Effects Assessment

Table 3

Range of Reported Home Range Sizes

Range of Reported Values

Common

for Home Range Size

Name

Scientific Name

square kilometers

Actitis macularia

Sandpiper

~ 0.0025

Lutra canadensis

River otter

2.95 to 4.0

Pandion haliaetus

Osprey

9.1 to 314

(4) Migration. A species that migrates away from the disposal site may

have more limited exposure than a local nonmigratory species.

Migratory patterns could also bring a species under the influence of

a dredged material management site during a particularly vulnerable

life stage (i.e., breeding period, larval development, etc.). Such

limited, but possibly critical, exposures may present significant

sources of uncertainty in estimating exposure. Avoidance or

attraction of wildlife to dredging or disposal sites also may

influence their exposure to COCs.

Overall, a moderate degree of uncertainty is associated with

parameters that describe the exposure duration of ecological

receptors (USEPA 1993c). Additional information that would

reduce this uncertainty could be obtained through field surveys and

laboratory measurements.

(5) Time-activity patterns for workers. There is both uncertainty and

variability in specifying the exact time-activity patterns of workers.

Time-activity patterns are an important component of estimating

exposures to contaminants in dredged materials. The most reliable

estimates will be obtained based on site-specific information. With

this information, the magnitude of uncertainty should be low and

easily quantified.

Effects Assessment

Toxicity end points for ecological receptors

Toxicity end points for mammalian and avian species have been evaluated

and compiled in "Toxicological Benchmarks for Wildlife: 1996 Revision"

(Sample, Opresko, and Suter 1996). Relatively few of the studies included in this

compilation determined safe levels (no observed adverse effect levels

(NOAELs)) for exposures in which wildlife were chronically exposed over an

entire lifetime or several generations. Although USEPA has no clear definition

for the duration of a chronic exposure, some approaches assume that a chronic

exposure is equal to at least 50 percent of a species' life span. In many cases,

however, the only information available is from short-term or subchronic

experiments on laboratory species (e.g., mice and rats). Estimating an NOAEL

Chapter 5 Uncertainty in Tier IV Risk Assessments