Tuesday August 9, 2011
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Chris Mason1 and Liam O'Sullivan2
PCBs measured in otter Lutra lutra spraints may derive from two sources, from unassimilated material from the gut or from material excreted in secretions from the anal gland. Otters assimilated 91,6 % of ingested PCBs in feeding experiments (Smit 1990), 8,4 % being passed through the gut with the spraints. Anal gland secretions of rnustelids may be rich in PCBs (Larssen et al. 1990) but preliminary observations have suggested that the contribution of PCBs from anal glands to individual spraints is small relative to the contribution of the diet (M. Smit, in litt.). On this basis the PCBs measured in spraints largely reflect the last meal. Nevertheless with samples of both spraints and otters from a range of sites with differing contamination, one might expect an overall correlation between PCBs in spraints and in tissues. This theme is explored below.
Of 33 otters found dead over the period 1984-90 in southwest Ireland, spraints were present in the rectums of 29. They were stored deep-frozen prior to analysis, as were the livers of the otters. In November and December 1991 207 spraints were collected from sites in southwest Ireland (mainly County Cork) and stored deep-frozen. Methods for sample preparation and analysis are given in Mason & O'Sullivan (1992) and O'Sullivan et al, (in press).
Detailed results of the analysis of otter livers are presented in Mason & O'Sullivan (1992). Of those otters whose rectums contained spraints, PCS concentrations in livers ranged from 0,18-1 23,2 mg kg-1 lipid. PCB concentrations in the spraints ranged from 0,21 - 18,22 mg kg-1 lipid. Although the ranges of concentrations of PCBs in livers and spraints are very different, the coefficients of variation are very similar (157 % for liver samples, 145 % for spraint samples).
PCB concentrations in liver tissue and rectum spraints are significantly correlated (r = 0,68, P < 0.001) and can be represented by the equation:-
liver concentration = 4,69 + 4,62 spraint concentration
The mean PCB concentration in spraints from the rectum (n = 29) was 2,69 mg kg-1 lipid, while the mean concentration in spraints from the environment (n = 207) was 1,45 mg kg-1 lipid. An analysis on long-transformed data showed the differences in means not to be statistically significant (F = 2.27, P>0.05).
That spraints from the rectum and from the environment had mean PCB concentrations which were not significantly different supports the view that PCBs in environmental spraint samples derive largely from the last meal i.e. that proportion of the total PCB ingested which is not absorbed through the gut wall. Spraints from the rectum could not have received PCB secreted from the anal gland.
The correlation between PCB levels in rectum spraints and livers shows that spraints can be used to assess the likely pollution burden of otters. Otters with high body burdens will be feeding in contaminated areas, which will be reflected in their diet and hence their spraints. It should be emphasized however, that, because otters have a diverse diet, even in contaminated sites, some of the prey will have low levels of contamination and spraints collected from a single site may have widely differing concentrations of PCBs, as indeed has bean shown with otters themselves. As many spraints as practicable should therefore be analyzed from a site or region before the likely impact of PCBs on an otter population is assessed.
ACKNOWLEDGEMENTS - This work formed part of a study funded by the World Wide Fund for Nature. U.K.
Larsson, P., Woin, P. & Knulst, J.
(1990). Differences in uptake of persistent pollutants for predators
feeding in aquatic and terrestrial habitats. Holarctic Ecology 13:
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