Heavy metal concentrations in marine sediments impacted by a mine-tailings spill, Marinduque Island, Philippines

A mine-tailings spill occurred on the island of Marinduque, Philippines, on 24 March 1996. Originating from the Marcopper Mine, tailings sludge flowed down the Boac River abruptly and during subsequent storm events. Most of the tailings material has since accumulated in the nearshore environment along the western coast of the island. Nineteen sediment cores were collected from this site and analyzed for heavy metals. Elevated concentrations of Cu (706-3,080 ppm), Mn (445-1,060 ppm), Pb (43-56 ppm), and Zn (131-276 ppm) are present in the tailings. Two horizons of high metal concentrations in the marine sediment profile are interpreted to correspond to two distinct tailings input events. The lower horizon corresponds to the original 1996 spill, whereas the spike near the surface is thought to be a combination of input due to dredging of the river in 1997 and reworking of sediments. A previous history of contamination is also deduced from the metal profiles. The volume of tailings material released into the marine environment due to the spill is estimated to be 180,000 to 260,000 m(3).