For several years now, one question has held the key to understanding just
how much we should worry about the hundreds of tons of DDT that had been
dumped off the coast of Los Angeles:

How, exactly, has this decades-old pesticide � a toxic chemical spread
across the seafloor 3,000 feet underwater � continued to reenter the food
web?

Now, in a highly anticipated study, researchers have identified tiny
zooplankton and mid-to-deep-water fish as potential links between the
contaminated sediment and the greater ecosystem.

For the first time, chemical analyses confirmed that these deep-sea
organisms are contaminated by numerous DDT-related compounds that match
similar chemical patterns found on the seafloor and animals higher up on
the food chain.

�This DDT pollution happened several decades ago, there�s no new source,
it�s been banned ... but this old source is still polluting the deep-ocean
biota, which is really alarming,� said Eunha Hoh, whose lab at San Diego
State�s School of Public Health led the study�s chemical analysis. �We�re
not talking about zooplankton collected in 1960 � we�re talking about
zooplankton collected now, in the deep ocean, that is still polluted with
DDT.�

Hoh�s team had already found significant amounts of DDT-related chemicals
in present-day dolphins and coastal-feeding condors (and a recent study by
another team even connected an aggressive cancer in sea lions to DDT). But
even though DDT has clearly been accumulating at the top of the food
chain, how the DDT reached these animals has been somewhat of a mystery.
Key questions remain on whether it has been coming from more shallow
sources (such as the Palos Verdes Shelf Superfund site, where DDT had been
discharged for years via the sewer system), or from the deep-sea sediment
itself.

�It really [hits home] this concept that nothing is untouched,� said
Lihini Aluwihare, a chemical oceanographer whose lab at UC San Diego�s
Scripps Institution of Oceanography helped piece together the many multi-
disciplinary aspects to the study. �Establishing the current distribution
of DDT contamination in deep-sea food webs lays the groundwork for
thinking about whether those contaminants are also moving up through deep-
ocean food webs into species that might be consumed by people.�

The study, published Monday in Environmental Science & Technology Letters,
is one of many research efforts sparked by a 2020 Los Angeles Times report
that detailed the little-known history of ocean dumping off the Southern
California coast � and how the nation�s largest manufacturer of DDT had
for years disposed of its waste at sea.

One team of scientists, in an attempt to map and scan the seafloor for
DDT-related waste, discovered instead a multitude of discarded military
explosives from the World War II era. Another team unearthed records
showing that barrels of radioactive waste had also been dumped at sea.

And during an urgent investigation into old and forgotten records, the
U.S. Environmental Protection Agency discovered that from the 1930s to the
early 1970s, 13 other areas off the Southern California coast had also
been approved for all manner of dumping � including the disposal of
various refinery byproducts and 3 million metric tons of petroleum waste.

Image of a discarded, leaking barrel sitting 3,000 feet deep on the ocean
floor near Santa Catalina Island.
Climate & Environment

History of DDT ocean dumping off L.A. coast even worse than expected, EPA
finds
Aug. 4, 2022

As for the DDT, which is short for dichlorodiphenyltrichloroethane,
scientists have so far confirmed that much of what�s still sitting on the
seafloor remains in its most potent form and is buried barely 6
centimeters deep � raising concerns about just how easily it could
remobilize and spread by reentering the food web.

In a world dominated with concerns over microplastics and �forever
chemicals,� DDT persists as an unresolved problem � long after the
pesticide was banned in 1972 following Rachel Carson�s book �Silent
Spring.�

screenshot
Climate & Environment

Here�s what we know about the legacy of DDT dumping off L.A.�s coast
May 6, 2024

With this latest study, researchers sought to demonstrate how the chemical
is still likely making its way up from the deep seafloor by coming into
contact with zooplankton, which get eaten by deep-sea fish, which then
swim around and get eaten by midwater fish and marine mammals higher and
higher up the food chain.

Hoh joined forces with Aluwihare�s lab at Scripps, where a microbiology
team also provided sediment analysis and a deep-sea biologist helped
determine which organisms to sample � and where across Southern California
to collect them.

