Joanna D Underwood


Over the past decade, growing attention has focused on chemicals that share three characteristics: they are toxic, they persist in the environment, and they bioaccumu-late in living organisms. This class of chemicals, called persistent, bioaccumulative toxins (PBTs), represents one of the greatest challenges for chemical companies that manufacture or use them, or that manufacture products that release them to the environment after disposal. In 2000, U.S. EPA made PBTs a top priority because of their ability "to travel long distances, to transfer rather easily among air, water, and land and to linger for generations in people and the environment".2

2U.S. EPA, "Persistent Bioaccumulative and Toxic (PBT) Chemical Program: Multimedia Strategy for Priority Persistent, Bioaccumulative and Toxic (PBT) Chemicals." Available at pbt/fact.htm (accessed September 2004).

The category of PBTs, as defined by U.S. EPA, includes mercury, lead, dioxins, and several dozen other substances. Mercury and lead have so far been the most widely targeted of these substances because, like other heavy metals (naturally occurring elements contained in rocks, sediments, and soils), they do not degrade at all. Polychlorinated dioxins are also PBTs, and while normally they are not purposefully manufactured, they are often generated as byproducts during the manufacture of chlorinated compounds and during incineration or combustion.3

Many PBTs, such as lead, mercury, and polychlorinated biphenyls (PCBs), have been well understood, though poorly controlled, for years. Newer chemicals, such as brominated flame retardants, are now emerging as key targets because of their prevalence in the environment, because they can bioaccumulate, and because there is growing evidence that humans are being exposed. (Environmental Working Group, 2003). Although U.S. EPA has not yet included brominated flame retardants on its official list of PBTs of concern, they are subjects of intense scrutiny because they have been found in human beings and the environment at rapidly increasing levels.4

Persistent bioaccumulative toxins pose both immediate and long-term threats to humans. The developing organ systems of fetuses and young children make them more vulnerable to the impacts of PBTs than adults.5 In addition, indigenous populations and others who rely on locally caught fish and wildlife for food may be more exposed to certain PBTs than the general population.6

The specific effects on humans from exposure to PBTs can be subtle or highly visible. A look at four of these substances exemplifies these differences.

• Mercury. In human beings, even low concentrations of mercury can be harmful. Each year, nearly 630,000 newborns are estimated to be at risk of developmental problems resulting from their mothers' exposure to mercury.7 Studies show that exposure to methyl mercury in the womb can cause neurological damage in the fetus and delayed development in young children. In the fetus, in children, and in adults alike, the greatest concern from chronic exposure to methyl mercury is damage to the central nervous system (U.S. EPA, 2001). A national study conducted by the U.S. Department of Health and Human Services found that "approximately 10 percent of women of child-bearing age have blood mercury concentrations above the levels U.S. EPA considers safe" (Centers for Disease Control, 2003).

3U.S. Agency for Toxic Chemicals and Disease Registry, "Toxicological Profile for Chlorinated Dibenzo-p-Dioxins." Available at (accessed September 2004).

U.S. EPA, "Brominated Flame Retardants to be Voluntarily Phased Out." Available at (accessed

September 2004).

5U.S. EPA, "Persistent Bioaccumulative and Toxic (PBT) Chemical Program: Frequently Asked Questions." Available at (accessed September 2004).

6U.S. EPA, "Persistent Organic Pollutants: A Global Issue, A Global Response." Available at http:// (accessed September 2004).

7Kathryn R. Mahaffey, U.S. EPA, "Methylmercury: Epidemiology Update." Available at http://www. (accessed September 2004).

• Lead. The persistence of lead in the environment (such as in homes where lead-containing paint was used before it was banned in 1978) is a key factor in the continuing problem of lead poisoning among children in the United States. Research indicates that children with high levels of lead in their blood suffer from impaired intelligence and are "frequently overactive, aggressive, more distractible, disorganized, and less able to follow directions" (Kurtin et al., 1997). Follow-up studies show that these children have a "lower class standing in the final year of high school, with increased absenteeism, lower vocabulary scores, and impaired motor function" (Kurtin et al., 1997). In adults, exposure to high levels of lead can result in damage to the renal, nervous, digestive, and reproductive systems.8 U.S. EPA has classified lead as a probable human carcinogen.9

• Dioxins. Estimates of background levels of exposure to dioxins through food range from 63 to 210 picograms per day for the average person (a picogram is one trillionth of a gram). For many age groups, the average daily intake of dioxins exceeds the level that the World Health Organization recommends as acceptable to protect human health. Low levels of chronic exposure to dioxins have been linked to developmental problems of the brain and thyroid in children exposed in the womb (European Commission, 1999). Background levels of exposure may also be associated with greater susceptibility to infectious diseases in children (Weisglas-Kuperus et al., 2000).

• PCBs. Exposure to PCBs can affect memory and learning ability in adults (Schantz et al., 2001), and there is evidence that exposure in the womb can cause lower birth weight, smaller head circumference, poor motor reflexes, a greater inclination to startle, and neurological, behavioral, and developmental problems in children. Eating PCB-contaminated fish has been associated with decreased fertility. Exposure to PCBs can increase the risk of cancer, immune and endocrine system dysfunction, non-Hodgkin's lymphoma, diabetes, and liver disease.10

Persistent bioaccumulative toxins have done extensive and long-lasting damage to fish and wildlife in the Great Lakes region, where 43 severely degraded geographic areas (known as "areas of concern") failing to meet criteria set forth by the Great Lakes Water Quality Agreement of 1978 have been identified.11 For example, despite the fact that PCBs were banned from commerce in the United States more than 25 years ago, they are still causing "reproductive problems, tumors, and

8U.S. EPA, "Health Effects of Lead," fact sheet. Available at Health_Effects_FINAL%20_12.pdf (accessed September 2004).

