Exposures to various fibers, fine particles, and dust occur in several industrial settings and are associated with increased cancer risks. Exposure can also occur in nonindustrial settings.
Asbestos fibers and all commercial forms of asbestos are human carcinogens. In a variety of occupations involving asbestos exposure, increased rates have been consistently observed of mesothelioma—a rare cancer of the lining of the lung and abdominal cavity—and cancer of the lung. Asbestos exposures account for the largest percent of occupational cancer, with the greatest risks among workers who smoke. Asbestos fibers are released into the environment from the use and deterioration of more than 5,000 asbestos products, including

• Roofing,
• Thermal and electrical insulation;
• Cement pipe and sheet;
• Flooring;
• Gaskets;
• Plastics; and
• Textile and paper products.

Workers in asbestos insulation, brake maintenance and repair, and building demolition jobs are exposed to high levels of asbestos. And because asbestos has been so widely used, the entire population may have been exposed to some degree. Since the restriction of asbestos in the United States, exposure to the general population has decreased. Nonetheless, through renovations, repairs, and demolitions, workers employed in construction trades and electricians and carpenters can still experience high levels of asbestos exposures.

Ceramic fibers are now used as insulation materials and are a replacement for asbestos. Because ceramic fibers can withstand high temperatures, they are used to line furnaces and kilns. Ceramic fibers have, however, caused lung cancer in experimental animals. Silica dusts are associated with an excess risk of lung cancer in humans and are found in industrial and occupational settings such as coal mines, mills, granite quarrying and processing, crushed stone and related industries, and sandblasting operations.

Wood dust, associated with cancers of the nasal cavities and sinuses, is a known carcinogen for unprotected workers exposed regularly from sanding operations and furniture manufacturing.

Dioxins are unwanted byproducts of chemical processes. Dioxins comprise chlorine and hydrocarbons (i.e., substances that contain both hydrogen and carbon). At least 100 different kinds of dioxins are known. Industry does not intentionally manufactured them; they are produced by

• Paper and pulp bleaching;
• Incineration of municipal, toxic, and hospital wastes;
• Certain electrical fires; and
• Smelters (i.e., plants in which metals are extracted from ores).

Dioxins are also found as a contaminant in some insecticides, herbicides, and wood preservatives. Dioxins are widespread environmental contaminants; they accumulate in fats and break down slowly. A particular dioxin likely to be carcinogenic to humans is TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin). TCDD is highly carcinogenic in animals, and, in highly exposed workers, increased overall cancer death rates have been reported. Fortunately, modifications of industrial processes such as bleaching and incineration have reduced dioxin emissions and have lowered dioxin levels in people. The general population remains exposed to low levels of TCDD primarily from eating dairy products, fish, and meat, including poultry.

A number of studies show increased incidence of cancer (lung, skin, and urinary cancers) in humans exposed to mixtures of polycyclic aromatic hydrocarbons (PAHs). The primary source of PAHs is the burning of carbon-containing compounds. Burning wood and other fuels in homes produces PAHs in air. They are also contained in gasoline and diesel exhaust, soot, coke, cigar and cigarette smoke, and charcoal-broiled foods. In addition, they are the byproducts of open fires, waste incinerators, coal gasification, and coke oven emissions. Foods that contain small amounts of PAHs include smoked, barbecued, or charcoal-broiled foods, roasted coffees, and sausages.

Arsenic compounds are associated with many forms of skin, lung, bladder, kidney, and liver cancers, particularly when high levels are consumed in drinking water. Occupational exposure to inhaled arsenic, especially in mining and copper smelting, has been consistently associated with an increased lung cancer risk. Arsenic is also used in wood preservatives, glass, herbicides, insecticides (ant killers), and pesticides and is a general environmental contaminant of air, food, and water.

Beryllium compounds are known to cause lung cancer, as worker studies in beryllium production facilities have shown. Beryllium compounds are used as

• Metals for aerospace and defense industries;
• For electrical components,
• X-ray tubes
• Nuclear weapons
• Aircraft brakes
• Rocket fuel additives
• Light aircraft construction, and the manufacture of ceramics;
• And as an additive to glass and plastics,
• Dental applications, and
• Golf clubs.

