Dioxin for Dinner?
Questions and Answers
Bonnie Liebman / Nutrition Action Healthletter 1oct00
increases as Fat intake increases
Reduction of dietary fats is important.
It's the most potent animal carcinogen ever tested. Evidence is building that it causes birth defects, diabetes, learning and developmental delays, endometriosis, and immune system abnormalities.
How can one chemical and its relatives be so devastating to so many parts of the body?
"Dioxin is diabolic," says epidemiologist Richard Clapp of the Boston University School of Public Health. "That's why I call it the Darth Vader of toxic chemicals. It disrupts many systems. You don't want it in your neighborhood."
Or in your food. Ninety percent of the dioxin that enters our bodies comes from meat, cheese, milk, butter, and other foods that contain animal fat.
Q: What is dioxin?
A: It's a complicated family of 75 chemicals, including dioxins, furans, and PCBs. One of the worst dioxins is 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). The molecule binds particularly strongly to intracellular receptors in the nuclei of animal and human cells. So dioxin can easily get into the nucleus, where the cell's DNA is located, and wreak havoc. If it damages the DNA, that could cause cancer or birth defects. It could also alter the DNA's instructions to make normal enzymes, hormones, and other proteins, which could lead to any of a number of diseases.
Q: Are the receptors there to admit things the cell needs?
A: We're not sure exactly what the receptors do. But we know that they allow the cell to respond to signals and reproduce genes and that they pick up other diesel toxins, like benzopyrene from diesel fuel or tobacco smoke.
Q: What about dioxin's cousins?
A: The polychlorinated dibenzofurans--often called furans--are closely related to dioxin. So are PCBs, or polychlorinated biphenyls [see "All in the Dioxin Family," p. 4]. There are 135 furans and 209 PCBs. Of the 419 chemicals from all three families, 30 have dioxin-like toxicity, but we're usually exposed to a mixture of toxic and non-toxic members of each family at the same time.
Q: How do they get into the environment?
A: PCBs were used as insulators in electrical equipment, but their production was banned in 1977. Today, they're mainly found in electrical transformers in large office or apartment buildings. When there's a fire in an old building, they're released into the atmosphere. That's unfortunate because when you burn PCBs, it produces furans, which are more toxic than PCBs.
Dioxins and furans can be produced when almost anything is burned under the right conditions. So two big sources have been municipal waste incinerators and hospital incinerators, though recently, government regulations appear to have cut those emissions dramatically.
Bleaching wood pulp with free chlorine to make paper white has been another major source. Dioxin is released into the waste water, although the amounts have declined because most plants no longer use free chlorine.
Q: How does dioxin get from incinerators to people?
A: It goes into the air. People can breathe in the particles, but a bigger problem is that the particles can settle on grazing land. Cows eat the grass and the dioxin gets concentrated in the fat in their meat and milk. It also gets concentrated in cattle and hogs that are fed dioxin-tainted grain.
Dioxin particles can also fall into rivers, streams, and other bodies of water--or get there in runoff. It settles on the bottom. When fish and shellfish ingest small particles of sediment, dioxin builds up in their fat or organs. In Maine, pregnant women are advised not to eat the green stuff in lobsters because it's high in dioxin. People call it the "tomalley," but it's actually a combined liver and pancreas--a hepatopancreas.
Q: So the dioxins get concentrated as they move up the food chain?
A: Yes. More than 90 percent of our exposure comes from food, mostly fish, meat, poultry, and non-skim dairy products. Fattier fish have more than leaner fish. Shellfish like lobsters are low in fat, but the dioxin may be in their hepatopancreas or organs, not the meat.
Q: And it accumulates in our bodies?
A: Yes. It's like the daily newspaper. It comes into the house every day but you don't notice it. It has a cumulative effect.
Q: Can you get rid of dioxin?
A: Yes. There's a dynamic within the body of accumulation and excretion of toxic substances. Dioxin is accumulated in fat, so if you lose weight, you lose some with the fat. If you're breastfeeding, you get rid of it through the breast milk. Humans get their greatest dose of dioxin during breastfeeding because it's concentrated in breast milk and because the infant is so small that the dose per pound of body weight is quite high. The benefits of breastfeeding still outweigh the risks of dioxin, though we'd rather not have to make such a choice.
Q: How long does it take to get rid of dioxin?
A: Its half-life is about seven years--in other words, it takes seven years for half of it to be excreted by the body. The average levels of dioxin in the U.S. population are declining, according to the Environmental Protection Agency [EPA]. So a 40-year-old today has less than a 40-year-old would have had 15 years ago.
ONE IN A HUNDRED
Q: What harm does dioxin cause?
