Fate and Transport in the Environment
Methods for Monitoring in the Environment
Methods for Measuring Human Exposure
Strategies for Preventing or Controlling Exposure
PCBs - Harmful Effects
PCBs - Dose Response
Sites of Toxicity
Mechanisms of Toxicity
Links for More Information
Exposure to environmental estrogens and other endocrine disruptors can occur through a variety of different pathways. Because they are ubiquitous in the environment, they are found in our food, air, water, soil, pharmaceutical products, household products, and cosmetics to name a few. The three main pathways of exposure include ingestion, inhalation and dermal contact. To illustrate how human exposure to endocrine disruptors occurs, listed below are six representative endocrine disrupting chemicals and their exposure pathways.
Kepone (chlordecone) Pesticide
Sources: Kepone is used as an insecticide, fungicide, pesticide for control of the banana root borer and tobacco wireworm, and bait for control of ants and cockroaches.
Fate in the environment: In the environment, kepone may persist for years in the water and soil due to its slow breakdown. It easily adheres to soil and sediment particles, does not dissolve in water, and evaporates little from surface water or surface soil. Kepone is unlikely to enter underground water from travel through the soil. Fish and other organisms can build up concentrations of kepone in their bodies from living in contaminated water or eating other contaminated animals.
Exposure to humans: Exposure to humans occurs through the dermal route by touching contaminated soil near hazardous waste sites or through ingestion of contaminated fish or other animals living near hazardous waste sites or through drinking breast milk of contaminated mothers. Exposure is unlikely to occur through drinking water or breathing air due to the chemicals difficulty dissolving in water or evaporating.
PCBs (Polychlorinated biphenyls) Persistant organohalogen
Sources: PCBs are synthetic organic chemicals that are not found naturally in the environment. In the United States, manufacturing of PCBs ended in 1977 due to their presumed health effects. Previous to 1977 they were widely used as coolants and lubricants in transformers, capacitors, and other electrical equipment. Today we may find PCBs in old microscope oil, old hydraulic oil, old fluorescent lighting fixtures, or electrical devices or appliances containing PCB capacitors made before their production was stopped.
Fate in the Environment: PCBs have entered the environment through their disposal into landfills, through spills and leaks during their transport, leaks due to burning PCB containing products, or by poor maintenance of hazardous waste sites. Once in the environment, PCBs can move between the air, water, and soil and are not easily broken down. They can enter the air through evaporation and then be transported over great distances either as vapor or solid particles contaminating lands far removed from the source. PCBs adhere strongly to soil and because they do not easily break down in soil, they may stay there for months or years. In water, they can be carried by currents, stick to sediment or evaporate back into the air. When in the gas phase, they can accumulate in leaves, plants and crops. Animals exposed to PCBs, such as fish and other small organisms can take it up into their bodies. When they are eaten by other fish or animals, it can accumulate to very high levels depending on how high up they are in the food chain.
Exposure to humans: One route of human exposure includes the inhalation of PCBs released in the air when old electrical devices/appliances or old fluorescent lighting fixtures containing PCBs get hot during operation. When inhaled, the PCBs can pass through your lungs into your bloodstream. Skin exposure can occur through leaks of these old devices. Primary exposure of PCBs occurs through ingestion of contaminated food (especially sportfish, meat and dairy products) and inhalation of contaminated air. Exposure by swallowing contaminated water while swimming is also possible, but to a lesser extent. People living near hazardous waste sites are especially in danger of these types of exposure. Once the PCBs enter the body, some of them are metabolized and the metabolites may be just as harmful as the original chemical. Some of these metabolites localize mainly to the fat and liver and can remain there for many months. Infants can be exposed to PCBs through their mothers breast milk while nursing.
Butylated hydroxyanisole (BHA) Food antioxidant
Sources: BHA is primarily used as an antioxidant and food preservative. It is used in food packaging, cosmetics, animal feed, and rubber and petroleum products. Use of BHA can preserve the flavor and increase the shelf life of many foods as well as prevent them from developing nasty odors. Oftentimes BHA is added to cooking oil as a way to transfer these properties to fried foods. Some common products containing BHA include, butter, meats, cereals, baked goods, sweets, beer, potato chips, nuts, meat products, glazed fruits and chewing gum. It can also be found in cosmetics and pharmaceutical preps.
