An assessment of metals in an estuarine wetlands ecosystem

Abstract

Biotic and abiotic samples from two physically proximate, temperate, estuarine Hackensack River wetlands (New Jersey) located in highly urbanized areas were analyzed for chromium (total and hexavalent), copper, and lead. The study was performed to determine if chromite ore processing residues (COPR) in fill material surrounding one of the two sites (i.e., the “Study Site”) were associated with statistically significant higher total chromium concentrations in the biotic media at the Study Site relative to the other site (i.e., the “Reference Site”). Copper and lead concentrations were evaluated to determine whether other metals may have accumulated at the Study Site due to factors other than COPR. Concentrations of the three metals were evaluated in samples of water, sediment, plant tissue (Phragmites root and shoot tissues), fish tissue (Fundulus sp. whole body tissue), and blue crab tissues (Callinectes sapidus muscle and hepatopancreas tissues). Physical and chemical characteristics of the two sites that could have influenced the environmental fate and bioavailability of the metals were also evaluated. Concentrations of each of the three metals were approximately an order of magnitude higher in sediment samples from the Study Site. Concentrations of “total” and “dissolved” metals, however, were similar between the water samples collected at the two sites. Tidal flushing of the Study Site was restricted by tidal gates, and the higher metal concentrations in the sediments were attributed to factors resulting from the restricted tidal flushing. Statistically significant higher biota metal concentrations were found at the Study Site only for total chromium in blue crab hepatopancreas tissue and for lead in Phragmites shoot tissue. Tissues from the Study Site contained statistically significant lower concentrations of copper in all the biotic samples and of lead in blue crab hepatopancreas tissue than corresponding tissues from the Reference Site. Despite the Study Site sediments containing metal concentrations three to nine times greater than those in the Reference Site's sediments, no pattern of higher metal concentrations in biotic samples from the Study Site was found. The metals, including total chromium, were tightly bound to the sediments and therefore not bioavailable. Study Site sediment characteristics apparently limiting metal bioavailability included high organic carbon content, reducing conditions, high sulfide concentrations, high specific surface areas associated with a high proportion of silt and clay components, and high cation content.