Trophic Cascade and Biomagnification: Should I eat the fish in Utah lake?

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TROPHIC CASCADE AND BIOMAGNIFICATION PACKET
Trophic Cascade
Bringing the Wolf Back to Yellowstone
Returning the Wolves is Helping Balance the Yellowstone Ecosystem
© Dorothy Patent

Wolves were killed off in Yellowstone in the 1920s, creating unforeseen ecological problems. Now the ecology is healing since wolves were returned 14 years ago.

Yellowstone National Park was established in 1872, mainly to preserve its geologic wonders--geysers, hot springs, colorful mud pots and spectacular canyons and waterfalls--for tourists. But park visitors also enjoyed the wildlife such as elk and deer, but they didn't appreciate the predators that hunted these animals, especially wolves. This attitude resulted in the wholesale slaughter of the Yellowstone wolves. By 1926, the wolves were all gone.
After the Wolves Were Gone, Elk Increased in Population
Safe from the wolves, elk became more numerous in the park as the years passed. When winters were mild, many elk survived, and without wolves to keep the population down, elk numbers swelled. Park rangers stepped in to control elk numbers. They trapped the elk and sent them to other parks and preserves, but sometimes they had to shoot hundreds of them to keep the population down.
The elk became complacent, hanging out in the shade of trees along the creeks and rivers and eating the tender shoots of young willows and aspen. These trees have a short life span, and before long, few young trees grew to replace the old ones.
Fewer willows and aspen meant fewer beavers, which use these trees for food and building materials for their lodges and dams. Since beaver ponds, with their surrounding trees, provide habitat for a great variety of birds, fish, frogs, and other living things, these, too, became less common in the park.
Too Many Coyotes
Without wolves, their smaller cousins, the coyotes, became more numerous. Coyotes feed on everything from elk calves to insects. But they eat mostly small rodents such as ground squirrels. With too many coyotes, life became harder for other small predators like foxes and badgers.
Another favorite food of coyotes is fawns of the pronghorn, an animal unique to North America. As the years went by, scientists wondered if the decline of the pronghorn population in Yellowstone was at least partly due to coyote predation on the fawns.
Consequences of Bringing Back the Wolf
As they learned more about the interconnections in nature among the animals and plants, ecologists and wildlife managers realized that Yellowstone needed wolves in order to provide a healthy, more complete ecosystem.
After years of political battling, wolves trapped in Canada were transported to the park and released in 1995 and 1996. They were kept in large pens at first to get them used to their new home. Once they were free, the wolves thrived and multiplied, and scientists began seeing positive changes in the ecosystem.
The wolves kept the elk on the move, so they can't hang out along the streams and rivers. The aspen and willows began growing back, and now more beaver have made their homes in the park. Thus the birds and other wildlife that depend on the ponds are returning, too.
The wolves killed and chased away many of the coyotes, giving the other small predators a better chance of survival. The pronghorn population also seem to be doing better now with fewer coyotes as well.
Even the grizzly bears seem to be benefiting from wolf return. When grizzlies leave their winter dens in the spring, they need to eat quality protein. Grizzlies are much bigger than wolves and can bully them away from their kills, providing the grizzlies with what they need to regain their strength in the springtime.
Lessons for Ecosystems Everywhere
The apparent improvements in how the Yellowstone ecosystem functions since wolves were returned show just how interconnected all the elements of an ecosystem are. Remove one piece, especially a major piece like a top predator, and unforeseen problems can develop. Fortunately, returning that piece of the puzzle can help heal the system.
References
Patent, D.H. (2008) When the Wolves Returned: Restoring Nature's Balance in Yellowstone
Smith, D.W. and G. Ferguson (2005) Decade of the Wolf: Returning the Wild to Yellowstone
The copyright of the article Bringing the Wolf Back to Yellowstone in Ecosystem Preservation is owned by Dorothy Patent. Permission to republish Bringing the Wolf Back to Yellowstone in print or online must be granted by the author in writing.

