Assessment and measurement end points

potentially sensitive organisms due to lack of data contributes to the uncertainty

of the dredged material assessment.

Assessment and measurement end points

Selecting assessment end points. Assessment end points are defined as

environmental characteristics or values that are to be protected, such as

abundance of a wildlife population, species diversity, or ecosystem productivity

(Suter, Barnthouse, and Bartell 1992). Lack of information with which to develop

assessment end points for some COCs is an important source of uncertainty for

the risk assessment.

In the conceptual model development stage, the uncertainty in selection of

appropriate assessment end points is not quantifiable, but clearly has the potential

to exert a significant influence on the direction of the analysis.

Selecting measurement end points. Measurement end points are quantitative

expressions of a biological response that are related to the assessment end points.

Measurement end points for ecological risk assessment are usually related to the

survival, growth, and reproduction of receptors of concern. These measurement

end points are assumed to be closely related to assessment end points, such as

changes in population structure and function. The correlation of stressor to

response is an indication of the strength of the relationship.

In some cases, assessment and measurement end points are closely related.

For example, fish that consume contaminated prey in the area of a dredged

material disposal site might accumulate body burdens of persistent chemicals,

such as organochlorine compounds, which might subsequently accumulate in the

eggs of fish-eating colonial birds. The amount of contaminant in the egg is a

measurement end point that has been linked to embryolethality (measurement

end point) and reproductive failure (assessment end point) in exposed

populations (Giesy, Ludwig, and Tillitt 1994). However, measurement end points

and assessment end points are not always so clearly related. For example,

appearance of lesions or tumors on older adult fish may have little impact on the

reproductive success of the population.

Uncertainty in the relationship between assessment and measurement end

points can contribute to significant uncertainty in estimates of risk to the

receptors. For example, consensus has not been reached on the appropriateness of

existing and proposed assays to detect the potential for endocrine disruption

properties of chemical substances and mixtures (Kendall et al. 1995). The results

of an expert panel on ecological risk assessment for sediments found that the

ecological relevance of measurement end points involving organic extracts and

elutriates was most uncertain relative to other toxicity tests (Ingersoll et al. 1997).

Lack of measurement end points. In some cases, measurement end points

will not be available. For example, although ERED provides information on the

critical body burden of some chemicals, it does not contain information for all

potential COCs. This information could be obtained through additional data

collection and analysis, but is typically beyond the scope of a site-specific risk

assessment.

Chapter 5 Uncertainty in Tier IV Risk Assessments