COMMENTARY — Metals in the environment

Safe levels of metals in the environment are being recommended with little or no consideration that metals have been there since the beginning.

The millions of tons of ash pumped into the atmosphere by volcanic eruptions and spread over thousands of square kilometres probably contain all 92 elements of the periodic table. In addition to the elements essential to life, such as carbon, nitrogen, oxygen, sodium, potassium, calcium, magnesium, iron, copper, zinc, phosphorus, sulphur and iodine, volcanoes also redistribute those elements that, under certain conditions, are regarded as harmful. These elements include arsenic, beryllium, cadmium, mercury, lead, radon and uranium.

Indeed, all known elements are present at some level of concentration throughout the natural environment. They are present in animal, vegetable and mineral materials, and their beneficial and harmful effects have been present since evolution began.

In addition, the question of natural background levels has important economic implications. Before governments commit scarce resources to clean up or protect the environment from man-made contamination, it would seem prudent to determine how much “contamination” merely reflects the pre-existing natural background. Likewise, it would seem appropriate to assess how much the natural background varies from place to place as a consequence of differences in geology, soil, climate and topography, and to determine the extremes of natural variation in the chemistry of the environment and the tolerance of natural ecosystems for variations in geochemical background.

To determine natural background levels, it is necessary to undertake geochemical mapping of the land surface. This began 50 years ago to aid mineral prospecting. Over the past 25 years, as a result of developments in analytical and computer technology, it has evolved into a specialization capable of revealing the complexities of the natural chemical environment.

Unfortunately, geochemical mapping and the resulting database have evolved in a very ad hoc manner. As a result, it is virtually impossible to make a quantitative comparison of data from different sources.

In 1988, the International Union of Geological Sciences (IUGS) and the United Nations Educational, Scientific and Cultural Organization (UNESCO) jointly authorized a project to review the situation. The outcome is a 1995 report by UNESCO that reviews, on a country-by-country basis, existing data and methods. The report also contains detailed recommendations both for the conduct of new work and for the establishment of a global geochemical reference network, which is regarded as essential for standardizing future work. As this report illustrates, there are virtually no published geochemical data for 80% of the global surface. Where data are available, they are inconsistent between countries and often within them.

This deficiency of knowledge should be of serious concern to both the mineral industry and the public. A systematic geochemical database that is both standardized and comprehensive is essential for the establishment of sensible environmental policy decisions. The report has also identified the need for the establishment of an international network of reference samples, analogous to a topographic grid in geodetic surveys.

Environmental phenomena are complex, and it is necessary to ensure that all the variables have been identified and documented before too many conclusions are drawn and regulations written. On the particular topic of metals in the environment, before quantitative limits are established, a global geochemical reference network is essential to establish global background values and to ensure measurements can be correlated and compared, irrespective of jurisdiction.

— From the newsletter of the International Council on Metals and the Environment. The author is the co-chairman of the International Union of Geological Sciences Working Group on Continental Geochemical Baselines.