Md. Code Regs. 26.11.16.03 - Screening Levels
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 x 10-3rd, for
mice by 9.0 x 10-4th, or for rabbits by 1.3 x
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 x 10-4th, for
mice by 1.3 x 10-4th, or for rabbits by 1.9 x
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 x 10-5th, for
mice by 1.4 x 10(-5th, or for rabbits by 2.0 x
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.
(4) General.
(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 x
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.
Notes
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