In her popular science work “Silent Spring” published in 1962, American author Rachel Carson told the story of the widespread use of pesticides represented by DDT, which caused irreversible harm to various organisms and the natural environment. Under the influence of the book, DDT has been banned in the United States since 1972. But in the past few decades, sea lions in California have been dying of mysterious cancers, until recently, after nearly 20 years of research by scientists, the mystery was finally solved – the existence of excessive levels of DDT in the sea lion’s living environment, PCBs and other chemicals, is the cause of their cancer.
In the background of DDT has long been banned, the U.S. West Coast near the water where a large number of DDT from the background of March 10 to 24, the University of California, San Diego Scripps Institution of Oceanography scientists through a scientific research, found in only 35 kilometers from the coast of Southern California, between Santa Catalina Island and Los Angeles coast, an area of 36,000 acres (about 145 square kilometers) of The bottom of the sea has at least 27,000 barrel-shaped objects suspected of containing DDT pesticide. Scientists analyzing sonar images of these anomalies collected by two deep-sea robots is “like counting the stars of the galaxy.
Half a million barrels of DDT-laden industrial waste on the seafloor near Los Angeles
This is not the first time scientists have found suspected evidence of incriminating DDT dumping in these waters. in 2011 and 2013, Professor David Valentine of the Department of Earth Sciences at the University of California, Santa Barbara, found 60 barrels deposited on the seafloor in the same area, and all of these barrels had extremely high concentrations of DDT around them. According to the Los Angeles Times, between 1947 and 1961, the Montrose Corporation, the largest U.S. producer of DDT based in Los Angeles, used to dump 2,000 barrels of DDT-laden industrial waste into this sea every month, discharging it into the Pacific Ocean.
DDT, chemically known as bis-p-chlorophenyl trichloroethane, helped soldiers fight mosquitoes and malaria during and after World War II, and was widely used worldwide to kill pests in crops, but is potentially harmful to birds, fish and humans.
For scientists at Scripps Institution of Oceanography, the newly discovered dump site was far larger than expected. The two-week study covered an area larger than the city of San Francisco, and scientists had trouble finding the boundaries of the dump site, with two deep-sea robots alternating down to a depth of 900 meters, each traveling up to 140 soccer fields in size per hour. The survey transmitted back more than 100 GB of sonar data. chief scientist Eric Trier, who led the expedition and is a professor at the Institute of Oceanography, said that based on analysis of sonar images, at least 27,000 barrel-shaped objects were eventually identified, and on the seafloor, more than 100,000 unusual objects and their debris were found, spread over 90 percent of the survey area. “The actual number of barrels should be more than 27,000, because some barrels are half-buried in the sediment and could potentially be missed in the computer analysis.”
Image credit: Screenshot from CBS8 video
By analyzing images of the survey area, the scientists found several different navigational tracks, meaning that the barrels, which may have contained industrial waste, were dumped repeatedly on the ship, with some lines as long as 18 kilometers, Trier said. “Although our mapping sonar was unable to measure the contents of the barrels, the target locations of the voyages were consistent with the previously identified dumpsites.” The area in which Trier’s team conducted this study was further expanded around the very site where Professor David Valentine of the University of California, Santa Barbara, found 60 barrels nearly 10 years ago. Valentine told China Newsweek that even so, in his opinion, there are still too many areas they have not covered and the means of observation taken may have been missed, so the number of barrels on the sea floor will be much higher. After Valentine discovered 60 barrels in 2013, he published his findings in the academic journal Environmental Science and Technology in 2019. Last October, the Los Angeles Times did a story on it, after which fellow academics and government officials emailed and called. It was against this backdrop that government agencies funded the Scripps Institution of Oceanography to conduct the scientific research.
Terrill said it has been an accepted practice for companies to dump industrial waste off the California coast since the 1930s. Over the next nearly 40 years, a total of 386 to 772 tons of waste is expected to have been dumped at offshore sites in San Pedro, Calif. In the midst of a wave of widespread use of DDT, Montrose opened a plant in California in 1947. According to the Los Angeles Times, as much as 767 tons of DDT was dumped into the nearby ocean from 1947 to 1961, according to projections from documents produced by Montrose. A young scientist at the California Regional Water Quality Control Board also found that when dumping, workers would use an axe to chisel away at the barrels in order to avoid them floating on the surface and not sinking. After DDT was banned in the United States in 1972, the Montrose plant continued to operate for another 10 years before it was discontinued because there was still a worldwide demand for it. At the time, little attention was paid to the dumping of deep-sea pollutants as people were more concerned about the destruction of ecosystems close to their own offshore. Around 2000, the U.S. Environmental Protection Agency (EPA) and other agencies began environmental remediation of this near-water area, which is still undergoing restoration. And according to the Los Angeles Times, there are still 500,000 barrels of industrial waste containing DDT waste on the ocean floor off the coast of Los Angeles, California.
