Fish still recovering from oceanic pesticide dumping

(CN) — Decades before the pesticide DDT was banned in the United States, it was dumped in the ocean off the coast of Los Angeles. The marine ecosystems are still recovering from it, but new research highlights methods to predict contaminants in fish.

A team of scientists, led by those at the University of California’s Scripps Institution of Oceanography, researched the lasting impacts of those years of chemical discharge and detailed their findings in a study published Monday in the journal Proceedings of the National Academy of Sciences.

DDT and other chemicals were dumped offshore with the assumption that the ocean would mitigate its impacts on humans and the environment by diluting and spreading pollutants. The scientists found that the areas near the historical dumping sites still show high DDT concentrations in sediment and in fish.

“The impacts of ocean dumping on marine ecosystems and fisheries resources remain place-based, despite the long-held belief that the vastness of the ocean holds nearly limitless capacity for contaminant mitigation via dilution and advection,” the authors wrote in the study.

When DDT breaks down, those products are referred to as DDX and the contaminants remain in the environment due to its resilience to degradation, according to the scientists.

This resilience poses a risk to both marine and human health.

By taking a close look at how differences in contaminant levels in sediment interact with ecological processes to impact overall bioaccumulation, the process by which fish absorb contaminants, the researchers created a model to predict areas where exposure may be high.

One of those areas is heavily industrialized or agricultural regions.

In the Southern California Bight, the curved coastline that runs south to the Mexican border, the largest producer of DDT in the U.S. discharged its industrial waste directly into the water from 1947 until 1971. Part of the discharge was deposited on the Palos Verdes Shelf through a wastewater treatment plant, while ships dumped other discharge in deeper waters.

Using decades-worth of contaminant monitoring data from the Southern California Bight, the scientists analyzed the changes in contamination levels in fish and sediment in the area.

The team focused on the six main DDX components, finding that DDE was the most commonly found in sediment and fish samples. Then, by analyzing the diets and habitats of fish species, they created models to predict DDX levels in sediments over time to understand how fish traits and locations impact DDT bioaccumulation.

DDX concentrations were highest near old dumping sites near the Los Angeles Harbor and Santa Monica Bay.

“Despite more than half a century since the cessation of industrial dumping in the SCB, local ecosystem contamination continues to mirror the spatial legacy of DDX disposal,” the scientists wrote.

The research expands on previous studies by the team and suggests that sediment can be a strong predictor of fish organic contamination. Researchers think the findings can help predict seafood safety using more robust data incorporating where the seafood comes from and how different species of fish live and feed.

While ecological traits have long been known to influence how organisms are exposed to contaminants and how those contaminants build up in their bodies, the scientists discovered that habitat surfaces as a more important predictor, showing that influencing factors are context-dependent.

“In relatively pristine (low contaminant) environments, the primary predictor of fish bioaccumulation is trophic magnification,” the scientists wrote. “In highly contaminated areas, however, habitat becomes a more important predictor of DDX burdens.”

As fish consumption serves as an important source of protein for many low-income communities, predicting contaminant levels is an important way to help people stay healthy. Grouping fish by general habitat types for fish contamination advisories is nearly as effective as focusing on each species individually, and it could make it easier to give advice for unmeasured species.

Looking ahead, the scientists warned against similar pesticide dumping.

“Our findings also support a cautionary approach to future ocean disposal of chemicals, where place-base impacts of dumping dominate the prediction of contaminant burdens in fisheries, decades, if not centuries, into the future,” the scientists wrote. “Leveraging this nuance should be an important part of efforts to safeguard both people and the environment against the legacy of ocean dumping.”