Metal Interactions in Mixtures

modeling joint action of mixed toxicants is based on whether the mixed chemicals are thought to be predominately independent or similar in action for an adverse effect. The joint effect Pui+ud of two independently acting metals (Ml and M2) combined at concentrations C x and that alone would produce and P, 2 proportions (or probabilities) of effect would be predicted with the model. 

As discussed in Chapter 8, any deviation from ideal independence might be detected by inserting a parameter (p) to be estimated into Equation (1.3) in place of the implied 1 and then testing for significant deviation from 1 for the parameter estimate (Newman and Clements 2008). 

Depending on study goals, a general linear modeling approach might be applied to these kinds of data. If there are more metals in the mixture, the independent joint action model can be expanded to Equation (1.5). 

The approach is different for mixed metals that are assumed to have a material degree of interaction due to a similar mode of action. Such situations produce toxicant effect-concentration relationships for each of the toxicants alone that have the same slopes (Slopecommoi) (Finney 1947). Extending the notation above to the case of similar joint action. 

Pr obit(PMx)=Intercept Ml+Slope common (Log Cmi) Probit(PM2)=Interceptm2+Slope common (Log 

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