Differential prevalence of arsenic speciation in the kelps Laminaria digitata and L. hyperborea

Large variability in highly toxic inorganic arsenic (iAs) has previously been reported for the kelp Laminaria digitata. This study aimed to compare iAs concentrations in two morphologically similar kelps species (L. digitata and L. hyperborea). Both species contained similarly high total arsenic concentrations. However, whilst L. hyperborea contained only trace levels of iAs (0.363 ± 0.161 mg/kg), iAs constituted the majority of arsenic species in L. digitata (61.6 ± 18.7 mg/kg). Since the identification of iAs relies on retention time of the arsenic species, co-elution of any other organoarsenicals was checked by determination of arsenosugars using HPLC-ICPMS and ESI-HR-MS. Additionally, hydride generation ICP-MS gave comparable results to HPLC-ICPMS analyses. Overall, given the previously observed variability in iAs within and across kelp biomass, and the possibility of commercial processing of mixed-species kelp biomass that may include L. digitata, it may be advisable to verify iAs concentration regularly in seaweed batches destined for any application that exposes humans or animals to risks associated with As toxicity.