The recovery of organic phosphorus in alkaline solvent may be improved by pretreating the soil with mineral acid [22]. This removes polyvalent bridging cations and dissolves salts of organic phosphate esters that are relatively insoluble in alkaline solution. Most early methods used a strong mineral acid such as concentrated hydrochloric acid [30], although dilute solutions (e.g. 0.1 M) are also effective [31] (Table 2).