Pollution phenomena are complex systems in which different parts are integrated by means of causal and temporal relationships. To understand pollution, children must develop some cognitive abilities related to system thinking and temporal and causal inferential reasoning. These cognitive abilities constrain and guide how children understand pollution processes. Hence, ascertaining whether changes among children's ideas of pollution are related to system thinking and inferential reasoning abilities could be useful in improving environmental education. Eighty participants between 9 and 16 years old were interviewed to evaluate how children explain different aspects of pollution-related systems. From the explanations found in these interviews, three progressive epistemic structures were reconstructed. The three epistemic structures differ in the type of causal and temporal relationship established by the participants and in the mechanisms that the participants used to relate the pollutant to its effects.