxicity of 2,4,6-TCP on six different resident Chinese aquatic species were determined. PNEC values were calculated and compared by use of two approaches: assessment factor (AF) and species sensitivity distribution (SSD). Values for acute toxicity ranged from 1.1 mg L⁻¹ (Plagiognathops microlepis) to 42 mg L⁻¹ (Corbicula fluminea) and the sub-chronic no observed effect concentrations (NOECs) ranged from 0.05 mg L⁻¹ (Mylopharyngodon piceus) to 2.0 mg L⁻¹ (C. fluminea). PNECs obtained by the assessment factor approach with acute (AF = 1000, 0.001 mg L⁻¹) or chronic (AF = 10, 0.005 mg L⁻¹) toxicity data were one order of magnitude less than those from SSD methods (0.057 mg L⁻¹). PNEC values calculated using SSD methods with a 50% certainty for 2,4,6-TCP was less than those obtained by use of the USEPA recommend final chronic value (FCV) method (0.097 mg L⁻¹) and the one obtained by use of the USEPA recommend acute-to-chronic (ACR) methods (0.073 mg L⁻¹). PNECs derived using AF methods were more protective and conservative than that derived using SSD methods.     

Joint action and lethal levels of toluene, ethylbenzene, and xylene on midge (Chironomus plumosus) larvae

Aquatic ecosystems are vulnerable to the exposure with petrochemicals such as toluene, ethylbenzene, and xylene (o-, m-, and p-xylene) (TEX) and their adverse effects. Considering the widespread use, occurrence, and high toxicity of TEX, the aim of this work was to investigate the differential toxicity of TEX against midge (Chironomus plumosus) larvae and reveal the joint action of binary and ternary mixtures of TEX using the predictive concentration addition model. More importantly, this research can afford the basic toxicity data and scientific reference for the establishment of water quality criteria or benchmark, water pollution control, and aquatic risk assessment. Single and joint toxic effects of TEX on C. plumosus larvae were investigated using a semi-static bioassay, and the type of joint effects of TEX was ascertained. In the single toxicant experiments, the toxicity of the three pollutants could be sequenced as ethylbenzene > xylene > toluene. Specifically, LC_50s of T, E, and X after a 48-h exposure were 64.9, 37.8, and 42.0 mg/L, respectively. In the binary mixture experiments, the interaction between toluene and ethylbenzene, ethylbenzene and xylene, and toluene and xylene was largely in conformity with partial additive or additive effect as determined by isobologram representation and toxic unit models. In the ternary mixture experiments, the interaction was basically dependent on the use of additive index and mixture toxicity index methods. However, the antagonistic and synergistic actions were not significant. Thus, the tertiary mixture interaction could be regarded as additive action. The concentration addition model could successfully predict the joint action of TEX mixtures on C. plumosus larvae. Particularly, the additive action of TEX on C. plumosus larvae can be further recommended to evaluate water quality criteria of TEX.     

Assessing single and joint effects of chemicals on the survival and reproduction of Folsomia candida (Collembola) in soil

Chemicals are often found in the environment as complex mixtures. There has been a large effort in the last decade to assess the combined effect of chemicals, using the conceptual models of Concentration Addition and Independent Action, but also including synergistic, antagonistic, dose-level and dose-ratio dependent deviations from these models. In the present study, single and mixture toxicity of atrazine, dimethoate, lindane, zinc and cadmium were studied in Folsomia candida, assessing survival and reproduction. Different response patterns were observed for the different endpoints and synergistic patterns were observed when pesticides were present. Compared with the previously tested Enchytraeus albidus and Porcellionides pruinosus, the mixture toxicity pattern for F. candida was species specific. The present study highlights the importance of studying toxicity of chemicals mixtures due to the observed potentiation of effects and confirms that for an adequate ecologically relevant risk assessment different organisms and endpoints should be included.     

