How Do PBT's Affect the World Around Me?

• The Concern With PBTs in Wisconsin
• How do PBTs Enter Wisconsin's Environment?
• How are Humans and Wildlife Exposed to PBTs?
• Effect of PBTs on Human and Wildlife Health?
• Impact of PBTs on Wisconsin’s Ecosystems: Plants, Animals, and Invertebrates?

The Concern With PBTs in Wisconsin

PBTs are of concern because of mounting evidence that they cause long-term harm to human health and the environment. Although many chemicals can have toxic effects on humans and the environment, PBTs pose a special challenge primarily because of their unique properties. PBTs do not break down or become diluted in the environment as easily as non-PBT chemicals. PBTs also tend to bioaccumulate in the bodies of humans, fish, and other wildlife. As they "move up the food chain," PBTs become increasingly concentrated, and may reach very high levels in both humans and wildlife that are at the top of the food chain. This concept is illustrated in Figure 1

Figure 1.

PBTs can be transported long distances and move readily from land to air and water. Because of their persistence and bioaccumulative properties, they are particularly difficult to clean up. Many PBTs are human-made and have only been in existence for a relatively short period of time. Other PBTs are found naturally in the environment. It is the refinement and concentrated human use of PBTs that creates the problem.

There is concern not only with historical PBT chemicals, such as DDT and PCBs, but also with PBT chemicals currently in production (like PBDEs) and new chemicals with similar properties entering commerce today or in the future.

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How Do PBTs Enter Wisconsin’s Environment?

A wide range of industrial and consumer activities produce and release PBTs into Wisconsin’s environment. These include highly visible sources such as large industrial manufacturing facilities as well as smaller less visible sources such as individual consumer products. Releases from these sources, both ongoing and historical, have resulted in measurable levels of PBTs in the air, water, soils and sediments throughout the state. In fact, levels of many PBTs in waters, sediments, and waterfowl and fish tissues have accumulated to levels that require the Department to list many waters in the state as impaired under the Federal Clean Water Act. In addition, the Department has issued fish or waterfowl consumption advisories for almost all waters of the state.

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How are Humans and Wildlife Exposed to PBTs?

There are many ways that adults, young children, and even a developing fetus can be exposed to PBTs. Mothers can pass PBTs to their offspring before birth through the cord blood or after birth through breast milk. Children playing in PCB contaminated soils may absorb some of the contaminant through their skin or ingest it by putting soil-covered hands into their mouths. For children between the ages of six months and 6 years, the EPA has ranked lead as the most common environmental health hazard. Lead exposure may come from lead-based paint chips, drinking water from lead-soldered pipes, soil and dust, certain glassware and ceramic dishes, and through cord blood for the developing fetus. Once in the body, lead can replace essential minerals in the blood, like calcium and iron, and may result in impaired growth and development. Some PBTs can also be taken up by plants, which are then eaten by people or animals. Although PBT exposure from any one source may be relatively small and infrequent, the compilation of multiple sources and exposure routes may add up to significant levels of PBTs accumulating in adults and children. The developing fetus or young child may be particularly susceptible to PBT exposure because important organs, such as the central nervous system, are still under development (EPA 1997).

The EPA estimated that 60,000 children nationwide are at risk of mercury exposure (NRC 2000). The relative risk may be even higher in Wisconsin because of the higher average rate of fish consumption. In fact, the greatest single source of exposure to mercury for many Wisconsin residents is through the consumption of fish. Animals and people who eat large amounts of fish from inland waters are likely to be exposed to mercury at higher-than-average levels. In one study of licensed Wisconsin anglers, it was found that the average consumption rate was 17.5 grams of fish per day, or 42 meals per year (Fiore and others 1989). This was 2.5 grams, or 6 meals more than the national average. In addition, the state has several populations of Native Americans and Hmong who, because of their cultural traditions, consume even larger amounts of fish (Peterson and others 1994, Hutchinson and Kraft 1994). For example, members of the Chippewa tribes in northern Wisconsin consume an average of 75 meals of fish per year, which is more than double the national average (Peterson and others 1994).

The Department, along with the Wisconsin Department of Health and Family Services (DHFS), annually issues a fish consumption advisory to inform fish consumers of potential health threats posed by eating fish from contaminated waters. Unfortunately, several studies conducted by the Wisconsin DHFS have shown that, despite the annual release of the Department’s fish consumption advisory, less than half of Wisconsin residents were aware of the advice to limit consumption of fish from some of the state’s waters due to the presence of PBTs (Tildon and others 1997).

