What difference might sewage treatment performance make to endocrine disruption in rivers? Andrew C. Johnson a, * , Richard J. Williams a , Pete Simpson b , Rakesh Kanda c,1 a Centre for Ecology and Hydrology, Maclean Building, Benson Lane, Crowmarsh Gifford, Wallingford, Oxfordshire, OX10 8BB, UK b Environment Agency, Waterlooville Laboratory, 4 The Meadows, Waterlooville, Hampshire, PO7 7XX, UK c WRc-NSF Ltd., Medmenham, Marlow, Buckinghamshire, SL2 2HD, UK Received 24 May 2006; received in revised form 1 August 2006; accepted 2 August 2006 Biological (trickling) filter sewage plants are less successful than other secondary sewage treatment plants at removing estrone from sewage effluent. Abstract An assessment of the steroid estrogen removing performance of 23 different sewage treatment plants (STPs) was performed. The assessment relied on a model to estimate influent concentrations, and completed questionnaires on the STP treatment details from the relevant water com- panies. This information was compared with observed effluent 17b-estradiol (E2) and estrone (E1) concentrations. The 10 biological filter plants (BFP) in the study performed poorly with only 30% (SD 31) removal on average for E1. This reduced E1 removal performance of the BFPs compared to all the other STP types in the survey was statistically significant ( p < 0.001). Scenarios of all the STPs as activated sludge types, and one as all BFP types were modelled using the GREAT-ER model set up for the Aire/Calder catchment in the UK. This differencewas shown to have an important effect on predicted river E1 concentrations and consequent risk classifications. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Estrogens; Estrone; Activated sludge; Biological filter; Removal 1. Introduction It is now well established that sexual disruption in UK wild fish is associated with sewage effluents, and the biologically active, endocrine disrupting, substances contained within them (Desbrow et al., 1998; Jobling et al., 1998; Jobling and Tyler, 2003). The most potent endocrine active substances contained within these effluents are believed to be natural and artificial steroid estrogens (of anthropogenic origin), although other non-steroidal substances have also been impli- cated, e.g., alkylphenol and alkylphenol polyethoxylates (Blackburn and Waldock, 1995; Sole ´ et al., 2000). The majority of sewage in the UK is treated either by bio- logical filter, or by activated sludge. The activated sludge plant (ASP) is most commonly associated with large towns and cit- ies. Activated sludge is an intensive biological treatment in which bacteria are suspended in a tank and vigorously aerated, with a hydraulic retention time (HRT) of 5e20 h plus (Cooper and Downing, 1998; Johnson et al., 2000). Biological, also known as percolating or trickling, filter plants (BFP) comprise of a tank with a biofilm supported on coarse media upon which the sewage liquor is sprayed following primary sedimentation (Boon et al., 1997). The water contact time with the biofilm is often quite short, around 30 min. To improve the effluent qual- ity an increasing number of BFP have some form of tertiary * Corresponding author: Tel.: þ44 (0)1491 838800; fax: þ44 (0)1491 692430. E-mail addresses: ajo@ceh.ac.uk (A.C. Johnson), rjw@ceh.ac.uk (R.J. Williams), peter.simpson@environment-agency.gov.uk (P. Simpson). 1 Present address: STL Reading, Britten Road, Reading RG2 0AU, UK. E-mail address: rakesh.kanda@stl-ltd.com (R. Kanda). 0269-7491/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.envpol.2006.08.032 Environmental Pollution 147 (2007) 194e202 www.elsevier.com/locate/envpol