Influence of Sulfur Dioxide and Hydrogen Fluoride as a Mix or Reciprocal Exposure on Citrus Growth and Development

The influence of exposure to mixtures of SO₂ and HF on Koethen sweet orange and mixtures and alternate exposure to these gases on Satsuma mandarin were tested using a rotating fumigation greenhouse. Effects of HF-SO₂ mixtures on linear growth and leaf area of Koethen orange were additive, not synergistic. No necrosis was observed on Koethen oranges exposed to HF, SO₂, or a mixture of HF and SO₂. Effects of the mixture on chlorosis of Satsuma mandarin foliage was also not synergistic. No significant difference in linear growth of Satsuma mandarin was found among all treatments. Alternate exposure to SO₂ followed by HF produced no synergistic injury to Satsuma mandarin. Satsuma mandarin appeared more sensitive than Koethen orange to HF, SO₂, and mixtures of these two gases using degree of chlorosis and leaf abscission as the criteria of sensitivity. If iinear growth and leaf area were the principal criteria considered, Koethen orange would appear more sensitive.     

Toxicity testing with luminescent bacteria – Characterization of an automated method for the combined assessment of acute and chronic effects

The luminescent bacteria test according to EN ISO 11348 is frequently applied in (eco) toxicity testing and is applicable for a huge variety of environmental and industrial samples. A big disadvantage of this method is the very short exposure time, which is expressed in a low sensitivity in regard to substances with a delayed effect. Chronic effects, i.e. interference with cell growth, cannot be assessed with this conventional standard method. The goal of this research was to develop an automated testing system for long term toxicity towards the luminescent bacteria Vibrio fischeri by implementing microtitration-based instrumentation. The optimized method, hereinafter referred to as “kinetic luminescent bacteria test”, can be described as a miniaturized combination of the conventional short-term luminescence inhibition test according to EN ISO 11348 and the Photobacterium phosphoreum growth inhibition test (DIN 38412-37). The validation procedure included the evaluation of six reference compounds (3,4-Dichloroaniline, 3,5-Dichlorophenol, Chloramphenicol, Streptomycin sulfate, Potassium dichromate, Zinc sulfate heptahydrate) and three different endpoints that are acute luminescence inhibition (acute LI) after 30 min, chronic luminescence inhibition (chronic LI) after 24 h and growth inhibition (GI) after 14 h. The optimized method allows the assessment of acute and chronic effects within one test, by what a misinterpretation of the toxicity of substances with delayed bacterial toxicity can be prevented, without abandoning most of the advantages of the conventional short-term test. Therefore, the kinetic luminescent bacteria test is exceptional as an initial screening test for environmental samples or substances with unknown (eco) toxicological characteristics.     

化学物质对发光菌的联合毒性评价方法

毒性单位法(TU)的理论基础来源于剂量加和模型(DA),目前仅在二元联合毒性评价中广泛应用。为了确定TU模型适合评价的混合物类型,实验选取5种剂量效应曲线类型不同的物质,采用微板光度计测试了一元、二元混合物对发光菌青海弧菌-Q67(Vibrio-qinghaiensis sp.-Q67)的急性毒性。根据物质的剂量效应曲线形状将物质分为A、B、C 3类,利用毒性单位法(TU)和联合作用定义法分别对AA类、AB类、AC类、BC类混合物进行分析。结果表明,TU法仅适合于由剂量效应曲线接近直线的物质组成的混合物进行联合毒性的评价。以效应为基准、TU模型为框架建立了TU’模型,该模型可以满足对任何类型已知成分的混合物或者未知成分的实际水样之间的多元联合作用的评价。     

Comparative examination on synergistic toxicities of chlorpyrifos,acephate, or tetraconazole mixed with pyrethroid insecticides to honey bees (Apis mellifera L.)

