Basis for the Chromate Threshold Limit Values

1
Basis for the Chromate Threshold Limit Values

• Michael S. Morgan
• University of Washington
• Non-voting Member, TLV Committee

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Strontium Chromate TLV

• History
• 1989 0.001 mg/m3 as Cr, proposed placed on
  Notice of Intended Changes list, 89-90
• 1991 0.0005 mg/m3 as Cr, revised proposal
  placed on NIC list, 91-92
• 1992 0.0005 mg/m3 as Cr, adopted published in
  1992-93 TLV booklet

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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

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Rationale for the TLV

• 1. TLV for Calcium chromate is 0.001 mg/m3
• (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/m3, A2

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Other Recommendations

• OSHA no specific PEL, regulated as Cr(VI)
• NIOSH REL 0.001 mg/m3 (lowest detectable
  current version of NIOSH Manual implies 0.0005
  mg/m3 is feasible, based on LOQ 0.2 µg, 400 L
  air sample)
• UK 0.05 mg/m3, 1995
• Sweden 0.02 mg/m3, 1984
• Germany TRK 0.05 mg/m3 as Cr 1992 no MAK

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Zinc Chromate compounds

• ZnCrO4 - Basic Zinc Chromate
• KZn2CrO42(OH) - Zinc Potassium Chromate
• 4ZnOK2O4CrO3H2O (approx.) - Zinc Yellow

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Zinc Chromates TLV

• History
• 1975 0.1 mg/m3 as CrO3, proposed placed on
  Notice of Intended Changes list
• 1976 0.05 mg/m3 as Cr ( 0.1 mg/m3 as CrO3),
  proposal revised placed on NIC
• 1977 0.05 mg/m3 as Cr, adopted published in
  1977 TLV booklet

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Zinc Chromates TLV

• 1986 0.01 mg/m3, 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

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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.

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Recommended TLV

• A2, Suspected Human Carcinogen
• 0.01 mg/m3, 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/m3
  as Cr, 0.05 mg/m3 as Pb.

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Other Recommendations

• OSHA PEL is 0.1 mg/m3 as CrO3, 15 minute ceiling
• NIOSH REL is 0.001 mg/m3 as Cr, as an insoluble
  Cr(VI) compound.
• UK 0.05 mg/m3 as Cr, 1991
• Sweden 0.02 mg/m3 as Cr, 1990
• Germany Human carcinogen, no MAK/TRK

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Some Insights into the TLV Process

• Committee 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,
  human
• Uncertainties are dealt with using safety margins
  and expert judgement

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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

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Steps in TLV Developmentcontinued

• 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

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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 (weve 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