Degradation of Pyridine Derivatives in Soil

The fate of pyridine and 25 substituted pyridines in soil (Aeric Ochraqualfs) was examined by measuring the quantity remaining and the inorganic N released as a result of degradation of the pyridine ring for a period of 64 d. Each compound was added to soil at 2 mmol kg −1 . Compounds studied included pyridine substituted with one or two hydroxyl, carboxyl, chlorine, amine, or methyl groups. During the 64‐d incubation period, extractability of pyridine derivatives with 2 M KCl + 0.01 M HC1 decreased from an average of 88 ± 8.8% to essentially 0 for all compounds except aminopyridines. From 36 to 94% of added aminopyridines was recovered after 64 d of incubation. Degradation of the majority of pyridine derivatives was confirmed by accumulation of N in amounts equivalent to 61 to 80% of the decrease in extractable pyridines at 64 d of incubation. Degradation of unsubstituted pyridine occurred within 8 d, whereas most hydroxypyridines were degraded within 32 to 64 d. Pyridinecarboxylic acids appear to be the most labile group of pyridine derivatives and were dissipated from soil in 4 to 16 d. Most chloropyridines persisted in soil and became weakly associated with some insoluble soil component. However, 4‐chloropyridine degraded in 16 d. Aminopyridines resisted degradation in soil while methylpyridines were degraded in 8 to 32 d. Degradability of the compounds generally followed the order pyridinecarboxylic acids > pyridine = mono‐hydroxypyridines > methylpyridines > aminopyridines and chloropyridines. This trend was consistent with previous results on biodegradability of the compounds in soil suspension cultures.