Me 4 
eg gt fe ig ety 2 Samah 
into the organism or adsorption of the herbicide to cell walls. The fungus, 
Cephalosporium sp., showed little or no degradation of paraquat whereas an 
unidentified bacterium produced at least two degradation products (156). 
After seven days exposure to ultraviolet light, 85% of the radioactivity 
of c!4_labeled diquat and paraquat was lost. Electrophoresis indicated three 
degradation products from paraquat and one or more from diquat (287). After 
irradiation of paraquat in aqueous solution and in the presence of oxygen, 
the NMR spectrum of one of the products was consistent with a methyl 
quaternary pyridinium compound substituted at the 4-position. Elemental 
analyses, paper chromatography, IR and UV analyses showed that the compound 
was the N-methyl betaine of isonicotinic acid. Further irradiation of the 
latter gave rise, via carbonyl compounds, to methyl amine and 4-carboxy-1l- 
methylpyridinium chloride. It was also shown that this reaction occurred 
on sprayed plants and that maximum breakdown of paraquat occurred when 
the chemical remained largely on the surface of treated leaves in sunlight 
(220, 508, 1316, 1317, 1318, 1632). 
In the absence of oxygen, UV irradiation of parquat gave rise to a 
brown resin, presumably polymeric (1317). 
Diquat underwent photochemical degradation in solution or after appli- 
cation to plants. Using Cl4_ring- or -ethylene bridge-labeled diquat, one 
major metabolite and several minor compounds were observed by paper chroma- 
tography. That the major metabolite was radioactive in both instances 
indicated at least one intact ring. Chemical reaction indicated the presence 
of nitrogen; an elemental analysis, together with infra-red, ultraviolet, 
nuclear magnetic resonance, and mass spectra showed the compound to be 
tetrahydro-oxo-pyrido-pyrazine. Structure was confirmed by synthesis and 
comparison of infra-red spectra and chromatographic properties (1321). 
Studies indicated that diquat and paraquat were strongly adsorbed, 
in similar amounts, to mineral soils kaolinite and montmorillonite; 
however, only montmorillonite appeared to hold herbicides in an unavailable 
form to wheat at extremely high rates. When added to plastic pools, mont- 
morillonite drastically reduced paraquat solution concentration within 24 
hours (287, 811, 1429). Addition of montomorillonite clay to solutions of 
diquat, in an amount calculated to adsorb one half of the cl4_diquat, re- 
duced clo. evolution to approximately one half. When sufficient mont~ 
morillonite was added to adsorb all of the diquat, no clo, was detected 
(1598). 
179 