Potential synergistic toxicity of pesticide mixtures has increasingly become a concern to the health of crop pollinators. The toxicities of individual and mixture of chlorpyrifos (CHL), acephate (ACE), or tetraconazole (TET) with nine pyrethroid insecticides to honey bees (Apis mellifera L.) were evaluated to reveal any aggregated interaction between pesticides. Results from feeding toxicity tests of individual pesticides indicated that organophosphate insecticides CHL and ACE had higher toxicities to honey bees compared to nine pyrethroids. Moreover, different pyrethroids exhibited considerable variation in toxicity with LC₅₀ values ranging from 10.05 (8.60–11.69) to 1125 (922.4–1442) mg a.i. L^?1 after exposure for 7 days. Among the 12 examined pesticides, a relatively low toxicity to A. mellifera was detected from the fungicide TET. All the binary mixtures of ACE or TET in combination with pyrethroids exhibited synergistic effects. However, TET in combination with pyrethroids showed greater synergistic toxicity to A. mellifera than ACE in combination with pyrethroids. Approximately 50% binary mixtures of CHL in combination with pyrethroids also showed synergistic responses in honey bees. In particular, CHL, ACE, or TET in combination with either lambda-cyhalothrin (LCY) or bifenthrin (BIF) showed the strongest synergy in A. mellifera, followed by CHL, ACE, or TET in combination with either zeta-cypermethrin (ZCY) or cypermethrin (CYP). The findings indicated that the co-exposure of various pesticides in natural settings might lead to severe injury to crop pollinators. Therefore, pesticide mixtures should be applied carefully in order to minimize negative effects on honey bees while maintaining effective management against crop pests.

     

Individual and mixture toxicity of three pesticides; atrazine,chlorpyrifos, and chlorothalonil to the marine phytoplankton species Dunaliella tertiolecta

This study analyzed the toxicity of three pesticides (the herbicide atrazine, the insecticide chlorpyrifos and the fungicide chlorothalonil) individually, and in two mixtures (atrazine and chlorpyrifos; atrazine and chlorothalonil) to the marine phytoplankton species Dunaliella tertiolecta (Chlorophyta). A standard 96 h static algal bioassay was used to determine pesticide effects on the population growth rate of D. tertiolecta. Mixture toxicity was assessed using the additive index approach. Atrazine and chlorothalonil concentrations > or = 25 microg/L and 33.3 microg/L, respectively, caused significant decreases in D. tertiolecta population growth rate. At much higher concentrations (> or = 400 microg/L) chlorpyrifos also elicited a significant effect on D. tertiolecta population growth rate, but toxicity would not be expected at typical environmental concentrations. The population growth rate EC50 values determined for D. tertiolecta were 64 microg/L for chlorothalonil, 69 microg/L for atrazine, and 769 microg/L for chlorpyrifos. Atrazine and chlorpyrifos in mixture displayed additive toxicity, whereas atrazine and chlorothalonil in mixture had a synergistic effect. The toxicity of atrazine and chlorothalonil combined was approximately 2 times greater than that of the individual chemicals. Therefore, decreases in phytoplankton populations resulting from pesticide exposure could occur at lower than expected concentrations in aquatic systems where atrazine and chlorothalonil are present in mixture. Detrimental effects on phytoplankton population growth rate could impact nutrient cycling rates and food availability to higher trophic levels. Characterizing the toxicity of chemical mixtures likely to be encountered in the environment may benefit the pesticide registration and regulation process.     

Novel approach to predicting hormetic effects of antibiotic mixtures on Vibrio fischeri

The determination of the hormetic effects of a mixture is quite difficult because of the moderate simulation and the complexity of measurement in low doses. In the present study, two typical models for mixture toxicity prediction, concentration additive (CA) and independent action (IA), were used to predict the hormetic effects of mixtures. The predictive power of those models was validated by the hormetic effects (24-h exposure) of antibiotic’s binary mixtures to Vibrio fischeri. The results showed that CA and IA were unable to predict the hormetic dose-response of mixture, especially those of the interactive mixtures. As an alternative, a novel model, which was named as “six-point” and developed based on the quantitative features in the determined dose-response curve and on the Quantitative Structure Activity Relationships (QSARs) approach, was proposed for predicting the hormetic effects of mixtures in low dose. The results indicated that the “six-point” model can accurately predict the mixture hormetic effects in low dose, not only for non-interactive mixtures but also for interactive mixtures. Therefore, the “six-point” model is a powerful tool to predict the mixture hormetic effects at low dose, and may offer an important approach in the environment risk assessment of mixtures.     

