BERYLLIUM AND BERYLLIUM COMPOUNDS

Anthropogenic sources of beryllium in soil include landfill disposal of coal ash (about 100 mg beryllium/kg) (Griffitts et al., 1977) and municipal waste combustor ash, land burial of industrial wastes (22.2 tonnes from monitored industries in 1988; ATSDR, 1993), and land application of beryllium-enriched sewage sludge. Deposition of atmospheric beryllium is also a source of beryllium in soil. Quantitative data regarding the relative significance of each of these sources were not located.

Beryllium in the atmosphere is transported to water and soil by both dry and wet deposition (US EPA, 1987). It is not known if beryllium oxide in air reacts with sulfur or nitrogen oxides to produce beryllium sulfate or nitrate, but such a conversion to water-soluble compounds would accelerate removal of beryllium from the atmosphere by wet deposition. In most natural waters, the majority of beryllium will be sorbed to suspended matter or in the sediment, rather than dissolved. For example, in the US Great Lakes, beryllium is present in sediment at concentrations several orders of magnitude higher than its concentration in water (Bowen, 1979; Lum & Gammon, 1985; Rossman & Barres, 1988). Beryllium in sediment is primarily adsorbed to clay, but some beryllium may be in sediment as a result of the formation and precipitation of insoluble complexes (ATSDR, 1993). At neutral pH, most soluble beryllium salts dissolved in water will be hydrolysed to insoluble beryllium hydroxide (Callahan et al., 1979), and only trace quantities of dissolved beryllium will remain (Hem, 1970). However, at high pH, water-soluble complexes with hydroxide ions may form, increasing the solubility and mobility of beryllium. Solubility may also increase at low pH; detectable concentrations of dissolved beryllium have been found in acidified waters (US EPA, 1998).

Beryllium is not significantly bioconcentrated from water by aquatic species (Callahan et al., 1979; Kenaga, 1980; US EPA, 1980). It is also apparently not bioaccumulated from sediment by bottom feeders; beryllium levels in clams and oysters from Lake Pontchartrain, Louisiana, USA, were similar to levels in the surface sediments (Byrne & DeLeon, 1986). Most plants take up beryllium from soil in small amounts, although a few species (e.g., hickory, birch, larch) act as beryllium accumulators (Nikonova, 1967; Griffitts et al., 1977). The plant/soil transfer coefficient for beryllium has been estimated as 0.01–0.1, depending on plant species and soil properties (Kloke et al., 1984). Very little of the beryllium taken up by the roots is translocated to other plant parts (Romney & Childress, 1965), although above-ground plant parts can also be contaminated via atmospheric deposition. There is no evidence for significant biomagnification of beryllium within food chains (Callahan et al., 1979; Fishbein, 1981).

Atmospheric beryllium concentrations at rural sites in the USA ranged from 0.03 to 0.06 ng/m³ (Ross et al., 1977). These background levels probably reflect fossil fuel combustion, and lower levels may be found in less industrialized countries. Ross et al. (1977) reported beryllium concentrations of 0.04–0.07 ng/m³ at suburban sites and 0.1–0.2 ng/m³ at urban industrial sites in Dayton, Ohio, USA. Annual average beryllium concentrations at urban monitoring stations throughout the USA ranged from <0.1 to 6.7 ng/m³ during 1981–1986 (US EPA, 1987). A survey of beryllium concentrations in Japanese cities reported an average value of 0.042 ng/m³ and a maximum value of 0.222 ng/m³ (Ikebe et al., 1986). Urban areas in Germany had beryllium concentrations ranging from 0.06 to 0.33 ng/m³ (Mueller, 1979; Freise & Israel, 1987).

Higher concentrations have been reported in the vicinity of beryllium processing plants, including a mean of 15.5 ng/m³ and maximum of 82.7 ng/m³ near a Pennsylvania, USA, factory (Sussman et al., 1959), an average of 1 µg/m³ at a distance of 400 m from a beryllium extracting and processing plant in the former USSR that was not equipped with emission controls (decreasing to 10–100 ng/m³ at a distance of 1000 m) (Izmerov, 1985), and a mean of 8.4 ng/m³ (range 3.9–16.8 ng/m³) near a coal-fired power plant in Czechoslovakia (Bencko et al., 1980).

Using an atmospheric transport model, McGavran et al. (1999) estimated the air concentrations of beryllium resulting from emissions from the Rocky Flats (nuclear weapons) plant in Colorado, USA, during its operation from 1958 to 1989. Emissions passed through high-efficiency particulate air filters prior to release. The highest beryllium concentration, 6.8 ×10^–2 ng/m³ (95th percentile), was predicted to occur on-site. The predicted 50th percentile air concentrations of beryllium at the predicted location of the highest off-site concentration ranged from 1.3 × 10^–6 ng/m³ in 1986 to 7.3 × 10^–4 ng/m³ in 1968, the year of the highest releases. These predicted off-site values do not exceed background.

Beryllium is widely distributed in soils at low concentrations. An overall average concentration of 2.8–5.0 mg/kg has been estimated (ATSDR, 1993), but this figure is skewed by relatively rare areas with large deposits of beryllium minerals, where concentrations can reach up to 300 mg/kg and average 60 mg/kg (Shacklette et al., 1971). Agricultural soils in the USA contained <1–7 mg beryllium/kg and averaged 0.6 mg beryllium/kg (Shacklette et al., 1971). In Japan, the mean soil concentration was 1.31 mg beryllium/kg (Asami & Fukazawa, 1985).

Surface waters have been reported to contain beryllium at concentrations up to 1000 ng/litre (Bowen, 1979). Beryllium concentrations ranged from <4 to 120 ng/litre in the US Great Lakes (Rossman & Barres, 1988) and from <10 to 120 ng/litre (10–30 ng/litre average) in Australian river waters (Meehan & Smythe, 1967). Based on the US EPA’s STORET database for the years 1960–1988, the geometric mean concentration of total beryllium in US surface waters was estimated to be 70 ng/litre (Eckel & Jacob, 1988). Sediments from lakes in Illinois, USA, contained 1.4–7.4 mg beryllium/kg (Dreher et al., 1977). Groundwater in Germany contained an average beryllium concentration of 8 ng/litre (Reichert, 1974). Reported levels in seawater are lower than those in fresh water, ranging from 0.04 to 2 ng/litre (Merril et al., 1960; Meehan & Smythe, 1967; Measures & Edmond, 1982). Sediments in Tokyo and Sagami bays in Japan averaged 1.29 mg beryllium/kg (Asami & Fukazawa, 1985). Beryllium concentrations in water and sediment will be higher in the vicinity of point sources; concentrations of 30–170 µg/litre have been reported in industrial effluents (ATSDR, 1993).

Beryllium is generally found in plant samples at concentrations below 1 mg/kg dry weight (IPCS, 1990), although certain species that concentrate beryllium from soils (e.g., hickory, birch, larch) may have concentrations up to 10 mg/kg dry weight (Nikonova, 1967; Griffitts et al., 1977). Concentrations up to 100 µg beryllium/kg fresh weight have been reported in various fish and other marine organisms (Meehan & Smythe, 1967; Byrne & DeLeon, 1986).

