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Is a mixture assessment factor (MAF) the right way forward? Thomas Backhaus University of Gothenburg thomas.backhaus@gu.se
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AreaSizeReference Environment100 Janssen, 2004; van Vlaardingen, 2007 Environment100Tørsløv, 2013 Human health100Muilerman, 2011 Human health10Tørsløv, 2013, Petersen, 2014 Suggested MAFs No explicit justification given
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easy to implement no additional data needed increased level of protection CONSPROS blanket type of approach hard to justify size
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Conservatism in Hazard Assessment REACH Guidance Document, Chapter R10, 2008
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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
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Hazard Assessment Assessment Factors Exposure Assessment Conservative Assumptions Consideration of Uncertainties
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Assessment of Single Substances Exposure AssessmentHazard AssessmentRisk Assessment
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Assessment of Mixtures Exposure AssessmentHazard AssessmentRisk Assessment
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A Mixture Assessment Factor needs to cover exposure and hazard assessment Assessment of Mixtures
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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
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Equals the number of expected compounds in a mixture MAF based on Concentration Addition if
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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
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Pesticide Mixture Result from the Swedish pesticide monitoring program n = 42 . Example
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Distribution of Risk Quotients 136
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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
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Distribution of Risk Quotients after risk mitigation 16.0
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Maximum Cumulative Ratio Equitoxic Mixture:
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4 different scenarios Mixture Typen Prior adjustment After risk mitigation for single compounds Risk quotient MCR Risk quotient MCR Pesticides421363.616.8017 Pharmaceuticals18 481.2 4.65 4.7 Anti-androgens15 2.01 2.00 Organic air pollutants 29 4.332.9 3.78 3.9
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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
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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
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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
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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
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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
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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
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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
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The specific uncertainty of coincidental mixtures cannot be lowered by “the actor” (chemical producer, importer, down-stream user) Task for regulatory authorities! Summary & Conclusions
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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…
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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…
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Is a mixture assessment factor (MAF) the right way forward? Thomas Backhaus University of Gothenburg thomas.backhaus@gu.se ThoBaSwe @Twitter 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
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