Qualitative and Quantitative Assessment of Microplastics Derived from Ship Paint during Hydroblasting: Estimation of Global Microplastics Emissions from an International Research Vessel study

Abstract

As global concerns over microplastic (MP) pollution continue to grow, the International Maritime Organization (IMO) has highlighted the potential risks of MP derived from ship paint, particularly during hull cleaning processes. Despite the growing awareness, there remains a significant data gap in quantifying the extent of MP emissions specifically derived from these cleaning activities. Our study aims to address this data gap by evaluating MP particles generated during hydroblasting, a common hull cleaning technique. After collecting samples from hydroblasting on globally operating research vessels, we identified the polymers constituting the paint using Fourier-Transform Infrared Spectroscopy (FTIR), and then measured the weight of particles smaller than 5 mm. Each particle was classified as a polymer such as alkyd, acrylate, epoxide, urethane, or polyester/polyether using FTIR. The weight of the paint particles was measured by multiplying the particle's volume with its density. Additionally, the value for the paint’s plastic components was cited to be 54.9%. To develop an MP emission factor, we estimated the amount of paint applied by multiplying the wetted surface area with coating film thickness, and the density of the paint. As a result, from the total paint applied (485.2 Kg), 60.5 Kg (12.5%) was generated as paint, and 33.2 Kg (6.8%) as MPs from hydroblasting. The MP emission factor was calculated as 0.0154 Kg/m2, which is the value of 33.2 Kg divided by the Wetted Surface area of 2161.8 m2. To estimate the global emission of MPs from ships, we multiplied these emission factors by the total wetted surface area of global ships (326,126,497 m2), considering the hull cleaning frequency which is once or twice every five years, corresponding to 0.2 or 0.4 times per year. As a result, the MP emission was approximately 10,004,470~20,008,939 Kg in 2023. Additionally, we estimated the global MP emissions from 2011 to 2023, categorizing by ship type, including bulk carriers, oil tankers, container ships, general cargo, and other types of vessels. The quantity of MP emissions has shown a consistent upward trend over the period. This data is not only used for risk assessment regarding the global MP emissions from ships, but also contributes to the development of ship cleaning regulations. To obtain more accurate MP emission values, analysis by the frequency of hull cleaning and by year of operation is necessary.