Valentine told China Newsweek that while he doesn’t know exactly what the contents of the 60 barrels identified through sonar, imaging and other technologies are, “we did find an accumulation of ultra-high concentrations of DDT in the vicinity of those barrels.” The concentration of DDT in one collected sample was 40 times the highest contamination concentration in the near-water area of the Palos Verdes Peninsula. “With concentrations this high, this must indicate that it was dumped here and that there was a spill. Montrose is the only local producer of DDT and, moreover, out-of-towners know they dump here. This result is not too surprising.” Valentine said.
Photo credit: Screenshot from CBS8 video
Biomagnification in the food chain
Another key point of concern for scientists is the “biomagnification” of toxins through the food chain: they move up the food chain and accumulate in animal tissues, where DDT is highly insoluble in water, stored in fat and takes a long time to break down.
The California coast has been infested with DDT for decades, and in 1969, mackerel shipped from Southern California were recalled because they contained up to 10 parts per million of DDT, twice the amount considered safe for consumption by the FDA at the time. And tumors began to appear in some fish that feed on undersea creatures. That same year, eggs laid by California brown pelicans that feed on fish had levels of DDT broken down to 12 parts per million, and scientists found that these chemicals caused the eggshells to thin to the point of death for the young. Together with brown pelicans, bald eagles, peregrine falcons and other birds of prey in the waters around Southern California have since disappeared. And sea lions with more than one thousandth of DDT in their fat will lay their young prematurely. Broad-nosed dolphins in nearby waters have DDT levels of up to two parts per thousand.
In the Environmental Health Laboratory at San Diego State University’s School of Public Health, in recent years, scientist Enha Ho has found that DDT is involved in dolphins in unexpected ways. Like humans, dolphins have to care for their young and have longer life cycles, allowing them to observe the effects of long-term chemical accumulation on their bodies and the next generation. As the larger predator in the ocean, it is also an important reference indicator of the overall health of the marine system. She sampled the blubber of eight adult dolphins residing deep under the sea around the California coast, all of which had been washed ashore and had died. She was surprised to find that the dolphin blubber, which contained 45 DDT-related compounds, had far higher compound levels than those found in dolphins in Brazil or elsewhere in the world.
Whether DDT pollution has intensified or slowed down in Southern California in recent years is the question that Enha Ho is pondering. In its assessment for the Palos Verdes Peninsula near-water area, the latest response from the U.S. Environmental Protection Agency says the latest data shows DDT levels are twice what they were in 2009, and says that while fish near the coast are contaminated, nature is repairing itself and bald eagles and peregrine falcons are returning. Mark Gold, a marine scientist who has been concerned about DDT since the 1990s, finds the “natural remediation” argument disgusting. In Enha Ho’s view, although DDT was banned decades ago, Southern California is in a different situation. She’s been searching for the source of DDT’s continued presence, and when she hears about the scattered barrels on the ocean floor, the answer puzzle seems more complete.
A study published late last year in the Journal of Frontiers in Marine Science, which lasted 20 years, showed that for decades, California sea lions have been dying from a mysterious cancer that may be caused by toxic substances from industrial waste, pesticides, and oil refinery waste. Researchers extracted fat from 394 sea lions that contained excessive amounts of DDT, PCBs and other chemicals. The high levels of these compounds left in the environment became a trigger for cancer in sea lions.
The longer-term effects of these contaminants on the environment are uncertain, and their eventual effects on people are of greater concern. In a developmental biology and environmental toxicology laboratory at the Scripps Institution of Oceanography, Ambro Hampton found through molecular studies that “persistent organic pollutants” such as DDT and flame retardants can prevent a key protein from removing toxins from the body, which may also explain why toxic substances are enriched in living organisms. This may also explain why toxic substances are enriched in living organisms. Even in small amounts, they can affect the immune system. Other studies have shown that younger generations of women whose mothers’ generation was exposed to DDT may face a risk of breast cancer.
Lishini Alouvihare, professor of chemical marine and earth sciences at the Scripps Research Institute, said that the high levels of DDT in the food chain’s higher predators have been known to the public for some time in the waters of Southern California, USA. The size of the dump found this time helps explain some of the previously observed phenomena. “But at the same time it raises questions about what the potential effects of sustained exposure to these toxic substances will be on the health of marine mammals, and what the effects of DDT will be on generations of humans, and that’s something to think about.” How such large amounts of DDT will be converted between these organisms on the seafloor and how its breakdown products will enter the water, food, are questions that still need to be explored, said Alouvehale.
Now, Trier’s team hopes their findings will push the relevant government departments to clean up DDT. Valentine told China Newsweek that the next step should be to determine the level of contamination based on the full picture of the mapped contaminants, and to consider the transport and transformation of the chemicals and conduct research to determine further disposal measures. Although it is not known how many of the 27,000 barrels contain DDT, the Trier team’s research has prompted California Senator Dianne Feinstein to send a letter to the EPA in March asking for “urgent and meaningful action to remedy the serious threat to human and environmental health as a matter of priority. At a congressional briefing on April 26, Feinstein also said the Justice Department would be asked to identify the companies that may be responsible for illegal dumping and determine “whether they should be held accountable for it.
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