DDT Pollutant Found in Deep Sea Fish

It is strongly suspected that the DDT compound enters the deep sea food network. This condition is dangerous if it spreads to mammals and humans.

SCHMIDT OCEAN INSTITUTE

Researchers on the Falkor Research Vessel used remotely operated robotic vehicles to collect sediments off the coast of Los Angeles, United States, during an expedition in July 2021.

The accumulation of pollutants over a long period of time has a long-term impact on the pollution of the area. This includes the toxic materialdichloro-diphenyl-trichloroethaneor DDT which in the 1940s and 1950s was dumped directly on the beaches of Los Angeles, United States, and its effects are still recorded today.

Researchers at the Scripps Institution of Oceanography University of California San Diego and San Diego State University (SDSU) discovered the content of DDT pollutant in deep sea fish in local waters. Even though the use of these pesticides was stopped decades ago (1972), even now their impacts can still be harmful to fauna/wildlife, even humans.

The Los Angeles beach has a history of being a dumping site for the largest DDT pesticide producer in the US. Although dumping was legal at that time, industrial-scale marine environmental pollution at the dumping site, about 24 kilometers off the coast near Catalina Island, remains a concern for scientists and the community.

Their concerns are justified. New evidence has been presented by scientists who found chemical contamination related to DDT in fish and sediment near the dumping site.

Also read: DDT, Health and the Environment

The research, published on Monday (6/5/2024) in the journal Environmental Science and Technology Letters, was funded by the US Oceanic and Atmospheric Administration (NOAA). Researchers suspect DDT-related chemicals that were dumped into the sea decades ago may still be entering marine food webs.

Risky to humans

Since the rediscovery of the offshore waste disposal site near Catalina Island, scientists have been trying to determine the severity of the current problem. The most urgent question is whether decades-old chemicals, now at the bottom of the ocean thousands of meters below the water's surface, remain there or whether these substances circulate in the marine ecosystem and can harm wildlife. When in the food chain, this can pose health risks to humans who consume them.

"This is a deep-sea organism that doesn't spend much time on the surface and they are contaminated with chemicals related to DDT," said Lihini Aluwihare, a marine chemistry professor at Scripps and one of the authors of the study, on the UC San Diego website on May 6, 2024.

KOMPAS/FERGANATA INDRA RIATMOKO

Farmers spray pesticides on loncang plants in their fields in Banyumudal Village, Sapuran, Wonosobo, Central Java, Saturday (2/9/2023) morning.

From 1948 until at least 1961, barges contracted by the DDT manufacturer, Montrose Chemical Corporation, departed from the port of Los Angeles towards Catalina and pumped production waste loaded with sulfuric acid and up to 2% pure DDT, directly into the Pacific Ocean. This activity was legal until 1972. However, this offshore waste dumping largely escaped public scrutiny because it was overshadowed by Montrose's other waste disposal practices, such as pumping more diluted acid sludge containing DDT through LA County's sewers and into the ocean off the coast of Palos Verdes.

It is estimated that 100 tons of DDT ended up in the Palos Verdes Shelf sediment. The Environmental Protection Agency declared the site an underwater Superfund site in 1996. In 2000, a judge ordered the company to pay $140 million to repair the environmental damage.

Research has linked DDT pollution in Palos Verdes Shelf with contamination and health issues in local wildlife. These animals include sea lions, dolphins, fish that feed on the ocean floor, and even condor birds (most likely because they feed on dead marine mammals) along the California coast.

In 2011 UC Santa Barbara researcher David Valentine used an underwater robot to rediscover a landfill off the coast of Montrose near Catalina at what is now known as Dumpsite 2. This discovery attracted public attention in 2020 when theLos Angeles Times publishes the first in a series exposing the toxic legacy of offshore waste dumping in the region.

Neither of these fish species is known to forage in seafloor sediments.

Researchers Valentine and Scripps have helped map the level of dumping. Until now, they have found chemical substances related to DDT in a wider underwater area than San Francisco City. What is still unknown is whether the pollution remains or moves through the underwater environment, posing a danger to marine life or humans.

