Application of the microtox system to assess the toxicity of pesticides and their hydrolysis metabolites

Effect of Concentration, Temperature, and Soil Moisture on the Degradation of Chlorpyrifos in an Urban Iowa Soil

“…At the higher concentrations of chlorpyrifos, the concentration of TCP formed was also higher. The mineralization of 14 C-TCP to 14 C02 can be significantly reduced due to the toxicity of the TCP to soil microorganisms (14). Although the relative percentage of TCP is lower in the soil treated with 1,000 ppm, the actual concentration of TCP is greater, resulting in greater toxicity to soil microorganisms and extended residual activity of the insecticide.…”

“…Radiolabeled [2,6-ring- 14 C]chlorpyrifos (25.5 pCi/mmol) (16) and nonlabeled Dursban TC were obtained from DowElanco for use in this study. The [ 14 C]chlorpyrifos was dissolved in acetone to yield a treating solution.…”

“…Extracts from the 0-wk samples were used to quantify (confirm) the amount of [ 14 C]chlorpyrifos initially applied. Unextractable, soil-bound 14 C residues in the 12-wk incubation samples were recovered by combustion of aliquots of soil to 14 C02 in a Packard Bell model 300 oxidizer. Radiocarbon in NaOH traps, soil extracts, and soil combustions were analyzed by liquid scintillation counting (LSQ.…”

Interactions Between Pesticides and Their Major Degradation Products

“…At 100 ppm, TCP inhibited the degradation of carbofuran and D0WC0 429X in problem soils but did not have any effect at 1 and 10 ppm (19). Recent studies have demonstrated the antimicrobial activity of this metabolite (20,21); the inhibitory effect of TCP could be a result of its microbial toxicity. The levels required to affect the microbes, however, are so high that the effect of a single application of chlorpyrifos or trichlopyr may not be sufficient to produce a significant effect.…”

“…Dietholate, an extender used in the new formulations of EPTC, is structurally very similar to fonofos. In laboratory toxicity studies, methyl phenyl sulfone (a metabolite of fonofos) was more toxic to Photobacterium phosphoreum t a bioluminescent bacterium phylogenetically related to several important soil bacteria, than fonofos (20). The antimicrobial activity of fonofos (22) could result from the toxicity of its degradation product, methyl phenyl sulfone.…”