Last updated March 29, 2026.

In late 2020, scientists discovered that up to 500,000 barrels of DDT, a highly toxic and banned pesticide, had been dumped in the Pacific Ocean near Santa Catalina Island in Southern California. To make matters worse, the barrels are leaking. Some barrels, unbelievably, are leaking because they were deliberately punctured to make them sink easier. DDT is super toxic, so how did this happen?

Montrose Chemical Corporation

Montrose Chemical was the nation’s largest manufacturer of DDT, located in Los Angeles. Starting in 1947 and continuing through 1961 (and perhaps even later), the company instructed its employees to transport barrels of DDT and acid sludge waste and dump them into the ocean. 

This is in addition to a DDT deposit of about 110 tons on the ocean floor off the Palos Verdes Peninsula, covering 17 square miles of ocean floor. From 1947 until 1971, Montrose discharged DDT into Los Angeles County sewers that empty into the ocean. It is the largest known deposit of DDT in the world and the EPA declared it a Superfund site in 1996. The fish found in the Palos Verdes Shelf area contain high concentrations of DDT as well as PCBs.

So for decades, Montrose Chemical dumped DDT and DDT acid sludge both down the drains and into the ocean. But the barrels likely caused far more damage. According to the Los Angeles Times, a sediment sample showed DDT concentrations 40 times greater in the ocean floor from the barrel dumpings than the highest contamination recorded at the Superfund site created by the DDT sewer discharges.¹⁷

Now back at that time, the common ‘wisdom’ was that the ocean was so big that it would dilute even the most dangerous poisons. It’s hard to believe now that ocean dumping was an accepted practice then, but laws protecting the ocean didn’t exist. “Federal ocean dumping laws dated back to 1886, but the rules were focused on clearing the way for ship navigation. It wasn’t until the Marine Protection, Research and Sanctuaries Act of 1972, also known as the Ocean Dumping Act, that environmental impacts were considered.”¹⁸

There have been several lawsuits filed against Montrose and its successor company, Bayer Corporation. As of October 2021, the companies settled and have agreed to pay for the cleanup of contaminated groundwater at the Montrose Chemical Superfund sites in Los Angeles County. In May 2021, the Center for Biological Diversity filed a lawsuit against Montrose and Bayer. It calls for the companies to take responsibility for the areas affected by the DDT barrel dumping.¹⁹

 But the damage is already done. 

The Los Angeles Times wrote a comprehensive and fascinating series of articles on the Montrose DDT ocean dumping. I’ve listed them under Additional Resources and I encourage you to read them.

“DDT — the all-but-indestructible compound dichlorodiphenyltrichloroethane, which first stunned and jolted the public into environmental action — persists as an unsolved and largely forgotten problem.” -Los Angeles Times²⁰

DDT’s History

While many people have heard of DDT, and may even be generally aware that it is ‘bad,’ they do not know exactly what it is or how it was used.

DDT, or dichloro-diphenyl-trichloroethane, was first concocted by a German chemist in 1874. But someone discovered it was powerful as a synthetic insecticide in the 1940s. “It was initially used with great effect to combat malaria, typhus, and the other insect-borne human diseases among both military and civilian populations. It also was effective for insect control in crop and livestock production, institutions, homes, and gardens.”²¹ The person who discovered its effectiveness as a pesticide won the Nobel Prize. But even he cautioned that even he didn’t fully understand how the chemical interacted with nature.

The military used DDT to treat and prevent lice in soldiers during World War II. “The U.S. Army’s chief of preventive medicine, Brig. Gen. James Simmons, famously praised the chemical as ‘the war’s greatest contribution to the future health of the world.'”²² After WWII, it was sprayed everywhere and sold in household products and in lice treatments. Companies even advertised it as safe for children.