Industry is also increasingly turning to beryllium for fiber optics and cellular network communication systems. Workers can be exposed through jobs related to the above-listed activities, as well as through recycling of computers, cell phones, and other high-tech products. Outside of these industries, beryllium exposure occurs primarily through the burning of coal and fuel oil. The general population can be exposed to trace amounts of beryllium by inhaling air and consuming food contaminated with beryllium residues. Small beryllium concentrations have been reported in drinking water, food, and tobacco.

Studies of worker groups show that cadmium metal and cadmium compounds are associated with an increased risk of lung cancer. Workers with the highest exposures are those involved in removing zinc and lead from minerals, producing cadmium powders, welding cadmium-coated steel, and working with solders that contain cadmium. Cadmium metal’s primary use is as a metal coating to prevent corrosion. Other uses are in plastic and synthetic products, in batteries, stabilizers for polyvinyl chloride, and in fungicides. The industrial processes involved in making these products release cadmium into the air, surface water, groundwater, and topsoil where cadmium can be taken up by both land and water plants and, in turn, transferred to animals. Contaminated topsoil that allows uptake into tobacco plants may be indirectly responsible for the greatest nonoccupational human exposure to cadmium—smoking. For nonsmokers, food is the main source of human exposure to cadmium.

Some chromium compounds are known to cause lung cancer. The steel industry is the major consumer. Chromium, is used for protection against corrosion of metal accessories, including automotive parts, as well as for electroplating, (i.e., layering one metal over another). Electroplating converts chromium(VI)—the carcinogenic form—into a noncarcinogenic form. This means that workers who handle chromium VI are at greater risk than is the general population. Other chromium uses include nuclear and high-temperature research, the textile and leather-tanning industry, pigments for floor covering products, paper, cement, and asphalt roofing, and creating emerald-colored glass. Chromium is widely distributed in the air, water, soil, and food. Through some of these media, the entire population is probably exposed. The highest chromium exposure occurs in occupations related to stainless steel production, welding, chrome plating, and leather tanning. Typical levels are low in most fresh foods.

Lead acetate and lead phosphate are, given the evidence of kidney and brain tumors in animal studies, likely human carcinogens. Lead acetate is used in cotton dyes; as a coating for metals; as a drier in paints, varnishes, and pigment inks; as a colorant in certain permanent hair dyes (progressive dyes); in explosives; and in washes to treat poison ivy. Lead phosphate is a stabilizer in certain plastics and specialty glass. Primary exposures are through skin contact, eating, and inhaling.

Nickel and nickel compounds are associated with several kinds of cancers in rats and mice. Human-population studies link nickel exposure to cancers of the nasal cavity, lung, and possibly the larynx (voice box). Nickel is used in steel, dental fillings, copper and brass, permanent magnets, storage batteries, and glazes. Because in the United States nickel is present in the air, water, soil, food, and consumer products, we are exposed through eating, breathing, and skin contact.

Arsenic

Skin, lung, bladder, kidney, liver

Wood preservatives, glass, pesticides

Yes

Smelting of ores containing arsenic, pesticide application, and wood preservation

Beryllium

Lung

Nuclear weapons, rocket fuel, ceramics, glass, plastic, fiber optic products

Yes

Beryllium ore miners and alloy makers, phosphor manufacturers, ceramic workers, missile technicians, nuclear reactor workers, electric and electronic equipment workers, and jewelers

Cadmium

Lung

Metal coatings, plastic products, batteries, fungicides

Yes

Smelting of zinc and lead ores, producing, processing and handling cadmium powders, welding or remelting of cadmium-coated steel, and working with solders that contain cadmium

Chromium

Lung

Automotive parts, floor covering, paper, cement, asphalt roofing; anticorrosive metal plating

Yes

Stainless steel production and welding, chromate production, chrome plating, ferrochrome alloys, chrome pigment, and tanning industries

Lead

Kidney, brain

Cotton dyes, metal coating, drier in paints, varnishes, and pigment inks, certain plastics, specialty glass

Probable carcinogen

Construction work that involves welding, cutting, brazing, or blasting on lead paint surfaces; most smelter workers, including lead smelters where lead is recovered from batteries; radiator repair shops

