Although the oceans are the least explored places on the planet, even their depths are not untouched by humans.
Drawing on more than 2,300 seawater samples collected across the Pacific, Atlantic and Indian Oceans, researchers found that hundreds of synthetic chemicals — many of them rarely monitored and originating from everyday products — are now woven into the fabric of marine organic matter.
The findings, published in Nature Geoscience, suggest that industrial and consumer compounds are far more pervasive and persistent than scientists realized, raising urgent questions about their role in carbon cycling, ecosystem health and the true extent of humanity’s chemical footprint on the sea.
“The ocean does not contain just a handful of these artificial compounds — marine organisms could be swimming through a mix of dozens or hundreds of human-made compounds in any given location,” said UC Merced environmental sciences Professor Michael Beman, a collaborator on the study.
The international analysis, led by biochemists at UC Riverside, allowed the researchers to capture a global perspective. The findings reveal an important insight: 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 Daniel Petras, the biochemistry professor at UC Riverside who led the study. “But another, largely invisible human footprint has been quietly 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.”
Even remote coral reef systems, often viewed as among the least-touched marine environments, showed clear chemical signatures of nearby human activity — from agricultural and coastal development to tourism, the researchers said.
Beman said he was surprised because many of the samples were collected well out into the open ocean, in seawater that seemed pristine. He and UC San Diego researchers Irina Koester and Professor Lihini Aluwihare were interested in natural carbon compounds and didn’t intend to find artificial contaminants.
“But the chemical imprint was evident in essentially every sample,” Beman said.
The researchers found that in coastal waters, human-made organic chemicals account for 20% of the total measured signal in their datasets. In the most extreme cases — such as river mouths impacted by untreated or poorly treated wastewater — that figure exceeded 50%. Even open-ocean samples consistently contained a few percent of artificial compounds. Overall, across all the samples analyzed, 248 human‑related compounds together accounted for about 2% of the total detected signal.
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 — make up the bulk of the human-caused chemical signal in the ocean.
Petras said some human-made compounds sit at the boundary between traditional organic molecules and nanoplastics, blurring the line between chemical 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 various research purposes, including coral reef health, algal blooms and carbon cycling.
A key innovation used by the research team was the combination of consistent, high-resolution mass spectrometry methods across multiple laboratories, along with scalable computational tools developed at UC Riverside. These technological advances allowed the group to combine and analyze thousands of samples from unrelated studies as a single, unified dataset.
“The technique that was used is new and powerful, so it detects a wide range of natural and artificial compounds,” Beman explained. “Although some human-made compounds may have no effect at all or may break down, a major concern is whether they negatively affect marine life.”
Despite the dataset's size, 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; it means scientists have not looked closely enough yet, the team said.
The authors acknowledged that this analysis serves as a first overview, and detailed analyses with precise quantification are still needed. Further, the effects of the cumulative chemical concentrations and their long-term ecological impacts remain largely unknown.
“The fact that hundreds of compounds are found around the world in varying amounts means that this isn't an easy problem to study and solve,” Beman said.
By making the data public, the researchers 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.
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.
“Some of the artificial compounds detected in the ocean are household names,” Beman said. "Although it can take extra effort, reducing plastic use and properly disposing of chemicals and pharmaceuticals can only help."
