Resumen

DIAS, R. M. S.; DUARTE, L.  y  SEMPITERNO, C. M.. Influence of soil grinding degree on the determination of total mercury concentration . Rev. de Ciências Agrárias [online]. 2007, vol.30, n.2, pp.122-128. ISSN 0871-018X.

According to ISO Standard 11464 (Soil quality - Pre-treatment of samples for physico-chemical analyses) for test samples below 2 g, the air dried soil sample must be ground to a particle diameter ≤ 0.25 mm, in order to have a homogeneous test sample and, therefore, minimize the variability of results. This is quite a time consuming task. The aim of this study was to compare the influence of two different degrees of grinding (<2 mm and <0.15 mm) on the determination of total mercury, with test samples of 1 g. This element was analysed in 7 different soils from Continental Portugal, derived from different parent material. Five representative samples were taken from each soil and manually crushed to pass a 2mm plastic sieve. Each sample was then split in two portions: in one of them, mercury was analysed directly on the fine earth fraction (< 2 mm); on the other portion, mercury analysis was carried out only after grinding the soil sample on a agate mill till it just passed a plastic sieve of <0.15mm. Mercury analysis consisted on the combustion of the soil sample and quantification by atomic absortion spectrometry on an Advanced Mercury Analyser AMA-254, at 253,65 nm. The influence of grinding was dependent on the type of soil, being significant (p≤0,05) in two of them, but even for those soils the levels of mercury are similar. Grinding the soil to 0.15 mm did not increase significantly (p>0.05) the precision of results suggesting that, for the determination of total mercury with a test sample of 1 g, it is not necessary to grind the soil to a fraction less than 2 mm.

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