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Marcello M. Veiga and John A. Meech
University of British Columbia,
Department of Mining and Mineral Process Engineering,
Vancouver, British Columbia, V6T 1Z4, Canada
About 70 tonnes of mercury is discharged annually from informal mining activity (garimpos) in the Amazon. This pollution derives from miners' lack of concern for the environment together with ignorance about efficient gold extraction methods. Skilled professionals, such as doctors, priests, hygienists, social workers, nurses, mines inspectors, and union leaders also have limited knowledge about mercury transformations in the environment, its accumulation into the food chain and the symptoms manifested by a mercurialism victim. This presentation describes educational features inherent in the technology of Expert Systems that address these deficiencies.
HgEX is a system that combines technical factors with the power of heuristic observations to diagnosis and recommend remedial procedures for a specific "hot spot". The system, developed in a natural-language programming-environment, is designed for use by both highly-skilled and uneducated personnel. A comprehensive Hypertext-based tutorial section provides details on Hg chemistry and distribution, amalgamation practices, bioaccumulation and the design of a site-specific monitoring programme. A field study of the Lilloett River delta in British Columbia documents the ability of organic acids to oxidize metallic mercury. Some of the highest water-born Hg levels ever reported have been measured in this region.
Conventional correlation of natural variables with Hg biota levels relies on empirical regression models that often produce errors too large to yield useful results. Projection of environmental variations onto the extent of bioaccumulation is fraught with uncertainties and unknowns such as internal correlations between variables and site-specific aspects of biota contamination. Often, assumptions about closed systems are invalid when applied to natural environments.
Instead, this work presents a heuristic approach to the problem in which amalgamation methods and natural variables are dealt with using an IF-THEN rule-based system to conclude about levels of emission and bioaccumulation risk. The system can handle uncertain or vague data and still provide useful output. Belief in mercury oxidation or dangerous conditions are characterized using fuzzy logic and neural network techniques. Belief levels derive from thermodynamic equilibrium data together with field observations of natural variables. The procedure reduces the need for analytical equipment and provides information and diagnosis for non-technical people.
Diagnosis can adapt to various situations that include time-dependencies and social-awareness together with economic and technical factors. Adaptation also accounts for other discharge sources such as forest fires estimated to contribute 26 percent more mercury than garimpos.
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