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Heavy metal pollution and environmental biochemical toxicology research
The Science o f the Total Environment, 20 (1981) 95--97 Elsevier Scientific Publishing Company, Amsterdam - - P r i n t e d in "The Netherlands
95
Editorial
HEAVY METAL POLLUTION AND ENVIRONMENTAL BIOCHEMICAL TOXICOLOGY RESEARCH
The aims of the new energy policy of the European Communities are the development of alternative sources of energy to satisfy the increasing energy demand together with the production of environmentally clean energy. As coal fired p o w e r plants become more important in energy production, a m o r e accurate assessment is necessary of the role which such plants may play in the additional mobilization of chemicals which are already mobilized by other sources of chemical pollution. In this respect it is not only the bulk emissions which give rise to concern but also minor components such as trace elements which may cause environmental pollution. Although modern technology prevents most of the anthropogenic trace elements escaping to the environment, the small amounts which escape the control devices represent in absolute terms potentially harmful quantities because of the enormous amounts of fuels which are consumed each year. For instance, in 1980 a b o u t 180 millions of tons of hard coal were burnt in coal-fired p o w e r plants situated in the territory of the European Community. Further, cases of heavy metal pollution associated with industry such as mercury poisoning from the discharge of industrial wastes in Minamate Bay (Japan), a specific Cd-induced disease "Itai-itai" in T o y a m a City (Japan) as well as (more recently) arsenic poisoning in Manfredonia (Italy) and thallium poisoning in Lengerich (F.R.G.) show h o w entire population groups can be exposed to trace elements in amounts and forms which are hazardous to human health. Since there is a constant release of trace elements into the environment the trend of human exposure to unnaturally high concentrations and often in unusual physico-chemical forms, is certainly likely to continue. As a consequence the protection of human health against heavy metal pollution demands the establishment of exposure limits and legal standards of environmental quality, based on levels of exposure and evidence of effects on health. A great multidisciplinary effort to establish dose-effects curves for each metal must be carried o u t in order to provide a sound scientific basis to any proposal for permissible levels of trace element exposure. This scientific basis is usually developed from toxicological studies on laboratory animals as well as from epidemiological investigations on professionally exposed and general populations. In this connection, remembering that laboratory animals experimentation should be of guidance for the human situation, several aspects of environmental biochemical toxicology of trace elements have a high degree of priority and certain research needs corresponding to the present status of the problem can be formulated: 0048-9697/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
96 (i) The levels of trace elements which typically occur in the polluted environment are n o t large enough to give rise to acute effects for general populations. Responses may be demonstrable only as an alteration in a physiological function or as a change in some measurable biochemical parameters in the target tissues. The determination of these subtle changes poses serious analytical difficulties and explains why much of the present biochemical knowledge a b o u t metals refers primarily to high doses. There is a need to study the biochemical effects of trace elements using current environmental levels of metals {low dose aspect). (ii) Trace element pollution has a persistent character because metal atoms are non-degradable and therefore accumulate. The subtle adverse effects are irreversible because t h e y are due to this accumulation which increases daffy as a result of human activity. In addition, to identify these subtle changes a long latent period is necessary before a threshold is reached. Since the knowledge available on these effects is almost all limited to short times and does n o t reflect the environmental situation, there is an urgent need for long term biochemical studies on living organisms at current environmental levels of trace elements (long term aspect). (iii) The enlargement of our knowledge a b o u t trace elements indicates that for assessment studies, the simple determination of the level of an element in the tissues must be related to the knowledge of the biological mechanisms responsible for trace element retention. This requires experiments at tissue and intracellular level with the identification of metallobiocomplexes {intracellular and molecular aspects). Further, a better understanding of the biochemical mechanisms may be obtained by studies on different animal species profiting by possible differences in the metal metabolism {comparative experimentation aspect). (iv) Man is exposed to trace elements by various routes. Experiments on laboratory animals should take into account studies in which trace elements are administered via all possible modes of exposure. Particularly important is inhalation-absorption for which there is little information and which generally leads to factors higher than the corresponding values for the same element when absorbed via the gastrointestinal tract {inhalation of trace metal aerosol aspect). (v) Man is simultaneously exposed to many elements as well as to different chemical species so that interrelationships between elements may occur. Particularly important is an estimation of the total dally intake of the different elements and the ratio between them {antagonistic and synergistic aspects). There is also a great need to study the oxidation state and the chemical species of trace elements in food and air to which man is exposed in order to expose experimental animals to these chemical species (chemical species exposure aspect).
