56
arsenophospholipid occurs in all aquatic plants in even more variable
amounts than do its water-soluble derivatives. Only Dunaliella species
and the representatives of the Chlorococcales have arsenolipids besides
the arsenoriboside of phosphatidylglycerol. The structure of the second
major (50%) arsenolipid of Dunaliella appears to be very different (Cooney, 1981, Wrench and Addison, 1981).
Arsenic Turnover Rates in Phytoplankton
Arsenic levels in most oceanic algal samples have been remarkably
low, 2-80 ppm dry wt. In some cases such as Sargassum species, higher
arsenic levels have been reported. There appears to be an inverse relationship between environmental phosphate concentrations and the accumulation of arsenic by algae. Such accumulation is related to arsenate
uptake and arsenic excretion rates for the organisms. Although no
direct measurements of arsenate uptake and arsenic excretion rates have
been made, the excellent data of Sanders (1983) and Sanders and Windom,
1980, for arsenate uptake by phytoplankton allow estimation of arsenic
turnover under phosphate-sufficient nutrient conditions. Using Sanders'
data for arsenate uptake by Skeletonema costatum and the concentration
of arsenic in such algae, a turnover of 8 percent per hour is derived.
More reliable turnover measurements for algae under a range of nutrient
stress conditions are desirable.
The Precursor of Arsenobetaine
The classic work of Edmonds et al., 1977, 1981 and Cannon et al.
1981, reported isolation and identification of arsenobetaine,
(CH3)3At-CH2-COO-,
as the arsenical responsible for the 29 ppm arsenic
found in commercial Western Australian rock lobster tail muscle and
probably in other organisms (Vaskovsky et al. 1972). Their discovery
allayed concern for arsenic toxicity hazards since Welch (1938, 1942)
and coworkers, forty years earlier, had studied the metabolism of
arsenobetaine and arsenocholine with laboratory rats. At levels of 1%
of the diet, no deleterious effects were noted after one week. Other
studies have indicated that natural dietary arsenic is readily excreted
by the mammalian kidney.
Production of arsenocholine in a marine food chain requires synthetic production of the trimethylarsonium group. The dimethyarsenosoribosides being trialkylarsineoxides are not obvious precursors of
trimethylarsonium compounds. Rather, they are oxidation products. Since
the identification of arsenobetaine in 1977, no precursors have been
recognized.
arsenophospholipid occurs in all aquatic plants in even more variable
amounts than do its water-soluble derivatives. Only Dunaliella species
and the representatives of the Chlorococcales have arsenolipids besides
the arsenoriboside of phosphatidylglycerol. The structure of the second
major (50%) arsenolipid of Dunaliella appears to be very different (Cooney, 1981, Wrench and Addison, 1981).
Arsenic Turnover Rates in Phytoplankton
Arsenic levels in most oceanic algal samples have been remarkably
low, 2-80 ppm dry wt. In some cases such as Sargassum species, higher
arsenic levels have been reported. There appears to be an inverse relationship between environmental phosphate concentrations and the accumulation of arsenic by algae. Such accumulation is related to arsenate
uptake and arsenic excretion rates for the organisms. Although no
direct measurements of arsenate uptake and arsenic excretion rates have
been made, the excellent data of Sanders (1983) and Sanders and Windom,
1980, for arsenate uptake by phytoplankton allow estimation of arsenic
turnover under phosphate-sufficient nutrient conditions. Using Sanders'
data for arsenate uptake by Skeletonema costatum and the concentration
of arsenic in such algae, a turnover of 8 percent per hour is derived.
More reliable turnover measurements for algae under a range of nutrient
stress conditions are desirable.
The Precursor of Arsenobetaine
The classic work of Edmonds et al., 1977, 1981 and Cannon et al.
1981, reported isolation and identification of arsenobetaine,
(CH3)3At-CH2-COO-,
as the arsenical responsible for the 29 ppm arsenic
found in commercial Western Australian rock lobster tail muscle and
probably in other organisms (Vaskovsky et al. 1972). Their discovery
allayed concern for arsenic toxicity hazards since Welch (1938, 1942)
and coworkers, forty years earlier, had studied the metabolism of
arsenobetaine and arsenocholine with laboratory rats. At levels of 1%
of the diet, no deleterious effects were noted after one week. Other
studies have indicated that natural dietary arsenic is readily excreted
by the mammalian kidney.
Production of arsenocholine in a marine food chain requires synthetic production of the trimethylarsonium group. The dimethyarsenosoribosides being trialkylarsineoxides are not obvious precursors of
trimethylarsonium compounds. Rather, they are oxidation products. Since
the identification of arsenobetaine in 1977, no precursors have been
recognized.