In vivo uptake of iodine from a Fucus serratus Linnaeus seaweed bath: does volatile iodine contribute?

Seaweed baths containing Fucus serratus Linnaeus are a rich source of iodine which has the potential to increase the urinary iodide concentration (UIC) of the bather. In this study, the range of total iodine concentration in seawater (22-105 µg L-1) and seaweed baths (808-13,734 µg L-1) was measured over 1 year. The seasonal trend shows minimum levels in summer (May-July) and maximum in winter (November-January). The bathwater pH was found to be acidic, average pH 5.9 ± 0.3. An in vivo study with 30 volunteers was undertaken to measure the UIC of 15 bathers immersed in the bath and 15 non-bathers sitting adjacent to the bath. Their UIC was analysed pre- and post-seaweed bath and corrected for creatinine concentration. The corrected UIC of the population shows an increase following the seaweed bath from a pre-treatment median of 76 µg L-1 to a post-treatment median of 95 µg L-1. The pre-treatment UIC for both groups did not indicate significant difference (p = 0.479); however, the post-treatment UIC for both did (p = 0.015) where the median bather test UIC was 86 µg L-1 and the non-bather UIC test was 105 µg L-1. Results indicate the bath has the potential to increase the UIC by a significant amount and that inhalation of volatile iodine is a more significant contributor to UIC than previously documented.