Seasonal study of speciation of mercury(II) and monomethylmercury in Spartina alterniflora from the Great Bay Estuary, NH

This paper describes the first detailed determination of mercury(II) [Hg(II)] and monomethylmercury cation (MeHg+) concentrations in the salt water cord grass, Spartina alterniflora. The rapid and simple method includes digestion by the new reagent tetrabutylammonium bromide/potassium hydroxide, derivatization by sodium borohydride, and detection by hydride generation–cold vapor atomic fluorescence spectrometry. We speciated mercury in S. alterniflora samples from Chapmanʹs Marsh of the Great Bay Estuary (NH) collected from May to October of the 1997 growing season. The seasonal ranges of concentrations in S. alterniflora are: Hg(II), 3.11–31.4 ng Hg/g dry wt.; and MeHg+, 0.45–4.12 ng Hg/g dry wt. The percent MeHg+ (of total mercury) ranged from 6.23% to 48.1%. The non-parametric Kendall test showed that Hg(II) concentration decreased throughout the growing season, but found no trend in MeHg+ concentrations. This test also demonstrated that percent MeHg+ increased from the first sample in May to late July, then decreased to the last sample in October.