MERCURY? QUESTIONS AND ANSWERS
Some of you may be interested in the question of mercury and its determination in the environment. This is a fascinating question with many aspects. It illustrates again the importance of analytical chemists looking at the whole picture.
Swedish scientists had developed a gas chromotographic method for the determination of alkyl and aryl mercuric compounds extracted from fish with benzene and dilute hydrochloric acid. They were interested in those compounds because of their use as slimicides, but it turned out that regardless of what compound was used, the mercury found in fish was present as a monomethylmercuric ion.
A number of questions about the behaviour of mercury remains to be answered. Several theories have been proposed as to how mercury might have gone from inorganic form in water or a bottom sediment, into a methylated form of a fish. One theory assumes anaerobic conversion in the mud to volatile dimethyl mercury which enters fish via the gills. Another assumes aerobic conversion to monomethyl mercury by bacteria, with subsequent transfer up to the food chain. Still another assumes that a fish itself can methylate mercury taken in either through the gills as elemental vapor, or via the stomach as inorganic ions, or in an adsorbed state in silt particles. Before all these questions can be answered, we need to develop highly sensitive methods for each individual form of mercury. At present the most sensitive methods can go down only to about 0.05 ppm inorganic mercury in water.
At the Conference on Environmental Mercury Contamination in 1970 in Ann Arbor, Michigan, USA a number of sources from which mercury may enter the environment were mentioned. Among them were the burning of fossil fuels, use of mercurial compounds for fungicides in agricultural seed treatments, use of elemental mercury in the electrical industry for manufacture of batteries and mercury vapour lamps, use of mercuric catalysts, and the disposal of domestic sewage sludges. It will be up to analytical chemists to evaluate all of the sources and to provide the data on which proper action can be based. This will be true not only for mercury, but for all environmental contaminants.
It is interesting that both Finnish and Swedish chemists have found fairly high mercury content in fish from certain lakes in northern parts of their countries, remote from any known source of pollution.
Another interesting fact is that mercury will be found in the hair of a person who has been exposed to it. The average person has about one or two ppm in his hair or even more.
Having analyzed sections of the hair of a long-haired person and having known its growth rate, one can approximate the time and intensity of exposure. Most of these analyses have been done by neutron activation, which is advantageous because very small samples can be employed. However, hair can be analyzed by the atomic absorbance method following the digestion procedure used for fish analysis. A 100-mg sample is sufficient for hair in the range of 1 to 10 ppm.
Date: 2016-03-03; view: 770