The general population may be exposed to trace amounts of beryllium by inhalation of air, consumption of drinking-water and food, and inadvertent ingestion of dust. The US EPA (1987) estimated total daily beryllium intake as 423 ng, with the largest contributions from food (120 ng/day, based on daily consumption of 1200 g of food containing 0.1 ng beryllium/g fresh weight) and drinking-water (300 ng/day, based on daily intake of 1500 g of water containing 0.2 ng beryllium/g), and smaller contributions from air (1.6 ng/day, based on daily inhalation of 20 m³ of air containing 0.08 ng beryllium/m³) and dust (1.2 ng/day, based on daily intake of 0.02 g/day of dust containing 60 ng beryllium/g). The concentration used for beryllium in food was the midpoint of a range of values reported for a variety of foods in an Australian survey (Meehan & Smythe, 1967). The concentration used for beryllium in drinking-water was based on a survey of 1577 drinking-water samples throughout the USA, where beryllium was detected in 5.4% of samples with mean and maximum concentrations of 190 and 1220 ng/litre, respectively (US EPA, 1980). The concentration used for beryllium in air was taken as a likely average concentration in a residential area based on air sampling results reported above. The concentration used for beryllium in household dust was estimated by assuming an indoor air concentration of 0.1 ng/m³ and an air/dust ratio of 600. Although intake from air and dust are minor under background conditions, these can be important pathways of exposure in the vicinity of a point source. Beryllium intake through air and dust can be increased 2–3 orders of magnitude in the vicinity of a point source, such as a coal-fired power plant (IPCS, 1990).

Tobacco smoke is another potential source of exposure to beryllium in the general population. Beryllium levels of 0.47, 0.68, and 0.74 µg/cigarette were found in three brands of cigarettes (Zorn & Diem, 1974). Between 1.6 and 10% of the beryllium content, or 0.011–0.074 µg/cigarette, was reported to pass into the smoke during smoking. Assuming the smoke is entirely inhaled, an average smoker (20 cigarettes per day) might take in approximately 1.5 µg beryllium/day (3 times the combined total of the other routes). Other potential exposures to beryllium in the general population from consumer products are limited but may include leaching of beryllium from beryllium–nickel dental alloys (Covington et al., 1985) and emission of beryllium from the mantle of gas lanterns (Griggs, 1973).

Occupational exposure to beryllium occurs in a variety of industries (see section 4), ranging from mining to golf club manufacturing. In these industries, beryllium is released into the air by various processing techniques (melting, grinding, welding, drilling, etc.). In the USA, it was estimated that 13 869 workers were potentially exposed to beryllium metal and 4305 were potentially exposed to beryllium oxide during the years 1981–1983 (NIOSH, 1989). Occupational standards of 1–5 µg beryllium/m³ (time-weighted average, or TWA) have been promulgated in the USA and other countries but are not always achieved. For example, workers at a US precious metal refinery in 1983 had TWA personal air exposures that ranged from 0.22 up to 42.3 µg beryllium/m³ (Cullen et al., 1987). Workers at a metal processing plant in Germany in 1983 who worked on beryllium-containing alloys had breathing zone air samples containing 0.1–11.7 µg beryllium/m³ (Minkwitz et al., 1983). In general, however, exposures are much lower now than in previous years. TWA daily beryllium exposures for some workers at a metal extraction and production plant that had been >50 µg beryllium/m³ during the mid-1960s and >30 µg beryllium/m³ during the mid-1970s were reduced to <2 µg beryllium/m³ in the late 1970s in compliance with the occupational exposure standard (Kriebel et al., 1988a). Prior to 1950 and implementation of emission controls, workplace concentrations exceeding 1 mg/m³ were not unusual in the USA (Eisenbud & Lisson, 1983), and similar conditions existed in the former USSR (Izmerov, 1985).

Few data are available on the particle characteristics of beryllium under occupational exposure conditions. However, Hoover et al. (1990) found that 5.7% of the particles released during sawing of beryllium metal had aerodynamic diameters smaller than 25 µm but larger than 5 µm, and 0.3% were smaller than 5 µm. For milling of beryllium metal, 12–28% of the particles had aerodynamic diameters between 5 and 25 µm, and 4–9% were smaller than 5 µm, depending on the milling depth. More than 99% of the particles generated from operations conducted with beryllium alloys were larger than 25 µm.

The temperature at which beryllium oxide is calcined influences its particle size (surface area), its solubility, and, ultimately, its toxicity. Calcination of beryllium oxide at 500 °C produces a more toxic oxide than calcination at 1000 °C, which has been attributed to the oxide’s greater specific surface area compared with that of the material calcined at 1000 °C (Finch et al., 1988; Haley et al., 1989).

7.1.1 Inhalation

Although inhalation is the primary route of uptake of occupationally exposed persons, no human data are available on the deposition or absorption of inhaled beryllium. The deposition and clearance of beryllium, like those of other inhaled particles, are governed by important factors such as dose, size, and solubility. Particles formed from volatile emissions as a result of high temperature by either nucleation (where gas molecules come together) or condensation (where gas molecules condense onto an existing particle) tend to be fine and much smaller in size than those produced by mechanical processes, where small but coarser particles are produced from larger ones.

Atmospheric beryllium is primarily in the form of particulate matter. The respiratory tract, especially the lung, is the primary target of inhalation exposure in animals and humans. Inhaled beryllium particles are deposited in the respiratory tract and subsequently cleared. Absorption of beryllium occurs following its mobilization by clearance mechanisms. Significant absorption, approximately 20% of the initial lung burden, was noted via inhalation or intratracheal instillation of soluble beryllium salts; however, for sparingly soluble compounds (e.g., beryllium oxide), absorption is slower and less substantial (Delic, 1992; HSE, 1994). Animal studies have shown that clearance of soluble and sparingly soluble beryllium compounds is biphasic via both inhalation and intratracheal administration, with an initial rapid phase attributed to mucociliary transport of particles from the tracheobronchial tree to the gastrointestinal tract, followed by a prolonged slow phase of clearance via translocation to tracheobronchial lymph nodes, uptake by alveolar macrophages, and solubilization of beryllium (Camner et al., 1977; Sanders et al., 1978; Delic, 1992; HSE, 1994). In rats, the half-time for the rapid phase is on the order of 1–60 days, while that for the slow phase is generally in the range 0.6–2.3 years and is dependent upon the solubility of the beryllium compounds — namely, weeks/months and months/years for the soluble and sparingly soluble compounds, respectively (Reeves & Vorwald, 1967; Reeves et al., 1967; Zorn et al., 1977; Rhoads & Sanders, 1985). The slow clearance from the lungs means that beryllium may remain in the human lungs for many years after exposure, and this has been observed in human workers (e.g., Schepers, 1962). The amount of beryllium remaining in the lungs at any time after exposure is a function of the amount deposited and the rate of clearance, which depend in turn on the dose, size, and solubility of the specific beryllium particles inhaled. Studies in guinea-pigs and rats indicate that 40–50% of the inhaled soluble beryllium salts are retained in the respiratory tract; however, similar data by this exposure route do not appear to be available for the sparingly soluble inorganic beryllium compounds or the metal (Delic, 1992; HSE, 1994). Rats and mice were acutely exposed by the nose-only route to aerosolized beryllium metal. A comparison of the single-dose studies demonstrated that a single, acute inhalation exposure to beryllium metal can chronically retard particle clearance and induce lung damage in rats (Haley et al., 1990) and mice (Finch et al., 1998a). Other single nose-only inhalation studies by Finch et al. (1994) using male F344/N rats exposed to beryllium metal concentrations (and a ⁸⁵Sr radioactive trace) sufficient to result in mean beryllium lung burdens of 1.8, 10, and 100 µg estimated a clearance half-life of between 250 and 380 days for these three groups of rats with these different lung burdens. In the case of mice (Finch et al., 1998a), lung clearance of beryllium was segregated into two discrete groups, with clearance half-times of 91–150 days (for 1.7- and 2.6-µg lung burden groups) or 360–400 days (for 12- and 34-µg lung burden groups). However, clearance half-times were similar for rats and mice in the two most affected groups. In general, more soluble beryllium compounds are cleared more rapidly than less soluble compounds (Van Cleave & Kaylor, 1955; Hart et al., 1980; Finch et al., 1990).

