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Total arsenic, inorganic arsenic (iAs), total cadmium concentrations and chemical forms of cadmium were analysed in Porphyra yezoensis collected monthly from January to April in 2011 and in Laminaria Japonica collected monthly from March to July in 2010. Results showed that total As concentrations in P. yezoensis were much lower than those in L. Japonica. The iAs concentrations in both macroalgae were all below the maximum limit according to the legislation in China, while total Cd concentrations in all samples of P. yezoensis exceeded the maximum limit. The percentage of iAs to total As decreased in both macroalgae with the time. The results provide important information showing that both macroalgae are able to metabolise inorganic arsenic to organic forms. Thus both macroalgae have evolved arsenic resistance which is linked to the capability of metabolising toxic inorganic arsenic. In addition, the results suggest that the transformation rate of arsenate to organic arsenic in both algae increases with the growth and metabolic rate that increase with elevated environmental temperature. Temperatures rise from January to April in Jiangsu province and from March to July in Liaoning Province. Most Cd was associated with pectates and protein (extractable by 1 M NaCl) in both algae, and only a small percentage of the Cd was inorganic (extractable by 80% ethanol). The Cd chemical forms have no obvious relationship with the time in both algae.

Arsenite [As (III)], arsenate [As (V)], methylarsonate (MMA), and dimethylarsinate (DMA) in five edible seaweeds (the brown algae Laminaria japonica, red algae Porphyra yezoensis, brown algae Undaria pinnatifida, brown algae Hizikia fusiformis, and green algae Enteromorpha prolifera) were analyzed using in vitro digestion method determined by high-performance liquid chromatography inductively coupled plasma mass spectrometry. The results showed that DMA was found in the water extracts of all samples; As (III) were detected in L. japonica and U. pinnatifida and about 23.0 and 0.15 mg/kg of As (V) were found in H. fusiformis and E. prolifera respectively. However, after the gastrointestinal digestion, As (V) was not detected in any of the five seaweeds. About 0.19 and 1.47 mg/kg of As (III) was detected in the gastric extracts of L. japonica and H. fusiformis, respectively, and about 0.31 and 0.10 mg/kg of As (III) were extracted from the intestinal extracts of Porphyra yezoensis and U. pinnatifida, respectively. The present results successfully reveal the differences of As species and levels in the water and biomimetic extracts of five edible seaweeds. The risk assessment of the inorganic arsenic in the five edible seaweeds based on present data showed almost no hazards to human health.

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