Abstract
Toxicants associated with sediments affect many natural aquatic ecosystems. Pocomoke River (PR) is one of the 150 rivers and streams that feed its sediment into the Chesapeake Bay. The objective of this study was to use USEPA Toxicity Identification Evaluation (TIE) tests to identify toxicants in the sediment-porewater of PR. Samples from three depths (0–7.7, 7.8–15.4 and 15.5–23.1 cm) at four sites (1.6 km upstream of, adjacent to and 1.6 and 3.2 km downstream of the municipal sewage treatment plant (STP) outlet) were collected. The porewater samples were tested for toxicity (EC 50) using the Microtox R marine luminescent bacteria ( Vibrio fischeri), TOXITRAK TM toxicity test (Inhibition-%I), and Ceriodaphnia dubia (48-h survival-%S). High toxicity values (EC 50 = 12.8%, % I = 93 and % S = 11) were observed for the samples collected at the site 1.6 km downstream of the STP outlet, which is near an intensive agricultural area including a poultry farm. Toxicity reduced significantly with increasing depth at every sampling site. Toxicity also decreased with distance from the most contaminated site both upstream and downstream. Qualitative MetPLATE TM analyses showed that toxic forms of metals were present in all the sampling sites except for the site 1.6 km upstream of the STP outlet. Phase I TIE tests suggested that the toxicity was due to oxidants, metals and organic compounds. Phase II TIE tests identified chlorine (total) and heavy metals [zinc (Zn), lead (Pb), copper (Cu), cadmium (Cd) and Arsenic (As)]. Polychlorinated biphenyls (PCBs) and organochlorine pesticides were found in PR porewater.
Published Version
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