Poly(ethylene terephthalate) (PET) bottles used in commercially available mineral water were compared to Teflon bottles for sampling and storage of river water samples prior to mercury determination. The metal concentration was in the range 0.3-2.0 ng L-1 for the reactive species, and in the range 1-9 ng L-1 for total mercury. A paired t-test showed no significant difference in the results for both reactive (p = 0.011) and total Hg (p = 0.024). Storage time was studied for PET bottles, using synthetic samples spiked with 10 ng L-1 Hg2+ ions, using two different types of preservation: (a) by freezing at -18 degrees C, and (b) by the addition of BrCl solution. Both procedures yielded the same results up to the 14th day of storage (ANOVA, p = 0.72 for BrCl and p = 0.12 for freezing). The freezing procedure proved to be more suitable for longer storage times, i.e., up to 40 d (significance level of 0.03, ANOVA).1253549551