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

Affected: IC 13-18-4

Sec. 8.4. The concentration to protect wildlife is the terrestrial life cycle safe concentration (TLSC). The minimum toxicity data requirement for derivation of a TLSC shall consist of an acute oral LD50 for rats. When mammalian and avian toxicity data are available, a TLSC shall be calculated for both groups. The final TLSC is the lowest of the two (2) values. The TLSC shall be derived by one (1) of the following methods, depending on the type and quality of the toxicity data base:

1. (1) If a chronic, subchronic, or subacute no observable adverse effect level (NOAEL) from mammalian or avian species exposed to toxicant contaminated water is available:

   Where:

   U

   =

   uncertainty factor (U = 10-100 depending on quality of study)

2. (2) If a chronic, subchronic, or subacute NOAEL from mammalian or avian species exposed to toxicant contaminated feed is available:

   Where:	C	=	weight of feed consumed daily expressed as a fraction of test animal's body weight
   	Wa	=	weight of test animal (kg)
   	Vw	=	volume of water consumed daily by the test animal

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

   Where:	Fw	=	fraction of days dosed per week

4. (4) If an oral rat LD50 is available:

   Where:

   M

   =

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

5. (5) TLSCs 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.
6. (6) 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).
7. (7) On the basis of available information, the TLSC 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 2-1-8.4; filed Feb 1, 1990, 4:30 p.m.: 13 IR 1036; errata, 13 IR 1861; errata filed Jul 6, 1990, 5:00 p.m.: 13 IR 2004; readopted filed Oct 18, 2024, 1:57 p.m.: 20241113-IR-327230810RFA)