For people concerned about chemical pollution, the US National Academy of Sciences has a disturbing message: Even the experts know very little about the hazards which the outpouring of man-made chemicals presents.
A report from the academy's operating agency, the National Research Council, notes that out of ''tens of thousands of commercially important chemicals, only a few have been subjected to extensive toxicity testing and most have scarcely been tested at all.'' It is the final report of a study carried out for the National Toxicology Program, a unit of the US Deparment Health and Human Services. This study documents an ignorance which many experts have long suspected. It highlights the fact that it is impossible, at this stage, for environmental policy to be based on an adequate knowledge of chemical hazards. Given this basic ignorance and given the widespread public concern about chemical poisons, there will be increasing pressure to restrict the release of chemicals into the environment whether or not there is direct evidence of a health hazard.
The new tight standards on the pesticide EDB are a case in point. There is little direct evidence of a substantial danger to human health from EDB residues in food, as opposed to damage done to laboratory animals by massive EDB doses. Yet lack of such direct evidence no longer reassures an apprehensive public. And rather than wait for a clearer scientific understanding of the possible hazards, the Environmental Protection Agency is phasing out the pesticide. By September it can no longer be used on citrus fruit sold in the United States. It will be totally out of the US food production system within three years.
This tendency to judge chemical pollution guilty until proved innocent is likely to spread throughout environmental regulation. Some experts who have long felt that tolerances for chemical residues should be set according to scientific assessments of their hazards are beginning to change their minds. They recognize that the general public isn't willing to give an unproven chemical the benefit of the doubt. A strong debate on that issue now is under way among water supply professionals.
Last year, Abel Wolman - who at age 92 is still considered the elder statesman of environmental engineering - told the annual conference of the Water Pollution Control Federation that public concern and not scientific risk assessment has become the dominant factor in setting pollution standards. He said that chemical pollution in water should be held below the level of detectability whether there is evidence that a small residual amount of a pollutant is dangerous or not.
Wolman had long insisted that water quality standards be based on scientific understanding and not on vague concern. Thus his statement was seen as a significant change of viewpoint. Indeed, he acknowledged that he might be accused of ''surrendering to public concern and fear, rather than insisting on waiting for scientific validation of the impact of toxic organics on man.'' But he added that ''such a stance presupposes a public acceptance of risk (which doesn't exist).'' The January issue of the federation's journal has a summary of the debate Wolman has stimulated.
The new report from the National Research Council will strengthen this tendency toward tougher standards on unproven chemicals. The study committee drew up a list of 65,725 chemicals from the 5 million or so compounds in the chemical literature. From this list, it took a sample of 675 chemicals which it further reduced to a randomly selected 100 chemicals for which there are at least some toxicity data available.
Based on such sampling, the committee concluded it could make adequate health hazard assessments for only 10 percent of pesticides and 18 percent of drugs and the inert ingredients mixed with them. Moreover, even in these relatively well-tested chemical groups, the committee found no toxicity data for 38 percent of pesticides and 25 percent of drugs. There may be some toxicity data unknown to the committee in secret files of industrial laboratories. However, the study strongly suggests that we simply do not know what dangers are being created by the widespread use of industrial chemicals.
Even if vigorous new efforts are made to test chemicals, there are too many of them for investigators to cope with. No one can be certain that supposedly safe disposal of chemicals in landfills, rivers, or the sea actually is benign. The conclusion seems inescapable that chemical wastes will have to be controlled at their source.