Standard Toxicity Tests Research Articles

Evaluation of the Physiology of Medaka as a Model Animal for Standardized Toxicity Tests of Chemicals by Using mRNA Expression Profiling

The fish acute toxicity test in the Organisation for Economic CoOperation and Development "OECD Guidelines for Testing of Chemicals" is an essential test for environmental toxicity. Here, we have tried to evaluate the physiology of medaka during these test procedures by using genomics. Genomics technology can provide genome-wide expression profiles of mRNA, and these profiles correspond to the physiology of organisms. Thus, a comparison of mRNA expression profiles gives information on the reproducibility of experimental conditions. Expression profiles of mRNA were measured for medakas maintained within the allowable range of the test conditions and also under extreme conditions beyond the guideline limits. We confirmed the high physiological reproducibility of medaka kept in the recommended conditions of the fish acute toxicity test in the "OECD Guidelines for Testing of Chemicals" from the expression profiles obtained under all experimental conditions, except for the types of feeding.

Evaluation of the ecotoxicity of model nanoparticles

Since society at large became aware of the use of nanomaterials in ever growing quantities in consumer products and their presence in the environment, critical interest in the impact of this emerging technology has grown. The main concern is whether the unknown risks of engineered nanoparticles (NPs), in particular their impact on health and environment, outweighs their established benefits for society. Therefore, a key issue in this field is to evaluate their potential toxicity. In this context we evaluated the effects on plants and microorganisms of model nanoparticles, in particular of a stable metal (Au, 10 nm mean diameter), a well-known bactericide (Ag, 2 nm mean diameter) and the broadly used Fe 3O 4 (7 nm mean diameter). The toxicity of these nanoparticles was assayed using standard toxicity tests. Specifically, germination (cucumber and lettuce), bioluminescent ( Photobacterium phosphoreum) and anaerobic toxicity tests were performed. Germination tests were conducted at a NP dose of 62, 100 and 116 μg mL −1 for Au, Ag, and Fe 3O 4, respectively. The bioluminscent testing ( P. phosphoreum) was conducted at a dose of 28, 45 and 52 μg mL −1 for Au, Ag, and Fe 3O 4, respectively. Finally, anaerobic tests were conducted at a NP dose of 10, 16 and 18 μg mL −1 for Au, Ag, and Fe 3O 4, respectively. In all cases low or zero toxicity was observed. However, some perturbation of the normal functions with respect to controls in germinating tests was observed, suggesting the necessity for further research in this field. At the same time, the effect of NP-solvents was sometimes more significant than that of the NPs themselves, a point that is of special interest for future nanotoxicological studies.

Characterization of the bottom sediments contaminated with polychlorinated biphenyls: Evaluation of ecotoxicity and biodegradability

At the locality of the former producer of PCBs Chemko Strážske in East Slovakia, a large amount of PCBs (the commercial mixture DELOR 103, an equivalent of AROCLOR 1242) is still persisting in sediments and negatively influences health of the population. The objective of this work was to provide a study of ecotoxicity and genotoxicity of PCBs in contaminated sediments. Toxicity of the PCB-contaminated sediments sampled from Zemplínska šírava and Strážsky canal (surroundings of the former producer of PCBs) was determined applying a standard aquatic plant toxicity test using Lemna minor. The endpoints for the test were frond numbers and frond areas. The sediment sampled from Zemplínska šírava was more toxic to L. minor than the one sampled from Strážsky canal. The results on genotoxicity showed that both sediments were not mutagenic toward the standard strains of the Ames test, Salmonella typhimurium TA98 and TA100. This work deals also with biodegradation of PCBs in two samples of the above mentioned contaminated sediments: a) in the natural sediments by autochthonous microbial consortium and b) in the bioaugmented sediments inoculated by allochthonous bacterial strains, two bacterial isolates from long-term PCB-contaminated soil Pseudomonas stutzeri and Alcaligenes xylosoxidans. Both approaches were applied under the biostimulation conditions, with addition of glucose or biphenyl as co-substrates, as well. The highest PCB degradation was observed in the bioaugmented sediment inoculated with bacterial strain P. stutzeri. Addition of biphenyl, as the co-substrate and the inducer, positively affected degradation of PCBs. The bphA1 gene, encoding enzyme biphenyldioxygenase, responsible for the start of PCB degradation, was identified in genome of P. stutzeri, a potential PCB-degrader isolated from long-term PCB-contaminated soil, but not in genome of A. xylosoxidans.

