Presentation on theme: "Basis for the Chromate Threshold Limit Values Michael S. Morgan University of Washington Non-voting Member, TLV Committee."— Presentation transcript:
Basis for the Chromate Threshold Limit Values Michael S. Morgan University of Washington Non-voting Member, TLV Committee
Strontium Chromate TLV History: 1989: 0.001 mg/m 3 as Cr, proposed; placed on Notice of Intended Changes list, 89-90 1991: 0.0005 mg/m 3 as Cr, revised proposal; placed on NIC list, 91-92 1992: 0.0005 mg/m 3 as Cr, adopted; published in 1992-93 TLV booklet
Biological Basis (1992) Animal Data: toxicity is attributable to chromate, not strontium High incidence of bronchial and pleural carcinomas in rodents, in two separate studies - both used implantation Judged to be a more potent carcinogen than calcium chromate, from animal data Human Data: no published studies available
Rationale for the TLV 1. TLV for Calcium chromate is 0.001 mg/m 3 (animal data only; based on comparison to animal data for zinc chromate, TLV =.01) 2. Strontium chromate is more potent 3. Inhaled hexavalent chromium compounds are known human carcinogens 4. Recommended TLV is 0.0005 mg/m 3, A2
Other Recommendations OSHA: no specific PEL, regulated as Cr(VI) NIOSH: REL = 0.001 mg/m 3 (“lowest detectable;” current version of NIOSH Manual implies 0.0005 mg/m 3 is feasible, based on LOQ = 0.2 µg, 400 L air sample) UK: 0.05 mg/m 3, 1995 Sweden: 0.02 mg/m 3, 1984 Germany: TRK 0.05 mg/m 3 as Cr 1992; no MAK
Zinc Chromates TLV History: 1975: 0.1 mg/m 3 as CrO 3, proposed; placed on Notice of Intended Changes list 1976: 0.05 mg/m 3 as Cr (= 0.1 mg/m 3 as CrO 3 ), proposal revised; placed on NIC 1977: 0.05 mg/m 3 as Cr, adopted; published in 1977 TLV booklet
Zinc Chromates TLV 1986: 0.01 mg/m 3, as Cr, proposed; on NIC for 1987-88 1988: 0.01 mg/m3, as Cr, adopted; published in 1989-90 TLV booklet 1992: Documentation revised, no change in Threshold Limit Value
Biological Basis Animals: high prevalence of lung carcinomas in two studies using implantation, none in another using intratracheal instillation. One or more of the zinc chromates appears to be carcinogenic. Humans: bronchial carcinoma in pigment workers in six small cohort studies; mixed with lead chromate, zinc speciation not consistent.
Recommended TLV A2, Suspected Human Carcinogen 0.01 mg/m 3, as Cr, based on human and animal data that suggest potency is similar to that of lead chromate. Lead chromate TLV is 0.012 mg/m 3 as Cr, 0.05 mg/m 3 as Pb.
Other Recommendations OSHA: PEL is 0.1 mg/m 3 as CrO 3, 15 minute ceiling NIOSH: REL is 0.001 mg/m 3 as Cr, as an insoluble Cr(VI) compound. UK: 0.05 mg/m 3 as Cr, 1991 Sweden: 0.02 mg/m 3 as Cr, 1990 Germany: Human carcinogen, no MAK/TRK
Some Insights into the TLV Process Committee is willing to set quantitative limits for carcinogens - some other regulatory agencies are notCommittee is willing to set quantitative limits for carcinogens - some other regulatory agencies are not The full spectrum of toxicologic and epidemiologic data is considered - model, animal, humanThe full spectrum of toxicologic and epidemiologic data is considered - model, animal, human Uncertainties are dealt with using safety margins and expert judgementUncertainties are dealt with using safety margins and expert judgement
Steps in TLV Development 1. TLV committee proposes a value, with notations, supported by draft documentation 2. Proposal appears in the Notice of Intended Changes (NIC) list in TLV booklet 3. Comments from all interested parties are requested during the (minimum) one year period on the NIC list
Steps in TLV Development continued 4. After at least one year on NIC list, proposal is revised, adopted or withdrawn. TLV Committee decisions are by majority of voting committee members 5. Review and approval by ACGIH Board of Directors 6. Publication in TLV Booklet, with Documentation
Additional Input To meet with the TLV committee: 1. Submit a request, on organizational letterhead, for an invitation 2. Provide written materials to the committee, in advance (we’ve shown you ours, now you gotta show us yours) 3. Be brief: present only what is new, or has not been included in the documentation