Influence of Dissolved Organic Matter from Waste Material on the Phytotoxicity and Environmental Fate of Triflusulfuron Methyl GIOVANNI GIGLIOTTI,* ,† ANDREA ONOFRI, † EURO PANNACCI, † DANIELA BUSINELLI, † AND MARCO TREVISAN ‡ Dipartimento di Scienze Agrarie e Ambientali, Universita ` degli Studi di Perugia, Borgo XX Giugno 72, Perugia, and Istituto di Chimica Agraria ed Ambientale, Universita ` Cattolica del Sacro Cuore, Piacenza, Italy Bioassays and chemical analyses were performed to study the effect of hydrophobic dissolved organic matter (HoDOM) extracted from a municipal waste compost (MWC) on the behavior of triflusulfuron methyl in soil and water. Bioassays with oilseed rape showed that HoDOM in culture solution lowered the effective dose 50 of triflusulfuron methyl by up to 4.8 times. Equilibrium dialysis experiments showed that in aqueous solution triflusulfuron methyl was adsorbed to HoDOM (K OC of 446.5 mL g -1 ). The half- life in water (pH 7.0) was increased from 52 to 76 days in the presence of HoDOM, but this cannot completely explain its phytotoxicity, as bioassays lasted for 21 days only. On the other hand, the addition of HoDOM to soils did not change the degradative behavior of triflusulfuron methyl. Fluorescein diacetate hydrolysis showed that HoDOM in soil did not significantly influence soil microbial activity, which may explain the above result on degradation in soil. Furthermore, in batch equilibrium experiments on soil, triflusulfuron methyl was only weakly adsorbed and the presence of HoDOM significantly modified the isotherm form. Results suggest that although the addition of exogenous HoDOM from MWC to soil did not influence the herbicide’s persistence, its enhanced mobility could be of environmental concern and may deserve further research. Introduction The application of treated organic waste to soil may be considered as an environmentally acceptable practice to increase soil fertility and as an economical waste disposal strategy. Recently, increased interest has been devoted to the investigation of how the application of composted or- ganic refuse may affect the behavior of xenobiotics in soil systems (1-6). In addition to humic-like substances, composted or stabilized organic waste contains water-soluble organic matter defined as dissolved organic matter (DOM) which can pass through a 0.45 μm filter (7). DOM consists of a complex mixture of polymeric materials and readily biode- gradable organic molecules such as neutral sugars, uronic acids, amino sugars, and amino acids (8). The influence of DOM originating from different organic waste materials on pesticide sorption-desorption in soil has given rise to considerable interest in recent years. However, very few studies are available in the literature on the influence of DOM on the degradation processes of pesticides. DOM may reduce pesticide sorption through stable DOM- pesticide interactions in solution (9-11) or by competing with pesticide molecules for sorption sites on the soil surface (12). However, it may also enhance pesticide sorption if the DOM sorbed on soil particles provides additional sites for pesticide sorption. The influence of DOM on pesticide degradation processes is not well-known. In soil, microbial processes are critical to several aspects of soil fertility and are influenced by a number of factors. Amendment may affect soil microbial activity and consequently the degradation rate of pesticides. Generally, amendments rich in stabilized organic matter provide readily biodegradable organic molecules that stimulate microbial activity and thus enhance pesticide degradation (1). In some cases soil amendment has led to a decrease in pesticide degradation possibly due to a preference of microorganisms to utilize fresh organic matter as carbon and energy sources rather than pesticides (2, 4, 6). Triflusulfuron methyl is a selective sulfonylurea herbicide used at low application rates (20-45 g of ai ha -1 ; ai ) active ingredient) for weed control in sugar beet. Like most sulfonylurea herbicides, triflusulfuron methyl exhibits low mammalian toxicity; however, because of the high herbicide efficacy of sulfonylureas, concerns have been expressed about its residual effect on soil and on the following crops (13-15). Although numerous studies have been carried out to evaluate the fate of triflusulfuron methyl in soil, they usually focused on determination of its retention and degradation as a function of soil characteristics (13-16). However, limited information is available on the effect of amendments on the fate of triflusulfuron methyl in soil, and no studies have dealt with the influence of exogenous DOM on the bioavailability and environmental fate of this herbicide. The main objective of this work was to assess the effect of hydrophobic DOM (HoDOM) extracted from a municipal waste compost (MWC) on (i) the phytotoxicity of triflusul- furon methyl to higher plants by in vivo bioassays, (ii) the degradative behavior and sorption of triflusulfuron methyl in aqueous solution, and (iii) the degradative behavior and overall sorption of triflusulfuron methyl in a microbially active soil. Materials and Methods Chemicals. Triflusulfuron methyl (methyl-2-[4-(dimethyl- amino)-6-(2,2,2-trifluoroethoxy)-1,3,5-triazin-2-ylcarbam- oxylsulfamoyl]-m-toluate; purity 99.0%) was supplied by Du Pont de Nemours and used in all experiments with the exception of bioassays, where Safari (triflusulfuron methyl, 500 g of ai kg -1 ; Du Pont de Nemours, Wilmington, DE) was used. The active ingredient was quoted to have a pKa of 4.3 in water (17). It must be noted that all the following experiments were performed under pH conditions above 4.3 and thus the most soluble anionic form of triflusulfuron methyl was always prevalent. All solvents were of HPLC grade (BDH Ltd., Poole, England) and were used without further purification. All other reagents were of analytical grade (Carlo Erba Reagenti, Milan, Italy). Soil and Compost. The soil used throughout this work was collected in April from the Ap horizon of a clay-loam soil located in central Italy (Tiber Valley, Umbria). After collection, the soil was air-dried approximately to 10% humidity content, * Corresponding author phone: ++39 0755856237; fax: ++39 0755856239; e-mail: gigliott@unipg.it. † Universita ` degli Studi di Perugia. ‡ Universita ` Cattolica del Sacro Cuore. Environ. Sci. Technol. 2005, 39, 7446-7451 7446 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 39, NO. 19, 2005 10.1021/es048234w CCC: $30.25  2005 American Chemical Society Published on Web 09/01/2005