Status of heavy metal pollution in the Lunawa lagoon

Abstract

Distribution offive types of heavy metals in the Lunawa Lagoon (Colombo District) was investigatedfrom April to June 2006. Water and bottom sludge samples were obtained at fortnight intervals fromnine sampling stations of the lagoon including three drains (Northern, Eastern and Uyana). Watersamples were preserved by adding Cone. HNOJ (Analytical Grade) to adjust the pH to < 2 andbottom sludge samples were treated by 'Wet Ashing Method' before analysis. Concentrations of Cu, Zn, Pb, Cd and Cr were determined by Atomic Absorption Spectrophotometry. Cu, Zn, Pb and Crwere found both in water and bottom sludge samples of all sites, while Cd was not recorded from anyof the sites. Significantly higher concentrations of heavy metals (Mean ± SEM: Cu 120.75 ug/g ±8.43; Zn 570.98 ug/g ± 11.53; Pb 204.37 flg/g ± 7.50; Cr 52.50 ug/g ± 4.36: One- way ANOYA;P<O.OI) were found in bottom sludge of the Southern lagoon than the Northern lagoon and the threedrains. This is possible because the Southern lagoon is situated away from the sea outfall and theintensity offlushing by sea water is relatively less in this sector. Heavy metal concentrations in waterin different sites did not differ significantly, however, water in the Southern lagoon contained a relativelyhigher concentrations ofCu (0.049 ppm ± 0.002) and Pb (0.096 ppm ± 0.006) while the highest levelof Cr (0.035 ppm ± 0.020) and Zn (0.151 ppm ± 0.017) were recorded from the Eastern Drain.Bottom sludge contained significantly higher concentrations of all heavy metals than in water (P<O.OOI)indicating accumulation of metal ions in the sludge for a long period of time. Lagoon water could havebeen contaminated by point sources (such as Automotive Workshops and Textile Factories) and nonpointsources (such as Service Stations along the Galle Road) of heavy metal pollutants.