The suggested threshold value for the sum of nonylphenol (NP), nonylphenol monoethoxylate (NP1EO) and nonylphenol diethoxylate (NP2EO) in sludge for use on land was initially 50 mg kg1 (EC, 2000) and later, in a more recent document, 450 mg kg1 (referenced in Milieu Ltd., WRc and RPA, 2010).