The possibility of using Culex pipiens (Diptera: Culicidae) larvae as a bioindicator of water pollution in Burullus Lake, Egypt

Abstract

The urgent environmental issue of heavy metal pollution in aquatic environments has brought attention to Burullus Lake due to its environmental and economic significance. Therefore, this study focused on using the third-instar larvae of Culex pipiens as bioindicators of metal pollution in two Burullus Lake sites: Al-Bughaz (site 1, reference) and the front of Drain 7 (site 2, polluted). The water physicochemical analysis confirmed site 2's higher pollution levels. Metal concentrations in water and larval midgut tissues from site 2 were significantly higher than in site 1. All biochemical parameters estimated in site 2's larval midgut tissues showed greater impacts compared to site 1. Concentration levels of malondialdehyde and metallothionein along with expression level of heat shock protein 70 were notably higher in site 2's larvae. Antioxidant biological markers, like reduced glutathione, superoxide dismutase, catalase, and glutathione peroxidase, as well as cytochrome P450 activity decreased significantly in site 2's larvae compared to the reference larvae from site 1. Analysis of DNA damage parameters in the midgut cells of site 2's larvae revealed significant rises in tail DNA%, tail length, and tail moment. DNA damage was increased in site 2's larvae due to migration of DNA fragments. Ultrastructure observations of site 2's larvae revealed structural alterations along the epithelial cells of midgut tissue like destroyed microvilli, an irregular nuclear envelope, vacuolated cytoplasm, increasing lysosomal bodies, disintegrated mitochondria, and the appearance of spherites and dense vesicles. In conclusion, C. pipiens larvae are reliable bioindicators for metal pollution in aquatic environments due to their sensitivity to metal bioaccumulation.