Heavy metal pollution and burden of aquatic animal health: A pilot study from an urban wetland in Sri Lanka.

Abstract

Contamination of aquatic environments due to anthropogenic activities is increasingly evident globally. Heavy metals which are exposed to the environment through industrial and domestic wastes and effluents are serious pollutants of the aquatic environment, most of which are highly toxic. Heavy metal contamination of aquatic ecosystems pose threats to aquatic organisms by two means; high persistence in water and ability to accumulate in organisms via food chains. Heavy metals are reported to influence species by affecting health, altering behavior, physiology and anatomy which ultimately pose adverse impacts on biodiversity. Associations between aquatic pollution and health impacts on species are, however, complex and often poorly characterized. The present study investigated impacts of Copper (Cu), Zinc (Zn), Lead (Pb), Cadmium (Cd) in water and aquatic biota in Bellanwila Attidiya Sanctuary (test site), an urban wetland situated close to Colombo, subjected to industrial waste release. We selected Euphlyctis hexadactylus (Indian Green frog) as the test species since amphibians are highly sensitive to aquatic pollution and act as environmental indicators. Health of the test animals were investigated by studying immunological parameters. Bolgoda South wetland was selected as the reference site with negligible amounts of heavy metals. The Bellanwila Attidiya site was found to bepolluted with significantly highlevels of heavy metal ions, of Cu, Zn, Pb and Cd compared with the reference site in Bolgoda. Accumulation of all four heavy metals in the liver and muscles of E. hexadactylus was significantly higher in the test site compared with the reference site. Some basic immunological parameters such as total and differential white blood cell counts, neutrophil/lymphocyte ratio, spleen weight/body weight ratio, spleenocyte count, basal immunoglobulin level were determined using standard methodology. All these tests confirmed significantly reduced immune capacity of frogs in the polluted site compared with those in the reference site. Reduced immunocompetency of frogs may result in increased susceptibility to other environmental stresses including diseases, parasitic infections and growth impairments. In conclusion, this preliminarystudy for the first time in Sri Lanka, demonstrated that heavy metal pollution impair the immune system of frogs, which could in turn affect their overall health. Thus, if unavoidable, steps should be taken to minimize heavy metal pollution in wetlands to conserve aquatic biodiversity.