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Marine Biological Laboratory, Woods Hole, Massachusetts 02543
Introduced species have been a problem in the marine and coastal environments for centuries. Historically, many of these introductions have a strong geophysical component often associated with natural disasters. However, in more recent times, "man, the supreme meddler" (1) has dramatically changed the rate, number, and geography of exotic species invasions through importation, transportation, intentional releases related to agriculture or aquaculture, as well as unintentional escapes. During the last century, the problem has dramatically accelerated with the advent of modern high-speed freighters and their methods of ballast water exchange.
Transport and discharge of biocontaminated ballast water constitutes a major route (29%) by which potentially invasive species—from plants and algae to fish, invertebrates, planktonic and bacterial micro-organisms, and even potential pathogens—are introduced into coastal waters worldwide. It is estimated that 3000 species are transported daily via ballast water (National Research Council, 2000). The Great Lakes have experienced the introduction of at least 129 non-indigenous species (2), while the San Francisco Bay estuary has recorded 234 exotic species with at least an additional 125 cryptogenic species (3). At the current estimated rate, a new species is introduced into the ecosystem every 14 weeks (3).
The problem is not confined to the United States but occurs worldwide. One noteworthy example is the introduction of the western Atlantic ctenophore, Mnemiopsis leidyi, into the Black and Azov Seas in 1987 and 1988, respectively. This invader has been blamed for a 20-fold decrease in zooplankton biomass, the subsequent sharp decline in anchovy and other pelagic fish stocks, and a marked disruption in these ecosystems (4).
The United Nations International Maritime Organization (IMO), established in 1991, developed a voluntary ballast water exchange (BWE) at sea policy that has now become mandatory (5). BWE is carried out either by draining and refilling the ballast tanks or by continuous flushing equivalent to three volume exchanges. The policy is based upon the rationale that coastal organisms will not survive at sea and vice versa, so BWE is simpler, less costly, and thus preferable to controls implemented before departure or upon arrival (i.e., land-based treatments). Unfortunately, BWE is only 90%–95% effective, and the exchange itself can be dangerous in foul weather or can produce excessive hull stress. Therefore, alternative ballast water treatments are being sought.
Some current technologies available for ballast water treatment include filtration, cyclone or hydrotech-drum settling, UV, ultrasonics, and heat. Additional secondary treatment methods include biocides, ozone, electric pulse or pulse plasma, deoxygenation, and biological. Some of the biocidal methods involve the storage of dangerous chemicals and cause unacceptably high levels of corrosion (e.g., hypochlorite). However, hydrogen peroxide, generated on-site at low (safe) concentrations, precludes these hazards and is more cost-effective than the sophisticated and high-energy-demanding equipment necessary for ozone generation. Neutral hydrogen peroxide has been effective in a number of studies, but only at moderately high concentrations (10–50 ppm; [6]), for planktonic and some small neustonic organisms. Because most marine organisms and bacteria cannot tolerate pH extremes (7), hydrogen peroxide combined with elevated pH (alkaline hydrogen peroxide) has the potential to produce synergistic effects useful for treating ballast water. Since alkaline peroxide has not been investigated for this application, and it is the consequence of the proposed generating process, we undertook a toxicological laboratory study to test the effects of alkaline peroxide on plankton. This study is designed to complement the development of an electrolytic cell (based on patented technology [8]) that is capable of producing alkaline hydrogen peroxide. An upscale design of the cell has been proposed for use onboard ship to treat ballast water to reduce the potential introduction of invasive species.
Plankton were collected from the local waters off Woods Hole, Massachusetts, by the Aquatic Resources Department of the Marine Biological Laboratory (MBL). Indigenous zooplankters (Table 1) were used in this study. The faunal composition of the plankton varied between collections, but the majority were dominated by crustaceans, both planktonic adults and larvae of benthic species. Particular attention was directed toward the effects of alkaline peroxide on the ctenophore, Mnemiopsis leidyi, a known invasive species (see above), which made up over 90% of many plankton collections.
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The ctenophore, Mnemiopsis leidyi, was tested with the same treatment regimes. Because of their size and buoyancy, even when dead, for accuracy it was necessary to record mortality times when the compound cilia of the comb rows and the cilia in the digestive tract both ceased beating. The test animals were placed back into NSW and observed for signs of recovery. All data were analyzed statistically using ANOVA or Student’s t paired comparisons.
Plankton placed in NSW with elevated pHs all survived for at least 24 h, and the majority of those in pH 8.5–9.5 were alive for as long as three days. Only those animals at pH 10 did not survive beyond 24 h. Mnemiopsis responded similarly.
When solutions containing mixed plankton and alkaline peroxide were tested, no significant differences were found between pH values within each peroxide concentration (ANOVA: F values < 2; P > 0.2) (Fig. 1). However, for each peroxide concentration, there were significant decreases in mortality times (Student’s t paired comparisons: t > 4.7; P < 0.001). Similar results were obtained with Mnemiopsis; i.e., there were no pH effects within each peroxide concentration (ANOVA: F < 1.8; P > 0.15). However, increases in peroxide concentrations significantly shortened mortality times (Fig. 2). When animals were placed in 10 ppm peroxide, beating of all the comb rows immediately stopped; and within seconds, the activity of the digestive cilia also ceased. Therefore, the effects of this concentration were not graphed. The difference between the means of the two peroxide concentrations (1 and 3 ppm) was highly significant, with Student’s t value t > 11.5 with P < 0.001.
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In summary, the data from these tests indicate that NSW at pHs slightly elevated above that of ambient, and containing concentrations of 1 ppm hydrogen peroxide, can be lethal to plankton composed of a wide phylogenetic mix of species (Table 1). It was interesting to discover that a concentration of 3-ppm peroxide has effects comparable to ozone levels (2.2 ppm) when tested on larvae of the nudibranch mollusc, Hermissenda crassicornis (9). The short exposures (i.e., mortality times) required at this concentration of peroxide should encourage the development and implementation of an onboard electrolytic system capable of generating the required peroxide levels at rates sufficient to treat ballast water of ships during uptake at sea or in coastal waters. This device would provide an efficient, low-energy cost treatment for ballast water, and would preclude the bulk and danger of storing concentrated biocide chemicals on board ships.
This research was supported by a Phase I, SBIR/EPA grant (68-D-01-017) to Eltron Research, Inc.
Footnotes
1 Eltron Research, Inc., Boulder, CO. 
Literature Cited
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