Generally speaking, for substances whose dietary intake exceeds 0.5 ppb, some amount of toxicity data will be needed to demonstrate its safety. For low dietary intakes of up to 50 ppb, this means submitting reports of in vitro genotoxicity assays, such as an Ames test and mouse lymphoma or chromosome aberration study. If the dietary exposure is higher than 50 ppb, it may be necessary to submit more extensive toxicity data, including a subchronic oral study in rats and, possibly, the same study in dogs. In this case, it is important that these studies demonstrate a clear no-observed adverse effect level (NOAEL) and that this NOAEL exceeds the calculated dietary exposure by a safe margin. Generally speaking, the minimum safe margin of exposure determined from subchronic studies should be 1,000-fold.