Ecological threshold concentrations for antimony in water and soil

Environmental context. Antimony (Sb) is a natural trace element with several industrial applications and anthropogenic emissions can increase Sb concentrations in the environment. In order to assess the potential risks of elevated antimony concentrations to aquatic and terrestrial organisms, toxicity thresholds must be known and environmental criteria defined. Setting such criteria for antimony is not straightforward because the Sb speciation in the standard toxicity test is likely to differ from that in the environment. Abstract. Ecologically relevant threshold concentrations for antimony are required in order to assess the potential risks of anthropogenic emissions of Sb to the environment. The present paper reports a summary of the ecotoxicity data available for various Sb substances and discusses the derivation of ecological threshold concentrations for Sb in freshwater and soils. It was concluded that data from tests with SbCl3 are useful for calculation of Sb toxicity thresholds in water. The results from SbCl3 in soil toxicity tests have little relevance because of demonstrated confounding factors of pH and salinity. The derivation of Sb threshold concentrations in soil was, therefore, based on toxicity tests in soils amended with the sparingly soluble Sb2O3 with correction for incomplete dissolution during the duration of the toxicity tests. The lowest chronic toxicity thresholds are 1.1 mg Sb L–1 in water and 370 mg Sb kg–1 dry weight for soil. These concentrations are more than 100-fold larger than typical natural background concentrations.

Effects of fluoxetine exposure on serotonin-related activity in the sheepshead minnow ( Cyprinodon variegatus) using LC/MS/MS detection and quantitation

Fluoxetine (FLX) is a selective serotonin reuptake inhibitor and is among the top 100 drugs prescribed yearly in the United States and the United Kingdom. Tissue and water extraction methods were developed to detect and quantify FLX, norfluoxetine and the associated biological compounds serotonin (5-HT), 5-hydroxyindole-3-acetic acid (5-HIAA), tryptophan (TRP) and melatonin (MEL) using LC/MS/MS. Acute mortality and sublethal physiological effects of FLX were assessed using standard static renewal toxicity tests in which juvenile sheepshead minnows ( Cyprinodon variegatus) were exposed to FLX. Fluoxetine did not cause significant mortality at levels near currently reported environmental concentrations. Significant changes in neurotransmitter levels were observed within the serotonergic system in juvenile sheepshead minnows exposed at concentrations approximately one order of magnitude above those currently reported in the environment. Transformation activity ratios of a product to a precursor compound (5-HT/TRP, 5-HIAA/5-HT and MEL/5-HT) also exhibited significant changes with FLX treatment. Fluoxetine exposure did not only affect 5-HT but had additional effects both upstream and downstream of 5-HT within its synthesis and metabolic pathways. These sublethal changes within the serotonergic pathway may result in behavioral changes which could, in turn, have implications for the ecological response of populations to additional environmental stressors.

Toxicity of Benzalkonium Chloride on Monoalgal Cultures and Natural Assemblages of Marine Phytoplankton

The current widespread use of benzalkonium chloride (BAC) in different cleaning and disinfecting products led us to investigate its potential toxic effect on phytoplankton. To this aim, different physiological variables were monitored to detect toxicity of four ecologically relevant concentrations of BAC (15–200 μg l−1) on batch cultures of the microalgae Isochrysis galbana and Chaetoceros gracilis, and on a coastal phytoplankton assemblage. Fluorescence variables measured by fast repetition rate fluorometry, specifically variable fluorescence (Fv), were the most suitable to be used as endpoint among all the variables recorded (biomass, growth rate, size structure, and species composition). Calculated effective concentrations from Fv data provided evidences of higher sensitivity in the natural assemblage at short exposure times (natural assemblage—EC50 [24 h] = 36.4 μg l−1 vs. monoalgae—EC50 [24 h] > 120 μg l−1). Despite these differences, standard monoalgal laboratory toxicity tests provided comparable estimates of safe concentrations for microalgae in the environment. Assessed EC10 fall within the range of BAC concentrations reported in the literature for different effluents.