7.1.2 Oral

Gastrointestinal absorption can occur by both the inhalation and oral (diet, drinking) routes of exposure. In the case of inhalation, a portion of the inhaled material is transported to the gastrointestinal tract by the mucociliary escalator or by the swallowing of the insoluble material deposited in the upper respiratory tract (Kjellstrom & Kennedy, 1984). Unlike inhalation, where a significant part of the inhaled dose is incorporated into the skeleton (ultimate site of beryllium storage, half-life of 450 days), oral administration results in <1% absorption and storage (as reviewed by US EPA, 1991). Most of the beryllium taken up by the oral route passes through the gastrointestinal tract unabsorbed and is eliminated in the faeces.

Beryllium is poorly absorbed from the gastrointestinal tract, probably because as soluble beryllium sulfate passes into the intestine, which has a higher pH, the beryllium is precipitated as the insoluble phosphate and thus is no longer available for absorption (Reeves, 1965).

7.1.3 Dermal

Beryllium is also poorly absorbed through the skin, which is likely due to the fact that beryllium is bound by epidermal (alkaline phosphatase and nucleic acids) constituents or converted to an insoluble beryllium compound at physiological pH (see Fig. 1). Only trace amounts of beryllium were absorbed through the tail skin of rats exposed to an aqueous solution of beryllium chloride (Petzow & Zorn, 1974).

Beryllium and its compounds are not biotransformed, but soluble beryllium salts are converted to less soluble forms in the lung (ATSDR, 1993). Insoluble beryllium, engulfed by activated phagocytes, can be ionized by myeloperoxidases (Leonard & Lauwerys, 1987; Lansdown, 1995).

Following inhalation exposure, beryllium cleared from the lungs is distributed to the tracheobronchial lymph nodes and the skeleton, which is the ultimate site of beryllium storage (Stokinger et al., 1953; Clary et al., 1975; Sanders et al., 1975; Finch et al., 1990). Trace amounts are distributed throughout the body (Zorn et al., 1977). Like inhaled beryllium, parenterally administered beryllium salts lead to accumulation in the skeletal system (Crowley et al., 1949; Scott et al., 1950). Following oral exposure, beryllium accumulates mainly in bone, but is also found in the stomach, intestines, liver, kidney, spleen, mesenteric lymph nodes, and other soft tissues (Furchner et al., 1973; Morgareidge et al., 1975; Watanabe et al., 1985; LeFevre & Joel, 1986). Systemic distribution of the more soluble compounds is greater than that of the insoluble compounds (Stokinger et al., 1953). Transport of beryllium across the placenta has been shown in rats and mice treated by intravenous injection (Bencko et al., 1979; Schulert et al., 1979).

Absorbed beryllium is eliminated primarily in the urine (Crowley et al., 1949; Scott et al., 1950; Furchner et al., 1973; Stiefel et al., 1980), whereas excretion of unabsorbed beryllium is primarily via the faecal route shortly after exposure by inhalation or intratracheal administration, through mucociliary clearance from the respiratory tract and ingestion of swallowed beryllium (Hart et al., 1980; Finch et al., 1990). In animal ingestion studies using radiolabelled beryllium chloride in rats, mice, dogs, and monkeys, the vast majority of the ingested dose was excreted in the faeces; in most studies, <1% of the administered radioactivity was excreted in the urine (Crowley et al., 1949; Furchner et al., 1973; LeFevre & Joel, 1986). Although biliary excretion of absorbed material can lead to high faecal elimination, this is not an important pathway for beryllium (Cikrt & Bencko, 1975). In parenteral studies using carrier-free ⁷Be, a far higher percentage of the dose was eliminated in the urine than in the faeces (Crowley et al., 1949; Scott et al., 1950; Furchner et al., 1973). This indicates that beryllium in the faeces following oral exposure is primarily unabsorbed material and that the best estimate for oral absorption is <1%, based on urinary excretion.

As with inhalation, the elimination of beryllium following percutaneous incorporation of soluble beryllium nitrate as ⁷Be demonstrated that more than 90% was eliminated via urine (Zorn et al., 1977). Mean daily excretion of beryllium metal was 4.6 × 10^–6 % of the administered dose (intratracheal instillation) in baboons and 3.1 × 10^–6 % in rats (Andre et al., 1987). Urinary excretion of beryllium following occupational exposure correlates qualitatively with degree of exposure (Klemperer et al., 1951). Elimination half-times of 890–1770 days (2.4–4.8 years) were calculated for mice, rats, monkeys, and dogs injected intravenously with beryllium chloride (Furchner et al., 1973). A half-life of 450 days has been estimated for beryllium in the human skeleton (ICRP, 1960). More than 99% of ingested radioberyllium as ⁷BeCl₂ was excreted in the faeces, and 0.002% of the ingested amount was transferred to the milk in dairy cows (Mullen et al., 1972).

8.1.1 Inhalation and intratracheal instillation

Inhaled beryllium is highly toxic by acute exposure. The acute 4-h LC₅₀ value for beryllium sulfate was reported to be 0.15 mg beryllium/m³ in rats; that for beryllium phosphate was 0.86 mg/m³ (Venugopal & Luckey, 1977). In guinea-pigs, the 4-h LC₅₀ for beryllium phosphate was 4.02 mg beryllium/m³. Single 1-h nose-only exposure to beryllium sulfate at 4.05 mg beryllium/m³ (mass median aerodynamic diameter 1.9 µm, geometric standard deviation [GSD] 1.89) resulted in the progressive development of pneumonitis and pleural plaques in rats (Sendelbach et al., 1989). Comparable exposure to sulfuric acid did not produce any significant pathological effects in the lungs, indicating that the effects were not due to the low pH of the beryllium sulfate dissolved in water (~2.7) or the anion.

Inhalation studies in rats and dogs exposed to beryllium oxide produced pneumonitis, granulomatous lesions, fibrosis, and hyperplasia. In beagle dogs, single, acute, nose-only inhalation exposure to beryllium oxide calcined at 500 or 1000 °C induced granulomatous pneumonia, lymphocytic infiltration into the lung, and positive beryllium-specific lymphocyte proliferative responses in vitro. The changes were more marked after exposure to beryllium oxide calcined at 1000 °C.

In testing the sensitivity of the transgenic heterozygous p53 knockout mouse model for predicting cancer via inhalation, mice of both sexes were exposed by nose-only inhalation to either air (controls) or beryllium metal (15 or 60 µg). Only the transgenic heterozygous mouse (p53+/–) was susceptible to carcinogenesis (Finch et al., 1998b).

Inflammatory and granulomatous lesions were observed after intratracheal instillation of beryllium oxide or beryllium hydroxide in rats and also in rats acutely exposed (nose-only) to beryllium metal via inhalation (Haley et al., 1990, 1992; Finch et al., 1994) or intratracheal instillation (LaBelle & Cucci, 1947).

A follow-up study demonstrated that short-term nose-only exposure to aerosolized beryllium metal can also retard particle clearance and induce lung damage in mice (Finch et al., 1998a). The mass of beryllium metal required to induce lung damage in mice is similar to that needed for rats. However, there is a significant accumulation of lymphocytes in mice, while no such change was observed in rats (Finch et al., 1994, 1996; Nikula et al., 1997).

