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

We compared the effects of preservation and storage methods on total alkalinity (A T ) of seawater, estuarine water, freshwater, and groundwater samples stored for 0 – 6 months. Water samples, untreated or treated with HgCl 2 , 0.45 µm filtration, or filtration plus HgCl 2 , were stored in polypropylene or borosilicate glass vials for 0, 1, or 6 months. Mean A T of samples treated with HgCl 2 was reduced by as much as 49.1 µmol kg −1 (1.3%). Borosilicate glass elevated A T , possibly due to dissolving silicates. There was little change in A T of control and filtered samples stored in polypropylene, except for untreated groundwater (~ 4.1% reduction at 6 months). HgCl 2 concentrations of 0.02–0.05% reduced the A T 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 A T of seawater. Adding glucose as a carbon source for microbial growth resulted in no A T changes in 0.45 µm-filtered samples. We suggest water samples intended for A T analyses can be filtered to 0.45 µm, and stored in polypropylene vials at 4 °C for at least 6 months. Borosilicate glassware and HgCl 2 can be avoided to prevent analytical uncertainties and reduce risks related to use of Hg 2+ .