APPENDIX I Toxicity Identification Evaluation Reports for Chollas ...

Toxicity Identification Evaluation of Chollas Creek
Stormwater using Hyalella azteca
Results
August 2006
The 0.025 mg/L PBO treatment increased toxicity in the 100 percent sample concentration (0%
survival) relative to toxicity in the unmanipulated Baseline test (80% survival in the 100 percent
sample concentration). The NOEC was less than 50%, and the LC 50 was 32.5%. Survival in
the 0.025 mg/L PBO treatment blank was 86.7%. The 0.050 mg/L PBO treatment also
increased toxicity in the 100 percent sample concentration (20% survival) relative to toxicity in
the unmanipulated Baseline test (80% survival in the 100 percent sample concentration). The
NOEC was less than 50%, and the LC 50 was 27.27%. Survival in the 0.050 mg/L PBO
treatment blank was 80 percent. The increase of toxicity in these manipulations suggests that
pyrethroids may be a causative agent in this stormwater sample. Specifically, it is well-known
that sublethal concentrations of PBO potentiate the toxicity of pyrethroids (Budavari, 1989).
A copper sulfate reference toxicant was tested at nominal concentrations of 62.5, 125, 250, 500
and 1000 µg Cu 2+ /L. The calculated 96-hour LC 50 (189.41 µg Cu 2+ /L) was within two standard
deviations of the laboratory mean (365.19 µg Cu 2+ /L) at the time of testing. This indicates that
the sensitivity of H. azteca used in this evaluation fell within the normal range.
Survival of H. azteca in three of the treatment blanks (Aeration, Filtration, and Methanol Elution
tests) was lower than expected. While reference toxicant tests demonstrated adequate
sensitivity of these test organisms, these tests use a higher volume of water (200 mL) than in
the TIE tests (50 mL), which likely is preferred by these test organisms. It is also possible that
test organisms used in the October TIE tests were more sensitive. More specifically, lower
tolerance to test conditions and lower survival in three of the treatment blanks may be related to
the source and age of the test organisms. Due to the last second nature of the October
stormwater sampling event, there was not sufficient time as to allow for the ordering of test
organisms from the standard source (i.e. Aquatic Indicators). Thus the organisms used in the
October TIE were those cultured according to standard protocols at Weston. As a result, slight
differences in age and source of organisms may explain the low tolerance to TIE test conditions,
and slightly reduced survival in the three treatment blanks.
4.1.2 Summary of TIE Performed on the October 18, 2005 Stormwater Sample
The results from the Phase I TIE performed on the Chollas Creek stormwater sample collected
in October indicated that pyrethroids may be the cause of the toxicity observed in the initial
toxicity tests. First, in the Baseline test, toxicity of H. azteca exposed to diluted and undiluted
stormwater (80 to 100% survival) was significantly lower than that in the initial toxicity test (7.5
to 42.5% survival). This indicates that during the time elapsed between the initial and baseline
toxicity tests, the causative agent in the stormwater sample had degraded, or had significantly
adsorbed to the plastic container in which the sample was held. Pyrethroids are known to
adsorb to plastic, thus leading to a time-dependent reduction in toxicity (Wheelock et al., 2005).
Second, the lack of toxicity reduction in the EDTA, STS, graduated pH, and aeration treatments
indicates that the causative agent was likely not a metal, an oxidative chemical, a pH-sensitive
chemical, or a volatile chemical or surfactant, respectively. However, the reduction in toxicity of
H. azteca following filtration of the stormwater sample indicates that the causative agent was
highly bound to particulates in the sample. Pyrethroids have physicochemical properties that
match the results of the present TIE; pyrethroids are insoluble in water but soluble in solvents
(have high K ow s), have low vapor pressures (indicating low volatility), and have high adsorption
coefficients, indicating their tendency to adsorb to particulates (Kidd and James, 1991). In
addition, toxicity was significantly increased in the diluted and undiluted PBO-treated stormwater
samples, as compared to toxicity in the baseline test (untreated diluted and undiluted
stormwater). These results also indicate pyrethroids as the causative agents because pyrethroid
toxicity is potentiated by PBO (Budavari, 1989).
Weston Solutions, Inc. 16