A single exposure of A/J (H-2^a haplotype) mice to beryllium sulfate via intratracheal instillation resulted in histological changes in the lungs but not in BALB/c or C57BL6/J mice. Similar histological changes were also induced in the lung by beryllium oxide, which correlated with bronchoalveolar lavage (BAL) cellularity, but these changes were greatly delayed and did not proceed to frank granulomas. Only BAL lymphocytes from mice preimmunized with beryllium sulfate/serum and challenged with beryllium sulfate/serum showed significant in vitro proliferation in response to beryllium sulfate (Huang et al., 1992).

8.1.2 Other routes

Soluble beryllium compounds administered orally are moderately toxic. Oral LD₅₀ values reported for beryllium compounds, including beryllium fluoride, beryllium chloride, beryllium sulfate, and a mixture of beryllium fluoride and beryllium oxide, ranged from 18.3 mg/kg body weight for the mixture (beryllium fluoride and beryllium oxide) to 200 mg/kg body weight for beryllium chloride in rats and 18–20 mg/kg body weight for beryllium fluoride to 140 mg/kg body weight for beryllium sulfate in mice (ATSDR, 1993). The sparingly soluble beryllium oxide had little or no effect on the LD₅₀ of beryllium fluoride.With the exception of beryllium fluoride (fluoride ion also contributes to toxicity), the differences in the LD₅₀ values of the other beryllium compounds are due to differences in solubility and the potential to form insoluble beryllium phosphate in the gastrointestinal tract (ATSDR, 1993).

No dermal single-dose studies were available for soluble and sparingly soluble beryllium compounds (Delic, 1992; HSE, 1994).

No data were located regarding the dermal or ocular irritancy of beryllium in laboratory animals. Both the soluble and sparingly soluble compounds of beryllium have been shown to be skin sensitizers in guinea-pigs, rabbits, mice, and pigs. Skin sensitization has been achieved following induction via the topical, intradermal, inhalation, or intratracheal routes of exposure. Cell-mediated passive transfer of the sensitized state has been demonstrated in guinea-pigs and mice. Several studies that have been identified in reviews (Delic, 1992; ATSDR, 1993; HSE, 1994) have demonstrated cutaneous hypersensitivity reactions to beryllium in guinea-pigs (Alekseeva, 1966; Belman, 1969; Marx & Burrell, 1973; Zissu et al., 1996). In these studies, guinea-pigs were sensitized by repeated intradermal injection or dermal application of small doses of soluble beryllium salts. In the study by Marx & Burrell (1973), skin reactions developed 6–8 h after the subsequent patch test challenge and lasted up to 3 weeks. The severity of the skin reaction was greater when a more soluble salt was used for the challenge (fluoride > sulfate > oxide). In a similar study, Krivanek & Reeves (1972) found that beryllium-sensitized guinea-pigs (beryllium sulfate) elicited different skin reactions depending on the beryllium compound used. The forms of beryllium used in the elicitation reaction were the sulfate, the hydrogencitrate, the albuminate, and the aurintricarboxylate. Each of these anions binds beryllium in solution with different tenacity. The beryllium–albuminate produced the greatest hypersensitivity, followed by beryllium sulfate, whereas beryllium–hydrogencitrate and beryllium–aurintricarboxylate produced essentially negative reactions due to the fact that the beryllium was strongly bound to the anion and therefore unavailable for interaction with the skin. Zissu et al. (1996) found hypersensitivity reactions in 30–60% of guinea-pigs sensitized with beryllium sulfate in response to challenge with beryllium–copper and beryllium–aluminium alloys. Vacher (1972) reported that skin contact was necessary for development of a hypersensitivity reaction to beryllium (parenteral administration did not elicit an immunological reaction) and that only forms of beryllium capable of complexing with skin constituents were immunogenic.

Respiratory sensitization studies in dogs exposed to aerosols of beryllium oxide demonstrated a sensitization that was specific to beryllium (based on immune responses of lymphocytes harvested from lung and blood) compared with a lack of a proliferative response when lymphocytes from treated dogs were tested against zinc sulfate and nickel sulfate and with a series of common canine antigens (Haley et al., 1997).

Other immunological studies that may not be relevant to human exposure via inhalation have been conducted. In the case of cynomolgus monkeys dosed intrabronchially with beryllium metal or beryllium oxide (calcined at 500 °C), beryllium-specific lymphocyte proliferation did not increase for lymphocytes from beryllium oxide-exposed (intrabronchiolar instillation) lung lobes, but did increase with exposure to the metal (Haley et al., 1994). In the case of mice (A/J and C3H/HeJ) exposed to a single, relatively high lung burden of inhaled beryllium metal, there were increases in lymphocyte proliferation in the lungs, but beryllium-specific proliferation of lymphocytes was not observed in the beryllium lymphocyte transformation test (BeLT) using lymphocytes from peripheral blood, the spleen, or bronchial lymph nodes. A lack of beryllium-specific proliferation of lymphocytes was also observed in mice (Balb/c or C57B1) administered a single intratracheal dose of beryllium sulfate using the BeLT with BAL lymphocytes (Huang et al., 1992). Although these two latter studies differed in the beryllium compound studied and neither demonstrated a beryllium-specific response, the observed granulomas did have an immune component.

8.3.1 Inhalation

With the exception of beryllium oxide and beryllium hydrogenphosphate (BeHPO₄), few sparingly soluble salts of beryllium have been studied via this exposure route (Delic, 1992; ATSDR, 1993; HSE, 1994). Short-term inhalation exposure to beryllium produces acute chemical pneumonitis in laboratory animals. Schepers (1964) exposed groups of four monkeys to aerosols (particle size not reported) of beryllium sulfate, beryllium fluoride, or beryllium phosphate for 7–30 days. Similar effects were noted in all exposed monkeys; however, in the monkeys exposed for only 7 days, recovery was observed. In contrast to beryllium fluoride, no notable effects were observed in other extrapulmonary tissues following exposure to beryllium sulfate. Observed effects included severe weight loss, dyspnoea, pulmonary oedema, congestion, and marked changes in the liver (hepatocellular degeneration), kidneys (glomerular degeneration), and other internal organs (adrenals, pancreas, thyroid, and spleen). The soluble salts produced these effects at lower concentrations (184 µg beryllium/m³ for the fluoride, 198 µg beryllium/m³ for the sulfate) than the slightly soluble phosphate (1132 µg beryllium/m³). The excessive toxicity observed with beryllium fluoride compared with beryllium sulfate cannot be explained on the basis of solubility (roughly the same) but is probably due to the toxicity exhibited by the fluoride anion, as was previously noted in section 8.1.2 with respect to LD₅₀ values of beryllium fluoride.

Insoluble beryllium oxide (low-fired at 400 °C) also produced pneumonitis in rats and dogs after a 40-day exposure to 3.6 mg beryllium/m³ (Hall et al., 1950). However, beryllium oxides high-fired at 1150 or 1350 °C did not produce pulmonary damage after a 360-h exposure to 32 mg beryllium/m³, possibly due to greater particle size and greater degree of aggregation in the high-fired beryllium oxides.

