Environmental Engineering Reference
In-Depth Information
food webs. Hg at the surface of the sediment is correlated with
Hg in surface-feeding worms, but deeper burrowing worms
contain greater Hg and meHg, showing that feeding ecology
is important for predicting Hg bioaccumulation.
Mercury can be transported in the atmosphere far from
its source—for example, to the Arctic. It appears that the
long-range transport of mercury from Asia is an important
source of atmospheric Hg to the Arctic. This Hg enters the
water and becomes meHg, which is both toxic and biomagni-
fies in food webs. Mercury concentrations in organisms have
increased and are controlled by a combination of meHg level,
food web structure, and animal behavior (e.g., feeding behav-
ior). Inuit people in the Arctic have high Hg in their blood and
hair. Their reliance on traditional foods such as marine mam-
mals, which are high in the food web, for subsistence means
that they are particularly at risk from Hg exposure, even
though they live very far from any Hg sources.
What are the toxic effects of different metals?
Mercury (Hg), especially meHg, is by far the most toxic. It
affects embryonic development and is particularly neurotoxic,
as is lead (Pb). Any chemical that affects the nervous system is
likely to affect behavior at low concentrations. Reduced feed-
ing and digestion are commonly observed after exposure to
a variety of pollutants, including metals. Decreased feeding
is not only a general response to contaminants, but the poor
nutrition that results can in turn make animals more suscep-
tible to contaminants and other stresses. Many organisms
respond to reduced food intake with reduced activity, which
may mean slower movements and reduced ability to catch
food and to escape from predators. In this way, alterations in
feeding and nutrient uptake can affect a population, and also
could have ecosystem-wide repercussions.
Various metals reduce the respiration and metabolic rate of
many organisms. Scientists usually measure oxygen consumption
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