Effect of organic amendments on the bioremediation of cyanazine and fluometuron in soil

Biostimulation may offer a viable approach to remediate soils containing high concentrations of herbicides. We determined the effects of cornmeal, ryegrass and poultry litter on the degradation of cyanazine and fluometuron (250 mu mol kg(-1)) in a Dundee silt loam. All three amendments enhanced cyanazine degradation with half lives of 18.2 d in ryegrass-, and 21 d in cornmeal- or poultry litter-amended soil, comcompared to 28.3 d in unamended soil. The amendments differentially affected patterns of metabolite accumulation. After 42 d, 45% of the C-14 was recovered as dechlorinated (hydroxy cyanazine) metabolites in ryegrass-amended soil compared to <16% in other treatments. Significantly less C-14 was extracted from cornmeal-amended soil than the other treatments, suggesting a relationship between cyanazine dissipation and incorporation into unextractable bound residues. Ryegrass had the greatest stimulatory effect on fluometuron degradation. Half lives For fluometuron were 41.0, 57.3, 27.7, and 66.4 d for cornmeal, poultry litter, ryegrass, and no additions. respectively. Desmethyl fluometuron was the major metabolite that accumulated in all treatments. Trifluoromethyl phenyl urea accumulated only in soils treated with poultry litter and ryegrass. All three amendments stimulated fluorescein diacetate hydrolysis, indicating enhanced microbial activity. Significant reduction of high concentrations of cyanazine or fluometuron may be achieved via biostimulation by selecting an appropriate amendment, i.e. ryegrass.