A new approach for determining trace platinum concentrations in macroalgae and evaluating tissue-specific distribution.

Platinum (Pt), extensively used in automotive catalytic converters and anti-cancer drugs, has led to elevated concentrations in the environment. Monitoring Pt levels in coastal ecosystems is crucial as excessive accumulation may cause ecotoxicological impacts. In this study, Undaria pinnatifida, a common edible macroalgae in Japan known for its high affinity for platinum group elements, was evaluated as a biomonitor for monitoring Pt concentrations and assessing its anthropogenic influences in coastal areas. An analytical protocol using inductively coupled plasma mass spectrometry (ICP-MS) was developed and optimized for Pt quantification in macroalgal tissues. The optimal digestion conditions included 0.24 mL/g of hydrofluoric acid and the addition of 7 mL/g of hydrochloric acid, which effectively reduced white precipitate formation and improved Pt recovery. The established method demonstrated excellent sensitivity, achieving a method blank of 16 ppt and a detection limit of 5 ppt, surpassing previously reported approaches. Applying this optimized protocol, tissue-specific Pt concentrations were determined in different parts of U. pinnatifida collected from various coastal zones. The results revealed significant spatial variations in Pt concentrations among plant organs: concentrations in blades, stipes, and sporophylls decreased from the outer bay to the inner bay, while holdfasts concentrations exhibited the opposite trend. These findings suggest distinct Pt accumulation behaviors between above-ground and below-ground tissues of U. pinnatifida, underscoring its potential for monitoring spatial variations of Pt in coastal environments.