Pore waters were collected for toxicological and chemical analyses at several stations on the coast of Marinduque, near the mouths of the Boac and Mogpog rivers, and near the causeways formed by mine tailings disposal. Porewater samples were also collected at the Tres Reyes Marine Reserve, so that these non-contaminated samples could serve as a reference for test performance.

Sea urchin embryological development and fertilization were only significantly impaired by two porewater samples, suggesting the presence of contaminants in toxic amounts at those stations. The toxic samples were collected near the up current side of the Calancan (Marcopper) mine tailings causeway (stations 2 and 3). The pore water from station 2 also had the highest levels of heavy metals, particularly cadmium, cobalt, copper, nickel, lead and zinc. The concentrations of cobalt, nickel and zinc were also elevated at station 3. Copper concentrations were also elevated at the two river mouth stations (8 and 9) and near the CMI tailings causeway (station 7).

Visual observations also indicated biological degradation due to heavy siltation and smothered coral at a gradient off the Calancan causeway, suggesting that siltation might also be causing a physical impact. This preliminary survey suggests that effects related to past mining activities are still evident and warrant a more comprehensive study to assess their severity and areal extent.

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