The data base generated for benzalkonium chloride was considered adequate for commercial approvals, particularly after revision in late 1982. Field trials, although not part of the approval criteria, generally supported commercial use; decay observed in one test (post and rails) after 6 years' exposure would have resulted in some caution in setting retentions. No laboratory trial, nor field trial, could have predicted the problems experienced during commercial operations. Substandard treatment was interpreted as being responsible for most of the insect attack and decay problems. The remainder were caused by misuse in service, depletion (by chemical or, less likely, by biological mechanisms) during long-term wet storage, or attack by apparently highly AAC-tolerant Coniophora spp. A strict protocol for preservative approvals is now being drawn up which will reflect a higher degree of conservatism and much more reliance on long-term field trials, even of above-ground commodities.

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