8.3.2 Oral

There appear to be no reports available on the short-term toxicity of soluble beryllium compounds and only a few addressing the toxicity of beryllium carbonate (BeCO₃), a sparingly soluble compound. A number of experiments have demonstrated that rats fed between 0.5 and 6% of beryllium carbonate in their diet over periods of 14–168 days developed rickets of the bone and teeth (Delic, 1992; HSE, 1994). Guyatt et al. (1933) and Kay & Skill (1934) reported rickets in rats fed diets containing up to 3% beryllium carbonate for 20–28 days. The observed bone lesions were not attributed to any direct effects from beryllium itself, but to phosphorus deprivation due to precipitation as beryllium phosphate in the intestine. Matsumoto et al. (1991) fed groups of 10 male Wistar rats diets containing 0 or 3% beryllium carbonate for 4 weeks, at which time the rats fed the beryllium diet weighed approximately 18% less than the controls (statistical significance not reported) and had significantly reduced serum phosphate and alkaline phosphatase levels. Although this study did not include examination of bone for rickets, the observed changes are consistent with effects reported by Guyatt et al. (1933) and Kay & Skill (1934). Jacobson (1933) caused growing rats to develop osteoporosis upon feeding them food deficient in calcium and rickets upon the addition of beryllium carbonate to their food. He concluded, like the other authors, that rickets is caused by phosphorus deprivation.

8.3.3 Dermal

With respect to the dermal route of exposure, no information was found on the effects of soluble and sparingly soluble beryllium compounds (Delic, 1992; HSE, 1994).

8.4.1 Inhalation

No medium-term (or long-term; see section 8.5) studies are available on non-neoplastic effects of beryllium oxide, the most environmentally relevant form of beryllium. Although a number of subchronic studies in laboratory animals have been conducted with other beryllium compounds, none has been done using modern criteria for high-quality toxicology studies. In addition, it is not clear which animal species, if any, is an appropriate model for humans. No laboratory animal model fully mimics all features of human chronic beryllium disease (CBD). In particular, animal models have not demonstrated a progressive granulomatous pulmonary response with a concomitant beryllium-specific immune response. However, several laboratory animal species (e.g., mice, guinea-pigs, dogs, and monkeys) respond to beryllium exposure with some of the features of human CBD, and one or more of these species may provide reasonable models for human CBD.

The pulmonary effects of beryllium following subchronic exposure in animals have been described by researchers. Stokinger et al. (1950) exposed rats, dogs, cats, rabbits, guinea-pigs, hamsters, monkeys, and goats via inhalation to 40, 430, or 2000 µg beryllium/m³ as beryllium sulfate tetrahydrate aerosols (particle size varied between 0.25 and 1.1 µm, with an average mass median diameter of the aerosol of 1 µm) for 6 h/day, 5 days/week, for 100, 95, or 51 days, respectively. Signs of toxicity in the exposed animals included weight loss, anaemia, and, in the two highest-dose groups, mortality. All histopathological lesions were confined to the lungs, with an interstitial and intra-alveolar infiltration of monocytes, polymorphonuclear leukocytes, lymphocytes, and plasma cells. Macrophages containing cellular debris were observed within the alveoli. The exposure levels at which histopathological lesions were observed in each species were not specified. Similar results were found in rats, rabbits, dogs, and cats exposed to 186 µg beryllium/m³ as beryllium fluoride for 6 h/day, 5 days/week, for 207 calendar days (Stokinger et al., 1953).

Vorwald & Reeves (1959) followed the time course of lung changes in rats exposed to an aerosol (particle size not reported) of beryllium sulfate at 6 or 54.7 µg beryllium/m³ for 6 h/day, 5 days/week, for over 9 months. Initially, inflammation consisted of histiocytes, lymphocytes, and plasma cells scattered throughout the lung parenchyma. Following more prolonged exposures, more focal lesions consisting primarily of histiocytes were observed. Subsequently, multinucleated giant cells, thickened alveolar walls, and fibrotic changes were also detected. Lung tumours, primarily adenomas and squamous cell cancers, developed in the animals sacrificed after 9 months of this exposure regime. Similarly, Schepers et al. (1959) found lung inflammation in monkeys after a 6-month (8 h/day, 5.5 days/week) exposure to beryllium sulfate at 28 µg beryllium/m³, followed by subsequent development of granulomas and adenomas months after the end of exposure (the study was continued until 18 months post-exposure).

8.4.2 Oral

Eight male albino rats (strain not specified) fed a standard diet and given a total dose of 20 mg (~0.14 mg/kg body weight per day) beryllium nitrate orally every third day for 2.5 months (40 doses administered) showed a number of histological alterations in the lungs relative to four male controls fed the standard diet (Goel et al., 1980). Although the method was not adequately described, it appears that the beryllium nitrate was placed on the food in a powder form; thus, the animals may have inhaled some of the beryllium. The histological alterations included congestion and ruptured ciliated epithelial cells of the respiratory bronchioles, thickened epithelial cells and necrosis in the alveoli, and damage to the arteriolar endothelium.

8.5.1 Inhalation

In a study to test the carcinogenicity of beryllium ores, Wagner et al. (1969) exposed groups of 12 male squirrel monkeys, 60 male CR-CD rats, 30 male Greenacres Controlled Flora (GA) rats, and 48 male golden Syrian hamsters to bertrandite or beryl ore at 0 or 15 mg/m³ for 6 h/day, 5 days/week, for 17 months (rats and hamsters) or 23 months (monkeys). The test atmospheres generated from the bertrandite ore (Be₄Si₂O₇(OH)₂; 1.4% beryllium) and beryl ore (Be₃Al₂Si₆O₁₈; 4.14% beryllium) contained 210 and 620 µg beryllium/m³, respectively, and the geometric mean diameters of the particles were 0.27 µm (GSD of 2.4) and 0.64 µm (GSD of 2.5). Both ores contained very high silicon dioxide (SiO₂) levels (63.9% by weight). Exposed and control monkeys, rats, and hamsters were serially sacrificed upon completion of 6 and 12 months of exposure — rats and hamsters at the 17th month, and monkeys at the 23rd month. Five control rats and five rats from the 12- and 17-month exposure groups were sacrificed in order to determine the free silica content of the lung tissue. At exposure termination, beryllium concentrations in the lungs were 18.0 and 83 µg/g fresh tissue in the bertrandite- and beryl-exposed rats, 14.1 and 77.4 µg/g fresh tissue in the bertrandite- and beryl-exposed hamsters, and 33 and 280 µg/g fresh tissue in the bertrandite- and beryl-exposed monkeys. Free silica (silicon dioxide) levels in the rat lungs were 30–100 times higher in the beryllium ore-exposed rats than in the controls.

Increased mortality was observed in the monkeys (11%), rats (13%), and hamsters (25%) exposed to either bertrandite or beryl ore, with the highest mortality rates in the bertrandite ore-exposed animals (no further details provided) (Wagner et al., 1969). No significant alterations in body weight gain were observed in the monkeys or hamsters. In the rats, decreased body weight gains were observed beginning after 6 months of exposure; terminal body weights were 15% lower than in controls. In the beryl-exposed rats, small foci of squamous metaplasia or tiny epidermoid tumours were observed in the lungs of 5/11 rats killed after 12 months of exposure. At exposure termination, lung tumours were observed in 18/19 rats (18 had bronchiolar alveolar cell tumours, 7 had adenomas, 9 had adenocarcinomas, and 4 had epidermoid tumours). Additional alterations in the lungs included loose collections of foamy macrophages and cell breakdown products, lymphocyte infiltrates around the bronchi, and polymorphonuclear leukocytes and lymphocytes present in most of the bronchiolar alveolar cell tumours. In the bertrandite-exposed rats, granulomatous lesions composed of several large, tightly packed, dust-laden macrophages were observed in all rats exposed for 6, 12, or 17 months. No tumours were observed. Neoplastic or granulomatous pulmonary lesions were not observed in the control rats. In the beryl- and bertrandite-exposed monkeys, the histological alterations consisted of aggregates of dust-laden macrophages, lymphocytes, and plasma cells near respiratory bronchioles and small blood vessels. No tumours were found. In the bertrandite-exposed hamsters, granulomatous lesions consisting of tightly packed, dust-laden macrophages were observed after 6 months, and the number did not increase after 17 months. These alterations were not observed in the beryl-exposed or control hamsters. Atypical proliferation and lesions, which were considered bronchiolar alveolar cell tumours except for their size, were observed in the hamsters after 12 months of exposure to beryl or bertrandite. After 17 months of exposure, these lesions became larger and more adenomatous in the beryl-exposed hamsters. It should be noted that silicosis was not observed in any of the animals exposed to the beryllium ores that contained a large amount of free silica. No significant gross or histological alterations were observed in the thymus, spleen, liver, or kidneys of the beryllium-exposed rats, hamsters, or monkeys.

