Contaminants may or may not be involved. It may take a dramatic effort to sort these out. On the other hand, other causes of mortality may overshadow the impacts of a contaminant. Known contaminant-related events may not be that useful when looking for emerging issues because the contaminant effect is already known and data are already available concerning specific usage, sites of application, species involved, etc. In gathering information BEST should locate and solicit areas of concern by agencies or states.
Incidents affect rare species.
Incidents are well documented and well studied so extrapolation to other areas is possible. A recurrent pattern allows for extrapolation. A contaminant looms large relative to other issues. Losses are from direct effects. The presence of contaminants can be identified.