Contaminants found in oysters could portend larger environmental and food safety problem

New research suggests contamination of oyster beds with plastics, paint, and baby formula in Asia could reveal a larger emerging global public health risk.

Scientists from the University of California, Irvine, in collaboration with Environmental Defense Fund, Cornell University, and Australia’s University of Queensland, found traces of plastics, kerosene, paint, talc, and milk supplement powders in the beds on the eastern Andaman Sea of Myanmar.

The scientists found similar pathogens and microplastics in some shellfish grown in U.S. waters.

Their study, “Coastal urbanization influences human pathogens and microdebris contamination in seafood,” released on 30 July, was carried out in the eastern Andaman Sea in Myanmar with the assistance of local researchers in the rural Tanintharyi region. Using an advanced technology to examine contaminants in oysters, the researchers concluded that urbanization in coastal areas and lack of sewage treatment lead to contamination in seafood poses potential risks to human health.

The scientists focused their research efforts on nine coral reefs off Myanmar’s Mergui Archipelago, which is located about 40 miles from Myeik, a city with around 250,000 residents. Using DNA sequencing, the researchers found 5,459 potential human pathogens with links to 87 species of bacteria while looking into contaminants in seawater and in oysters. More than half of the examined pathogens are believed to be harmful to people’s health, they concluded.

Additionally, using infrared spectroscopy, the scientists discovered 78 types of contaminant materials in the oysters they studied, out of the 1,225 individual microdebris particles examined.

“While 48 percent of the microparticles were microplastics – a finding representative across numerous ocean ecosystems – many other particles were not plastic and originated from a variety of human-derived materials that are constituents of fuels, paints and cosmetics,” UC Irvine Assistant Professor Joleah Lamb, one of the study’s senior authors, said in a press release. “We were particularly surprised to find three different brands of milk powder formula, which comprised 14 percent of the microdebris contaminants.”

Beside the human bacterial pathogens, the contamination of microplastics and other types of microparticles detected in seafood could negatively affect both the environment and human health. Several plastic particles can contain toxins, which may be ingested by people through the seafood taken from the ocean.

“The uptake of microplastics in the marine environment could have far-reaching consequences for human consumption of seafood and can be an emerging risk to public health globally,” the study said.

More than half of the microdebris contaminants found in the Myanmar oyster tissues were formed from non-polymer materials, such as kerosene, saponin and talc, ingestion of which possibly does harm to people’s health.

“This study is important in its global implications. There is strong evidence of transferability of the findings from Myanmar to other seafood sources around the world,” Douglas Rader, chief scientist for the EDF Oceans program and collaborator on the study, said. “It also shows clearly the need for better science related to the potential impacts of these contaminants, and the need for better testing programs so that seafood consumers can rely on its wholesomeness.”

With a big share of seafood exports originating in developing countries, the study will give cause for concern to sourcing companies and consumers. With waste management struggling to keep up with rapid urbanization in developing countries, better testing programs will be needed so that consumers can have assurance the seafood they eat is free from contamination that could be harmful to their health, Rader said.

“We didn’t do this specifically to investigate Myanmar – versus other places – but as new work within a broader study of impacts on Myanmar’s marine environment, including its fisheries,” explains Rader. “I would fully expect similar results from all over Asia and many if not most parts of the world.”

Rader explained how large volumes of seafood are shipped from Myanmar to China and other processing nations, and then travel to many other locations around the world.

“Just as one example, spiny lobster, mud crabs, snapping shrimp, and many finfish move from this region of Myanmar into Chinese value chains,” Rader said. He pointed to a huge “shedding” facility for mud crabs at Myeik, which sources from coastal areas for many miles around for export to China and elsewhere. 

The contaminants found in this study indicate that even the Mergui Archipelago in largely rural Myanmar has significant and widespread pollution from runoff of agricultural and human waste that can affect downstream food sources like oyster beds.

The study’s authors said they worry that the uptake of microplastics in the marine environment could have far-reaching consequences for human consumption of seafood. The pathogens encountered in the study includes a long list of contaminants that can cause humans to become sick with sufficient exposure.  For instance, Clostridium perfringens is among the most important causal agents in “food poisoning”, while Collinsella aerofaciens contributes to a whole host of digestive system problems, including irritable bowel syndrome. Coxiella burnetii is responsible for “Q fever,” which is flu-like in mild cases, but can be deadly. 

“Actually, taken together diarrheal diseases are among the most important causes of premature mortality, globally, accounting for an estimated 1.6 million deaths per year – including more than half a million children under five,” Rader said. “Thus, food system contamination is a big deal.”

Much more scientific research is needed to understand the risks.

“In my view, the study points to a more general need to understand all the things that filter feeders accumulate, and what that means for both ecosystem health and the health of human consumers, both in seafood producing nations and across the value chains,” Rader said. “[There is] clear need for improving what we know in this developing field – how general are these problems, and what do they mean? There is [also] clearly a need for better monitoring of seafood supply chains across the world, and of course for improved sewage collection and treatment systems, waste management systems for plastics, reductions in single use plastics, and then management of watershed level contamination in seafood source grounds.” 

With Asia becoming an ever greater source of global seafood supply, there is “ample reason for consuming nations to partner with source nations to protect people who eat seafood both here and there,” Rader said, a sentiment echoed by postdoctoral researcher Raechel Littman, the study’s lead author.

“It’s important to keep in mind that much of our seafood is imported from overseas, from places that may be contaminated, emphasizing the importance of both adequate testing and improvements to coastal water quality worldwide,” Littman said.

Photo courtesy University of Califorina, Irvine