Mercury in the body produces a selenium deficiency state that increases toxicity.
Spiller HA. Rethinking mercury: the role of selenium in the pathophysiology of mercury toxicity. Clinical Toxicology. 2018;56(5):313-326.
This study makes the case that mercury’s multifaceted interactions with selenium are a central feature of mercury toxicity. The authors argue that “the previously suggested ‘protective effect’ of selenium against mercury toxicity may in fact be backwards”—because of mercury’s affinity for selenium, mercury can actually produce a selenium deficiency state that promotes oxidative stress and inhibits the body’s regenerative mechanisms. Depending on the form of mercury and other factors, selenium supplementation may have some benefits for restoring adequate selenium status and mitigating the toxicity of mercury, but it does not appear to promote increased elimination of mercury.