Arsenic in the marine environment—Contents, speciation, and its biotransformation

Arsenic has been famous as “the king of poisons and the poison of kings,” because of its potency to kill that used by many rivals to kill the ruling king in history. Presently it is a ubiquitous metalloid in the marine environment and has complex biogeochemistry that has significant implications for its toxicity to marine organisms and their consumers. It is a potent lung, bladder, and skin carcinogen as well as a neurological and liver toxin. The average concentration of total arsenic in uncontaminated seawater ranges from 1 to 2 μg/L and in marine sediments from 5 to 15 μg/g dry weight (near-shore and estuaries sediments), and the average concentration is about 40 μg/g (deep-sea sediments). The dominant form of arsenic in seawater is inorganic arsenate. The most toxic and potential carcinogen, inorganic arsenite, is rarely found in oxic seawater and marine sediments. Marine organisms, such as phytoplankton, bacteria, and algae, accumulate arsenate from surrounding seawater and reduce it to arsenite, and subsequent methylation leads to the synthesis of organoarsenicals, which are ultimately released/excreted in the seawater. Marine animals have limited ability to accumulate inorganic arsenic from seawater, whereas they largely accumulate organic forms of arsenic consumed from their food chain. Arsenic-containing seafood is the main route of arsenic access to the human body. Arsenobetaine, the major organic form of arsenic in seafood, is nontoxic and/or noncarcinogenic to humans. The majority of organoarsenicals present in the seafood are rapidly excreted, little of which is accumulated by human beings. However, recently a few forms of methylated arsenicals, trivalent arsenosugars, and some forms of arsenolipids have been reported to exert their toxic effects in in vitro studies.