Starting in 2021, Aluwihare, a research partner of Eunha Hoh from SDSU, and other collaborators embarked on a series of research efforts to answer two key questions: Are DDT-related chemicals hidden in the seafloor near Dumpsite 2 mixed and swallowed by marine life at depth? And, can they identify a unique chemical fingerprint of contamination from Dumpsite 2 and other offshore waste disposal sites that can be used to distinguish it from pollutants originating from the Palos Verdes Shelf?

SCRIPPS INSTITUTION OF OCEANOGRAPHY/UC SAN DIEGO

Map of DDT waste disposal locations.

By chance, the team collected sediment and marine specimens from the water column in the San Pedro Basin near Dumpsite 2 to test various compounds related to DDT. The research cruise ship for collecting these samples was funded by the National Science Foundation and the Schmidt Ocean Institute.

Usually, DDT testing looks for four to eight chemicals, but a 2016 paper written by Hoh and Aluwihare identified 45 DDT-related chemicals in dolphin fat off the coast of Southern California. The results showed that wildlife is exposed to significantly higher amounts of DDT compounds in the real world.

In this study, the team examined a larger series of chemicals related to DDT, known as DDT+, in hopes of developing chemical fingerprints for Dumpsite 2 and other coastal waste disposal sites used by Montrose. In addition, testing DDT+ will provide a more comprehensive picture of contamination levels in sediment and wildlife that may go undetected.

Also read: Don't be reckless in adding chemical fertilizers and pesticides to agricultural land

When researchers analyzed sediment to determine the presence of DDT+, they found no less than 15 chemicals, 14 of which had previously been detected in birds and marine mammals in Southern California.

Researchers collected 215 fish that covered three common species near Dumpsite 2. Chemical analysis revealed that the fish contained 10 compounds related to DDT, all of which were also found in sediment samples.

Two fish species were collected at depths of 546-784 meters (Cyclothone acclinidens and Melanostigma pammelas) and Leuroglossus stilbius were collected at 0-546 meters. Species collected at shallower depths contained lower concentrations of contaminants and did not contain a pair of DDT-related compounds present in the deepest fish.

REUTERS/MIKE BLAKE

Activities on the beach in Oceanside, Southern California, United States, some time ago.

"Not a single species of fish is known to forage on the seafloor sediment," says Anela Choy, a marine biologist expert at Scripps and one of the authors of the research.

He believes there is another mechanism that causes deep-sea fish to be exposed to DDT contamination. One possibility is the existence of physical or biological processes that resuspend sediments around Dumpsite 2 and allow contaminants to enter deeper water food chains.

This finding cannot eliminate the Palos Verdes Superfund Site as a potential source of fish contamination, according to Aluwihare. However, some evidence discovered in this research - lower overall concentrations and the disappearance of two compounds related to DDT in shallow-water fish species, as well as overlap between contaminants found in sediment and those found in marine mammals and birds - indicate a worrying possibility that pollution is transferring from the ocean floor to the marine food chain.

"Regardless of the source, this is evidence that DDT compounds enter deep sea food chains," said Margaret Stack, an environmental chemist at SDSU and lead author of the study. She believes that this condition is worrying if the contaminant reaches marine mammals or even humans. DDT can cause serious health issues such as cancer and sexual disruption in humans.

Also read: Marine Pollution Threatens Fishermen's Livelihoods

Hoh stated that understanding the pathway of chemicals related to DDT entering the food chain is crucial. The findings will also help in mitigating and developing offshore activities that can worsen the problem.

Aluwihare said that there is still a lot of research that needs to be done to determine the exact source of the DDT contaminant they found in deep-sea fish. Another task is to see if the same contamination also occurs in larger, open-sea fish species that are consumed by humans.

Additional research is being conducted to answer these urgent questions. Researchers at Scripps and SDSU are currently analyzing samples from fish species targeted by recreational and commercial fishing, including bass and sanddab, for DDT+. Comparing the chemicals and concentrations found in these fish with sediment samples collected from the Palos Verdes Shelf and Dumpsite 2 allows the team to determine the source of toxins in the fish.

"We still see DDT contamination in deep-sea organisms and sea sediment more than 50 years after it was dumped there," said Hoh.