Contaminant concentrations of sediment samples collected approximately 10 years apart are compared in an attempt to establish current status of contaminant concentrations in Casco Bay, to determine whether contaminant concentrations are increasing, decreasing or remain unchanged, and to examine any changes in the geographical distribution of contaminants. This process is complicated by the potential of re-suspension of older sediment back to the surface, the non-homogeneity of sediments, low concentrations for some analytes and variability of different analytical methods. In spite of these complications several trends are observed. As expected, most of the contaminants appear to be decreasing in concentrations. Total PAH concentrations in the sediment are an exception. When comparing total PAH concentration in 1991 and 2001, there is neither an increase nor a decrease when the analytical uncertainties are considered. The continuing increased use of fossil fuels that may add additional PAH to the sediments appears to be balanced by increasing controls that lower PAH inputs. Total pesticides as well as 4,4-DDE, 4,4-DDD and total DDTs indicate a decrease from 1991 to 2000/2001. Total PCB concentrations also suggest a decrease over this time period. Silver is the only trace element increasing in concentration at most sampling sites from 1991 to 2001. The reason for this difference is not clear. Concentrations decreased at the majority of the sampling sites for cadmium, chromium, mercury, nickel, and selenium with no apparent difference for arsenic, copper lead and zinc. Tributyltin and total butyltin concentrations decreased over the time period from 1994 to 2000/2001. The overall indication for dioxin/furans is no change between sampling periods. The planar PCB indicates no change (PCB 77) or decreasing concentrations (PCB 126). With the many complicating factors, the interpretation of these data needs to be done with care. There is no indication from these data that any of the contaminants measured has increased by more than a factor of 2. At most Casco Bay sites and for most analytes there is either no change or a decrease. There are sites where increases are apparent and many of these sites are at the shallow water sites or at the Inner Bay sites where concentrations are higher and new inputs are more likely
Sediments from the Inner Bay region of Casco Bay; closest to Portland, ME; contain the highest levels of trace metals, PCBs, DDTs, and chlordane. For contaminants other than PAH (and these only at a few locations) and PCBs at one location, the levels of contamination in Casco Bay would not be considered high on a national basis, based on Macauley et al. (1994). The geographical distribution of most contaminants remains similar to those determined in 1991/1994. There are generally higher contaminant concentrations in the vicinity of Portland and other populated and industrial areas. Toxicity tests for selected sites and comparison of 2 contamination concentrations to ERL or ERM indicate the sediments are not toxic. The overall conclusion based on the available data is that the contaminant loading for Casco Bay, as a whole, is decreasing or remaining the same and these concentrations are not likely to adversely affect the biota. The geographic distribution of sediment contaminants is generally confirmed in the analysis of mussel tissue by the Casco Bay Estuary Project and the Maine Department of Environmental Protection (DEP) (Doggett, DEP, personal communication).
Wade, T.L., & Sweet, S.T. (2005). Assessment of Sediment Contamination in Casco Bay. Portland, ME: University of Southern Maine, Muskie School of Public Service, Casco Bay Estuary Partnership.