Contaminant exposures at the 4H shell mounds in the Santa Barbara Channel

• Published in: Marine pollution bulletin 2006-12, Vol.52 (12), p.1668-1681
• Main Authors: Phillips, Charles R., Salazar, Michael H., Salazar, Sandra M., Snyder, Barry J.
• Format: Article
• Language: English
• Subjects: Animal, plant and microbial ecology; Animals; Applied ecology; Applied sciences; Bioaccumulation; Bioassays; Biological and medical sciences; Biological and physicochemical properties of pollutants. Interaction in the soil; Biological Assay - methods; Contaminants; Earth sciences; Earth, ocean, space; Ecotoxicology, biological effects of pollution; Engineering and environment geology. Geothermics; Environmental Exposure; Environmental Monitoring; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Geologic Sediments - analysis; Geologic Sediments - chemistry; Marine and brackish environment; Mytilus - chemistry; Mytilus - drug effects; Oil and gas; Particle Size; Pollution; Pollution, environment geology; Polychaeta - chemistry; Polychaeta - drug effects; Santa Barbara Channel; Seawater; Shell mounds; Soil and sediments pollution; Survival Analysis; Temperature; Time Factors; Water Movements; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - toxicity
• ISSN: 0025-326X; 1879-3363
• DOI: 10.1016/j.marpolbul.2006.06.012

Remobilization, bioavailability, and potential toxicity of chemical contaminants were evaluated at the 4H shell mounds – the site of abandoned offshore oil and gas production platforms in the Santa Barbara Channel region of the Southern California Bight. Evaluations used a weight-of-evidence approach based on results from bulk phase chemical analyses and laboratory toxicity testing of shell mound cores, in situ field bioassays using caged mussels, and surficial sediment chemistry. Shell mound cores contained elevated concentrations of metals associated with drilling wastes (e.g., Ba, Cr, Pb, and Zn), as well as monocyclic and polycyclic aromatic hydrocarbons (PAHs). The highest concentrations along with pockets of free oil were associated with the middle “cuttings” stratum. Sediments composited from all core strata caused significant acute toxicity and bioaccumulation of Ba and PAHs in test organisms during laboratory exposures. In contrast, caged mussels placed at each of the shell mounds for a period of 57–58 days had greater than 90% survival, and there were no significant differences in survival of mussels placed at the shell mounds and corresponding reference sites. While all mussel samples exhibited increases in shell length, whole animal weight, and tissue lipid content, in some cases growth metrics for the shell mound mussels were significantly higher than those for the reference sites. Concentrations of metals, PAHs, and polychlorinated biphenyls (PCBs) in tissues of the shell mound mussels were not significantly different from those at reference sites. The presence of labile aromatic hydrocarbons in shell mound cores and absence of significant contaminant accumulation of tissues of caged mussels indicated that chemical contaminants are not being remobilized from the 4H shell mounds. Surficial bottom sediments near the shell mounds contained elevated Ba concentrations that probably were associated with drilling wastes. However, concentrations did not exhibit clear spatial gradients with distance from the shell mounds. Despite a number of storm events during the mussel exposures, maximum currents were 34 cm s −1 and unlikely to erode materials from the shell mounds. Thus, Ba distributions in bottom sediments probably were due to episodic disturbance such as platform removal or trawling rather than ongoing erosion and dispersion of shell mound solids by near-bottom currents. These results suggest that, in the absence of physical disturbances, contam