Technical problems in determining safe re-entry intervals.

Organophosphate pesticide residues have been responsible for periodic outbreaks of acute intoxication among California fieldworkers for over 30 years. In 1971, California established 're-entry intervals' to protect workers against overexposure to these residues. These intervals are stipulated times which must elapse between pesticide application and entry into the field for work involving substantial foliar or soil contact. The re-entry strategy depends upon a relatively predictable relation between time post-application and the level of the pesticide residue. It now appears that there are thiophosphates for which the residue hazard is not related to time in a stable way. This circumstance and the continued occurrence of poisoning incidents have focused attention on the quantitative aspects of the relationships between pesticide residue and toxicological response in humans. In the last decade, considerable progress has been made in elucidating these relationships and it now appears to be possible to outline the data requirements for a comprehensive regulatory solution to this longstanding occupational health problem.