Report Number: 81
Year: 1997

Analysis of In-Place Contaminants in Marine Sediments from Four Harbor Locations on Guam

During 1997, a preliminary survey was carried out to determine concentrations of heavy metals, polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) in sediment core composites (5 x 30 cm) from four harbor locations on Guam (Agana Boat Basin, Outer Apra Harbor, Agat Marina, and Merizo Pier). Overall, a total of 46 subtidal sites were examined. The survey clearly demonstrated enrichment of all contaminant groups in Agana Boat Basin, Outer Apra Harbor, and Merizo Pier, although by world standards, the majority of sites within each location were considered to be relatively clean. The highest levels of all three chemical groups were found at Apra Harbor, the largest and oldest port on Guam. Here, moderate to heavy enrichment of various heavy metals, PCBs and PAHs were identified in sediments collected in the vicinity of Hotel Wharf, Commercial Port, and Dry Dock Island. The lowest contaminant levels were almost always encountered at Agat Marina, a recently constructed small boat harbor to the south of Agana.

The range of mean heavy metal concentrations (μg/g dry wt.) for all 46 sites were as follows. silver (Ag) – all < 0.2; arsenic (As)– 1.00 to 10.7; cadmium (Cd) – < 0.2 to 2.18; chromium (Cr) – 3.61 to 39.5; copper (Cu) – 0.56 to 142; mercury (Hg) – 0.004 to 0.403; nickel (Ni) – < 0.2 to 71.0; lead (Pb) – < 0.6 to 96.3; tin (Sn) – < 0.1 to 7.37; and zinc (Zn) – 2.3 to 130. Mean total PCB and PAH concentrations ranged from < 0.04 to 341 ng/g dry wt. and < 10 to 8140 ng/g dry wt., respectively.

Heavy metal levels in Outer Apra Harbor were generally well below those reported earlier by the U.S. Navy for sediments from the Naval Reservation Area, within Inner Apra Harbor. Most notable from this particular study were the excessively high levels of total Sn (148 to 1055 μg/g dry wt.) and Hg (0.4 to 2.4 μg/g dry wt.) recorded. The impact of these elements on the indigenous biota, within Inner Apra Harbor and immediately adjacent waters of the outer harbor area, is currently unknown.

PCB-enriched sediments from Outer Apra Harbor were dominated by Cl4-Cl7 homologues while those from lightly contaminated sites frequently contained proportionately higher amounts of the lower chlorinated members, suggesting transport from relatively distant sources. PCB profiles, determined in sediments from Hotel Wharf and the Commercial Port area, closely resembled those of Aroclor 1254, a commercial PCB mixture that was once widely used as a dielectric fluid in electrical transformers. In contrast, PCBs in sediments from the southeastern end of Dry Dock Island were similar in profile to Aroclor 1260, another popular ingredient of transformer fluids of the past.

PAH profiles varied substantially between sites, although there was a tendency for some of the lighter components (e.g., acenaphthylene and anthracene) to dominate in sediments from relatively clean areas. Sedimentary fluoranthene/pyrene and pyrene/benzo(a)pyrene ratios were indicative of petrogenic hydrocarbon spillages at Hotel Wharf, the Shell Fox-1 Fuel Pier at the western end of Commercial Port, and Cabras Power Plant. Fossil fuel combustion was considered to be the primary source of PAH at most other sites examined.

The data for all three chemical groups are further discussed in relation to possible sources of input, and are compared and contrasted with findings reported by other researchers elsewhere in the world. Guidelines are proposed for classifying Guam's harbor sediments according to their contaminant loading, and the issue of open water disposal of dredged sediments is briefly addressed. Future directions for continued research are recommended.

Gary R. W. Denton
Rick H. Wood
Lucrina P. Concepcion
Galt H. Siegrist Jr.
Vance S. Eflin
Danzel K. Narcis
Greg T. Pangelinan