Document Type

Editorial and Commentary

Publication Date



Measurement is very important in science. Early lessons in the science classroom involve teaching students to measure lengths, volumes, weights, specific gravities and anything else within the mental and economic compass of the teacher. At the same time, the question of significance is drummed into the students' heads. Thus, if one has a meter-rule which is subdivided into centimeters (but not millimeters), one is taught that the measurement of its length to one decimal point (for example, 10.3 em) is acceptable, but that the addition of any more figures (for example, 10.325 em) is mere braggadocio. The eye can only make a rough guess at the subdivision between the centimeter divisions, and adding more figures after the decimal point does not improve the accuracy of the estimate.

However, adding more numbers, without increasing the accuracy of the measurement, is precisely what is being attempted when the LD50 is used as a measure of the acute toxicity of chemicals. (The LD50 is the amount of a substance which, if administered in a single dose to a target group of animals, will kill 50 percent of them). Normally, 50 to 200 animals are used to estimate the LD50 and provide its standard deviation from the mean. For some reason, regulators and some toxicologists appear to believe that an LD50 with its fiducial limits is more accurate and more relevant than a rough estimate of the acute toxicity, an estimate that can be obtained by using as few as six animals (rather than the 50-200 animals needed for an LD50).

The point at issue, therefore, is simply this: Animal welfare groups and many toxicologists want to see the LD50 (performed on 50 or more animals) replaced within the next year by a rough estimate of acute toxicity. The regulatory authorities have so far resisted making the necessary changes.