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Basis for the Chromate Threshold Limit Values Michael S. Morgan University of Washington Non-voting Member, TLV Committee.

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Presentation on theme: "Basis for the Chromate Threshold Limit Values Michael S. Morgan University of Washington Non-voting Member, TLV Committee."— Presentation transcript:

1 Basis for the Chromate Threshold Limit Values Michael S. Morgan University of Washington Non-voting Member, TLV Committee

2 Strontium Chromate TLV History: 1989: mg/m 3 as Cr, proposed; placed on Notice of Intended Changes list, : mg/m 3 as Cr, revised proposal; placed on NIC list, : mg/m 3 as Cr, adopted; published in TLV booklet

3 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

4 Rationale for the TLV 1. TLV for Calcium chromate is 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 mg/m 3, A2

5 Other Recommendations OSHA: no specific PEL, regulated as Cr(VI) NIOSH: REL = mg/m 3 (“lowest detectable;” current version of NIOSH Manual implies 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

6 Zinc Chromate compounds ZnCrO 4 - Basic Zinc Chromate KZn 2 [CrO 4 ] 2 (OH) - Zinc Potassium Chromate 4ZnOK 2 O4CrO 3 H 2 O (approx.) - Zinc Yellow

7 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

8 Zinc Chromates TLV 1986: 0.01 mg/m 3, as Cr, proposed; on NIC for : 0.01 mg/m3, as Cr, adopted; published in TLV booklet 1992: Documentation revised, no change in Threshold Limit Value

9 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.

10 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 mg/m 3 as Cr, 0.05 mg/m 3 as Pb.

11 Other Recommendations OSHA: PEL is 0.1 mg/m 3 as CrO 3, 15 minute ceiling NIOSH: REL is 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

12 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

13 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

14 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

15 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


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