Lecture No. 1: Introduction to Environmental Geochemistry
Introduction
This course is Geology 431, Environmental Geochemistry. Prerequisites for this course include
There will be an all-day field trip, later in the semester.
A course outline is posted on the course web site.
There is no textbook for this course, but there will be readings on reserve in the library and some handouts in class. There are also some books on reserve for general knowledge:
The Berner and Berner book is a good introduction to some aspects of environmental geochemistry. Snoeyink and Jenkins is a good introduction to the inorganic geochemistry of water. Stumm and Morgan is a more advanced book, and the going gets a little heavy, but it is a useful reference for geochemical information.
This class has a web site (www.cs.umt.edu/GEOLOGY/classes/Geol431/) that can be reached by a link from the Geology Department home page. Lecture notes from past classes will be posted on the site. Those lectures will likely be modified for this term and reposted as soon as possible. I will tell you in class which posted lectures are appropriate for this year as I get them modified. The updated class schedule and possibly other materials will also be on the site.
In this course we will examine the processes of contaminant transport and fixation in aquatic systems and will concentrate on metals and metalloids. There will not be much on organic contaminants or air pollution. Chemistry 541, Environmental Chemistry, covers those topics.There will be a lot of material on river systems, sediments, soils, aquifer materials, and aqueous interactions.
Definitions (from Faure, 1991, Environmental Geochemistry)
Geochemistry is the science of learning to understand why some stones are "good" and how they form. (In this context, "good" is relative to resource extraction, so it primarily concerns ores.)
Environmental geochemistry grows out of the need to understand why some stones went "bad".
Why we care about bad stones:
Bad rocks affect water consumption and water quality: drinking water, human health, animals, soils, etc.
They do economic damage, including resource damage.
Every drainage in Montana has one or more abandoned mines draining pollutants into its headwaters. Some, like Rock Creek, are only slightly polluted; others, like Silver Bow Creek, are dead or nearly dead from the pollution.
Alternate Definition
There is another way to define environmental geochemistry. We might define it as the study of the geologic processes that interacts strongly with the materials in the crust. This emphasizes weathering of rock, soil formation, solutes in surface and ground water, atmospheric transport, and worldwide cycling of elements, especially contaminant elements.
The second definition is closer to what this course is about. However, a major portion of the course’s emphasis will be on the effects of mining and other human activities.
Minerals
In this course you will encounter some minerals that don’t show up very often in other geology courses, since one of our main concerns will be the forms in which metals and metalloids move through the hydrosphere. In between time spent in solution, these elements tend to occur in authigenic oxide, hydroxide, sulfate, carbonate, and phosphate minerals. (Authigenic = formed in place; allogenic = formed elsewhere.)
Thus we will see things like
Authigenic sulfate minerals:
The above sulfate minerals are deposited from acid solutions and usually contain some acid.
Phosphate minerals:
These phosphate minerals are important in controlling the phosphate cycle in acid soils. (They often cause phosphorus deficiencies.)
Scorodite is the arsenic counterpart of strengite. It is only stable within a limited pH range. At higher pH it converts to iron and arsenic oxides.
Iron (III) oxyhydroxides:
(The above 3 are collectively found in "limonite.")
Aluminum oxyhydroxides:
(These are the main constituents of bauxite.)
Carbonates:
There are complete solid solution series between siderite and rhodochrosite and between siderite and magnesite, but there is only limited solid solution between magnesite and rhodochrosite. On the other hand, there is a complete solution series between dolomite and kutnahorite and between dolomite and ankerite, but only limited solution between ankerite and kutnahorite.
Other manganese minerals:
Other authigenic minerals:
Environmental Effects of Mining Activities
[Slides]
Examples of Health Impacts From Metal And Metalloid Contamination
Mercury
Known to the Greeks and Romans. Only metal which is liquid at room temperature. Produced from the ore cinnabar (HgS), either by roasting:
HgS(s) + O2(g) --> SO2(g) + Hg
or by oxidation with lime (CaO):
4HgS(s) + 4CaO(s) --> 4Hg + 3CaS(s) + CaSO4(s).
World production of mercury is about 9000 tonnes/year and this is mostly used in the chloralkali industry. It is also used in scientific and electrical apparatus, metallurgical processes, and antifungicides.
In the chloralkali industry, the major process is electrolysis of aqueous NaCl solution to produce NaOH and chlorine. Mercury cells were in wide use because they are more economic; they are being replaced now by less polluting techniques. The NaOH, the spent NaCl solutions and other plant effluents from this process carry traces of mercury which are discharged into into lakes and rivers. In 1970, chloralklai plants lost about 600 tonnes/year .
Mercury is extremely toxic, and toxicity depends largely on the form and amount of mercury ingested/inhaled.
Mercury (I) chloride, calomel, is used in medicine as a purgative. The fillings of teeth are mercury amalgams with gold or silver.
Mercury has long been known to be a hazard. Mercury (II) nitrate was used to soften fur in the making of felt hats. The phrase "mad as a hatter" -- and the Mad Hatter of Lewis Carroll's Alice in Wonderland -- both are from the same source, which is the toxic effect of mercury on the central nervous system, producing mental effects and "hatter's shakes". The workers in the felt hat industry, and also those in mercury smelters, were the only ones constantly exposed to high enough mercury levels to exhibit obvious symptoms.
The different forms of organic mercury, such as methylmercury, CH3Hg, and other organomercury compounds such as the mold preventative phenylmercury acetate used in fertilizers, C6H5-Hg-OCOCH3, are much more dangerous. Over 90% of the intake of methylmercury, for example, is absorbed into the bloodstream whereas only about 2% of inorganic mercury is absorbed.
Organic mercury compounds are manufactured artifically, but are also formed by bacteria that have the ability to convert inorganic mercury compounds into organic mercury. Inorganic mercury can be converted into the more toxic forms of mercury by these processes.
The organic mercury compounds are concentrated in the food chain. Over 90% of the methylmercury in fish is held tightly to the fish protein and cannot be removed by cooking. The organic mercury enters the small fish by direct absorption through the gills, or by their eating of phyto-plankton containing mercury. Organic mercury compounds are further concentratedor biomagnified up the food chain to very high levels. E.g., pike flesh may contain 3000 times as much Hg as the surrounding water.
The background, or natural, levels of mercury in freshwater lakes and rivers is about 0.03 parts per billion (1 ppb = 0.001 ppm); this mercury appears to arise from the weathering of rocks. The mercury level in the oceans is variable depending upon location but is in the range of 0.03 - 5.0 ppb. Concentration of mercury ingeneral oceanic fish flesh is greater than 0.15 ppm and has been so since at least the 1930s. For mercury in fish flesh, the "safe level", U.S.A.-Canada, is 0.5 ppm; Sweden recommends 0.2 - 1.0 ppm and then not more than once a week.
There have been several recorded instances of mercury poisoning, of which the most well-known occurred at Minimata Bay and nearby Niigata, Japan, in 1952, 1965, and 1973. The mercury source was plastic plant effluent. The plant waste was dumped into Minimata Bay. The fish and shellfish in the bay concentrated mercury in their tissues and as a result, 397 are known to have been affected, of which 68 died; of those affected, 22 were unborn children. The estimates over several decades were thousands of people effected. The methylmercury was absorbed by eating fish and shellfish from contaminated oceanic water. Levels of mercury in fish flesh in Minimata Bay in 1952 were 5 - 10 ppm. The 1965 instance in Niigata, Japan was a similar case to Minimata Bay; 330 persons are known to have been affected, of which 13 died.
Cases of mercury poisoning occurred in Iraq in 1961, in Pakistan in 1963, and in Guatemala in 1966. In each case over 30 persons were poisoned by flour made from seed grains treated with organomercurial preservatives. In Iraq in 1972, there was a similar case, with several hundred deaths reported and possibly as many as several thousand with ong-term effects. In New Mexico in 1961, a farmer and his family ate a hog fed on garbage and fungicide-treated grain. Three children were seriously affected, with sight damage, hearing damage, or coma. In 1970 Ontario, Canada, banned all fishing in the St. Clair River, Lake St. Clair, and the Detroit River. No clear data are available on numbers affected with no known dead. Levels of mercury in fish flesh from Lake St. Clair, in 1935, were 0.07 - 0.01 ppm; but in 1970, some were 7.0 ppm, average 0.5 ppm. Reported (and questionable) levels in fish flesh from Lake Wabigoon, in 1970, were 24 ppm. 1. Minimata Bay, Japan.
Cadmium (Itai-itai Disease)
"Itai" is the Japanese word corresponding to the English "ouch." The disease is a form of cadmium poisoning.
First seen from contamination from a zinc mine which allowed contaminants from its ore milling operation to get into a stream. Cadmium is a close chemical cousin of zinc and often occurs in the same ores (as an impurity in sphalerite, for example).
The cadmium was carried by river sediments into irrigation water used about 50 km downstream to water rice fields. The rice plants took up the cadmium, and people ate the rice.
Itai-itai disease commonly takes 5-10 years and in some cases about 30 years to develop. The symptoms progress as follows:
Cadmium replaces calcium in bones and other tissues. People in the late stages of the disease find almost any movement or contact painful — hence the name "itai-itai".
Arsenic
Arsenic is probably the best known human poison. It was the poison of choice for royalty and murderers until a method of chemical analyses was discovered to detect arsenic in human tissue. Global arsenic contamination is of major concern because of the large amount of arsenic potentially available to the environment from industrial production and mining wastes. Industrial production alone (as arsenic trioxide) produces about 50,000 metric tons per year, which at the known fatal dose to humans of approximately 300 mg per person, is enough arsenic trioxide produced every year to kill about 170 billion people—27 times the entire world population. The release of even a tiny fraction of this arsenic to surface and ground water systems can have major ramifications for human and ecosystem health.
Arsenic is probably the best known human poison. It was the poison of choice for royalty and murderers until a method of chemical analyses was discovered to detect arsenic in human tissue. Global arsenic contamination is of major concern because of the large amount of arsenic potentially available to the environment from industrial production and mining wastes. Industrial production alone (as arsenic trioxide) produces about 50,000 metric tons per year, which at the known fatal dose to humans of approximately 300 mg per person, is enough arsenic trioxide produced every year to kill about 170 billion people—27 times the entire world population. The release of even a tiny fraction of this arsenic to surface and ground water systems can have major ramifications for human and ecosystem health.
Arsenic can also be of concern from natural sources. For example hot springs and geysers from Yellowstone National Park produce a very large amount of arsenic that "contaminates" the Madison River and upper Missouri River and associated groundwater near the river. The most extensive natural arsenic contamination is in West Bengal, India and Bangladesh. (See the site ar http://www.bicn.com/acic/)
In this region as many as 1 million wells are contaminated with arsenic above drinking water standards. The arsenic originates from the dissolution of arsenic associated with alluvial/deltaic sediments deposited by the Ganges and other rivers (we will look at the geochemistry of this later in the course). Concentrations are up to 1000 ppb well above the U.S. drinking water standard of 50 ppb and the WHO standard of 10 ppb.
Arsenic poisoning causes a number of diseases including:
"Tens of millions of persons in many districts [of Bangladesh and India] are drinking ground water with arsenic concentrations far above acceptable levels. Thousands of people have already been diagnosed with poisoning symptoms, even though much of the at-risk population has not yet been assessed for arsenic-related health problems."
There are now 7000 people diagnosed with acenicosis in Bangladesh and upwards of 175,000 in India. Estimates are as high as 24 million people are affected by arsenic contaminated water and risk major health prolems. This is the largest poisoning event ever recorded and has no simple resolution.
Next Lecture: Lecture No. 2. Chemical Fundamentals
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