Alkalinity of diverse water samples can be altered by mercury preservation and borosilicate vial storage

Benjamin Mos,Symon A Dworjanyn,Isaac R Santos,Ceylena Holloway,Brendan P Kelaher

doi:10.1038/s41598-021-89110-w

Benjamin Mos, Symon A Dworjanyn + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-89110-w

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Abstract

We compared the effects of preservation and storage methods on total alkalinity (AT) of seawater, estuarine water, freshwater, and groundwater samples stored for 0–6 months. Water samples, untreated or treated with HgCl2, 0.45 µm filtration, or filtration plus HgCl2, were stored in polypropylene or borosilicate glass vials for 0, 1, or 6 months. Mean AT of samples treated with HgCl2 was reduced by as much as 49.1 µmol kg−1 (1.3%). Borosilicate glass elevated AT, possibly due to dissolving silicates. There was little change in AT of control and filtered samples stored in polypropylene, except for untreated groundwater (~ 4.1% reduction at 6 months). HgCl2 concentrations of 0.02–0.05% reduced the AT of fresh, estuarine, and ground water samples by as much as 35.5 µmol kg−1 after 1 month, but had little effect on the AT of seawater. Adding glucose as a carbon source for microbial growth resulted in no AT changes in 0.45 µm-filtered samples. We suggest water samples intended for AT analyses can be filtered to 0.45 µm, and stored in polypropylene vials at 4 °C for at least 6 months. Borosilicate glassware and HgCl2 can be avoided to prevent analytical uncertainties and reduce risks related to use of Hg2+.

Highlights

We compared the effects of preservation and storage methods on total alkalinity (AT) of seawater, estuarine water, freshwater, and groundwater samples stored for 0–6 months
The AT of seawater, estuarine water, and freshwater samples stored in polypropylene vials for 0, 1, or 6 months were not different than the AT of their respective benchmark controls, except for mercury and filter + mercury treatments where mean AT was reduced by 0.9–12.7 μmol kg−1 compared to the benchmark controls (Fig. 1)
The mean A T of samples held in glass and polypropylene vials generally declined by 7.6–153.0 μmol kg−1, except for the filter only treatment where A T was generally equivalent to the benchmark control (Fig. 1)

Summary

Introduction

We compared the effects of preservation and storage methods on total alkalinity (AT) of seawater, estuarine water, freshwater, and groundwater samples stored for 0–6 months. It is important that storage and preservation methods are investigated for non-marine water samples given there is growing interest in quantifying the role of estuarine, freshwater, and groundwater systems in the global carbon cycle[12,13]. HgCl2 became established as the primary preservation method for AT samples after 2007 when standard operating procedures (SOP) for analyses of seawater carbonate chemistry were d escribed[7]. There is, substantial concern about global mercury levels and pollution[17] including the use of HgCl2 for water preservation[18], and the applicability of H gCl2 to samples other than seawater.

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