Selection of the Database

3 Selection of the database. The types of studies that make up a complete database for estimating an RfD of high confidence for chemicals causing deterministic effects from data in laboratory animals include  

These studies may show a need for special studies to assess, for example, neurotoxic or immunotoxic responses. In such cases, the database may not be complete without the special studies. 

EPA does not consider data on developmental toxicity, standing alone, as an adequate basis for estimating RfD. Investigators use acute or short-term exposures for these studies. Therefore, they are of limited use in estimating the threshold for deterministic responses. However, if developmental toxicity is the critical response for a chemical with a complete database, EPA will derive RfD from that study. 

EPA uses the following hierarchy for choosing the study, species, and NOAEL used to calculate an RfD  

A subchronic (90 d) bioassay in a mammalian species by oral exposure is the recommended minimum data for estimating an RfD. The study must meet EPA s minimum standards of quality. Ideally, the study should identify a NOAEL and a LOAEL. In the absence of these minimum data, EPA assigns the chemical to a not verifiable group, and EPA then seeks or waits for additional data before estimating RfD for that chemical. 

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