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Chemical Pollution and Mother's Milk

Glossary of Terms in Environmental Health

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Persistent Bioaccumulative Toxics (PBTs)
PBT pollutants are toxic chemicals that persist in the environment and bioaccumulate in food chains. They threaten human health, as well as the health of ecosystems. PBTs transfer easily among air, water and land, and span boundaries of geography and generations. The term PBT is used primarily by the U.S. Environmental Protect Agency, as part of its preparation of a list of such chemicals that will receive special regulatory emphasis.

Persistent Organic Pollutants (POPs)
Persistent Organic Pollutants (POPs) are chemical substances that persist in the environment and bioaccumulate through the food web. They threaten human health, as well as the health of ecosystems. The term POPs is commonly used in the context of the United Nations Environment Program (UNEP). POPs are subject to international negotiations aiming toward global elimination.

For all practical purposes, POPs and PBTs are the same; the difference has more to do with whether one is speaking of the work of the UNEP or the EPA. The two agencies have developed similar, but not identical, lists of substances that meet their respective definitions:

EPA's Current List of PBTs UNEP's Current List of POPs
Aldrin Aldrin
Dieldrin Dieldrin
Chlordane Chlordane
Mirex Mirex
Toxaphene Toxaphene
Hexachlorobenzene Hexachlorobenzene
Dioxins and Furans Dioxins and Furans
Octachlorostyrene Heptachlor
Benzo(a)pyrene Endrin

Endocrine Disruptors
Endocrine disruptors are chemicals that interfere with hormones in the body. Currently known or suspected endocrine disruptors are in pesticides, plastics and other common chemicals. Some endocrine disruptors are also POPs/PBTs; some are not. But even brief exposure during a vulnerable period -- fetal life or early development, for example -- can have serious long-term effects. The endocrine system is one of the three fundamental communication systems in the body (endocrine, nervous, immune). Hormones regulate numerous daily functions (appetite, metabolic rate, menstrual cycling, sperm production etc). In the womb, hormones regulate development.

Dioxins and Furans
Dioxins and furans are chemicals created by heating or burning chlorine-containing compounds in the presence of organic (carbon-containing) materials. Dioxins and furans are among the most toxic chemicals currently known to science. They are known human carcinogens and known endocrine disruptors and result in subtle disruption to infant development at ultra-low (parts per trillion) doses. They also accumulate in fat and breast milk. Major sources are incinerators, power plants, pulp and paper mills, diesel engines, refineries, etc.

Polychlorinated Biphenyls (PCBs)
PCBs are chemicals used primarily, as flame-retardants, as coolants in industrial processes and in electrical transformers. PCBs were widely used between 1950 and 1970 in the United States, and are still used in many other nations. They resemble the dioxins and furans in their structure and environmental properties. They accumulate in fat and are probable human carcinogens. PCBs mimic estrogen and interfere with thyroid hormone. Recent studies show these chemicals probably interfere with normal development of the brain, resulting in deficits in learning, reading and IQ.

Pesticides are chemicals whose purpose is to kill insects, weeds, molds, rodents, algae or other undesirables. The term takes in a very complex set of chemicals with a wide variety of structures, a range of environmental persistence and many different toxic properties. Some pesticides are relatively non-toxic; garlic and hot pepper are registered pesticides, for example. But other pesticides include POPs or PBTs, and many have toxic properties.

Organophosphates (OPs) are a specific class of insecticides, developed initially in the 1940s. They attack the nervous system by poisoning the critical enzyme, acetylcholinesterase, which is essential for breaking down chemically delivered nerve impulses. OPs are designed to kill insects, but because the relevant chemical processes in are similar in humans and animals, they can also can cause poisoning and death in humans, and children in particular. OPs include malathion, methyl parathion, diazinon, azinphos-methyl (Guthion), chlorpyrifos (Dursban).

The term organocholorine encompasses a large and motley group of chemicals characterized by carbon and chlorine components. Many are environmentally persistent (POPs or PBTs); some are pesticides (DDT, dicofol, atrazine, etc.). Some are not persistent, but are toxic (trichloroethylene, perchloroethylene). Dioxins, furans and PCBs are all organochlorines. Also may be referred to as "chlorinated chemicals."

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last revised 3.25.05

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