Waterfowl on lateral lakes of the Coeur d'Alene River and on Lake Coeu
r d'Alene have been poisoned for many years by lead (Ph) from mining a
nd smelting. In 1992 we undertook a study in the area to determine the
importance of sediment ingestion in exposing wood ducks (Air sponsa)
to Pb. Digesta were removed from the intestines of wood ducks collecte
d from contaminated and reference areas. The mean Pb concentration in
the digesta of wood ducks from the contaminated area was 32 p.p.m. dry
weight. The sediment content was estimated to average less than 2% of
the dry weight of the wood duck diet. The lead concentrations in the
digesta were closely correlated with the concentrations of acid-insolu
ble ash, Al, Ti and Fe in the digesta and these four variables are ass
ociated with sediment. Samples containing low concentrations of these
variables also had low concentrations of Pb. These results suggest tha
t most of the Pb in the digesta came from ingested sediment, rather th
an from plant material in the diet. The importance of ingested sedimen
t as a source of lead was unexpected, because wood ducks are surface f
eeders on aquatic plants and they rarely dabble beneath the surface or
feed on the bottom. However, it appears that sediment ingestion is so
metimes the principal route of exposure to environmental contaminants
that are not readily taken up by plants and invertebrates and this rou
te should be considered in risk assessments of waterfowl.