Arsenic Species in Edible Seaweeds Using In Vitro Biomimetic Digestion Determined by High-Performance Liquid Chromatography Inductively Coupled Plasma Mass Spectrometry

Overview

Zhao and colleagues measured total arsenic and four extractable arsenic species in five edible seaweeds purchased from Qingdao supermarkets. The paper separates water-extract, simulated-gastric, and simulated-intestinal arsenic species, so As(III), As(V), DMA, and MMA are recorded separately below. The source is directly relevant to seaweed/kelp foods, especially because the high total arsenic in Hizikia fusiformis is paired with high water-extract As(V) but lower simulated-gastric As(III).

Key numbers

Table 3 reports total arsenic in seaweed as mg/kg, dry weight, mean ± SD with n = 3:

Table 4 reports arsenic species in water, gastric, and intestinal extracts as mg/kg, dry weight, calculations based on arsenic contents, mean ± SD with n = 3:

Source-stated interpretation and risk-context values:

• The authors state that Hizikia fusiformis water-extract As(V) occupied about 27.9% of total As in the study.
• They state that As(V) and MMA were not detected in any gastric or intestinal extract, including Hizikia fusiformis.
• The simulated-digestion risk calculation used an adult body weight of 60 kg, a hijiki seaweed amount of 25 g, and the maximum gastrointestinal inorganic-arsenic concentration of 1.47 mg/kg, yielding inorganic arsenic intake of 0.6 µg/kg bw per day.

Quality-control and calibration values:

• CRM GBW 08517 Kelp: measured 13.2 ± 1.8 mg/kg; certified 13.9 ± 2.4 mg/kg.
• CRM GBW 08521 Laver: measured 40.2 ± 2.5 mg/kg; certified 41 ± 3 mg/kg.
• HPLC retention times were 3.07 min for DMA, 3.76 min for As(III), 6.60 min for MMA, and 9.00 min for As(V).
• Calibration curves covered 1 to 100 ng/mL; correlation coefficients were higher than 0.998; relative standard deviations for calibration points were 3.2% to 7.8% for 1 and 5 ng/mL and 0.8% to 4.5% from 10 to 100 ng/mL.

Methods (brief)

Five edible seaweeds were randomly purchased from Qingdao supermarkets during August and October 2012, oven-dried at 60°C to constant weight, ground, and homogenized. Total arsenic used 0.5 g dry weight portions digested with 5 mL concentrated nitric acid and 2 mL hydrogen peroxide in a microwave-assisted digestion system, followed by ICP-MS. Water-extract speciation used 0.5 g dried seaweed, 38 mL deionized water, ultrasonic extraction for 40 min, 2 mL of 3% (v/v) acetic acid for protein removal, centrifugation at 8000 ×g, 4°C, and 0.45 µm filtration before HPLC-ICP-MS. In vitro digestion used 1.0 g seaweed powder with saliva, gastric juice, duodenal solution, and bile at 37°C, simulating 5 min mouth, 2 h stomach, and 7 h intestine residence times; arsenic species were identified by matching HPLC retention times to standards.

Implications

This source contributes seaweed/kelp food occurrence evidence for both total arsenic and extractable inorganic arsenic species. It is especially useful for keeping Hizikia fusiformis water-extract As(V) (23.0 ± 2.5 mg/kg) separate from the simulated-gastric As(III) value (1.47 ± 0.20 mg/kg) and from total arsenic (82.5 ± 3.6 mg/kg). Downstream extraction should preserve the extract basis and should not use total arsenic (As), DMA, or MMA as inorganic-arsenic substitutes.

Related evidence

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

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