The understanding of the passive membrane permeation is crucial to gain insight into mechanism of action, disposition, toxicity of pollutants. Passive diffusion is the main limitation of penetration of small pollutant molecules and thus the main barrier for their infiltration into living cells. This phenomenon can be understood based on free energy calculations using metadynamic technique. By means of atomistic modeling, the changes in the membrane structure and the required energy for the transport can be determined. The aim of the project is to determine the energy barrier of the passive transport of a set of pesticides and pollutants in order to identify the key molecular features of fast transport. With these features in hand, prediction of the environmental hazard can be made.