Contributions to ecological chemistry CXL: Isolation and identification of a metabolite of pentachlorophenol- 14C in rice plants

Pentachlorophenol (PCP) is a fungicide used in wood protection and a herbicide used against weeds in various crops^2–4, especially in rice. Up to 1971, it contributed more than 50% to the herbicides used in Japan. However, because it has a high fish- and shellfish-toxicity, its application to paddy fields has been restricted since 1971. Today, PCP is still in use to a fair extent in paddy fields and upland crops either as a single herbicide or in combination with others⁴. Numerous publications are concerned with its abiotic decomposition^5–8 including photomineralization⁹ and microbial degradation^4,10–16 leading to the formation of carbon dioxide^17–18. Furthermore, studies with bacteria using PCP as a sole carbon source have been done^13,19. At least ten metabolites have been isolated from soil and identified^{4,10–11,14, 20–21}, the main metabolic steps being methylation of the hydroxyl group, dechlorination resulting in tetrachloro- and trichlorophenols, and hydroxylation to chlorinated hydroquinones or catechols.According to our knowledge, no reports are available on identification of metabolites in the protected organisms, the higher plants. In one study it has been suggested that cotton plants accumulate and metabolize PCP, but no metabolites were reported²². This first paper on our respective experiments deals with the isolation and identification of a metabolite found in rice plants.