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Seaweed can accumulate inorganic arsenic (iAs) from seawater as hydrogen arsenate (HAsO 4 2- ) in place of the phosphate anion (HPO 4 2- ). While it is rapidly metabolised to organoarsenic species, predominantly arsenosugars and arsenolipids, iAs may be present in seaweed biomass and this poses a potential health concern for consumers of seaweed products. Here, the distribution of total (As TOT ) and iAs was determined in thallus parts of the kelp Laminaria digitata and the intertidal fucoid Ascophyllum nodosum (both Phaeophyceae) using inductively-coupled plasma mass spectrometry (ICP-MS) and high performance liquid chromatography - ICP-MS (HPLC-ICP-MS). As TOT ranged from 36 to 131 mg kg -1 dry weight (DW) in L. digitata, and from 38 to 111 mg kg -1 DW in A. nodosum, with no statistically significant differences between different thallus parts. iAs was detected in all A. nodosum samples, comprising less than 1% of the As TOT content. Concentrations of iAs in L. digitata were significantly higher, ranging from 2.2 to 87 mg kg -1 , increasing through the thallus from the stipe to the decaying distal blades. iAs comprised more than 50% of As TOT in the middle to decaying distal blades. This finding has potential implications for harvesting, processing and use of Laminaria digitata in agri-, food and health applications., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Inorganic arsenic (iAs) in 13 store-bought edible seaweed samples and 34 dried kelp ( Laminaria digitata) samples was determined by a newly developed, field-deployable method (FDM) with the aid of a field test kit for arsenic in water. Results from the FDM were compared to results from speciation analysis achieved by using high performance liquid chromatography coupled to inductively coupled plasma mass spectrometry (HPLC-ICP-MS). The FDM consisted of a simple extraction method using diluted HNO to quantitatively extract iAs without decomposing the organoarsenicals to iAs followed by the selective volatilisation of iAs as arsine (AsH) and subsequent chemo-trapping on a filter paper soaked in mercury bromide (HgBr) solution. Method optimization with a sub-set of samples showed 80-94% iAs recovery with the FDM with no matrix effect from organo-arsenic species in the form of dimethylarsinic acid (DMA) on the iAs concentration. The method displayed good reproducibility with an average error of ±19% and validation by HPLC-ICP-MS showed that the results from the FDM were comparable (slope = 1.03, R = 0.70) to those from speciation analysis with no bias. The FDM can be conducted within an hour and the observed limit of quantification was around 0.05 mg kg (dry weight). This method is well suited for on-site monitoring of iAs in seaweed before it is harvested and can thus be recommended for use as a screening method for iAs in seaweed. [ABSTRACT FROM AUTHOR]