Background Anthropogenic disturbances can lead to intense selection pressures on traits and very rapid evolutionary changes. Evolutionary responses to environmental changes, in turn, reflect changes in the genetic structure of the traits, accompanied by a reduction of evolutionary potential of the populations under selection. Assessing the effects of pollutants on the evolutionary responses and on the genetic structure of populations is thus important to understanding the mechanisms that entail specialization to novel environmental conditions or resistance to novel stressors. Results Using an experimental evolution approach we exposed Caenorhabditis elegans populations to uranium, salt and alternating uranium-salt environments over 22 generations. We analyzed the changes in the average values of life history traits and the consequences at the demographic level in these populations. We also estimated the phenotypic and genetic (co)variance structure of these traits at different generations. Compared to populations in salt, populations in uranium showed a reduction of the stability of their traits structure and a higher capacity to respond by acclimation. However, the evolutionary responses of traits were generally lower for uranium than salt and the evolutionary responses in the alternating uranium-salt environment were between those of constant environments. Consequently, at the end of the experiment, the population rate of increase were higher in uranium than in salt and intermediate in the alternating environment. Conclusions Our multigenerational experiment confirmed that rapid adaptation to different polluted environments may involve different evolutionary responses resulting demographic consequences. These changes are partly explain by the effects of the pollutants on the genetic (co)variance structure of traits and the capacity of acclimation to novel conditions. Finally, our results in the alternating environment may confirm the selection of a generalist type in this environment.