1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 2: PROBLEM FORMULATION
2.5.2 Exposure Pathway Inclusion/Exclusion
The exposure pathway inclusion/exclusion evaluation is based on information gathered
from the problem formulation (Sections 2.2, 2.3, and 2.4) and the selection of representative
species, the probable completeness of each exposure pathway, and the potential for that
pathway to be a major or minor route of exposure and risk.
A complete exposure pathway must exist for an exposure to occur. A complete exposure
pathway must have the following elements, in addition to the presence of suitable habitat
for ecological receptors:
• Contaminant source (e.g., chemicals in waste sumps, etc.)
• Mechanism for contaminant release and transport (e.g., surface dispersion)
• Exposure point (e.g., wetland Cell, creek, or soil)
• Feasible route of exposure (e.g., ingestion)
• Receptor (e.g., fish, bird, or mammal)
Contaminant sources and release mechanisms in the Bolsa Chica Lowlands consist primarily
of onsite source areas (waste sumps, pipelines, and maintenance areas) and runoff/surface
dispersion of chemicals from the onsite areas or from offsite sources (such as urban runoff).
Ecological receptors can be exposed to chemicals in soil, sediment, or surface water via direct
or secondary exposure pathways. Direct exposure pathways include ingestion, dermal
contact, root update, uptake/transport access gills, and potentially the inhalation of organic
vapors or soil particulates. Secondary exposure pathways are limited to food-chain transfer
of chemicals that bioaccumulate. Potential exposure pathways for representative species are
summarized in Table 2-23 along with the rationale for inclusion/exclusion in the quantitative
and qualitative evaluations to be conducted in the ERA.
Terrestrial and aquatic plants can absorb chemicals via root uptake from sediment/soil or
surface water. Many chemicals absorbed by plants are deposited in the leaves. In addition to
direct toxicity to the plant, chemicals that bioaccumulate within plant tissues (e.g., leaves)
may result in food chain transfer of chemicals to higher trophic-level organisms.
Terrestrial and aquatic invertebrates can absorb chemicals through their epidermis and can
accidentally or purposefully ingest sediment during feeding or burrowing. Benthic
organisms are especially prone to exposure to chemicals in sediments as some consume the
organic materials from within the sediment (e.g., chironomids). Aquatic invertebrates also
serve as a major route of food chain transfer, because they are prey for other aquatic
organisms (e.g., fish) and semi-aquatic wildlife (e.g., shorebirds).
Terrestrial and semi-aquatic birds (e.g., shorebirds) and terrestrial mammals can be exposed
to chemicals in sediment/soil or surface water from several different behaviors. Animals
can inadvertently or purposefully ingest sediment/soil while grooming, burrowing, or
consuming contaminated prey species. Surface water can be ingested as a drinking water
source or during bathing or grooming activities. Dermal contact with sediment/soil or
surface water is considered a secondary route of exposure for birds and mammals. Dermal
contact is of concern primarily with organic chemicals that are lipophilic (i.e., have an
affinity for fats) and can cross the epidermis of the exposed organism. Although some of the
COPECs (e.g., DDT ) are highly lipophilic and can bioaccumulate, they are of greater
concern in the food chain pathway as opposed to direct contact.
SAC/143368(002.DOC) 2-17 ERA REPORT
7/31/02