For decades, this chemical was used in neighborhoods, recreation areas, agricultural areas, and farms. Fogging trucks sprayed it in residential areas, such as neighborhoods and beaches, and airplanes sprayed over vast swaths of agricultural land. “During the 1940s, 1950s and 1960s, approximately 675,000 tons of DDT were applied to U.S. soil. The peak year for use in the United States was 1959 – nearly 80 million pounds were applied.”²³ Many insect populations developed resistance to the pesticide, which led to using increased concentrations of it.

“During summers in New Jersey, I remember the fog machine – at least, that’s what we called it, the fog machine; we loved it because it spewed out this mist, and my sisters and I would go riding after it on our bicycles so we could get lost in the fog. I remember our mother screaming at us to get away from it, just screaming. These were exterminators, who came almost every evening in the summer when the sun was setting, to kill mosquitos…I cannot imagine how they sprayed pesticides like that every night, and that kids were allowed to be out there in it.” -Alice Waters, referring to DDT fogging trucks²⁴

Banning DDT

Studies into the effects of DDT started as early as 1945, and scientists discovered fish, birds, and mammals died from exposure to it. Rachel Carson, a writer, scientist, and ecologist who worked for the U.S. Bureau of Fisheries, wrote some of the press releases about these studies and proposed writing a story for Reader’s Digest to reach a wider audience. But the publication turned her down. The New Yorker released Silent Spring as a series, and then Carson published the book in 1962.²⁵ It “exposed the hazards of the pesticide DDT, eloquently questioned humanity’s faith in technological progress and helped set the stage for the environmental movement.”²⁶

Carson’s research was instrumental in the eventual ban of the chemical, although that took 10 more years. Many big chemical and agriculture companies fought it. “Pesticide advocates claimed that without chemicals, agriculture would collapse. In 1963 Monsanto published “The Desolate Year,” a parody of “A Fable for Tomorrow,” Silent Spring’s opening chapter, which described a starving world without chemical pest control. The Montrose Chemical Company…publicized 1970 Nobel laureate Norman E. Borlaug’s prediction that without DDT and pesticides, modern agriculture would fail and mass starvation would ensue.”²⁷

At the very end of 1972, the EPA banned DDT use based on its adverse environmental effects, such as those to wildlife, as well as being a human carcinogen. Carson, herself, died of breast cancer at age 56, in 1964. The book is still in print today and frequently referenced. She was posthumously awarded the Presidential Medal of Freedom in 1980.

“We have seen that [pesticides] now contaminate soil, water, and food, that they have the power to make our streams fishless and our gardens and woodlands silent and birdless.” -Rachel Carson²⁸

DDT is Extremely Toxic and Poisonous 

DDT is highly persistent in the environment and in the body, meaning it does not dissolve or wash away. After the use of DDT was banned in the U.S., its concentration in the environment and animals has decreased, but because of its persistence, it still poisons.²⁹ The chemical affects the nervous system, reproductive system, the liver, and causes cancer. “Laboratory animals exposed to DDT develop hyperexcitability, tremors, incoordination, and convulsions,” rats became sterile after eating DDT, and it is highly toxic to aquatic animals and fish.³⁰ Human symptoms include vomiting, tremors or shakiness, and seizures, and is it acknowledged by both the EPA and CDC as a ‘probable’ carcinogen.

DDT is absorbed by ingesting, breathing, or touching products contaminated with the chemical. But people are most likely to be exposed to DDT from eating meat, fish, and dairy products. In the body, DDT is converted into several breakdown products called metabolites. One of these includes the metabolite dichlorodiphenyldichloroethylene (DDE). Both DDT and DDE are bioaccumulators, meaning the chemicals accumulate in the body’s fatty tissues. In pregnant women, DDT and DDE can be passed to the fetus and both chemicals are found in breast milk.³¹ These chemicals can then affect children’s overall growth and development, as well as brain development and function.

