Baseline assessment of organic contaminants in surficial sediment from Kachemak Bay, Alaska

Organic contaminant inputs to coastal Alaska ecosystems are mostly driven by long range oceanic currents and atmospheric transport from lower latitudes, known as the “grasshopper effect.” This study characterized the distribution of organic compounds, including polycyclic aromatic hydrocarbons (PAHs), polychrlorinated biphenyls (PCBs), and a suite of organochlorine pesticides (dichlorodiphenyl tricholoroethane (DDTs), cyclodienes and hexachlorocyclohexanes (HCHs), in five strata in Kachemak Bay, as well as sediment total organic carbon (TOC) content and grain size. PAHs varied broadly throughout the study area. While the presence of substituted naphthalenes might be linked to spilled fuel and oil, incidences of pyrene and alkylated high molecular weight PAHs indicate pyrogenic sources (burned fuel). However, the dominant PAH was perylene (40%-60% of the total PAHs), and is indicative of possible terrestrial weathering (diagenic) input. PCBs, DDTs and the other organochlorine pesticides also varied throughout the study area, but their concentrations along with those of the PAHs were below the National Oceanic and Atmospheric Administration (NOAA) sediment quality guidelines. In most cases, the distributions of the organic contaminants were strongly influenced by the sediment grain size and TOC content, with elevated concentrations being found in depositional areas with fine-grain sediment.