Authority: IC 13-14-8; IC 13-18-3

Affected: IC 13-18-4

Sec. 8.5. The concentration to protect public health from threshold effect toxicants is the human life cycle safe concentration (HLSC). The minimum toxicity data requirement for derivation of an HLSC shall consist of an acute oral LD50 for rats. The HLSC shall be derived in the following manner:

1. (1) The HLSC shall be derived from appropriate toxicological data using the following formula:

   Where:	MgT	=	maximum milligrams of toxicant per day causing no adverse effects to humans when ingested daily for lifetime
   	WC	=	volume of water consumed daily in liters (two (2) liters per day for surface water protected for drinking water supply; one-hundredth (0.01) liter per day for surface water not protected for drinking water supply)
   	F	=	sixty-five ten-thousandths (0.0065) kilograms per day, daily consumption of fish by humans
   	BCF	=	bioconcentration factor in as determined in section 8.7 of this rule

2. (2) The MgT shall be derived by one (1) of the following methods depending on the type and quality of the toxicity data base:

   1. (A) If a scientifically valid maximum contaminant level (MCL) from the national interim primary drinking water regulations is available:

      Where:

      Vh

      =

      two (2) liters per day, volume of water consumed daily by humans

   2. (B) If a chronic, subchronic, or subacute no observable adverse effect level (NOAEL) for humans exposed to toxicant contaminated drinking water is available:

      Where:

      U

      =

      uncertainty factor (U = 10 - 100)

   3. (C) If a scientifically valid acceptable daily intake (ADI) is available from the federal Food and Drug Administration regulations: MgT = ADI.

   4. (D) If a chronic, subchronic, or subacute NOAEL from mammalian test species exposed to toxicant contaminated drinking water is available:

      Where:	Vw	=	volume of water consumed daily by test animal (liters per day)
      	Wa	=	weight of test animal (kg)
      	Wh	=	seventy (70) kilograms, weight of human
      	B	=	uncertainty factor (B = 100–1,000 depending on quality of study)

   5. (E) If a chronic, subchronic, or subacute NOAEL from mammalian test species exposed to toxicant contaminated food is available:

      Where:

      C

      =

      daily food consumption expressed as a fraction of the animal's body weight

   6. (F) If a chronic, subchronic, or subacute NOAEL from mammalian test species exposed to toxicant by gavage is available:

      Where:	Fw	=	fraction of days dosed per week

   7. (G) If an oral rat LD50 is available:

      Where:

      M

      =

      one-ten thousandth (0.0001), acute to chronic application factor

   8. (H) If an acceptable NOAEL is lacking, the lowest observable adverse effect level (LOAEL) may be substituted in some cases for NOAEL, with an additional uncertainty factor of one (1) to ten (10).
   9. (I) HLSCs are best derived from data involving oral exposure. However, if available oral data are insufficient, it may be useful to use data from other exposure routes. Use of such data will depend on the specific pharmacokinetic and toxicological properties of each chemical.
   10. (J) On the basis of available information, the HLSC is evaluated as to whether it is consistent with sound scientific judgment. If not, the commissioner will direct the evaluation of appropriate modifications of these procedures.

(Water Pollution Control Division; 327 IAC 2-1-8.5; filed Feb 1, 1990, 4:30 p.m.: 13 IR 1037; errata filed Jul 6, 1990, 5:00 p.m.: 13 IR 2004; readopted filed Oct 18, 2024, 1:57 p.m.: 20241113-IR-327230810RFA)