The aim of this study was to test field relevance of the prospective methodology for the assessment of environmental risk described in the EU technical guidance document (TGD) [European Commission 2003. Technical guidance document in support of Commission Directive 93/67/EEC on Risk assessment for new notified substances and Commission Regulation (EC) No 1488/94 on Risk assessment for existing substances and Commission Directive (EC) 98/8 on biocides, second ed. European Commission, Luxembourg, Part 1, 2 and 3, 760pp.]. To achieve this goal, an environmental risk assessment was performed according to the TGD for two major contaminants, atrazine and diuron, that are present in the Seine River estuary (France) and listed in the EU Water Framework Directive (Directive 2000/60/CE). Results showed that atrazine presented a source of risk in the upper- and mid-estuary throughout the 1993 and 1996 spring seasons. Diuron introduced a risk into the same areas throughout spring periods of 1993-2005. Results are discussed and some suggestions for a more realistic in situ risk assessment are given. For the computation of a more relevant PNEC for pesticides, their specific mode of action should be taken into consideration as well as ecotoxicological data on species endemic to the considered area. (C) 2008 Elsevier Inc. All rights reserved.