Principles for prevention of the toxic effects of metals

Abstract Prevention of the toxicity of metals begins with identification of the populations at highest risk of exposure and at greatest vulnerability to adverse effects. Industrial workers, long the principal focus of concern, remain a group at high risk due to their excess exposures. Nonoccupational populations — young children and pregnant women in particular — are increasingly at risk today via exposures to metals in air, food, water, and consumer products. These nonoccupational exposures are the result of the wide and expanding environmental dissemination of metals that now affects millions of persons and has spread to countries all around the world. Because women and children are highly susceptible to metals, toxic effects may occur in them at exposure levels far below those that cause adverse effects in adult workers. The toxic effects of metals in persons of any age may be clinically evident or they may be subclinical. Some metals are necessary in small amounts to sustain human life. Preventive interventions to control exposures to metals should always seek to target the sources of exposure. Such interventions need to identify, evaluate, control, and if possible eliminate the sources of the problem. Hazard identification is a critical component of the prevention process and includes recognition of the sources and routes of exposure and elucidation of the full range of effects on health, including effects on early development. Evaluation may involve monitoring of the workplace or general environment and biological monitoring, and/or health examinations of exposed populations. Medical examinations of high-risk populations can sometimes pinpoint reasons for increased susceptibility and guide remedial action. Control involves reduction of workplace or environmental exposures using the technologies of industrial hygiene such as engineering and environmental controls. It may also involve administrative controls and/or the use of personal protective equipment, but these are far less effective strategies. Elimination of an exposure at its source — termed primary prevention — is always the most effective and cost-effective mode of prevention. When prevention fails, treatment may be necessary as a last resort. Training and education of managers, workers, health professionals, policy makers, and the general public about the health risks posed by toxic metals and approaches for risk reduction are of great importance, but can never replace direct control of exposure. To be effective, all of these programs must be supported by authority , which is usually based in law and regulation. Such authority may involve outright bans of certain uses of toxic metals, which eliminates the exposures and is thus the most effective protective strategy. Great success has been achieved over the past century in reducing the toxic effects of metals in both occupational and nonoccupationally exposed populations. Examples include the worldwide removal of lead from gasoline, control of exposure to arsenic in drinking water in Chile, control of “black foot disease” caused by arsenic in drinking water in Taiwan, and the disappearance of “mad-hatters” disease in workers exposed to mercury. Nonetheless, much work remains to be done, and the need for increased prevention is especially great in low- and middle-income countries, where many of the world’s mines, smelters, and other metals factories are located today, too often in circumstances of weak or nonexistent occupational and environmental controls. In addition, new hazards continue to arise and require constant vigilance, such as the proposed introduction of the manganese-containing compound methylcyclopentadienyl manganese tricarbonyl (MMT) to gasoline supplies worldwide. In the years ahead, as multinational corporations continue to shift hazardous factories and toxic wastes from industrialized to developing countries, it will be very important that these companies are required to adhere to the same environmental and safety standards in their new locations as in their former homes. Precaution should guide all decisions on whether to permit further dissemination of metals into the environment. No metal should be disseminated into the environment until its environmental fate, transport, and persistence have been thoroughly characterized and until health assessments indicate that the proposed uses of the metal are safe even for the most vulnerable members of society.