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Journal of Medical Entomology. 40(3): 338–347. 2003.

Biomagnification: The tendency of certain chemicals to become concentrated as they move into and up the food chain. training.fema.gov/EMIweb/downloads/is5/glossary%20appdx%20a.doc


http://www.friendsofstclair.ca/images/biomagnification2-copy.jpg
Often, industrial pollutants which exist in trace amounts in the environment (such as certain heavy metals and organic agents found in pesticides) become concentrated in creatures near the top of the food chain. In an estuary, for example, microorganisms called plankton may absorb small amounts of pollutants such as PCBs (polychlorinated biphenyls); fish that eat lots of plankton might retain the pollutants in their tissues; birds or people that eat the fish might concentrate the pollutants still more. This process, called biomagnification, can produce health problems for animals in an ecosystem, including humans! http://www.nationalgeographic.com/xpeditions/lessons/08/g912/greatlakes.html

http://www.btoxicfree.com/images/biomagnification%20in%20the%20food%20chain.gif

http://www.gulfofmaine.org/images/gulfwatch/biomagnification.jpg

http://www.permaculture.org.au/images/biomagnification.gif

http://www.woodrow.org/teachers/esi/1997/10/biomag.gif


Contaminants in the Arctic Human Population (from Loke Films and teacherdomain.com)
The animals and people who live in the cold Arctic environment rely on fat in their bodies for both insulation and for energy. Unfortunately, toxic chemicals known as persistent organic pollutants (POPs) are lipophilic, meaning that they have an affinity for fat and accumulate in fatty tissues and organs. In addition, organisms in the Arctic are particularly vulnerable to pollutants because atmospheric circulation and ocean currents carry pollution from lower latitudes to the Arctic, where the cold conditions trap the contaminants and prevent further migration.
Pollutants, such as polychlorinated biphenyls (PCBs) and mercury, are released into the environment through various industrial and agricultural processes. In the environment, mercury can convert to methylmercury—an organic form of mercury that is particularly toxic and easily absorbed by organisms. These pollutants enter into ecosystems at the bottom of the food chain when organisms absorb them from the air and water. In species at low trophic levels on the food chain, the concentrations of contaminants are not much higher than those found in the air and water. However, once the contaminants enter the food chain, they can reach toxic levels through the process of biomagnification. When a predator consumes its prey, it takes in all the toxins in the organism as well as the food energy; the more contaminated organisms it eats, the more toxins it acquires and stores in its fatty tissues. Thus, at each successive trophic level, the contaminant burden increases.
People who consume the fat and meat of contaminated animals are at risk from exposure to high concentrations of toxins; POPs can affect reproductive, neurologic, and immunologic health. However, different populations of people in the Arctic have different diets and therefore have varying health risks. For example, whale is a common traditional subsistence food source; however, some types of whale are more toxic than others. The Iñupiat in northern Alaska hunt bowhead whales. These are baleen whales that primarily eat krill and shrimp, which are organisms low on the food chain. Thus bowhead whales accumulate low levels of contaminants and do not pose much risk to the people who eat them. On the other hand, people in the Faroe Islands are at greater risk because they eat pilot whales, which are higher on the food chain (they eat squid and fish). The people in the northern and eastern regions of Greenland are also exposed to high levels of toxins; as part of their traditional diet, they eat polar bear, which is at the top of the Arctic food web, and, as a result, has the highest level of contaminants of any Arctic species.
With respect to POPs, eating animals from lower trophic levels will reduce the health risks. However, proximity to source regions of pollutants also affects contamination levels. For example, there are higher concentrations of POPs in the western North American Arctic, near industrialized Asia, compared to farther east. Thus, public health advisories must be made regionally. Such advisories consider pollution levels as well as weigh the risks and benefits of altering the traditional diet, which—in addition to providing important nutrients—is part of a cultural identity.

