Safety Evaluation of Organoarsenical Species in Edible Porphyra from the China Sea

Overview

Wei and colleagues measured total arsenic and extractable arsenic species in edible Porphyra seaweed from five Chinese locations. The occurrence-relevant table reports dry-weight total arsenic and extractable arsenosugar PO4/OH in market Porphyra; the heating and volunteer urine sections are exposure and metabolism context. The source reports organoarsenic species, not inorganic arsenic, so total arsenic and arsenosugar values should not be substituted for inorganic arsenic (iAs).

Key numbers

Table 3 reports total arsenic, extractable arsenic, and extraction efficiency in Porphyra as mg/kg as arsenic dry weight, mean ± SD with n = 3:

The Results text summarizes the total-arsenic range as 2.1 to 21.6 mg/kg (dry wt), with an average value of 8.6 mg/kg (dry wt) and “standard variance” of 7.7 mg/kg.

Table 4 reports extractable arsenosugar concentrations in mg/kg as arsenic dry weight, mean ± SD with n = 3:

Table 4 peak-abundance context:

The authors state that the Porphyra extract peaks did not match inorganic arsenic, MMA, DMA, or AsB standards under their HPLC conditions, and that ES-MS-MS confirmed the two extract species as arsenosugar PO4 and arsenosugar OH. They state that arsenosugars accounted for the complete arsenic content of the Porphyra extract.

Heating and volunteer-metabolism context:

• Guangzhou Porphyra extract was heated at 100 °C in an oil bath for 10 min; Figure 4 showed no chromatographic difference before versus after heating, and the authors concluded that the arsenosugars remained stable toward short-term heating.
• Six adult volunteers, five male and one female, refrained from seafood for at least 72 h before consuming 15 g (dry weight) of heated Guangzhou Porphyra in one meal.
• The ingested Guangzhou Porphyra portion contained ∼324 µg of arsenic as arsenosugars OH and PO4.
• Urine before ingestion contained total arsenic 10-30 ng/mL; after ingestion, urine arsenic peaked between 18 and 35 h.
• The 20-30 h urine window gave the highest concentration, 92.5 µg/L, reported as the average value of 19 samples collected during that period.
• The final urine sample collected after 80 h contained <30 ng/mL.
• Figure 6/7 HPLC-ICP-MS urine speciation assigned the major post-ingestion peak as DMA; the authors state that the concentration was almost 15-20 times higher than before ingestion.

Quality-control context:

• For NIST SRM 1571 Orchard Leaves, the certified value was 10 ± 2 mg of As/kg; the study measured 9.5 ± 0.3 mg of As/kg.

Methods (brief)

Chinese seaweeds were collected from Guangzhou, Fujian, Dalian, Qingdao, and Zhejiang in July 2001; three Porphyra samples were bought at local public markets in each location and stored at room temperature before analysis. Total arsenic used 0.5 g subsamples digested with nitric acid and hydrogen peroxide in a microwave oven, then ICP-MS with iridium internal standard. Species extraction rinsed crude seaweed with deionized water, oven-dried samples at 50 °C for 18 h, ground them, extracted 1 g (dry weight) with 20 mL H2O/MeOH (1:1, v/v) by sonication for 15 min and centrifugation, and repeated the extraction twice more. Speciation used anion- and cation-exchange HPLC-ICP-MS, with ES-MS-MS confirmation of arsenosugar identities; urine arsenic species were measured by PRP-X100 anion-exchange HPLC-ICP-MS.

Implications

This paper adds direct seaweed occurrence evidence for Chinese-market Porphyra with dry-weight total arsenic from 2.1 ± 0.1 mg/kg to 21.6 ± 1.4 mg/kg and extractable arsenosugar PO4/OH values reported separately. Its main routing use is the seaweed/kelp food row, but it should not be treated as an inorganic-arsenic source because the extractable species were organoarsenic arsenosugars and no Porphyra iAs concentration was reported. The volunteer data are useful exposure/metabolism context for arsenosugar conversion to urinary DMA, not a product occurrence row.

Related evidence

• Seaweed/kelp foods (nori, wakame, kombu, dulse — as food products)
• Seaweed
• Arsenic, Total

Update history

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