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AbstractThis paper describes a straightforward modeling procedure to derive 'expected risk' (ER) of chemical substances. Starting from proposed use volumes, intended uses, physical and chemical substance properties and toxicity information, the procedure combines multimedia environmental fate modeling with species sensitivity modeling to derive the probability that exposure concentrations exceed critical effect concentrations. The procedure was tested on 1977 so-called mono-constituent organic chemicals that had been registered to be marketed in the EU, after 'possibility to be used safely' had been demonstrated by showing that the possible Risk Quotients (RQ) defined as PEC/PNEC ratios (Predicted Exposure Concentration & Predicted No Effect Concentration) were expected to remain below the value of 1, as required by REACH. It appears from this study that (i) RQ and ER of chemicals can be calculated readily, reliably, transparently and reproducibly, that (ii) both RQ and ER can be used to assess whether a new chemical may exceed a chosen acceptability level, but that (iii) in addition ER can be straightforwardly used to rank chemicals according to expected environmental safety. In conclusion, the paper states that modeling ER of chemicals (instead of estimating RQ values), could strengthen the scientific basis of environmental risk assessment for use in REACH. The paper further recommends that more robust environmental risk calculation can be done by using acute EC50, instead of chronic NOEC as critical effect concentration.