Can sodium hypochlorite reduce the risk of species introductions from diapausing invertebrate eggs in non-ballasted ships? Derek K. Gray a, * , Ian C. Duggan b , Hugh J. MacIsaac a a Great Lakes Institute for Environmental Research, University of Windsor, Windsor, Ont., Canada N9B 3P4 b Centre for Biodiversity and Ecology Research, University of Waikato, Hamilton, New Zealand Abstract Many transoceanic vessels enter the Great Lakes carrying residual ballast water and sediment that harbours live animals and diap- ausing eggs. In this study, we examine the potential for sodium hypochlorite (NaOCl) to reduce the risk of species introductions from diapausing invertebrate eggs in residual ballast sediment. We collected sediment from three transoceanic vessels and from Lake Erie and exposed them to NaOCl concentrations between 0 and 10,000 mg/L for 24 h. Hatching success was reduced by >89% in all four exper- iments at 1000 mg/L relative to unexposed controls. Fewer species hatched at high than at low NaOCl concentrations. Based on an aver- age residual ballast of 46.8 tonnes, the volume of NaOCl required to treat inbound vessels is 374 L. Impacts of NaOCl use could be minimized by neutralization of treated residuals with sodium bisulfite. Further research is needed, however, to evaluate the effect of NaOCl on ballast tank corrosion. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Diapausing eggs; Sodium hypochlorite; Ballast; NOBOB; Nonindigenous species 1. Introduction Greater than 90% of inbound shipping traffic to the Great Lakes is comprised by vessels carrying cargo (Cola- utti et al., 2003). These vessels declare no-ballast-on-board (NOBOB) status when entering the Great Lakes, and are exempt from existing ballast exchange regulations. Such regulations in ballasted ships are intended to purge non- indigenous species (NIS) from ballast tanks, and kill those remaining in the tanks with high salinity water (United States Coastguard, 1993). Owing to design constraints, bal- last tanks on NOBOB vessels typically contain residual water and sediment that support an abundance and variety of live invertebrate species, and hundreds of thousands of viable invertebrate diapausing eggs, including those of NIS (Bailey et al., 2003, 2005a; Duggan et al., 2005). Such species can be introduced to the Great Lakes when a NOBOB vessel loads and then subsequently discharges ballast during multi-port operations within the system. Diapausing eggs may enter the system either directly by disturbance of the residual sediment during deballasting, or, more likely, as live individuals after hatching within the ballast tanks (Bailey et al., 2005b). Designing treatment strategies to reduce the risk posed by diapausing invertebrate eggs could prove difficult because they are contained within the ballast sediments and are not easily flushed from the tanks (Bailey et al., 2005a), and because the eggs are resistant to a wide array of adverse conditions including freezing, desiccation, dis- infection, and anoxia (Gilbert, 1974; Hairston, 1996; Williams, 1998). Laboratory experiments indicate that salt water exposure, as might be achieved with open ocean bal- last tank flushing, is an ineffective treatment method for this life stage but effective for water-borne active stages (Gray et al., 2005; Bailey et al., 2006). Here we examine 0025-326X/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2005.11.001 * Corresponding author. Tel.: +1 519 253 3000x2734; fax: +1 519 971 3616. E-mail address: grayh@uwindsor.ca (D.K. Gray). www.elsevier.com/locate/marpolbul Marine Pollution Bulletin 52 (2006) 689–695