Biodegradation of pyridine derivatives in soil suspensions

Relationships between structure and biodegradability were evaluated for 28 pyridine derivatives in nutrient solutions inoculated with soil and incubated at 24°C. Compounds studied included pyridine; mono- and disubstituted pyridinecarboxylic acids; and hydroxy-, chloro-, amino-and methylpyridines. Disappearance of the pyridine added was measured by UV spectrophotometry, and the ammonium released by cleavage of the pyridine ring was measured by colorimetry. Volatilization was estimated by analysis of the pyridines collected on the polyurethane foam stoppers used to plug the incubation vessels; sorption by soil was estimated from the initial decrease in solution concentration upon addition of soil. Pyridinecarboxylic acids, monohydroxypyridines and the unsubstituted pyridine ring did not volatilize and were degraded within 7 to 24 d. Methylpyridines were intermediate in degradability, disappearing in from less than 7 to more than 30 d. None of the aminopyridines was completely degraded in 30 d. Of the chloropyridines tested, only 4-chloropyridine was completely degraded in 24 d. The susceptibility of 4-chloropyridine to degradation may be attributed to the ease with which a chlorine group is removed from position 4 on the pyridine ring. No degradation was detected in 30 d for any of the other chloropyridines. Chloro-and methylpyridines volatilized extensively.