Discussion

Our measurements of occurrence and quantity of anthropogenic debris in seafood are conservative, as we did not quantify the particles observed which were smaller than 0.5 mm in every dimension or fibers that matched the color of our lab coats or clothing. Still, across both locations, we found anthropogenic debris in the gut contents of greater than a quarter of individual fishes and shellfish and in the majority of species sampled—all marketed for human consumption. This result may not be surprising given both countries rank among the top 20 for mismanaged anthropogenic waste (Indonesia ranks 2nd and the USA 20th)34.

Overall, the frequency of occurrence of plastic debris in seafood was similar between locations. We sampled 76 individuals from each location and found anthropogenic debris in 21 from Indonesia and 19 from the USA. For fish only, we found anthropogenic debris in 21 individuals from Indonesia and in 16 from the USA. Although the frequency of debris in fish was similar, there was a trend for individual Indonesian fish to contain a higher number of particles (Fig. 2). This trend may be due to differences in the management of waste between Indonesia and the USA and warrants further analysis. While the use of plastic and textiles in the US is greater than in Indonesia35, waste management is more advanced in the US. For example, Indonesia has an order of magnitude greater mismanaged plastic waste than the US (3.22 million metric tons as opposed to 0.28 in the US)34.

The most striking difference between locations is the type of anthropogenic debris found in fish between Indonesia and the USA (Fig. 3). All anthropogenic debris found in fish from Indonesia was composed of plastic, whereas in fish from the USA only 20% of anthropogenic debris found in fish could be confirmed as plastic. In contrast, the majority (80%) of anthropogenic debris found in fish from the USA was composed of fibers from textiles, whereas not a single fiber was detected in fish from Indonesia. Many studies report procedural contamination of fibers in samples, and omit fibers from quantification unless laboratory blanks have been used. Here, the same methods were used in Indonesia and the USA, which included laboratory blanks and the exclusion of fibers that matched our laboratory coats and clothing. The lack of fibers in fish from Indonesia helps confirm that our procedures were robust. While there is a chance that gutting of some USA fish by fishermen might have introduced fibers to gut contents, we also found fibers in the guts of whole fish. Thus, we conclude that the presence of fibers in samples from the USA occurred from ingestion in nature prior to sampling.

Although we cannot explain the cause of this stark contrast between types of anthropogenic debris between sampling locations, one hypothesis may concern the differences in waste management strategies on land between countries. In Makassar, Indonesia where fish were collected, 30% of solid waste generated is not processed and an increasing amount of waste is directly discarded along the coast, rivers and into drainage channels36; thus, it is common for plastic items to end up in the ocean where they degrade into fragments over time37. In California, waste management systems are more advanced and thus it is less common for plastic items to be discarded in the ocean. Together, this may have led to a higher frequency of plastic fragments in fish from Makassar than California. In regards to the contamination from fibers in fish from the USA only, a more advanced waste management system may explain the higher concentration of fibers off the coast of California. There are more than 200 wastewater treatment plants discharging billions of liters of treated final effluent just offshore in California38. Even though treatment results in a reduction of many contaminants, synthetic fibers from washing machines can remain in sewage effluent, and may be delivered to aquatic habitats in large concentrations via wastewater outfalls39,40. One study found one fiber per L of wastewater effluent39. In this sense, we might expect that billions of fibers are discarded into the Pacific Ocean from wastewater treatment plants in California everyday. Without this concentrated source of fibers in Makassar, we may expect a lower concentration of fibers in fish from Indonesia. Still, the complete lack of fibers in fish from Indonesia was not expected and future research should test hypotheses about such patterns.

Anthropogenic debris has become widespread in the marine environment globally. As such, concern has been raised about whether the ingestion of anthropogenic debris by marine animals can cascade up the food web to influence human health1. There may be direct effects when shellfish, whole fish and/or the intestines of fish are ingested whole. In South Sulawesi fish guts are a local favorite providing a direct route for ingestion of anthropogenic debris by people. The physical harm that anthropogenic debris causes to marine animals at several levels of biological organization27 can potentially threaten local food security in locations where debris is abundant and seafood is a major source of protein to the local population (e.g., Indonesian island communities). Moreover, anthropogenic debris is associated with a cocktail of hazardous chemicals25, some of which are bioavailable to wildlife upon ingestion. Recent evidence demonstrates that chemicals associated with plastic anthropogenic debris are bioavailable to seabirds41,42,43, amphipods44, crickets45, lugworms23,46and fish47 upon ingestion.

Our results, showing anthropogenic debris in more than 25% of individual animals and over half of the species purchased and/or collected from fish markets and fishermen selling fish for human consumption, demonstrate that anthropogenic debris has infiltrated marine foodwebs to the level of humans via seafood. Because anthropogenic debris is associated with a cocktail of priority pollutants25,30, some of which can transfer to animals upon ingestion23,44,45,46,47, this work supports concern that chemicals from anthropogenic debris may be transferring to humans via diets containing fish and shellfish, raising important questions regarding the bioaccumulation and biomagnification of chemicals and consequences for human health Our results provide the impetus for further research to test hypotheses about the linkages between plastic contamination of seafood and human health. It is important to understand any hazards associated with how the ghost of waste management past may be haunting us in our own seafood. Future risk assessments should consider anthropogenic debris as another factor for seafood safety advisories relevant for consumers.