Occurrence and Distribution of Arsenic Compounds in Marine Samples

Occurrence and Distribution of Arsenic Compounds in Marine Samples 

Thermodynamic considerations suggest that in oxygenated seawater, arsenic should exist almost entirely as arsenate (71). It was apparent from the early work on arsenic in seawater, however, that arsenite was also present in significant concentrations and could at times predominate over arsenate (7,8, 72, 73). Marine bacteria (74) and marine phytoplankton (75) were shown to reduce arsenate to arsenite, thereby providing an explanation for the observed As(III)/As(V) ratio in seawater. The compounds MMA and DMA also occur in seawater, generally as minor constituents (9, 34, 71, 76). The concentrations of As(III), MMA, and DMA are positively correlated with primary productivity, 

The total dissolved arsenic concentrations for the stations off British Columbia were 3-52 /u.g/liter (41), consistent with results for fjord porewaters (42) and estuarine porewaters (84). These results, however, rely on analytical techniques that would not detect the hidden or refractory arsenic levels reported earlier as occurring in seawater, and the true values may be slightly higher than those reported. The identity of the hidden and refractory arsenic remains unknown possible candidates include arsenosugars, TeMA, arsenobetaine, and arsenocholine. 

Clearly there is much to be learned from further examination of arsenic levels in seawater and porewaters. However, low concentrations and analytical difficulties presented by the salt matrix continue to complicate these analyses (33, 85). Techniques such as HPLC/ICP-MS suffer from interference by the molecular ion 40Ar35Cl +, formed by combination of the plasma gas and chloride ion, with the monoisotopic 75As+. Techniques to separate the arsenic compounds from the salt matrix before HPLC/ICP-MS have not been fully investigated because they may result in fractionation of the compounds and loss of speciation information. Nevertheless, methods to establish the presence or otherwise in seawater of some of the arsenic-containing compounds important in other marine compartments is worth pursuing. 

The early work adopted a natural products approach and focused on the brown algae (Phaeophyta) primarily because of their high arsenic 

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Marine biological material, radioactivity of, 3 315-316 Marine samples arsenic in, 44 148-151 compounds found, 44 151-162 occurrence and distribution, 44 149-151, 162-169... 

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