Classification of dangerous substances and pesticides in the European economic community directives: a proposed revision of criteria for inhalation toxicity.

Criteria for the classification of dangerous substances with respect to their inhalation toxicity were originally proposed by the European Economic Community (EEC) on the basis of a 1-hr LC50, as were the similar United Nations (UN) "transport" criteria. Both sets of criteria have since been amended for a 4-hr LC50, but whereas the UN criteria limits have been decreased to compensate for the increased exposure time, the EEC limits have not. This has introduced an anomaly into the EEC classification scheme whereby substances are classified more severely than they were previously. The EEC scheme is now out of line with the UN criteria and other international guidelines and gives a much more stringent toxicity classification for individual substances by inhalation than by the oral route, as well as causing an unjustifiable duplication of animal tests. This anomaly has led to a proposal by the Federal Republic of Germany for revised criteria. This paper examines the scientific basis for the relationship between inhalation exposure duration and toxicity, and for a comparison of the LD50 and LC50 classifications for individual substances. It is concluded that the proposed German revised classification scheme is more in line with the UN transport criteria and international guidelines and provides a rational basis for a classification scheme for inhalation toxicity. The classification criteria therefore should be harmonized by a revision of the EEC classification limits for inhalation toxicity.