The determination of arsenite and arsenate ions in fish and shellfish by selective extraction and polarography

Overview

Reinke and colleagues developed a selective extraction and polarographic method for arsenite and arsenate in fish and shellfish tissue. The occurrence-relevant table reports total arsenic and total inorganic arsenic, defined by the paper as As3+ plus As5+, for eight fish or shellfish tissues. The key finding is that high total arsenic in several marine foods was not matched by high inorganic arsenic, except for lobster hepatopancreas at 0.9 ppm.

Key numbers

Table 4 reports inorganic arsenic and total arsenic content of white muscle from fish and shellfish, as mean duplicate analyses in ppm.

The method section reports that levels down to about 0.5 ppm inorganic arsenic could be determined, but an interfering wave was noticed at the lower limit. The abstract states that tested specimens had total arsenic levels up to 40.5 ppm and little inorganic arsenic. Table 3 reports duplicate recovery of arsenite and arsenate added as a 1:1 mixture by weight to lobster hepatopancreas: 30 µg added gave 73 and 80% recovery; 20 µg gave 83 and 78%; 10 µg gave 93 and 91%; 5 µg gave 98 and 98%; 2.5 µg gave 97 and 96%; and 1 µg gave 120 and 86%.

Methods (brief)

Arsenite, as arsenic trichloride, was extracted into benzene from strongly acidified tissue homogenates, then back-extracted into water and analyzed polarographically in 1 N HCl. Arsenate left in the homogenate was reduced to arsenite with cuprous ion and isolated by the same extraction procedure; treating the homogenate with cuprous ion before extraction produced the paper’s total inorganic arsenic measurement. Total arsenic values were reported beside the inorganic arsenic values, but the table does not describe a separate arsenic speciation profile beyond arsenite and arsenate.

Implications

This source supplies early seafood occurrence evidence showing that total arsenic and inorganic arsenic must remain separate for fish and shellfish. The lobster tail row is especially useful as a speciation example: total arsenic was 40.5 ppm, while inorganic arsenic was reported as <0.5 ppm. The lobster hepatopancreas row should be kept distinct from edible white-muscle rows because it is an organ tissue with 0.9 ppm inorganic arsenic.

Update history

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