Fig. 2.

(A) The full Aggregate Exposure Pathway (AEP) for estradiol is presented here for two primary biological targets – humans and fish can act as both as a target site of exposure (TSE) as well as an intermediate key exposure state (KES). This full AEP is used as an inset (top-left) for (B) and (C), with the KESs (rectangles) and key transitional relationships (KTRs) of interest highlighted in red and remaining as dark arrows, respectively. (B) Concentrations of estradiol are higher in riverine sediment when adsorption is greater under cool weather conditions, as sparse algal populations during this period result in pH levels below the pK_a value for estradiol in water (left panel). During periods of warm temperature, algal blooms can cause pH levels to rise above estradiol’s pK_a value and lead to lower adsorption into sediment (right panel) and higher estradiol concentrations in overlying water. (C) The reciprocal nature of AEP development is demonstrated here. A partial AEP for a stressor is provided through data generated from individual studies and can contribute KESs and/or KTRs to a full AEP. A partial AEP can be extracted from a full AEP for specific applications, such as developing an exposure model. In this example, KESs that represent estradiol concentrations in wastewater treatment plant (WWTP) influent and effluent from New Orleans municipal facilities and in Mississippi River Water were obtained from published literature (Wang, et al., 2012).