High-throughput mercury speciation analysis of breast milk using HPLC-ICP-MS

Abstract

Despite concerns regarding infant exposure to methylmercury (MeHg⁺), few studies have investigated the separate determination of mercury species in breast milk, and breast milk collection methodology has not been adequately examined.

In this study, a high-throughput analytical method was developed for the simultaneous quantification of inorganic mercury (Hg²⁺) and MeHg⁺ in human breast milk using high-performance liquid chromatography equipped with inductively coupled plasma mass spectrometry (HPLC-ICP-MS).

Quality control was performed using NIST SRM 1953, a certified reference material for breast milk containing Hg²⁺ and MeHg⁺, and the accuracy was 99 %. Furthermore, a 4-month study was conducted in which monthly breast milk samples from 10 participants were analyzed to examine the effects of the collection method (foremilk or hindmilk) and collection time. The median concentrations (ng g⁻¹) for the 80 samples were 0.109 (5th-95th percentile: 0.014–0.365) for Hg²⁺ and 0.220 (5th–95th percentile: 0.046–0.792) for MeHg⁺. The total mercury concentrations obtained via HPLC-ICP-MS analysis were compared with those measured using inductively coupled plasma mass spectrometry (ICP-MS), and a high correlation was achieved (Pearson’s correlation coefficient = 0.946).

ICP-MS analysis was conducted to determine the content of several additional elements in the breastmilk samples, and an association was found between the Selenium and Hg²⁺ contents. In contrast, the MeHg⁺ and fat contents were correlated, with the MeHg⁺ concentration being higher in hindmilk.