Crossed effects of helminth infection and lead exposure on fitness: An experimental study in feral pigeons (Columba livia).

Living organisms are exposed to multiple environmental factors that can affect their fitness. The negative effects of these simultaneous stressors can be additive or can interact in negative synergistic or antagonistic ways to affect the health of exposed individuals. Parasites can accumulate pollutants in their own tissues and have been shown to increase the tolerance of their hosts to different pollutants (antagonistic interaction between parasites and pollutants).

The "parasite detoxification hypothesis": lead exposure potentially changes the ecological interaction from parasitism to mutualism.

In urban areas, organisms are exposed to high pollutant levels, especially element trace metals that may impact host-parasite interactions. Indeed, parasites have been reported to reduce the negative effects of pollutants on their hosts. The fitness of parasitized organisms in polluted environments may therefore be greater than that of unparasitized organisms.