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How do in vitro bioassay test results, such as Microtox EC 50 values, relate back to the volume of water sampled?

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How do in vitro bioassay test results, such as Microtox EC 50 values, relate back to the volume of water sampled?

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To answer this question, we use as an example Microtox EC50 values that are given in units of mg SPMD/mL of sample carrier solvent. If the Microtox EC50 value is 3.1 mg/mL, then it only took an equivalent of 3.1 mg of a standard 1-g triolein SPMD to elicit a toxic response. Depending on the sampling rates of the toxicant(s) detected in the bioassay, 1 mg of an SPMD would have extracted chemicals from about 0.5 to 10 mL of water per day. Assuming that the SPMD sampled toxicants from a site at about 5 mL day-1 mg-1, and the exposure was 7 days, then the 3.1 mg/mL EC50 value represents the response to the amount of toxicant contained in 108 mLs of sample water. Typically residue extracts are transfered into 1-mL of carrier solvent for assay, resulting in a 108 fold concentration factor. However, if only 0.1 mL of the carrier solvent is used for the assay, then this sample represents the chemical in only 10.8 mL of test water. Clearly, if only 1 mL of sample water was extracted or used dir

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