Effect of Seasonal Variations of Selected Heavy Metals in Water and Grey Mullet (Mugil cephalus) Fish Tissues from Negombo Estuary.

Abstract

Heavy metal pollution is of particular concern as they have deleterious effects on biota through mobilization and accumulation in various tropic levels. Industrial pollution and domestic solid waste dumping are considered as the major pollution sources of the Negombo estuary. The different localities within the estuary are polluted at different rates due to changes in input levels. The objectives of this study were to assess the seasonal variations of heavy metal levels in water (rainy and non rainy periods) and fish tissues in selected sites. Four sampling sites were selected along the estuary. For this study, water and fish samples were collected from eight sampling locations along the north (n =2), south (n=2), west (n=2), east (n=2) regions during the one year study period from January to December 2014. The levels of Hg metals were analyzed by cold vapor atomic absorption spectrophotometer whereas the other metals were analyzed by flame furnace atomic absorption spectrophotometer. The results revealed that the average concentration of metals Pb, Cd and Hg in water were 0.01 to 0.005 ppm, 0.0 to 0.01 ppm and 0 to 0.013 ppm respectively. The detected average concentration of mercury in water was above the maximum permissible limits of the proposed tolerance limits for the discharge of industrial wastewater quality standards for Central Environmental Authority, (2001) Sri Lanka. This study showed that the concentrations (mg/kg) of metals in the fish tissues were (Pb) 0 to 0.3, (Cd) 0.35 to 1.104 and (Hg) 0.0005 to 0.05 mg/kg respectively. The mean concentration of Pb and Hg metal levels in fish were much below when compared to the international standard limits. The results showed that there is a significant differences of (P < 0.05) of Pb and Hg levels in fish tissues and also for all metals in water. The levels of heavy metals in water and fish tissue were higher in north region of the estuary due to the discharge of industrial effluents and domestic solid waste into the estuary. The seasonality in the heavy metal levels of water and fish tissue were observed with a peak periods from May and June to October and November, which apparently coincided with the South West monsoon and the onset of second inter monsoon of the island respectively.