Introduction

Naturally occurring chromium is usually present as trivalent Cr(III). Hexavalent Cr(VI) in the environment is almost totally derived from human activities [WHO 1990].

Air Contamination

According to the Toxics Release Inventory, in 1997, the estimated releases of chromium were 706,204 pounds to the air from 3,391 large processing facilities which accounted for about 2.2% of total environmental releases.

Cr(III) and Cr(VI) are released to the environment primarily from stationary point sources (facilities that are identified individually by name and location) resulting from human activities. The estimates of atmospheric chromium emissions in 1976 and 1980 in the Los Angeles, CA and Houston, TX areas indicate that emissions from stationary fuel combustion are about 46-47% of the total, and emissions from the metal industry range from 26 to 45% of the total [ATSDR 2000].

Coal and oil combustion contribute an estimated 1,723 metric tons of chromium per year in atmospheric emissions; however, only 0.2% of this chromium is Cr(VI). In contrast, chrome-plating sources are estimated to contribute 700 metric tons of chromium per year to atmospheric pollution, 100% of which is believed to be Cr(VI) [ATSDR 2000].

Cr(III) in the air does not undergo any reaction. Cr(VI) in the air eventually reacts with dust particles or other pollutants to form Cr(III). However, the exact nature of such atmospheric reactions has not been studied extensively [EPA 1998].

Water Contamination

According to the Toxics Release Inventory, in 1997, the estimated releases of chromium was 111,384 pounds to water from 3,391 large processing facilities which accounted for about 0.3% of total environmental releases [ATSDR 2000].

Electroplating, leather tanning, and textile industries release relatively large amounts of chromium in surface waters. Leaching from topsoil and rocks is the most important natural source of chromium entry into bodies of water. Solid wastes from chromate-processing facilities, when disposed of improperly in landfills, can be sources of contamination for groundwater, where the chromium residence time might be several years.

A survey conducted from 1974 to 1975 provides estimates of chromium concentrations in U.S. drinking water. The survey reported the concentration of chromium in tap water in U.S. households was from 0.4 to 8.0 micrograms per liter (µg/L). [ATSDR 2000] (EPA's maximum contaminant level for chromium in drinking water is 100 µg/L.)

Soil Contamination

According to the Toxics Release Inventory, in 1997 the estimated releases of chromium was 30,862,235 pounds to soil from 3,391 large processing facilities accounted for about 94.1% of total environmental releases [ATSDR 2000].
Total chromium has been identified in 939 soil and 472 sediment samples collected from 1,036 National Priority Lists (NPL) hazardous waste sites [HazDat 2000].

Chromium waste slag containing potentially hazardous levels of Cr(VI) compounds was used as fill material at more than 160 residential, industrial, and recreational sites. Persons living or working in the vicinity of the sites may have been exposed through inhalation, ingestion, or skin contact with contaminated soils and dusts [Fagliano, Savrin et al. 1997].

Community exposure from this fill occurred in a variety of ways. Wind erosion of the soil could have made slag particles airborne, increasing the opportunity for inhalation of chromium. Chromium compounds leached by rainwater could have migrated through cracks in soil, asphalt roadways, and masonry walls, forming high-content chromium crystals on their surfaces. In soil and roadways, these particles might have been eroded by wind and foot traffic and carried as chromium-laden dust into homes and workplaces. Children playing in areas where the slag was used as fill might also have been exposed through skin contact with chromium-contaminated dust, dirt, and puddles and /or ingestion of contaminated soil.

Other Environmental Sources

Other environmental sources of chromium are cement-producing plants (cement contains chromium), the wearing down of asbestos linings that contain chromium, emissions of chromium-based automotive catalytic converters, and tobacco smoke.

The general population is exposed to chromium by eating food or food supplements, drinking water, and inhaling air that contain chromium. The mean daily dietary intake of chromium from air, water, and food is estimated to be <0.2-0.4, 2.0, and 60 micrograms, respectively [ATSDR 2000].

One study found increased blood chromium level after total hip replacement using metal-metal pairings where metal ions of the alloys are released [Schaffer, Pilger et al. 1999].

Summary of Environmental and Occupational Sources of Chromium Exposure

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