Valorization of Agro-Industrial Wastes as Organic Amendments to Reduce Herbicide Leaching into the Soil

High levels of pesticide use are associated with intensive crop production. Pesticides are becoming more and more prevalent in surface and groundwater, which is a major environmental concern. Various methods have been developed to improve the retention and/or degradation of pesticides in soils. These methods are mainly based on soil modification with organic wastes to control both diffuse and point pollution of soil and water. In addition, there has recently been increased interest in assessing the influence of organic waste additions on pesticide movement in soils with low organic matter content. Agriculture and related industries generate large amounts of waste each year. Because of their components, they have great potential for producing high-value products for environmental restoration. This study reports on the influence of four different agro-industrial wastes (orange peel, beer bagasse, grape pomace and gazpacho waste) used as organic amendments on the leaching of metobromuron and chlorbromuron (phenylurea herbicides) on a silty clay loam soil (Gypsic-Calcaric Regosol) with low organic matter content from a semiarid area (southeastern Spain). Adsorption, leaching and dissipation processes of these herbicides were evaluated on a laboratory scale in amended and unamended soils. In addition, the main leaching indices (GUS, LIX, LEACH, M LEACH, LIN, GLI, HI and ELI) commonly used to assess groundwater protection against pesticide pollution were evaluated. The sorption coefficients (KOC) increased in the amended soils. Metobromuron was found in leachates in all cases, although a marked reduction was observed in amended soils, while chlorbromuron was mainly retained in soils, especially in the top layer. The disappearance time (DT50) for metobromuron and chlorbromuron in soil ranged from 11-56 d and 18-95 d, respectively. According to the leaching index used, metobromuron had high-medium leachability, whereas chlorbromuron had low-medium leachability in amended and unamended soils.