9U.S. EPA, Integrated Risk Information Center, "Lead and compounds (inorganic)," IRIS Summary (CASRN 7439-92-1). Available at (accessed September 2004).

10Agency for Toxic Substances and Disease Registry, "Public Health Implications of Exposure to Poly-chlorinated Biphenyls (PCBs)." Available at (accessed September 2004).

11Great Lakes Information Network, "Areas of Concern in the Great Lakes Region" (accessed September 2004).

other deformities" in fish and wildlife in most of the Great Lakes, according to the National Biological Service (Minnesota Office of Environmental Assistance, 2002).

Numerous studies have linked a high incidence of fish tumors of the liver and skin to chemical contaminants such as polycyclic aromatic hydrocarbons (PAHs) in sediments of the Buffalo River in New York State.12 Caspian terns - birds that live year-round in Michigan's Saginaw River and Bay, where there are elevated levels of PCBs and other persistent organochlorine pollutants and heavy metals -have experienced "an unusually high incidence of birth defects and poor reproductive success."13 The Minnesota Pollution Control Agency found that "lead poisoning accounted for 26 percent of the dead loons sent to research centers for autopsy" (the loon is Minnesota's state bird). Many of these birds had lead fishing tackle in their stomachs (Minnesota Office of Environmental Assistance, 2002). And the list goes on.

Because PBTs do not break down, their levels in our environment are building up. Contamination of water and fish with dangerously high levels of mercury and other PBTs is a challenging national (and international) problem. According to U.S. EPA, fish and wildlife consumption advisories apply to 35 percent of the nation's total lake acreage (not including the Great Lakes) and 24 percent of the nation's total river miles, as well as 71 percent of the nation's coastal waters.14 The United States has experienced a significant increase in consumption advisories over the past decade, in large part because of ongoing and extensive fish-tissue sampling. In 2003, 48 states - all but Alaska and Wyoming - were under fish advisories for mercury, up from 44 states in 1993, and approximately 12,069,319 lake acres and 473,186 river miles were under advisory.

Nationally, five PBTs - mercury, dioxins, PCBs, chlordane (an insecticide), and DDT - are largely responsible for about 98 percent of all fish consumption advisories, with 76 percent involving mercury.

Recent reports indicate that much more recently manufactured brominated flame retardants appear to be ubiquitous and are increasing in the environment (Sjodin et al., 1999). They have been found around the globe, in the blood of workers at computer assembly and recycling facilities, in breast milk, in whale blubber, and in sewage sludge, sediments, and the air of office buildings (Swedish National Chemical Inspectorate, 1999). According to Environment Canada, "The levels of PBDEs [a form of brominated flame retardant] in North Americans appear to be doubling every two to five years" and "will become a problem" if releases of these substances into the environment are not halted (Betts, 2001).

How are people exposed to PBTs? Most of the public's exposure to chemicals such as mercury and dioxins is from food. However, INFORM research documented in 2000 that the majority of PBTs leaving factories leave in consumer products,

12U.S. EPA, "Buffalo River Area of Concern." Available at buffalo.html (accessed September 2004).

13U.S. EPA, "Saginaw River/Bay Area of Concern." Available at sagrivr.html (accessed September 2004).

14U.S. EPA, Office of Water, Update: National Listing of Fish and Wildlife Advisories, EPA-823-F-04-016, August 2004. Available at (accessed September 2004).

rather than in manufacturing byproducts and industrial waste. These chemicals are therefore likely to be released from trash incinerators, metal smelters, and other solid waste disposal facilities after product disposal. Also, PBTs are also discharged into water via sewage treatment plants when pesticides, products contaminated by mercury or containing mercury as a preservative, and other products are flushed down the drain. People can be exposed to PBTs in the buildings where they live, work, or go to school. The state of Vermont has documented that "health care facilities, educational and research institutions and businesses have experienced significant employee exposures, and incurred significant costs due to accidental mercury releases" (Vermont Senate Natural Resources and Energy Committee, 2001).

Overall, PBTs are most pervasive in consumer goods (U.S. EPA, 1998b). While the use of some PBTs (such as PCBs, DDT, lead in house paint, and mercury in most batteries) is banned or restricted in the United States, many substances with similar characteristics continue to be added to products or generated as byproducts during manufacturing or after disposal. A review (conducted by INFORM) of the most recent data from the expanded right-to-know programs in Massachusetts and New Jersey indicates that the quantity of PBTs going into products is 20 to 25 times greater than the amount generated as industrial waste (data from INFORM, 2000). Hundreds of consumer products contain PBTs; a few examples include electronics with lead solder, nickel-cadmium batteries, fluorescent lamps, thermostats and thermometers, vehicles and appliances with mercury switches, wood preservatives, plastics containing heavy-metal stabilizers, several pesticides, some industrial cleaning supplies, and diesel fuel. (An extensive list of PBT-containing products is available on INFORM's website at

The bottom line is that, whenever PBT-containing products are made, used, or discarded, the toxins they contain are very likely to be released into the air or water, adversely impacting people and wildlife in the near or long term in subtle or in very visible ways. Hence, the challenge to industry is to seek the most effective near-term steps to ensure that PBT-containing products are retrieved for reuse or recycling and, ultimately, that PBTs as a class are phased out of use in commerce as completely as possible.

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