Thursday, July 17, 2014

Selected Readings on Human Health, Disease, and the Environment

The following are responses and summaries of various readings related to Human Health, Disease, and the Environment. 
Life Support: Environmental Endocrine Disruption
Chemicals found in the environment have effects on fetuses much more than on adults because even the slightest of changes in the hormone levels of the undeveloped human can have very drastic consequences.  These chemicals are able to directly bind to or block the hormone receptors making gene transcription initiated by the hormone receptors erroneous.  Similar exposure levels in adults do not show nearly as great physiological changes.  Possible abnormalities include feminization of males, abnormal sexual behavior, birth defects, altered sex ratio, lower sperm density, decreased testis size, altered time to puberty, cancers of the mammary glands or testis, reproductive failure and thyroid dysfunction.  Studies that have been conducted have difficulty in consistency due to the time between exposure and the resultant effects, such as cancer showing decades after first exposure, and finding a control population, since any control population is going to already have some degree of exposure.  Organochlorine contaminated food has been shown to affect the brain development of lab animals and children exposed have shown delayed psychomotor development and increased distractibility.  Some pesticides result in decreased brain density of some nerve receptor types and hyperactive behavior.  Because hormones act at such low levels even the slightest of chemical exposure can result in very bad developmental effects.  One of the main failures of past studies is their focus on the individual rather than the population as a whole, though the size and seriousness of the health threat is still uncertain.  Work by the International Joint Commission, United States and Canada, has begun striving towards the elimination of volatile chemicals.  They hope for zero discharge of chemicals from human activities, analysis of chemical effects from creation to destruction and afterwards, and reversing the burden of proof from showing that a chemical is harmful to showing that a chemical is not harmful before it is allowed to be used.

Body Burdens of Industrial Chemicals in the General Population
The United States produces and uses over 70,000 chemicals and each year over 1500 new chemicals enter the market.   The main problems with these chemicals is that some of them cannot be processed by the metabolic system of the human body and therefore collect in the fatty tissues of people.  According to studies, the general population of the US contain nearly 700 different chemical contaminants within their fatty tissues.  Work began in earnest about three decades ago in assessing the health risks of those exposed either occupationally or environmentally to chemical contaminants.  More recently the National Health and Nutrition Examination Survey has begun regularly studying the chemicals contained within our bodies.  This survey will allow for future reports to show how our health is being affected by environmental exposure.  One of the most important aspects of the survey however is to merely define a control group, or to show what chemicals are expected to be seen in the general population and to what degree they should be found.  One of the most detrimental chemicals on our health are organochlorines.  Organochlorines hold firmly in our environment due to the fact that chlorination changes the stability of organic chemicals.  They are also lipophilic, more soluble in fats than in water, thereby accumulating in fatty tissues.  These chemicals affect all species but carnivores especially.  Being at the top of the food chain humans are especially contaminated due to our high intake of fat based meats which undoubtedly contain the chemicals.  The concentrations of chemicals in the fatty tissues increase with age and therefore the elderly hold a much greater concentration than the middle aged.  Between males and females males generally have a much greater body burden of chemicals due to the fact that females are able to secrete much of the accumulated contaminants through the mammary glands while breast feeding.  There has been little evidence that race plays much of a role in the degree of body burden, however occupation seems to present the greatest variation.  Those who work in high exposure environments are much more likely to have a higher body burden.  It does appear that generations pass contamination down the line causing the next generation to have a much greater body burden. 
Cancer and the Environment
The rate of cancer cases and deaths overall have been decreasing in the last three decades however what is of great concern are the types of cancer which have seen increases in the number of cases and mortality rates.  Some have been linked with exposures, both environmental and occupational, to known carcinogens.  The mortality rates of breast and gynecological cancer in females, prostate and lung cancer in males, and colorectal cancer in males and females has declined.  The first half of the 1990s saw a two and half percent decline in cancer deaths, however the rate of decrease has not nearly kept pace with other advances in medicine such as with heart disease and stroke considering that a similar amount of resources has been devoted to the reduction of cancer.  Cancer may soon overtake heart disease as the United State’s number one cause of death.  In 1981 Doll and Peto ousted tobacco and diet as the greatest causes of cancer in the U.S. while occupational and industrial pollution made up a small percentage.  More recent studies have more or less backed up these claims while also adding that exposures to electric and magnetic fields and environmental estrogens may also play an important role.  Exposure to carcinogens in the work place is usually greater than to those in the community, however community exposure can be much more dramatic as it includes infants, children, and the elderly who are more susceptible to the effects.  Therefore environmental regulations are much more strict than workplace related legislation for similar substances. 
Climate Change:Health and Environmental Effects – US EPA
Rising temperatures cause glaciers to shrink, permafrost to thaw, shorter length of ice freeze in river and lake areas, longer growing seasons, and shifts in plant and animal ranges.  As industry continues to contribute more carbon dioxide, methane, and nitrous oxide to the atmosphere global temperatures will continue to rise.  Climate change can affect human health both directly and indirectly: directly such as an extreme increase in temperature could lead to loss of life, while indirectly change can enable infective parasites to have a greater range thereby endangering previously unexposed populations.  An increase in average temperature will increase the number of cases of respiratory disorders due to pollution.  Temperature increase, rainfall patterns, concentrations of CO2, pollution levels and more extreme weather events, could have detrimental effects on agriculture.  These same causes could also limit the species variation and geographical dominance of American forests.  Extreme and quick climate change could have a very detrimental effect on ecosystems, especially on the biodiversity of species.  Organisms have adapted to the climate over millions of years, however the speed of the current climatic changes is virtually instantaneous to evolutionary adaptation.  Higher temperatures will result in an estimated rising of the sea level from .6 to 2 feet over the next century.  These higher water levels will result in the flooding of low lying lands, erosion of beaches, and salt contamination of water tables.  Climate change could increase the incidences and degree of extreme weather events: less or warmer cold days and more or warmer hot days, longer more frequent heat waves, more and lengthier heavy precipitation events, larger areas affected by drought over longer periods of time, more drastic hurricanes and tropical storms, and an increase in extreme sea levels would have a very bad affect on agriculture, human health, industry and society, and water sources.

Readings above may have been drawn from the following sources:
Six Modern Plagues and How We are Causing Them, Mark Jerome Walters; Shearwater Books, 2003, ISBN 155963992X
Life Support, The Environment and Human Health, Michael McCally, editor, MIT Press, 2002, ISBN 0-262-63257-8
Rx for Survival,  Philip Hilts, Pengquin Books.  ISBN 0-7394-6974-6
Emerging Infectious Diseases,  Stuart A. Hill, Pearson Eductation Inc., publishing as Benjamin Cummings.  ISBN 0-8053-3955-8
Under the Weather:  Climate, Ecosystems and Infectious Disease, National Research Council, National Academy Press.  ISBN 0-309-07278-6

This article originally written October 21st, 2008 for OU IPE 3913 - Human Health, Disease, and the Environment.

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