• What exposure metrics should be used to evaluate air and surface contamination or skin exposure? Will the metrics for sensitization and CBD differ from those for cancer risk?

We first describe beryllium sources and uses and then briefly review beryllium toxicokinetics. Exposure data on naturally occurring, background, and occupational exposure to beryllium are described next, and later sections examine sampling and analytic methods and exposure metrics for air and surface contamination and skin exposure.

SOURCES AND USES

This section reviews forms and characteristics of beryllium that are present in natural and anthropogenic settings. Beryllium metal, with atomic number 4, belongs to group IIA of the periodic table (alkaline-earth elements) and is chemically similar to aluminum; it has a high charge-to-nucleus ratio that leads to amphoteric behavior and a strong tendency to hydrolyze (EPA 1998b; ATSDR 2002). It has many unique chemical properties, being less dense than aluminum and stiffer than steel (EPA 1998b). Because of its small atomic size, its most stable compounds are formed with small anions, such as fluoride and oxide. Beryllium is also capable of forming strong covalent bonds and may form organometallics, such as dimethyl beryllium [Be(CH3)2] (EPA 1998b).

Beryllium has been estimated to be present in the earth’s crust at 2-5 mg/kg, and soil concentrations in the United States were reported to average 0.63 mg/kg and to range from less than 1 to 15 mg/kg (ATSDR 2002). In its review of beryllium, the Agency for Toxic Substances and Disease Registry (ATSDR 2002) reported that surveys had detected beryllium in less than 10% of samples of U.S. surface water and springs, but detection limits are not reported in the review. The low concentrations in water probably reflect beryllium’s typically entering water as beryllium oxide, which slowly hydrolyzes to the insoluble compound beryllium hydroxide (EPA 1998b).

Beryllium concentrations in U.S. air have typically been lower than the detection limit of 0.03 ng/m3 (ATSDR 2002). Natural sources of airborne beryllium are windblown dust and volcanic particles, which are estimated to contribute 5 and 0.2 metric tons per year, respectively, to the atmosphere (Table 2-1). The principal anthropogenic contributor to airborne emission is coal combustion. World coals have been reported to have a wide range of beryllium concentrations, from 0.1 to 1,000 mg/kg (Fishbein 1981), and the range in U.S. coal is 1.8-2.2 mg/kg (ATSDR 2002). On the basis of coal combustion of 640 million metric tons per year and a beryllium emission factor of 0.28 g/ton, the U.S. Environmental Protection Agency (EPA 1998b) has estimated that as much as 180 metric tons of beryllium may be emitted each year from U.S. coal combustion; fuel oil is burned at the rate of 148 million metric tons per year and has a beryl-



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