McKay, Donald. "Front matter" Multimedia Environmental Models ...

exists between toxicologists and chemists about the relative importance of toxicity
and exposure, but fundamentally this argument is about as purposeful as squabbling
over whether tea leaves or water are the more important constituents of tea.
Most difficult is the issue of genotoxicity, including carcinogenicity, and teratogenicity.
In recent years, a battery of tests has been developed in which organisms
ranging from microorganisms to mammals are exposed to chemicals in an attempt
to determine if they can influence genetic structure or cause cancer. A major difficulty
is that these effects may have long latent periods, perhaps 20 to 30 years in humans.
The adverse effect may be a result of a series of biochemical events in which the
toxic chemical plays only one role. It is difficult to use the results of short-term
laboratory experiments to deduce reliably the presence and magnitude of hazard to
humans. There may be suspicions that a chemical is producing cancer in perhaps
0.1% of a large human population over a period of perhaps 30 years, an effect that
is very difficult (or probably impossible) to detect in epidemiological studies. But
this 0.1% translates into the premature death of 30,000 Canadians per year from
such a cancer, and is cause for considerable concern. Another difficulty is that
humans are voluntarily and involuntarily exposed to many toxic chemicals, including
those derived from smoking, legal and illicit drugs, domestic and occupational
exposure, as well as environmental exposure. Although research indicates that multiple
toxicants act additively when they have similar modes of action, there are cases
of synergism and antagonism. Despite these difficulties, a considerable number of
chemicals have been assessed as being carcinogenic, mutagenic, or teratogenic, and
it is even possible to assign some degree of potency to each chemical. Such chemicals
usually rank high on priority lists. As was discussed earlier, endocrine modulating
substances are of more recent concern. It seems likely that ingenious toxicologists
will find other subtle toxic effects in the future.
3.2.5 Long-Range Transport
As lakes go, Lake Superior is fairly pristine, since there is relatively little industry
on its shores. In the U.S. part of this lake is an island, Isle Royale, which is a
protected park and is thus even more pristine. In this island is a lake, Siskiwit Lake,
which cannot conceivably be contaminated. No responsible funding agency would
waste money on the analysis of fish from that lake for substances such as PCBs.
Remarkably, perceptive researchers detected substantial concentrations of PCBs.
Similarly, surprisingly high concentrations have been detected in wildlife in the
Arctic and Antarctic. Clearly, certain contaminants can travel long distances through
the atmosphere and oceans and are deposited in remote regions.
This potential for long-range transport (LRT) is of concern for several reasons.
There is an ethical issue when the use of a chemical in one nation (which presumably
enjoys social or economic benefit from it) results in exposure in other downwind
nations that derive no benefit, only adverse effects. This transboundary pollution
issue also applies to gases such as SO2,
which can cause acidification of poorly
buffered lakes at distant locations. A regulatory agency may then be in the position
of having little or no control over exposures experienced by its public. The political
implications are obvious.
©2001 CRC Press LLC