A: First of all, it's a known carcinogen. TCDD is the most potent animal carcinogen ever tested. It causes tumors in both genders of every species and every strain of animal that's been tested. And the animals get different types of tumors, so it doesn't just initiate tumors, it also promotes the growth of tumors caused by other initiators.
Q: And it's more potent than we thought?
A: Yes. The EPA recently released a draft report that projected an excess cancer risk of one in 100 for the most sensitive people who consume a diet high in animal fats. In other words, the risk of getting cancer from dioxin--over and above the risk of cancer from other sources--is one in 100 for some people. That's a worst-case scenario. It's for the most sensitive responders among the five percent of the population who consume the most dioxin. It's an upper bound estimate--the lower bound is zero. But it's still shocking.
And the EPA's draft estimates that the upper bound risk for the most sensitive responders to average exposure is one in 1,000. That's not a small risk.
Q: Are the EPA's draft estimates reliable?
A: They're the most reliable ones we have. The estimates now go to the EPA's Scientific Advisory Board, which includes outside consultants to the agency. I was a consultant on the Board five years ago, when it reviewed the EPA's last estimates. But there are also representatives from the American Paper Institute and consultants from industry-funded groups like Harvard's Center for Risk Analysis.
Q: What happened at the Advisory Board's last review?
A: In 1995, the Board told the EPA to redo parts of the risk estimates. That led the agency to gather more science to justify its final draft. But the evidence led the agency to increase its risk estimates, so it backfired on the industry folks. Since then, several studies have looked at workers who sprayed or manufactured herbicides that contained dioxin, and data showing how much harm was caused by each level of exposure to the herbicides were added to the animal data.
Q: What kind of cancer does dioxin cause in people?
A: Some studies suggest that it promotes soft-tissue sarcomas, which are cancers of the fat and muscle, and lung cancer. Most of the studies indicate an increased risk of all cancers. They don't focus on one because there are so few individual cancers in small studies of exposed populations.
Q: How powerful is dioxin compared to other carcinogens?
A: It doesn't cause as much cancer as smoking. It may be in the same ballpark as radon or second-hand tobacco smoke. But that's based on mathematical projections from models, and all of the projections are shaky.
Q: Do dioxins impair learning behavior?
A: PCBs appear to lower IQ or cause developmental delays in the children of women who ate large quantities of PCB-tainted fish during pregnancy. The studies that monitor these children are still going on, so we don't know for how long the adverse effects last. Up until age seven, researchers are still finding measurable developmental delays. Over time, those delays may become imperceptible, but we don't know about IQ.
It's also possible that PCB exposure may only affect learning in a minority of children who, for some reason, are more vulnerable. In one study, a majority of highly exposed children scored in the normal range on a memory scale. But a minority was also twice as likely as other kids to score in the "poor" range.
Q: How does dioxin affect reproduction?
A: Dioxins seem to impair the development of the human reproductive system. There have been case reports of hypospadias--a birth defect in which the urethra opens on the underside of the penis--in populations exposed to dioxin.
Researchers have also found a decrease in the number of male babies born in Seveso, Italy, since July 10, 1976, when there was an explosion at a chemical plant making pesticides like 2,4,5-T--the "T" stands for trichlorophenoxyacetic acid. The containment vessel exploded, sending a black plume of smoke into the sky. Black dust and particles of the dioxin-contaminated pesticide fell on people who lived miles downwind from the explosion. The dioxin killed pets and contaminated the soil.
A recent study of former Seveso residents compared the ratio of males to females born in Zone A, which was closest to the explosion, and Zone B, which was further away, to ratios elsewhere. Usually, 51 percent of newborns are male and 49 percent are female. But among children of men who lived in Seveso, only 44 percent were male in the years since 1976. And among children of men who were younger than 19 when the explosion occurred, only 38 percent were male.
Zone A is still evacuated, 24 years after the explosion. In the U.S., dioxin was the most worrisome contaminant at Times Beach in Missouri and at Love Canal in New York State.
Q: How might dioxin harm males?
A: We don't know. One theory is that it's toxic to the male fetus. Another is that it damages the Y chromosome, so sperm with Y chromosomes don't fertilize eggs. It's the Y chromosome that makes a fertilized egg develop into a male.
Q: Does dioxin have other effects on males?
A: Yes. In animal studies, we see decreased testicular size and decreased sperm production. That's in adult rats who were exposed to dioxins before they were born. Dioxin also lowers testosterone levels in men.
Q: And it causes birth defects?
