The answer would be parasitism.
Let's define each term.
Parasitism: A relation between organisms in which one lives as a parasite on another.
Commensalism: A type of relationship between two species of plant, animal, fungus, etc., in which one lives with, on, or in another without damage to either.
Pollution: The introduction of harmful substances or products into the environment; the act of polluting or the state of being polluted.
Under some conditions, parasitism poses a major hazard to hosts, and environmental pollution has a detrimental impact on organism health as well. The concomitant effects of contaminants and parasites on an organism's physiological homeostasis are poorly understood. The current study indicates that parasites can: I affect how pollutants are metabolized by infected hosts; (ii) interact with pollution in positive or negative ways; and (iii) cause physiological changes in hosts that were previously assumed to be caused by pollution. Fish infected with acanthocephalans have lower metal levels than uninfected hosts, according to experimental studies on the uptake and accumulation of metals by fish. For instance, Pomphorhynchus laevis lowers lead levels in fish bile, which lessens or impedes the cycling of lead in the liver and intestines, potentially lowering the amount of metals available to fish. Thus, changes in pollutant absorption and accumulation caused by parasites in various intermediate and ultimate hosts are crucial to the study of ecotoxicology. Along with these changes, there is a strong relationship between the impacts of pollutants and parasites that appears to be partly mediated by the endocrine system, which is intimately linked to the immune system in fish. Studies in the lab on eels that had been artificially infected with the swimbladder worm Anguillicola crassus have shown that harmful substances like polychlorinated biphenyls have immunosuppressive effects that make parasite infection easier. Similar to this, a decrease in anti-A. crassus antibody levels is associated with an increase in blood cortisol concentration in eels as a result of chemical exposure and infection. Additionally, parasites are capable of inducing physiological modifications that are ascribed to substances with endocrine disrupting action, for instance, the cestode Ligula intestinalis is known to inhibit roach gonad growth. Roach are the best instances of endocrine disruption in wild fish, and it is likely that this disruption may be brought on by parasites like L. intestinalis or members of the phylum Microspora in addition to chemical action.
Thanks,
Eddie