CAS No. 7440-33-7
Tungsten is a steel-gray to tin-white metal that occurs naturally in the earth's crust, mainly as scheelite (CaWO4). Tungsten is used mainly for producing hard metals, which are used in rock drills and metal-cutting tools, and for producing ferrotungsten, which is used in the steel industry. Tungsten compounds are used as lubricating agents, filaments for incandescent lamps, bronzes in pigments, and as catalysts in the petroleum industry.
Most background environmental exposures to tungsten are from the soluble forms such as tungstate salts that may occur in drinking water. Occupational exposure is from dusts released during grinding or drilling of hard metals. Human health effects from tungsten at low environmental doses or at biomonitored levels from low environmental exposures are unknown. Little information is available on the toxicity of tungsten. Human illness from low-level environmental or occupational exposure has not been well established. Although workers occupationally exposed to tungsten carbide may develop serious lung disease ("hard metal disease"), their illness may stem from exposure to cobalt mixed with tungsten carbide rather than to tungsten alone. Evidence is lacking for the carcinogenicity of tungsten, and it has not been classified with respect to human carcinogenicity by either IARC or NTP. Workplace air standards for external exposure have been established by ACGIH and recommended by NIOSH. Information about external exposure (i.e., environmental levels) and health effects is available from ATSDR at http://www.atsdr.cdc.gov/toxprofiles/index.asp.
Levels of urinary tungsten reflect recent exposure. A nonrandom subsample from NHANES III demonstrated slightly higher values than those found in NHANES 1999-2000, 2001-2002, and 2003-2004 (Paschal et al., 1998), possibly due to methodologic, population, or exposure differences. A study of 14 unexposed adults yielded values similar to those in the U.S. population (CDD, 2012; Schramel et al., 1997). In a Nevada community where tungsten was measured and found at increased levels in drinking water, the residents' median urinary levels were as much as 15-fold higher than median levels in the U.S. population (CDC, 2003, 2005).
Workers involved in grinding operations that released tungsten metal into the air had elevated urinary levels that were more than 900 times higher than the overall geometric mean of the U.S. population in the NHANES 1999-2000 (Kraus et al., 2001). Using neutron activation analysis to measure urinary tungsten, Nicolaou et al. (1987) found that a control group of non-metal workers had mean levels that were similar to the 95th percentiles in the National Report on Human Exposure to Environmental Chemicals (CDC, 2012), whereas the tungsten-worker group had mean urine levels 35 times higher. Patients with medically-inserted tungsten embolization coils showed elevated tungsten levels in blood, urine, and hair (Bachthaler et al., 2004). Urinary tungsten levels in many patients were hundreds-fold higher than observed in the U.S. population (CDC, 2012).
Finding a measurable amount of tungsten in the urine does not imply that the level of tungsten causes an adverse health effect. Biomonitoring studies on levels of tungsten provide physicians and public health officials with reference values so that they can determine whether people have been exposed to higher levels of tungsten than are found in the general population. Biomonitoring data can also help scientists plan and conduct research on exposure and health effects.
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