Chlorinated phenoxy acids and their dioxins: Mode of action, health reisks and environmental effects

234 Although a proceedings, like a newspaper or magazine, has a limited life due to its pertinence to current problems, all researchers, regulators and layman concerned with the need for adequate food production and the use of wastes without polluting will find this book exceedingly valuable. I read the book completely in preparation of this review because I found that it contained so much interesting material. FRANK G. VIETS Jr. (Ft. Collins, Colo., U.S.A.)

CHLORINATED PHENOXY ACIDS AND DIOXINS

Chlorinated Phenoxy Acids and Their Dioxins: Mode o f Action, Health Risks and Environmental Effects. C. Ramel (Editor). Ecological Bulletin No. 27, published by The Swedish Natural Science Research Council, NFR, Box 23136, S--104 35 Stockholm, Sweden, 1978, 302 pp, illus. This book on chlorinated phenoxy acids and their dioxins comprises the proceedings of a symposium that was arranged by the Royal Swedish Academy of Sciences and held in Stockholm, Sweden, 7--9 February 1977. The chlorinated dioxins include a group of 75 different aromatic tricyclic compounds in which the number of chlorine atoms can vary from 1 to 8. About a decade ago it became apparent that certain of these compounds could arise as reaction products in the synthesis of some phenoxy acid herbicides. The dioxin of greatest environmental concern is 2,3,7,8tetrachlorodibenzo-para-dioxin (TCDD), a highly toxic chemical which has been found as an impurity in formulations of 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and 2,4,5-trichlorophenoxypropionic acid (2,4,5.TP or Silvex), but not in 2,4-dichlorophenoxyacetic acid (2,4-D) or in 4-chloro-2-methylphenoxyacetic acid (MCPA). The reason for this is that 2,4,5-T and its derivatives are synthesized from starting products which, if reaction temperatures are too high, can lead to the formation of substantial amounts of TCDD. There are some dioxins that can arise during the synthesis of 2,4-D and MCPA; however, these are probably 100 times less toxic than TCDD. Concentrations of this dioxin in some phenoxy acid herbicide formulations in the nineteen-sixties ranged as high as 100 ppm, but have now supposedly decreased to less than 1.0 ppm because of governmental regulations and better quality control both in the U.S.A. and abroad. TCDD is one of the most toxic chemicals yet synthesized, approximately 100 times more toxic than strychnine. Since the phenoxy acid herbicides are used in such large quantities all over the world, a thorough evaluation of their chemical properties and biological effects is urgently needed.

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That evaluation is very admirably provided by this book as it fillsm a n y of the gaps in our knowledge, and explores the potential impact of the phenoxy acid herbicides and their dioxins, particularly T C D D , on m a n and his environment. The editor has done a commendable job in organizing the various chapters into five major sections on the chemistry of the phenoxy acids and their dioxins, effect of these compounds on plant physiology, their toxicology, effect on genetics, and possible impact on ecology and economy. The book contains a total of 26 chapters prepared by recognized international authorities on these topics. Each of the major sections begins with a concise and well-written summary of the chapter contents which comprise that section. This is especially helpful to readers w h o wish to gain a quick overview of a pkrticular topic. Finally, the editor has thoughtfully included a special section on conclusions and recommendations which in effect summarizes the entire proceedings, as to the state of our knowledge of the effects of the phenoxy acid herbicides and their dioxins on plants, animals, and microorganisms, and provides recommendations for minimizing the environmental hazards from these compounds. Some of the conclusions on T C D D are noteworthy. For example, photolysis is the primary m o d e of degradation on environmental surfaces; microbiological degradation of T C D D occurs slowly in soil;the estimated halflife of T C D D in soil has been estimated at I to 1.5 years; growing plants take up littleor no T C D D from soil;bioaccumulation of T C D D resulting from normal use of 2,4,5-T is insignificant;people in potential risk groups, i.e.pregnant w o m e n and individuals with chronic liverdisease, should avoid high levels of exposure of T C D D , such as manufacturing and occupational spraying; if the level of T C D D in herbicide formulations remains below 0.1 ppm, health risks should be based primarily on the potential toxicity of the phenoxy acid herbicides per se and not on contaminants such as T C D D ; there is no definitive indication that the phenoxy acids and T C D D are carcinogenic; the evidence is fairly conclusive that T C D D is mutagenic in tests with bacteria; both T C D D and 2,4,5-T have caused teratogenic effects in small animals. A number of recommendations were submitted by the symposium and some of them are worth citing in this review. For example, manufacturers should utilize processes that minimize the formation of TCDD, thereby reducing the risks associated with exposure to this dioxin; manufacturers should adopt methods and techniques to minimize environmental pollution by TCDD in the event of industrial accidents (such as the one that occurred on 10 July 1976, in Seveso, Italy); strict precautions should be taken to ensure safe disposal of TCDD-containing residues; since the actual mechanism(s) of toxicity of TCDD is unknown, additional research is needed to determine how this and other dioxins act in living systems; the stability and bioaccumulation of TCDD should be thoroughly investigated under field conditions, including various types of climates and soils.

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This book is highly recommended to those concerned with the formulation and application of phenoxy acid herbicides, their mode of action, their risk/benefit relationships, their behavior and persistence in the environment, and the safe disposal of wastes from this industry. In this reviewer's opinion, scientists and engineers throughout the pesticide industry, as well as university research and extension workers would benefit from the very current information contained in this book, and from the conclusions and recommendations of this symposium. J.F. PARR

(Beltsville, Md, U.S.A.) CLIMATIC CHANGE AND AGRICULTURE IN NORTHWESTERN EUROPE

Climatic Change, Agriculture and Settlement. M.L. Parry. Dawson Archon Books, 1978, 214 pp, 44 figs, 5 tables, 8 plates, notes, refs and bibliography, £ 9.00, ISBN 0--208--01722--4. Climatic change is a fascinating subject, one that can stimulate the imagination. The climatic extremes known to have occurred throughout geological time seem remote and unreal; and yet, the years of climatic extremes suffered within a human lifetime would, with persistence for even a few years, tend to produce those extremes of geological time. Such changes, even for a few years, have had significant effects on food production, disease, mortality and the welfare of communities. In this book the author has set out to "narrow the area of continuing speculation and uncertainty that surrounds the role of climatic change in agricultural history". He does this by examining harvest yield and harvest failure in relation to some parameters of climatic change. He relates this to the sensitivity of marginal agriculture which in the areas he has studied in northern Europe depends upon accumulated temperatures and minimum levels of warmth, the degree of wetness and exposure. These of course, are quite different parameters for marginal agriculture from those in many other parts of the world where incidence of drought in terms of both amount and distribution of rainfall are often the key parameters. The objective of the book is to "summarize existing views on the scale and direction of climatic change in Europe since about A.D.1000 and to evaluate its impact on past agricultural economies". This is done by focusing on the marginal areas and using the evidence of the use or abandonment of these areas as the most plausible indication of an effective climatic change. The author describes briefly climatic processes and the possible causes of climatic variations and then discusses the kind of evidence used for tracing the chronology of climatic change. This includes instrumental records, meteorologic descriptions by writers and diarists, and proxy evi-