Governments Link PCBs and Cancer

Most government health agencies, including those listed below, consider PCBs a "probable carcinogen" for humans and a "known carcinogen" for animals, based on extensive cancer research studies included on these pages. All PCB mixtures cause cancer in animals.
World Health Organization
U.S. Environmental Protection Agency (EPA)
U.S. Department of Health and Human Services (DHHS)
U.S. Agency for Toxic Substances and Disease Registry (ATSDR)
The International Agency for Research on Cancer (IARC)
The National Toxicology Program
The National Institute for Occupational Safety and Health (NIOSH)
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Local Cancer Risks
In 1991, the U.S. Environmental Protection Agency estimated that 38,255 people (or 547 people per year) faced an increased cancer risk in the Great Lakes region over a 70 year lifetime --- due to consumption of fish contaminated with 5 toxic chemicals (PCBs, Mercury, chlordane, DDE/DDT, and Dieldrin --- the last 3 are pesticides). PCBs were considered the dominant risk factor.
The risks were due primarily to consumption of Great Lakes sport fish, plus some consumption of less contaminated commercial and non-Great Lakes sport fish. Reference: U.S. EPA, Region 5. 1991. "A Risk Analysis of Twenty-six Environmental Problems - Draft." Region 5 Comparative Risk Project, Draft Working Documents.
In 1999, the draft Fox River clean-up proposal included a local cancer risk assessment for recreational anglers and subsistence anglers due primarily to consumption of fish containing PCBs. Using fish concentration data from 1990 on (and Walleye data from 1989 in Green Bay), the cancer risks were as high as 1.1 in a 100 for recreational anglers, and 1 in 67 for subsistence anglers. These risks are more than 1,000 times greater than the standard 1-in-a-million cancer risk level used by Wisconsin to regulate hazardous waste sites. These risks are 23 times higher than the cancer risks from fish-eating from Lake Winnebago, which the DNR considers a background level for PCBs (though it’s clear that Lake Winnebago fish are also contaminated.) Reference: ThermoRetec. Feb. 1999. "Draft Feasibility Study, Lower Fox River, Wisconsin, Summary of Baseline Human Health and Ecological Risk Assessment." Section 3.2.1.
In this area, we have roughly 47,000 recreational anglers, based on fishing licenses, and between 2,000 and 5,000 subsistence anglers, based on a variety of surveys. If they all fished the Fox River and lower Bay at average rates, up to 510 recreational anglers, and 30 to 75 subsistence anglers could develop cancer locally over their lifetimes. We hope people are heeding the fish advisories and not consuming contaminated fish, but subsistence fishers often need to fish for financial and/or cultural reasons.
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Human Cancer PCB Studies
The following are studies which suggest PCBs cause cancer. Government agencies generally require larger and more repeated studies before declaring a substance a "known carcinogen" in humans.
The agencies used the "weight of evidence" approach to classify PCBs as probable human carcinogens. They looked at the cumulative results of the studies below, plus other human studies and the overwhelming evidence that PCBs cause cancer in animals. PCB cancer risk assessments are primarily based on detailed animal cancer studies extrapolated to humans, plus human evidence.
Human cancers are largely due to chemical pollutants and unhealthy lifestyles, not genetics, according to recent research by Paul Lichtenstein of the Karolinska Institute of Stockholm, Sweden, who led a giant study of 89,576 twins and reported results in the New England Journal of Medicine (2000). The researchers found even an identical twin has about a 90% chance of not getting the same cancer as his or her cancer-afflicted twin.
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Multiple Cancer Types
