Degradation of ioxynil and bromoxynil as measured by a modified spectrophotometric method.

A modified spectrophotometric method was developed to estimate ioxynil and bromoxynil residues. The method when compared with a 14C-tracer method was less sensitive but allowed rapid and accurate estimation of the herbicides. A clay loam soil with high organic matter content, which degraded ioxynil completely to CO2, also degraded bromoxynil completely. Bromoxynil degradation proceeded at a faster rate than that of ioxynil. The half-life of degradation was estimated to be 7 days for bromoxynil and 9-10 days for ioxynil. However, soil microorganisms which degraded ioxynil either completely to CO2 or partially did not seem to completely degrade bromoxynil. Degradation products from bromoxynil were detected on thin-layer chromatograms of extracts from pure cultures containing an exogenous carbon source. Complete degradation of bromoxynil and ioxynil in soil could be due to the action of different microorganisms.