Exposure to 35 µg beryllium/m³ as beryllium sulfate mist for as many as 4070 h over a 7-year period produced lung tumours in 8/12 rhesus monkeys (age 18 months at the start of the study) that survived the first 2 months of the study (four animals died of acute chemical pneumonitis during the first 2 months) (Vorwald, 1968). Several other studies also reported lung tumours (adenoma, adenocarcinoma, squamous cell cancers) in rats exposed to beryllium sulfate aerosols (Schepers et al., 1959; Vorwald & Reeves, 1959; Reeves et al., 1967; Reeves & Deitch, 1969). In addition to the proliferative lung response, an inflammatory lung response (accumulation of histiocytic elements, thickened alveolar septa, increased lung weight) was also typically present. Exposure concentrations in these studies ranged from 6 to 54.7 µg beryllium/m³. Exposure durations that produced tumours were as short as 3 months, although the tumours generally did not develop before 9 months. The earliest proliferative response was hyperplasia, which was observed as soon as 1 month after the start of exposure. Age at the initiation of exposure may be a more important variable than duration of exposure for tumour development. Reeves & Deitch (1969) found that lung tumour incidence in young rats exposed for 3 months (19/22, 86%) was the same as in young rats exposed for 18 months (13/15, 86%), but was higher than in older rats exposed for 3 months (3–10/20–25, 15–40%). Nickell-Brady et al. (1994) showed that a single brief exposure (8–48 min) to a high concentration of beryllium metal aerosol (410–980 mg beryllium/m³), producing a lung burden of 40–430 µg of beryllium, was sufficient to induce subsequent development of lung tumours in rats. In limited studies, beryllium oxide and beryllium chloride have also induced lung tumours in rodents after inhalation exposure (IARC, 1993).

8.5.2 Oral

Morgareidge et al. (1976) conducted a long-term feeding study in which groups of five male and five female beagle dogs (aged 8–12 months) were fed diets containing 0, 5, 50, or 500 ppm (mg/kg) of beryllium as beryllium sulfate tetrahydrate for 172 weeks. Because of overt signs of toxicity, the 500 ppm group was terminated at 33 weeks. At this time, a group of five male and five female dogs was added to the study and fed a diet containing 1 ppm beryllium for 143 weeks. Using estimated TWA body weights and the reported average food intake, the 1, 5, 50, and 500 ppm concentrations correspond to doses of 0.023, 0.12, 1.1, and 12.2 mg beryllium/kg body weight per day for male dogs and 0.029, 0.15, 1.3, and 17.4 mg beryllium/kg body weight per day for females. The following parameters were used to assess toxicity: daily observations of appearance and behaviour, food consumption, body weight, haematology, serial serum clinical chemistry, serial urinalysis, organ weights, and extensive histopathology.

Two moribund animals in the 500 ppm group were sacrificed during week 26; the remainder of the animals in the 500 ppm group were killed during week 33 (Morgareidge et al., 1976). Overt signs of toxicity observed in the 500 ppm group included lassitude, weight loss, anorexia, and visibly bloody faeces, indicating that the maximum tolerated dose (MTD) is less than 500 ppm. Four other animals died during the course of the study or were killed moribund; two dogs died during parturition (dose groups not reported), and one male and one female dog in the 50 ppm group died. The appearance, behaviour, food intake, and body weight gain of the animals in the other beryllium groups did not differ from controls. No beryllium-related haematological, serum chemistry, or urinalysis alterations were observed in the 1, 5, or 50 ppm groups. In the 500 ppm group, a slight anaemia (slight decreases in erythrocyte, haemoglobin, and haematocrit; statistical analysis not reported), more apparent in the females than in the males, was observed after 3 and 6 months of exposure; however, no bone marrow changes were noted, and none of the animals was seriously affected. The authors suggested that the anaemia may have been related to the gastrointestinal tract haemorrhages (see below) rather than a direct effect of beryllium on the haematological system. No alterations in organ weights were observed. All animals in the 500 ppm group showed fairly extensive erosive (ulcerative) and inflammatory lesions in the gastrointestinal tract. These occurred predominantly in the small intestine and to a lesser extent in the stomach and large intestine and were regarded by the authors as treatment-related. The female dog that died in the 50 ppm group (after 70 weeks of treatment) showed gastrointestinal lesions occurring in the same locations and appearing to be the same types, but less severe, as those in dogs administered 500 ppm. The authors stated that the death of this animal appeared to be related to beryllium administration. Gastrointestinal lesions were not reported in the male that died at this dose level. Other animals in this treatment group survived until study termination and had no remarkable gross or microscopic findings. No treatment-related effects were reported in the 1 or 5 ppm group dogs. Combined incidence rates for gastrointestinal lesions in male and female dogs were 0/10, 0/10, 0/10, 1/10, and 9/10 in the 0, 1, 5, 50, and 500 ppm groups, respectively. No neoplasms were observed in the beryllium-exposed dogs. Reproductive end-points are discussed in section 8.7. An independent review of the study report supported the researchers’ conclusion that the gastrointestinal lesions were treatment-related.8.5.3 Other routes

Beryllium metal, passivated beryllium metal (99% beryllium, 0.26% chromium as chromate), beryllium–aluminium alloy, beryllium hydroxide, and low- and high-fired beryllium oxide have been shown to produce lung cancer in rats by intratracheal instillation. Beryllium metal, zinc beryllium silicate, beryllium silicate, beryllium oxide, and beryllium phosphate produced osteosarcomas in rabbits by intravenous injection, and beryllium oxide, zinc beryllium silicate, and beryllium carbonate produced osteosarcomas in rabbits after injection into the medullary cavity of bones (US EPA, 1987; IARC, 1993).

Genotoxicity studies of beryllium have produced mixed results. Most studies have found that beryllium chloride, beryllium nitrate, beryllium sulfate, and beryllium oxide did not induce gene mutations in bacterial assays, with or without metabolic activation. In the case of beryllium sulfate, all mutagenicity studies (Ames Salmonella typhimurium [Simmon, 1979; Dunkel et al., 1984; Arlauskas et al., 1985; Ashby et al., 1990]; Escherichia coli pol A [Rosenkranz & Poirer, 1979]; E. coli WP2 uvr A [Dunkel et al., 1984]; and Saccharomyces cerevisiae [Simmon, 1979]) were negative, with the exception of results reported for Bacillus subtilis rec assay (Kada et al., 1980; Kanematsu et al., 1980) and E. coli rec assay (Dylevoi, 1990).