等浓度配比法研究苯酚、硝基苯和问硝基苯胺对发光菌的联合毒性作用

分别测定了苯酚、硝基苯和间硝基苯胺对发光菌的单一毒性，以及等浓度配比和等毒性配比的二元及三元混合体系的联合毒性，采用相加指数法对其联合效应进行了评价。结果表明，等浓度比和等毒性比混合体系的联合作用结果一致：苯酚＋间硝基苯胺二元体系为协同作用，其他各体系为相加作用。为简化联合毒性实验方法，建议在研究相关系列化合物的联合毒性作用机制中，可采用等浓度配比方法。     

等浓度配比法研究苯酚、硝基苯和间硝基苯胺对发光菌的联合毒性作用

分别测定了苯酚、硝基苯和间硝基苯胺对发光菌的单一毒性,以及等浓度配比和等毒性配比的二元及三元混合体系的联合毒性,采用相加指数法对其联合效应进行了评价。结果表明,等浓度比和等毒性比混合体系的联合作用结果一致:苯酚+间硝基苯胺二元体系为协同作用,其他各体系为相加作用。为简化联合毒性实验方法,建议在研究相关系列化合物的联合毒性作用机制中,可采用等浓度配比方法。     

Assessment of combined antiandrogenic effects of binary parabens mixtures in a yeast-based reporter assay

To date, toxicological studies of endocrine disrupting chemicals (EDCs) have typically focused on single chemical exposures and associated effects. However, exposure to EDCs mixtures in the environment is common. Antiandrogens represent a group of EDCs, which draw increasing attention due to their resultant demasculinization and sexual disruption of aquatic organisms. Although there are a number of in vivo and in vitro studies investigating the combined effects of antiandrogen mixtures, these studies are mainly on selected model compounds such as flutamide, procymidone, and vinclozolin. The aim of the present study is to investigate the combined antiandrogenic effects of parabens, which are widely used antiandrogens in industrial and domestic commodities. A yeast-based human androgen receptor (hAR) assay (YAS) was applied to assess the antiandrogenic activities of n-propylparaben (nPrP), iso-propylparaben (iPrP), methylparaben (MeP), and 4-n-pentylphenol (PeP), as well as the binary mixtures of nPrP with each of the other three antiandrogens. All of the four compounds could exhibit antiandrogenic activity via the hAR. A linear interaction model was applied to quantitatively analyze the interaction between nPrP and each of the other three antiandrogens. The isoboles method was modified to show the variation of combined effects as the concentrations of mixed antiandrogens were changed. Graphs were constructed to show isoeffective curves of three binary mixtures based on the fitted linear interaction model and to evaluate the interaction of the mixed antiandrogens (synergism or antagonism). The combined effect of equimolar combinations of the three mixtures was also considered with the nonlinear isoboles method. The main effect parameters and interaction effect parameters in the linear interaction models of the three mixtures were different from zero. The results showed that any two antiandrogens in their binary mixtures tended to exert equal antiandrogenic activity in the linear concentration ranges. The antiandrogenicity of the binary mixture and the concentration of nPrP were fitted to a sigmoidal model if the concentrations of the other antiandrogens (iPrP, MeP, and PeP) in the mixture were lower than the AR saturation concentrations. Some concave isoboles above the additivity line appeared in all the three mixtures. There were some synergistic effects of the binary mixture of nPrP and MeP at low concentrations in the linear concentration ranges. Interesting, when the antiandrogens concentrations approached the saturation, the interaction between chemicals were antagonistic for all the three mixtures tested. When the toxicity of the three mixtures was assessed using nonlinear isoboles, only antagonism was observed for equimolar combinations of nPrP and iPrP as the concentrations were increased from the no-observed-effect-concentration (NOEC) to effective concentration of 80 %. In addition, the interactions were changed from synergistic to antagonistic as effective concentrations were increased in the equimolar combinations of nPrP and MeP, as well as nPrP and PeP. The combined effects of three binary antiandrogens mixtures in the linear ranges were successfully evaluated by curve fitting and isoboles. The combined effects of specific binary mixtures varied depending on the concentrations of the chemicals in the mixtures. At low concentrations in the linear concentration ranges, there was synergistic interaction existing in the binary mixture of nPrP and MeP. The interaction tended to be antagonistic as the antiandrogens approached saturation concentrations in mixtures of nPrP with each of the other three antiandrogens. The synergistic interaction was also found in the equimolar combinations of nPrP and MeP, as well as nPrP and PeP, at low concentrations with another method of nonlinear isoboles. The mixture activities of binary antiandrogens had a tendency towards antagonism at high concentrations and synergism at low concentrations.     