Fate in the environment: Because BHA is an antioxidant, it is always hunting for free radicals. It has a melting point of 45-63&Mac176;C, a boiling point of 264-270&Mac176;C, is insoluble in water, but freely soluble in 50% alcohol, propylene glycol, petroleum ether, and fats and oils. Prolonged exposure to sunlight leads to its degradation. BHA can also emit pungent fumes when heated to decomposition. It is volatile at 150-170&Mac176;C and is easily lost from steam generating processes.
Exposure to humans: Exposure to BHA primarily occurs through ingestion or dermal contact with contaminated products. Examples of exposure through ingestion include eating butter, cereals, or fried foods. Use of lipstick and eye shadow are some common examples of exposure through the dermal route.
Di(2-ethylhexyl) phthalate (DEHP) - Phthalate
Sources: Di(2-ethylhexyl) phthalate (DEHP) is a manufactured chemical that is commonly added to plastics to make them flexible. DEHP is present in products such as wall coverings, vacuum pumps, tablecloths, floor tiles, furniture upholstery, shower curtains, garden hoses, swimming pool liners, rainwear, baby pants, squeeze toys and dolls, shoes, automobile upholstery and tops, packaging film and sheets, sheathing for wire and cable, medical tubing, and blood storage bags. It is also used as an acaricide for use in orchards and as an additive in cosmetics.
Fate in the environment: DEHP is everywhere in the environment because of its widespread use. Land application of sewage sludge might also release DEHP to soil. It attaches strongly to soil particles and does not move very far away from where it was released. In hazardous waste sites, the presence of common organic solvents such as alcohols and ketones might increase the solubility of relatively insoluble compounds such as DEHP, thereby increasing the amounts that might leach from the waste site into subsoil and groundwater. Releases to water are found in industrial effluents from the manufacture and processing of DEHP. In water, DEHP is predominantly sorbed to suspended particulates and sediments, but some remains dissolved in the aqueous phase. Adsorption of DEHP to marine sediments might be greater than adsorption to freshwater sediments, due to reduced solubility of DEHP in saltwater. DEHP in air will bind to dust particles and therefore it is removed from the atmosphere by both wet (rain and snow) and dry (wind and settling) deposition. Indoor releases of DEHP to the air from plastic materials, coatings, and flooring in home and work environments, although small, can lead to higher indoor levels than are found in the outdoor air. But overall, the average air level of DEHP is very low because it does not evaporate easily.
Exposure to humans: Bioconcentration of DEHP has been observed in invertebrates, fish, and terrestrial organisms. However, accumulation of DEHP is minimized by metabolism, and biomagnification of DEHP in the food chain does not occur. There is potential risk for exposure due to inhalation, however because of a relatively low vapor pressure and Henrys law constant and a relatively high octanol/water partition coefficient and soil sorption coefficient, DEHP is found to only a limited extent in air. Also, because it does not dissolve in water easily, there is minimal risk of exposure associated with drinking water. Exposure through dermal contact with products containing DEHP is unlikely to cause harmful effects because it cannot be taken up easily through the skin. DEHP can enter the body during certain medical procedures. The greatest risks are during blood transfusions, kidney dialysis, intravenous fluid administration and use of a respirator to support breathing.
Bisphenol A-Other Compounds
Sources: Bisphenol A (BPA) is a lightweight, high-performance plastic that possesses a unique balance of toughness, optical clarity, high heat resistance and excellent electrical resistance. BPA is an important industrial chemical that is used primarily to make polycarbonate plastic and epoxy resins. For example, polycarbonate is used in eyeglass lenses, medical equipment, water bottles, CDs and DVDs, cell phones, computers, electrical equipment, household appliances, reusable food and drink containers, safety shields, sports equipment, and in automobiles. Epoxy resins are used in industrial floorings, adhesives, industrial protective coatings, powder coatings, automotive primers, can coatings and printed circuit boards.
Fate in the Environment: Bisphenol A is a solid with low volatility at ambient temperature conditions, water solubility of 120-300 milligrams per liter and a greater solubility at alkaline pH values. Based on these properties, equilibrium models predict that about 50% of BPA in the environment has the potential to bind to sediments or soils with the rest remaining in the water column. BPA is extensively removed in wastewater treatment systems. For instance, 92-98% removal is reported in the most common type of sewage treatment systems. Bisphenol A dust (particulates) is controlled by workplace practices and engineering design and is not a significant contributor to environmental exposures.
