Chemist: The molecules of a certain weed-killer are always present in two forms, one the mirror image of the other  One form of the molecule kills weeds, while the other has no effect on them  As a result, the effectiveness of the weed-killer in a given situation is heavily influenced by which of the two forms is more concentrated in the soil, which in turn varies widely because local soil conditions will usually favor the breakdown of one form or the other
Thus, much of the data on the effects of this weed-killer are probably misleading
Almost all of the data on the effects of the weed-killer are drawn from laboratory studies in which both forms of the weed-killer's molecules are equally concentrated in the soil and equally likely to break down in that soil.