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    arsenic (As)

    arsenic
    Massive native arsenic with quartz and calcite.
    Credit: Aram Dulyan & Wikipedia
    A toxic, semimetallic element of group V of the periodic table. Compounds containing arsenic are used as a poison for rodents, insects, and weeds, and to harden lead and make semiconductors. Three allotropes are known: white arsenic, black arsenic, and a yellow, nonmetallic form.

    Arsenic was discovered by Albertus Magnus in the 13th century. The name comes from arsenikon, the Greek name for the yellow pigment orpiment.

    The major ore of arsenic is arsenopyrite (iron arsenide-sulfide, FeAsS). It is found with precious metal ores in high-temperature veins and occurs as monoclinic system prismatic crystals or granular masses. Arsenopyrite is a metallic white-gray, has a hardness of 5.5–6, and has a specific gravity of 6.


    atomic number 33
    relative atomic mass 74.922
    relative density 5.7
    sublimes 613 °C (1,135 °F)


    Arsenic in drinking water

    Worldwide, more than 140 million people are exposed to toxic levels of arsenic in their drinking water. It enters the body's cells by diffusion and, once inside, disrupts how the cells function by binding to their machinery, inactivating it, and disrupting the way energy is transported. Long-term exposure can lead to skin disease and kidney and bladder cancer, and it is thought to stunt the intellectual development of children.

    The most arsenic-contaminated regions are in India, Pakistan, and China, where soluble arsenic in ground waters exceeds the World Health Organization's (WHO) suggested maximum safe level of 10 parts per billion.


    Arsenic-metabolizing bacteria

    Although arsenic is toxic to most animal life, researchers have discovered certain types of bacteria that can fuel themselves using arsenic and sunlight. The bacteria were found in Mono Lake, California, which is fed by hydrothermal waters that leach out arsenic-containing minerals from the surrounding rocks. The American scientists who made the discovery suspect that these organisms harness an ancient metabolic pathway that was present in photosynthesizing bacteria on Earth before oxygen was present in the atmosphere.

    Understanding how arsenic is metabolised by bacteria could help scientists comprehend its damaging affects inside human cells.


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