Arsenolipids are not uniformly distributed within two brown macroalgal species Saccharina latissima and Alaria esculenta

Brown macroalgae Saccharina latissima (30–40 individuals) and Alaria esculenta (15–20 individuals) were collected from
natural populations in winter in Iceland. The algal thalli were sectioned into different parts (e.g. holdfast, stipe, old frond, young
frond and sori-containing frond sections) that differed in age and biological function. The work elucidated that arsenic (As) was
not uniformly distributed within the two brown macroalgal species, with lower levels of total As were found in the stipe/midrib
compared to other thallus parts. The arsenosugars mirrored the total arsenic in the seaweed mainly due to AsSugSO3 being the
most abundant As species. However, arsenic speciation using parallel HPLC-ICP-MS/ESI-MS elucidated that the arseniccontaining
lipids (AsL) had a different distribution where the arsenosugarphospholipids (AsPL) differed by approximately a
factor of 4 between the sections containing the lowest and highest concentrations of AsPLs. When placing the sections in order of
metabolic activity and an estimate of tissue age, there appeared to be a relationship between the activity and AsPLs, with lower
levels of AsPLs in oldest parts. This is the first time such a relationship has been shown for AsLs. Hence, by applying
sophisticated analytical techniques, it was possible to gain a deeper understanding of arsenolipids in seaweed.