1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 4: RISK CHARACTERIZATION
Dermal contact with sediment or surface water is considered to be a minor 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 COPECs are highly lipophilic (e.g., DDT) and can
bioaccumulate, they are of greater concern in the food chain pathway as opposed to direct
contact.
Inhalation of volatiles from sediment/soil or surface water is considered a minor exposure
route, primarily because of the low frequency of detection and the short half-life of most
volatile chemicals.
Exposure route assumptions were also made for each representative species, including rates
of ingestion and intake of exposure media (sediment/soil and biota). These factors, plus
other biological characteristics, influence potential exposure by a particular species and may
cause the selected species to be not truly representative of their guild. These differences may
not be accounted for by the representative species selected, which could result in an underor
overestimation of potential exposure (intake), depending on the species.
4.3.2.2 Ecological Effects Characterization
Uncertainties associated with the ecological effects characterization include salinity
adjustments required in the toxicity bioassays conducted on site sediment, pore water, and
surface water; the evaluation of those results through regression analyses; and the selection
of RTVs for use in the ERA.
The bioassays were conducted on standard toxicity testing organisms, but most of the
sediments and extracted pore waters had salinities outside of the tolerance ranges of the test
organisms. These sediments and pore waters had to be adjusted to salinities within the
tolerance range prior to bioassay test initiation so that false results would not be observed.
Salinity adjustments were required for more than one-half of the sediment samples used for
amphipod and Nereis tests and for more 80 percent of the pore waters used for Mytilus tests.
For pore waters, the dilution from salinity adjustment could be related to the actual test
dilutions used in the bioassays, but additional uncertainty arose in many samples because
the salinity dilutions resulted in no toxicity to test organisms when there were high
concentrations of chemicals in the undiluted sample. Adjusting the sample for salinity could
have also resulted in dilution of chemical concentrations or resulted in changes to
bioavailability or toxicity of some COPECs. The effects of dilution could not be quantitated
based on the methodologies used.
For the sediment bioassays, no correlation could be made because all sediments were tested
at 100 percent sample, and changes in salinity were made via the overlying waters. The
potential or actual changes in concentrations of other chemicals as a result of these
adjustments could not be quantified in any reliable way.
The evaluation of bioassay data through regression analyses provided an additional level of
data evaluation and additional effect concentrations. The uncertainties associated with the
regression analyses include data transformations, assumption that chemical concentrations
decreased linearly with dilution of the test medium for Mytilus bioassays, and the
estimation of EC 50 . The data were transformed to maximize the regression analyses so that a
ERA REPORT 4-26 SAC/143368(004.DOC)
7/31/02