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Possible Appearance of Degradation Products of Paraquat in Crops

Abstract

Chemical analysis has established that residue levels of paraquat in crops harvested after use of the chemical are at such a low level as to constitute no hazard to the consuming public. (Paraquat dichloride is 1,1'-dimethyl-4,4'-bipyridylium dichloride). There remained the possibility that toxic metabolites or other conversion products of paraquat might appear in crops. This paper is concerned with attempts to evaluate this possibility, and demonstrates that no hazard arises from the formation of degradation products. It has been shown, using paraquat labelled with {sup 14}C in the methyl groups and in the pyridine nuclei, that the chemical is not metabolically degraded in plants. However, photochemical degradation of paraquat can occur on the surface of leaves in sunlight. In vitro experiments involving ultra-violet irradiation of aqueous solutions of {sup 14}C-paraquat have shown that 4-carboxy-1-methylpyridinium chloride and methylamine hydrochloride are the only products formed in significant amount in the photochemical degradation. Paper chromatography and isotope dilution have shown that these products are formed on leaves of plants treated with {sup 14}C-paraquat (mostly after the plants are dead). Whole plant radioautography has established that 4-carboxy-1-{sup 14}C methylpyridinium chloride is not translocated at all from the dead leaves on which it is formed  More>>
Authors:
Slade, P. [1] 
  1. Imperial Chemical Industries LTD., Jealott's Hill Research Station, Bracknell, Berks. (United Kingdom)
Publication Date:
May 15, 1966
Product Type:
Conference
Report Number:
IAEA-SM-69/9
Resource Relation:
Conference: Symposium on the Use of Isotopes in Weed Research, Vienna (Austria), 25-29 Oct 1965; Other Information: 7 refs., 2 tabs.; Related Information: In: Isotopes in Weed Research. Proceedings of the Symposium on the Use of Isotopes in Weed Research| 251 p.
Subject:
60 APPLIED LIFE SCIENCES; AQUEOUS SOLUTIONS; CARBON 14; CHEMICAL ANALYSIS; CHROMATOGRAPHY; CROPS; HARVESTING; HAZARDS; IN VITRO; IRRADIATION; LEAVES; METABOLITES; METHYLAMINE; PYRIDINE; RADIOACTIVITY; RESIDUES; SOLANUM TUBEROSUM; SURFACES; TOXICITY; TUBERS
OSTI ID:
22118935
Research Organizations:
International Atomic Energy Agency, Vienna (Austria); Food and Agriculture Organization of the United Nations, Rome (Italy)
Country of Origin:
IAEA
Language:
English
Other Identifying Numbers:
Other: ISSN 0074-1884; TRN: XA13M2191075571
Submitting Site:
INIS
Size:
page(s) 113-120
Announcement Date:
Aug 08, 2013

Citation Formats

Slade, P. Possible Appearance of Degradation Products of Paraquat in Crops. IAEA: N. p., 1966. Web.
Slade, P. Possible Appearance of Degradation Products of Paraquat in Crops. IAEA.
Slade, P. 1966. "Possible Appearance of Degradation Products of Paraquat in Crops." IAEA.
@misc{etde_22118935,
title = {Possible Appearance of Degradation Products of Paraquat in Crops}
author = {Slade, P.}
abstractNote = {Chemical analysis has established that residue levels of paraquat in crops harvested after use of the chemical are at such a low level as to constitute no hazard to the consuming public. (Paraquat dichloride is 1,1'-dimethyl-4,4'-bipyridylium dichloride). There remained the possibility that toxic metabolites or other conversion products of paraquat might appear in crops. This paper is concerned with attempts to evaluate this possibility, and demonstrates that no hazard arises from the formation of degradation products. It has been shown, using paraquat labelled with {sup 14}C in the methyl groups and in the pyridine nuclei, that the chemical is not metabolically degraded in plants. However, photochemical degradation of paraquat can occur on the surface of leaves in sunlight. In vitro experiments involving ultra-violet irradiation of aqueous solutions of {sup 14}C-paraquat have shown that 4-carboxy-1-methylpyridinium chloride and methylamine hydrochloride are the only products formed in significant amount in the photochemical degradation. Paper chromatography and isotope dilution have shown that these products are formed on leaves of plants treated with {sup 14}C-paraquat (mostly after the plants are dead). Whole plant radioautography has established that 4-carboxy-1-{sup 14}C methylpyridinium chloride is not translocated at all from the dead leaves on which it is formed and certainly this compound will not appear in harvested crops. This has been confirmed in an experiment in which {sup 14}C-paraquat was used to desiccate the tops of potato plants before harvesting the tubers. All the radioactivity subsequently found in the tubers could be accounted for as paraquat (level 0.08 ppm). There was no evidence for the presence of significant amounts of other radioactive compounds in the tubers, even though chromatography of extracts of the desiccated plants showed that photochemical degradation products were formed on the leaves: these were not translocated into the tubers. (author)}
place = {IAEA}
year = {1966}
month = {May}
}