A: Yes. During the Vietnam War, the U.S. military used an herbicide called Agent Orange to defoliate the jungles of Southeast Asia. The herbicide is 50 percent 2,4,5-T. Small amounts of dioxin are produced when 2,4,5-T is made, so it's an unavoidable contaminant. Studies on Vietnam vets exposed to Agent Orange suggest that their children have an increased risk of spina bifida.
That's a birth defect that occurs when the neural tube--which develops into the spinal cord--fails to close during the first six weeks of gestation. Children born with spina bifida often lack bowel and bladder control, and many are paralyzed from the waist down or suffer from mental retardation. The evidence that dioxin causes the defect is strong enough that Vietnam vets are compensated if their children are born with spina bifida.
Other than that, we don't have strong evidence that dioxin causes specific birth defects in humans. But in animal studies, it's a powerful teratogen--something that causes birth defects. Its teratogenic effects in animals are as dramatic as its carcinogenic effects. It causes different defects in different organs in different species and strains of animals. For example, it causes cleft palate in mice, malformed kidneys in rats, and extra ribs in rabbits.
Q: Does dioxin impair the immune system?
A: Yes. One of the EPA's dioxin experts, Linda Birnbaum, calls dioxin an "immune modulator," because it makes the immune systems of animals both under-reactive and overreactive to stimuli. An over-reactive immune system may raise the risk of auto-immune diseases like lupus. An under-reactive immune system is less able to respond to an antigenic challenge--that is, it makes vaccines less effective and leaves the animal less able to fight off infections and possibly diseases like cancer.
The evidence in humans is limited. But after the residents of Quail Run, Missouri, were exposed to dioxin-contaminated oil and debris from Agent Orange manufacturing plants, they had a large number of welts on a skin-prick test, which is designed to detect allergies. That meant that they were allergic to many things--it's a sign of an over-reactive immune system--though the welts diminished over time.
Q: Does dioxin cause diabetes?
A: The risk of diabetes seems to be elevated in the Ranch Hands--the Air Force troops who had the job of spraying Agent Orange in Vietnam. Researchers recently studied Ranch Hands who weren't exposed to Agent Orange, which means that their dioxin levels were similar to most Americans'. They found that those with higher dioxin levels--within the normal range--had a higher risk of diabetes than those with lower dioxin levels.
Q: Does dioxin have any other long-term effects?
A: It has been shown to cause either endometriosis or a proliferation of endometrial tissue in monkeys, mice, and rats. In humans, the evidence is less clear, but one small study found higher levels of PCBs in infertile women with endometriosis than in infertile women without the disease.
Q: Which of dioxin's adverse effects are conclusive?
A: Everyone, except perhaps some industry groups, accepts that dioxin is a human carcinogen. IARC, the International Agency for Research on Cancer, which is part of the World Health Organization, reclassified it as a human carcinogen in 1997. The studies on veterans are strong enough that they get compensated if their children are born with spina bifida. We have animal evidence for developmental delays and reproductive hormonal effects. The human evidence is not as strong for endometriosis and immunotoxic effects.
Epidemiologist Richard Clapp is an associate professor of Environmental Health at the Boston University School of Public Health. He has done extensive research on veterans and workers who have been exposed to dioxin. Clapp spoke to Nutrition Action's Bonnie Liebman.
RELATED ARTICLE: DODGING DIOXIN
It starts out as emissions from incinerators and spills from electrical transformers. It ends up in cheeseburgers, chicken wings, and pizza.
Dioxin and its chemical cousins, the furans and the dioxin-like PCBs, make their way from the air, water, soil, and sediment into plants. As animals eat the plants, and people eat the animals, the concentration of dioxin climbs.
Clearly, one way to minimize your exposure to dioxin is to avoid animal foods, including dairy products. A more targeted approach is to eat less animal fat, since that's where dioxin and its fat-soluble relatives reside.
"In most instances, anyone who reduces the amount of animal fat in their diet will reduce the amount of dioxin they consume," says Dwain Winters of the U.S. Environmental Protection Agency (EPA). "Vegans--who eat no animal products--should get the lowest levels, but ovo-lacto-vegetarians who substitute full-fat dairy products and eggs for meat can be exposed to levels similar to those found in a typical diet."
The EPA recently released draft estimates of dioxin, furan, and PCB levels in beef, pork, poultry, milk, and seafood (see "The Dioxin is Cast"). The seafood numbers aren't as bad as they seem. The EPA's draft estimates for dioxin levels in fish and shellfish are higher than for other animal foods, but they're the least certain because only limited information is available.
Dioxin levels in fish and shellfish are the toughest to estimate "because it's much harder to get representative samples of the seafood we eat," says Winters. "And the levels of dioxin depend on where the fish live, what they have eaten, and where they are on the food chain."
