Coprecipitation of Mercury from Natural Iodine-Containing Seawater for Accurate Isotope Measurement

Abstract

Oceans play a key role in the global mercury (Hg) cycle, but studies on Hg isotopes in seawater are rare due to the extremely low Hg concentration and the lack of a good preconcentration method. Here, we introduce a new coprecipitation method for separating and preconcentrating Hg from seawater for accurate isotope measurement. The coprecipitation was achieved by sequential addition of 0.5 mL of 0.5 M CuSO 4 , 1 mL of 0.5 M Na 2 S, and 1 mL of 0.5 M CuSO 4 reagents, which allowed for quantitatively precipitating Hg from up to 10 L of seawater. The protocol was validated by testing synthetic solutions with varying Hg and iodide (I − ) concentrations and by comparing the reaction times of various reagents added. The method resulted in a quantitative recovery of 98 ± 12% (n = 32, two standard deviations, 2 SD) and a relatively low procedure blank (103 pg of Hg, n = 8). The precipitates were filtrated and analyzed for Hg isotopes. Repeated measurements of synthetic seawaters spiked with certificated standard materials (NIST 3133 and 3177) using the entire method gave identical Hg isotope ratios with near-quantitative Hg recovery, indicating no isotope fractionation during preconcentration. A total of six nearshore seawater samples from the Yellow Sea and the Bohai Sea (China) were analyzed using the coprecipitation method. The data showed a large fractionation of Hg isotopes and revealed the possible impact of both atmospheric and anthropogenic inputs to the coastal seawater Hg budget, implying the potential application of this method in studying marine Hg systematics and global Hg cycling.

Online determination of mercury isotopic compositions at ultratrace levels by automated purge and trap coupled with multicollector inductively coupled plasma-mass spectrometry

“…64 The highest concentration was found in one sample from Ya-Er Lake (LW-Y1, 46.1 AE 0.8 ng L −1 ), consistent with the reported data. 63 The isotopic compositions in these water samples ranged from −1.61& to 0.42& for d 202 Hg and from −0.20& to 0.17& for D 199 Hg (Table 2), roughly in the range of published values of natural water (lake and stream water in Canada, d 202 Hg −2.22 to −1.27& and D 199 Hg 0.21-1.91&; 22 coastal seawater worldwide, d 202 Hg −2.85-0.12& and D 199 Hg −0.19-0.56& 13,21,65,66 ). The combined results from the CRMs and natural water suggested high sensitivity with accurate results of the proposed method, which provides the ability to directly measure Hg isotopic compositions in natural water samples and other matrices at low Hg levels.…”

“…20 Additionally, natural water, as a crucial segment of the global Hg cycling, connects the atmospheric and aquatic ecosystems. 21,22 Up to now, it has been difficult to directly analyze isotopic compositions in these samples with low Hg contents by CV introduction.…”

Determination of the Isotopic Composition of Aqueous Mercury in a Paddy Ecosystem Using Diffusive Gradients in Thin Films

“…NIST SRM 997 thallium (25 ng mL −1 in 3% HNO 3 ) was utilized to enable internal inter-elemental correction of instrumental isotopic fractionation. 18 NSBA-DGT was purchased from DGT Research Ltd., UK (Serial No: LSNBN-AP). It consists of 0.4 mm thick NSBA resin gel 38 embedded in 1.5% agarose diffusive gel of various thicknesses (0.40 mm, 0.80 mm, and 1.2 mm) 39 and a 0.14 mm-thick polyether sulfone (PES) membrane filter (Pall, U.S.) with 0.45 μm pore size (Figure 1).…”

“…, rock, soil, sediment, and biomass samples) have been well established. ,, However, the methods for measuring Hg isotopes in natural waters remain less available due to the analytical challenges caused by low concentration (usually at ng L –1 levels). The available methods, based on SnCl 2 reduction of Hg­(II) using a large volume of sample (>10 L) and preconcentration of the produced Hg(0) into a few mL of reverse aqua regia trapping solution, are frequently laborious and time-consuming. , Water in glass containers are prone to degradation and contamination during the collection, preservation, and transportation of field samples . In addition, grab sampling does not allow longer-term monitoring of transformation processes. , A method for an effective, low-cost, in situ collection of Hg in natural waters for Hg isotope analysis is therefore needed.…”

“…The available methods, based on SnCl 2 reduction of Hg(II) using a large volume of sample (>10 L) and preconcentration of the produced Hg(0) into a few mL of reverse aqua regia trapping solution, 17 are frequently laborious and time-consuming. 17,18 Water in glass containers are prone to degradation and contamination during the collection, preservation, and transportation of field samples. 19 In addition, grab sampling does not allow longer-term monitoring of transformation processes.…”