Health effects of long term pollutant exposure – A known unknown?: Part I

In his 1973 book, “Small is Beautiful: A Study of Economics As If People Mattered”, the German born economist E. F. Schumacher stated:

“No degree of prosperity could justify the accumulation of large amounts of highly toxic substances which nobody knows how to make “safe” and which remain an incalculable danger to the whole of creation….”

The “substances” Schumacher was referring to were the radioactive waste products generated by the nuclear power industry. We will discuss the nuclear power industry and the background and implications of the full Schumacher quote at another time. Nevertheless, this quote equally applies to the great number of highly toxic chemical pollutants realeased into the environment on a daily basis through human activities. And as they have also not been “made safe” before release, they pose a potential threat to our health and wellbeing. Rather than accepting responsibility for cleaning up our messes, we either rely on nature to make them “safe” for us or hope we are diluting them enough to make them safe by dumping them into something as large as a river or ocean: The “Dilution is the solution to pollution” approach. Certainly, many of the toxic chemicals from industrial and agricultural waste products are gradually degraded into less toxic materials by nature, either through chemical processes, like heat, light and UV radiation, or through the action of microorganisms in the soil or water. But is it really this simple?

Of course there are a number of important assumptions we make about this whole process. First, we assume there is negligible impact on the environment while nature detoxifies our waste products for us. We know this is not true as there are numerous examples of the harmful effects of our waste products on living organisms (1). After all, if we use, for example, chemical sprays to kill insects or fungal pests, it is not surprising there is – in a phrase so beloved by the military – “collateral damage”. These sprays do not discriminate between pests and non pests and therefore may and do kill beneficial organisms as well. A second assumption is whatever we release into the environment will be broken down fairly rapidly before it causes any harm. Unfortunately, this isn’t necessarily true either as some substances are degraded very slowly or not at all. Some examples include the polychlorinated biphenyls (PCBs), the polybrominated dipheyl ethers (PBDEs), organochlorine pesticides like DDT and heavy metals like lead and mercury to name but a few (2, 3 and 4). Radioactive pollutants like those released from Chernobyl and, more recently, Fukushima also fit into this category. And while microorganisms may be able to chemically alter radioactive pollutants, whatever chemical form they are in is still radioactive, sometimes for decades or generations to come. The problem with these more resistant substances is they can be taken up by both marine and land animals as food and so can enter our food chain (4). Indeed, through the phenomenon of biomagnification, there can be a significant build up of toxic substances in the tissues of animals we rely on for food, particularly fish. So much so as to cause poisoning (eg mercury poisoning in Minamata, Japan, 4). Sadly, these are not isolated incidents with governments advising certain vulnerable members of the community, in particular pregnant women and nursing mothers, to restrict their intake of certain foods because of the potential health effects of heavy metal contamination (13).

Yet another assumption we make needs exploring. This assumption is even the pollutants which are not degraded are present in amounts so small compared to the vastness of the planet, they could not possubly have any impact on humans. Is it really true tiny amounts of chemicals are without any effect? The answer to this question is an emphatic no. The power of how tiny amounts of substances can produce dramatic effects on us was very well illustrated on a recent trip to the country when we stopped at a farm and bought a punnet of strawberries which we put on the back seat of the car. Within minutes, the fragrant smell of fresh strawberries filled the car. Of course, this phenomenon is not unique to strawberries but can be observed with many different fruits. The volatile constituents of fruit, some of which provide the characteristic smell, are released in tiny amounts into the air. From there they enter the nasal passages where they bind to special receptors triggering signals which are sent to the brain. Providing we have a normal sense of smell, the brain is able to identify the source and induce the appropriate physiological responses in the body. What is particularly interesting is it requires only tiny amounts of the volatile chemicals from the strawberries to set the process off, perhaps as little as millionths of a gram. And yet, these tiny amounts of volatile chemicals set up a whole cascade of biochemical and physiological processes in my wife and I, cascades many times larger than the original signals which set them off. We both started to salivate, our stomachs rumbled and our hunger intensified so much the strawberries never made it home!

There are many other examples of how small amounts of chemicals can produce significant effects. While everyone knows how important vitamins are to keeping us healthy, most people would be surprised to learn how little we need on a daily basis to do thye job. For example: Around 2-3 micrograms (a microgram is a millionth of a gram and much smaller than the head of a pin) of vitamin B12 on a daily basis is enough to keep us from developing a form of anaemia; 5 micrograms of vitamin D daily is sufficient to prevent rickets (a bone disease) in children; and 10-20 micrograms of vitamin K is enough to prevent bleeding in very young children (5). Conversely, people would also be surprised to learn how little of certain poisons are required to cause illness. For example, one microgram or less of the botulism or tetanus toxins is sufficient to cause harm or even death (6). There are other, more common examples of how small amounts of chemicals have the potential to cause harm or even death. People with severe allergies to certain foods may need to eat as little as a few milligrams (thousandths of a gram) of peanuts, egg or milk to cause a potentially fatal reaction. The actual amount of chemicals responsible for triggering these responses is much less than this of course, perhaps in the tens of microgram range, because the active component in the food causing the allergy, mostly a protein, may only be a very small proportion of the food components. There is therefore no question amounts of chemicals we consider tiny do have the potential to keep us healthy or even kill us. It all depends on the nature of the chemical, the length of time we are exposed (smoking and asbestos exposure are good examples of the influence of time) and the various bodily processes it affects. So small dose exposure of some things can be lethal.

In Part II of this blog, we will look at the unexpected and unpredictable effects of some of these environmental pollutants.

Until Part II, stay happy and healthy.

References

(1) Hamlin, H. J. and Guillette, L. J., Syst Biol Reprod Med 56, 113-121, 2010.
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/20377310
(2) Sharma, C. M., et al; Environ. Pollut. 157, 2452-2458, 2009.

Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/19329237
(3) Ikonomou, M. G., et al; Environ. Toxicol. Chem. 30, 1261-1271, 2011.

Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/21360729
(4) Ekino, S., et al; J. Neurol. Sci., 262, 131-144, 2007.

Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/17681548
(5) Garrow, J. S., et al; Human Nutrition and Dietetics. 10th Edition. Published by Churchill Livingstone, 2000.
(6) Toxins of Biological Origin; Environmental Health and Safety, University of Florida.

Available online at: http://www.ehs.ufl.edu/bio/toxin.htm

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