Most of the seafood people eat is marine or farm-raised freshwater fish, which have lower levels of dioxin than wild freshwater fish. Two of the most commonly eaten fish are pollock--the white fish that ends up in most fish sticks and fried fish sandwiches--and tuna. "They tend to have lower levels of dioxin because they live in open marine waters that are cleaner," says Winters.
Catfish is the most popular freshwater fish, thanks to restaurants like Red Lobster and Cracker Barrel. Most catfish and trout are now farm-raised and fed largely plant meal, which means that they tend to have lower dioxin levels than their wild-caught, carnivorous cousins.
"EPA's draft freshwater fish numbers are taken from wild-caught fish in the late 1980s," says Winters. "They're not necessarily indicative of wild fish caught today or farm-raised freshwater fish." As for salmon, "much of it is farm-raised in the ocean, but you'd expect even wild-caught salmon to be lower in dioxin, because they spend their adult life in the ocean."
Other fish, like rockfish, striped bass, snapper, and redfish, might have more dioxin, because they often breed in estuarine waters. That's where the ocean meets freshwater, so it's more contaminated than the oceans.
"Seafood in the marketplace is harvested from all over the globe, not just from our local waters," says Winters, "which means that overall you're less likely to get dioxin-contaminated seafood. There's a great leveling."
And because dioxin in the environment keeps dropping, older data may not reflect current levels. "More effort is going to be put into measuring dioxin levels in fish and shellfish," says Winters, "and we also want to periodically go back and do beef, pork, poultry, and other foods because everything's changing."
It's not seafood, but the animal fat from meal poultry, seafood, and dairy foods that boosts the average person's dioxin burden the most. But you can't take the EPA's draft estimates at face value.
The beef, pork and poultry numbers represent averages for all cuts. If you eat leaner cuts of meat (like sirloin, round steak, or pork tenderloin) or poultry (like breast or drumstick), you get less dioxin. Trimming fat and skin is a key strategy, and that goes for the skin of fish, too.
And you can avoid much of the dioxin in milk, cheese, yogurt, and ice cream by buying fat-free or low-fat versions. Likewise, egg whites or the egg substitutes made out of egg whites (like Egg Beaters) should have less dioxin.
But there's a catch: For middle-aged or older adults, eating less dioxin now doesn't mean you've cut the amount of dioxin in your body proportionately.
"If you cut your dioxin intake in half, you haven't reduced your overall risk in half," says Winters. "It's not that you are what you eat; you are what you ate. Your body burden is a product of your lifetime consumption, and adults who make radical shifts in their diets don't get immediate results. But reducing the intake for children for their lifetimes is going to have more of an effect.
"Many of us are still carrying the exposure from the 1950s and '60s, when levels in the environment were much higher. My three-year-old daughter will have much lower levels than mine when she grows up."
The Good News
Today's children will be exposed to less dioxin because the EPA has cracked down on the major sources.
"Our regulations will reduce the dioxin emitted from municipal and medical waste incinerators and from pulp and paper facilities by at least 95 percent," says Winters. Most of these regulations will be fully in effect by 2002, but most incinerators and paper-making plants are already meeting the levels set by the regulations.
"For instance, in the late 1980s, municipal incinerators were emitting more than 8,000 grams of dioxin a year in the U.S.," says Winters. "Under the new regulations, they'll emit less than 12 grams.
"Now that we've addressed the major industrial sources, we're shifting our focus to better understand how uncontrolled combustion, like backyard trash-burning and forest fires, contributes dioxin to our food supply."
THE DIOXIN IS CAST
The numbers for dioxin in freshwater fish do not reflect current levels in the most popular farm-raised fish, like catfish, salmon, and trout. What's more, the numbers are averages. Lower-fat versions of these foods have less dioxin--and higher-fat versions have more--than shown here.
Dioxins, PCBs, Food (4 oz. unless & Furans otherwise indicated) (picograms)(1)
Freshwater fish 274
Marine shellfish 95
Marine fish 70
Eggs (2) 13
Milk (1 cup) 11
Vegetable oil (1 Tbs.) 1
(1) Because all foods contain a mixture of dioxins, furans, and PCBs, the Environmental Protection Agency's draft estimates give greater weight to the most harmful contaminants.
Source: Adapted from "Draft Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds," Volume 3, Chapter 3, Table 3-56, U.S. Environmental Protection Agency www.epa.gov/ncea/pdfs/dioxin/part1and2.htm , click on Volume 3, Chapter 3).
For more information, see www.epa.gov/NCEA/dioxin.htm
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