FACILITATED TRANSPORT OF NAPROPAMIDE BY DISSOLVED ORGANIC-MATTER IN SEWAGE SLUDGE-AMENDED SOIL

The application of sewage sludge to agricultural soils is practiced to minimize landfill disposal. Organic matter amendments to soil are gen erally thought to improve soil quality, but pesticide application to t hese soils may lead to groundwater contamination problems. The complex ation of pesticides with a water-soluble carrier such as dissolved org anic matter (DOM) may facilitate chemical movement through soil. Sewag e sludge amendments may lead to greater downward movement of organic c hemicals if associated with DOM, Napropamide [2-alpha-napthoxy)-N,N-di ethylpropionamide] was applied to a silt loam soil,vith (SS) and witho ut (NoSS) sewage sludge application. Laboratory batch equilibrium and soil column studies were performed to determine the potential for herb icide complexation with DOM, Over 98% of the herbicide in soil columns followed typical adsorption and transport behavior as the center of m ass of the lower organic matter soil (NoSS) moved twice the depth as t hat of SS, However, napropamide was detected in the initial leachate e luted from repacked soil columns with steps taken to prevent preferent ial now, Napropamide concentrations in the initial leachate of SS were twice that from NoSS with <1.5% of the total applied chemical mass el uting from the bottom of each column. A strong positive relationship w as found between napropamide concentration and DOM content in soil lea chates, Equilibrium dialysis methods were used to determine that napro pamide moving through the soil columns was complexed with DOM, The res ults show that DOM can facilitate herbicide movement through soil and that sewage sludge-derived DOM mag lead to enhanced chemical transport in sludge-amended soils.