THE SPATIAL DISTRIBUTION OF Al, Fe, Cu, Cd AND Pb IN THE SURFACE SEDIMENT OF BRUNEI BAY, BORNEO DURING THE SOUTHWEST AND NORTHEAST MONSOONS

Abstract

A geochemical assessment of Al, Fe, Cu, Cd and Pb was carried out for the surface sediment of Brunei Bay. Samples were collected during July 2013 and January 2014 representing the Southwest and Northeast Monsoon respectively. Fe, Pb, Al and Cu were high in July 2013 samples whereas Cd had a similar range of concentration during both sampling periods. Cd showed no particular spatial distribution pattern whereas Fe and Pb were highly distributed at the transect stations compared to the coastal stations due to the river flshed out. In contrast, Al and Cu were uniformly distributed between all stations. The Al, Fe and Pb in Brunei Bay sediment were dominantly bound to the mineral fraction which is also an indicator of natural sources whereas Cu was more dominant in the ion exchangeable fraction which is the most bioavailable fraction. The risk assessment code (RAC) indicated that Al has no risk (RAC<1%) whereas Fe and Pb showed a low risk (RAC<10%) to the benthic organisms. However, Cu presented a very high risk (RAC>50%) in both sampling periods. Even though the RAC showed some risk of these metals on the ecosystem, the geoaccumulation index indicated no serious pollution by these metals. Additionally, the surface sediment of Brunei Bay was dominated by silt and very fie sand. The apparent changes in metals distribution and metals fractionation during January 2014 corresponded to the effects of monsoons. Port activities, aquaculture, fiheries, palm oil and paper mill industries are the potential sources of metals in the Brunei Bay ecosystem.