1.1 MB pdf - Bolsa Chica Lowlands Restoration Project

SECTION 3: ANALYSIS
100 percent of sample. EC 50 s for larval development ranged from 0.2 percent of sample to
100 percent of sample. LC 50 s for survival ranged from 0.17 to 100 percent of sample. However,
many of these were also the maximum sample concentrations tested because of salinity
adjustments to bring the samples into the tolerance range of the test organism. Chemical
concentrations associated with the NOECs, LOECs, EC 50 , LD 50 are presented in Appendix G.
Further analyses of these bioassay data are provided in Section 3.2.2.
Surface Water
Bolsa Chica surface water samples were evaluated for toxicity to topsmelt, Atherinops affinis,
Ceriodaphnia dubia, and Mysidopsis bahia. The toxicity tests for each species are described
below.
Topsmelt
Toxicity tests with topsmelt followed the procedures outlined in U.S. EPA (1995a)
guidelines. The tests were conducted by CH2M HILL at its Corvallis, Oregon, laboratory.
Chronic toxicity of surface waters was tested by using five or six concentrations ranging
from 1 to 100 percent sample. The tests were started by adding five fish per chamber into
five replicate chambers per concentration used.
Upon arrival at the laboratory, salinity of surface water samples ranged from 23 to 99 ppt.
All samples were adjusted to 30 ppt by the addition of either Tropic Marin® sea salts (to
raise salinity) or distilled water (to lower salinity). The test was conducted for 7 days with
daily renewal of the test solutions. Prior to each solution renewal, pH, dissolved oxygen,
and salinity were measured in each test chamber, and any dead fish were recorded and
removed. In addition to the periodic measurements, temperature was monitored on a
constant basis throughout the 7-day test period. Growth was measured by determining the
dry weight of topsmelt at the conclusion of the chronic definitive tests.
Statistical analyses were used to compare the growth and survival data among each test
concentration and the control solutions. IC 25 values (the percent of sample causing a
25 percent reduction in biological measurement, e.g., growth) were calculated for growth
effects in the chronic tests. The NOEC and the LOEC for survival and growth were also
calculated.
The results of the surface water toxicity tests are summarized in Table 3-14. They show that
the percentage of sample resulting in NOECs for development and survival among the test
samples ranged from 30.3 percent of sample to 100 percent of sample. These were also the
highest concentration of each sample that was tested because of the dilution to adjust
salinity within the tolerance range for the test organism. Because there was no effect in any
of the samples, the LOEC, EC 50 , and LC 50 were greater than the tested concentrations.
Further analyses of these bioassay data are provided in Section 3.2.2. Chemical
concentrations associated with the NOECs, LOECs, EC 50 , and LC 50 are presented in
Appendix G.
Ceriodaphnia dubia
Toxicity tests with Ceriodaphnia were conducted following U.S. EPA (1994e) guidelines for
short-term toxicity tests for freshwater organisms. The tests were conducted by ToxScan,
Inc. in Watsonville, California. Upon receipt at the lab, the stormwater monitoring samples
were tested for electrical conductivity. Of the five surface water samples, two had specific
SAC/143368(003.DOC) 3-29 ERA REPORT
7/31/02