Surveying the Effects of the Deep-Sea Tailings Disposal of Mine Wastes in Toledo City, Cebu, Philippines Three Decades After Mine Closure

Abstract

Abstract From 1971 to 1991, a major mining company performed submarine tailings disposal (STD) with the outfall at the coast of Ibo, Toledo, reaching up to 100,000 tons per day. In this study, five sampling points were selected near the outfall to determine if the STD is still a major factor in the physicochemical conditions and concentration of heavy metals in the areas near the outfall in Tañon Strait 28 years after the last disposal of mine tailings. The study found that Fe, Mn, and Cu contents on beach sediments significantly decreased around the outfall, as well metal contents on seawater which are within the DAO-2016-08 standards. Physicochemical parameters showed values within the normal range and standards. Comparing the species count from 1983 to 2019, the drastic decline can be attributed to ocean acidification, acid mine drainage, and siltation from Sapangdaku River.