Researchers link hull coatings to microplastic pollution at sea

Ship Wake

Researchers at the University of Oldenburg hypothesize that large ships leave in their wake a “skid mark” of microplastics similar
to tire tracks on pavement.

Given the painted area of all of the hulls at sea, it stands to reason that in the harsh ocean environment, some of that coating material might come off. According to German researchers, the material is indeed coming off, and it could represent a significant source of microplastic pollution.

A recent study by the University of Oldenburg’s Institute of Chemistry and Biology of the Marine Environment found that most of the plastic particles in water samples taken from the German Bight in the North Sea originated from binders used in marine paints. The bight is an area crisscrossed by shipping lanes, including traffic to and from the Baltic Sea.

“Our hypothesis is that ships leave a kind of ‘skid mark’ in the water which is of similar significance as a source of microplastics as tire-wear particles from cars are on land,” Dr. Barbara Scholz-Bottcher, the leader of the research team, wrote in February in the journal Environmental Science & Technology. 

The testing that formed the basis of the study was done in 2016 and 2017 and focused on particles less than 1 millimeter in diameter. The collected particles were subjected to a bulk chemical analysis to determine the concentration of different polymers. The particles turned out to consist mostly of polyvinyl chloride (PVC), acrylates and polycarbonates. Together, these types of molecules represented about two-thirds of the total weight of the microplastic pollution. The balance was made up of polymers more typical of the consumer-goods sector, such as polyethylene and polyethylene terephthalate (PET).  

The researchers said they had expected consumer-goods chemicals to be the primary components of the microplastic mass. In some coastal and estuary areas, this was true — these chemicals were more prevalent.

The scientists’ conclusion was that most of the “two-thirds” likely originated from marine coatings. This, and the fact that many anti-fouling coatings contain toxins, is something that should be of concern, according to the German researchers.

The International Maritime Organization (IMO) has developed an action plan for microplastics and plastic ocean litter in general. It includes a large number of record-keeping and regulatory measures, among them maintaining a “garbage record book” on vessels of a certain size — despite the fact that garbage traditionally refers to organic material, not polymers. The proposal is slated for review in 2023 to assess “the effectiveness of the actions … against the intended outcomes.”

It is not clear whether the German study has further energized the IMO on this topic. At press time, the United Nations agency had not responded to a request for comment. 

The American Coatings Association, which represents the industry in the United States, said it could not comment on the German study. Scott Hunsberger, a spokesman for Sherwin-Williams Protective & Marine, said the company “had no comment at this time.” PPG Industries, MCU Coatings International and DuPont Coatings & Color Technologies did not respond to inquiries.

Categories: Maritime News