SILVER METAL

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 7440-22-4; Chemical Formula: Ag

The current OSHA standard for silver metal and soluble compounds (including the metal dust and fume) is 0.01 mg/m³, as Ag. NIOSH has no REL for this substance, but the ACGIH has established a 0.1 mg/m³ TLV for silver metal dust and fume. NIOSH concurs with OSHA’s decision not to increase the limit for silver (Ex. 8-47). Silver is a hard, brilliant, white, ductile, malleable metal.

The previous TLV of 0.01 mg/m³, which was established for all forms of silver, was designed to protect workers against developing argyria. This condition arises from the accumulation of silver in the body and results in an unsightly, widespread blue-grey discoloration of the skin that can persist for long periods of time. The skin of exposed workers may also become black and have a metallic luster. Argyria may manifest in the conjunctiva of the eye, which may be affected sufficiently to cause lens and visual disturbances.

In arriving at the previous TLV of 0.01 mg/m³ for silver, the ACGIH relied on a publication by Pillsbury and Hill (1939, as cited in ACGIH 1986/Ex. 1-3, p. 529), which stated that an accumulated intake of from 1 to 5 grams of silver would lead to generalized argyria. Assuming a 20-year exposure duration, a 10 m³/day respiratory volume, and a 50-percent body retention, the ACGIH estimated that exposure to 0.05 mg/m³ was sufficient to cause argyria. The former TLV of 0.01 mg/m³ thus appeared to incorporate a safety factor to account for the uncertainties involved in using this approach to develop a TLV. The ACGIH’s current TLV of 0.1 mg/m³ for silver metal dust and fume was determined in a similar fashion, except that the ACGIH assumed a lower percent retention and apparently did not incorporate a safety margin (ACGIH 1986/Ex. 1-3).

OSHA received several comments on its proposal to retain the existing limit for silver (Ex. 8-47, 8-57, 3-876, 46, and 105; Tr. pp. 9-126 to 9-127). The American Mining Congress (Ex. 3-876) stated that argyria, the blue-grey discoloration of the skin caused by exposure to silver, is caused only by exposure to the soluble silver salts and not by metallic silver. BP America, a company that operates a silver smelting and refining operation in Utah, is also of the opinion that OSHA should increase its limit for silver (metal, dust, and fumes) because, although argyria “can be cosmetically unpleasant, it is not known to result in any adverse health consequences” (Ex. 8-57).

OSHA responds to these commenters as follows. First, OSHA does not agree that having one’s skin discolored, on a semipermanent basis, is a “minor” effect. On the contrary, OSHA believes that argyria causes emotional stress, acute personal discomfort, and feelings of insecurity, all of which are symptoms of severe psychological distress.

In addition, although the American Mining Congress is certain that only the soluble forms cause argyria, OSHA notes that Wolf Wagner, Manager of Industrial Hygiene for BP America, expressed uncertainty on this point at the hearing; he reported that argyria is “most likely due to a soluble silver rather than an insoluble silver” (Ex. 8-57; Tr. pp. 9-126 to 9-127). OSHA agrees that considerable uncertainty surrounds the issues of the causative agents of argyria and the specific level at which this effect occurs. As the ACGIH (1986/Ex. 1-3, p. 529) reports:

• The concentration of silver in the air which will result in generalized argyria is not known with certainty.

Thus, OSHA concludes that the evidence needed to raise the limit for silver is lacking. OSHA is therefore retaining its former limit for silver (metal, dust, and fume) of 0.01 mg/m³ as an 8-hour TWA.