A long-banned pesticide lingers in fish across the US. Its toxic effects on the brain have never been incorporated into fish consumption advisories.

Six years ago, I worked at the Illinois Natural History Survey testing roadkill otter carcasses for contaminants that build up in the bodies of animals that eat fish.

Jocelyn Tamashiro

One of the contaminants we found was dieldrin – a banned pesticide formerly used on corn crops. Since otters and people share a habit of eating self-caught fish, I wondered about the science used to protect people from the potential dangers of dieldrin.

I collected pieces of information from the Food and Drug Administration, the Environmental Protection Agency, state agencies, and scientific studies. It became apparent that some states, including Illinois, still rely on an antiquated FDA standard for dieldrin that allows for people to be exposed to hundreds of times more dieldrin in fish than the EPA recommends. Other state agencies rely on EPA science that's half a century old – from a time when scientists were still in the dark about all of dieldrin's health effects.

In the decades since then, studies uncovered dieldrin's toxicity to the brain, including links between dieldrin and Parkinson's Disease. But just how much dieldrin may be "too much" for the brain remained unknown. That changed this year when a study used cell cultures from newborn rats to determine the amount of dieldrin that permanently changed the developing brain networks.

This new information may be the key to finally incorporating dieldrin's effects on the brain into fish consumption advice. But will state agencies be able to use it?

From soil to fish 

Estimated historical use of aldrin plus dieldrin in agriculture in the conterminous United States. (Credit: USGS)

In the 1950s, corn farmers, mostly those in the Midwest, began treating crops with the pesticide aldrin, which morphs into dieldrin in the environment. At the same time, people started using dieldrin to control termites and Japanese Beetles. In 1962, Silent Spring highlighted the use of dieldrin in Illinois. Environmental and potential human health concerns including cancer led the EPA to limit the use of aldrin and dieldrin in 1974; all uses were banned in 1987. Since then, dieldrin concentrations have been steadily decreasing in the bodies of fish in the U.S.

But it still remains. During 2008-2009, the EPA analyzed concentrations of contaminants in fish from rivers and streams of the U.S. Dieldrin was detected in 71 percent of samples, each of which consisted of five fish mixed together from the same location.

Dieldrin is "water-phobic," attracted to fat. It's bound to soil that's washed into aquatic environments. Small organisms ingest the contaminated sediment. Each time a fish eats a contaminated organism, most of the dieldrin transfers to the fish's fat. The same thing happens when a predator, whether otter or human, eats a dieldrin-contaminated fish. It takes the human body one year to excrete just half the dieldrin absorbed from a meal.

Dieldrin has been detected in the blood of people who eat self-caught fish. Studies have also confirmed dieldrin in fat-rich sites such as human brains and breast milk, as well as placentas, umbilical cords, and in the blood of infants.

Contaminant cocktails

When fish contain dieldrin, it's within a cocktail of contaminants. Ideally, protection from eating too much of one contaminant can protect fish consumers from eating too much of all the other contaminants.

"We live in a world where contaminants are everywhere, even in the Arctic. They even fall in the rain," Joanna Burger, professor at Rutgers University who has studied fish consumption around the globe, told EHN. "So fish everywhere have a mixture of contaminants."

Whether a certain level of a contaminant will be harmful depends in part on how much fish a person eats. This means exposure to dieldrin in fish is not only relevant to people who eat fish from sites where dieldrin was intensively applied in the Midwest.

It's also relevant in places where contamination may be lower, but fish consumption is high, such as tribal land. According to environmental regulators in both Guam & the U.S., the U.S. Territory of Guam is an example where sites with elevated levels of dieldrin contamination are also sites where people consume self-caught fish.

Setting standards without science 

Credit: Heather Mongilio/EHN

A lack of health-based standards for dieldrin begins in the soil that carries dieldrin to the fish in the first place. Earlier this year, a study reported that as of 2014, the amount of dieldrin in soil considered to be "too much" in Illinois was about 10 billion times higher than what was considered "too much" in Oregon. This type of standard has influenced decisions about whether to clean up dieldrin-contaminated soil. In Illinois, the limit for dieldrin in soil was not based on science about potential health effects.

Similarly, in some states, the use of an FDA standard has left the health effects of dieldrin out of decisions about fish consumption advisories.

When agencies use the FDA Action Level as a screening value, 300 parts per billion (ppb) of dieldrin is considered "too much" dieldrin in fish— the trigger for determining whether people should be given advice to prevent exposure.

It has been clear for decades that issuing advice based on the FDA Action Level for dieldrin is not protective of people's health. The origin of the FDA Action Level is unknown, likely pre-dating the EPA itself. In 1993, a guidance document for developing fish consumption advice in the Great Lakes stated, "…now there is general agreement that the current FDA tolerances for market fish are not adequately protective of public health, particularly those who consume sport fish." This statement was echoed in US EPA guidance in 2000.

During the EPA's national 2008-2009 fish tissue survey, the five states with highest concentrations of dieldrin were Ohio, Illinois, Indiana, Iowa, and Missouri.

Missouri and Indiana relied on the FDA Action Level for dieldrin until they stopped regularly testing fish for dieldrin. Illinois still uses the FDA Action Level. Last year the Illinois EPA found a fish from Lake Michigan to have 74 parts per billion of dieldrin, according to a Freedom of Information Act request obtained by EHN. Since it was well below the 300 parts per billion screening level, no action was required.

Inquiries to all three states about risk assessment for dieldrin garnered mixed responses. In Missouri, risk assessment for dieldrin will be reevaluated next year, Jeff Wenzel, Bureau Chief of Environmental Epidemiology in Missouri's Department of Health and Senior Services Bureau, told EHN.

