[A study of the relationships between exposure periods and no-effect doses in repeated dose toxicity tests]

In the risk assessment of chemicals to humans, it is a very important step to determine no-observed-adverse-effect-levels (NOAEL) or lowest-observed-adverse-effect-levels (LOAEL) from animal experiments. Recently, short-term screening tests, such as 28-day repeated dose toxicity test, are carried out in accordance with the regulative guidelines for the safety evaluation of chemicals. However, many problems still remain in the risk assessment to human based on short-term toxicity studies. For this reason, we studied the relationships between the exposure periods and NOAELs or LOAELs in repeated dose toxicity tests using available test results of 18 halogenated compounds. The ratios between each NOAEL or LOAEL of short-term tests (14, 28 days, 13 weeks and 6 month) and those of long-term tests (longer than one year) were calculated on the basis of same animal species, route and toxic effect. From this study, it was considered that exposures above 13 weeks were needed to satisfy the present safety factor considerations for setting an acceptable daily intake (ADI).