 |
||
|
|
||
| |||||||||||||||
|
|
 shellfish, from either marine or freshwater sources) which contains contaminants of
concern. A complete exposure pathway must include:
a. A source and mechanism of release of contaminants.
b. A retention or transport mechanism for exchange of contaminants between
media.
c. An exposure point (e.g., sediment, water) where contact occurs.
d. An exposure route (e.g. ingestion, dermal uptake) by which contact occurs
(USEPA/OERR 1989).
Direct exposure pathways
In most dredged material management activities, the direct human exposure
pathway is unlikely to be of concern. Therefore, the body of this guidance does not
provide detailed information. In many cases, particularly for offshore disposal,
direct human exposure to contaminated sediments at aquatic dredged material
management sites is unlikely because the exposure pathways are incomplete. The
direct pathways may be more likely at containment islands and nearshore
management facilities. They may also occur during transport and handling of
material.
Direct exposure to sediments. Although the sediments are a source of
contaminants, there is no strong exchange mechanism between the sediments and
the overlying water since the contaminants are sediment sorbed in most cases. This
makes transport to the surface through desorption and dissolution unlikely for most
contaminants. Direct exposure through the water column may be event mediated as
in the case of storms or erosive events. Exposures due to direct contact with
sediments through activities such as swimming, recreational activities, or fishing are
also unlikely in offshore aquatic sites because:
a. Distance offshore and water depths at dredged material management sites
are generally incompatible with recreational swimming.
b. Depth to the bottom makes direct contact with sediments by fishermen and
boaters unlikely.
Direct exposure to water. There is potential for human contact with a waterborne
plume near or at the dredged material disposal site immediately following disposal
operations. However, the duration of this contact would be short, and the frequency
of contact would be low because it would occur only during disposal operations.
Therefore, this direct exposure pathway is likely to be insignificant. Disposal in
nearshore environments may warrant consideration of direct exposure pathways.
When to consider the direct exposure pathways. There may be instances where
direct exposure pathways are likely during a dredged material management activity.
Whether to incorporate these pathways into the human health exposure assessment
depends on various site specific factors. Table 2 provides guidance on when these
77
Chapter 4 Human Health Risk Assessment
|
|
Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing |
