Thimerosal, an ethylmercury compound used as a preservative in vaccines, has been the subject of controversy due to concerns about mercury accumulation. While it was recommended to reduce its use in childhood vaccines in the late 1990s, studies have shown that ethylmercury is eliminated from the body more efficiently than methylmercury, which is found in fish. Large-scale epidemiological studies have not indicated any significant long-term neurodevelopmental effects related to thimerosal in vaccines.