In Indiana, there is no plan to reassess dieldrin, Ali Meils, environmental manager with the Indiana Department of Environmental Management, told EHN.

A statement provided to EHN by the Illinois Department of Public Health indicated that a new, health-based screening value for dieldrin has not been discussed or developed. A spokesperson added, "our challenges lie in developing laboratory capacity and acquiring equipment to test for new contaminants."

Among less dieldrin-contaminated states, Pennsylvania and New York still use the FDA Action Level for dieldrin, and Michigan used it until monitoring fish for dieldrin ceased.

In all of these states, it's unclear whether advice to protect people from the health effects of mercury or PCBs has prevented exposure to too much dieldrin. Especially since the FDA Action Level allows for 250-1,000 times more dieldrin in fish than the EPA recommends.

Cancer concern 

Credit: USGS

The EPA began providing guidance on how to screen fish based on the cancer potency of dieldrin in 1994. As of 2000, the agency recommends a cancer-based screening value of 1.5 ppb dieldrin in fish tissue for people who eat four meals of fish in a month (an even lower screening value is recommended for people who eat more fish).

However, since contaminants in fish tissue are not covered under the Clean Water Act, state agencies can decide whether or not to take the EPA's suggestion. "States, territories, or tribes are not required to issue fish advisories and can use toxicity information from sources other than EPA," Karl Markiewicz, Senior Toxicologist with the Centers for Disease Control and Prevention, told EHN.

Some agencies have taken the EPA's recommendation. For example, California, Delaware, Guam, Kansas, Florida, New Jersey, and Texas screen for fish based on the effect of cancer. With the exception of Florida, they all have fish consumption advisories for dieldrin in at least one body of water.

Two reviews about dieldrin and cancer that were published in 2014 came to different conclusions. One proposed that the estimated cancer potency of dieldrin be lowered; the suggested changes would result in an approximate doubling of the screening value in fish to about 3.5 ppb. The other review concluded the estimate for dieldrin's cancer potency should remain unchanged, and pointed to a need for more science on dieldrin and breast cancer.

Some scientists have pointed out that the benefits of eating fish likely outweigh any corresponding increase in cancer risk, and that cancer risks may be over-estimated. In states where cancer risk is considered an inappropriate basis for fish consumption advice, they instead focus on dieldrin's ability to cause liver damage. This typically results in a screening value between 100 and 200 ppb. In 1988, liver damage was identified by the EPA as the worst non-cancer health effect of dieldrin, based on research conducted with rats in 1969.

Toxic brain effects

In the decades since then, brain-altering effects of dieldrin have become apparent. Studies suggest dieldrin makes the brain more vulnerable to Parkinson's Disease, especially in people with certain types of genes.

One study found that people who were exposed to dieldrin both at work and at home were 6 times more likely to develop Parkinson's Disease compared to people who did not have a history of exposure. Elevated concentrations of dieldrin have been identified in the brains and blood of Parkinson's Disease patients.

Exposure to dieldrin in the womb or via breastmilk may also change the brain's vulnerability to Parkinson's Disease. A study found that when female mice were exposed to dieldrin, their pups had lasting brain alterations that rendered them more vulnerable to Parkinson's Disease later in life – even when there was no dieldrin in their bodies as adults.

However, until this year, a specific concentration of dieldrin that may be "too much" for a brain was unknown. In January, a study published in Toxicology and Applied Pharmacology identified a "point of no return" when dieldrin was added to developing brain cell cultures from newborn rats. As the neurons developed networks and fired electrical bursts of activity, the researchers applied different concentrations of dieldrin to find the amount of dieldrin it took to permanently alter the way that brain networks developed.

But will any of this new information change fish advisories?

Using modern science 

Credit: Jocelyn Tamashiro/Environmental Restoration, NAVFAC Pacific

To understand whether there is a standard method for using results from studies on animal cells to extrapolate to risk to human health, I spoke with Ivan Rusyn, professor of toxicology at Texas A&M who develops tools to study the health effects of chemicals.

According to Dr. Rusyn, results from studies on cells are currently not used at all to calculate the risk posed by a chemical like dieldrin. When I asked how long it may be until a method for this will be widely used, he said, "probably not in the next 5 to 10 years."

However, the same regulatory freedom that allows state agencies to use no science at all in determining how to protect fish consumers also allows them to use the best available science, such as the tools that scientists are actively developing for using cellular data to estimate the risk of chemicals.

One potential obstacle in applying these tools to dieldrin is the dilemma that risk assessors typically face in deciding when new science should change environmental standards. James Fabisiak, associate professor of environmental health at the University of Pittsburgh and director of the Center for Healthy Environments and Communities told EHN, "On one hand, it's impractical to reset regulatory thresholds each time a new paper is published. On the other, the wheels of policy-making move much slower than scientific technological advancement."

When asked about this dilemma with regards to dieldrin, Fabisiak continued, "Dieldrin seems like an excellent case-study with which to incorporate this new paradigm. The data seem compelling, point to a serious health effect previously ignored, and would receive little resistance from industry considering the use of dieldrin is already banned."

If attempts to use these new techniques are successful, state agencies can assess whether current fish consumption advice is adequately protective of developing brains. This is relevant to parents and women who may become pregnant, including Native Americans, a group identified with a high prevalence of Parkinson's Disease.

Even if attempts to use these new techniques fail, the health of people who eat self-caught fish can still benefit from agencies re-evaluating their environmental standards for dieldrin. Zijian Li, author of the recent study on screening values for dieldrin in soil, engineer associate at Parsons Corporation, commented on the implications.

"When we fail to develop environmental standards from a human health perspective, we endanger ourselves, we endanger the next generation."