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

In Part I of this blog, we looked at the possible health effects of environmental pollutants. In the conclusion we will look at their unexpected and unpredictable effects.

There is also no doubt some of the environmental chemicals we are exposed to in our every day lives are harmful if taken in large enough amounts. Certainly, many of the pesticides, metals such as arsenic, lead and mercury and a great number of the industrial waste products are considered toxic. Yet governments believe in the amounts we are exposed to, they do not pose a risk to our health. The main reason for this – and this applies to most environmental chemicals – is the amounts finding their way into our bodies are so minute it is difficult to see how they can be harmful. Unfortunately, it may not be this simple. There is plenty of evidence – from reputable medical and scientific sources – to show tiny amounts of enviromental chemicals and pollutants can produce quite unexpected effects. A good example is the well known herbicide, glyphosate – commonly called Roundup®. At the amounts suggested by the manufacturers, it is highly toxic to broad leaf plants but apparently safe to humans. But a surprisingly different effect has been observed at concentrations much lower than those required to kill weeds. At these tiny non-toxic doses, like those generated by the drift of glyphosate spray from neighbouring farms, the herbicide may actually stimulate growth of certain plants (7). Another example is the antioxidant resveratrol, present in food and abundant in red wine. Its presence in red wine is thought by some to explain the “French paradox” – ie the apparently low incidence of heart disease in the French despite a relatively high intake of butter and cream. At higher concentrations, resveratrol can kill a variety of different cancer cells. This is the good news. However, the bad news is at much lower doses, the antioxidant may actually stimulate tumour growth, at least in the test tube (8).

So, these examples show we cannot always predict what a chemical substance will do at very low concentrations. Some scientists refer to this phenomenon as “hormesis”(8). While there was initially a fair amount of skepticism amongst scientists over this, there is increasing acceptance there is a degree of unpredictability about how chemicals can affect biological systems at low concentrations. Indeed, this unpredictability is a good example of what Donald Rumsfeld, the former US Defence Secretary termed “a known unknowns” in his now infamous press briefing of February 12, 2002.

But wait: It’s even more complicated than this!

While small amounts of certain chemicals can produce significant effects on their own and sometimes the effects may be unexpected, what happens if we are exposed to mixtures of tiny amounts of different chemicals, each with their own effects? This is important because, our food and water and the air we breathe, contains a cocktail of different substances and pollutants. We already know certain chemical mixtures can act synergistically with each other. “Synergism” is when the combined effects of two or more substances is much greater than would be expected from the activity produced by each of the individual substances. A bit like 1 + 1 = 5. The phenomenon of synergism has been well known for many years and can explain the serious side effects from certain drug interactions. Synergistic effects have also been observed in the immune system. Here, exceedingly small amounts of bacterial cell remnants, (even in the fractions of a microgram range), can work with certain proteins produced naturally in the body to trigger massive responses (9).

There is evidence “pesticide cocktails” can act synergistically on animals (10), so it is likely various pollutants will also act synergistically in humans.

So just because there are only trace amounts of environmental chemicals in our food, water and air in amounts considered harmless, it does not necessarily follow they really are totally inert and harmless. The number and diversity of chemicals in our bodies is significant and, with the increasing industrialisation of two of the most populous countries on the planet (India and China), it will doubtless increase unless steps are taken to regulate their release.

Now before we become too neurotic about it, it should be emphasised we are not totally defenseless against this chemical burden because each of us have exquisite mechanisms for getting rid of potentially harmful substances. Our organs, particularly our livers, have the capacity to detoxify the chemicals we come in contact with, while our kidneys work very hard to excrete what may harm us in the urine. If the body does not know what to do with them it can even remove them from our blood and store them in certain parts of our bodies like our hair and fat, where they are less likely to cause harm. Despite this, the daily chemical assault on our bodies is relentless and ongoing. The worry for us is this chemical assault has the potential to do harm and may, in ways we do not understand, even threaten those systems in our bodies like the immune and gene repair systems, which correct and heal any damage.

So called “environmental factors” have been thought to contribute to degenerative diseases like cancer, heart disease, Parkinson’s disease, diabetes, chronic fatigue syndrome etc. We know these factors can include viruses, bacteria, diet, UV radiation, radioactivity and exposure to certain chemicals like tobacco, alcohol and asbestos. What we do not know is what effect the small- and long-term doses of environmental chemicals may have in causing disease, which is where Mr Rumsfeld’s “known unknowns” come in. There is certainly increasing evidence they do. A recent publication has received the support of the American Heart Association, which reported air pollution can contribute to cardiovascular disease (11). There is yet other evidence of a link between air pollution and respiratory diseases (12). The jury is still out on whether the small amounts of chemicals in our food and water contribute to disease. It should be remembered however, it was a long time before we were certain the chemicals in tobacco smoke contributed to lung cancer. Because we do not know, it makes sense to reduce our exposure to environmental chemicals as much as we can. There are ways to do this, some of which have been mentioned in our earlier blogs. More detailed information is also available in two books available for purchase through this website (“The Silent Threat” and “Organic Food: A Guide for Consumers”). A sequel to “The Silent Threat” is also in preparation and will be published on this website in the next few months. In this coming book we will discuss the pollutants released from different human activities like industry, mining, manufacturing and in the workplace and examine the evidence for their effects on our health.

Meanwhile, 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.
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(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
(7) Velini, E. D., et al; Pest. Manag. Sci., 64, 489-496, 2008.
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/18293284
(8) Calabrese, E. J. et al; Hum. Exp. Toxicol., 29, 980-1015, 2010.
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/21115559
and
Calabrese, E. J. et al; Hum. Exp. Toxicol., 29, 1034-1037, 2010.
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/21115567
(9) Rothstein, J. L. and Schreiber, H.; Proc. Natl. Acad. Sci. USA, 85, 607-611, 1988.
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/3422444
Full text available online at: http://www.pnas.org/content/85/2/607.long
(10) Nørgaard, K. B. and Cedergreen, N.; Environ. Sci. Pollut. Res. Int., 17, 957-967, 2010.
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/20077025
(11) Brook, R. D., et al; Circulation 121, 2331-2378, 2010.
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/20458016
Full text available online at: http://circ.ahajournals.org/cgi/reprint/121/21/2331
(12) Faustini, A., et al; Eur. Respir. J., January 11, 2011 (Epub ahead of print).
Abstract available online at: http://www.ncbi.nlm.nih.gov/pubmed/21233266
(13) What fish should pregnant women avoid? U.S. Food and Drug Administration (FDA), March 2004.
FDA / EPA Health Advisory available online at: http://www.fda.gov/Food/FoodSafety/Product-SpecificInformation/Seafood/ConsumerInformationAboutSeafood/ucm122607.htm

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