G, P Larsson, H Linge, L Okla and N Szarzi. 1998. Biotransport
of organic pollutants to an inland Alaska lake by migrating sockeye
salmon (Onchorhynchus nerka). Arctic 51:478-485.
[Press coverage] Persistent organic pollutants like PCBs, DDT, etc., reach
remote areas of the earth via atmospheric and oceanic transport.
This paper identifies another important mechanism for transport,
animal migration. Ewald et al. show that the quantity of
pollutants carried from the ocean to interior lakes of Alaska by
migrating salmon can actually be significantly greater than that
salmon spawn in freshwater and then migrate downstream to the ocean
where they spend the majority of their lifecycle. Prior to migration
back upstream for spawning, they accumulate lipids both for the
energy required for migration as well as for gonadal development.
As they accumulate these lipids, they also accumulate lipophilic
pollutants, contaminants such as PCBs and DDT.
et al. compared pollutant levels in two populations of a
non-migratory fish, the arctic grayling in the Copper River delta
of SE Alaska. One of the populations lived in a lake to which migratory
salmon had no access. The other population lived in a salmon spawning
lake. In this lake, grayling feed on salmon roe. They also could
acquire pollutants through the food chain based upon degrading salmon
carcasses, an important source of nutrients in this ecosystem.
research revealed several interesting patterns. Most important,
there were dramatic differences between the pollution levels in
the grayling of lakes with vs. without salmon. The authors conclude
that this "biotransport" of pollutants is far more significant
than atmospheric transport, for three reasons.
is quantitatively a larger contributor to local contaminant loads
for lakes within reach of salmon migration. Grayling in the spawning
lake had concentrations of organic pollutants at more than twice
the concentration as those in the salmon-free lake.
reaching the lakes via biotransport are biologically more available
more quickly than those arriving via atmospheric transport. This
is because migrating salmon, their roe and carcasses are fed upon
directly by a host of predators. Atmospherically-transported pollutants
must enter the food web via abiotic processes before they enter
into a bioaccumulation process, and they enter it at much lower
concentrations. Thus the biotransported pollutants are more readily
available for bioaccumulation in the local food web.
pollutants are less vulnerable to environmental degradation because
they are within lipid stores and protected from various oxidation
processes like UV-radiation. This means that some pollutants that
might never be sufficiently persistent to reach the remote lakes
by atmospheric transport could arrive via biotransport.