Nickel

Nasal cavity, lung

Steel, dental fillings, copper and brass, permanent magnets, storage batteries, glazes

Nickel metal: Probable carcinogen
Nickel compounds: Yes

Battery makers, ceramic makers, electroplaters, enamellers, glass workers, jewelers, metal workers, nickel mine workers, refiners and smelters, paint-related workers and welders

The particles in diesel exhaust are suspected carcinogens because of the elevated lung cancer rates found in occupational groups exposed to diesel exhaust, such as railroad workers, mine workers, bus garage workers, trucking company workers, car mechanics, and people who work around diesel generators. Cancer risks are unknown from lower exposures in day-to-day living.

Aflatoxins are cancer-causing substances produced by certain types of fungi growing on food. Grains and peanuts are the most common foods on which these fungi grow. Meat, eggs, and milk from animals that eat aflatoxin-contaminated feed are other exposure sources. Agricultural workers are potentially at risk if they inhale contaminated airborne grain dust. Exposure to high levels of aflatoxins increases the risk of liver cancer. In most countries, including the United States, peanuts are screened for aflatoxin, before processing. The risk of aflatoxin exposure is higher in developing countries where screening for the fungus does not occur.

Vinyl chloride, a colorless gas, is a human carcinogen associated with lung cancers and angiosarcomas (blood vessel tumors) of the liver and brain. In the United States it is used almost exclusively by the plastics industry in manufacturing many consumer products, including containers, wrapping film, electrical insulation, water and drain pipes, hosing, flooring, windows, and credit cards. Human exposure occurs primarily in workers in the plastic industry—not in using the end products such as vinyl siding or hosing. The plastics industries are believed to be the major source of vinyl chloride releases into the environment. Although people living near a plastics plant are exposed by breathing contaminated air, exposure of the general population away from a plastics plant is essentially zero.

Benzidine was one of the first chemicals recognized as associated with increased cancer risk in humans. As early as 1921, increased cases of bladder cancer were reportedly associated with benzidine, a compound used in the production of more than 250 benzidine-based dyes for textiles, paper, and leather products. Human exposure to either benzidine or benzidine-based dyes is now known as carcinogenic. Once inside the body, the dyes break down into benzidine. In most cases, dyes that metabolize to benzidine are hazards only near dye and pigment plants where wastes may escape or may be discharged.

Key Points

• Exposures to various fibers, fine particles, and dust occur in several industrial settings and are associated with increased cancer risks.
• Dioxins are unwanted chlorine- and hydrocarbon-containing byproducts of chemical processes. A particular dioxin likely to be carcinogenic to humans is TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin). TCDD is highly carcinogenic in animals, and increased overall cancer death rates have been reported in highly exposed workers.
• A number of studies show an increased incidence of cancer in humans exposed to mixtures of polycyclic aromatic hydrocarbons (PAHs).
• Arsenic compounds are associated with many forms of cancers, particularly when high levels are consumed in drinking water.
• Beryllium compounds are known to cause lung cancer, based primarily on worker studies in beryllium production facilities.
• Studies of groups of workers show that cadmium metal and cadmium compounds are associated with an increased lung cancer risk.
• Some chromium compounds are known to cause lung cancer. Chromium is widely distributed in the air, water, soil, and food. The entire population is probably exposed to some of these compounds.
• Lead acetate and lead phosphate are likely human carcinogens, based on animal-study evidence of kidney and brain tumors.
• Nickel and nickel compounds are associated with several kinds of cancers in rats and mice. Because in the United States nickel is present in the air, water, soil, food, and consumer products, we are exposed through eating, breathing, and skin contact.
• The particles in diesel exhaust are suspected carcinogens because of the elevated lung cancer rates found in occupational groups exposed to diesel exhaust.
• Aflatoxins are cancer-causing substances produced by certain types of fungi growing on food.
• Vinyl chloride is a human carcinogen used almost exclusively in the United States by the plastics industry in manufacturing many consumer products
• Benzidine was one of the first chemicals recognized as associated with increased cancer risk in humans. It is used in the production of dyes.