Hello,
I have a question regarding the calculation of the human health effect factor. I am curious what is the utility of multiplying the ED50 quantity by the value (0.5). If each and every EF contains this operation, then what added value does it give to the final result? Wouldn't it be acceptable to leave the EF as equal to the term (365 x LT x BW x ED50h)?
Best,
Michael
Thank you for your question.
The human-toxicological effect factor EF of a chemical equals:
EF = α / ED50
where α is the slope factor that relates the inverse of the ED50 to a potential probability of getting a certain (cancer or non-cancer) effect. The USEtox default value of α = 0.5 assumes a linear effect with 50% additional chance to get the effect while taking in (ingesting or inhaling) a quantity equal to the ED50 over lifetime.
Note that α is not a unitless value, but relates ED50 [kg intake per person per lifetime] to EF [disease case per kg intake]. Further details are given in Rosenbaum et al. (2011).