Is a mixture assessment factor (MAF) the right way forward? Thomas Backhaus University of Gothenburg
AreaSizeReference Environment100 Janssen, 2004; van Vlaardingen, 2007 Environment100Tørsløv, 2013 Human health100Muilerman, 2011 Human health10Tørsløv, 2013, Petersen, 2014 Suggested MAFs No explicit justification given
easy to implement no additional data needed increased level of protection CONSPROS blanket type of approach hard to justify size
Conservatism in Hazard Assessment REACH Guidance Document, Chapter R10, 2008
No biotransformation No abiotic transformation High production volumes, resp. market share High emission rates Emission takes place in a confined space Emission happens suddenly (peak concentrations) Conservatism in Exposure Assessments
Hazard Assessment Assessment Factors Exposure Assessment Conservative Assumptions Consideration of Uncertainties
Assessment of Single Substances Exposure AssessmentHazard AssessmentRisk Assessment
Assessment of Mixtures Exposure AssessmentHazard AssessmentRisk Assessment
A Mixture Assessment Factor needs to cover exposure and hazard assessment Assessment of Mixtures
The simultaneous presence of compounds as mixtures is ignored Not all components included Insufficient (eco)toxicological knowledge on the mixture components Sole use of CA Interactions (synergistic, antagonistic) Mixture-specific uncertainties
Equals the number of expected compounds in a mixture MAF based on Concentration Addition if
Equals the number of expected compounds in a mixture E.g.: the CA-expected effect of a mixture is lower than 10%, if all components of a 100-compound mixture are below a concentration of EC10/100 MAF based on Concentration Addition
Pesticide Mixture Result from the Swedish pesticide monitoring program n = 42 . Example
Distribution of Risk Quotients 136
Several individual compounds are present at concentrations above their EQS. Need for regulatory action already on the single substance level Assumption: successful risk mitigation, i.e. all compounds are present at a concentration below their respective EQS. Environmental Risk of the pesticide mixture
Distribution of Risk Quotients after risk mitigation 16.0
Maximum Cumulative Ratio Equitoxic Mixture:
4 different scenarios Mixture Typen Prior adjustment After risk mitigation for single compounds Risk quotient MCR Risk quotient MCR Pesticides Pharmaceuticals Anti-androgens Organic air pollutants
Maximum exceedance of a safe level in various situations ‘n’ known Individual RQ’s < 1 RQ’s quantified Info. on interactions? MAF nounknownno arbitrary value yesunknownno arbitrary value yes no number of mixture components*IF yes no interactions unlikely number of mixture components yes noMCR*IF yes interactions unlikely MCR yes case-by-case based on weight of evidence
Maximum exceedance of a safe level in various situations ‘n’ known Individual RQ’s < 1 RQ’s quantified Info. on interactions? MAF nounknownno arbitrary value yesunknownno arbitrary value yes no number of mixture components*IF yes no interactions unlikely number of mixture components yes noMCR*IF yes interactions unlikely MCR yes case-by-case based on weight of evidence
Maximum exceedance of a safe level in various situations ‘n’ known Individual RQ’s < 1 RQ’s quantified Info. on interactions? MAF nounknownno arbitrary value yesunknownno arbitrary value yes no number of mixture components*IF yes no interactions unlikely number of mixture components yes noMCR*IF yes interactions unlikely MCR yes case-by-case based on weight of evidence
Maximum exceedance of a safe level in various situations ‘n’ known Individual RQ’s < 1 RQ’s quantified Info. on interactions? MAF nounknownno arbitrary value yesunknownno arbitrary value yes no number of mixture components*IF yes no interactions unlikely number of mixture components yes noMCR*IF yes interactions unlikely MCR yes case-by-case based on weight of evidence
Maximum exceedance of a safe level in various situations ‘n’ known Individual RQ’s < 1 RQ’s quantified Info. on interactions? MAF nounknownno arbitrary value yesunknownno arbitrary value yes no number of mixture components*IF yes no interactions unlikely number of mixture components yes noMCR*IF yes interactions unlikely MCR yes case-by-case based on weight of evidence
Mixture hazard assessment not possible without prior /parallel exposure assessment Transparent use of AF’s: which uncertainty is covered? Uncertainties in mixture assessment –incomplete exposure data –incomplete hazard data –synergism, antagonism Summary & Conclusions
n is a sufficiently protective MAF under the assumption of CA MCR / STU seems a good descriptor for a MAF for coincidental mixtures, if no single compound has a RQ>1. Only applicable to well characterized mixtures Summary & Conclusions
The specific uncertainty of coincidental mixtures cannot be lowered by “the actor” (chemical producer, importer, down-stream user) Task for regulatory authorities! Summary & Conclusions
A MAF basically lowers the critical threshold for regulatory action from a risk quotient of 1 to a lower value. Needed, because a risk quotient below 1 implies a ‘safe situation’ (no need for action). Wrong conclusion. A step in a different direction…
We need to overcome the notion that a risk quotient below one indicates ‘no risk’ and no need for action. A risk quotient should not be taken as an indication of risk per se, but as the contribution of a compound to the total risk in a given scenario. A step in a different direction…
Is a mixture assessment factor (MAF) the right way forward? Thomas Backhaus University of Gothenburg Thomas Backhaus, Mikael Gustavsson, Anke Hartmann, University of Gothenburg, Sweden Michael Faust, F&B Environmental Consulting, Germany Markus Klar, Henrik Sundberg, Stefan Gabring, Gunilla Ericson, Sten Flodström, Swedish Chemicals Agency, Sweden