Name /entc/24_505 01/26/2005 02:55PM Plate # 0-Composite pg 37 # 1 Environmental Toxicology and Chemistry, Vol. 24, No. 5, pp. 000–000, 2005  2005 SETAC Printed in the USA 0730-7268/05 $12.00 + .00 EFFECT OF UREA ON DEGRADATION OF TERBUTHYLAZINE IN SOIL ANNA BARRA CARACCIOLO,*² G IUSEPPE GIULIANO,² P AOLA GRENNI,² C ARLO CREMISINI,‡ ROBERTO CICCOLI,‡ and CARLA UBALDI‡ ²Istituto di Ricerca sulle Acque (IRSA), Via Reno 1, 00198 Roma, Italy ‡ENEA C.R. Casaccia, Via Anguillarese 301, 00060 Roma, Italy ( Received 19 May 2004; Accepted 20 October 2004) Abstract—Pesticide and nitrate contamination of soil and groundwater from agriculture is an environmental and public health concern worldwide. The herbicide terbuthylazine (CBET) has replaced atrazine in Italy and in many other countries because the use of the latter has been banned because of its adverse environmental impacts. Unlike atrazine, knowledge about the fate of CBET in soil is still not extensive, especially regarding its transformation products, but recent monitoring data show its occurrence and that of its main metabolite, desethyl-terbuthylazine (CBAT), in groundwater above the limit of 0.1g/L established by European Union Directive and Italian legislation. The objective of this work was to investigate if the presence of the fertilizer urea affects CBET degradation in the soil. Laboratory CBET degradation experiments in the presence/absence of urea were performed with microbiologically active soil and sterilized soil. Terbuthylazine degradation rates under the different experimental conditions were assessed, and the formation, degradation, and transformation of the metabolite CBAT were also studied. Terbuthylazinedegradation was affected by the presence of urea, in terms both of a higher disappearance time of 50% of the initial concentration and of a lower amount of CBAT formed. These findings have practical implications for the real-life assessment of the environmental fate of triazine herbicides in agricultural areas since these herbicides are frequently applied to soils receiving ureic fertilizers. Keywords—Terbuthylazine Degradation Urea Soil INTRODUCTION Soil and groundwater pollution from pesticides and nitrates is the subject of public and regulatory concern worldwide [1,2] because of the impact on human health and ecological systems [3,4]. The s-triazine herbicides (characterized by a symmetrical hexameric ring consisting of alternating carbon and nitrogen atoms) and nitrogen fertilizers frequently occur as groundwater cocontaminants. Triazines are among the herbicides most used in the world for selective weed control in several crops. Ter- buthylazine (CBET) has replaced atrazine in Italy and in many other countries where its use has been banned. However, ground- water monitoring data show that CBET and desethyl-terbuthy- lazine (CBAT) often occur at levels above the 0.1-g/L limit established in the Directive for Drinking Water [5,6], and since CBAT has a very similar chemical structure to desethylatrazine, which is toxic like atrazine, [7,8] it may be considered a haz- ardous contaminant for groundwater. Unlike atrazine, knowledge about the fate and the behavior of CBET is still not extensive, especially regarding its trans- formation products. Terbuthylazine is recognized to be more stable and less mobile in soil than atrazine, and since it is strongly adsorbed by soil, less possibility of a microbial attack exists [9]. Studies with 14 C-labeled CBET report a low vola- tilization and mineralization of CBET in soil [9,10]. In soil, one of the primary mechanisms of its transformation has been found to be a biotic oxidative N-deethylation with the for- mation of CBAT [10–12]. Desethylterbuthylazine dechlori- nation may then occur with the formation of 2-hydroxydes- thylterbuthylazine (OBAT) [6,10,13]. Nonbiologically and biologically mediated dehalogenation processes may convert intact CBET as well as its deethylated metabolite to corre- * To whom correspondence may be addressed (caraccio@irsa.rm.cnr.it). sponding hydroxylated forms [14]. The latter compounds have lower solubility and preferentially accumulate in the surface 10 cm of the soil and therefore may be considered less mobile. On the contrary, CBAT can be leached more easily than its parent compound [15,16], as it is more persistent and more mobile in soil [6,9,17]. The mineralization of s-triazine herbicides, including CBET, has been identified in laboratory experiments using bacterial communities enriched with atrazine. Dechlorination occurred before degradation of the s-triazine ring; the for- mation of cyanuric acid as an intermediate and then its trans- formation to biuret was found to be the common step before mineralization, although the sequence of pathway steps varied among degraders. Since CBET was always degraded at slower rates, the efficiency of degradation was ascribed to the size of the alkyl chain tert-butyl [18–20]. Because of their chemical structure, triazine herbicides and their N-heterocyclic derivates may be metabolized in complex pathways and used as sources of carbon and nitrogen, de- pending on the availability of the latter molecules in the en- vironment [18,21]. Consequently, it is reasonable to ask if CBET biodegradation might be affected in the presence of urea since this herbicide is frequently applied to soils receiving nitrogenous fertilizers. The knowledge of such processes is essential for the development of optimal strategies for pre- venting or remedying the adverse effects of these contami- nants. The purpose of this work was to assess, in controlled lab- oratory experiments, if the degradation of CBET in soil may be influenced by the presence of urea, one of the potential last by-products of the herbicide before its mineralization. Our preliminary results on the CBET degradation showed that a lower amount of CBAT was formed in the presence of urea. ?1