Use of microbiotests to compare the toxicity of water samples fortified with active ingredients and formulated pesticides

Abstract

In Portugal rice occupies a relevant position among other irrigated crops and, since treated water is frequently discharged to the surrounding water bodies, field studies to determine the influence of pesticides used in rice treatments to aquatic biota are being performed. In order to better understand the toxicity results obtained in field conditions, particularly the influence of the pesticide formulations in the toxic effects, laboratory studies were performed using water samples fortified with the active ingredient and the respective formulated product (commercial product) of some pesticides (molinate, MCPA, propanil, endosulfan, chlorfenvinphos) usually applied in Portuguese paddies. The range of concentrations tested reflects the rates used by the farmers in real field conditions. The toxicity values observed in the laboratory during 1998 with the microbiotests Daphtoxkit magna FTM, Thamnotoxkit FTM, Artoxkit MTM, and Algaltoxkit FTM are presented and discussed in this study. The results obtained until now suggest that organic solvents and surfactants present in some of the tested formulations may affect the toxicity of the sample. In fact, water samples fortified with formulated pesticides seemed to be, in the majority of the cases, more toxic than the respective active ingredients solutions, particularly in the case of the three tested crustaceans. The microbiotests used seem to be a useful tool to evaluate toxicity with relative low cost, rapidity, and simplicity, compared with the traditional tests. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 401–405, 2000