Risk assessment is a scientific evaluation that is used to characterize known or potential adverse health effects resulting from human exposure to soil contaminants. Risk assessment models identify inputs (pathways, exposure and toxicity factors) and uncertainties. Regulatory policy and protocols structure inputs to these assessments to support decisions. Risk managers define the “acceptable risk”, sampling protocols for soil characterization, pathways to be addressed, and specific exposure and toxicity factors to be used. Using these policies, regulatory agencies define soil screening levels and the process to define areas where unacceptable risks should be addressed. For soil contaminated sites, these assumptions are generally conservative, resulting in screening values that would not be of concern for future exposures.  

During litigation, each of the factors used to derive agency screening values may be challenged (soil depth, alternate calculations, controversy over toxicity values, additional pathways like gardens, degradation, etc.). Arguments are made to suggest that past exposures to residents are over or under-estimated. Although the scientific structure remains consistent, conflicting messages from technical experts, agencies and legal representatives on the assumptions result in confusing or conflicting messages. This leads to distrust, and makes it more difficult to provide convincing information . Rather than representing levels of no concern, residents perceive concentrations above  conservative cleanup levels as posing harm, even for short term exposures. This is inconsistent with the health consultation conclusions there are no risks. Scientists do not convey a consistent and believable message.

For dioxin impacts in a residential neighborhood adjacent to a Superfund site, experts continue to debate toxicity assumptions. Residents concerns for involuntary exposure to site related impacts do not consider background, other dioxin-like compounds in our homes, and other predominant exposure pathways through the diet. Better understanding of public concerns and more consistent messages are needed to resolve conflicts and restore confidence in neighborhoods after implementation of remedial actions.