Exposure to Humans: Although the vast majority of BPA is converted at manufacturing sites into products, low-level releases of BPA to the environment are possible. BPA is classified as readily biodegradable in sediments. The trace amounts of BPA remaining in treated wastewater continues to biodegrade in receiving waters and downstream of treatment plants. The relatively small amount of vapor released to the atmosphere is also rapidly degraded by sunlight. Bisphenol A does not accumulate in aquatic organisms to any appreciable extent and is not classified as bioaccumulative by the U.S. Environmental Protection Agency. There is some risk for Bisphenol A to leach out of the lining in cans, which could potentially contaminate the foods and liquids contained inside.
Cadmium Heavy Metals
Sources: Cadmium is a natural element in the earth's crust. It is usually found as a mineral combined with other elements such as oxygen (cadmium oxide), chlorine (cadmium chloride), or sulfur (cadmium sulfate, cadmium sulfide). Cadmium itself is a heavy metal with widespread use, including in electroplating, photoelectric cells, soft solder and solder tor aluminum; deoxidizer in Ni plating, storage batteries; process engraving, electrodes for cadmium vapor lamps, photometry of ultraviolet sun-rays. The powder is also used as an amalgam in dentistry. Cadmium chloride is used in photography, in paints, pigments, glass and glazes, in electronic components, as a nemoticide, pesticide and a fungicide, in the manufacture of cadmium yellow, in the manufacture of special mirrors, and as a lubricant. Cadmium oxide is used in electroplating, storage battery electrodes, catalyst, semiconductors, manufacture of silver alloys, ceramic glazes, and as an ascaricide in pigs (i.e., it kills ticks).
Fate in the environment: All soils and rocks, including coal and mineral fertilizers, contain some cadmium. Small amounts of cadmium enter the environment from the natural weathering of minerals, forest fires, and volcanic emissions, but most is released by human activities such as mining and smelting operations, fuel combustion, disposal of metal-containing products, and application of phosphate fertilizer or sewage sludges. Cadmium in soil may exist in soluble form in soil water, or in insoluble complexes with inorganic and organic soil constituents. It can also get into the soil through land disposal of cadmium-containing wastes (including batteries). Cadmium may be released to water by natural weathering processes, by discharge from industrial facilities or sewage treatment plants, or by leaching from landfills or soil. In surface water and groundwater, cadmium can exist as the hydrated ion, or as ionic complexes with other inorganic or organic substances. Cadmium is not known to form volatile compounds in the aquatic environment, so partitioning from water to the atmosphere does not occur. It often enters air from mining, industry, and burning coal and household wastes. Cadmium and cadmium compounds have negligible vapor pressures, but may exist in air as suspended particulate matter derived from sea spray, industrial emissions, combustion of fossil fuels, or the erosion of soils. When emitted to the atmosphere from combustion processes, it is usually associated with very small particulates that allow them to travel long distances before falling to ground or water. Larger cadmium containing particles from smelters and other pollutant sources are also removed from the atmosphere by gravitational settling, with substantial deposition in areas downwind of the pollutant source. The chief fate of airborne cadmium is to be dispersed by the wind and, subsequently, deposited by wet or dry processes.
Exposure to humans: Human exposure to cadmium can result from consumption of food, drinking water, or incidental ingestion of soil or dust contaminated with cadmium; from inhalation of cadmium-containing particles from ambient air; from inhalation of cigarette smoke; or from working in an occupation involving exposure to cadmium fumes and dust. Smoking is an important source of cadmium exposure and typically doubles the total daily absorption of cadmium. Ingestion of food is the largest source of cadmium exposures in humans. Levels of cadmium in soil may be increasing as a result of the application of municipal sludge or phosphate fertilizers, and this may result in greater human exposures from food chain accumulation in plants and animals. Cadmium in soil tends to be more available when the soil pH is low. Therefore, grain and cereal products usually contribute the greatest percentage of dietary cadmium; potatoes, leafy vegetables, and root vegetables also contain relatively high levels. Fish, plants, and animals take up cadmium from the environment, and occur in all levels of the food chain. It is found in highest concentrations in shellfish, and liver and kidney meats of animals that eat the plants. Most drinking water contains only very low levels of cadmium and is usually not an important route of exposure, although water may leach cadmium from plumbing. Cadmium may also enter the body system from leaching out of some sealants used in dentistry.