Aquatic toxicity, ecological risks, and risk tradeoff analysis of biocide treatment for unballasted vessels

The release of nonindigenous species through ballast water is one of the greatest threats to aquatic biodiversity worldwide. Using chemical biocides to reduce the number of organisms transported by ballast water is one treatment option under consideration; acceptance of this approach, however, will depend on both effectiveness and environmental acceptability. This dissertation characterizes the potential efficacy and environmental impacts of using the biocide glutaraldehyde to treat unballasted vessels trading in the Great Lakes. With respect to efficacy, the results from laboratory studies indicate that glutaraldehyde is toxic to a range of aquatic organisms, although interspecific differences in sensitivity may require higher treatment concentrations (Chapter 2). In addition, efficacy in laboratory experiments against benthic organisms diminished in the presence of sediments, which apparently afford physical protection. With respect to potential environmental impacts, results from chronic toxicity bioassays indicate that algal species are particularly sensitive to glutaraldehyde, with effect-level concentrations occurring at less than 1 mg L-1 glutaraldehyde after 96-hr exposures (Chapter 3). To predict in situ efficacy and potential release concentrations, a biocide decay model was developed to simulate changes in glutaraldehyde concentrations associated with temperature variations during vessel transits (Chapter 4). These simulations indicate that glutaraldehyde treatment concentrations can likely be maintained during a trans-Atlantic journey lasting approximately 10 days. The release concentrations at a Great Lakes port are predicted to vary temporally, with higher release concentrations predicted in the early spring and late fall. The potential ecological impacts of release concentrations were evaluated with an ecosystem simulation model (Chapter 5). Results suggest that ecological risks of glutaraldehyde are small, declining rapidly with small decreases in glutaraldehyde concentrations; however, certain populations of organisms may incur greater risks during the spring months, when glutaraldehyde concentrations are projected to be higher. Finally, the potential ecological impacts of glutaraldeyde are compared with those of established nonindigenous species in the Great Lakes using a risk-tradeoff analysis framework (Chapter 6). Results indicate that although some elements of these ecological risks may be qualitatively similar, the spatial and temporal scale of impacts of invaders is much greater than any potential ecological effects due to glutaraldehyde release.