This paper proposes a method to estimate the inherent environmental friendliness of a chemical process plant by considering the potential toxicity impact on the aquatic, terrestrial and atmospheric environments. A worst-case scenario of a total loss of containment in the plant is assumed. The method proposed by [Gunasekera, M.Y., Edwards, D.W. (2003). Estimating the environmental impact of catastrophic chemical releases to the atomosphere: an index method for ranking alternative chemical process routes. Trans. IChemE., Part B, Process Safety and Environmental Protection, 81(B6), 463-474] for determining the inherent atmospheric environmental friendliness of a chemical plant is combined with the method proposed by [Cave, S.R., Edwards, D.W. (1997). Chemical process route selection based on assessment of inherent environmental hazard. Computers Chem. Engng., 21, S965-S970], which estimates the inherent friendliness to the aquatic and terrestrial environments. Application of this method to six routes to produce methyl methacrylate shows that the acetone cyanohydrin based route is potentially the least inherently environmentally friendly. The highest potential hazard is observed in the aquatic environment due to the chemicals associated with the acetone cyanohydrin route. (c) 2005 Elsevier Ltd. All rights reserved.