Characterization of mercury concentration from soils to needle and tree rings of Schrenk spruce (Picea schrenkiana) of the middle Tianshan Mountains, northwestern China.

• Mercury in soil, needles, and tree rings varied and responded to point pollution source. • The cement factory was the main Hg point-pollution source in our study site. • The Hg accumulation occurred in needles and tree bark recorded the highest Hg concentration compared to the others. • Needles, tree bark, and tree rings are the effective bioindicators for Hg pollution. Mercury (Hg) is a potent neurotoxin in low concentrations and can be transported over a long distance in the atmosphere. Due to Hg accumulation, plant tissues could be used as a low-cost and efficient biological indicator. A significant linear relationship was found between Hg value and organic carbon content in soil, and the highest Hg concentration reached up to the level of 267.1 ng/g in the topsoil layer near the coal-fired power plant. There were evident distance-dependent variations of Hg concentration in needles close to the cement factory. There was a significant Hg accumulation in the needles from all sites, and the highest Hg concentrations were observed in needle samples from the site nearest to the cement factory (HXG1). Hg in tree rings increased by year gradually for all sites, with the highest concentrations of Hg recorded in the site closest to the cement factory. The tree bark of the HXG1 site recorded the highest Hg concentration (65.8 ng/g), reflecting the total Hg deposition from the atmosphere and cement dust associated-Hg loading over the region. Due to the limited data, however, we cannot confirm the possible translocation of Hg from tree bark to outmost tree rings at this time. Overall, we concluded that in our study area, most of the accumulated Hg emissions originated from the cement factory. Even at low Hg concentrations, Hg in tree-rings, needles and barks could not only be used as bioindicators for Hg pollution but also infer the pollution history over long-term periods and to enhance our understandings of the biogeochemical Hg cycling in the forest ecosystems. [ABSTRACT FROM AUTHOR]