Persistent Organic Pollutants and Heavy Metals (Including Mercury) - The Changing Arctic Environment: The Arctic Messenger - page 130

gineer would use the term fugacity . However, the Arctic Messenger wants us
all to understand what is going on, so we will explain it this way. Any sub-
stance - whether it be a solid or a fluid - will have a tendency for its molec-
ules to escape as a gas. This escape activity or volatility largely depends on
temperature. A semivolatile substance is one where the balance of the beha-
viour to evaporate or to condense takes place over the range of environmental
atmospheric temperatures we find in nature. If it is warm, the substance will
tend to evaporate. If it is cold, it condenses.
Something else was intriguing. Metals are natural, but gaseous mercury and lead can travel
in the atmosphere and another form of methylmercury can biomagnify.
We found it remarkably easy to come up with a working hypothesis to explain the
puzzle when we used the overseas expertise from Garth's 1989 evaluation and from discus-
sions with Richard Addison, Len Barrie, Dennis Gregor, Lyle Lockhart, Derek Muir, Don
Mackay and Ross Norstrom. Readers have probably worked it out already. Organochlor-
ines released into the environment in low or mid-latitudes evaporate into the atmosphere,
where they stay until the air reaches a cold enough temperature for them to condense. This
is regulated by their vapour pressure (or fugacity) characteristics. On a warm day, up they
go again until another cold spell leads to condensation. In this way, they progressively hop
towards the Arctic (the grasshopper effect), where they are trapped by the cold temperat-
ures (cold trapping). The ability to resist degradation robs the Arctic of a mechanism to get
rid of them, while their efficient biomagnification leads to amplification in Arctic top pred-
ators and people who use these animals as their main source of food. The end result can
be contaminant exposure at levels considered to be of concern in top predators (including
people) even when the ambient concentrations in water and air around the animal are close
to detection limits.
Wewillpausehereforanotherdigression.Iremarkedearlierthatthewidespreadaccu-
mulation of organochlorines from mid-latitude sources in the Arctic should not have come
as a surprise. Richard Addison was reporting organochlorines in beluga whales and ringed