§ 799.9110 TSCA acute oral toxicity.
(a) Scope. This section is intended to meet the testing requirements under section 4 of the Toxic Substances Control Act (TSCA). In the assessment and evaluation of the toxic characteristics of a substance, determination of acute oral toxicity is usually an initial step. It provides information on health hazards likely to arise from short-term exposure by the oral route. Data from an acute study may serve as a basis for classification and labeling. It is traditionally a step in establishing a dosage regimen in subchronic and other studies and may provide initial information on the mode of toxic action of a substance. An evaluation of acute toxicity data should include the relationship, if any, between the exposure of animals to the test substance and the incidence and severity of all abnormalities, including behavioral and clinical abnormalities, the reversibility of observed abnormalities, gross lesions, body weight changes, effects on mortality, and any other toxic effects.
(b) Source. The source material used in developing this TSCA test guideline is the Office of Prevention, Pesticides, and Toxic Substances (OPPTS) harmonized test guideline 870.1100 (August 1998, final guideline). This source is available at the address in paragraph (f) of this section.
(c) Definitions. The following definitions apply to this section.
Acute oral toxicity is the adverse effects occurring within a short period of time after oral administration of either a single dose of a substance or multiple doses given within a 24–hour period.
Dosage is a general term comprising the dose, its frequency, and the duration of dosing.
Dose is the amount of test substance administered. Dose is expressed as weight of test substance (milligrams, grams) per unit weight of test animal (e.g., milligrams per kilogram).
Dose-effect is the relationship between the dose and the magnitude of a defined biological effect either in an individual or in a population sample.
Dose-response is the relationship between the dose and the proportion of a population sample showing a defined effect.
LD50 (median lethal dose) is a statistically derived estimate of single dose of a substance that can be expected to cause death in 50% of animals when administered by the oral route. The LD50 value is expressed in terms of weight of test substance per unit weight of test animal (milligrams per kilogram).
(d) Alternative approaches to the determination of acute toxicity. (1) EPA will accept the following procedures to reduce the number of animals used to evaluate acute effects of chemical exposure while preserving its ability to make reasoned judgments about safety:
(i) Estimation of acute oral toxicity. When further study is warranted, EPA generally supports limiting such tests to those using the lowest number of animals feasible. EPA will accept three alternative Organization for Economic Cooperation and Development (OECD) test methods in place of the “traditional” acute oral toxicity test. The three OECD alternatives are the following:
(A) The up and down procedure as described in OECD Guideline 425 referenced in paragraph (f)(4) of this section.
(B) The acute toxic class method as described in OECD Guideline 423 and referenced in paragraph (f)(6) of this section.
(C) The fixed dose method as described in OECD Guideline 420 and referenced in paragraph (f)(5) of this section.
(ii) Limit test. When data on structurally related chemicals are inadequate, a limit test may be considered. If rodents are used, a limit dose of at least 2,000 mg per kilogram of body weight may be administered to a single group of five males and five females using the procedures described in paragraph (e) of this section. If no lethality is demonstrated, no further testing for acute oral toxicity is needed. (Under current policy and regulations for pesticide products, precautionary statements may still be required unless there are data to indicate the LD50 is greater than 5,000 mg/kg.) If compound-related mortality is produced in the limit test, further study may need to be considered.