The effect of bacteria on the sensitivity of microalgae to copper in laboratory bioassays

Although single-species laboratory toxicity tests with microalgae are sensitive and highly reproducible, they lack environmental realism. Interactions between algae and their associated bacteria, either in the plankton or in biofilms, may alter algal sensitivity to contaminants, which are not mimicked in laboratory toxicity tests. This study investigated the effects of simple algal-bacterial relationships on the sensitivity of laboratory-cultured algae to copper using 72-h algal growth-rate inhibition bioassays. Four species of microalgae were used, two isolates of each; a strain of algae with no microscopically visible and no culturable bacteria present (operationally defined as axenic) and a non-axenic strain. The four algae used were the marine diatom Nitzschia closterium, the freshwater green alga Pseudokirchneriella subcapitata and two tropical Chlorella spp. Under control conditions (no copper), N. closterium and P. subcapitata grew better in the presence of the bacterial community. Sensitivity to copper (assessed as the concentration to inhibit the growth rate by 50% after 72-h (IC50)) was not significantly different for the axenic and non-axenic strains of N. closterium, P. subcapitata or for Chlorella sp. (PNG isolate). At pH 5.7, the axenic Chlorella sp. (NT isolate) had a 72-h IC50 of 46 μg Cu L −1, while in the presence of bacteria the IC50 increased (i.e., sensitivity decreased) to 208 μg Cu L −1. However, when the bacterial status of both the operationally defined axenic and non-axenic cultures of N. closterium and Chlorella sp. (NT isolate) was investigated using polymerase chain reaction (PCR) amplification of 16S rRNA followed by DNA fingerprinting using denaturing gradient gel electrophoresis (DGGE), it was found that bacteria were actually present in all the algal cultures, i.e. the axenic cultures were not truly bacteria-free. Based on sequence information, the bacteria present were nearly all identified as alphaproteobacteria, and a number of isolates had high similarity to bacteria previously identified as symbionts or species endophytically associated with marine organisms. The “axenic” cultures contained less bacterial phylotypes than the non-axenic cultures, and based on band-intensity, also contained less bacterial DNA. This supported the findings of few differences in copper sensitivity between strains, and suggests that standard microalgal toxicity tests probably inadvertently use non-axenic cultures in metal assessment.

Pesticide exposure strongly enhances parasite virulence in an invertebrate host model

Parasites are a common and constant threat to organisms at all levels of phyla. The virulence of a parasite, defined as the impact on survival and reproduction of its host, depends on the specific host–parasite combination and can also be influenced by environmental conditions. Environmental pollution might be an additional factor influencing host–parasite interactions. We here aimed to test whether the combined stress of pollutant exposure and parasite challenge results in stronger impacts on host organisms than expected from the single stressors applied alone. We used the water flea Daphnia magna and two of its endoparasites, the bacterium Pasteuria ramosa and the microsporidium Flabelliforma magnivora, as invertebrate host–parasite models. For each parasite, we tested in a full‐factorial design for interactions between parasitism and pollution using the neurotoxic pesticide carbaryl as a model substance. Sublethal concentrations of the pesticide synergistically enhanced the virulence of both parasites by increasing host mortality. Furthermore, host castration induced by P. ramosa was accelerated by carbaryl exposure. These effects likely reflect decreased host resistance due to direct or indirect immunosuppressive activity of carbaryl. The present study provides experimental evidence that the in vivo development of infectious diseases can be influenced by a pesticide at environmentally realistic concentrations. This implies that host–parasite interactions and subsequently co‐evolution might be influenced by environmental pollution at toxicant concentrations being sublethal to parasite‐free hosts. Standard toxicity testing as employed in the current way of conducting ecological risk assessments for anthropogenic substances does not consider natural antagonists such as infectious diseases, and thereby likely underestimates the impact these substances may pose to natural populations in the environment.

