Fenitrothion metabolism

Yamamoto T, Egashira T, Yoshida T, et al. 1982. Comparison of the effect of an equimolar and low dose of fenitrothion and methylparathion on their own metabolism in rat liver. J Toxicol Sci 7 35-41. 

Metabolism of Organophosphorus Insecticides in Aquatic Organisms, with Special Emphasis on Fenitrothion... 

In this article metabolism and bioaccumulation of fenitrothion in several aquatic species are dealt with under laboratory conditions. 

Thus, although organophosphorus compounds like fenitrothion may be metabolized in aquatic organisms through oxidative desulfuration, side chain oxidation, hydrolytic cleavage of P-O-arryl linkage, as well as O-demethylation, the turn-over rate apparently is much lower than in mammals. 

Table II. Metabolic activities in liver of animals for fenitrothion and fenitrooxon.

In water, the percentage of these degradation products increased with time and amounted to one quarter of the remaining radiocarbon at 24 hr the quantity of 3-methyl-4-nitrophenol and both demethylated products is ca. 7% and 5.5%, respectively. Fenitrooxon was also detected. Because fenitrothion was stable in water under the present experimental conditions, these degradation products are presumably produced by fish metabolism. 

Thus, in the static ecosystem the translocation and metabolism of fenitrothion is very complicated, apparently due to decomposition by soil organisms. Nevertheless, the data presented here may imply that rapid bioaccumulation of the radioactive compounds derived from fenitrothion in snail or in fish is unlikely to occur in the natural environment. 

In a static model ecosystem, several amino derivatives of fenitrothion, probably derived from the soil metabolism, were demonstrated in carp tissues, together with the nitro-containing compounds. The concentration of fenitrothion in carp, snails, daphnids and algae decreased with time, although its bioaccumulation ratio relative to the concentration in water tended to increase gradually in snails, daphnids and algae, presumably due to lower metabolic activity and/or slow excretion. 

In order to evaluate the potential hazards chemical insecticides pose to forest environments, it is essential that adequate and reliable research data be generated on their environmental chemistry (distribution, persistence, movement, metabolic degradation, toxicity, fate, etc.). This paper gives a brief account of some laboratory and field research activities carried out at the Forest Pest Management Institute, Canadian Forestry Service to meet this requirement. Using two chemical insecticides which are extensively used now in forest insect control programs in Canada Viz aminocarb [Trade name, Matacil 4-dimethylamino-m-tolyl N-methylcarbamate] and fenitrothion [0,0-dimethyl 0-(3-methyl-4-nitrophenyl) phosphorothioate], studies conducted at the Institute to elucidate the environmental behavior and fate of forestry insecticides in general will be discussed. 

Takimoto, Y., Miyamoto, J. (1976) Studies on the accumulation and metabolism of sumithion in fish. J. Pest. Sci. 1, 261-271. Takimoto, Y., Ohshima, M., Miyamoto, J. (1987) Comparative metabolism of fenitrothion in aquatic organisms. I. Metabolism in the euryhaline fish, Oryzalias latipes and Mugil cephalus. Ecotox. Environ. Saf. 13, 104—117. 

Microbial reduction of toxic organics is carried out by reduction enzymes. Major reduction reactions of selected toxic organics are shown in Table 13.5. The reduction of the nitro group to amine involves the formation of a nitro and a hydroxyamino group. This type of reduction reaction occurs during the microbial metabolism of various pesticides. Organophosphorous pesticides such as para-thion, paraoxon, or fenitrothion are often reduced to nontoxic amino compounds (Miyamoto et al., 1966 Matsumura and Benezet, 1978). 

Takimoto Y, Ohshima M, Miyamoto J (1987b) Comparative metabolism of fenitrothion in aquatic organisms. III. Metabolism in the crustaceans, Daphnia pulex and Palaemon paucidens. Ecotoxicol Environ Saf 13 126-134... 

Figure 1. Metabolic pathway of fenitrothion by Burkholderia sp. NFIOO...

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