Decay model for biocide treatment of unballasted vessels: application for the Laurentian Great Lakes.

A biocide decay model was developed to assess the potential efficacy and environmental impacts associated with using glutaraldehyde to treat unballasted overseas vessels trading on the Laurentian Great Lakes. The results of Monte Carlo simulations indicate that effective glutaraldehyde concentrations can be maintained for the duration of a vessel's oceanic transit (approximately 9-12 days): During this transit, glutaraldehyde concentrations were predicted to decrease by approximately 10% from initial treatment levels (e.g., 500 mgL(-1)). In terms of environmental impacts, mean glutaraldehyde concentrations released at Duluth-Superior Harbor, MN were predicted to be 100-fold lower than initial treatment concentrations, and ranged from 3.2 mgL(-1) (2 SD: 2.74) in April to 0.7 mgL(-1) (2 SD: 1.28) in August. Sensitivity analyses indicated that the re-ballasting dilution factor was the major variable governing final glutaraldehyde concentrations; however, lake surface temperatures became increasingly important during the warmer summer months.

Chronic toxicity of glutaraldehyde: differential sensitivity of three freshwater organisms.

The biocide, glutaraldehyde, is a potential environmental contaminant due to its widespread use in medical applications, off-shore oil extraction, and pulp mill processing. It has also been proposed as a candidate for treating the ballast water of vessels, which could result in a substantial increase in environmental release. To assess the potential for environmental impacts associated with glutaraldehyde, three standard chronic toxicity bioassays were performed: 96-h phytoplankton growth bioassays using Pseudokirchneriella subcapitata (formerly, Selenastrum capricornutum), three-brood reproduction bioassays using Ceriodaphnia dubia, and an embryo-larval bioassay using steelhead trout, Oncorhynchus mykiss. For the green alga, P. subcapitata, significant decreases in growth were observed at glutaraldehyde concentrations greater than or equal to 1.0 mg L(-1). Embryos of O. mykiss demonstrated a similar sensitivity with exposures of 2.5 mg L(-1) resulting in a 97% reduction in hatch rate. In most cases, this failure to hatch was due to the inability of the embryo to leave the chorion and not to early embryo mortality. In contrast, reproduction and mortality rates in C. dubia were not as sensitive to glutaraldehyde: decreased reproduction was detected at 4.9 mg L(-1) (the lowest observed effect concentration), and is similar to concentrations causing acute mortality in adults (4.7 mg L(-1) for the estimated LC(50), or 50% lethal concentration). These data indicate that both algae and fish embryos may be particularly sensitive to long-term glutaraldehyde exposure; however, this is predicated on whether glutaraldehyde concentrations will achieve high enough environmental concentrations and for a sufficient period of time to elicit such effects.