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GLERL 2004 Milestone Reports
< GLERL 2004 Milestone main page
GOAL: Protect, Restore and Manage Use of Ocean and Coastal Resources Through Ecosystem Management Approaches
Scientist: Dr. Peter Landrum (GLERL)
NOAA Performance Measure: Increased number of invasive species under control
OAR / ISP Performance Measure: Number of ballast water treatment technologies that can meet a 95% removal standard (of organisms)
Milestone: Develop a risk assessment of ballast water disinfectant discharge for Duluth Harbor
Purpose: The spread of nonindigenous species through ballast water continues to threaten the biological diversity of aquatic ecosystems worldwide. Treating ballast water with chemical biocides is one possible method for reducing the risk of future introductions. The use of biocides is particularly appropriate for the majority of ships that arrive in the Great Lakes with “No-Ballast-On-Board” (NOBOB) that carry on average 60 m3 of residual ballast water, which contains both viable organisms and resting stages of aquatic species. NOBOB vessels are thought to be a major contributor to the spread of invasive species and are currently not subject to ballast water exchange. To assess the potential efficacy and environmental impacts of using a biocide for NOBOB vessels, a risk assessment is being developed for the use of the potential disinfectant glutaraldehyde for which previous studies were performed to set expected dosing levels.
Efforts and Results (to date): As the first step in
this process, a ballast tank decay model was developed for the biocide,
glutaraldehyde, in an application for treating unballasted overseas vessels
trading on the Laurentian Great Lakes. The results of Monte Carlo simulations
indicate that initial glutaraldehyde concentrations (500 mg L-1) should
be maintained for much of the duration of the vessel transit across the
Atlantic (approximately 11 - 15 days). Because these vessels generally
take on large volumes of lake water prior to discharge, the final predicted
glutaraldehyde concentrations at the Duluth Harbor, MN, were more than
100-fold lower than treatment concentrations. Predicted mean concentrations
at Duluth Harbor ranged from 3.2 mg L-1 (2 S.D.: 2.74) in April to 0.7
mg L-1 (2 S.D.: 1.28) in August (Figure 1).
Figure 1. Predicted mean glutaraldehyde concentrations at Duluth Harbor, MN. Data are provided for both the worst case reballasting in Detroit, MI, and best case reballasting in Oswego, NY, scenarios. The error bars represent ± 2 standard deviations from the mean.
Sensitivity analyses indicated that the reballasting dilution was the major variable governing final glutaraldehyde concentrations, but that lake surface temperatures had an increasing impact during the warmer summer months. These results suggest that effective concentrations of glutaraldehyde could be maintained for a sufficiently long period of time to achieve high mortality rates, and that the potential for environmental impacts will depend largely on the reballasting volumes of unballasted vessels.
The data from this model will be used as the exposure conditions for a dispersion and ecological effects model that will produce probability predictions of risk for the Duluth Harbor, a major port of call for overseas vessels.
Customer(s): Regulators and scientists working on preventing invasions of new exotic species
Cause Factors (if milestone not met): N/A
.
Revised Completion Date (if milestone not met): N/A
Last updated: 2004-09-15 js