There is evidence that there are limits, at least locally, to the demands we can make on the natural environment to assimilate this multitude of waste products. For example, the natural water flow conditions from the hydrological cycle are often insufficient to maintain adequate water supply to the polluted areas. There are urban areas where adverse climatic conditions do not permit self-cleaning of the atmosphere through wind currents and natural convection. In agriculture, there is a growing body of evidence that the widespread dispersion of chemicals leads to their reappearance in other parts of the ecological system. The increased use of plastic and glass containers leaves a large residue of undegradable waste products which accumulate indefinitely. The imbalance between the rate at which man produces waste products and nature assimilates them drastically changes the nature of the responsibilities of governments. Today a 'laissez-faire' policy of allowing free use of natural resources is no longer possible. Welfare considerations require that governments adopt a policy of deliberate control of human activities in order to preserve the quality of the environment.