“How could intelligent beings seek to control a few unwanted species by a method that contaminated the entire environment and brought the threat of disease and death even to their own kind?” -Rachel Carson³²

Endangered Species

DDT completely infiltrates the environment and food chain because it bioaccumulates in ecosystems. It also enters the food chain through biomagnification, a process in which pesticide concentrations increase as one organism consumes another.³³

The chemical settles into sediment in the water, evaporates into the air, or is absorbed by marine life.”When it rained, DDT would wash off the soil and into the waterways. There, aquatic plants absorbed it and animals ingested it. Fish ate the plants and animals, and then eagles ate the fish.”³⁴ It permeates every aspect of any ecosystem.

DDT causes thinning of eggshells in birds, which is exactly how the American Bald Eagle became endangered, first declared in 1967. In fact, Carson’s Silent Spring was so titled because she was referencing the noticeable reduction of songbirds. “DDT levels become more concentrated as they travel up the food chain, and by the time apex predators like bald eagles ingest such chemicals by eating fish, other birds, and small mammals, the dose is potent…By disrupting the way their bodies process calcium, it caused sterility and weakened fragile eggshells.”³⁵ 

Eagles were not the only bird species affected by these toxins. Peregrine falcons were once on the brink of extinction because of DDE. Additional bird species negatively impacted by DDT and DDE included the brown pelican, Mariana crow, Northern Aplomado falcon, Mariana gray swiftlet, California condor, Wood stork, and marbled murrelet.³⁶ 

“DDT levels can register thousands of times higher in wildlife than in water.” -Brontë Spencer, National Wildlife³⁷

DDT in Our Environment Today

DDT doesn’t go away. Past contaminations of waterways still linger, and it still affects many species, including ourselves. There are hundreds of cases related to DDT’s continued long-term effects on humans and wildlife. The following are just a few of them.

“Used in great abundance during World War II to control malaria and typhus among the troops, [DDT] worked to kill off insects because it was an estrogen. Rachel Carson‘s 1962 book Silent Spring indicated that DDT was a cause of animal disease and human cancer. The pesticide was banned in the United States in 1972 and in Mexico in 1997. Here’s the kicker: DDT has been absent from the United States for four decades, yet its metabolite DDE can still be found in the urine of pregnant women, even those who were born after 1972. Among the many implications for health, the concentration of DDE in pregnant women’s urine predicts the weight of their children at age 3. Almost assuredly, DDE is creating extra fat cells before the baby is even born. Could this be driving childhood obesity?” -Dr. Robert H. Lustig³⁸

Arizona

The sign from Maricopa County, Arizona (see below) is a good example. Fish and aquatic wildlife are dangerous to eat because of DDT contamination. Additionally, residues from the chemical have made their way into the milk people drink. “DDE routinely shows up in trace amounts in Arizona’s milk supply, transferred to cows through hay grown in contaminated soil,” according to a 2005 article in the Phoenix New Times.

In 1958 alone, 500,000 pounds of DDT were applied to farmland in that area to fight the cotton bollworm. By the 1970s, the Gila [River] was the most DDT-contaminated stream in the western United States. In the 1980s, federal wildlife officials found that DDE residues in birds collected in the Goodyear-Avondale area were among the highest in the nation.” The state began posting signs like the one below in the 1990s.³⁹ 

Michigan

In St. Louis, Michigan, a Superfund site is still the likely culprit for dying birds. The Velsicol Chemical Corporation, formerly Michigan Chemical, manufactured pesticides until 1963. The EPA took control of the site in 1982 and the plant was demolished in the mid-1990s, but it left behind 3 Superfund sites in the small 3.5-square mile town. “Of most concern is the 54-acre site that once contained Velsicol’s main plant, which backs up to the neighborhood where residents have found dead birds on their lawns.”⁴⁰ 

Velsicol Chemical is infamous for a major chemical disaster in 1973, involving polybrominated biphenyls, or PBBs, a flame retardant compound it manufactured. The company accidentally mixed PBBs with a cattle feed supplement, poisoning thousands of cattle. This led to widespread contamination in Michigan.

