Determination of the Reference Dose

4 Determination of the reference dose. EPA determines RfD from NOAEL or LOAEL obtained from an animal study or, occasionally, a human study using the following equation  

The product of UF and MF is the safety factor, which also is referred to as the safety and uncertainty factor since it accounts for uncertainties in the data. 

H Interhuman Generally use a factor of 10 when extrapolating from experimental results in studies using prolonged exposure of average healthy humans. EPA intends that this factor account for variation in sensitivity in humans. 

---

Clegg, D. J., and van Gemerl. M. (1999a). Determination of the reference dose for chlorpyrifos Proceedings of an expert panel. J. Toxicol. Environ. Health 2,211-255. 

---