Toxicity study of a Chesapeake Bay tributary - Wicomico River

The aquatic life in the Chesapeake Bay is being harmed by the inflow of nutrients, sediments and toxic contaminants. Wicomico River is one of the 150 rivers and streams that feed into the Bay. The objective of this study was to use USEPA Toxicity Identification Evaluation (TIE) tests to identify the toxicants in the sediment-porewater of Wicomico River. Samples from three different depths (7.7, 15.4 and 23.1 cm) at four different sites (1.6 km before, adjacent to, 1.6 and 3.2 km after the municipal sewage treatment plant outlet) were collected. The sediment-porewater samples were tested for toxicity (EC50) using the MicrotoxR marine luminescent bacteria (Vibrio fischeri), TOXITRAKTM toxicity test (Inhibition-%I), and Ceriodaphnia dubia (48-hr survival-%S). High toxicity values (Microtox EC50 = 21.3%, Toxitrak % I = 85.6 and Ceriodaphnia dubia % S = 22) were observed for the samples collected adjacent to the sewage treatment plant outlet. Toxicity reduced significantly with depth at every sampling site. Qualitative MetPLATETM analyses showed that toxic forms of heavy metals were present only in the sampling site adjacent to the sewage treatment plant outlet. Phase I TIE tests indicated that the toxicity was due to a pH sensitive toxicant (such as ammonia) and heavy metals and not from organic compounds. Phase II TIE tests identified ammonia, zinc (Zn), lead (Pb), copper (Cu) and cadmium (Cd) as the toxicants.