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(P481) Comparison of biocide effectiveness in treating unballasted foreign vessels.
Sano, Larissa*,1, Landrum, Peter2, Gossiaux, Duane2, Mapili, Mark1, 1 University of Michigan, Ann Arbor, MI, USA2 Great Lakes Environmental Research Laboratory, Ann Arbor, MI, USA
ABSTRACT- The release of residual ballast tank material into the Laurentian Great Lakes from foreign NOBOB (no ballast on board) vessels currently constitutes a potential risk for the introduction of nonindigenous species. This study assessed the potential effectiveness of three biocides for reducing the number of organisms released from these tanks. The biocides tested were glutaraldehyde, glutaraldehyde plus a surfactant adjuvant, and sodium hypochlorite (NaOCl). Biocide efficacy was evaluated with 24 h acute toxicity experiments and with 11 day ballast tank simulation experiments. Under 24 h water-only exposure conditions, NaOCl was the most effective compound tested, with LC90 values ranging from 0.12 mg/L for Daphnia magna to 4.66 mg/L for Hyalella azteca. The addition of sediments to the test chambers had a profound effect on biocide efficacy. Under these conditions, NaOCl effectiveness was substantially reduced, requiring >1000 mg/L of hypochlorite to achieve 90% mortality with the oligochaete, Lumbriculus variegatus (compared to a 24 h LC90 of 1.6 mg/L under water-only conditions). Both glutaraldehyde and the glutaraldehyde-surfactant mixture demonstrated an approximate 8-fold increase in LC50 estimates with sediment addition. To assess efficacy under more realistic exposure conditions, 11 day acute toxicity bioassays were conducted using sediments collected from tanks of foreign NOBOB vessels. Results from these experiments generally corroborated results from 24 h acute water-sediment toxicity bioassays: At a treatment concentration of 500 mg glutaraldehyde/L, there was 1% survival of H. azteca and 3% survival of L. vareigatus after 24 h of toxicant exposure followed by a 10 day recovery period. For the glutaraldehyde-surfactant mixture, concentrations of 250 mg glutaraldehyde/L resulted in complete mortality for both H. azteca and L. variegatus. For NaOCl, concentrations of 2000 mg hypochlorite/L resulted in 100% mortality rates for both H. azteca and L. variegatus. These results will be discussed in the context of the overall feasibility of biocide treatment of residual water and sediments in unballasted tanks.
Key words: nonindigenous species, acute toxicity, sediment toxicity testing, Great Lakes
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