1 December 1995

Justification for safer claim

IT IS no illusion, modern herbicides are generally much safer than older materials, according to Dr Ken Davies of the SAC.

He countered the argument that todays much lower-dose but more potent products are no more environmentally friendly than their predecessors. He did so by calculating "toxicity ratios" for all new compounds reported at Brighton since 1953, combined with other information back to 42.

By combining application rates and the so-called rat oral LD50 measurement for each compound, he showed the toxicity ratio of herbicides introduced from 1942-69 was 1670. By 1970-79 it was down to 689. With the introduction of sulfonylureas in the 1980s it slid to 173, and todays figure is just 58.

Dr Davies conceded his analysis ignored the fact that spray drift from modern chemicals might be more environmentally damaging than that from older, less active ones. "But this has to be balanced against the apparently lower hazards from normal commercial use."