Assessment of herbicide sorption by biochars and organic matter associated with soil and sediment Ke Sun a, b , Bo Gao c , Kyoung S. Ro d , Jeff M. Novak d , Ziying Wang a , Stephen Herbert b , Baoshan Xing b, * a State Key Laboratory of Water Simulation, School of Environment, Beijing Normal University, Beijing 100875, China b Department of Plant, Soil & Insect Sciences, University of Massachusetts, Amherst, MA 01003, USA c State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing 100038, China d USDA-ARS Coastal Plains Soil, Water & Plant Research Center, 2611 W. Lucas Street, Florence, SC 29501, USA article info Article history: Received 26 September 2011 Received in revised form 1 December 2011 Accepted 3 December 2011 Keywords: Sorption Organic matter Herbicides Biochar Fluridone Norflurazon abstract Sorption of two herbicides, fluridone (FLUN) and norflurazon (NORO), by two types of biochars, whole sediment, and various soil/sediment organic matter (OM) fractions including nonhydrolyzable carbon (NHC), black carbon (BC) and humic acid (HA) was examined. The single-point organic carbon (OC)-normalized distribution coefficients (K OC ) of FLUN and NORO at low solution concentration (C e ¼ 0.01S W , solubility) for HA, NHC, and BC were about 3, 14, and 24 times and 3, 16, and 36 times larger than their bulk sediments, respectively, indicating the importance of different OM fractions in herbicide sorption. This study revealed that aliphatic moieties of the hydrothermal biochars and aromatic moieties of NHC samples, respectively, were possibly responsible for herbicide sorption. The hydrothermal biochar and condensed OM (i.e., NHC and BC) showed relatively high or similar herbicide sorption efficiency compared to the thermal biochar, suggesting that the hydrothermal biochar may serve as an amendment for minimizing off-site herbicide movement. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction Extensive and worldwide herbicide usage has increased dramatically during the last two decades due to changes in farming practices and increasingly intensive agriculture. It has been esti- mated that 2.5 million tons of pesticides are applied worldwide each year and the application rates are increasing with the passage of time (Tariq et al., 2007). The pesticide industry is very big because pesticides are an integral component of intensive world agriculture. World-wide pesticide sales in 2004 were a record $32.7 billion. Herbicides accounted for 45.4% of the pesticide market (Pacanoski, 2007). The use of herbicides has created considerable controversy worldwide. It has been reported that herbicides are lost from agricultural fields and aquatic sediments to surface- and groundwater by run-off and leaching (Konstantinou et al., 2006). Herbicide run-off and leaching are recognized as serious environ- mental concerns and a primary source of pollution for surface- and groundwater (Carter, 2000). To alleviate the environmental risk of leached herbicides, innovative strategies are needed to reduce the amount lost from application sites and transported to surface waters. Sorption process can retard or even prevent the movement of herbicide and affect its availability for plant or microbial uptake; it is one of the main processes reducing the mobility of herbicides in soils (Morillo et al., 2002). Moreover organic matter (OM) asso- ciated with soil and sediment has been known to play an important role in pesticide sorption. It is well known that the OM has highly heterogeneous structures (Chefetz and Xing, 2009; Cornelissen et al., 2005; Xing and Pignatello, 1997). To ascertain the chemical structures of OM, it is commonly separated from solid phases into various extracted fractions and black carbon (BC) (Gelinas et al., 2001; Kang and Xing, 2005; Ran et al., 2007). The knowledge of herbicide sorption capacity of these OM fractions and black carbon is very important in understanding of the herbicide leaching and transport characteristics. However, knowledge on herbicide sorption on these individual OM fractions from the same soil or sediment sample is very limited (Cornelissen et al., 2005; Sun et al., 2010a). In addition to natural OM, herbicide leaching can be reduced by intentionally enhancing the sorption potential of soil by adding biochar (Yang and Sheng, 2003). Biochar is the solid charred and carbon-rich residue from pyrolysis or incomplete combustion of biomass (Cao et al., 2009; Giusquiani et al.,1995; Sun et al., 2011). Biochar has attracted widespread attention because of its potential use as a soil amendment to improve soil quality (Lehmann, 2007; * Corresponding author. E-mail address: bx@pssci.umass.edu (B. Xing). Contents lists available at SciVerse ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol 0269-7491/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2011.12.015 Environmental Pollution 163 (2012) 167e173