Mercury speciation and stable isotope signatures in marine sediments of Honda Bay (the Philippines) impacted by abandoned mercury mine

Mercury speciation and isotopic composition was determined in ore, soil, sediment, and biota (lobster) samples collected from the vicinity and coastal area near the abandoned mercury mine in Palawan, Philippines. This study reported significant mass-dependent mercury isotopic fractionization among ore, soil, sediment and biota in the vicinity of abandoned mercury mine. Mercury isotopes in ore, soil and sediment samples had the lowest δ 202 Hg (−0.59‰ to −1.61‰) and Δ 199 Hg (+0.00 to +0.24‰) and small variance measured values but there was significant positive Δ 199 Hg and negative δ 202 Hg values in the biota that were correlated with light penetration depth in the sea. This suggests photochemical degradation of methylmercury prior to incorporation of remaining mercury into the food web. Mercury speciation identified oxidized Hg(II) as the dominant species in the marine sediment which is explained by quick transport of soil particles from the mine to the coast during heavy rains and flooding. Fewer Hg(I) were measured in the sediment, suggesting partial photoreduction of Hg(II) to Hg(0).