The importance of natural variabilities in the total analytical scheme.

Concentrations of synthetic organics and trace metals in tissues or sediment may vary by hundreds of percents even when replicate samples are collected from the same biological population, i.e. school of fish, or the same location on the bottom of the stream. Without a knowledge of these variations, decisions based on analytical data interpretations are difficult and often in error. Some reasons for these variations will be discussed, with examples presented from field data which include: trace metals and pesticides in bottom sediments, pesticides in suspended sediments and plankton, pesticides in fish populations and trace metals in mollusks.