Effects assessment is the third step of and ERA. This step describes the relationship between a stressor and a receptor and is used to link a contamination to a biological response. Essentially, characterizing effects involes describing the effect elicited by the stressor, linking effects to the assessment endpoint and evaluating how effects change with varying stressor levels. This link is usually made through literature searches for toxicity data or by conducting site -specific toxicity testing experiments, but other approaches are also possible.