Selenium may be absorbed through inhalation and ingestion, while some selenium compounds may also be absorbed dermally. Once in the body, selenium is distributed mainly to the liver and kidney. Selenium is an essential micronutrient and is a component of glutathione peroxidase, iodothyronine 5'-deiodinases, and thioredoxin reductase. Organic selenium is first metabolized into inorganic selenium. Inorganic selenium is reduced stepwise to the intermediate hydrogen selenide, which is either incorporated into selenoproteins after being transformed to selenophosphate and selenocysteinyl tRNA or excreted into the urine after being transformed into methylated metabolites of selenide. Elemental selenium is also methylated before excretion. Selenium is primarily eliminated in the urine and feces, but certain selenium compounds may also be exhaled. Silver compounds can also be absorbed orally and dermally. It distributes throughout the body in the blood, particularily to the liver. Insoluble silver salts are transformed into soluble silver sulfide albuminates, bind to amino or carboxyl groups in RNA, DNA, and proteins, or are reduced to metallic silver by ascorbic acid or catecholamines. Metallic silver is oxidized and may deposit in the tissues, causing arygria. Silver is eliminated primarily in the faeces. (L808, L619)
Selenium readily substitutes for sulfur in biomolecules and in many biochemical reactions, especially when the concentration of selenium is high and the concentration of sulfur is low. Inactivation of the sulfhydryl enzymes necessary for oxidative reactions in cellular respiration, through effects on mitochondrial and microsomal electron transport, might contribute to acute selenium toxicity. Selenomethionine (a common organic selenium compound) also appears to randomly substitute for methionine in protein synthesis. This substitution may affect the structure and functionability of the protein, for example, by altering disulfide bridges. Inorganic forms of selenium appear to react with tissue thiols by redox catalysis, resulting in formation of reactive oxygen species and causing damage by oxidative stress. Metallic silver is oxidized and may deposit in the tissues, causing arygria. The silver ion is known to inhibit glutathione peroxidase and NA+,K+-ATPase activity, disrupting selenium-catalyzed sulfhydryl oxidation-reduction reactions and intracellular ion concentrations, respectively. Silver nanoparticles are believed to disrupt the mitochondrial respiratory chain, causing oxidative stress, reduced ATP synthesis, and DNA damage. (L808, A243, A244, A245, A246, L619)
来源:Toxin and Toxin Target Database (T3DB)
毒理性
致癌物分类
3, 其对人类致癌性无法分类。
3, not classifiable as to its carcinogenicity to humans. (L135)
Chronic oral exposure to high concentrations of selenium compounds can produce a disease called selenosis. The major signs of selenosis are hair loss, nail brittleness, and neurological abnormalities (such as numbness and other odd sensations in the extremities). Animal studies have shown that selenium may also affect sperm production and the female reproductive cycle. Exposure to high levels of silver for a long period of time may result in a condition called arygria, a blue-gray discoloration of the skin and other body tissues. Argyria is a permanent effect but does not appear to be harmful to health. While silver itself is not toxic, most silver salts are, and may damage the liver, kidney, and central nervous system, as well as be carcinogenic. (L808, L809, L810, L619)
Short-term oral exposure to high concentrations of selenium may cause nausea, vomiting, and diarrhea. Brief exposures to high levels of elemental selenium or selenium dioxide in air can result in respiratory tract irritation, bronchitis, difficulty breathing, and stomach pains. Longer-term exposure to either of these air-borne forms can cause respiratory irritation, bronchial spasms, and coughing. Exposure to high levels of silver for a long period of time may result in a condition called arygria, a blue-gray discoloration of the skin and other body tissues. Argyria is a permanent effect but does not appear to be harmful to health. Exposure to high levels of silver in the air has resulted in breathing problems, lung and throat irritation, and stomach pains. Skin contact with silver can cause mild allergic reactions such as rash, swelling, and inflammation in some people. (L808, L619)
