"Non-concept" of "no-threshold": chemicals in the environment.

Present confusion that equates the presence of a biological effect with a deleterious implication ignores several concepts. To believe that a single molecule's presence in a cell implies a definite potential for deleterious effect disregards stochastic considerations. To believe that such molecules cause an undesirable effect disregards the presence of multiplicity of interferring substances. Such thinking also does not take into account the fact that the dose of a foreign atom may be related to the probability of its interacting with an available active site, or that similar probability governs the answers to the question of whether interactions will occur at discrete topographical loci upon a structural or functional molecule (or on a possible precursor). While the construction of stochastically sound model is remote, the reasonableness of the hierachy of cellular element concentrations as these relate to metabolic function suggests that a threshold for biological activity exists within a cell at 10(4) atoms. The cellular organism operates within a quantitative rate limit that transcends any statements having only qualitative bases. Thus concepts concerning encroachments on response capabilities over a lifespan are inadequate descriptors of biological activity in the absence of quantitative qualifiers.