Various institutions and research groups have been measuring DDT contamination in fish and sediment off the coast of Southern California for decades. Starting in 2023, McGill and his co-authors have been working to compile these data to better understand the overall picture of DDT contamination and how it has changed over time. Ta. The researchers also wanted to investigate potential links between contamination levels in fish and ecological factors such as fish location, habitat preference, and diet.
Key data sources include the Southern California Bay Area Monitoring Program, the Coastal Fish Contamination Program, the Statewide Coastal Screening Survey, the City of San Diego Marine Monitoring Program, and the Los Angeles County Sanitation District Regional Trends Assessment.
“There was actually a lot of information about DDT in fish and sediment, but it wasn’t easily accessible,” said study co-author Toni Slew, a doctoral candidate at Scripps. “Combining data sets makes them even more powerful, and it’s reassuring for the public to know that these surveillance efforts have been around for a long time and are fairly comprehensive. It may become.”
This compilation includes nine datasets spanning 60 fish species collected throughout the Southern California Gulf from 1998 to 2021. First, the team analyzed DDT concentrations in marine sediments and fish. The researchers then used statistical models to understand the relationship between the distribution of DDT in sediment and contamination levels in fish in relation to fish location, diet, and habitat.
The study found that, half a century later, the original dump site still has the highest concentrations of DDT in marine sediments. DDT levels in fish generally reflected the degree of sediment contamination where the fish were collected, but the strength of the relationship varied depending on the fish’s habitat and diet.
Sediment DDT levels were most strongly linked to contamination of fish species living near the bottom. However, sediment contamination was not as good a predictor for fish living near the surface or higher up the food chain, which had relatively consistent DDT levels across locations.
According to the researchers, these findings indicate that certain chemical pollutants persist in the ocean, while also indicating that the remaining danger from DDT in Southern California is relatively local and not generalizable. The results also show that it appears to follow a similar pattern.
“If DDT pollution is moving through the ocean in a predictable way, we can use the ocean to reduce exposure,” said Bryce, a marine biologist at Scripps Oceanography and co-author of the study.・Mr. Semmens said.
Overall, DDT levels in fish decreased between 1998 and 2021.
“The jury is still out, but I think one of the main reasons for the decline is that contaminated sediment is slowly being buried by new sediment,” Semmens said. “This may be why observations in the food web decrease over time.”
Although the majority of the fish included in the study did not contain levels of DDT contamination exceeding California’s edible guidelines, the study’s samples focused on near-shore fish and sediment contamination, and deep-sea Semmens pointed out that he could not speak directly about the dump site. It was discovered further offshore in 2020.
“Whether DDT from these deep dumps is more problematic than what our results reflect remains to be seen,” Semmens said. “Researchers at Scripps and other Southern California institutions are currently working on this question.”
The researchers used the results to identify individual species, even those not included in the study, based on sediment data near where the fish were caught and information about the species’ ecology. We created a framework for predicting contamination of fish.
Researchers, in collaboration with students in the Environmental Data Science Master’s Program at the University of California, Santa Barbara, created a user-friendly system where anglers can enter catch details and receive information about expected DDT contamination and consumption guidelines. I am developing a website. A beta version of the site, called SaferSeafood, is currently live. This website aims to improve the accuracy of consumption advisories, which could benefit vulnerable communities that rely on fishing for food.
A follow-up study led by Sleugh is currently underway to measure current DDT concentrations in a variety of fish in Southern California. This study includes additional measurements such as fish age and diet that were not included in previous datasets but may prove to be important factors in contamination levels in individual fish. I am planning to do so.
In addition to McGill, Slew and Semens, the study’s co-authors include Colleen Petrick and Lihini Alwihea of Scripps, and Kenneth Schiff and Karen McLaughlin of the Southern California Coastal Water Research Project.
