Trace Elements
Trace
metals, including arsenic (As), cadmium (Cd), chromium, copper (Cu),
lead (Pb) , nickel, mercury (Hg), selenium (Se), silver, and zinc are
known to concentrate in some marine organisms and can be toxic at high
concentrations, although several are also essential to the maintenance
of life (Dept. of Comm., 1992). Evidence regarding trace metal concentrations
in cetaceans is quite limited. For example, an analysis of samples from
forty-one stranded pilot whales (Globicephala melaena) from Newfoundland
indicated that mercury concentrations in the liver and blubber were
positively correlated with age (Muir, et al. 1988). However, a comparative
study of PCB and trace metal (Hg, Pb, Cd, Mn, Cr, and Se) concentrations
in bottlenose dolphin specimens obtained from the 1987-88 mid-Atlantic
mass mortality indicated no significant difference (with the exception
of mercury) with those of the reference species. Mean concentrations
of mercury were highest in adult females, where it was suggested that
toxicity may be offset by a 1:1 ratio of selenium (Kuehl, et al., 1994).
Meador,
et al. (1993) examined the of levels toxic metals found in pilot whales
from Cape Cod strandings in 1986 and 1990. The results of this study
revealed metal concentrations similar to those found in Newfoundland.
The concentrations of arsenic, cadmium, copper, mercury, lead, and selenium
were measured in 17 adult and 8 fetal animals. Total mercury and selenium
occurred in very high concentrations in the liver and kidney. Concentrations
of Hg, Pb, and Se in the liver were significantly correlated to animal
length (and each other) indicating bioaccumulation over time. As in
the bottlenose dolphins mentioned above, protection from mercury toxicity
was believed to be provided by a 1:1 ratio of Hg to Se. Cadmium concentrations
were consistently high, particularly in the fetal kidney. All non-essential
elements were found in critical fetal tissues which is indicative of
maternal transfer.
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