Neurobehavioral deficits and brain oxidative stress induced by chronic low dose exposure of persistent organic pollutants mixture in adult female rat

Persistent organic pollutants (POPs) are long-lived organic compounds that are considered one of the major risks to ecosystem and human health. Recently, great concerns are raised about POPs mixtures and its potential toxicity even in low doses of daily human exposure. The brain is mostly targeted by these lipophilic compounds because of its important contain in lipids. So, it would be quite interesting to study the effects of exposure to these mixtures and evaluate their combined toxicity on brain cells. The present study was designed to characterize the cognitive and locomotors deficits and brain areas redox status in rat model. An orally chronic exposure to a representative mixture of POPs composed of endosulfan (2.6 μg/kg), chlorpyrifos (5.2 μg/kg), naphthalene (0.023 μg/kg) and benzopyrane (0.002 μg/kg); the same mixture with concentration multiplied by 10 and 100 was also tested. Exposed rats have shown a disturbance of memory and a decrease in learning ability concluded by Morris water maze and the open field tests results and anxiolytic behaviour in the test of light/dark box compared to control. Concerning brain redox homeostasis, exposed rats have shown an increased malondialdehyde (MDA) amount and an alteration in glutathione (GSH) levels in both the brain mitochondria and cytosolic fractions of the cerebellum, striatum and hippocampus. These effects were accompanied by a decrease in levels of cytosolic glutathione S-transferase (GST) and a highly significant increase in superoxide dismutase (SOD) and catalase (CAT) activities in both cytosolic and mitochondrial fractions. The current study suggests that environmental exposure to daily even low doses of POPs mixtures through diet induces oxidative stress status in the brain and especially in the mitochondria with important cognitive and locomotor behaviour variations in the rats.     

Ecological risk assessment for aquatic species exposed to contaminants in Keelung River, Taiwan

An ecological risk assessment was conducted for Keelung River in northern Taiwan. The objective of this study was to assess the risk to fish, aquatic insects, and benthic macroinvertebrates associated with chemical-of-potential-concern (COPC) in the river and to rank ecological risk for these chemicals. The protection of at least 95% of the species 90% of the time from acute and chronic COPC exposures was the defined assessment endpoint. Nine inorganic and organic contaminants were selected to evaluate the impact to aquatic community in the Keelung River. The quotient method served as screen level estimation of risk. The Aquatic Ecological Risk Assessment model was used to analyze exposure and ecological effects and to estimate community level risk. The logarithmic regression model between probability and lethal concentration was established. The combined risks of multiple chemicals were evaluated under assumption of additive risk. The results indicated that zinc and copper pose higher risk among metals. Ammonia, copper, and zinc posed virtually all of the risk, while organic COPCs posed a negligible risk. Potential ecological risk from ammonia exposure was greatest. The probability of more than 5% of the species being affected by acute or chronic toxicity of COPCs is about 100%. In average (50% of the time), 99% of the species would be affected by acute toxicity of COPCs, and about all the species would be affected by chronic toxicity of COPCs. Uncertainties in this assessment were associated with variability in ecosystem stressors, exposure data, ecological effect data, and risk characterization.