A. Screening Levels for Toxic Effects Other than Cancer.
(1) TLV-Based Screening Levels. TLV-based screening levels shall be determined as follows:
(a) If a toxic air pollutant (TAP) has a threshold limit value-time weighted average (TLV-TWA), divide the TLV-TWA by 100 to calculate an 8-hour time-weighted average screening level;
(b) If a TAP has a ceiling TLV (TLV-C) or a short term exposure limit (TLV-STEL), divide the TLV-C or TLV-STEL by 100 to calculate a 1-hour time-weighted average screening level;
(c) If a TAP has both a TLV-TWA and TLV-STEL, calculate both 8-hour and 1-hour time-weighted average screening levels as described above.
(2) Threshold-Based Screening Levels.
(a) If a TAP has neither a TLV, nor a special screening level, nor an acceptable ambient level, then a person may use one of the following formulae, given in order of preference, to develop an 8-hour threshold-based screening level in milligrams/cubic meter. In these formulae, a NOEL is a No Observed Effect Level, and an LC50 or LD50 is a concentration or dose, respectively, expected to cause the death of 50 percent of an entire defined experimental animal population. The following are formulae to be used:
(i) Divide a 90-day inhalation NOEL in milligrams/cubic meter for rats, mice, or rabbits by 100;
(ii) Multiply a 90-day oral NOEL in milligrams/kilograms for rats by 2.7 × 10-3rd, for mice by 9.0 × 10-4th, or for rabbits by 1.3 × 10-3rd;
(iii) Divide a 7-day inhalation NOEL in milligrams/cubic meter for rats, mice, or rabbits by 700;
(iv) Multiply a 7-day oral NOEL in milligrams/kilograms for rats by 3.8 × 10-4th, for mice by 1.3 × 10-4th, or for rabbits by 1.9 × 10-4th;
(v) Divide an LC50 in milligrams/cubic meter for rats, mice, or rabbits by 10,000; or
(vi) Multiply an oral LD50 in milligrams/kilograms for rats by 4.1 × 10-5th, for mice by 1.4 × 10(-5th, or for rabbits by 2.0 × 10-5th.
(b) When two or more animal test data acceptable to the Department are available for use under a subparagraph in §A(2)(a) of this regulation, the screening level shall be calculated using the data producing the lowest screening level.
(c) The above formulae are not the only ones appropriate for developing screening levels. These are acceptable formulae to the Department at this time. Other formulae may be used to calculate special screening levels.
(3) Special Screening Level. If a special screening level for a toxic air pollutant is listed in Regulation .09 of this chapter, the special screening level or levels in Regulation .09 of this chapter replace applicable TLV-based or threshold-based screening levels for that toxic air pollutant.
(a) The Department may adopt special screening levels for TAPs that ACGIH has identified as carcinogens. A person should contact the Air Management Administration before using a TLV-based screening level for any of these TAPs.
(b) The Department will provide information on TLV-based screening levels upon request.
(c) The Department will maintain a list of AALs under consideration pending their adoption into this chapter, and will make a list available upon request.
B. Screening Level for Carcinogenic Effects.
(1) "Risk-based screening level" means the annual average concentration, in micrograms per cubic meter, that would increase a person's lifetime cancer risk by 1 in 100,000 (1 × 10-5th) if the person were continuously exposed to the concentration for 70 years. The Department will calculate the risk-based screening level using:
(a) If available, a unit risk factor developed by the Cancer Assessment Group of the U.S. Environmental Protection Agency (termed a CAG unit risk factor); or
(b) If a CAG unit risk factor is not available, an upper bound unit risk factor developed in accordance with EPA's Risk Assessment Guidelines.
(2) The Department will maintain an up-to-date list of available risk-based screening levels and will provide information on these levels upon request.