The multimedia environmental fate model SimpleBox is applied to compute steady-state concentration ratios with the aim to harmonize environmetal quality objectives of air, water, sediment and soil. In 1995 the Dutch Health Council recommended validation of the model. Several activities were initiated since then, a.o. an update of various model assumptions and analysis of the operational uncertainty. This report describes the last phase of the validation exersize, i.e. validation of the model as a whole. Specific model output with respect to a model compound is compared with field observations. Di(2-ethylhexyl) phthalate (DEHP) and di n-butyl phthalate (DBP), two high volume production chemicals, were monitored in the environmental compartments air, water, fish, sediment, soil and vegetation in the period 1997- 2001. Concentration ratios as measured between the compartments, displayed a considerable spread. Probabilistic techniques were used to obtain steady state concentration ratios. In stead of a deterministic output a distribution is calculated. The width of the distribution is largely determined by very uncertain emission rates of both phthalates. The 50th percentile differed less than a factor of 10 with respect to concentration rates obtained from monitoring. From this report it is tentatively concluded that application of SimpleBox to harmonize environmental quality objectives should be retained.