The residual level of isoprothiolane in paddy field surface water and its acute toxicity level on freshwater prawn, Macrobrachium lanchesteri

Abstract

The application of isoprothiolane in rice cultivation may give a risk to the aquatic ecosystem. The present study was undertaken to determine the level of isoprothiolane in surface water of paddy fields in the district of Mukim 5, Seberang Perai Utara, Penang, and consequently to determine the acute toxicity level of isoprothiolane on freshwater prawn, Macrobrachium lanchesteri. Water samples from 12 sampling points were collected from sampling sites and extracted by solid-phase extraction method. The samples were then analysed by GC–MS to quantify the level of isoprothiolane detected in the samples. Isoprothiolane residue was detected in both the vegetative stage (maximum tillering) and ripening stage of paddy growth. The concentration of isoprothiolane residue found in the ripening stage was significantly higher than in the vegetative stage. The highest amount of isoprothiolane residue detected was at 9.37 mg/L from water sample collected at the ripening stage. Lethal concentration 50 (LC50) of isoprothiolane on M. lanchesteri was determined after 96 h of exposure, interpreted by probit analysis. The results showed that LC50 of isoprothiolane was 18.21 mg/L. Risk quotient assessment method was used to characterize ecological risk generated by isoprothiolane. The results indicate an unacceptable risk for representative organisms. The application of isoprothiolane is therefore an activity generating high risk for the ecosystems.