In 2000, Wisconsin changed its fish consumption advisory for mercury to reflect recent scientific findings that includes evidence of negative effects of low level mercury exposure on the developing nervous system in fetuses. This change was made with the goal of better protecting human health. The state now issues consumption advice when fish tissue exceeds 0.05 parts per million in mercury. Because nearly all of Wisconsin’s tested inland waters contain fish with mercury levels exceeding this level, the state has issued the same general advice for all lakes statewide, regardless of whether a lake has been tested. In addition, the state lists individual waters with a corresponding consumption advice where fish are tested to be particularly high in mercury, as well as waters where PCBs, dioxin, or pesticides are the predominant contaminant. The Wisconsin fish consumption advisory can be viewed on the Department’s Web site.

Humans are not alone in ingesting PBTs through their consumption of fish. Fish make up a major part of the diet for a number of wildlife species, including loons, eagles, ospreys, and mink. These animals are likely to also be consuming high levels of PBTs in their diet.

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Effects of PBTs on Human and Wildlife Health

While scientists have yet to fully understand the long-term health effects associated with current levels of contamination, there is a growing body of scientific evidence supporting the need to take actions to reduce and, where possible, eliminate exposures to PBTs. For example, scientists have associated individual PBT substances with a wide range of effects in animals in natural and laboratory situations. Behavioral changes, mortality, reproductive failure, eggshell thinning, developmental abnormalities, impaired growth and development, altered blood chemistry, increased rate of disease outbreaks, organ and central-nervous-system damage, and impaired immune-system response are just some of the reported effects of PBTs in wildlife (Gilbertson and others 1991, Fox 1992, Leatherland 1992, Tillett and others 1992, Tillett and others 1993, Anthony and others 1993, Henny and others 1996, EPA 1997). Potential adverse effects on human health involve the nervous system, reproductive and developmental problems, immune-response suppression, and cancer (EPA 1997, EPA 2000).

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Impact of PBTs on Wisconsin’s Ecosystems: Plants, Animals, and Invertebrates

The Historic Situation

The serious decline of the bald eagle in the 1960's is perhaps the most well known example of how PBTs can adversely impact wildlife. The fish in the diet of the affected eagles contained DDT, a pesticide and PBT that has been banned in the United States. Although the DDT did not directly kill or sicken the birds, it caused severe thinning of their eggshells. Female birds incubating their eggs often crushed the eggs underneath them, resulting in a reduced number of young that hatched, which ultimately led to population declines.

During the 1940s to 1970s many Wisconsin wildlife species at the top of the food chain were exposed to high concentrations of PBTs such as organochlorine (OC) pesticides (DDT, dieldrin, toxaphene, etc.) and industrial compounds or byproducts (PCBs and dioxins/furans). This exposure caused dramatic declines of many raptor and water bird populations in Wisconsin and throughout North America. Species such as the bald eagle and peregrine falcon declined to such low numbers that they received protection under the Federal Endangered Species Act. Most uses of OC pesticides and industrial chemicals were dramatically curtailed in Wisconsin and the United States during the early 1970s, and as a result, populations of bald eagles and peregrine falcons, among others, are recovering.

The Present Situation

Despite the recovery of bald eagles and peregrine falcons, elevated OC levels persist in the eggs and blood of Wisconsin bald eagles nesting on Green Bay and Lake Michigan and along some industrialized stretches of the Menominee, Wisconsin, Mississippi, and Fox Rivers. Eggs and blood collected from ospreys nesting on the Castle Rock and Petenwell Flowages of the Wisconsin River have 100 times greater levels of dioxins and furans than ospreys nesting upstream of these flowages.

Mercury, a PBT, was once thought to be a problem related solely to industrial discharge. Research has shown that atmospheric transport of mercury emitted from the stacks of coal-burning electric utility plants and municipal waste incinerators has resulted in mercury contamination of fish in almost all lakes in Wisconsin. Fish-eating wildlife, particularly the common loon, also exhibit high levels of mercury exposure when they nest on some northern Wisconsin Lakes. Furbearers, such as mink and otters, also have been shown to have elevated PBTs in their tissues when trapped in areas with populations of contaminated eagles, ospreys, and loons; however the impacts of PBTs on furbearer populations is less well understood. PCB exposure is still great enough to threaten mink reproduction along stretches of the Green Bay shoreline and estuaries of the Oconto, Fox, and Menominee Rivers as well as stretches of the Sheboygan and Red Cedar Rivers.

In addition to eating contaminated food, wildlife may be exposed to PBTs by absorption through their skin. For example, certain amphibians and reptiles may be exposed to high concentrations of PBTs when they burrow into contaminated soil or sediments to hibernate during the winter.

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