1. a) Minimum Data Requirements

   1. 1) Tier I. The minimum data set sufficient to derive a Tier I LMHHTC must include at least one epidemiological study or one animal study of greater than 90 days duration; or
   2. 2) Tier II. When the minimum data for deriving Tier I criteria are not available, a more limited database consisting of an animal study of greater than 28 days duration must be used.

2. b) Principles for Development of Tier I Criteria and Tier II Values

   1. 1) The experimental exposure level representing the highest level tested at which no adverse effects were demonstrated (NOAEL) must be used to calculate a criterion or value. In the absence of a NOAEL, a LOAEL must be used if it is based on relatively mild and reversible effects;

   2. 2) Uncertainty factors (UFs) must be used to account for the uncertainties in predicting acceptable dose levels for the general human population based upon experimental animal data or limited human data:

      1. A) A UF of 10 must be used when extrapolating from experimental results of studies on prolonged exposure to average healthy humans;
      2. B) A UF of 100 must be used when extrapolating from results of long-term studies on experimental animals;
      3. C) A UF of up to 1000 must be used when extrapolating from animal studies for which the exposure duration is less than chronic, but greater than subchronic;
      4. D) A UF of up to 3000 must be used when extrapolating from animal studies for which the exposure duration is less than subchronic;
      5. E) An additional UF of between one and ten must be used when deriving a criterion from a LOAEL. The level of additional uncertainty applied will depend upon the severity and the incidence of the observed adverse effect;
      6. F) An additional UF of between one and ten must be applied when there are limited effects data or incomplete sub-acute or chronic toxicity data;
   3. 3) The total uncertainty (∑ of the uncertainty factors) must not exceed 10,000 for Tier I criterion and 30,000 for Tier II value; and
   4. 4) All study results must be converted to the standard unit for acceptable daily exposure of milligrams of toxicant per kilogram of body weight per day (mg/kg/day). Doses must be adjusted for continuous exposure.

3. c) Tier I Criteria and Tier II Value Derivation

   1. 1) Determining the Acceptable Daily Exposure (ADE)

      ADE = test value / ∑ of the UFs from subsection (b)(2)

      Where:

      acceptable daily exposure is in milligrams toxicant per kilogram body weight per day (mg/kg/day)

   2. 2) Determining the Lake Michigan Basin Human Health Threshold Criterion (LMHHTC) or the Lake Michigan Basin Human Health Threshold Value (LMHHTV)

      LMHHTC or LMHHTV =

      {ADE x BW x RSC } /

      {WC + [(FC_TL3 x BAF_HHTL3) + (FC_TL4 x BAF_HHTL4)]}

      Where:

      LMHHTC or LMHHTV is in milligrams per liter (mg/L)
      ADE	=	acceptable daily intake in milligrams toxicant per kilogram body weight per day (mg/kg/day)
      RSC	=	relative source contribution factor of 0.8
      BW	=	weight of an average human (BW = 70 kg)
      WC	=	per capita water consumption (both drinking and incidental exposure) for surface waters classified as public water supplies = two liters/day; or per capita incidental daily water ingestion for surface waters not used as human drinking water sources = 0.01 liters/day
      FCTL3	=	mean consumption of trophic level 3 fish by regional sport fishers of regionally caught freshwater fish = 0.0036 kg/day
      FCTL4	=	mean consumption of trophic level 4 fish by regional sport fishers of regionally caught freshwater fish = 0.0114 kg/day
      BAFHHTL3	=	human health bioaccumulation factor for edible portion of trophic level 3 fish, as derived using the BAF methodology in Section 302.570
      BAFHHTL4	=	human health bioaccumulation factor for edible portion of trophic level 4 fish, as derived using the BAF methodology in Section 302.570

The LMHHTC or LMHHTV is derived for all toxic substances from the most sensitive endpoint for which there exists a dosage or concentration below which no adverse effect or response is likely to occur.

(Source: Amended at 47 Ill. Reg. 4437, effective March 23, 2023)