The sea-surface microlayer of puget sound: Part II. Concentrations of contaminants and relation to toxicity

Many aquatic contaminants, because of low water solubility (hydrophobicity) or association with floatable particles, concentrate at the sea surface. Thirty-six samples of the sea-surface microlayer (SMIC), the upper 50 μm, were collected from sites in Puget Sound, Washington State. Sites included three urban bays, central Puget Sound, and a rural reference site. Exposure of floating fish eggs to approximately half of these samples resulted in sublethal and lethal toxic effects (Hardy et al., 1987c).Chemical analyses revealed high concentrations of contaminants in many of the samples. Major temporal and spatial differences in sea-surface chemistry occurred, but maximum (for all) and mean (for 1985) concentrations were aromatic hydrocarbons, 8030 (mean 132) μg liter⁻¹: saturate hydrocarbons, 2060 μg liter⁻¹: pesticides, 43·8 (mean 0·46) ng liter⁻¹; PCBs, 3890 (mean 631) ng liter⁻¹; and total metals, 4750 (mean 626) μg liter⁻¹. Stepwise multivariate regression indicated that the percentage of fish eggs developing to normal live larvae decreased with increasing concentrations of a complex mixture of contaminants. Principal component analysis demonstrated that the major types of contaminants did not differ greatly in their statistical contribution to the toxicity, i.e. no single chemical was responsible for the observed toxicity.The chemical composition of the SMIC samples suggested that contamination originated from a variety of sources including atmospheric deposition, terrestrial runoff of fossil fuel combustion products, and sewage disposal.     

Sea-surface microlayer metals enrichments in an urban and rural bay

The sea-surface microlayer is an important interface between the atmosphere and ocean and a collection point for many anthropogenic materials including potentially toxic metals. We developed a glass plate sampler to collect the upper 30 to 55 micrometers of the sea surface. Samples of the microlayer and subsurface bulk water from an urban and rural bay were analysed for concentrations of Pb, Zn, Cu, Cd and Fe. Metal concentrations in both the microlayer and bulk water were generally 2 to 15 times greater in the urban than in the rural bay. Concentrations of metals in the microlayer of both bays averaged 6 to 65 times greater than those in the bulk water. In the urban bay, microlayer concentrations of Pb, Zn and Cu from 10 to > 100 μg 1^?1 were common. Measured microlayer metals concentrations agree well with those predicted from atmospheric deposition rates using a previously derived empirical model developed from laboratory microcosm studies. Further work will be required to determine whether or not these high microlayer metal concentrations contain significant biologically available fractions which could impact fisheries recruitment of larval icthyoneuston.     

Distribution of silver, mercury, lead, copper and cadmium in central puget sound sediments

Distributions of five of the more toxic heavy metals have been assessed for Puget Sound sediments. Twenty-one Kasten cores were collected for the study. Analysis by Zeeman-corrected graphite-furnace atomic absorption spectroscopy has made possible the accurate and precise determination of silver and cadmium in Puget Sound sediment cores for the first time. Data show that Puget Sound is moderately impacted by anthropogenic Ag, Hg, Pb and Cu. No enrichment of Cd was found. The study also indicates that Puget Sound is quite well mixed with respect to the residence time of particle-bound metals. Toxic metal accumulation sites in the central Sound are determined almost exclusively by grain size, rather than proximity to sources. Estimates are made of trace metal fluxes to the sediments as a function of sediment type and areal distribution.     

A laboratory study of the accumulation and toxicity of contaminants at the sea surface from sediments proposed for dredging

