ES&T
LETTERS
Environmental toxicology Dear Sir: The Hoffmann article is an excellent comprehensive overview of the field of testing for mutagenicity of environmental substances (ES& T, Vol. 16, No. 10, 1982, p. 560A). However, there is an assay for detecting germ cell mutations in mammals, developed at NCTR, which is not mentioned in the review. This is especially puzzling because on page 571A Dr. Hoffmann states, "Genetic tests for detecting mutations in mammalian germ cells are still badly needed; emphasis should be placed on methods that detect defined genetic events, preferably scoring for effects in many genes simultaneously." This need is met uniquely by our assay. The Biochemical Mutation Test detects germ cell mutations in mice that affect the activity of one or more of 19 different enzymes. Since enzyme activity is affected by many different parameters, it is likely that this test monitors at least several hundred genetic loci for the induction of mutations. Development of this assay has been described at numerous scientific meetings over the past few years and in several publications, the definitive ones being Feuers et al., Mutation Research 1982, 95, 263-71 and Bishop and Feuers, Mutation Research 1982, 95, 273-85. Ronald W. Hart, Director National Center for Toxicological Research Jefferson, Ark. 72079 Author's response My recent article in ES&T discusses the application of mutagenicity tests in environmental toxicology; it is not intended to review all genetic toxicology tests that have been used or are now under development. In the review, I covered test systems in a table that presents kinds of tests and examples. In selecting examples, I included tests that are widely used, offer a large data base, have been applied in environ112A
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mental monitoring, or figure heavily in efforts to assess risks posed by environmental mutagens. Several tests for mutations in mammalian germ cells are listed. New methods to detect and characterize mutations in mammalian germ cells are still needed, and I would certainly encourage efforts toward that end. My failure to mention the biochemical mutation test that is being developed at NCTR was not intended to slight either the test or the efforts of Drs. Feuers and Bishop and their colleagues in developing it. The test is, however, at an earlier stage of development than are some other mammalian assays; the papers cited by Dr. Hart present data for only one mutagen, and the total number of variants that the authors report as "confirmed mutants" is eight. Because the line between methods under development and established assays is indistinct, any selection of tests is somewhat subjective. I believe, however, that the table in my review presents an appropriate selection of assays and references for a balanced overview of available test methods. George R. Hoffmann Department of Biology College of the Holy Cross Worcester, Mass. 01610
Herbicides, some clarification Dear Sir: Throughout the year, I have found the general articles in Environmental Science & Technology very helpful. The article on p. 645A of the December 1982 issue, entitled "Herbicides in Agriculture," also contains many excellent points that the scientific community should be aware of. However, the author included a few statements that are based on pre-1945 agricultural practices, and not on current practice. One such statement is that herbicide use entails farm practices that have deleterious effects on long-term fer-
tility. If the fertility of the soil decreases, it is because the quantity of nutrients applied by the farmer is less than the quantity removed in the harvested crop and by erosion and volatilization. With rotational farming, livestock were usually a part of the system, and the rate of harvesting the nutrients was less than for continuous grain cropping. The increased population and the larger percent of the population living in cities mean that a larger percentage of the nutrients in feed and food is disposed of hundreds of miles from the field. Using pre-1945 farming systems would require a redistribution (and probably decrease) of the population so that the nutrients in animal and urban wastes could be returned to the field of origin. Although many farmers do rotate corn and soybeans, the inclusion of forage crops would require large capital investments by many farmers to house, feed, and contain the animals. The country is already producing an excess of meat and milk. The use of hard labor for hoeing and of additional mechanical cultivation implies that our society is willing to spend a larger proportion of its income on food and less on other items. The statement "weed killers make it possible to employ no-till and minimum tillage methods" is correct, but, it also should have been stated that most farmers using conventional tillage also use herbicides. Frequently, the rates used per acre are almost equal for the two methods—conventional vs. reduced. Mechanical cultivation and hand hoeing are held to a minimum mainly for economic reasons but also because of a lack of dependable workers at the proper time. As Bette Hileman's article illustrates, it is difficult to separate "the good old days" practices from current practices. F. L. Himes, Professor The Ohio State University Department of Agronomy Columbus, Ohio 43210
