Coastal ocean chemistry now substantially shaped by humans

The international study, led by the University of California, Riverside, analyzed seawater samples collected over a decade from coastal regions from the Pacific, Atlantic, and Indian Oceans. NIOZ Biogeochemists Andreas Haas and Lisa Schellenberg collected and analyzed the data from Curacao and the Caribbean Netherlands. They also sampled parts of the data from Mo'orea, French Polynesia.

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. 

Another, largely invisible human footprint

The findings show that industrial chemicals, many of which are rarely monitored, are far more abundant and widespread than previously recognized. Daniel Petras, an assistant professor in biochemistry at the University of California: "For decades, scientists have tracked plastic debris floating on the ocean’s surface and measured rising temperatures that signal climate change. 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."

From agricultural development to tourism

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 no place that we sampled that showed no human chemical influence", said Jarmo Kalinski, a postdoctoral researcher in Petras’ research group.

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

An unrecognized role

Petras explained that some of the human-made compounds are 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." 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 percent of detected organic matter. "At a global scale, that’s a huge amount of material", Petras adds. 

A key innovation

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. 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, assistant professor in 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.

Collaborators around the globe and open science

"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.

A first overview

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

Everyday activities contribute chemicals

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

More information

• Read the full paper: Widespread presence of anthropogenic compounds in marine dissolved organic matter.

Text: Royal Netherlands Institute for Sea Research (NIOZ)
Images: NIOZ (lead photo: filtration setup in Mo'orea that was used to collect the seawater metabolomics samples in this study)