ECO65: Characterizing the uncertainty in MAF values for aquatic receptors estimated using the KEMI MAF

Description

In a recent report the Swedish Chemical Agency proposed a methodology for setting MAF values (KEMI, 2021). This methodology (hereafter the KEMI MAF approach) suggests that MAF value of 25 and higher are required to protect aquatic receptors in the waters of contaminated rivers. While the KEMI MAF correctly models the impact of MAFs to reduce combined exposures and is an improvement on other proposed methods the approach has limitations. The methodologies for characterizing combined risks used in the examples of the report are screening approaches that are designed to overestimate combined risk. This results in overestimates of the size of the MAF values needed to protect ecological receptors. In addition, the KEMI MAF approach assumes that only the minimum level of control will be required (i.e., just meeting the standard). This assumption is not consistent with pollution control technology which can rarely be designed to exactly match a standard.  

The publications on the KEMI MAF do not disclose these biases, but instead use the large values to advocate for a MAF value much larger than the value of three to five currently under discussion.