APPENDIX I Toxicity Identification Evaluation Reports for Chollas ...

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Toxicity Identification Evaluation of Sweetwater River Stormwater Using Selenastrum capricornutum August 2006 1. EXECUTIVE SUMMARY As part of the San Diego municipal stormwater monitoring permit (NPDES Order 2001-01) for the San Diego, California region, stormwater runoff from Sweetwater River is evaluated every stormwater monitoring period for chemical constituents, toxicity to test organisms, and health of the benthic community. A decision matrix based on these three lines of evidence is then used to determine whether Toxicity Identification Evaluations (TIEs) will be initiated at Sweetwater River to identify the causative agents of toxicity in stormwater samples collected during major storm events. This decision matrix includes detection of high frequency contaminants of concern, persistent toxicity, and evidence of an impaired benthic community. In the 2004-2005 stormwater monitoring period for the San Diego County Municipal Stormwater Copermittees, total dissolved solids (TDS) exceeded water quality objectives measured in Sweetwater River stormwater samples (Weston 2005). While no other contaminants exceeded water quality objectives in the 2004-2005 monitoring period, the organophosphate pesticide diazinon exceeded water quality objectives in six out of the nine storm events prior to the 2004-2005 wet weather season. In addition, persistent toxicity was found because more than 50% of the toxicity tests conducted to date with this species had a NOEC of less than 100%. The benthic community was determined to be impacted. Based on these findings it was determined that TIEs would be performed at Sweetwater River if toxicity was observed during the standard toxicity testing of stormwater samples during the 2005-2006 monitoring period. During the October 18, 2005 storm event, Sweetwater River water caused significant toxicity, measured as reduced growth, to S. capricornutum. The IC 50 at 96 hours was estimated to be 95.7% of the stormwater sample concentration. The NOEC was 50% of the sample concentration. Weston initiated TIE testing on November 1, 2005 with this sample using the manipulations described below. All Selenastrum capricornutum baseline tests and TIE tests following sample manipulation followed general methods described in the U.S. EPA guidance manual, “Short-term Methods for Estimating the Chronic Toxicity of Effluents and Receiving Waters to Freshwater Organisms” (USEPA, 2002). TIEs were conducted according to guidelines for characterizing toxic effluents (USEPA, 1991, 1992, 1993a, and 1993b). Phase I TIEs included the following battery of tests to help establish potential causative agents of toxicity in stormwater samples: • Baseline tests were performed to benchmark toxicity of the unmanipulated stormwater samples run concurrently with the TIE tests for comparative purposes. • Ethylenediaminetetraacetic Acid (EDTA) tests were performed to determine whether metals were a potential contributor to the toxicity of the sample. • Solid Phase Extraction (SPE) Tests (followed by methanol elution) were performed to evaluate whether non-polar organics could be contributing to toxicity of the sample. • Piperonyl butoxide (PBO) tests were performed to determine whether organophosphate pesticides or pyrethroids could be potential contributors to toxicity. Results of TIE tests conducted on stormwater samples collected from Sweetwater River during the 2005-2006 monitoring season provided some evidence that one or more ions comprising TDS were the causative agents of toxicity. The results of the 8 mg/L EDTA manipulation demonstrated that the 8.0 mg/L EDTA test significantly reduced toxicity in the 100% sample concentration (106.96 RFU Chlorophyll) relative to toxicity in the unmanipulated Baseline test (69.70 RFU Chlorophyll in the 100% sample concentration). This indicated that the causative agent of toxicity was a cation, such as a free metal ion (e.g., cadmium, mercury, lead) or a Weston Solutions, Inc. 1
Toxicity Identification Evaluation of Sweetwater River Stormwater Using Selenastrum capricornutum August 2006 dissolved inorganic salt (e.g., sodium, calcium, magnesium), or a cationic organic compound such as a cationic surfactant, because EDTA is a chelating agent that is well known to bind inorganic and organic cationic chemicals (USEPA 1991). Chemical analyses of Sweetwater stormwater samples demonstrated that TDS measured in the Sweetwater sample was 2640 mg/L, a concentration that exceeds the water quality objectives for this measure, or 1500 mg/L, in the lower Sweetwater River (RWQCB 1994). In contrast, no organophosphate pesticides were detected in stormwater samples and the only metals detected were arsenic, nickel, and zinc, all of which were found at low concentrations, or concentrations far below water quality objectives. In addition, the causative agents of toxicity in the Sweetwater River stormwater samples did not share similar physicochemical properties to those of many other classes of chemicals. The lack of toxicity reduction in the SPE and PBO tests indicate that the causative agent was likely not a non-polar organic, or a common-use pesticide, respectively. It is well known that elevated concentrations of ions comprising the TDS may be toxic to aquatic organisms. Thus, the results of this TIE provide some evidence that the causative agent of toxicity may have been due to elevated TDS levels in the Sweetwater River sample collected in October 18, 2005. No additional toxicity was found in Sweetwater River samples in subsequent standard S. capricornutum tests during the 2005-2006 monitoring period, indicating that the causative agent was not persistent during this monitoring period. Additional studies would be necessary to confirm whether elevated TDS in Sweetwater River water were the causative agent of toxicity to S. capricornutum. Weston Solutions, Inc. 2
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