ABSTRACT
This study investigated the effect of persistent heavy metal exposure on the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) of the freshwater snail, Lymnaea natalensis. Malondialdehyde (MDA) levels were also measured as an index of lipid peroxidation. The snails were exposed to cadmium, copper, lead and mercury for a total of 28 days at 0.1 mg/L, 0.1 mg/L, 0.2 mg/L and 0.1 mg/L respectively. Samples were collected at 1, 7, 14, 21 and 28 days intervals. Analysis of SOD showed significant initial increases in enzyme activity following exposure to copper, lead and mercury, while cadmium exposures caused increases from Day 14 onwards. Copper, cadmium and lead caused significant initial increases in CAT activity and mercury caused an increase only on Day 28. Copper caused a significant increase in GPx activity on Day 28 while MDA levels diminished significantly at Days 7-28. Similarly, cadmium caused significant increases of GPx activity on Day 28 whereas MDA levels were significantly reduced. Lead also caused a significant increase in GPx activity on Days 14-28 whilst no significant changes occurred in MDA levels. Mercury exposures caused significant increases in GPx activity on Days 7 and 21, whilst MDA levels were significantly reduced on Days 7 and 14. These findings suggest that persistent exposure of snails to heavy metals induces the antioxidant defence system, and decreases lipid peroxidation.
