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<br />quality test known as acute toxicity. Acute toxicity testing uses Ceriodaphnia Dubia, a <br />small crustacean found in vernal pools and freshwater ponds throughout the world, to test <br />if a water sample is toxic to aquatic organisms (Katznelson 1997; Riveles 1997). <br />According to Katznelson (1997, 2): <br /> <br />Ceriodaphnia are very sensitive to pesticides, heavy metals and other toxic chemicals <br />used by humans and discharged into surface waters. These properties make <br />Ceriodaphnia a good organism for testing the toxicity of freshwater. Natural waters <br />can become poisonous to the organisms that live in those waters when pollutants <br />enter the water in too high concentration. Toxicity refers to the effect on aquatic <br />organisms, rather than the concentration of pollutants. <br /> <br />In a typical toxicity test, Ceriodaphnia are placed in "test chambers" full of sample <br />water and are periodically observed for a given length of time, for example 48 hours, <br />and their survival (or death) rate is recorded. In addition, some Ceriodaphnia are <br />placed in test chambers full of clean, healthy water to provide an experimental <br />"contro1." If the organisms in the control live and organisms in the sample die, we <br />know that they were initially healthy and something which is present in the sample, <br />and not in the control, caused their mortality. The water sample is considered "toxic." <br /> <br />If water is toxic to aquatic organisms, it is likely that the same water is toxic to <br />terrestrial organisms, including humans. Acute toxicity testing is one strategy utilized by <br />the U.S. Environmental Protection Agency to indicate the existence of pollutants that <br />may cause toxicity to humans and aquatic ecosystems. It is a strategy that may be <br />implemented at a low cost to identify toxicity and hence locate sources of pollutants in <br />Tijuana's urban rivers and groundwater basins. <br /> <br />Besides acute toxicity testing, the Chollas Creek program requires on-site field <br />observations and testing. Figure 4 is a field data sheet delineating field water quality <br />testing protocol, geographical data parameters, visual observation parameters, and <br />chemical parameters (i.e., conductivity, nitrates, color, etc.). The chemical and visual <br />observation parameters are designed for clear and simple data collecting. The Chollas <br />Creek program is an example of a low-cost water quality testing program that can be used <br />to identify sources of pollutants and even, to a limited extent, identify certain pollutants <br />such as nitrates. If funding opportunities expand, the following water quality parameters <br />should be sampled and mapped during dry and wet weather conditions: <br /> <br />· microbial organisms and pathogens <br />. nitrates <br />. heavy metals <br />. total organic carbons <br />. chlorine <br />. hardness <br />. detergents <br />(Campo EPA 1994; City of San Diego 1996). <br /> <br />. pesticides <br />. pH <br />. grease and oil <br />· biological oxygen demand <br />. phosphates <br />· dissolved solids <br /> <br />26 <br /> <br />