Investigation of Copper Speciation in Pig Slurry by a Multitechnique Approach SAMUEL LEGROS, † PERRINE CHAURAND, ‡ J ´ ERÔME ROSE, ‡ ARMAND MASION, ‡ VAL ´ ERIE BRIOIS, § JEAN-HENRY FERRASSE, | HERV ´ E SAINT MACARY, ⊥ JEAN-YVES BOTTERO, ‡ AND EMMANUEL DOELSCH* , ⊥ CIRAD, UPR Recyclage et risque, F-97408 Saint-Denis, Re ´union, France, CEREGE UMR 6635 CNRS/Aix-Marseille University, Europo ˆle Me ´diterrane ´en de l’Arbois, BP 80, 13545 Aix-en-Provence Cedex 04, France, Synchrotron SOLEIL, L’Orme des Merisiers, Saint-Aubin - BP 48, Gif-sur-Yvette F-91192, MSNM-GP UMR 6181 CNRS Universite ´ Paul Ce ´zanne, Europo ˆle Me ´diterrane ´en de l’Arbois Pavillon Lae ¨nnec, BP 80, 13545 Aix en Provence Cedex 4, France, and CIRAD, UPR Recyclage et risque, F-34398 Montpellier, France Received February 18, 2009. Revised manuscript received July 19, 2010. Accepted August 2, 2010. It is now well-known that copper (Cu) can accumulate on the surface of soils upon which pig slurry has been applied. This is due to the high quantity of Cu in pig slurry resulting from its use as a growth promoter in animal feeds. The mobility and bioavailability of Cu from pig slurry spreading can be better predicted by determining the speciation of this element in addition to its total concentration. The aim of this study was to present a multitechnique approach to investigate Cu speciation in pig slurry. First, size fractionation and chemical characterization of each size fraction were performed to complement results obtained in raw samples. Micro X-ray fluorescence spectroscopy ( μXRF) highlighted the colocalization of Cu and sulfur (S). Finally, X-ray absorption near-edge structure spectroscopy (XANES) showed that Cu speciation in raw pig slurry and size fractions could be described by Cu 2 S and that its oxidation state is Cu(I). In addition, geochemical calculation demonstrated that chalcocite (Cu 2 S) was the major Cu species present under pig slurry lagoon physical -chemical conditions. This Cu speciation in pig slurry may be the main reason for the observed Cu accumulation at the soil surface. Introduction According to the Food and Agriculture Organization of the United Nations (FAO) (1), world pig production rose from around 830.6 million heads in 1997 to some 989.9 million heads in 2007, which represents a 19% increase, with a concomitant increase in the quantity of pig slurry produced. For instance, French pig breeding farms (14 million pigs produced) generate about 24 million t of pig slurry annually (2). Pig slurry spreading in fields is the most common way of managing this waste (3). As elements essential for plant life (i.e., nitrogen (N), phosphorus (P), and potassium (K)) are found in pig slurry, it can thus be used as a fertilizer in crop fields (4). Unfortunately, pig slurry also contains heavy metals (e.g., zinc and copper). It has been demonstrated that intensive pig slurry spreading can have impacts on field ecosystems. Heavy metals can accumulate at the soil surface (5), and high concentrations are phytotoxic. This accumula- tion, through the enhancement of heavy metal mobility, can therefore ultimately lead to surface water and/or groundwater contamination (6). Hence, it is essential to assess heavy metal speciation in pig slurry, i.e., determine the bearing phases, atomic coordination, and oxidation state of heavy metals, to evaluate their mobility. This is essential to determine the overall environmental impact of pig slurry spreading on agricultural soils. Among the heavy metals found in pig slurry, there is a high quantity of copper (Cu), i.e., 360-800 mg kg -1 dry matter (dm) (7, 8). Cu addition (in CuO and/or CuSO 4 form) is currently authorized, even at very high concentration, in pig feeds (20-220 mg kg -1 dm), because Cu is a growth promoter. Pigs assimilate very little Cu, so 80-90% Cu is excreted and found in pig slurry (7). Pig slurry is a complex matrix composed of liquid (urine + water) and solid (feces) phases in which organic (C, N) and inorganic (N, P, K) chemical elements are present (4). To date, only a few studies (based on conventional sequential extraction protocols) have focused on Cu speciation in pig slurry, and the results are contradictory. Robel and Ross (8) detected copper sulfide, whereas Miller et al. (9) identified Cu bound to organic matter, and L’Herroux et al. (10) observed a mixture of Cu bound to organic matter along with Cu bound to Fe-Mn oxides. One could expect that these different copper species have different fates in the environ- ment. For example, while copper sulfide (which is very insoluble in the soil environment (11) would accumulate in soil, copper bound to organic matter could be more bio- available (12). These inconsistencies among the different studies could be attributed to sequential extraction shortcomings, including incomplete dissolution of the target phase, and/or dissolution of the nontarget species (13). In these studies, sequential extraction fractions were therefore only operationally de- termined through the extraction procedure (14). Studying Cu speciation in pig slurry is thus a scientific challenge that can be addressed through an in situ multitechnique approach. The unique feature of the present study is that it involved a combination of techniques to investigate Cu speciation in pig slurry. This study was conducted in two steps: charac- terization analyses first focused on raw pig slurry, and then, due to the great complexity of the sample, size fractionation was performed in an attempt to separate individual Cu species. Laboratory chemical microanalyses were performed using micro X-ray fluorescence spectroscopy (μXRF) to locate Cu within pig slurry and identify spatial correlations between elements. The results were compared with those obtained through geochemical calculations of the pig slurry lagoon geochemical system. These calculations were performed to determine the major Cu species in pig slurry. Finally, more detailed insight into Cu speciation was obtained using synchrotron-based X-ray absorption spectroscopy (XAS). XAS is one of the best known structural in situ techniques for direct determination of the speciation of chemical elements in complex matrices. This technique includes X-ray absorp- * Corresponding author phone: +33 (0)442 971 775; fax: +33 442 971 559; e-mail: doelsch@cirad.fr; current address: CEREGE, Europole de l’Arbois, BP 80, 13545 Aix en Provence cedex 04, France. † CIRAD, UPR Recyclage et risque, Re ´union, France. ‡ CEREGE UMR 6635 CNRS/Aix-Marseille University. § Synchrotron SOLEIL. | MSNM-GP UMR 6181 CNRS Universite ´ Paul Ce ´zanne. ⊥ CIRAD, UPR Recyclage et risque, Montpellier, France. Environ. Sci. Technol. 2010, 44, 6926–6932 6926 9 ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 18, 2010 10.1021/es101651w  2010 American Chemical Society Published on Web 08/24/2010