Microcosm laboratory experiments assessed the impact of floatable materials and associated contaminants transported to the surface millilayer (SMIL) after sediments composed of potential dredged materials were disturbed. Urban bay sediments collected from the Everett Harbor, WA, and clean sediments from Sequim Bay, WA, were mechanically disturbed and the resulting floatable fractions transported to the SMIL during a 48-h period were removed for analysis. Sediment, water and SMIL concentrtaions oforganic carbon, suspended solids, a suite of hydrocarbons, metals, sulfides and extractale mtaerials were quantified and compared to EPA's water quality criteria. Bioassay experiments examined the effects produced by exposing sea urchin embryos to these impaired SMIL samples.Contaminants transported to the surface layer within 48h were 0% to 0·2% of the total mass of contaminants in the test sediments. These experimental results were compared with those predicted by a computer model with reasonably close agreement. Contaminant concentrations in one SMIL impacted by Everett Harbor sediments exceeded EPA water quality criteria limits established for Cu, Zn, Pb, Hg and PAH. The other Everett Harbor sediment sample exceeded the water quality standards for Cu and Pb. Both of these samples were toxic to the developmental phases of sea urchins as shown by the bioassay. According to the numerical model, these SMIL contaminant concentrations would require high dilution ratios before background concentrations could be achieved. The experimental results suggest that dredged material disposal may influence the chemistry and biology of the ocean's surface layer.     

Copper bioavailability to marine bivalves and shrimp: Relationship to cupric ion activity

Studies were performed to determine the effects of dissolved substances present in natural seawater and sediment on the bioavailability of added Cu⁺². Whole clams Macoma inquinata and shrimp, Pandalus danae, were exposed to four concentrations of Cu in a flow-through seawater system. Bioaccumulation of Cu was reduced in shrimp, Pandalus danae, clams, M. inquinata, and excised clam gills, Protothaca staminea, exposed to an aged, compared with an unaged, Cu-seawater solution. This is thought to be due to slow complexation of the Cu by dissolved substances present in natural seawater. In a static system, with added sediment, more than 50% of the added Cu⁺² became bound to the organic fraction of the sediment and was unavailable to suspension feeding clams, Protothaca staminea. In contrast, deposit feeding clams, Macoma inquinata, placed in the sediment approximately doubled in Cu body burden within two months.Complexed Cu appears to be less bioavailable than ionic Cu and hence measurements of ionic and weakly complexed Cu by differential pulse anodic stripping voltametry provide a better prediction of bioavailable Cu than conventional measurements of total Cu-seawater concentrations.     

Determination of mercury in seawater at sub-nanogram per liter levels

Using a refined two-stage gold amalgamation preconcentration technique in conjunction with cold vapor atomic absorption (CVAA) detection, mercury in various Pacific Northwest coastal waters has been determined. Through the use of extremely clean reagents and special handling techniques, the blank has been reduced and reproducibility greatly improved for both “easily reducible mercury” and “total mercury”.Samples of unfiltered water, taken at the surface, as well as at 10 m, 100 m, and 175 m have all yielded “easily reducible mercury” at between 0.1 and 0.5 ng l^?1, and “total mercury” between 0.2 and 1.0 ng l^?1. Variability within replicate field samples is less than 10%, although variations of greater than 100% may be seen over a period of hours in Sequim Bay.     

Ecosystem modelling in the southern Benguela: comparisons of Atlantis,Ecopath with Ecosim,and OSMOSE under fishing scenarios

Ecosystem-based management of marine fisheries requires the use of simulation modelling to investigate the system-level impact of candidate fisheries management strategies. However, testing of fundamental assumptions such as system structure or process formulations is rarely done. In this study, we compare the output of three different ecosystem models (Atlantis, Ecopath with Ecosim, and OSMOSE) applied to the same ecosystem (the southern Benguela), to explore which ecosystem effects of fishing are most sensitive to model uncertainty. We subjected the models to two contrasting fishing pressure scenarios, applying high fishing pressure to either small pelagic fish or to adult hake. We compared the resulting model behaviour at a system level, and also at the level of model groups. We analysed the outputs in terms of various commonly used ecosystem indicators, and found some similarities in the overall behaviour of the models, despite major differences in model formulation and assumptions. Direction of change in system-level indicators was consistent for all models under the hake pressure scenario, although discrepancies emerged under the small-pelagic-fish scenario. Studying biomass response of individual model groups was key to understanding more integrated system-level metrics. All three models are based on existing knowledge of the system, and the convergence of model results increases confidence in the robustness of the model outputs. Points of divergence in the model results suggest important areas of future study. The use of feeding guilds to provide indicators for fish species at an aggregated level was explored, and proved to be an interesting alternative to aggregation by trophic level.