Fróðskaparrit - 01.07.2004, Blaðsíða 128

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MERCURY IN THE FAROE ISLANDS — A REVIEW OF AVAILABLE DATA
of the Faroes climate may have a role in the
mercury cycling, so as to produce what
may be ideal conditions for the production
of methylated mercury which in turn is ef-
fectively absorbed and maintained in for in-
stance fish. Also of importance for the bio-
availability of mercury deposited on the
ground, is the natural and manmade erosion
that has been shown to increase the mer-
cury mobilisation into runoff water to a
larger extent than was earlier assumed
(Gustin et al., 2002). The implication of
this is not only that the actual influence of
such processes needs to be clarified, but
also that it becomes imperative to keep a
record on and preferentially also a check on
the land use in the watersheds and in the
coastal areas where sampling for environ-
mental purposes are done.
Assuming that the import of mercury
with long-range transported air pollution is
low, it may be of interest to check the mag-
nitude of other potentially important vec-
tors. It has been shown that fish and in par-
ticular whale meat is a likely major source
of mercury in the Faroese diet (Grandjean
et al., 1995a), and it is therefore pertinent to
get an overall estimate of the magnitude of
the mercury flow through the pilot whale
pathway. The total import of mercury with
long-finned pilot whale catches may be es-
timated by assuming that the overall 2
mg/kg mercury in muscle that was found in
10 schools in 1997 (Dam and Bloch, 2000)
is representative, and multiply with the av-
erage amount of whale meat harvested in
the years of 2000 to 2003 of 5233 skinn pr.
year (Bloch, 2004). When one skinn is
equivalent to 38 kg muscle and 34 kg blub-
ber (Bloch and Zachariassen, 1989), this
gives a net import of approx. 0,4 kg mer-
cury per year. Of these 0,4 kg, an average of
64% (Juelshamn et al., 1987), or 0,25 kg,
was present as methyl-mercury, which is
readily taken up by the consumers (EHC
101, 1990). The highest concentration of
mercury in pilot whales is found in the liv-
er (Caurant et al., 1993) where an average
for the school may be in the range of 50 and
100 mg/kg (Juelshamn etal., 1987, HS An-
nual Report 1976/78 and HS Journal 1979-
89; Caurant et al., 1993). Assuming an av-
erage liver mass of 5 kg for the mean of 660
individuals taken each year during 2000-
2003, it can be calculated that the liver will
contribute a mercury amount in the range
0,16 g to 0,33 kg/year which is comparable
to the one in the muscle mass but this
amount is then deposited at sea, as livers
are not eaten.
Compared to the input via the atmos-
pheric pathway, which even if it is not ele-
vated above the common Scandinavian lev-
el, still amounts to a calculated net wet de-
position of mercury of approx. 6,6 ^g/m2/
year (Daugaard, 2003) on the total land
area of approx. 1 400 km2 ( 140 *107 m2)
amounts to 9 kg per year. The dry deposi-
tion was estimated to 10 pg Hg/m2/year
(Christensen, 2003) that gives a total of 14
kg/year. The study of Shotyk et al., (2004)
gives a 1998 rate of total mercury deposi-
tion of 15,9 pg/m2/year from measure-
ments of mercury in dated peat-segments,
which then fits well with the sum of the
measured and modelled amounts in wet
and dry deposition respectively, and which
amounts to in all 23 kg mercury per year.