There are still studies to monitor the effects of PBBs in the community. But not DDT, even though people find dead birds all the time. “The birds apparently have been poisoned by eating worms living in contaminated soil near the old chemical plant. No studies have been conducted to see whether the DDT has contaminated any vegetables or fruits grown in yards.” Beginning in 2006, the EPA began cleaning up homeowner’s yards to remove DDT and PBBs. But Velsicol was right on the Pine River, and its sediment was also contaminated with DDT and PBBs. “Traces of a chemical that is a byproduct of DDT manufacturing, pCBSA, have been found in the city’s water system, so new water mains will tap into a nearby town’s water supply.”⁴¹ It’s a never-ending battle with persistent chemicals for a company that made millions but no longer exists.

Arkansas

In 2014, researchers investigating white-nose syndrome in bats discovered something unexpected: high levels of banned pesticides, including DDT, in a colony of Rafinesque’s big-eared bats living near Bayou Bartholomew in Drew County, Arkansas. Despite being banned in the U.S. in 1972, DDT and its toxic metabolites were still present in local wildlife, more than 40 years later.⁴²

DDT Affects Grandchildren

Scientific American published an article in 2021 about the findings of Barbara Cohn, an epidemiologist at Oakland’s Public Health Institute, who studies the long-term effects of DDT. In a past study, she “found that the daughters of mothers exposed to the highest DDT levels while pregnant had elevated rates of breast cancer, hypertension and obesity.” But her newest study focused on the exposed women’s grandchildren and showed that the effects of DDT can persist for at least three generations. “The study linked grandmothers’ higher DDT exposure rates to granddaughters’ higher body mass index (BMI) and earlier first menstruation, both of which can signal future health issues.”⁴³ Given that DDT is a persistent chemical, this makes sense. But humans used it all over the world for decades. How many people had or have long-term illnesses or poor health effects from it?

DDT around the World

Some areas of the world still use DDT today to control mosquitos that transmit the microbe that causes malaria, a disease that kills millions of people. The EPA has been participating in international negotiations to control the use of DDT and other persistent organic pollutants (POPs) used around the world since 1996. Through the United Nations Environment Programme many countries negotiated a treaty, known as the Stockholm Convention on POPs, in order to enact global bans and/or restrictions on POPs, including DDT.⁴⁴

The Convention allows an exemption for the control of the spread of malaria. The World Health Organization (WHO) also supports the indoor use of DDT in African countries where malaria remains a major health problem. They believe that the benefits outweigh the health and environmental risks of DDT.⁴⁵

“While it’s illegal to use DDT in this country, it’s perfectly legal to manufacture and export it. Eventually, it finds its way back to us in foods grown abroad that have been treated with the chemical. So in addition to endangering animals around the world, we’re also poisoning ourselves.” -Jeff Corwin⁴⁶

Knowledge is Key

We have to protect ourselves from these chemicals. But it’s not as simple as staying away from contaminated areas, assuming you even know where they are and have the means to live elsewhere (not everyone does). Knowing the facts about DDT and other persistent chemicals is important. We have to fight for remediation and cleanups while protecting our health, children’s health, wildlife, and our own habitats. Thank you for reading. Please share and subscribe!

Additional Resources:

Article, “L.A.’s coast was once a DDT dumping ground: No one could see it – until now,” The Los Angeles Times, October 25, 2020.

Article, “Stunning DDT dump site off L.A. coast much bigger than scientists expected,” The Los Angeles Times, April 26, 2021.

Announcement, “Montrose Chemical Corp. Agrees to $77M in Consent Decrees in 31-Year Lawsuit Over DDT Pollution,” The Recorder, Law.com, October 04, 2021.

Press Release, “EPA Reaches $56.6 million Settlement for Groundwater Cleanup at Los Angeles Area Superfund Sites,” Environmental Protection Agency, August 14, 2020.

Parody, “The Desolate Year,” Monsanto Magazine, October 1962, accessed January 3, 2022.

Article, “Rachel Carson Dies of Cancer,” The New York Times, April 15, 1964.

Article, “Signs Warn Shore Anglers of Contaminated Fish,” Patch.com, June 3, 2011.

Footnotes: