Environmental Geology
Geol 406/50

Module 11
Environmental Health

Reading Assignment:  Chapter 13

Email your two tasks to:  hughscot@isu.edu

I. INTRODUCTION

Disease and Geology have always been intertwined.   Illnesses tend to arise from imbalances in nature.  This relationship reaches to the beginning of mankind's cultural interactions.  Early societies suffered from cholera, typhoid and other diseases brought about by rapid population expansion before proper sanitation measures existed.  People tended to believe that the basic, natural elements were "good/pure". Elements such as metals, fire, water and soil were highly valued.  The Romans believed this (for example) yet lead poisoning may have been what caused the downfall of the Roman Empire! The Romans relied heavily upon lead and constructed their aqueducts, glasses, plates, utensils and all sorts of other things from the metal.

Industrialization saw a rise in lung cancer, asthma and similar diseases.  The disturbance of forests and rivers has also brought disease. For example, the construction of the Aswan Dam in Egypt and the resulting stagnation of the Nile waters has lead to severe outbreaks of schistosomiasis - "snail fever".   The snails love to breed in the stagnant river water. As the disruption of our environment quickens its pace, who knows what the future will bring.

II. EARTH'S GEOCHEMICAL CYCLE

On earth's surface we tend to think in terms of the non-living crust and the living plants and animals.  Although very different in some ways, all things are composed of elements - both living and non-living.  Elements are broken into three categories which are defined on the basis of concentration.

1. TRACE ELEMENTS -   <1,000ppm on average  [ppm is either mg/kg (m/m) or ml/L (v/v)]
2. MINOR ELEMENTS -  1,000 - 10,000ppm
3. MAJOR ELEMENTS -   >10,000ppm (or about 1% by volume)

Let's compare
mineral makeup!

All of the other known elements occur as trace elements.

There are a number of "essential" trace elements required for health.
These tend to be toxic in larger doses.

Where are elements found?

Elements are found in everything.   They are in the lithosphere, the biosphere, the hydrosphere and  the atmosphere.

Where do elements go?

Elements move through the different spheres. Primarily via the ROCK CYCLE (through weathering, transport, lithification etc.) and the HYDROLOGIC CYCLE (through evaporation/transpiration, condensation, precipitation etc.)

What frees trace elements from rocks?

Both natural and artificial mechanisms free trace elements from rocks.  The primary natural mechanism is WEATHERING which can be chemical or mechanical.  The primary artificial process is MINING.  When you comminute (crush) rocks you drastically increase their surface area to volume ratio.   While this does decrease ability to transmit water, it increases interactions with water, oxygen and other substances dramatically.  This results in a greater production of leachates and solutions that may be loaded with trace compounds.  For example, mine tailings are highly susceptible to leaching and are major sources of trace pollutants such as Zn, Cu, As, Hg, S and Pb.  For this reason mining operations using chemical leachates must construct leach pads.  Leach pads consists of a clay liner overlain by a plastic liner.  Crushed rock is placed on the leach pad and treated with chemicals to dissolve sought after metals.  The resulting metal containing leachate is trapped by the liner and collected.

Trace metals freed from rock can undergo many types of interactions and reactions.  Examples include:

1. COMPLEXING - Metals are very susceptible to complexing. Complexing can dramatically increases solubility which in turn enhances transport and dispersion.

2. ACIDIFICATION - Example: SO4- (sulfate ion) + H+ (hydrogen ion) ----> H2SO4 (sulfuric acid)

3. REACTION - Sulfide compounds react readily with trace metals such as Cu, Pb, Zn, Hg, and Fe.
                           Oxides react readily with trace metals such as Cr, Ti, and Al.

III. DOSE, RESPONSE HEALTH

In the early 1960's T.J. Chow wrote a book called "Our Daily Lead".  He was inspired to do so by the discovery of a significant concentration of lead polluting our atmosphere.  A scientific experiment measuring Pb isotopes in rocks picked up on this atmospheric contaminant.  It was quickly realized that the lead in the air was coming from automobile emissions.  This inspired new legislation and technologies that reversed the problem.

Lead is not an essential trace element for life, but many other metals are. Cobalt, selenium, zinc, iodine, chromium, iron and others are all necessary for the proper functioning and maintenance of living organisms.  Above certain concentrations, however, these metals become toxins. For example, fluorine is required for the formation of teeth and bones.  A person is considered to be fluorine deficient at concentrations below 1ppm.  When fluorine concentration exceeds about 7ppm, excessive bone formation occurs.  If fluorine concentrations continue to increase, death may result. What can cause excessive exposure to trace elements? Direct contact, bioaccumulation and a number of other mechanisms may all serve as exposure vectors.

DOSE/RESPONSE CURVES are used to determine at what concentrations trace elements will cause harm or death. Each element has its own characteristic dose/response curve.

READ PAGE 353 IN YOUR TEXT AND LOOK AT FIGURES 13.3 AND 13.4
BECOME FAMILIAR WITH THIS MATERIAL!
I WILL POST A DETAILED FIGURE ON THIS LATER IN THE WEEK. 

Geology plays an important role in determining trace element status.

SOME FACTS:

• There are zinc deficiencies in 32 states. This is caused by a lack of zinc in the soils and by poor soil management practices.
• Selenium is an essential trace element and is beneficial at concentrations up to about 1ppm. At concentrations over 4ppm it becomes toxic.  Strangely, there are areas that have very high selenium content in the soils yet have no related toxicity problems, while other areas with a low selenium content do have problems.  In order to understand this phenomenon you must take other factors into account.  The average concentration of selenium in earth's crust is 0.05ppm. In Hawaii concentrations are as high as 6-15ppm but selenium poisoning does not occur because the selenium is not bioavailable. The Hawaiian volcanic soils are acidic, and they create a soil environment that favors formation of the reduced, unavailable forms of selenium.  In other areas, concentrations as low as <1ppm can be toxic if the soils are alkaline.  This is because oxidation of selenium makes it extremely soluble and hence very bioavailable.
• The same type of processes influence the effects of other trace elements such as U and Te.
• Methylation can greatly enhance the bioavailability of many metals such as Hg.

THE IMPORTANT POINT HERE IS THAT WE LIVE IN A HETEROGENEOUS WORLD.  ALL OF OUR SYSTEMS ARE INTERTWINED AND CONNECTED!

IV. RADON

RADON GAS is a radioactive noble gas. It is an intermediate decay product in the decay series of Uranium-238 to stable Lead-206.   Figure 13.17 on page 368 of your text provides a good summary illustration of this decay chain.

LOOK AT the complete series of alpha and beta decays.

Clearly a lot of potentially harmful alpha and beta decays occur in this sequence. There are a lot of problematic daughter products.

The major point of concern however is the alpha decay from Radon-222 to Polonium-218

Radon gas is a significant environmental health hazard.  It occurs naturally in areas with uranium containing soils.  It also results from the decay of uranium contaminated mine tailings that have historically been used for such things as backfill, foundations and road surfaces.

The characteristics of Radon make it seem an unlikely candidate for an environmental toxin:

• It is a noble gas, and so is itself unreactive

• It is an alpha emitter. As you recall from Module 10, alpha emitters generally only cause harm when they are inhaled or ingested

• Radon has a short half life - only 3.82 days

• It can diffuse freely for only about 1 meter before it decays

Radon causes problems because it has a high affinity for entering small, low-lying areas where it can accumulate to harmful concentrations.  Shower stalls, basements, excavation pits and so on are all potential radon sources.  Fortunately the characteristics of radon actually  make it easy to remediate.   All it takes is proper ventilation.

EPA has set the maximum occupational exposure limit of Radon at 200pCi/L of air/hour. This limit only applies to a total monthly exposure of 170 hours. The maximum exposure limit outside of the workplace is only 4pCi/L air/hour. [1 picoCurie(pCi) = 1/1,000,000,000,000 curie]

V. WEB SITES