At an Italian capacitor manufacturing plant, researchers studying 290 males and 1,020 females had statistically significant increased numbers of deaths from all types of cancer. In males, there was a statistically significant increase in deaths (roughly 3 times higher) from gastrointestinal tract cancers, otherwise described as higher deaths from cancers of the digestive system, the peritoneum, the lymphatic, and hematopoietic tissues. In females, all causes of death were significantly elevated, and there was a statistically significant excess risk of death from hematologic (blood-based, or leukemia) cancers compared with local, but not national rates. The study looked at workers employed at least 1 week and exposed to PCBs (specifically PCB Aroclor 1254 and 1242, both mixtures present in the Fox River). Reference: Bertazzi, Riboldi, Pesatori, Radice and Zocchett. 1987. "Cancer Mortality of Capacitor Manufacturing Workers," AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, 11:165-76.
In a study in which organochlorine compounds were measured in patients who had died of cancer and patients who had died of other diseases, higher concentrations of PCB and DDE were found in the samples for the cancer patients. The mean PCB adipose (fat) levels in 11 male cancer patients was 8.8 mg/kg and in 212 non-cancer patients, 5.9 mg/kg. Although these differences are not large, they were statistically significant. Reference: Unger, M., and Olsen, J. 1980. "Organochlorine compounds in the adipose tissue of deceased people with and without cancer." ENVIRONMENTAL RESEARCH 23: 257-263.
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Liver, Gall Bladder and Biliary Tract Cancers
In New York and Massachusetts, researchers found statistically significant excess mortality from cancer of the liver, gall bladder, and biliary tract in a study of 2,588 capacitor manufacturing workers exposed to PCB Aroclors 1254, 1242, and 1016. Reference: Brown, D.P., Jones,M. 1981 "Mortality and industrial hygiene study of workers exposed to polychlorinated biphenyls." ARCHIVES OF ENVIRONMENTAL HEALTH. 36:120-9 Also: Brown, D.P. 1987. "Mortality of workers exposed to polychlorinated biphenyls – an update." ARCHIVES OF ENVIRONMENTAL HEALTH. 42(6):333-339.
A smaller study was inconclusive because of the small sample size, but suggested similar cancer increases. Reference: Gustavsson P, Hogstedt C, Rappe C. 1986. "Short-term mortality and cancer incidence in capacitor manufacturing workers exposed to polychlorinated biphenyls." AMERICAN JOURNAL OF INDUSTRIAL MEDICINE. 10:341-344.
Another small study was also inconclusive because of the small sample size, but was suggestive of increased cancer risk. Reference: Nicholson WJ, Landrigan PJ. 1994. "Human health effects of polychlorinated biphenyls." In: "DIOXINS AND HEALTH" (Schecter A, ed). New York: Plenum, pp. 487-524.
Incidents in Japan and Taiwan where humans consumed rice oil contaminated with PCBs showed liver cancer at 15 times the normal rate, but this has been attributed, at least in part, to heating of the PCBs and rice oil, causing formation of chlorinated dibenzofurans (known as "furans"). However, commercially produced PCBs, such as those used in the Fox River Valley, were routinely contaminated with furans during creation, so BOTH chemicals are present at significant levels in our river. Reference: Urabe H. Koda H, Asahi M. 1979. "Present State of Yusho Patients." ANNULS OF THE NEW YORK ACADEMY OF SCIENCES. 320:273-6. Online: http://www.cdc.gov/niosh/86111_45.html#Toxicity Also: Masuda Y, Yoshimura H. 1984. "Polychlorinated biphenyls and dibenzofurans in patients with Yusho and their toxicological significance: review." AMERICAN JOURNAL OF INDUSTRIAL MEDICINE. 5:31-44. Also: Masuda Y. 1994. "The Yusho rice oil poisoning incident." In: Schecter A, editor. "DIOXINS AND HEALTH." New York: Plenum, p 633-59.
For more details, see PCBs and Liver Cancer in Humans
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Skin Cancer - Melanoma

