APPENDIX I Toxicity Identification Evaluation Reports for Chollas ...

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Toxicity Identification Evaluation of Sweetwater River Stormwater Using Selenastrum capricornutum August 2006 5. DISCUSSION Results of this TIE indicate that one or more cations that comprise the total dissolved solids (TDS) found in stormwater samples from Sweetwater River may be responsible for the reduced growth of S. capricornutum. First, the results of the 8 mg/L EDTA test allowed for the increased growth of S. capricornutum or demonstrated that toxicity was reduced through the addition of EDTA to the 100% stormwater sample. This indicates that the causative agent of toxicity was a cation, such as a free metal ion (e.g., cadmium, mercury, lead), a 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). In addition to TIE tests, chemical analyses of Sweetwater stormwater samples indicate that cations comprising the TDS may be the causative agent(s) of toxicity. Concentrations of TDS measured in the undiluted stormwater sample were 2640 mg/L (see results in complete stormwater report), 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. TIE test results also indicate that 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 indicates that the causative agent was likely not a non-polar organic, or a common-use pesticide (e.g. pyrethroid or organophosphate), respectively. Statistical analyses of TIE results also provide some evidence that the causative agent could be a ion imbalance; growth was diminished in the undiluted 100% stormwater sample, relative to all treatments while growth was elevated in the 50% and 75% stormwater sample relative to the dilution water (0% stormwater) sample. This result indicates that the causative agent was toxic in the undiluted stormwater sample but significantly less toxic in the diluted stormwater samples. In contrast, in the dilution water control, the lack of ions may have led to diminished growth relative to the diluted stormwater samples. This result is not surprising because others have shown that elevated growth in TDS-enriched natural waters as compared to TDS-poor synthetic mediums (LeBlond and Duffy 2001). It is well known that elevated concentrations of ions comprising the TDS, or an imbalance of the ions comprising the TDS may be toxic to aquatic organisms; however, the concentration of TDS that causes toxicity is highly dependent on the species and types of ions comprising the TDS. While most species are tolerant of concentrations of TDS that exceed 1000 mg/L, some spawning or larval fishes are highly sensitive to TDS. Concentrations of 350 mg/L TDS reduced spawning of striped bass (Morone saxatilis) in the San Francisco Bay-Delta (Kaiser Engineers, 1969). In contrast the LC 50 for TDS for fathead minnows (Pimphales promelas) has been shown to range from 2,000 mg/L to 15,000 mg/L in natural waters, depending in part on the types of ions comprising the TDS (Mount et al. 1997). To the best of our knowledge, little is known about the effects of TDS on S. capricornutum. Weston Solutions, Inc. 11
Toxicity Identification Evaluation of Sweetwater River Stormwater Using Selenastrum capricornutum August 2006 In summary, 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, 2005. Because no additional toxicity was found in Sweetwater River samples in S. capricornutum tests conducting during storm events in January and February of 2006, it is likely that the causative agent was reduced in this sample during the second and third stormwater sampling events. Additional studies would be necessary to confirm whether an ion imbalance or TDS were the causative agent of toxicity to S. Capricornutum. Weston Solutions, Inc. 12
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APPENDIX I Toxicity Identification
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APPENDIX I Toxicity Identification Evaluation Reports for Chollas ...

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