Compositions and toxicity potentials of antifouling chemicals in the effluents from ship's hull cleaning: in-water cleaning vs. haul-out cleaning

Abstract

The effluent generated during a ship’s hull cleaning as a biofouling measure, either by in-water cleaning or haul-out cleaning, can be of great concern to the marine environment, once it is released without appropriate treatments. Wastewaters from the ship’s haul-out cleaning by hydroblasting and in-water cleaning by brushing for the same vessel were collected and analyzed to understand the potential impacts of the effluent release to the marine environment. Metals and booster biocides in the effluents from three vessels covering regional to oceanic voyages were analyzed. Copper and zinc were the most abundant metals in the wastewaters, with ranges of, as total concentrations, 6.24 – 87.4 mg/L and 78.3 – 259 mg/L, respectively from haul-out cleaning, and 0.556 – 8.25 mg/L and 1.49 – 5.71 mg/L from in-water cleaning. Dissolved copper and zinc concentrations ranged from 1.45 to 9.11 mg/L and from 1.80 to 22.4 mg/L, respectively for haul-out cleaning, and 0.0637 to 0.204 mg/L and 0.222 to 3.82 mg/L from in-water cleaning, exceeding LC50 values of many test species reported in the ECOTOX database. Zinc pyrithione and copper pyrithione were the most abundant booster biocides, exceeding the LC50s of 6.3 – 49% of test species for zinc pyrithione, and 6.0 – 53% for copper pyrithione, based on the database. Environmental concentrations were predicted using a hydrodynamic and chemical fate model with representative release rates of 34.8 and 61.4 μg/cm2 from haul-out cleaning for copper and zinc respectively, and 2.84 and 13.4 μg/cm2 from in-water cleaning. Risk assessment based on the predicted environmental concentrations revealed that adverse effects on the marine environment are expected by release of the wastewater from multiple cleanings. These chemical and toxicological characterizations of wastewater from ship’s hull cleaning will give insights into the biofouling management in terms of chemical hazard concerns.