In Indiana, researchers found excess cancer mortality among workers at a capacitor manufacturing plant where PCB Aroclor 1242, then 1016, had been used. The study examined 3588 workers employed at least 1 day. Compared with national rates, there was a statistically significant excess risk of death from skin cancer (roughly 4 times higher.) All were malignant melanomas. Reference: Sinks T, Steele, G, Smith AB, Watkins K, Shults RA. 1992. "Mortality among workers exposed to polychlorinated biphenyls." AMERICAN JOURNAL OF EPIDEMIOLOGY, 136:389-98.
Another study of electric utility workers exposed to PCBs showed significantly increased mortality from malignant melanoma (skin cancer) and brain cancer Reference: Loomis D, Browning SR, Schenck AP, Gregory E, Savitz DA. 1997. "Cancer mortality among electric utility workers exposed to polychlorinated biphenyls. "OCCUPATIONAL ENVIRONMENTAL MEDICINE. 54:720-8.
On another front, in a June 24, 1976 letter, Mobil Oil Corporation reported to the National Institute for Occupational Safety and Health (NIOSH) preliminary results of an epidemiological analysis based on medical records of employees exposed to PCBs at their Paulsboro, New Jersey plant.

The study included Mobil employees reported to have had varying exposure to PCB Aroclor 1254.The research and development employees were exposed to PCBs between 1949 and 1957 and refinery plant employees between 1953 and 1958. The extent of exposure to other chemicals is not known. The cancer incidence among these workers for the period 1957 through 1975 was determined using Mobil medical records. Because medical records for 37 employees were incomplete, these workers were excluded from this analysis. Among the 92 workers in these two groups for whom adequate medical records were available, eight cancers (in seven workers) were observed between 1957 and 1975. Of these eight cancers, three were malignant melanoma and two were cancer of the pancreas. This is significantly more skin cancer (melanoma) and pancreatic cancer than would be expected in a population of this size. The remaining cancers were found at three other sites in two employees; sarcoma of the right thigh and multiple myeloma in one employee, and recto-sigmoid cancer in the other. Reference: Bahn AK, Rosenwaike I, Herrmann N, Grover P, Stellman J, O’Leary K. 1976. "Melanoma after exposure to PCBs." Letter. NEW ENGLAND JOURNAL OF MEDICINE. 295: 450 (1976). Also: DHHS (NIOSH), CURRENT INTELLIGENCE BULLETIN 7, polychlorinated (pcbs) November 3, 1975,updated 05-01-1998. Online: http://www.cdc.gov/niosh/78127_7.html
For more details see Skin Cancer and PCBs
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Brain Cancer

In another study, electric utility workers exposed to PCBs had significantly increased mortality from brain cancer and malignant melanoma. Reference: Loomis D, Browning SR, Schenck AP, Gregory E, Savitz DA. 1997. "Cancer mortality among electric utility workers exposed to polychlorinated biphenyls. "OCCUPATIONAL ENVIRONMENTAL MEDICINE. 54:720-8. Also, refer to: Johnson BL, Hicks HE, Jones DE, Cibulas W, Wargo A, De Rosa CT. 1998. "Public health implications of persistent toxic substances in the Great Lakes and St. Lawrence basins. JOURNAL OF GREAT LAKES RESEARCH 24:698-722. Online at http://www.atsdr.cdc.gov/DT/pcb007.html


