Data from: Assessing environmental pollution in birds: a new methodological approach for interpreting bioaccumulation of trace elements in feather shafts using geochemical sediment data

Environmental trace element composition can have an important impact on
ecosystem and population health as well individual fitness. Therefore,
carefully assessing bioaccumulation of trace elements is central to
studies investigating the ecological impact of pollution. Colonial birds
are important bioindicators since non-invasive sampling can easily be
achieved through sampling of chick feathers, which controls for some
confounding factors of variability (age and environmental heterogeneity).
However, an additional confounding factor, external contamination (ExCo),
which remains even after washing feathers, has frequently been overlooked
in the literature. We developed a new method to reliably interpret
bioaccumulation of 10 trace elements (As, Cd, Cr, Cu, Hg, Ni, Pb, Se, Sn
and Zn) in feathers using chicks of a colonial species: the Greater
Flamingo, Phoenicopterus roseus. First, only shafts were used to remove
ExCo retained in vanes. Secondly, we applied a thorough washing procedure.
Thirdly, we applied a new analytical method to control for ExCo, which
assumes that ExCo is mainly due to adhered sediment particles and that the
relative concentration of each trace element will be similar to the
sediment geochemical composition of sampling sites. We validated this new
methodology by comparing trace element composition and particle
composition (by scanning electron microscopy and mass spectrometry) of
washed and unwashed feathers. The washing procedure removed >99% of
K indicating that most of the ExCo from salt was removed. Scanning
electron microscopy and mass spectrometry revealed that some sediment
particles remained after washing, especially clays which are likely to
severely bias bioaccumulation interpretation. We successfully controlled
for ExCo by calculating the ratio of ExCo due to sediment using the
geochemical fingerprint of sediment samples. Our methodology leads to
conservative estimates of bioaccumulation for As, Cd, Cr, Cu, Hg, Ni, Pb,
Se, Sn and Zn. We have validated a new more reliable method of analysing
trace element concentrations in feathers, which effectively controls for
ExCo, if geochemical sediment data can be meaningfully compared to ExCo of
feathers. We have demonstrated that overlooking ExCo leads to potentially
erroneous conclusions, and we urge that the method applied in this study
be considered in future studies.