Metals such as copper and mercury are the most diffused and hazardous organ specific environmental contaminants that exist in wide variety of physical and chemical status, each endowed with unique characteristics of target organ specificity. Aimed at correlating the tissue concentration of these heavy metals (copper and mercury) with oxidant defense levels and lipid peroxidation, different aquatic species with different life strategies (fish, Tilapia mossambica; snail, Pila globosa; crab, Oziotelphusa senex senex) were collected from freshwater environment in and around Tirupati, Andhra Pradesh, India. After due acclimatization to laboratory conditions, the test animals were exposed to sublethal concentrations of both the metals and studies were conducted for accumulation, antioxidant defense and lipid peroxidation after 7- and 15-days exposure periods and also after 15 days depuration period to clean water. The levels of the two antioxidant enzyme activities revealed that they are species dependant with fish liver showing higher reduction in glutathione S-transferase (0.28 ±0.02 mM/mg protein/min) and catalase (0.19±0.02 mM/mg protein/min) than snail glutathione S-transferase (0.18±0.09 mM/mg protein/min) and catalase (0.16±0.04 mM/mg protein/min). After 15 days in captivity and depuration the antioxidant enzyme activities in liver further decreased to reach normalcy. However, the hepatic lipid peroxidation was elevated in all the three aquatic species under study with increased levels of accumulation of the two metals in the liver tissue. In conclusion, the results highlight that while both copper and mercury contribute to oxidative stress, the observed species-specific differences in bioaccumulation and antioxidant response suggest that these species may require tailored management approaches in polluted freshwater environments.
Reddy et al. (Mon,) studied this question.