Shipboard testing of the efficacy of SeaKleen as a ballast water treatment to eliminate non-indigenous species aboard a working tanker in Pacific waters.

Trials were conducted aboard the tanker Seabulk Mariner to test a natural product, SeaKleen, as a biocide controlling non-indigenous populations of plankton and bacteria in ballast water. SeaKleen was dosed into matched ballast tanks at two different concentrations, 0.8 mg L(-1) active ingredient (a.i.) and 1.6 mg L(-1) a.i. during ballasting off the Oregon coast during a three-day passage to Prince William Sound, Alaska. Live organism counts from treated ballast water were compared with those from untreated (control tank) water collected from the same source location. Shipboard chemical analyses were made to verify dose and quantify chemical degradation and residuals following dilution. Results indicated that both SeaKleen doses resulted in complete zooplankton and phytoplankton mortality and that the higher dose (1.6 mg L(-1) a.i.) caused a two-log removal of culturable bacteria over a 92 h grow-out period. Spectrophotometry confirmed initial dosing to within 5% of nominal values. Shipboard bioassays were conducted using larval fish (Cyprinodon variegatus), brine shrimp (Artemia salina) and the bioluminescent dinoflagellate Pyrocystis lunula. Exposure of the test organisms to water drawn from treated ballast tanks 48 h after SeaKleen was added to the tanks resulted in 100% mortalities in Cyprinodon and Pyrocystis at both doses. Corresponding mortalities for Artemia larvae were 100% and 60% for high and low SeaKleen doses, respectively. Toxicity testing of treated water, subjected to varying dilutions, indicated that residual toxicity to even the most sensitive organisms would be eliminated once the discharge had dispersed beyond 100 feet from the vessel.

Screening of natural product biocides for control of non-indigenous species.

Several benzo-, naphtho- and anthraquinones were tested for their efficacy as biocides in controlling aquatic nuisance species in ships' ballast water. A requirement of this application was broad spectrum aquatic toxicity, coupled with a relatively rapid rate of degradation, in order to comply with coastal discharge requirements. Compounds were screened using a suite of toxicity bioassays designed to establish their relative toxicity to an array of planktonic organisms including larval bivalves Dreissena and Crassostrea, various developmental stages of the estuarine copepod Eurytemora affinis, brine shrimp larvae (Artemia salina), the freshwater invasive water flea Bythotrephes, larval sheepshead minnows CCyprinodon variegates) and two unicellular algal genera Isochrysis and Neochloris.. The majority of the data were recorded as the lowest concentration of the test compound resulting in complete mortality or inactivation of test organisms (LC ,m). The naphthoquinones juglone, plumbagin, menadione and naphthazarin showed the highest toxicity to the broadest range of organisms, often at levels much less than 1 mg l(-1), and most of the attention was focused on this group. While plumbagin and juglone appeared overall to be the most toxic compounds, it was concluded that menadione was probably the most cost-effective candidate compound for shipboard use for controlling invasive species in ballast water, particularly in view of the large volumes of water that would require treatment.

Naphthoquinones as broad spectrum biocides for treatment of ship's ballast water: toxicity to phytoplankton and bacteria.

Current UN International Maritime Organization legislation mandates the phased introduction of ballast water treatment technologies capable of complying with rigorous standards related to removal of waterborne organisms. Doubts concerning mechanical treatments at very high ballasting rates have renewed interest in chemical treatment for very large vessels. High removal rates for biota require broad spectrum biocides that are safe to transport and handle and pose no corrosion problems for ships' structure. The current study focuses on the naphthoquinone group of compounds and extends a previously reported set of screening bioassays with an investigation of the toxicity of four naphthoquinones to select protists and prokaryotes, representative of typical ballast water organisms. Vegetative dinoflagellate cysts exposed to 2.0 mg/L of the naphthoquinones juglone, plumbagin, menadione and naphthazarin showed varying degrees of chloroplast destruction, with menadione demonstrating the most potency. Laboratory and mesocosm exposures of various phytoplankton genera to menadione showed toxicity at 1.0 mg/L. Juglone demonstrated the most bactericidal activity as judged by a Deltatox assay (Vibrio fischeri) and by acridine orange counts of natural bacterial populations.