Biologic responses of rice field crab Esanthelphusa nani (Naiyanetr, 1984) to herbicides in paddy fields, Nan province

Abstract

Nowadays, herbicides have been widely used with increasing intensity in Nan Province. Since herbicides may pose adverse effects on non-target organism, it is crucial to monitor herbicide contamination and potential health hazards to animal living in agricultural area. Environmental screening with chromatographic techniques showed that detectable level of atrazine was found in water of the herbicide utilization area. In addition, a rice field crab Esanthelphusa nani was selected as a sentinel species for herbicide contamination and related biologic responses. Crabs were collected from two study sites: a reference site where no herbicides were used and a contaminated site where herbicides were used routinely. Crabs were subjected to analyses for herbicide contamination, changes in detoxifying enzyme activity, lipid peroxidation and morphometric and gravimetric analyses. Herbicide residue analysis showed that detectable levels of atrazine, glyphosate and paraquat was found in the crab tissue, with significant site-related difference in level of atrazine. Activities of hepatopancreas glutathione S-transferase (GST), a crucial detoxifying enzyme, of both male and female crabs were significantly elevated in the contaminated site compared to the reference site crabs. Although level of lipid peroxidation, an indicative of cell damage, was not significantly different between sites, it strongly correlated with levels of GST and atrazine in the crab. Relative body weight of male crabs in the contaminated site was significantly lower than those from the reference site. Sexually dimorphic traits of the crab including abdominal area and major claw size of male crabs from the contaminated site were also significantly smaller compared to those of the reference site animals. Correlation analysis indicated that atrazine in crab tissue was associated with decreased major claw size as well as increased hepatopancreas GST activity and LPO levels of crabs in the contaminated area. The results of this sentinel study could be used for assessing a potential impact of herbicide contamination on non-target organisms in agricultural environment.