Use of Comprehensive Two-Dimensional Gas Chromatography with Time-of-Flight Mass Spectrometric Detection and Random Forest Pattern Recognition Techniques for Classifying Chemical Threat Agents and Detecting Chemical Attribution Signatures.

In this proof of concept study, chemical threat agent (CTA) samples were classified to their sources with accuracies of 87-100% by applying a random forest statistical pattern recognition technique to analytical data acquired by comprehensive two-dimensional gas chromatography with time-of-flight mass spectrometric detection (GC × GC-TOFMS). Three organophosphate pesticides, chlorpyrifos, dichlorvos, and dicrotophos, were used as the model CTAs, with data collected for 4-6 sources per CTA and 7-10 replicate analyses per source. The analytical data were also evaluated to determine tentatively identified chemical attribution signatures for the CTAs by comparing samples from different sources according to either the presence/absence of peaks or the relative responses of peaks. These results demonstrate that GC × GC-TOFMS analysis in combination with a random forest technique can be useful in sample classification and signature identification for pesticides. Furthermore, the results suggest that this combination of analytical chemistry and statistical approaches can be applied to forensic analysis of other chemicals for similar purposes.

Adverse outcome pathways during early fish development: a conceptual framework for identification of chemical screening and prioritization strategies.

The fish early life-stage (FELS) test guideline (OECD 210 or OCSPP 850.1400) is the most frequently used bioassay for predicting chronic fish toxicity and supporting aquatic ecological risk assessments around the world. For each chemical, the FELS test requires a minimum of 360 fish and 1 to 3 months from test initiation to termination. Although valuable for predicting fish full life-cycle toxicity, FELS tests are labor and resource intensive and, due to an emphasis on apical endpoints, provide little to no information about chemical mode of action. Therefore, the development and implementation of alternative testing strategies for screening and prioritizing chemicals has the potential to reduce the cost and number of animals required for estimating FELS toxicity and, at the same time, provides insights into mechanisms of toxicity. Using three reference chemicals with well-established yet distinct adverse outcome pathways (AOPs) in early life stages of fish, we proposed FELS-specific AOPs as conceptual frameworks for identifying useful chemical screening and prioritization strategies. The reference chemicals selected as case studies were a cardiotoxic aryl hydrocarbon receptor agonist (2,3,7,8-tetrachlorodibenzo-p-dioxin), neurotoxic acetylcholinesterase inhibitor (chlorpyrifos), and narcotic surfactant (linear alkylbenzene sulfonate). Using qualitative descriptions for each chemical during early fish development, we developed generalized AOPs and, based on these examples, proposed a three-tiered testing strategy for screening and prioritizing chemicals for FELS testing. Linked with biologically based concentration-response models, a tiered testing strategy may help reduce the reliance on long-term and costly FELS tests required for assessing the hazard of thousands of chemicals currently in commerce.

Genotoxicity evaluation of chlorpyrifos to amphibian Chinese toad (Amphibian: Anura) by Comet assay and Micronucleus test.

In the present study, the genotoxicity of chlorpyrifos was evaluated in the Chinese toad by using Comet assay and Micronucleus test (MN), as the potential tools for the assessment of genotoxicity. The first step was determined by the acute toxicity of chlorpyrifos. Tadpoles were exposed to the series of relatively high concentrations of chlorpyrifos for 96 h. LC(50) values at 24, 48, 72, and 96 h were 3.63, 1.17, 0.82, and 0.80 mgl(-1), respectively. Secondly, the Micronucleus test was used for detecting chromosome damage in Chinese toad tadpoles exposed to the sublethal concentrations of chlorpyrifos and methyl methane sulfonate (MMS), which indicated that they induced chromosomal lesion in erythrocytes of Bufo bufo gargarizans tadpoles. Thirdly, the significant (P < 0.05 concentration-dependent increase in DNA damage (as indicated by Tail DNA%, Tail length, Olive tail moment)) were observed in erythrocytes and liver cells of tadpoles exposed to the sublethal concentrations of chlorpyrifos and MMS by Comet assay. To our knowledge, this is the first report to describe the use of B. bufo gargarizans for genotoxicity assessment of chlorpyrifos.