What is the relationship between ecological and human health risk assessment?

Technical Note DOER-R1

September 1998

What is the relationship between ecological and human health risk assessment? At

most sites, risk assessment will address two general types of risk, ecological risk and human health

risk. Ecological risk assessment focuses on potential risk to nonhuman biota likely to occur at a

disposal site. Human health risk assessment focuses on carcinogenic and noncarcinogenic risk to

humans from potential exposure. A major difference between the two is that a human health risk

assessment addresses potential effects to one type of receptor, human beings, while ecological risk

assessment can address risk to several receptors, chosen to represent the ecosystem associated with

the dredged material disposal site.

These two types of risk assessment address the fate and transport of contaminants in similar if not

identical manners. Those physical and chemical processes driving the distribution of contaminants

are the same for the two types of risk assessment. The two are linked in that the estimates of

contaminant uptake by biota (evaluated in the ecological risk assessment) may result in exposure

to humans if people eat that organism. Clearly, the feeding habits of a commercial species, an

ecological characteristic, will to a large extent determine whether that species can pass a contaminant

on to a human. This is the point where ecological risk and human health risk are most closely linked.

They diverge in the discussion of toxicological processes and how these processes relate to potential

effects.

Who can conduct a risk assessment? The selection of personnel to conduct a risk

assessment depends on the level of complexity addressed in the risk assessment. For example, a

rough estimate of exposure based on a simple sediment-water partitioning equation may be sufficient

to demonstrate little probability of bioavailability of a chemical, and hence risk. In such a case,

operations personnel with expertise in engineering, chemistry, or marine geology may be the only

necessary personnel. In the most complex assessments (and these are likely to be the least frequently

encountered), an interdisciplinary team of engineers, biologists, chemists, and physical scientists

may be necessary.

What new tools are available or under development by USACE to conduct a risk

assessment for a dredged material management project? As indicated earlier, risk

assessment is well integrated into various state and Federal regulatory programs. With this

integration, these programs have developed various risk assessment frameworks, guidance

documents, on-line databases, case studies, and program experts available for consultation. USACE

is developing or has planned numerous resources for dredged material managers and operations

personnel and will publish these sequentially. They include several documents and databases.

Ecological and Human Health Risk Assessment Guidance for Aquatic Sites. This detailed

technical document (currently in draft form) includes specific guidance for developing

site-specific risk assessments for dredged material management sites in aquatic environments

(anticipated publication in winter 1999). It demonstrates the development of conceptual

models that show the likely sources of risk, transport pathways, types of receptors,

assessment end points, and physical or chemical relationships among them for ecological and

human health exposures. This document illustrates the use of risk assessment with a

continuous case study and reviews available Federal, regional, and state guidance and

methods used by human health and ecological risk assessors. The appendices include a review

of the content and availability of various text and on-line information important in conducting