IRIS presents 2 types of toxicity values for vinyl chloride yet the SL table shows only a single number. Which number was chosen and why?
The vinyl chloride calculations were based on the examples given in the Toxicological Review for vinyl chloride, which appears on IRIS. IRIS presents “continuous lifetime exposure during adulthood” and “continuous lifetime exposure from birth” slope factors and inhalation unit risks. Because the equations used on this website show the individual lifetime segments, the “continuous lifetime exposure during adulthood” toxicity values are chosen. The examples in the Toxicological Review indicate that, during childhood, both pro-rated and non-pro-rated risks should be generated using the lower slope factor or IUR. When estimating the risk using this method and considering the lifetime segments during childhood and adulthood, it is clear that the cancer risks early in life are higher than those that would be generated if the typical pro-rated risks were simply generated using the lifetime CSF or IUR. This finding is consistent with the IRIS assessment’s statements that cancer risk is increas
