HEAVY METALS IN MERCENARIA CLAMS FROM NEW JERSEY AND NORTH CAROLINA ESTUARIES: INFLUENCE OF GROWTH HABITAT AND SIZE

This comparative study investigates the bioaccumulation of heavy metals in quahog clams (Mercenaria mercenaria) harvested from Atlantic coastal bays near Cape Lookout, North Carolina (NC) and Great Egg Harbor, New Jersey (NJ). Data on metal concentrations in bivalve mollusk tissue can provide baseline environmental information and also can inform shellfish consumption guidelines. Small aquacultured clams (1 inch thick) from both NC and NJ were grown near the surface in suspended cage (rack and bag) arrays. In addition to clams grown by aquaculture operations, wild clams from NC were harvested from intertidal sediment substrates. Wild, infaunal NC clams spanning a range of sizes from 1 to 2.5 inches thick) were collected to investigate metal accumulation with increasing age. Clam body tissues were freeze-dried, pulverized, and dissolved in nitric acid; concentrations of arsenic, cadmium, copper, lead, nickel, and zinc were analyzed by ICP-MS.

Preliminary results are as follows: larger specimens of infaunal wild-caught NC clams had higher heavy metal concentrations overall, excluding Cd which was lower, compared with aquacultured NJ clams. The measured concentrations of As, Cd, and Ni were well below 2007 FDA action levels of 86, 4, and 80 ppm, respectively for those elements. Concentrations of Pb for both NJ and NC clams were variable but a number of samples from both sites tested above the 2007 FDA Pb action level of 1.7 ppm. Notably, no size dependency on Pb concentration was observed. The data in hand do show increasing element concentrations with organism size for As, Cu, Ni, and Zn, however. Ongoing analyses should clarify which factors (e.g., specimen age/size; growth environment) control the observed pattern of heavy metal abundances.