The researchers identified 248 human-derived compounds in the samples of ocean water with the help of high-resolution mass spectrometry. The most widespread pollutants were industrial chemicals, particularly plasticizers, UV filters used in sunscreen and synthetic fragrances. The top five industrial pollutants were detected in more than 30% of all samples, including open ocean sites far from land. Pharmaceuticals such as anti-anxiety medications and pesticides like DEET were more prevalent closer to coastlines with larger human populations, declining sharply with distance from shore.
Across all samples, human-made compounds, known to scientists as xenobiotics, typically made up about 2% of what the instruments detected. Generally, the levels of xenobiotics were highest closest to the coast and lowest far from shore. The most contaminated samples came from estuaries, where human-made compounds accounted for up to 76% of the chemicals detected by the analysis, while in the open ocean the proportion ranged from 0.5% to 4%. Some coral reef sites also showed significant contamination. Among samples from Puerto Rico, the Caribbean Netherlands and Hawaii, xenobiotics typically made up about 20%, 11% and 10%, respectively, of the compounds the instruments detected.
While the share of xenobiotics detected in the open ocean may seem small, their presence underscores how widespread the chemical traces of humanity have become. The effects of the cumulative chemical concentrations and their long-term ecological impacts remain largely unknown.
“Determining whether the presence of these molecules has in some way altered or reshaped the way marine ecosystems function is the big next step,” said Aluwihare. “Xenobiotics are widespread, so whatever ecological impacts they are having are also likely to be widespread.”
Another key question Aluwihare and her collaborators will look to answer is whether the presence of these human-made compounds far from shore is indicative of relatively constant inputs from human activities such as shipping or if the chemicals are persistent and long-lasting in the environment.
The researchers note that their results likely undercount the share of xenobiotics. Some pollutant classes, such as PFAS and PCBs, are not detected using the current methodology, while others don’t yet exist in the reference libraries used to identify chemicals in the samples.
Despite the size of the dataset, it was not globally comprehensive. The study’s data were heavily concentrated in North America and Europe, with limited coverage in the Southern Hemisphere and almost no representation from regions such as Southeast Asia, India and Australia.
The authors call for large-scale, coordinated monitoring programs with standardized sampling and analytical protocols that combine the non-targeted approach used here with methods that can provide additional measurements, such as the absolute concentration of a given compound.
“No single person or lab could have collected data from all these places around the world,” said Aluwihare. “This shows what’s possible with truly open science and international collaboration.”
Besides Aluwihare, other Scripps co-authors include Irina Koester, Brandon Stephens, Ralph Torres, Lucia Cancelada, Zachary Quinlan and Linda Wegley Kelly. The full author list can be found in the study text.
The research was supported by the Simons Foundation International, NASA and U.S. National Science Foundation, and included data from long-term ecological research programs in California and French Polynesia, and the German Research Foundation.
The study also involved contributions from multiple national and international institutions, including Rhodes University in South Africa; University of Tuebingen in Germany; University of São Paulo in Brazil; Royal Netherlands Institute for Sea Research; University of Amsterdam in the Netherlands; UC San Diego; National Taiwan University; Helmholtz Centre for Ocean Research in Germany; University of Hawaiʻi at Mānoa; UC Santa Barbara; University of Concepción in Chile; UC Merced; Perry Institute for Marine Science in Vermont; Harvard University in Massachusetts; University of Denver in Colorado; Sefako Makgatho Health Sciences University in South Africa; and Kiel University in Germany.
