Biological and chemical analysis in the detection of methamidophos in soil: ecotoxicological test with liquid chromatography/mass spectrometry

The development of analytical methods which meet the resolution to quantify pesticides residues in complex environmental matrices still represents a challenge for many laboratories. The integration of two analytical methods, an ecotoxicological and a chemical one, demonstrates the potential for environmental analysis of methamidophos. This study tested two soils: a clayey and a sandy one. Both soils, when in contact with methamidophos, followed the kinetic pseudo-second order model. The clayey soil showed a greater adsorption of methamidophos and followed the Freundlich model, while the sandy, followed the Langmuir model. The technique of LC-MS/MS analytical (Liquid Chromatography/Mass Spectrometry) displayed satisfactory validation parameters, such as linearity, interval, precision, accuracy, and sensitivity. In chronic ecotoxicological tests with Ceriodaphnia dubia, the NOEC (No Observed Effect Concentration) were 4.93 and 3.24 ng L-1 for the elutriates of sandy and clayey soils, respectively. The ecotoxicological test with Ceriodaphnia dubia showed excellent sensitivity for detecting methamidophos in clayey and sandy soils, and it was used for screening the results. However, by decreasing the concentration of the standard analytical methamidophos and adjusting the chemical validation parameters, one could find the limit of quantification (LOQ) in ng L-1, compatible with the established in the ecotoxicological test. The described methods were used as an analytical tool of methamidophos in soils.