Hypoxia Does Not Influence the Response of Fish to a Mixture of Estrogenic Chemicals

Chemical risk assessment procedures assign a major role to standardized toxicity tests, in which the response of a particular organism to a single test substance is determined under otherwise constant and favorable conditions in the laboratory. This approach fails to consider the potential for chemical interactions, as well as failing to consider how the toxicological response varies, depending on the conditions of exposure. As yet, the issue of confounding factors on chemically mediated effects in wildlife has received little attention, despite the fact that a range of physicochemical parameters, including temperature, water quality, and pH, are known to modify chemical toxicity. Here, we consider how the estrogenic response of fish varies with regard to hypoxia. Fathead minnows (Pimephales promelas) were exposed to a mixture of estrogenic chemicals under hypoxic or normoxic conditions. Their estrogenic response was characterized using an in vivo assay, involving the analysis of the egg yolk protein, vitellogenin (VTG). The results revealed that there was no effect of hypoxia on the VTG response in either treatment group at the end of the exposure period. This suggests that this end point is robust and relatively insensitive to the effects of any physiological changes that arise as a result of hypoxia. The implications of these negative findings are discussed in terms of their relevance with regard to the development of risk assessment policy.

Using field data and weight of evidence to develop water quality criteria

In the United States, ambient aquatic life water quality criteria are derived using guidelines developed in 1985 that include a clear and consistent methodology using data from standard toxicity tests. The methodology from these guidelines has been successful, but a broader methodology is needed because some effects of pollutants do not lend themselves to conventional toxicity testing. Criterion assessment is proposed as that methodology. In criterion assessment, a specific environmental goal is translated into a measurable benchmark of effect that is used together with a modeled exposure-response relationship to estimate a range of exposures that will achieve the specific goal. The model of the exposure-response relationships and the benchmark effect are developed from field data and laboratory data using multiple analytical methods. Then the model is solved for the effect, thereby estimating the criterion, an upper threshold for acceptable exposures. The resulting candidate criteria are synthesized to select criteria and other benchmark values, such as remedial goals. The criterion assessment process is illustrated using the US Environmental Protection Agency Framework for Developing for Suspended and Bedded Sediments Water Quality Criteria, which recommends developing alternative candidate criterion values and then evaluating them to select a final criterion. Candidate criteria may be derived from models of field observations, field manipulations, laboratory tests, or empirical and theoretical models. Final selection of a criterion uses a weight-of-evidence comparison that engenders confidence because causal associations are confirmed on the basis of different assumptions, independent data sets, and varied statistical methods, thereby compensating for the concerns raised by individual studies and methods. Thus, it becomes possible to specify criteria for agents with biological or physical modes of action, as well as those with chemical modes of action, to best achieve environmental goals.

Accuracy of chronic aquatic toxicity estimates determined from acute toxicity data and two time–response models

Traditionally, chronic toxicity in aquatic organisms and wildlife has been determined from either toxicity test data, acute to chronic ratios, or application of safety factors. A more recent alternative approach has been to estimate chronic toxicity by modeling the time course of mortality as determined in standard acute toxicity tests, but these approaches have received limited validation. The accuracy of chronic toxicity estimates from two time-response models, linear regression analysis (LRA) and accelerated life testing (ALT), was investigated using a dataset of more than 150 matched species pairs of standard acute toxicity test data and measured chronic no-observed-effect concentrations (NOECs). Chronic survival was more accurately modeled by both ALT (accuracy, 69%) and LRA (accuracy, 76%) than was reproduction, growth, or the most sensitive endpoint (accuracy, 50-60%). In general, LRA estimates of chronic toxicity were less conservative than ALT estimates, with 66 to 79% of LRA estimates being greater than the measured NOEC. Acute datasets with early mortality produced estimates of chronic survival that were more accurate (ALT, 92%; LRA, 89%) compared to all datasets but were less conservative (84% of ALT estimates were overestimated vs 93% of LRA estimates). Acute datasets with late mortality resulted in poor ALT and LRA estimates of chronic toxicity for all endpoints. Additional survival time measurements did not improve the accuracy of ALT or LRA estimates of chronic toxicity over the standard four acute measurement times (24, 48, 72, and 96 h). The time course of mortality should be considered when applying time-response models to estimate chronic aquatic toxicity, with greater accuracy likely for chronic survival than for growth or reproduction.