97 (vi) Data on trace elements in human tissues are relatively abundant. However, many of them come from sections of the population which are exposed to higher levels than those encountered by general populations, such as occupationally and accidentally exposed people. In many cases data on general populations are repetitive and obtained without any critical approach to such factors as epidemiological sampling. Further, from the analytical point of view much of the information provided is "below t h e detection limit" of the technique applied. To evaluate these data it is necessary to identify those which may be useful for assessment studies. There should be greater emphasis on the comparison of normal levels in general populations with those reached by workers (critical reassessment aspect). All investigations on human tissues should be related to animal experimentation to learn more a b o u t the biochemical mechanisms involved in the bioavailability of trace elements. As in studies on laboratory animals special effort should be devoted to investigations on human tissues at intracellular and molecular levels. The lack of this t y p e of information proves a severe gap when setting up dose-response curves to be used when evaluating a safe level of exposure for humans (human metallobiochemistry aspects). Concerning the analytical aspect, trace element environmental biochemical toxicology studies based on the different aspects mentioned require the use of sophisticated analytical techniques. It is not surprising, therefore, that non-traditional techniques such as neutron activation analysis and mass spectrometry have been used in this field. Finally, the research needs in metal environmental biochemical toxicology include more than the development and use of new techniques. It is necessary to stress that full assessment of biological effects on humans arising from trace metal exposure is possible only with the necessary development of the associated basic research. In this connection, trace elements will u n d o u b t e d l y play a major role.
Ispra, Varese (Italy)
E. Sabbioni
95
Editorial
HEAVY METAL POLLUTION AND ENVIRONMENTAL BIOCHEMICAL TOXICOLOGY RESEARCH
The aims of the new energy policy of the European Communities are the development of alternative sources of energy to satisfy the increasing energy demand together with the production of environmentally clean energy. As coal fired p o w e r plants become more important in energy production, a m o r e accurate assessment is necessary of the role which such plants may play in the additional mobilization of chemicals which are already mobilized by other sources of chemical pollution. In this respect it is not only the bulk emissions which give rise to concern but also minor components such as trace elements which may cause environmental pollution. Although modern technology prevents most of the anthropogenic trace elements escaping to the environment, the small amounts which escape the control devices represent in absolute terms potentially harmful quantities because of the enormous amounts of fuels which are consumed each year. For instance, in 1980 a b o u t 180 millions of tons of hard coal were burnt in coal-fired p o w e r plants situated in the territory of the European Community. Further, cases of heavy metal pollution associated with industry such as mercury poisoning from the discharge of industrial wastes in Minamate Bay (Japan), a specific Cd-induced disease "Itai-itai" in T o y a m a City (Japan) as well as (more recently) arsenic poisoning in Manfredonia (Italy) and thallium poisoning in Lengerich (F.R.G.) show h o w entire population groups can be exposed to trace elements in amounts and forms which are hazardous to human health. Since there is a constant release of trace elements into the environment the trend of human exposure to unnaturally high concentrations and often in unusual physico-chemical forms, is certainly likely to continue. As a consequence the protection of human health against heavy metal pollution demands the establishment of exposure limits and legal standards of environmental quality, based on levels of exposure and evidence of effects on health. A great multidisciplinary effort to establish dose-effects curves for each metal must be carried o u t in order to provide a sound scientific basis to any proposal for permissible levels of trace element exposure. This scientific basis is usually developed from toxicological studies on laboratory animals as well as from epidemiological investigations on professionally exposed and general populations. In this connection, remembering that laboratory animals experimentation should be of guidance for the human situation, several aspects of environmental biochemical toxicology of trace elements have a high degree of priority and certain research needs corresponding to the present status of the problem can be formulated: 0048-9697/81/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