For more details see Brain Cancer, PCBs and Dioxin
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Non-Hodgkin’s Lymphoma
Many countries are reporting a rapid increase in incidence of non-Hodgkin’s lymphoma.
Recent case-control studies have found associations between non-Hodgkin's lymphoma and PCB concentrations in adipose (fat) tissue (Hardell, 1996) and blood serum (Rothman, 1997). In the Rothman study of persons without known occupational exposure to PCBs, mean PCB blood levels of 13.3 ppb yield highly significant increased odds of non-Hodgkin's lymphoma. Reference: Hardell L, van Bavel B, Lindström G, Fredrikson M, Hagberg H, Lijergren G, Nordstrom M, and Johansson B.. 1996. "Higher concentrations of specific polychlorinated biphenyl congeners in adipose tissue from non-Hodgkin's lymphoma patients compared with controls without a malignant disease." INTERNATIONAL JOURNAL OF ONCOLOGY 9:603-608. Also: Rothman N, Cantor KP, Blair A, Bush D, Brock JW, Helzlsouer K, Zahm SH, Needham LL, Pearson GR, Hoover RN, et al. 1997. "A nested case-control study of non-Hodgkin lymphoma and serum organochlorine residues." LANCET 350:240-244.
In a 1998 study, researchers state: "In epidemiologic studies, non-Hodgkin’s lymphoma (NHL) has been associated with exposure to chemicals such as phenoxyacetic acids; chlorophenols; dioxins; organic solvents including benzene, polychlorinated biphenyls, chlordanes; and immunosuppressive drugs. Experimental evidence and clinical observations indicate that these chemicals may impair the immune system. The risk is increased for NHL in persons with acquired and congenital immune deficiency as well as autoimmune disorders. Also, certain viruses have been suggested to be of etiologic significant for NHL. In some cases of NHL the common mechanism for all these agents and conditions may be immunosuppression, possibly in combination with viruses." Reference: Hardell L, Lindstrom G, van Bavel B, Fredrikson M, and G Liljegren. 1998. "Some aspects of the etiology of non-Hodgkin’s lymphoma." ENVIRONMENTAL HEALTH PERSPECTIVES. 106 (Suppl 2):679-681.
Another study found an association between PCBs and hairy cell leukemia, which is a subgroup of Non-Hodgkin Lymphomas. Researchers found an "increased risk for the sum of the immunotoxic PCB group." Reference: Nordstrom M, et al. 2000. "Concentrations of organochlorines related to titers to Epstein-Barr virus early antigen IgG as risk factors for hairy cell leukemia." ENVIRONMENTAL HEALTH PERSPECTIVES 108(5):441-5.
See also PCBs and Immune System Damage
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Pancreatic Cancer
Researchers have found an association between PCB levels and pancreatic cancers. Reference: Hoppin JA, et al. 2000. "Pancreatic cancer and serum organochlorine levels." CANCER EPIDEMIOLOGY, BIOMARKERS, AND PREVENTION; 9(2):199-205.
In a second study, in a recent issue of the British journal, LANCET, pancreatic cancer patients with a specific gene mutation called K-ras show high levels of DDT, DDE, and PCBs, known as organochlorine compounds. Roughly 78 percent of patients with pancreatic cancer have the K-ras mutation, and scientific studies have established that the mutation is not inherited. This study is the first to suggest that the K-ras mutation is linked to a chemical agent in the environment. "Pancreatic cancer patients with a K-ras mutation have significantly higher levels of DDT, DDE and three major PCBs than pancreatic cancer patients without the mutation or the controls," says the lead researcher, Miguel Porta. But, he adds, "we do not think that organochlorine compounds directly cause the mutations." So what could be happening? "One possibility is that something causes the mutation and then these compounds provide some advantage for the mutated cells to grow," so that instead of dying, for example, a mutated cell continues to grow and multiply. "The other possibility is that these substances enhance the action of mutagens of K-ras." For example, PCBs may push abnormal cells that are still in a pre-cancerous phase into becoming completely cancerous.
For more detailed information, see Pancreatic Cancer, PCBs and Dioxin
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Lung Cancer
A PCB-exposed group in Japan had a statistically significant increase in lung cancer deaths. This was a case involving rice oil contaminated with PCBs and furans. [Some scientists argue that the cancers were due to the furans, not the PCBs; however, commercial mixtures of PCBs generally came contaminated with furans from the manufacturer. The Fox River is contaminated with both PCBs and furans as a result, and both chemicals are picked up and accumulated in fish.] Reference: Kuratsune, Nakamura, Ikeda, & Hirohata. 1987. "Analysis of Deaths Seen Among Patients with Yusho-A Preliminary Report," CHEMOSPHERE, 16:8/9, 2085.
A second study noted that lung cancer deaths among ex-employees at a capacitor plant were higher than might have been expected, but concluded that "there were apparently no grounds for associating lung cancer deaths (although increased above expectations) and exposure in the plant." Reference: Bertazzi, Riboldi, Pesatori, Radice and Zocchett. 1987. "Cancer Mortality of Capacitor Manufacturing Workers," AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, 11:165-76.
A study followed employees who had worked at Monsanto's PCB production plant. The researchers found that the incidence of lung cancer deaths among these workers was somewhat higher than would ordinarily be expected. The increase, however, was not considered statistically significant. Reference: J. Zack & D. Munsch, Mortality of PCB Workers at the Monsanto Plant in Sauget, Illinois (Dec. 14, 1979)(unpublished report), 3 Rec., Doc. No. 11.
For more details, see Lung Cancer and PCBs
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Kidney Cancer
A study of workers exposed to PCBs found a consistent increase in kidney cancer, although the actual number of cases was small. Reference: Longnecker, MP, WJ Rogan and G Lucier. 1997. "The human health effects of DDT (dichlorodiphenyltrichloroethane) and PCBs (polychlorinated biphenyls) and an overview of organochlorines in public health," ANNUAL REVIEW OF PUBLIC HEALTH, 18:211-244.
For more details, see Kidney, Bladder & Urothelial Cancer and PCBs

