Earthworms as agents for arsenic transport and transformation in roxarsone-impacted soil mesocosms: A μXANES and modeling study A.K. Covey a , D.J. Furbish a , K.S. Savage a,b, ⁎ a Earth and Environmental Sciences, Vanderbilt University, Nashville, TN, USA b Environmental Studies, Wofford College, Spartanburg, SC, USA abstract article info Article history: Received 26 June 2009 Received in revised form 17 January 2010 Accepted 6 February 2010 Available online 11 March 2010 Keywords: Oligochaetia Soil management Contaminant transport Borings XANES spectra Mathematical models Earthworms influence soil mixing during their feeding and burrowing activities by causing physical displacement and chemical transformations, potentially impacting the distribution and speciation of soil contaminants. This study investigates the effects of burrowing earthworms on arsenic speciation and mobility in soil mesocosms treated with roxarsone, an increasing anthropogenic source of arsenic used in the poultry industry as a feed supplement. Experiments were designed to test the hypothesis that earthworms and burrows provide means for biotransformation and redistribution of arsenic. Arsenic distribution was determined following earthworm bioturbation in artificial soil columns that were initially constructed with a contaminated layer of designated thickness and depth. The resulting depth profiles were used to indicate bioturbation rates by fitting them to a simple one-dimensional advection/diffusion model with a biodiffusivity that decreases with depth. Synchrotron X-ray methods reveal additional small-scale displacement of arsenic near the burrow and in the bulk soil. Microbeam X-ray Absorption Near Edge Structure spectra were collected to determine arsenic speciation. Arsenic initially introduced as roxarsone tended to be in a methylated form after 30 days. Within the earthworm tissue, arsenic–glutathione complexes were formed. Results are viewed in the context of poultry litter used as agricultural fertilizer. A decrease in tillage arising from soil conservation efforts allows earthworm populations to increase and burrows to become more permanent. This study suggests that (1) burrows serve as macropores allowing rapid transport of arsenic to greater depths during infiltration events; (2) bioturbation rates appear to be depth-dependent; and (3) earthworm soil mixing produces potentially mobile forms of arsenic that may become bioaccessible as arsenic is transported through the subsurface. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Since 2001, when the United States Environmental Protection Agency (EPA) passed stricter regulations on arsenic in drinking water, reducing allowable concentrations from 50 to 10 μg/L, increasing attention has been given to the agricultural feeding practices of poultry and swine. In particular, 3-nitro 4-hydroxphenylarsonic acid or roxarsone (ROX) is used as a supplemental additive in poultry feed. ROX is an organoarsenic compound first introduced to feed in the 1940s in order to increase weight gain, feeding efficiency (ratio of feed eaten to slaughter weight), and to control pigmentation and coccidial intestinal parasites (Han et al., 2004; Nachman et al., 2005; Cortinas et al., 2006; Jackson et al., 2006; Nachman et al., 2008). With more attention on arsenic poisoning, concern has been growing over the levels contained in tissue and meat (Lasky et al., 2004; Wallinga, 2006), although the majority of arsenic is excreted into the litter (Morrison, 1969). 1.1. Arsenic in poultry litter According to the Poultry—Production and Value 2007 Summary Report (NASS, National Agricultural Statistics Service, 2008) there were 8.9 billion broilers produced in the U.S (∼ 7% increase since 1996). If the average bird produces up to 4.9 kg of waste in its 48-day lifetime (ASAE, American Society of Agricultural Engineers, 2005) the annual production would be 44 billion kilograms of waste. Garbarino et al. (2003) estimate that 70% of broilers are treated with ROX and each excretes 150 mg of ROX. Based on the 2007 production census, this is expected to result in 9.3 × 10 5 kg of ROX or 2.7 × 10 5 kg As. With an increase in poultry production, along with decreasing numbers of farms, the problems associated with disposal of litter waste in concentrated areas are growing. The current practice is land application for fertilizer, while other uses are slowly coming online, such as biomass-fueled power plants and pelletization (Nachman et al., 2008). Geoderma 156 (2010) 99–111 ⁎ Corresponding author. Present address: Environmental Studies, Wofford College, Spartanburg, SC, USA. E-mail address: savageks@wofford.edu (K.S. Savage). 0016-7061/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.geoderma.2010.02.004 Contents lists available at ScienceDirect Geoderma journal homepage: www.elsevier.com/locate/geoderma