96 (i) The levels of trace elements which typically occur in the polluted environment are n o t large enough to give rise to acute effects for general populations. Responses may be demonstrable only as an alteration in a physiological function or as a change in some measurable biochemical parameters in the target tissues. The determination of these subtle changes poses serious analytical difficulties and explains why much of the present biochemical knowledge a b o u t metals refers primarily to high doses. There is a need to study the biochemical effects of trace elements using current environmental levels of metals {low dose aspect). (ii) Trace element pollution has a persistent character because metal atoms are non-degradable and therefore accumulate. The subtle adverse effects are irreversible because t h e y are due to this accumulation which increases daffy as a result of human activity. In addition, to identify these subtle changes a long latent period is necessary before a threshold is reached. Since the knowledge available on these effects is almost all limited to short times and does n o t reflect the environmental situation, there is an urgent need for long term biochemical studies on living organisms at current environmental levels of trace elements (long term aspect). (iii) The enlargement of our knowledge a b o u t trace elements indicates that for assessment studies, the simple determination of the level of an element in the tissues must be related to the knowledge of the biological mechanisms responsible for trace element retention. This requires experiments at tissue and intracellular level with the identification of metallobiocomplexes {intracellular and molecular aspects). Further, a better understanding of the biochemical mechanisms may be obtained by studies on different animal species profiting by possible differences in the metal metabolism {comparative experimentation aspect). (iv) Man is exposed to trace elements by various routes. Experiments on laboratory animals should take into account studies in which trace elements are administered via all possible modes of exposure. Particularly important is inhalation-absorption for which there is little information and which generally leads to factors higher than the corresponding values for the same element when absorbed via the gastrointestinal tract {inhalation of trace metal aerosol aspect). (v) Man is simultaneously exposed to many elements as well as to different chemical species so that interrelationships between elements may occur. Particularly important is an estimation of the total dally intake of the different elements and the ratio between them {antagonistic and synergistic aspects). There is also a great need to study the oxidation state and the chemical species of trace elements in food and air to which man is exposed in order to expose experimental animals to these chemical species (chemical species exposure aspect).
97 (vi) Data on trace elements in human tissues are relatively abundant. However, many of them come from sections of the population which are exposed to higher levels than those encountered by general populations, such as occupationally and accidentally exposed people. In many cases data on general populations are repetitive and obtained without any critical approach to such factors as epidemiological sampling. Further, from the analytical point of view much of the information provided is "below t h e detection limit" of the technique applied. To evaluate these data it is necessary to identify those which may be useful for assessment studies. There should be greater emphasis on the comparison of normal levels in general populations with those reached by workers (critical reassessment aspect). All investigations on human tissues should be related to animal experimentation to learn more a b o u t the biochemical mechanisms involved in the bioavailability of trace elements. As in studies on laboratory animals special effort should be devoted to investigations on human tissues at intracellular and molecular levels. The lack of this t y p e of information proves a severe gap when setting up dose-response curves to be used when evaluating a safe level of exposure for humans (human metallobiochemistry aspects). Concerning the analytical aspect, trace element environmental biochemical toxicology studies based on the different aspects mentioned require the use of sophisticated analytical techniques. It is not surprising, therefore, that non-traditional techniques such as neutron activation analysis and mass spectrometry have been used in this field. Finally, the research needs in metal environmental biochemical toxicology include more than the development and use of new techniques. It is necessary to stress that full assessment of biological effects on humans arising from trace metal exposure is possible only with the necessary development of the associated basic research. In this connection, trace elements will u n d o u b t e d l y play a major role.
Ispra, Varese (Italy)
E. Sabbioni