Principles

Toxicologists are guided by principles and three of those are:

1. you only find what you are looking for...;

3. only living material can measure toxicity

Principle 1, you only find what you are looking for and you only find it if it is in concentrations high enough to be detected by the method being used to analyze for it, may best be explained by example. Chemical-specific analyses have been and still are used to monitor water quality under some regulatory programs. In some cities in some parts of the United States the sign shown in Figure 2 can be seen as one enters a city. The city displaying the Superior Public Water Supply System sign was given the right to display the sign because when the water they are providing to the public was tested it was found to meet the standards for the parameters it was required to test. While the parameters the water provider was required to test for are considered important for public water supplies, they certainly do not include all the possible contaminants of the water supply. For example, historically the gasoline additive MTBE was not tested for in water supplies but has subsequently been found to be widely distributed. The same can be said for the herbicide atrazine among other chemicals. You only find what you are looking for!

The axiom given in principle 2 is attributed to the physician Paracelsus (Figure 3) who stated, ''All substances are poisons, there is none which is not a poison.

Single species x

Microcosm

Figure 1 Aquatic toxicity tests used to establish biologically safe concentrations of potential toxicants.

Watersheds

Figure 1 Aquatic toxicity tests used to establish biologically safe concentrations of potential toxicants.

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