A environmental sample can be called representative, when it is collected and handled in a manner which preserves its original physical form and chemical composition. Accordingly, in the statistical sense, representative samples are an unbiased subset of the population measured.
To retain valid representativeness after collection, samples must be handled and preserved using methods adequate for preventing changes in the concentration of materials to be analyzed, by loss or by introduction of outside contamination. Failure to take account of each of the factors which can potentially reduce the representativeness of samples for the target environment is likely to result in analyzing samples which are not truly representative.
Analysis of samples which are not representative of the environment being assessed is inevitably a wasted effort and may lead to wrong and even expensive conclusions. The data from analyses may be precise and accurate in relation to contaminants of interest in the samples, but if the samples are not intrinsically representative of the environment, then the data has little relevance to the location or sites in question.
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