text: The evidence that arsenic may be a beneficial nutrient at trace levels below the background to which living organisms are normally exposed has been reviewed. Some organoarsenic compounds found in nature are arsenobetaine and arsenocholine, both being found in many marine organisms.  Some As-containing nucleosides (sugar derivatives) are also known.  Several of these organoarsenic compounds arise via methylation processes.  For example, the mold Scopulariopsis brevicaulis produces significant amounts of trimethylarsine if inorganic arsenic is present. The organic compound arsenobetaine is found in some marine foods such as fish and algae, and also in mushrooms in larger concentrations. In clean environments, the edible mushroom species Cyanoboletus pulverulentus hyperaccumulates arsenic in concentrations reaching even 1,300 mg/kg in dry weight; cacodylic acid is the major As compound. A very unusual composition of organoarsenic compounds was found in deer truffles (Elaphomyces spp.). The average person's intake is about 10–50 µg/day. Values about 1000 µg are not unusual following consumption of fish or mushrooms; however, there is little danger in eating fish since this arsenic compound is nearly non-toxic.
  A topical source of arsenic are the green pigments once popular in wallpapers, e.g. Paris green. A variety of illness have been blamed on this compound, although its toxicity has been exaggerated.
  Trimethylarsine, once known as Gosio's gas, is an intensely malodorous organoarsenic compound that is commonly produced by microbial action on inorganic arsenic substrates.
  Arsenic (V) compounds are easily reduced to arsenic (III) and could have served as an electron acceptor on primordial Earth. Lakes that contain a substantial amount of dissolved inorganic arsenic, harbor arsenic-tolerant biota.