Beryllium nitrate was negative in the Ames assay (Tso & Fung, 1981; Kuroda et al., 1991) but positive in a B. subtilis rec assay (Kuroda et al., 1991). Beryllium chloride was negative in a variety of studies (Ames [Ogawa et al., 1987; Kuroda et al., 1991]; E. coli WP2 uvr A [Rossman & Molina, 1986]; and B. subtilis rec assay [Nishioka, 1975]). In addition, beryllium chloride failed to induce SOS³repair in E. coli (Rossman et al., 1984). However, positive results were reported for B. subtilis rec assay using spores (Kuroda et al., 1991), E. coli KMBL 3835, lacI gene (Zakour & Glickman, 1984), and hprt locus in Chinese hamster lung V79 cells. Beryllium oxide was negative in the Ames assay and B. subtilis rec assays (Kuroda et al., 1991).

Gene mutations have been observed in mammalian cells cultured with beryllium chloride (Hsie et al., 1979a,b; Miyaki et al., 1979), and culturing mammalian cells with beryllium chloride (Vegni-Talluri & Guiggiani, 1967), beryllium sulfate (Larramendy et al., 1981; Brooks et al., 1989), or beryllium nitrate has resulted in clastogenic alterations. Beryllium sulfate did not induce unscheduled DNA synthesis in primary rat hepatocytes (Williams et al., 1982), but did induce morphological transformations in cultured mammalian cells. Data on the in vivo genotoxicity of beryllium are limited to two studies. Beryllium sulfate (1.4 and 2.3 g/kg body weight, 50% and 80% of median lethal dose) administered by gavage did not induce micronuclei in the bone marrow of CBA mice, although a marked depression of erythropoiesis suggestive of bone marrow toxicity was evident 24 h after dosing. No increase in mutations was found in p53 or c-raf-1, and only a small increase in mutations was detected in K-ras, in lung carcinomas (tumours became apparent by 14 months after exposure, and the incidence, apparently for all groups combined, was 64% over the lifetime of the rats) from F344/N rats given a single nose-only exposure to beryllium metal (Nickell-Brady et al., 1994).

Ionized beryllium can bind to nucleic acids (Leonard & Lauwerys, 1987; Lansdown, 1995), and beryllium sulfate and beryllium chloride have been shown to affect enzymes required for DNA synthesis (Leonard & Lauwerys, 1987).

There are limited data available regarding the reproductive and developmental toxicity of beryllium compounds in animals by routes of exposure that are relevant to humans. In the chronic dog oral exposure study conducted by Morgareidge et al. (1976) (described in section 8.5.2), the male and female dogs exposed to 1, 5, or 50 ppm (mg/kg) beryllium sulfate in the diet (0.023, 0.12, or 1.1 mg beryllium/kg body weight per day for males and 0.029, 0.15, or 1.3 mg beryllium/kg body weight per day for females) were housed together at the time of the second heat after treatment initiation and allowed to mate and wean (at 6 weeks of age) their pups, which were then returned to community floor pens (with the exception of the first litter, which was killed 5 days after whelping). The number of pregnant females exposed to 0, 1, 5, and 50 ppm was 3, 2, 5, and 3, respectively. Treated females had between 1 and 3 litters; controls had 1–4, each litter by the same sire. First-litter pups surviving to postnatal day 5 were sacrificed for soft tissue gross examination and were stained for evaluation of skeletal malformations. Pups from subsequent litters were grossly examined at weaning. Beryllium did not appear to adversely affect reproductive or developmental end-points (number of pregnancies, number of pups, number of live pups, pup weight) in the beryllium-exposed dogs. No beryllium-related decreases in postnatal survival (day 7 or weaning) were observed. The authors reported no gross or skeletal abnormalities in the surviving first litter pups, but data were not shown; stillborn or cannibalized pups dying within the first few postnatal days were not examined.

No animal experiments of the reproductive or developmental toxicity of inhaled beryllium are available.

Studies by parenteral routes of administration have produced mixed results regarding the reproductive and developmental toxicity of beryllium. Selivanova & Savinova (1986) reported increased fetal mortality, decreased fetal weight, and increased percentage of pups with internal abnormalities in rats treated with 50 mg beryllium/kg body weight as beryllium chloride or beryllium oxide by intratracheal injection on days 3, 5, 8, and 20 of gestation. Mathur et al. (1987) administered intravenous injections of 0.021 mg beryllium/kg body weight as beryllium nitrate to mated Sprague-Dawley rats (n = 5–8 per group) on postcoital day 1, 11, 12, 13, 15, or 17. Rats were laparotomized on gestation days 10 and 20 and then allowed to deliver. All experimental groups were contrasted with control groups, which received an equal volume of distilled water through the intravenous route at day 1 postcoitum and were laparotomized on day 20 postcoitum. All pups died within 2–3 days of birth, and all pups in the group injected on postcoital day 11 died in utero, but these effects may have been due to the repeated surgeries. Clary et al. (1975) found no effect on the average number of pregnancies, number of live or dead pups per litter, lactation index, or fetal body weight in continuous breeding experiments using male and female Sprague-Dawley rats given a single intratracheal administration of beryllium oxide (200 µg beryllium) calcined at 960 °C or 500 °C prior to the first mating. A review of these three parenteral studies reveals no information regarding maternal toxicity.

An immune component has also been demonstrated in several animal models for CBD: mice (Huang et al., 1992), guinea-pigs (Barna et al., 1981, 1984), dogs (Haley et al., 1989), and monkeys (Haley et al., 1994) (rats are the notable exception). In guinea-pigs, for example, Barna et al. (1981, 1984) demonstrated that intratracheal instillation of beryllium oxide can induce both immune granulomas containing a T-lymphocyte component and a beryllium-specific immune response. The studies in mice and guinea-pigs demonstrated genetic control of the immune response in these species because the response was observed in some strains, but not others. In the case of the guinea-pigs, the immune response was seen in strain 2, but not strain 13, which differs from strain 2 at a single locus (MHC Ia) (Barna et al., 1984). Dermal hypersensitivity studies in laboratory animals are discussed in section 8.2. In addition to the above studies, other immunological studies via parenteral routes of exposure to various beryllium compounds (beryllium sulfate, beryllium hydroxide, or beryllium oxide) are cited in Delic (1992) and HSE (1994).

Lesions that would be associated with neurological effects in the brain and spinal cord were absent in rats exposed orally (diet) for 2 years to ³ 31 mg beryllium/kg body weight per day as beryllium sulfate tetrahydrate.

The lung is the primary target of inhalation exposure to beryllium in humans. Information on the subchronic toxicity of beryllium following inhalation exposure to humans was unavailable; however, information regarding acute and chronic exposure via inhalation is extensive, especially chronic data. Short-term or repeated exposures of humans to beryllium or its compounds can result in an acute (chemical pneumonitis) or chronic (berylliosis) form of lung disease, depending upon the exposure concentration. Both acute beryllium disease (ABD) and CBD result from exposure to both soluble and insoluble forms of beryllium (ATSDR, 1993).

ABD is defined as beryllium-induced pulmonary disease of less than 1 year’s duration (Hamilton & Hardy, 1974; Sprince & Kazemi, 1980) and is likely to be due to direct toxicity, unlike the immune mechanism of CBD. ABD, which is in fact a chemical pneumonitis, may be fatal in 10% of cases. The severity of ABD appears to depend directly on the magnitude of the exposures received. Early investigations by Eisenbud et al. (1948) found that chemical pneumonitis occurred in almost all workers exposed to 1000 µg beryllium/m³ and above and in none exposed to less than 100 µg/m³ and appears to be reversible at concentrations of less than 1000 µg beryllium/m³ (Delic, 1992; HSE, 1994).

