Biodegradation and bioaccumulation of fenitrothion in rat liver.

Abstract

The biodegradation of fenitrothion O,O-dimethyl-O-(3-methyl-4-nitro phenyl) phosphorothioate was investigated in rat liver after administration of various doses (5 mg/100 g body weight and 20 mg/100 g body weight) in acute treatment and 1 mg/100 g body weight in chronic treatment. High performance liquid chromatography of the pesticide and its metabolites formed in liver in acute treatment showed time-dependent sequential conversion of pesticide into three major metabolites within 24 h. These metabolites were separated and purified to homogenity by HPLC and characterized by IR spectroscopy as O,O-dimethyl-O-(3-methyl-4-amino phenyl) phsophorothioate (metabolite 1), O,O-dimethyl phosphorothioate (metabolite II) and O,O-dimethyl phosphate (metabolite III) in the fi rst dose (5 mg/100 g body weight). Metabolite II was found to be different in the second dose (20 mg/100 g body weight) and identified as O,O-dimethyl O-3-methyl-4-amino phenyl phosphate. The results with the fi rst dose indicated reduction of the nitro group in fenitrothion as step I followed by hydrolytic clevage of the P-O-aryl bond in metabolite I and oxidative desulphurylation of metabolite II. At higher dose (20 mg/100 g body weight) oxidative desulphurylation takes place as step II followed by hydrolysis of metabolite II. The bioaccumulation of fenitrothion within 60 days during chronic treatment showed no metabolite but continuous reduction in fenitrothion concentration, indicating excretion of pesticide and its products in urine and in faeces.