Evans RM, Scholze M, Kortenkamp A. Examining the feasibility of mixture risk assessment: A case study using a tiered approach with data of 67 pesticides from the Joint FAO/WHO Meeting on Pesticide Residues (JMPR). Food Chem Toxicol. 2015 Oct;84:260-9. doi: 10.1016/j.fct.2015.08.015. Epub 2015 Sep 4. PubMed. Free access on ScienceDirect (until 30th Dec. 2015).
Our recently published paper presents a case study testing a tiered approach to mixture risk assessment (MRA) using data for 67 pesticides. Our main conclusions were:
- The data requirements of a tiered approach can grow dramatically so that low tiers, with lower data requirements, can be completed but higher tiers, with the highest data requirements, cannot.
- This is likely to leave many assessments in ‘limbo’, being unable to conclude that the risk of mixture toxicity is either acceptably low or unacceptably high.
- Nonetheless, tiered approaches may indicate data gaps that, once filled, can allow an assessment to progress; and may provide indications for the best use of resources in managing any risk.
- More systematic data collection, perhaps in high throughout systems, and open access to toxicology data may improve the situation.
Abstract: The way in which mixture risk assessment (MRA) should be included in chemical risk assessment is a current topic of debate. We used data from 67 recent pesticide evaluations to build a case study using Hazard Index calculations to form risk estimates in a tiered MRA approach in line with a Framework proposed by WHO/IPCS. The case study is used to illustrate the approach and to add detail to the existing Framework, and includes many more chemicals than previous case studies. A low-tier MRA identified risk as being greater than acceptable, but refining risk estimates in higher tiers was not possible due to data requirements not being readily met. Our analysis identifies data requirements, which typically expand dramatically in higher tiers, as being the likely cause for an MRA to fail in many realistic cases. This forms a major obstacle to routine implementation of MRA and shows the need for systematic generation and collection of toxicological data. In low tiers, hazard quotient inspection identifies chemicals that contribute most to the HI value and thus require attention if further refinement is needed. Implementing MRA requires consensus on issues such as scope setting, criteria for performing refinement, and decision criteria for actions.