METAL CONTAMINATION IN TWO OYSTER SPECIES FROM SOUTHWEST PUERTO RICO

As coastal marine systems are increasingly affected by changes in land use and other anthropogenic impacts, bivalves may be an important tool for understanding ecosystem health and monitoring coastal water quality. Two common oyster species (Crassostrea rhizophorae and Isognomon alatus) were collected from thirteen coastal mangrove sites from Gilligan’s Island, Guánica Harbor, Ensenda, and west, central, and east La Parguera along the southwest coast of Puerto Rico. Oyster tissue was extracted, acid digested and analyzed for a suite of thirteen trace metals (Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Se, V, and Zn) with an Inductively Coupled Plasma Mass Spectrometer (ICP-MS). Overall, higher concentrations of most metals (except As) were found in C. rhizophorae than I. alatus. Sites with more coastal development, including Guánica Harbor and central La Parguera had higher concentrations of metals than those with less coastal development. Contamination sources may include industrial, waste, and stormwater runoff from the more developed towns of Guánica and La Parguera, as well as their associated marinas. Combined elevated levels of Cr, Co, and V, particularly in La Parguera oysters, suggest contamination from motor oil used in automobiles and/or boats. Furthermore, metal contamination per oyster (for both species and all sites) surpasses tolerable daily intake (TDI) levels recommended by the Environmental Protection Agency (EPA) for adult consumption. Comparison to local Mussel Watch values collected between 1992 and 2010 further indicate that half of the metals (Ag, Cd, Cr, Cu, and Ni) were found in higher concentrations in 2015 than previously measured, while As, Fe, Mn, Se, and Zn remained unchanged compared to historic values. Altogether, these findings indicate the continued, long-term, and pervasive contamination of oysters and their associated coastal marine environment from human activity in southwest Puerto Rico.