Total mercury (THg) concentrations in soil, roots and shoots were
measured by thermal decomposition atomic absorption spectrometry
with gold amalgamation (LECO model AMA-254), as described by
Costley et al. (2000). The analysis is performed directly on the sample
(sample mass varied in the range 5–150 mg d.w.), without digestion
or specific pre-treatment, avoiding mercury losses or contamination as
well as matrix interferences. At least three replicate measurements
were carried out for each sample (acceptable relative standard deviation
among replicates: b10%). Several blanks (i.e. an empty sample nickel
boat) were run before and between sample analyses to ensure that
mercury was not being carried over between samples. Detection and
quantification limits obtained through blank measurements (n = 20)
were 0.01 ng Hg (defined as the mean value plus 3.3 standard deviation)
and 0.03 ng Hg (defined as the mean value plus 10 standard deviation),
respectively