Abstract

HERNANDEZ QUIROZ, Manuel et al. Microwave assisted extraction and solid phase cleaning as a method of analysis for organophosporus pesticides determination in Ambystoma mexicanum. Rev. Int. Contam. Ambient [online]. 2013, vol.29, n.2, pp.189-200. ISSN 0188-4999.

In recent years the population of Ambystoma mexicanum has declined dramatically in their natural habitat in the canals of Xochimilco and Chalco. Among others, the proposed main causes for its decline are poaching, depredation and competition with introduced non-native species in their habitat, and adverse effects due to contaminants. The latter is of growing global concern owing to the sublethal effects of organophosphorus pesticides in humans and animals, including their possible role in the overall decline of amphibian populations. Unlike other vertebrate groups, several aspects make amphibians more vulnerable to environmental changes such as "naked", glandular and permeable skin. This feature makes amphibians to be considered as good indicators of environmental quality. In this respect, the development of optimum methods for the detection of organophosphorus pesticides in the environment and the organisms under study is a fundamental aspect for toxicological studies, especially when their concentrations are found at sublethal levels. The analysis of pesticides in aquatic organisms is not a simple procedure due to the fact that tissues are a highly complex matrix that contains a diversity of compounds and substances, all with the possibility of interfering in the determination of the pollutant. All pesticide analysis require an extraction and a cleaning step to avoid interference in the detection of the pesticides of interest. Therefore the objective of this study is to propose an efficient method for the determination of organophosphorus pesticides (ethoprophos, diazinon, methyl parathion, malathion and chlorpyrifos) in axolotl tissue with gas chromatography (GC) quantification. The present study describes the use of microwave-assisted extraction (MAE) for the extraction of organophosphorus pesticides in A. mexicanum. It was demonstrated that the use of MAE with dichloromethane for 15 min at a power of 1200 W is a suitable extraction method, simple and effective to prevent the loss of the analytes to be extracted in a single step in a closed system. The cleaning of the extract with C18-Florisil® cartridges achieved recoveries above 90% for all the organophosphate pesticides studied. The validation parameters of the method, linearity, limit of detection and quantification, repeatability, reproducibility and HorRat index were evaluated to certificate it as a trustworthy method. Appropriate values for the identification of the organophosphorus pesticides ethoprophos, diazinon, methyl parathion, malathion and chlorpyrifos in the axolotl were obtained for the validation parameters. The method was successfully used to evaluate the bioaccumulation of chlorpyrifos in axolotls exposed to sublethal concentrations (0.05 and 0.1 mg/kg) of the pesticide.

Keywords : axolotl; amphibians; microwave assisted extraction; gas chromatography.