Prostate Cancer
PCBs may cause or promote prostate cancer through early alteration of hormonal development of the male in the womb, and/or through changes in the levels of glutathione enzymes. The International Agency for Research on Cancer (IARC) found an association between PCBs and prostate cancer.
For more details, see Prostate Cancer and PCBs
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Breast Cancer

In Wisconsin, researchers have found breast cancer population clusters, where the disease rate is much higher than average. Two of them are in zip codes on the east side of the City of Green Bay, in the old downtown along the Fox River and along the east shore of the Bay. (Zip codes 54301 and 54311) The statistics were age-adjusted so results wouldn’t be skewed.)
In general, Wisconsin’s breast cancer rate among women aged 65 and older is higher than the national average.

Our detailed Breast Cancer section includes summaries of 128 studies on the links between breast cancer and exposure to PCBs or dioxin.
At least 24 studies of human populations show a possible link between PCBs and breast cancer. More than 50 additional laboratory studies illustrate in animals or cell cultures how PCBs may cause or promote breast cancer. Also, three studies of humans show a link between dioxin and breast cancer. These last three are important because certain PCBs are dioxin-like and PCBs are frequently contaminated with dioxins.
On the other hand, approximately 13 human studies did not show that PCBs increase breast cancer risk. Nevertheless, several such studies, when re-examined statistically, have found that certain PCBs were associated with risks, or that certain subgroups of women appeared to be more vulnerable to PCBs.
For more details, see Breast Cancer, PCBs and Dioxin
http://www.foxriverwatch.com/cancer_pcb_pcbs_1.html#top

http://www.fishadvisories.utah.gov/docs/111708_PCBs_in_Utah_Lake_Sediment_Study.pdf

Figure 1. Mean Total PCB Concentration in Fish Collected from Utah Lake in June 2006.
Common carp are bottom-feeding omnivores that consume aquatic plants, insects, and
other fish. Carp dominate the ecology of Utah Lake making up an estimated 90.9% of its
total biomass (2). Their presence has lead to the decline of native fish species including
the June Sucker, which was listed on the Endangered Species List in 1986. The June
Sucker Recovery Implementation Program has been initiated to address its listing and to
recover the species so that it no longer requires protection under the Endangered Species
Act.
Total [PCBs] in Fish from Utah Lake
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
200.0
Fish Species
Total [PCB], ppb
Fillet 14.3 10.2 80.5 104.4 7.1
Offal 59.5 34.8 130.6 176.8 30.7.7