FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

F. Roos-Barraclough et al. / The Science of the Total Environment 292 (2002) 129–139
Table 1
Results of the analysis of six certified standard reference materials
using the suggested program on the Leco AMA 254
SRM Measured wHgx n Certified wHgx
(ngyg) (ngyg)
NIST 45.1"0.8 13 44"4
1515
NIST 32.3"1.4 17 31"7
1547
NIST 118.9"0.9 2 150"50
1575
NIST 99.2"2.7 2 93.8"3.7
1630a
BCR 16.6"0.5 2 21"2
281
IAEA 170.2"0.1 2 200"40
336
to 0.025 ng Hg (ns2).It was therefore concluded
that the effect of the length of program was
negligible with respect to increased blank values
due to increased Hg from the oxygen supply during
longer programs.
The result of 10 analyses of in-house peat
standard OGS 1878 P, which were made up to
95% water (RH OG18
V), using the recommended
2
y1
drying times, was 84.0"18.0 ng g Hg: a relative
standard deviation of 22%.The result of 10 anal-
y1
yses of the dry material was 76.6"2 ng g Hg:
a relative standard deviation of 8%.Thus, analysis
of dried samples appears to reduce the standard
deviation of the results.
Analysis using a decomposition time of 125 s
resulted in the lowest standard deviation among
10 analyses of OGS 1878P (1.9% compared to
5.15, 8.87 and 9.68% at 100, 150 and 175 s,
respectively).Six SRMs analysed using this program
gave the results shown in Table 1.
3.2. Effect of prolonged drying at high temperatures
in unfertilised and artificially fertilised peat
The results (Fig.1) show overall trends in
changes in Hg concentration at a rate of 6.7 ng
y1 kg y1 h y1 at RT, 2.48 ng kg y1 h at 30 8C, y
y1 2.36 ng kg y1 h y1 at 60 8C, y3.12 ng kg y1 h
y1 at 90 8C and y8.52 ng kg y1 h at 105 8C for
these samples (Table 2).Therefore, it appears that
there is an increase over time in wHgx in peat,
133
which is left to air dry at low temperatures,
probably due to absorbance of Hg from the lab
air.In contrast, there is a decrease in Hg concentrations
in samples dried at higher temperatures,
probably due to loss of Hg by volatilisation.This
loss is so gradual that drying at low temperatures
for a few hours should not measurably affect the
Hg concentrations.However, prolonged drying at
higher temperatures could result in a significant
loss of Hg and extensive drying at room temperature
could give rise to significant Hg
contamination.
Artificial fertilisation of the peat was carried out
to stimulate microbial activity.Artificial fertilisation
has been found in the past to increase Hg loss
by volatilisation (Lodenius et al., 1983).Average
changes in Hg concentrations over the whole
y1 y1
temperature range were y0.26 ng kg h for
y1 y1
N-fertilised peat, y2.38 ng kg h for P-
y1 y1
fertilised peat, 1.18 ng kg h for K-fertilised
y1 y1
peat, y3.08 ng kg h for N, P and K-fertilised
y1 y1
peat and y0.28 ng kg h for unfertilised peat.
These results indicate that the addition of phosphorus
in particular increases mercury losses, probably
due to increased microbial activity.The
addition of potassium, however, appeared to
decrease Hg loss.
3.3. Effect of air-drying at room temperature on
Hg content of peat
The Hg concentration profile in the Arctic peat
core was measured once using samples which had
remained frozen since collection and once using
samples which had been air-dried at RT in a cleanair
cabinet overnight.Both sets of samples were
corrected for bulk density and the results are
displayed as volumetric concentrations (ng cm , y3
Fig.2).The average difference in Hg concentration
between Hg content of the samples was 0.3"0.9
y3 ng cm , ns63, with the wet samples being on
average slightly lower in Hg than the air-dried
samples.This difference can be accounted for by
a combination of the error involved in the bulk
density determination and uptake of Hg from the
lab air during air-drying.However, the previous
experiment suggested a rate of increase in Hg
y1 y1
concentration of 6.7 pg g h during air drying