Tracing the natural and anthropogenic influence on the trace elemental chemistry of estuarine macroalgae and the implications for human consumption

Overview

Ownsworth and colleagues measured trace elements and arsenic species in brown macroalgae from the Forth Estuary and Firth of Forth in Scotland, with Japanese Laminaria japonica samples used for comparison. The occurrence-relevant results are dry-weight seaweed values for total arsenic, inorganic arsenic, lead, cadmium, and other trace elements. The paper also tests hot-water, cold-water, and soup-style leaching of selected seaweed samples.

Key numbers

The Results section reports total arsenic and speciation:

The iodine Results report overall iodine 67-5061 ppm; Average = 1193 +/- 1676 ppm, 1SD. Japanese Laminaria japonica iodine ranged 1205-4076 ppm, with average 1974 +/- 1717 ppm, 1SD; the RMJK reference material averaged 2308 +/- 63.5 ppm, 1SD, n = 7.

Cooking/leaching experiments used about 2 g of KB-2, KB-3, and HOK2. For total and inorganic arsenic, the soup experiment produced the greatest losses from the solid seaweed: total arsenic (As) 87-91% and inorganic arsenic (iAs) 75-96%. Hot water gave the least loss: total As 21-39% and iAs 3.4-61%. Cold water caused moderate loss: total As 45-91% and iAs 65-66%. The remaining liquids had their highest As and iAs abundances in the soup experiment.

The trace-element discussion uses the highest abundances of lead (Pb) 0.94 ppm and cadmium (Cd) 0.029 ppm in Scottish Laminaria digitata and the highest Pb 0.2 ppm and Cd 0.9 ppm in Japanese Laminaria japonica for source risk calculations. It also notes that lead abundance was reduced in all leach experiments.

Methods (brief)

The study collected 50 brown macroalgal samples from 25 Scottish Forth locations and added Japanese comparison material from Hokkaido and a commercial reference sample. Samples were washed, dried, cut or crushed to less than 5 mm, and stored in glass vials; holdfast and stipe were excluded. Trace metals were measured after 16 N HNO3 digestion by quadrupole ICP-MS. Total arsenic was measured after microwave-assisted digestion by ICP-MS, and arsenic speciation used HPLC-ICP-MS methods described by Bralatei et al. (2017). Cold, hot-water, and soup experiments used about 2 g macroalgae portions.

Implications

This source provides seaweed-food occurrence evidence for total arsenic, inorganic arsenic, lead, cadmium, and other trace metals across Scottish and Japanese brown macroalgae. It is especially useful for preserving species-level differences: Laminaria digitata carried much higher inorganic arsenic fractions than Fucus vesiculosus or Japanese Laminaria japonica. Downstream extraction should keep total arsenic, inorganic arsenic, dry-weight basis, and leached-solid versus remaining-liquid values separate.

Update history

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