Effect of sludge-amendment or nutrient addition on the biodegradation of the herbicide isoproturon in soil

Adding sludge to agricultural soil results in added organic matter, nutrien ts and metallic and/or organic pollutants. These components may modify the behaviour of pesticides in the soil. We monitored possible changes in the d egradation of the herbicide isoproturon (production of CO2 and degradation products) in soil amended with sludge, heavy metals or nitrogen and phospho rus. The treated and control soils were incubated under controlled conditio ns for 60 days. The nitrogen and phosphorus had the greatest effect on isop roturon degradation, independent of the presence of pollutants. Mineralisat ion of the herbicide to CO2 was slow and seemed to be linked to a fast degr adation and to the accumulation of a complex degradation product that was n either catabolized nor adsorbed, 4,4 ' -diisopropylazobenzene. This degrada tion pathway also produced smaller amounts of non-extractable residues. Sew age sludge had no significant effect on isoproturon degradation, despite a large increase of organic matter mineralisation (factor 2). (C) 2001 Elsevi er Science Ltd. All rights reserved.