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In this study, the amphipod Corophium volutator and the polychaete Arenicola marina were evaluated as test organisms for use in sediment toxicity tests by adapting standard protocols developed by the EPA/COE and Thain et al. (1994) respectively for conducting 10-day sediment toxicity tests. Although these species have been used to assess the toxicity of marine and estuarine sediments, the detailed ecotoxicologies of these animals are not well documented. In particular, the effects of specific contaminants of known concentrations on this bioassay are not known. Here, I report several experiments carried out using clean intertidal sediment contaminated with the heavy metals copper, zinc and cadmium, and employing the Corophium and the Arenicola bioassay protocol. Concentrations of copper, zinc and cadmium were determined in tissues of Corophium exposed for 4 and 10 days to contaminated sediment using four protocols to allow for any material present in the gut. Significant differences in metal concentrations occurred between the protocols where gut contents were removed and those where they were left intact. These findings have implications for the way in which analyses of metal burdens are carried out for invertebrates in ecotoxicological work. Corophium survival in seawater with dissolved copper, zinc and cadmium was higher in the presence of sediment than without sediment, although the concentrations of these metals in Corophium tissues were the same in both cases. Bioconcentration factors (BCF) were inversely related to seawater concentrations of copper, zinc and cadium, with the lowest exposure concentration, (0.1 mg l-1 for both copper and zinc, 0.01 mg l-1 cadmium) having the highest BCF. Both live amphipods and those that had died accumulated copper, zinc and cadmium in their bodies during the bioassay, and bioconcentration factors were always higher for dead than for living amphipods for each metal.

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A posterior gill of the common shore crab Carcinus maenas (Crustacea:Decapoda) was used to study the effects of sublethal copper concentrations on gill morphometry, and gill cell ultrastructure and distribution. Primarily, the ultrastructure and distribution of gill cells in the untreated gill of crabs acclimated to 35‰ seawater were characterised. Gill ultrastructure was subsequently shown to vary markedly at 10‰ compared to 35‰ seawater. Ultrastructural and distributional, rather than gross morphological, change occurred in the gill following exposure to copper at each salinity. Ultrastructural studies showed that as the length of copper exposure increased the gill epithelial layer became highly vacuolated, the number of plasma membrane infoldings and mitochondria became reduced, the microtubular network became disrupted, the endoplasmic reticulum became swollen and the cell cytoplasm contained many free ribosomes. Copper exposure also resulted in an increase in the number of haemocytes in the gill, some of which became attached to the basal epithelial cell surface or actually infiltrated into the epithelial cell cytoplasm. Ultrastructural change was more extensive when copper was administered at 35‰ rather than 10‰ seawater. These effects are described and correlated with previously documented biochemical and physiological responses to heavy metals in crustaceans. In addition, the elemental composition of the gill granular haemocytes suggested they play an important role in the immobilisation and removal of copper-from the gill. This study has shown the way forward in creating a better understanding of the mechanisms behind heavy metal toxicity in marine organisms is the use of environmentally realistic concentrations of heavy metal administered in flow-through seawater systems.

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Concentrations of 18 metals, including toxic metals (As, Cd, Cr, Ni and Pb) and essential metals (Al, Ba, Be, Co, Cu, Fe, Li, Mg, Mn, K, Sr, V and Zn) in various compartments (sediment, floc, and periphyton) were measured in the Florida Everglades to (i) establish the spatial distribution pattern of the metals in the Everglades and (ii) quantify the major sources of the 18 metals present in the Everglades. The highest mean concentrations of all metals analyzed in the Everglades were detected in soil, followed by floc and periphyton. Most metals exhibited random spatial distribution patterns. Risk assessment using Sediment Quality Guidelines (SQGs) concluded that all toxic metals (Cd, Cr, Pb, Ni, Cu, Zn and As) exhibited average concentrations that were well below FL guidelines as well as other domestic and international guidelines. On the basis of the current study, the Everglades can be considered a pristine environment.

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