What causes whole effluent toxicity test variability?
Clearly there are many factors that can affect inter-laboratory and intra-test variability. A few of the greatest concern include the nature of the sample and sampling, the physical and chemical testing conditions, the test protocol, technician expertise, and test organism health, age, and handling. Grab samples, particularly low-volume ones, are more likely to catch spikes or ebbs in effluent toxicity. Sample toxicity may be reduced with increased holding time and sample disturbance. Therefore, if samples are handled and shipped differently, response variations are likely to occur. Highly toxic samples or samples with sharp toxicity response curves can produce data that is less suitable for statistical analysis. Samples may also have toxicants that are strongly affected by exposure time (volatile samples) and test chamber conditions. Samples are sometimes manipulated prior to testing, such as when the sample’s salinity or pH is adjusted to meet testing parameters. Differences in adjus
