Environmental Engineering Reference
In-Depth Information
Uncomfortable Realities, Including the Arctic Dilemma
As we approach the present day in the POPs and heavy metal stories, the Arctic Messenger
has a few axes to grind.
The first concerns the significance of the epidemiological studies we have been looking
at concerning prenatal and low chronic exposure to POPs and mercury. Much earlier, we
met sixteenth-century physician Paracelsus and his assertion that as the dose of a potentially
toxic substance goes up, so does the risk of effects. You could think of alcohol consump-
tion as a classic example of this so-called monotonic relationship. The simple monotonic
paradigm remains as the foundation for how the toxicity of substances is evaluated. Test an-
imals are given different doses to ascertain the risk posed by a particular substance. The res-
ults are then plotted on a graph to arrive at values called the lowest observed adverse effect
level (LOAEL) and the no observed adverse effect level (NOAEL). Usually, toxicologists
design their testing in anticipation of particular types of effects, such as the appearance of
tumours or birth defects. To be on the safe side before publishing guidance values for long-
term chronic exposure, public health authorities will then add a safety factor to the LOAEL
or NOAEL (the size of which is usually related to how confident they are about the toxicity
mechanisms involved with respect to the animals tested and to humans).
This all sounds straightforward and logical. Chemists can now measure substances at
ever-decreasing levels of concentration, enabling epidemiologists to examine the frequen-
cies of occurrence of a wider variety of potential effects from low exposure levels that can
be discriminated using sophisticated statistics. Furthermore, this can be carried out on hu-
man populations and the vulnerability of different parts of our life cycle can be examined.
What has been found from these studies is that some substances are capable of producing
effects at doses that according to the accepted NOAEL models should not pose a risk. The
neurological and behavioural studies in Arctic and non-Arctic populations involving prenat-
al exposure to POPs and mercury are examples. Furthermore, it is becoming clear from an-
imal studies that a number of substances (particularly those that disrupt endocrine function)
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