Predicted Environmental Concentrations of Metals and their Environmental Risks, Anticipated by Concurrent In-Water Hull Cleanings of Ship’s Biofouling in an International Harbor

Abstract

When organisms grow on ship’s hull, the drag they produce slows the ship’s movement, increasing the consumption of fuel and leading to higher emissions of greenhouse gases. Furthermore, the growth of these organisms can lead to a transfer of invasive species from one place to another, which could lead to the destruction of local ecosystems. By periodic in-water cleaning (IWC) of ship’s hull, the biosecurity risk can be mitigated, and the ship’s fuel efficiency can be improved. However, during the cleaning of the hull, the active substances (e.g., heavy metals) in the antifouling paints can be released and introduced directly into the marine ecosystem. The active substances can be a source of hazards to marine organisms in the environment. To understand the risk posed by IWC, environmental concentrations of metals released during IWC were predicted using a steady-state 2D integrated hydrodynamic and chemical fate model in one of the world’s largest international harbors and compared to no-effect concentrations to characterize risk of target chemicals. Release rate of metals from hull surface was calculated based on the information collected during actual IWC cases, which include metal concentrations in the effluents, effluent volumes, and hull areas. A release rate under realistic worst-case scenario was used for model prediction as a conservative approach. The predicted environmental concentrations were proportional to the number of cleanings and the size of ships under cleaning. A single hull cleaning of any size seems not to clearly damage the marine environment. However, when considering concurrent IWC of ships berthing in the harbor, the predicted environmental concentration exceeded local standards set for the protection of marine environment. Predicting environmental concentration only for single cleaning cannot appropriately assess the environmental risk in a given site, where multiple operations are expected. The daily demand for in-water cleaning at the site should be estimated and this demand needs to be accounted for risk assessment. In-water cleaning should only be allowed if the predicted environmental concentrations is within the threshold of the environmental capacity. The risk assessment framework proposed in this study can be used for environmental management purposes in port areas expecting frequent and multiple in-water cleaning activities.