The paper presents the results of sensitivity and data uncertainty analyses of a box model simulating the fate of persistent organic pollutants in the environment. The model has 39 parameters which describe chemical and environmental properties. All of these parameters are influenced by uncertainties. Therefore we performed sensitivity analysis by the means of finite difference method and data uncertainty analysis using Spearman's rank correlation coefficients. The results show significant changes in solution which confirm the expectations that the concentrations of chemicals (and the model itself) are strongly dependent on several parameters, mainly temperature and rain density.