Cadmium and Mercury
Cadmium and mercury are toxic metals with no nutritional value. They have been associated with major environmental catstrophes resulting in human fatality. Both are mutagenic in bacteria and in cell cultures and known causes of severe respiratory damage following inhalation. Cadmium fume fever is documented and neurological toxicity occurs with inhalation of mercury vapour. Cadmium is mutagenic, genotoxic and cytotoxic and a cause of impaired DNA repair, release of reactive oxygen species and inflammatory change. Animal studies indicate that cadmium is a cause of prostatic and testicular tumours but studies are inconsistent. Clinical evidence points to lung cancer being an occupational hazard in cadmium-related industries, including Ni : Cd battery workers. Cadmium is a constituent of cigarette smoke and this must be contributory to the lung cancers seen in cadmium-related industries. Human case and epidemiological studies provide limited statistically significant evidence that cadmium alone is a cause of respiratory tract or prostatic cancer. The carcinogenicity of mercury is complex. Mercury and methyl mercury are evaluated but complications arise through bacterial oxidation of residues and environmental instability of bioactive ions. At the moment, there is no convincing evidence from clinical cases or epidemiological studies that the metal is carcinogenic but concerns have been raised over the risks of inhaling mercury vapour amongst dentists and mercury contamination of some oriental medicines. Mercury is a neurotoxin but at the moment it is not conclusively established as a neuro-carcinogen. Thimerosal is still used as a preservative in vaccines but no carcinogenic risk has been established by limited studies available.