CBD, formerly known as "berylliosis" or "chronic berylliosis," is an inflammatory lung disease that results from inhalation exposure to both soluble and insoluble forms of beryllium. CBD in humans exposed to beryllium involves a cell-mediated immune response to beryllium in the lung. It is characterized by the formation of granulomas (pathological clusters of immune cells) with varying degrees of interstitial fibrosis and involves a beryllium-specific immune response. With respect to the present knowledge of the mechanism of this chronic disease, the initial response is of an inflammatory nature caused by beryllium-induced phagocytosis and the subsequent release of lysosomal enzymes. The release of such enzymes is thought to be responsible for the damaging effects observed with respect to lung architecture. Unlike other particles (e.g., alpha quartz), beryllium is unusual in that it also initiates cell-mediated immune responses. Because the beryllium ion is too small to be antigenic per se, it may function as a hapten, binding with a large carrier molecule (e.g., protein) to form an antigen. There is ample evidence for the existence of cell-mediated immune responses to beryllium (Kriebel et al., 1988b). Once the antigen is created by the macrophage, it is presented to helper T-cells, which form sensitized T-cells. Once a population of sensitized T-cells is created, these cells transform and actively secrete lymphokines, which actively regulate subsequent events, leading to the formation of clusters of macrophages commonly known as "granulomas."

A particularly important part of the diagnosis of CBD is to distinguish it from sarcoidosis, a granulomatous lung disease of unknown cause. The Beryllium Case Registry (BCR) lists the following criteria for diagnosing CBD:

Cases were entered into the registry if they met at least three of the criteria (Hasan & Kazemi, 1974).

The criteria for diagnosis of CBD have evolved with time, as more advanced diagnostic technology has become available. These varying definitions of CBD should be considered in comparing results from different studies. More recent criteria have both higher specificity than earlier methods and higher sensitivity, identifying subclinical effects. Recent studies typically use the following criteria:

The availability of transbronchial lung biopsy facilitates the evaluation of the second criterion, by making histopathological confirmation possible in almost all cases.

A key aspect of the identification of CBD is the demonstration of beryllium sensitization in the BeLT (also known as the LTT, BeLPT) (Newman, 1996). In this test, lymphocytes obtained from either BAL fluid or peripheral blood are cultured in vitro and then exposed to soluble beryllium sulfate to stimulate lymphocyte proliferation. The observation of beryllium-specific proliferation indicates beryllium sensitization. Early versions of the test had high variability, but the use of tritiated thymidine to identify proliferating cells has led to a more reliable test (Rossman et al., 1988; Mroz et al., 1991). In recent years, the peripheral blood test has been found to be as sensitive as the BAL assay, although larger abnormal responses are generally observed in the BAL assay (Kreiss et al., 1993; Pappas & Newman, 1993). False-negative results can occur with the BAL BeLT in cigarette smokers, who have a marked excess of alveolar macrophages in lavage fluid (Kreiss et al., 1993). The BeLT has also been used in animal studies to identify those species with a beryllium-specific immune response (see section 8.8). As described below, the BeLT test can detect beryllium sensitization and has a higher predictive value in CBD screening than clinical exam, spirometry, or chest radiography.

Occupational studies show compound-specific differences in beryllium toxicity, but are less clear about whether beryllium metal or beryllium oxide is more toxic, probably due to variability in particle size or solubility differences. Eisenbud & Lisson (1983) found a higher prevalence of CBD in people who worked with beryllium metal than in those who worked with beryllium oxide, and Sterner & Eisenbud (1951) found a much higher prevalence of CBD in people who worked with beryllium oxide than in those who worked with other beryllium compounds. By contrast, Cullen et al. (1987) found a greater frequency of CBD in workers presumably exposed to beryllium oxide fume compared with the beryllium metal, but the small particle size of the fume compared with the beryllium metal dust may have contributed to the higher toxicity of the beryllium oxide in this study. Owing to the markedly decreased levels of occupational exposure to beryllium, acute chemical pneumonitis is now quite rare, except in instances where there are accidental exposures that exceed the US occupational standard (Eisenbud et al., 1949).

Evaluation of the exposure–response to beryllium has been made more difficult because CBD is an immune disease, and only a small percentage of the population (1–5%) appears to be susceptible. Nonetheless, exposure–response relationships are evident. Several studies have observed CBD in people chronically exposed in modern plants, which are generally in compliance with the beryllium permissible exposure limit of 2 µg/m³.

In contrast to inhalation and oral routes of exposure, exposure of humans to beryllium compounds has been shown to cause skin and eye irritation (Van Orstrand et al., 1945; De Nardi et al., 1953; Nishimura, 1966; Epstein, 1990). Direct skin contact with soluble beryllium compounds, but not beryllium hydroxide or beryllium metal, can cause dermal lesions (reddened, elevated, or fluid-filled lesions on exposed body surfaces) in susceptible persons (McCord, 1951). The lesions appear after a latent period of 1–2 weeks, suggesting a delayed allergic reaction. Curtis (1951) conducted patch tests showing that soluble beryllium compounds do produce an allergic contact dermatitis. The dermal reaction occurs more rapidly and in response to smaller amounts of beryllium in sensitized individuals (Van Orstrand et al., 1945). Introduction of soluble or insoluble beryllium compounds into or under the skin as a result of abrasions or cuts at work can result in chronic ulcerations with granuloma formation (Van Orstrand et al., 1945; Lederer & Savage, 1954).

Kreiss et al. (1996) conducted a cross-sectional study of 136 of the 139 beryllium workers in a plant that made beryllia ceramics from beryllium oxide powder. An additional 15 workers who had been exposed to beryllium at other jobs were excluded from exposure calculations because their earlier exposure was not known. Because the plant opened in 1980, high-quality industrial hygiene measurements were available for almost the entire exposure period. Measurements from 1981 and later (for each job title) were reviewed and included area samples, process breathing zone samples, and personal lapel samples (the last year only). Cumulative beryllium exposure for individuals (quarterly daily-weighted average [DWA]) was estimated by summing the quarterly DWAs for their job titles, weighted by days of employment in the job title during the quarter. However, general area and breathing zone samples were not recorded for machining processes until the last quarter of 1985, soon after machining production was transferred to that plant, even though a limited amount of machining had been conducted since 1982. Although total beryllium exposure was generally well characterized for most of the affected workers, two of the seven beryllium-sensitized machinists started machining prior to the systematic environmental monitoring. Since exposure levels generally declined with time, exposure of these two subjects may have been underestimated. The median breathing zone measurement of beryllium was 0.6 µg beryllium/m³ for machining and 0.3 µg beryllium/m³ for other processes. The frequency of excursions to higher exposure levels decreased with time, with the percentage of machining breathing zone measurements above 5 µg beryllium/m³ falling from 7.7% during early sampling years to 2.1% during later sampling years.

BeLTs were performed by two different laboratories on blood samples collected from 136 employees (Kreiss et al., 1996). Positive results from one or both laboratories were confirmed by analysing a subsequent blood sample. Of the 136 tested employees, 5 had consistently abnormal blood BeLT results and were diagnosed with CBD based on observation of granulomas in lung biopsy samples. An additional two employees had abnormal blood results from one of the two laboratories and had no granulomas in lung biopsy samples. Both employees developed abnormal blood results in other laboratory tests within 2 years. One of these two employees also developed symptoms of CBD. The other employee declined clinical follow-up. An additional case of CBD was found during the study in an employee hired in 1991, who had a non-healing granulomatous response to a beryllium-contaminated skin wound. This subject had a confirmed abnormal blood test and after several additional months developed lung granulomas. Only one CBD case had an abnormal chest X-ray (defined as small opacity profusion of 1/0 or greater). An additional 11 former employees had CBD, for a total prevalence of 19/709 (2.7%). Beryllium-sensitized cases were similar to non-sensitized ones in terms of age, ethnic background, and smoking status, but did