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We desperately need better tools to predict human risk from exposure to toxic chemicals. The information that will be useful will eventually arise from the development of a conceptual toxicity-evaluation scheme resulting from the recent advances in molecular genetics and biochemistry. This will enable scientists to target chemicals and substances of potential concern much more easily without needing a complex (and time-consuming) series of traditional toxicity tests.

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risks. For some, however, important adverse environmental effects emerged. The search to replace those without further environmental effects has become a strong driving force in industry, in the scientific community, and in the general public. The focus has been mostly on testing for acute human toxicity with surrogates and on estimating long-term chronic effects in humans, primarily emphasizing cancer, again with surrogates. Increasingly, researchers will strive to include effects on entire ecosystems, and long-term, multigenerational effects on fertility, reproductive quality, and hormonal functions. Of major interest will be chemicals with the potential to be persistent, toxic, and bioaccumulative (PTB). However, chemicals that are persistent but not toxic or bioaccumulative, such as CFCs, have also led to environmental problems, as have chemicals that are persistent and toxic but not bioaccumulative. Evaluations of such chemicals are also needed.

Some of the surprise effects of chemicals have been due to a failure to predict the scale on which technologies might be used once they were shown to be beneficial when used on a limited scale. For example, DDT has side effects that have increased nonlinearly with the scale of application; as a result, the incremental benefits of a seemingly benign technology reversed when it was applied on a larger scale. New technologies have to be constantly reevaluated in anticipation of scale effects.

Following are some examples of products or processes that created unforeseen environmental problems after their introduction.

  1. Products

    • Pesticides, such as DDT, endrin, dieldrin, and benzene hexachloride (BHC).

    • Alkylbenzene sulfonate (ABS) synthetic detergents.

    • Polychlorinated biphenyls (PCBs).

    • Chlorofluorocarbons (CFCs).

    • Lead used in gasoline and paint.

    • Some chlorinated solvents.

    • Wood preservatives.

  1. Processes

    • Chlorination for disinfection (in some situations).

    • Mercury release from chlor-alkali cells.

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