Brown algae arsenic

Arsenic concentrations in marine algae are generally considerably higher in brown algae than in either red or green algae. Reasons... 

A number of arsenic-containing ribosides, also referred to here simply as arsenosugars, occur in marine samples. Most of the arsenosugars are dimethylarsinoylribosides (Fig. 2, compounds 9 to 25). This group of compounds was unknown prior to 1981, when 9 and 12 were isolated from a brown alga (55). Structures for the two compounds were origi-... 

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

Stoeppler, M., Burow, M. and Backhaus, F. (1986) Arsenic in seawater and brown algae of the Baltic and the North Sea. Marine Chemistry, 18(2-4), 321-34. 

Harrington, C.F., Ojo, A.A., Lai, VW.-M., Reimer, K.J. and Cullen, W.R. (1997) The identification of some water-soluble arsenic species in the marine brown algae Fucus distichus. Appl. Organomet. Chem., 11, 931—940. 

D. Kuehnelt, K. Irgolic, W. Goessler, Comparison of three methods for the extraction of arsenic compounds from the NRCC standard reference material DORM-2 and the brown alga Hijiki fuziforme, Appl. Organomet. Chem., 15 (2001), 445-456. 

Thirty different types of Chinese edible seafood, including brown algae, red algae, fish, crab, shrimp, mussels, oysters, and clams, which are very popular foodstuffs in the Chinese cuisine, were examined for their total content of arsenic as well as its different compounds [146]. 

Tables I to III provide a summary of some representative data for total arsenic concentrations in sediments, marine algae, and marine animals. There can be considerable variation in the arsenic levels in these samples, in contrast to the levels in seawater, which are reasonably uniform in the world s oceans at about 0.5-2 p.g/liter (9,10). For sediments, there is perhaps a tendency for arsenic concentrations to be lower in samples from coastal regions and estuaries compared with deep-sea sediments. Industrial discharges of arsenic-enriched effluents can, however, result in arsenic contamination of near-shore sediments (11,12). Arsenic concentrations in marine algae are generally considerably higher in brown algae than in either red or green algae. Reasons...

Most marine algae contain only small quantities of arsenate, although in some species of brown algae it can be the major arsenic form (2). The presence of high concentrations of arsenate in Hizikia fusiforme (marketed as a dried food product called hijiki) is of particular interest because this alga is widely consumed, especially in Japan. Arsenite is less commonly reported in marine algae (4). 

Two quaternary arsoniosugars (diastereoisomers), previously isolated as an unresolved mixture (see Fig. 2, structure 14, epimeric at the carbon bonded to the carboxyl group) from the brown alga Sargassum lacerifolium, were separated by HPLC and their structures proposed on the basis of NMR spectral data (17). Electrospray mass spectrometric analysis of the unresolved mixture supports the proposed structures by demonstrating a [M + H]+ molecular species with m/z 569 (Pedersen and Francesconi, unpublished results). The presence of these two compounds in S. lacerifolium formed the basis of a more general scheme for the formation of naturally occurring arsenic compounds (17). 

This species, which is consumed in Japan under the name of yuna, contains a sulfated ribitol substituted by a dimethylarsinoyl group. This type of arsenic derivative in found in some brown algae (see Chapter 14), but this is the first example of such a compound in a red alga (Edmonds et al., 1997). 

This last compound is a mixture of diastereoisomers separable by HPLC (Edmonds, 2000). With 40 ppm of arsenic (per fresh weight), the species Sargassum lacerifo-lium is the alga that accumulates this element the most (Francesconi et al, 1991). Some 30 arsenate derivatives isolated either from brown algae, or from the invertebrates that consume them, are currently known and their biosyntheses derived from biomethylation of sedimentary arsenates via S-adenosyl-methionine (Figure 14.18). 

The presence of arsenic-containing sugars, however, is not specific to brown algae, as several of them have recently been identified in the green, red, and brown algae of the Adriatic Sea (Slejkovec et al, 2006). The broader presence of arsenic derivatives (arsenolipids, arsenobe-taine, arsenocholine) is also not limited to marine organisms for a major review on this subject, see Dembitsky and Levitsky (2004). 

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