Combined Actions and Interactions of Chemicals in Mixtures

If yes, there may be potential health hazard due to interactions and/or additivity.
Step 7b
Apply qualitative WOE: is combined score positive?
If no, health hazard likely to be less than indicated by HI or by separate HQ for
unique critical effect.
If yes, there may be potential health hazard due to interactions and/or additivity.
4.5.2 ATSDR strategy for carcinogenic effects
Step 1 and step 2 ask questions as to whether the mixture has already been either
regulated or scientifically evaluated in which case this information should be used.
If this is not the case further steps are proposed:
Step 3
Are estimated risks equal to or greater than 1x10 -6 for at least 2 of the individual
mixture components?
If no, additivity and interactions are unlikely to result in health hazard.
If yes, further evaluation of additivity and interactions is necessary for the
components of concern (risk equal to or greater than 1x10 -6 ).
Step 4
Is a relevant PBPK/PD model or studies on joint toxic action available for mixture
of components of concern?
If yes, use model or study to evaluate potential health hazard.
If no, go to step 5.
Step 5
Is the sum of the risks for the components equal to or greater than 1x10 -4 ?
If no, go to step 6a. If yes (potential health hazard due to additivity; evaluate
interactions), go to step 6b.
Step 6a
Apply qualitative WOE: is combined score positive?
If no, health hazard is unlikely
If yes, there may be potential health hazard due to interactions and/or additivity.
Step 6b
Apply qualitative WOE: is combined score positive?
If no, health hazard likely to be less than indicated by the sum of risks.
If yes, there may be potential health hazard due to interactions and/or additivity.
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