Effects Of Exposure To Lead And Zinc On Antioxidant Enzyme Activity In Lymnaea Natalensis And Helisoma Duryi.

Presented at the Biochemistry and Molecular Biology Society Conference held at the University of Zimbabwe in October 2002,Metals such as Zinc (Zn) are is found in high concentrations in mine drainage, while lead, as tetra-ethyl lead in petrol, causes contamination of water, soil and air can lead to severe health consequences. Zinc has been shown to reduce the efficiency of oxygen transport across the gill membrane of fish, as well as the respiration and ammonia excretion rates of freshwater shrimp. Molluscs have been shown to accumulate a wide variety of pollutants and have, in some instances, proposed as indicators of environmental pollution by metals. The effect of lead (Pb) and Zn on the antioxidant enzymes (AOE's) of two aquatic snail species, namely Lymnaea natalensis and Helisoma duryi was studied with a view to developing a biomarker of freshwater metal pollution. Adult snails reared in the laboratory were exposed daily for three days to 0.01 ppm, 0.1 ppm and 1.0 ppm of either Pb or Zn S-9 fractions were prepared form whole snails. The S-9 fractions were used to measure the activity of AOE's such as DT-diaphorase, catalase and glutathione-S-transferase as well as reduced glutathione (GSH) and the product of lipid peroxidation, malondialdehyde (MDA). Lead exposure tended to increase enzymatic activity several fold. Significant changes were observed after exposure to 0.01 ppm and 0.1 ppm in L. natalensis. Zinc also increased activity of the enzymes but to a lesser extent. Levels of markers of oxidative stress, MDA and glutathione GSH were also altered, with MDA generally decreased in L. natalensis. In H duryimetal exposure resulted in an increased GSH levels when exposed to 0.1 ppm and 1.0 ppm of Pb as well as by all three concentrations of Zn but not in a dose dependent manner. In H duryi, but not L. natalensis metal exposure resulted in an increased (up to 75'7'0) MDA level. Our data suggest that antioxidant status, as a result of exposure to heavy metals in aquatic snails metals is not altered in a dose dependent or manner and is also species specific. Thus, the alterations in AOE's using either L. natalensisor H duryi, are not sufficiently reliable to develop a biomarker of heavy metal pollution in aquatic systems.,Biochemistry and Molecular Biology Societ