may vary and thus be less problematic in some plant parts, but the assumption should be that all parts of a plant containing toxins pose a risk unless there is credible evidence suggesting that dangerous levels of toxins are not present in the part marketed as a dietary supplement. In this case, selection of plant material at a specific growth stage to avoid incorporation of potentially toxic plant parts is desirable.

In addition to concentration of toxic compounds in particular plant parts, levels of toxins in plants may also be influenced by growth stage, time of collection, environmental stress, herbivory, and a multitude of other factors (Fong, 2002). Blending of plant material from a number of locations will tend to dilute toxin levels that are higher in some plants if other plants are lower in toxin levels. However, in the absence of comprehensive studies, it is not possible to delineate precisely the overall influence of such conditions on constituent levels, although their role must be recognized in evaluating the safety of dietary supplements. When sporadic adverse incidents occur in association with a botanical supplement ingredient with no previous indication of risk, it may well be possible that environmental changes have resulted in an increase in levels of toxic constituents. If a plant’s content of a hazardous phytochemical varies significantly with environ-