Toxicity and transformation of insecticide fenamiphos to the earthworm Eisenia fetida.

This study was conducted to investigate the toxicity of the organophosphate insecticide fenamiphos to earthworms (Eisenia fetida) under laboratory conditions. Earthworms were exposed to soils differing in their physico-chemical properties spiked with fenamiphos at concentrations ranging from 10 to 200 mg kg(-1) for a period of 4 weeks. Residues of fenamiphos and its metabolites were determined in both soils and earthworms after 4 weeks of pesticide exposure. Fenamiphos was degraded faster in the alkaline soil than in the neutral and acidic soils. Median lethal concentration of fenamiphos in the neutral soil was 228 mg kg(-1) soil. Residues of fenamiphos caused a significant reduction in the biomass of worms, especially the ones exposed to the pesticide in the acidic soil. In vitro experiments suggested that fenamiphos was biotransformed in the earthworms principally to its oxide metabolite. To our knowledge, this is the first study demonstrating the biotransformation of fenamiphos by E. fetida.

Hydrolysis of fenamiphos and its toxic oxidation products by Microbacterium sp. in pure culture and groundwater.

A bacterium with an exceptional ability to hydrolyse fenamiphos and its toxic oxidation products fenamiphos sulfoxide and fenamiphos sulfone, all possessing POC bond was isolated from soil. Based on 16S rRNA gene determination, this bacterium was putatively identified as Microbacterium esteraromaticum. The phenols (fenamiphos phenol, sulfoxide phenol and sulfone phenol) formed during bacterial hydrolysis resisted further degradation in mineral salts medium and sterile groundwater, but were transitory in non-sterile groundwater due to the catabolism of native microorganisms. Also, the cell-free preparation of this bacterium was highly effective in hydrolysing fenamiphos and its oxides. These results demonstrate the potential of this bacterium to detoxify pesticide waste in the environment including the groundwater.

Effect of insecticide fenamiphos on soil microbial activities in Australian and Ecuadorean soils.

The effect of fenamiphos, a widely used organophosphorus pesticide, on important soil microbial activities such as dehydrogenase, urease and potential nitrification in four soils from Australia and Ecuador were studied. The results showed fenamiphos in general was not toxic to dehydrogenase and urease up to 100 mg/Kg soil. However potential nitrification was found to be highly sensitive to fenamiphos with a significant inhibition recorded even at 10 mg/Kg soil. In general, the nitrification activity in soils was decreased with an increase in fenamiphos concentration. The calculated EC(50) values for nitrification in all the tested soils ranged between 19 and 56 mg fenamiphos/kg dry soil. This study suggests that fenamiphos is likely to be detrimental to nitrification at field application rates.

Biodegradation of the pesticide fenamiphos by ten different species of green algae and cyanobacteria.

The degradation of an organophosphorus pesticide, fenamiphos, by different species of five green algae and five cyanobacteria was studied. All the species tested were able to transform fenamiphos to its primary oxidation product, fenamiphos sulfoxide (FSO), while the majority of these cultures were able to hydrolyze FSO to fenamiphos sulfoxide phenol (FSOP). Fenamiphos sulfone phenol, FSOP, and FSO were detected in the culture extracts of these algae and cyanobacteria. This is the first report on the biodegradation of a toxic pesticide, fenamiphos, by cyanobacteria. The ability of these algae and cyanobacteria to detoxify fenamiphos can be gainfully used in bioremediation of this pesticide and its toxic metabolites.

Sorption of fenamiphos to different soils: the influence of soil properties.

Fenamiphos (0-ethyl-0(3-methyl-4-methylthiophenyl)-isopropylamido-phosphate) is a widely used nematicide and insecticide in bowling greens and agriculture, but information on its sorption including its metabolites is limited. Hence, the sorption of fenamiphos (nematicide) and its major degradation products fenamiphos sulfoxide (FSO) and fenamiphos sulfone (FSO2) were determined in thirteen contrasting soils collected from Australia and Ecuador. The sorption coefficients (Kd) exhibited a wide range of variation from 2.48 to 14.94 L/Kg for fenamiphos; from 0 to 7.42 L/Kg for FSO and from 0 to 9.49 L/Kg for FSO2. The sorption affinity of the three compounds for all soils tested was as follows: fenamiphos > fenamiphos sulfone > fenamiphos sulfoxide. The results showed that the sorption of fenamiphos and its metabolites in some soils is very low, and in one case is nonexistant for the metabolites. This is of particular concern as due to its low sorption coefficient, the compound could easily migrate and contaminate water bodies. Fenamiphos and its oxidation products have been reported to be highly toxic to aquatic invertebrates and therefore, the information generated in this study assumes great importance in the risk assessment of fenamiphos and its metabolites in the environment.