A mixed-order model to assess contaminant declines

We introduce a generalized form of the common first-order (exponential) dec ay model, that has potential utility for describing contaminant declines in environmental applications, particularly when declines are a mixture of ma ny underlying processes. The exponent on contaminant concentration is left as a free parameter allowing the order of the reaction to be determined by the data. The mixed-order model is more flexible than models with the expon ent determined a priori, facilitating an improved fit to observed behavior. We demonstrate the utility of this model, and compare it to two other mode ls, by estimating PCB concentration declines in Lake Michigan fishes.