For decades, regulatory agencies have built marine monitoring programs primarily around pesticides and pharmaceuticals, treating them as major chemical threats to ecological and human health.
This assumption has left much larger categories of compounds, such as industrial chemicals incorporated in packaging, furniture, and everyday personal care products, largely unexplored. The chemicals were found to be widely distributed. And now they can be found in places that some people would consider to be pristine, such as the coral reefs of the Caribbean Sea.
These compounds are biologically active and some interfere with microbial metabolism. natural earth sciencethey could be changing the way the ocean cycles carbon, one of Earth’s most important biogeochemical processes.
“What really surprised us, beyond the usual (pesticides and pharmaceuticals), is that even higher levels of everyday industrial chemicals are occurring almost everywhere, not just in coastal areas and polluted areas,” said Daniel Petras, a biochemist at the University of California, Riverside.
The study, led by Petras and Jarmo Charles Kalinsky, a postdoctoral researcher at Rhodes University’s Center for Biotechnology Innovation, reanalyzed 21 publicly available datasets of seawater samples collected over a decade across the Pacific, Indian and North Atlantic Oceans, including the Baltic Sea and Caribbean Sea.
All of the groups the researchers studied (industrial pollutants, pharmaceuticals, and pesticides) belong to a class called xenobiotics (human-made organic compounds that are foreign to natural systems). Pesticides and pharmaceuticals were prevalent in the coastal samples, as expected given their well-documented entry through agricultural runoff and drains.
However, industrial compounds behaved differently. Polyalkylene glycols used in hydraulic fluids, phthalates in polyvinyl chloride (PVC) packaging, organophosphate flame retardants in furniture and electronics, and surfactants in personal care products were found to be much more prevalent across all ecosystem types than pesticides or pharmaceuticals. “These are chemicals that we use all the time, so they end up being widely distributed,” Petras said.
A glimpse of what was always there
To map the ocean’s complete chemical landscape, researchers analyzed more than 2,300 samples from temperate coastal areas, coral reefs, and the open ocean, searching for the presence of xenobiotics and examining the percentage of dissolved organic matter (DOM), a pool of carbon-containing molecules dissolved in seawater. The research team identified a total of 248 known xenobiotic molecules. Their study provides the most comprehensive chemical map of anthropogenic organic pollution in the oceans to date.
The researchers used a combination of untargeted mass spectrometry and scalable computational tools. Unlike traditional targeted analysis, which tests only a predefined list of known harmful molecules, this open-ended approach can detect thousands of chemicals simultaneously, even at low concentrations. The team then applied molecular networks, a computational technique that allows the identification of not only known substances, but also their “families” and derivatives.
Coral reefs as remote hotspots
“With potential anthropogenic sources now almost everywhere, our traditional idea of ‘as nature is’ needs to be seriously reconsidered.”
For Petras, finding these compounds in coral reefs like those in French Polynesia was a surprise. Coral reefs are usually considered perfect “postcard-style” paradises. However, a closer look reveals that these areas are rarely actually isolated. Agriculture, urban runoff, hotel infrastructure, and cruise ship traffic all contribute to pollutants. Signs of human activity, such as sunscreen, wastewater, and boat fluids, are concentrated near coral reefs.
“Plasticizers and flame retardants were particularly detected in these remote areas,” Petras said. “This suggests that our traditional idea of ‘as nature is’ needs to be seriously reconsidered, as potential anthropogenic sources are now nearly ubiquitous.”
Anastasia T. Banasac, a researcher at the Coral Reef Systems Unit at the National Autonomous University of Mexico who was not involved in the study, emphasized the far-reaching implications for coral reef conservation, saying: “Inappropriately treated urban sewage discharges pose risks to coral reefs and the success of restoration projects.” Such releases raise nutrient levels and encourage the proliferation of macroalgae, which grow faster than corals and compete with them for space. Banaszak noted that this pressure on ecosystems will intensify as climate change shifts the baseline against which recovery outcomes are measured.
Carbon…and microorganisms?
Beyond coral reefs, these synthetic compounds may be influencing the ocean’s carbon cycle. The DOM is one of Earth’s largest carbon reservoirs, comparable in size to all the carbon dioxide (CO2) in the atmosphere. Marine microorganisms convert it from an easily degradable form to a biologically resistant form. Refractory DOM that escapes consumption by microorganisms accumulates in the ocean and acts as an important climate regulator.
However, industrial compounds account for up to 63% of DOM in some estuarine samples (compared to a global estimate of 10%), suggesting that microbial loops are probably facing chemical conditions that they have not evolved to cope with. This change means that the efficiency of the ocean’s carbon pump, the mechanism that captures carbon dioxide from the atmosphere, could be compromised in ways that are not yet understood.
“The data suggests they are present at significant levels,” Petras said. “It’s good enough that it should be taken into account in models of the carbon cycle.”
deal with the invisible
Finding xenobiotics is only the first step, the authors say. They offered some suggestions for next steps. For example, governments should mandate open-ended approaches as standard monitoring tools, not just targeted testing of pre-selected chemicals. Ocean data must also be publicly available and standardized according to FAIR (searchable, accessible, interoperable, reusable) principles.
“We already have a strong track record of building long-term datasets such as trace metals and nutrients, and we hope that untargeted analysis will become part of such long-term efforts,” Petras concluded. “We have been active in establishing these tools for our community.”
—Mariana Mastache-Maldonado (@deerenoir.bsky.social), Science Writer
