Which mercury form is better absorbed via the GI tract?

• A. Elemental mercury
• B. Mercuric salts
• C. Organic methyl and ethyl mercury
• D. Mercury does not get absorbed

Answer: (C)

Absorption from the GI tract depends on the chemical form’s ability to cross the intestinal barrier. Organic mercury compounds, particularly methylmercury and ethylmercury, are lipid-soluble and readily cross membranes. Methylmercury, for example, forms a complex with cysteine that resembles the amino acid methionine, allowing uptake by amino acid transporters in enterocytes and rapid entry into the bloodstream. This high gut absorption is why organic mercury from contaminated fish is a major exposure concern.

In contrast, elemental mercury is metallic and poorly soluble in the gut, and mercuric salts are ionic and not easily permeable across the intestinal epithelium, so their GI absorption is limited. Thus, the organic forms are the best absorbed via the GI tract.