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Biochar can be used as a sorbent to remove inorganic pollutants from water but the efficiency of sorption can be improved by activation or modification. This review evaluates various methods to increase the sorption efficiency of biochar including activation with steam, acids and bases and the production of biochar-based composites with metal oxides, carbonaceous materials, clays, organic compounds, and biofilms. We describe the approaches, and explain how each modification alters the sorption capacity. Physical and chemical activation enhances the surface area or functionality of biochar, whereas modification to produce biochar-based composites uses the biochar as a scaffold to embed new materials to create surfaces with novel surface properties upon which inorganic pollutants can sorb. Many of these approaches enhance the retention of a wide range of inorganic pollutants in waters, but here we provide a comparative assessment for Cd, Cu, Hg, Pb, Zn, NH, NO, PO, CrO and AsO.

The importance of earthworms to ecosystem functioning has led to many studies on the impacts of metals on earthworms. Far less attention has been paid to the impact that earthworms have on soil metals both in terms of metal mobility and availability. In this review we consider which earthworms have been used in such studies, which soil components have been investigated, which types of soil have been used and what measures of mobility and availability applied. We proceed to review proposed reasons for effects: changes in microbial populations, pH, dissolved organic carbon and metal speciation. The balance of evidence suggests that earthworms increase metal mobility and availability but more studies are required to determine the precise mechanism for this.

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Impact of the earthwormHuman activities have resulted in an increase in the concentrations of metals and 37 metalloids in urban and rural soils due to diffuse and point source pollution. These 38 disruptions to the natural biogeochemical cycle of metals and metalloids can lead to 39 toxic effects on flora and fauna. Earthworms are found in soils containing elevated 40 levels of metals and metalloids (Spurgeon and Hopkin, 1996; Langdon et al., 2001; 41 Vijver et al., 2007) and represent a major constituent of soil fauna. Bioavailable-rather 42 than total-concentrations determine metal toxicity in soils (Harmsen, 2007) and this is 43 dependent on mobility and speciation in the living soil environment (Di Toro et al., 44 2001; Thakali et al., 2006; Arnold et al., 2007). In order to assess properly the risks that Generally earthworms increase the mobility and availability of metals and metalloids in 50 soils (Sizmur and Hodson, 2009). This can result in greater concentrations of metals 51 leaching out of the soil into ground water (Tomlin et al., 1993) or greater uptake into 52 plants (Ma et al., 2003; Yu et al., 2005; Wang et al., 2006) and soil animals (Currie et 53 al., 2005; Coeurdassier et al., 2007). In addition to this, earthworms may reduce the 54 efficiency of soil remediation by mobilising recalcitrant metals (Udovic et al., 2007). 55The mechanisms for earthworms increasing metal mobility and availability are unclear, 56 but may involve changes in microbial populations, pH, dissolved organic carbon or 57 metal speciation (Sizmur and Hodson, 2009 BS7755-3.9, 1995) and cation exchange capacity was measured at 93 pH 7 using the ammonium acetate method (Rowell, 1994). Pore water was extracted from moist bulk soil from each pooled sample by centrifuging 128 at 6000rpm for 60 min. This extracted 51 % (SD = 0.9, n = 2), 56% (SD = 3.3, n = 2) 129 and 65% (SD = 0.7, n = 2) of the soil moisture from the Rookhope, Wisley and DGC 130 soils respectively. Pore water samples were analysed for pH (Jenway 3310 pH meter), 131 7 elements (ICP-OES), major anions (Dionex DX-500 ion chromatograph), and Total 132Organic Carbon (TOC) (Shimadzu TOC 5000). Speciation of Cu, Pb and Zn in pore 133 water samples was modelled using WHAM VI (Tipping, 1998). In the absence of 134 characterisation of the TOC fractions, we assumed that 50% of TOC was fulvic in 135 origin and that the fulvic acid contained 50% C (Tipping, 1996; Pribyl, 2010). 137Arsenic speciation in pore waters extracted from the DGC soil was determined in a 138 separate experiment. This was carried out at the Analytical Geochemistry Laboratory at 139British Geological Survey, Keyworth separately to the previous experiment to ensure 140 that freshly produced pore waters were analysed within 24 hours of extraction. 166Recoveries of these elements were 103%, SD = 2.4, n = 2 for Cu, 93%, SD = 4.2, n = 2 167 for Pb and 90%, SD = 0.81, n = 2 for Zn. Arsenic was below detection limits in the in- Results 173Earthworm mortality was low in the contaminated ...