In addition to zooplankton, which are a window into the base of the food
chain, one particular type of fish, myctophids, proved to be key.

Also known as lanternfish, myctophids are tiny, unassuming fish that
travel remarkable distances from the deep ocean all the way to the
surface. (One of the most abundant and widespread fish in the world,
myctophids make up roughly 65% of all deep-sea biomass on Earth.) The
researchers methodically ground up each fish sample, extracted the lipid
(DDT tends to be stored in fat), and assessed the contamination with an
unprecedented level of scrutiny.

The findings have been sobering: Wherever they looked, they found DDT.
Even the �control� samples they tried to collect � as a way to compare
what a normal fish sample farther away from the known dumping area might
look like � ended up riddled with DDT.

�This is one of the missing pieces that we�ve been waiting to see,� said
David Valentine, who has been leading the broader research community on
this issue since his team at UC Santa Barbara first shed light on the
startling amounts of DDT still spread across the seafloor. �We know
there�s a ton of stuff down there ... but seeing these compounds in deep-
dwelling organisms really points to a link.�

A corroded, partially buried steel drum rises from the ocean seafloor.
Research into Southern California�s history of ocean dumping was spurred
by the discovery of mysterious and corroded barrels dumped off the coast
of Los Angeles. (David Valentine / ROV Jason)
Valentine, who was not involved in the study, noted a number of
interesting new clues.

One key to tracking the legacy of DDT through the marine ecosystem is
identifying and then comparing the patterns of every chemical that appear
in various animals � a technique called �non-targeted analysis.� That can
help fingerprint where all the DDT is coming from, and how it�s moving and
accumulating at different levels of the food chain.

Monitoring programs typically use a targeted approach � searching for only
four to eight specific DDT compounds. But by using non-targeted methods,
scientists in this new study were able to identify an entire suite of DDT-
related chemicals, including a particularly suspicious compound, TCPM,
that poses unknown threats to the ecosystem. These currently unmonitored
chemicals were also present in the blubber of dolphin carcasses that had
washed ashore, as well as in the sediment collected near the known dumping
area.

�This gives us a much more realistic view of what the potential ecological
and human health impacts can be,� said Mark Gold, an environmental
scientist at the Natural Resources Defense Council. The study, he says,
lays bare how the traditional approach to testing and monitoring for only
a few DDT compounds �grossly underestimates the concentrations of DDT in
the sediment and in organisms.�

Gold, who was not affiliated with the study but has spent more than 30
years pushing for DDT cleanup along the coast, said much more work needs
to be done on all fronts to truly reckon with the chemical�s legacy in
Southern California. In addition to the DDT spread across the deep sea and
the Palos Verdes Shelf, the mouth of the Dominguez Channel has also been
identified for decades as a hot spot.

The road ahead is long. Twenty-four members of Congress, led by U.S. Sen.
Alex Padilla (D-Calif.) and Rep. Salud Carbajal (D-Santa Barbara),
recently urged the Biden administration to dedicate long-term funding to
both studying and remediating the issue. Officials at the EPA, meanwhile,
have been considering their next steps in collaboration with a number of
state and federal agencies.

Academic research groups, including the ones in San Diego and the one led
by Valentine at UC Santa Barbara, are also continuing to seek answers.
Chief among them are determining the boundary of the dump site, mapping
the spread of the pollution and tracking its migration across the food
web.

For environmental chemists Margaret Stack, the first author of the latest
study, and fellow author Raymmah Garcia, a doctoral candidate at Scripps,
seeing once-popular pesticides such as DDT continue to move so pervasively
through the ecosystem makes them wonder about all the other chemicals
still being used today without question � chemicals that might also come
back to haunt us many decades from now.

�I often find myself feeling frustrated when looking at this data and then
seeing that we�re still using chemicals without testing them, without
understanding their impacts,� said Stack, a research specialist at San
Diego State�s School of Public Health. �It feels like we�re not doing
anything differently.�

�How many more times,� she said, �are we going to go through the same
story?�

https://www.latimes.com/environment/story/2024-05-06/concerning-levels-of-
ddt-found-in-deep-sea-fish-off-l-a