Does The Standard Toxicological Testing Paradigm for Industrial Chemicals Apply to Screening for Children's Health Risks?

Questions have been raised concerning whether standard toxicological testing paradigms for characterizing hazards are applicable for children. In this paper, the standard toxicological testing paradigm for industrial chemicals 1 is examined. The analysis includes examination of the basic principles and elements of hazard characterization methodology based on animal toxicity data, examination of the characteristics of the standard toxicity tests that apply to assessing haz- ards of industrial chemicals to children's health, and an appraisal of specific industrial chemical hazard characterizations developed by USEPA covering more than 200 substances (High Production Volume (HPV) Challenge datasets 2 ) with re- gard to their relevancy for use in screening for potential risks to children's health. We conclude that the standard toxicity tests used for industrial chemicals that comprise the USEPA's HPV Challenge provide adequate information for develop- ing screening-level hazard characterizations for children's health, and when coupled with child-specific exposure informa- tion should provide adequate screening-level risk evaluations for children. Key Word: Children's health, HPV chemical, hazard characterization, toxicity testing, industrial chemicals.

A Daphnia magna feeding bioassay as a cost effective and ecological relevant sublethal toxicity test for Environmental Risk Assessment of toxic effluents

Environmental Risk Assessment of chemical products and effluents within EC countries require the use of cost effective standardized toxicity tests that in most cases are restricted to acute responses to high doses. Thus, subtle ecological effects are underestimated. Here we propose a short-term one day Daphnia magna feeding inhibition test as a cost effective and ecological relevant sublethal bioassay. The sensitivity and reliability of the proposed bioassay was tested in the laboratory against standardized bacteria, algae growth, D. magna and fish acute toxicity test by using 16 chemical mixture × water type combinations that included four different water types fortified with four complex chemical mixtures. Water types included ASTM hard water and three selected effluents diluted 1/10 in water to mimic worse field situations that many overexploited arid river ecosystems suffer during summer months when effluents are discharged into them with little dilution. The results obtained denoted a greater sensitivity of the proposed feeding bioassay in 51 out of 65 tests performed with an average sensitivity 50 fold greater than that of the standardized tests. The greater differences were obtained for mixtures that included narcotic chemicals and the lowest differences for those containing pesticides. Furthermore, feeding responses to the studied contaminant mixtures behaved differently to increasing TOC content than those based on bioluminescent bacteria and algae. Increasing TOC coming from sewage treated effluents decrease toxicity to the latter bioassays but increased those of D. magna feeding bioassays. These results empathize the need to include additional bioassays to monitor more accurately and realistically the toxicity of effluents or surface waters dominated by effluent discharges, a quite common situation in America and Mediterranean arid regions.

Species selection considerations for preclinical toxicology studies for biotherapeutics

Background: Preclinical efficacy and safety studies, especially chronic studies, can be difficult to perform when the candidate therapeutic agent is a human protein due to the specificity of these molecules for the human target. The main issues are: i) the human protein or target may not be pharmacologically active in rodents or dogs, the standard toxicology species; or ii) the therapeutic agent may be so immunogenic in these species, that longer duration studies are not possible due to the formation of neutralizing antibodies. Thus, preclinical safety testing of biotherapeutics poses a particular challenge in selecting a relevant animal species for use in toxicology studies. Objective: This article will discuss the considerations that are unique to safety assessment of biotherapeutics and will provide alternatives to the standard toxicity testing which is conducted for small molecules. Methods: This article is based on published information with regards to species selection considerations as well as information from the FDA website on several marketed compounds. In addition, discussions of this topic that have occurred in public forums as well as the experience of the author are considered. Conclusion: The most important consideration in species selection for a biotherapeutic is that the drug is pharmacologically active in the preclinical species. This is a key consideration as biotherapeutics are highly targeted and rarely, if ever, demonstrate off-target toxicity. Because of this species specificity, nonhuman primates are often the only relevant species that can be used to assess the safety of a biotherapeutic. Other alternatives such as use of a homologous protein in rodents or the use of transgenic or knockout mice can also be used to assess safety although the caveats to these approaches must be considered.

The Road to Green Nanotechnology

The Road to Green Nanotechnology

Avoidance tests in site‐specific risk assessment—influence of soil properties on the avoidance response of collembola and earthworms

The ability of organisms to avoid contaminated soils can act as an indicator of toxic potential in a particular soil. Based on the escape response of earthworms and Collembola, avoidance tests with these soil organisms have great potential as early screening tools in site-specific assessment. These tests are becoming more common in soil ecotoxicology, because they are ecologically relevant and have a shorter duration time compared with standardized soil toxicity tests. The avoidance response of soil invertebrates, however, can be influenced by the soil properties (e.g., organic matter content and texture) that affect behavior of the test species in the exposure matrix. Such an influence could mask a possible effect of the contaminant. Therefore, the effects of soil properties on performance of test species in the exposure media should be considered during risk assessment of contaminated soils. Avoidance tests with earthworms (Eisenia andrei) and springtails (Folsomia candida) were performed to identify the influence of both organic matter content and texture on the avoidance response of representative soil organisms. Distinct artificial soils were prepared by modifying quantities of the standard artificial soil components described by the Organization for Economic Co-operation and Development to achieve different organic matter and texture classes. Several combinations of each factor were tested. Results showed that both properties influenced the avoidance response of organisms, which avoided soils with low organic matter content and fine texture. Springtails were less sensitive to changes in these soil constituents compared with earthworms, indicating springtails can be used for site-specific assessments of contaminated soils with a wider range of respective soil properties.

Relative Toxicity of Malathion to Trematode-Infected and Noninfected Rana palustris Tadpoles

Amphibian populations around the world are facing threats that include disease and pollution. Although the effect of environmental contaminants on susceptibility to infection has been demonstrated for several amphibian species, to our knowledge, the opposite interaction, infection status affecting contaminant susceptibility, has not been studied. We conducted standard 48-h toxicity tests to compare susceptibility to malathion, a widely used organophosphate insecticide, of uninfected pickerel frog (Rana palustris) tadpoles and tadpoles infected with two levels (10 or 30 cercariae) of the trematode Echinostoma trivolvis. Trematode encystment rates were high (>90%) in both trematode treatment groups. LC(50) values ranged from 16.5 to 17.4 mg/L, within the range reported for other amphibian species. However, we found no differences in susceptibility to malathion among parasite treatments. Although we detected no effect of parasites on pesticide susceptibility in this system, it is important to investigate this question using other pesticides, parasites, and amphibian hosts before dismissing this potentially threatening interaction.

Variable toxicity of ionic liquid–forming chemicals to Lemna mino and the influence of dissolved organic matter

Ionic liquids (ILs) are nonvolatile organic salts that remain liquid over a wide range of temperatures. Ionic liquids are promoted as environmentally friendly alternatives to the volatile organic solvents that are currently in widespread industrial usage. Although ILs are unlikely to contribute to air pollution, their potential effects on aquatic ecosystems are largely unknown. Furthermore, information is lacking on how ILs will interact with common features of aquatic environments, such as dissolved organic matter (DOM). We assessed the effect of five IL-forming chemicals on the growth of duckweed, Lemna minor, a common aquatic vascular plant. In general, 1-alkyl-3-methylimidazolium chemicals with longer alkyl chains were more toxic to L. minor than those with short alkyl chain lengths. The concentration that produced a 50% reduction (the EC50) in root growth was 8.56 ppm when a butyl chain was present but was 0.25 ppm (i.e., much more toxic) when an octyl chain was substituted. Butyl-substituted 3-methylpyridinium (root growth EC50 of 7.49 ppm) and 3-methylimidazolium cations had similar toxicity, whereas a tetrabutyl ammonium cation was considerably less toxic (root growth EC50 of 32.71 ppm). When we tested whether DOM reduced the toxicity of these cations, we saw no effect of a low-molecular-weight organic acid or commercial humic matter. In contrast, natural DOM reduced the toxicity of imidazolium, but only at low concentrations. Design and use of ILs and other new chemicals should incorporate not only standard toxicity tests but also information on how such chemicals will interact with other components of aquatic ecosystems.

Occurrences and ecological risks of roxithromycin, trimethoprim, and chloramphenicol in the Han River, Korea

We evaluated the occurrence of three antibiotics (roxithromycin, trimethoprim, and chloramphenicol) in surface water and effluents from several sewage treatment plants (STPs) on the Han River, Korea. In addition, standard acute toxicity tests were conducted using the microbe Vibrio fischeri, freshwater macroinvertebrates Daphnia magna and Moina macrocopa, and fish (Oryzias latipes) for these antibiotics. Antibiotics were more frequently detected at higher amounts in effluent samples and in samples collected during the low-flow season. For trimethoprim and chloramphenicol, the levels observed in surface water during low flow were, on average, 108 and 31 ng/L, respectively. These levels were comparable to those measured in the municipal effluents (average, 80 and 37 ng/L, respectively), suggesting the presence of other sources upstream (e.g., livestock wastes). For roxithromycin, surface water levels were approximately an order of magnitude lower than effluent levels. Adverse effects of roxithromycin, trimethoprim, and chloramphenicol were observed at mg/L levels in standard acute aquatic ecotoxicity tests. Based on hazard quotients calculated for the three antibiotics, minimal risks to aquatic systems are suggested. To further increase scientific understanding about the potential impacts of these pharmaceuticals in the environment, however, chronic ecotoxicology studies, with more subtle but ecologically meaningful end points or in combination with other mechanistically related contaminants, may be beneficial.

QSAR modelling of acute toxicity in the fathead minnow

There are more than 70000 chemicals in use today and many more being synthesized. It is vital to assess the influence of these compounds on the environment and on human health. Experimental testing is both time-consuming and expensive, and accordingly, there is a pressing requirement for accurate in silico methods to assess the toxicity. QSAR studies of the environmental fate of chemicals are widely used for this purpose. One of the broadly used toxicity database is the Distributed Structure-Searchable Toxicity (DSSTox) database from the U.S. Environmental Protection Agency (http://www.epa.gov). It provides various data including EPA Fathead Minnow Aquatic Toxicity Database (EPAFHM), which currently contains structures of 617 chemicals of which 580 structures have toxicity data (EPAFHM_v3b_617_10Apr2006). The toxicity end-points are based on the 96 h LC50 (mmol/L) values for the fathead minnow, which used for standard toxicity test described by the U.S. Environmental Protection Agency. We used QNA (Quantitative Neighbourhoods of Atoms) descriptors and Self-Consistent Regression for QSAR modeling of acute toxicity in the fathead minnow. The statistical parameters of the correlation are the follows: N = 580, R2 = 0.804, F = 32.508, SD = 0.670, Q2 = 0.759. For 522 compounds (90%), the deviation of the predicted values from the observed ones is less than 1 logLC50 (mmol/L). Leave-10%-out cross-validation procedure was used for assessment of prediction ability of the method. It was performed 20 times and average R2 of prediction was 0.606, the highest value of R2 = 0.815, the lowest value of R2 = 0.501. Applicability domain was estimated for test set by leave-10%-out cross-validation procedure. These results confirmed robustness and satisfactory predictive ability of the method, hence, it can be used for computational assessment of acute toxicity in new compounds.