THE IMPACT OF CHROMIUM ACCUMULATION IN AN ESTUARINE ENVIRONMENT

THE IMPACT OF CHROMIUM ACCUMULATION IN AN ESTUARINE ENVIRONMENT JUDITH MCDOWELL CAPUZZO This study is an investigation of the effects of chromium wastes from the tanning industry on the benthic en­ vironment of the Great Bay estuary of southern New Hampshire. Three aspects were of major concern: (1) the accumulation of chromium in the sedimentary phase of the estuary and its use in predicting sedimentation rates; (2) benthic faunal diver­ sity at areas most affected by chromium accumulation; and (3) the effect of chromium accumulation on filtration rates and metabolic activity of the blue mussel Mytilus edulis L. and the soft-shelled clam Mya arenaria L. To estimate the sedimentation rate and effect of chromium pollution in the Great Bay estuary, a series of cores were taken from the Cocheco, Salmon Falls, and Piscat­ aqua Rivers and analyzed for chromium content, size fractions, and combustible matter. Chromium concentrations were strong­ ly correlated with the clay-silt fraction of sediments and it was possible to distinguish between natural and artifi­ cial or enhanced levels of chromium. The results indicate that chromium is accumulating in higher than natural levels at least in the upper reaches of the estuary and may he used as an indicator of sedimentation rates. The henthic community of the upper reaches of the Great Bay estuary was studied in relation to the chromium content of recent sediments and fluctuating salinity condi­ tions. As the distance from the discharge outlet of chro­ mium increased, chromium concentrations declined, salinity conditions became more stable, and a shift from a polychaete dominated community to an amphipod dominated community was observed. The low abundance of amphipod species at stations where great seasonal fluctuations in salinity and high chro­ mium concentrations prevail suggests that chromium accumula­ tion in recent sediments may be altering the community struc­ ture of the benthos in the upper reaches of the Piscataqua River of the Great Bay estuary. The association of chromium with the clay-silt fraction of sediment may present a greater physiological problem to populations of filter feeding organ­ isms than to other members of the benthic community. Defi­ nite conclusions concerning the impact of chromium accumula­ tion on benthic diversity can not be confirmed without addi­ tional chromium data and faunal diversity data from other benthic environments, as well as detailed information on the physiological tolerances of individual species. A reduction of filtration rates in Mytilus edulis L. and Mya arenaria L. resulted with exposure to chromium con­ taminated sediments and pure clay suspensions with comparable concentrations of chromium. The degree of toxicity was depen­ dent on the nature of chromium exchange with the various clay minerals and the method of chromium uptake by the bivalves. Diffusion of chromium and ingestion of particulate matter were important routes of chromium uptake in Mytilus, but only uptake by diffusion produced toxic effects in Mya. The re­ duction of filtration rates was due to an impairment of the ciliary mechanism of the gill, particularly of the laterofrontal cilia. Reduction of oxygen consumption rates of ex­ cised gill tissue was observed with exposure to chromium and it is suggested that chromium interferes with an energy sup­ plying metabolic process. It can be concluded that high chromium sediments present a stress situation to the resident bivalves of the Great Bay estuary.