Environmental Genotoxicity of Pesticides in Non target Organisms

Abstract

Pesticides are used to control agricultural and house-hold pests. However, they pose significant risk to non-target aquatic organisms including fish, tadpoles etc. In the present study genotoxic and cytogenetic effects of sublethal concentrations of chlorpyrifos (an organophosphate) and cypermethrin (a pyrethroid) were observed in the erythrocytes and gill cells of Labeo rohita using Comet assay and Micronucleus test. In addition, effects of these pesticides on the hematological parameters and behavior of the fish were also investigated. The 96h LC 50 value of pesticides were estimated by Trimmed Spearman-Karber (TSK) software. On the basis of LC 50 value, the fish were exposed to sublethal concentrations of pesticides for 96h. Blood and gill samples were collected at every 24h and were subjected to the Comet assay and Micronucleus assay. A temporal concentration-dependent effect was observed in DNA damage, micronucleus frequencies with tested concentrations of pesticides. Furthermore, it was observed that the gill cells are more sensitive to pesticides, as it revealed more DNA damage as compared to the erythrocytes of fish. During the experimental period, hematological parameters like total erythrocytes count (TEC), hemoglobin and packed cell volume (PCV) decreased, whereas total leukocytes count (TLC) increased. Fish exposed to different concentrations of pesticides showed different neurotoxic behavioral responses. It was concluded that chlorpyrifos and cypermethrin are genotoxic, cytotoxic and neurotoxic insecticides causing DNA damage, micronucleus induction and neurotoxic effects in Labeo rohita. In the second part of this study, genotoxic effects of sublethal concentrations of chlorpyrifos were observed in the erythrocytes of common Indus valley toad (Bufo stomaticus). chlorpyrifos induced a significantly (P < 0.05) higher DNA damage in the erythrocytes of Bufo stomaticus tadpoles as compared to negative control, depicting the genotoxic nature of chlorpyrifos to amphibians. A significant concentration-dependent increase in DNA damage was observed at all the exposure concentrations of chlorpyrifos. The lower two sublethal concentrations of chlorpyrifos (155 and 233μg/L) showed significant DNA damages as compared to negative control, but did not show any significant (P < 0.05) different results with respect to each other. The highest concentration (465μg/L) induced significantly (P < 0.05) higher DNA damages as compared to negative control and other two chlorpyrifos concentrations at all the exposure time durations. Acute sublethal effects of chlorpyrifos were observed on the swimming and feeding performance of fathead minnow (Pimephales promelas) larvae. These responses were then compared to the transcriptional changes of selected genes. Significant differences were observed in the swimming performance and feeding performance of fish larvae exposed to different sublethal concentrations of insecticide as compared to the methanol control. Transcription of the Cyp1a gene was significantly up-regulated at all the exposure concentrations of chlorpyrifos whereas Aspa was significantly down-regulated at 67.5μg/L chlorpyrifos. Genes involved in detoxification (Cyp1a and GST), energy metabolism (CK) and neuromuscular activities (Aspa) were related with the impairment of swimming and feeding performance in the larvae. Transcriptional responses of different genes, quantified by quantitative real time PCR, correlated with the effects on the swimming and feeding performance providing a link between changes occurring at molecular and whole organism levels. Based on the investigations described in this thesis, it is concluded that representative pesticides of organophosphate and pyrethroid groups are genotoxic to non target organisms in the laboratory conditions. However, a potential future aspect of this study would be to look at the genotoxic effects on non target organisms in the field conditions.