Coastal ocean chemistry now substantially shaped by humans

A global analysis of more than 2,300 seawater samples from more than 20 field studies around the globe indicates that human-made chemicals make up a significant portion of organic matter in coastal oceans.

Daniel Petras

The international study, led by biochemists Jarmo Kalinski and Daniel Petras at the University of California, Riverside, analyzed seawater samples collected over a decade from coastal regions from the Pacific, Atlantic, and Indian Oceans. Reported in Nature Geoscience, the findings show that industrial chemicals, many of which are rarely monitored, are far more abundant and widespread than previously recognized.

"For decades, scientists have tracked plastic debris floating on the ocean's surface and measured rising temperatures that signal climate change," said Petras, an assistant professor of biochemistry. "But another, largely invisible human footprint has been accumulating in the sea: thousands of synthetic chemicals. Even in places we consider relatively pristine, we found clear chemical fingerprints of human activity. The extent of this influence was surprising."

According to Petras, even remote coral reef systems, often viewed as among the most pristine marine environments, showed clear chemical signatures of nearby human activity - from agricultural and coastal development to tourism.

"There was virtually nowhere we sampled that showed no human chemical influence," said Kalinski, a postdoctoral researcher in Petras' group.

The study found that in datasets from coastal environments, median signal levels of human-made organic molecules reached up to 20%, compared to lowest values of about 0.5% in the open ocean. In extreme cases, such as river mouths impacted by untreated or poorly treated wastewater, that figure exceeded 50%. Across all samples, 248 human-derived compounds made up a median of ~2% of the total detected signal.

Jarmo Kalinski, a former postdoctoral researcher in the group of Daniel Petras, and lead author of the study, sets up a chromatography system for the analysis of marine dissolved organic matter. (UCR/Petras lab)

While pesticides and pharmaceuticals were expected to be most concentrated near shorelines, the study found that industrial compounds, including substances used in plastics, lubricants, and consumer products, dominate the anthropogenic chemical signal in the ocean.

"Industrial chemicals make up the bulk of the human chemical signal we're seeing," Kalinski said.

Petras explained that some of the human-made compounds sit at the boundary between traditional organic molecules and nanoplastics, blurring the line between chemical pollution and plastic pollution.

"These chemicals contribute substantially to the ocean's organic matter pool. That means they may play an unrecognized role in marine carbon cycling and ecosystem function," he said.

The researchers also found that anthropogenic chemicals persist well beyond the coastline. Even more than 20 kilometers offshore, human-derived compounds accounted for roughly 1% of detected organic matter.

"At a global scale, that's a huge amount of material," Petras said.

The study represents one of the most comprehensive chemical meta-analyses of coastal oceans to date, drawing on samples collected for many different research purposes, including coral reef health, algal blooms, and carbon cycling.

Daniel Petras (left) and Mingxun Wang, both assistant professors at UCR, replace a control board of the mass spectrometer used for the analysis of marine dissolved organic matter. (UCR/Petras lab)

A key innovation the research team used was the combination of consistent, high-resolution mass spectrometry methods across multiple laboratories, as well as the use of scalable computational tools developed by Mingxun Wang, an assistant professor of computer science at UCR. Thanks to these technological advances, the group was able to combine and analyze thousands of samples from unrelated studies as a single, unified dataset.

"This work was only possible because of the efforts of our collaborators around the globe and open science," Petras said. "By making our data public, we hope to accelerate research and enable a more complete understanding of human chemical impacts on the ocean."

All data from the study are publicly available, allowing other researchers to reanalyze the results or integrate new datasets as they emerge.

Despite the size of the dataset, the researchers note that large parts of the world remain understudied. 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 absence of data doesn't mean the problem isn't there," Kalinski said. "It means we haven't looked closely enough yet."

The authors acknowledged that this analysis serves a first overview, and detailed targeted analyses with precise quantification are still needed. Further, the effects of the cumulative chemical concentrations and their long-term ecological impacts remain largely unknown.

Tilman Schramm, a doctoral student in the group of Daniel Petras and co-author on the study, extracts dissolved organic molecules from sea water sample for mass spectrometry analysis. (UCR/Petras lab)

"We know humans are altering marine chemistry, but we don't yet know what that means for marine life, food webs, or ecosystem resilience," Kalinski said. "Our study provides a foundation for asking those questions."

The findings also highlight a broader, often overlooked reality: everyday activities, driving, cleaning, food packaging, and personal care contribute chemicals. Washed down drains or carried by rainwater, they move through rivers and wastewater systems and eventually reach the ocean.

"What we use on land doesn't disappear," Kalinski said. "It often ends up in the ocean, the final sink."

The findings have also shaped Petras' own habits.

"I try to reduce plastic use, avoid excessive packaging, and limit processed foods," he said. "Not just for environmental reasons, but also because I don't want unnecessary chemical exposure."

The research was supported by the Simons Foundation International, NASA, U.S. National Science Foundation, including the long-term ecological research programs in California and French Polynesia, and the German Research Foundation, with 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.

The title of the paper is "Widespread presence of anthropogenic compounds in marine dissolved organic matter."

Header image credit: imagedepotpro/iStock/Getty Images Plus.

Share this Article

Science / Technology