Coconut shell-based salt pot, “Lunu Polkatta,” in mitigating microplastic contamination in food-grade granular crystal salt

Microplastic (MP) contamination of food-grade salt represents an increasing food safety concern, yet practical household-level mitigation strategies are limited. This study evaluated the effectiveness of the traditional Sri Lankan coconut shell-based salt pot (lunu polkatta) in reducing MP contamination in food-grade, iodized, granular crystal salt during storage. Salt solutions were stored in two independent coconut shell-based salt pots for three months under plastic-free conditions, with parallel glass-container controls. MPs were extracted using membrane filtration (0.45 µm), quantified by a dissecting microscope, and selected particles were identified using ATR-FTIR spectroscopy. One-way ANOVA revealed a significant difference in MP counts among the initial salt solution, salt retained inside the shells, and salt accumulated on the outer layers (F = 82.33, p < 0.001). Post hoc analysis indicated significantly lower MP counts inside the shells compared to both the initial salt solution and the outer salt layers, and MP counts in the outer layers also differed significantly from those in the initial salt solution. No significant changes were observed in the control samples stored in glass containers over three months (t = −0.024, p = 0.981). These findings demonstrate that lunu polkatta consistently reduced MP abundance within stored salt through passive, shell-mediated processes, offering a reproducible, low-cost, and culturally integrated approach for mitigating dietary MP exposure.