Fróðskaparrit - 01.07.2004, Side 81

KYKSILVUR í LIVUR, EGGUM OG FJØÐUR
CEPPHUS GRYLLE FAEROENSISIN THE FAROE ISLANDS
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The mercury concentration in the two
feather samples (from the back and under
one wing) was not significantly different (at
P=0,05) in the two locations Hestoy and
Sveipur (Mann-Whitney U-test) and thus
the two samples may be seen as a unity.
Also liver samples from the birds whose
feather mercury concentration was deter-
mined were analysed for mercury. Thus a
comparison of feather mercury concentra-
tion to that of the liver is possible (Fig. 4).
In the plot, the data series from the two sites
Sveipur and Hestoy are shown separately
regardless of the fact that there, as already
mentioned, were no significant differences
in the feather mercury concentrations at
these two locations. The samples from
Sveipur consist of liver and feather from 4
adult females and 3 juvenile males, where-
as the Hestoy sample is composed of tissue
from 3 adult males (hereof one outlier
Cg0058) and five juveniles of both sexes.
The four Hestoy samples whose feather
mercury concentration is elevated in com-
parison to the inserted regression line for
the Sveipur material (Fig. 4) are juveniles.
The outlier Cg0058, an adult male, in the
Hestoy batch had a feather mercury con-
centration of 21,9 mg/kg and a liver mer-
cury concentration of 3,77 mg/kg (Olsen et
al., 2003).
The overall mean feather and liver mer-
cury concentrations were 4,72 mg/kg and
1,11 mg/kg respectively, thus with a ratio
between them of 4,2. A standard value for
this ratio of feather to liver mercury con-
centration of 2,3 (fresh weight) has been
suggested (Appelquist etal., 1985; Thomp-
son et al., 1990). However, the validity of
this ratio has been questioned (Thompson
et ai, 1990). Given the fact that mercury is
excreted from the liver (Stickel et al., 1977)
but once deposited in the feather is no
longer bioactive, it is plausible that such a
ratio may only be valid if all parameters in-
fluencing the mercury concentration are
constant.
Eggs
Mercury concentration in black guillemot
eggs is given in Tab 1 along with data on
the fractionation of stable isotopes of nitro-
gen and carbon in these (Olsen et al., 2003;
Ólafsdóttir, 2002). Judging from this data
there appears to be a trend of decreasing
mercury concentration at both locations of
egg sampling, going from a mean 0,46
mg/kg mercury at the two sites in 1999 to
0,33 mg/kg in 2001. This decrease is equiv-
alent to a relative decrease of almost 30%
from 1999 to 2001, and represents quite a
substantial change. At the same time there
is a gradual increase in 615N, going from
an approx. average of 10 %c at the two lo-
cations in 1999 to approx. 12 %c in 2001,
that is an increase of 18% since 1999. This
increase corresponds to roughly a Vi trophi-
cal level elevation and could have been ex-
pected to be accompanied by an increase in
mercury concentration, but this expected
increase is not found. On the contrary a de-
crease is seen. In addition to the observed
decrease in egg mercury concentration,
there is a parallel decrease also in PCB
(Hoydal et al., 2003). This is seen as an in-
dication that the reason for the decrease
may be that the birds have a decreasing in-
take of “typical” mercury and PCB carriers,