Document wD63wk7k53en9NV4LZ7abD0NQ

1 Fiont the desk </ i KIA1KR P. V'ill'K! v /Jrf Cotmei. Toxicol. Vol. 9, pp. 65-80. Pergamon Press 1971. Printed in Great liritain Review Section Trace Chemical Contaminants in Food: Potential for Harin*t L. Golbcko Institute ofExperimental Pathology and Toxicology, Albany Medical College, Albany, New York J220S, USA (Received 20 August 1970) Introduction Tlic organizers of this Symposium arc to be congratulated on its timeliness. No one can deny that we arc going through a stressful period in the history of food safety evaluation. During three decades of steady progress, immense benefits were conferred on the public through advances in agriculture and food technology, developments that had involved the introduction into food of a variety of chemical additives arid contaminants. Considering the state of knowledge at the time when decisions were made on the acceptability of these materials, the record of safely of these chemicals is truly remarkable and stands os a tribute to those on whom the burden fell to make the critical judgements. Despite the fact that some of these men arc now being vilified, we honour them and recognize, as History will, the magnitude of their achievements. The reaction we arc witnessing is a well-known social phenomenon, in which established standards in general arc in process of demolition. Not only is there a movement in mnnv countries to ban food additives as unnecessary and dangerous, but the harm lessness of tiacc contaminants is particularly called in question. It is appropriate that we undertake a ciitica) reappraisal. My task, as 1 see it, is to explore the wider implications of food contaminants in order to assess, in practical terms, the problems and degrees of hazard associated with some of (he major categories of these chemical agents. Scope of the* issues considered When the Food Protection Committee (J959) defined safety as "practical ccitainty that injury will not result from use of a substance in a proposed quantity or manner'' they had in mind a degree of certainty which, while not the theoretically desirable stale of perfect assurance, is yet an attainable measure in practice. In the present climate of opinion, questions are raised: Is practical certainly acceptable when the potential hazard, however remote, is one that may be shared unwittingly by vast numbers of people of various ,vcs and in various stales of health? Not only is this degree of safety deemed insufficient, but Krscatch reported here was supported by Rcscnich Grant P-0!-l".S-2?6-02 from the National Institute c>f Environmental Health Science*, NJII, USt'ilS, by the National Institutes of Health 'Itaimng Grant 5'101-LS OOOIM-OJ, and by lb*.* P.M.A. 1 oumlalion. J Presented at a Symposium on "Chemical Contaminants in rood Ha/.nd or Not?", sponsored1 by the Pood and Drujs Directorate, Depaitincul of National Health and Welfare, Ottawa, Ontario, and held in Ottawa on IS-19 June J970. rctme/l--I 65 MQNS 085398 66 L. COLDERO equally inadequate is much or the traditional supporting evidence of safety--as, for instance, long history of safe use of a chemical agent that contributes a trace residue to food. Roistering the insistence on `absolute' safety is the introduction of what one might call `tenets of uncertainty', many of which would not have been regarded as insurmountable in the recent past. As a reflection of this uncertainly, much of my presentation will be concerned with categories or potential hazard regarding which, in the opinion of some authorities and many would-be experts, no gcncrally-acccplablc assessment can be made to day. The process began with the concept of "zero tolerance' for chemical carcinogens, and the Delaney Amendment has enshrined this dogma beyond the reach of scientific criticism or the exercise of informed judgement. The irndcrlying reasoning has been set out by Weisburger A Weisburper (196S) and in the Keport of the Secretary's Commission on Pesticides and 'I heir Relationship to Environmental Health, the so-called Mruk Report (Commission on Pesticides. 1969, p. 492). Almost imperceptibly, the same reasoning has been extended to teratogenic cllVcts of food contaminants: even though, in my view, the scientific basis of zero tolerance for carcinogens is inapplicable to teratogens. The strong emotional reaction stirred up by fears of genetic hazard to future generations has sufficed to stretch the zero tolerance concept yet further, to the area of mutagenic effects. To my knowledge, not a single case exists in which a food contaminant of any sort, even a mycoloxin, is known to have produced mutagenic effects in nmn. As the crowning pediment of the entire .structure of largely hypothetical hazards, we have the thesis that the phenomena of mutagenesis, caicinogcr.csis and terntopenesis arc so closely linked that n positive result in any one of these areas auto matically renders the compound suspect on all three counts. On the other hand,'should it happen that a chemical agent turns out negative in all the tests applied, it remains under suspicion until such time ns someone can discover an organism, devise a route of adminis tration or achieve a sufficiently heroic dose to produce some positive biological result, however bizanc. Thus there is an obvious premium on ingenuity and persistence! Carried to their logical conclusion, these considerations of carcinogenesis, tciatogcncsis and mutagenesis strike at the very roots of technological advance in food production, processing and distribution. Hence (he practical reality of the potential hazards in these categories merits special discussion in (he context of food contaminants. Carcinogenesis Numerous factors are known to influence an animal's response to a dietary carcinogen, so that any extrapolation to man of a no-cflcct level in animals is fraught with great un certainty. The statisticians have embellished this plain biological fact with mathematical adornments (Commission on Pesticides, 1969, p. 493), but what they have failed to stress arc the uncertainties attending the demonstration of weak carcinogenic activity, Even with a compound as extensively studied ns DDT, the conclusions based on the Rionctics study (Junes, Ulland, Valerio, Pctrucclli, I'ishbcin, Hart, Pallolta, Rales, Falk, Clart, Klein, Mitchell A Peters, 1969) arc subject to dispute both on statistical gioundx (Weil, 1969, 1970) and on such questions as the interpretation of liver nodules without antecedent study of their pathogenesis, without looking for possible regression on discontinuing administra tion of the test compound, without adequate attempts to transplant the hepatic nodules without trying to grow the ceils making up the nodules in tissue culture (SJifkin, Merkow, Pardo, Epstein, Leighton A barber, 1970) and without detailed attention to pulmonary mctnstnscs, both in controls and test animals. MONS 085399 The i; if this is foithcm fund.irn, impoit.i t (ration i | or for r I IVslicU I ductioa j coinnv: I crimiu.i: | of a co | hypenn j ((it.,-mi appiopr tliesuK | prob.il>! i Tiratn** In chi height i Icial rot i In ;iii> ; rcfhvuv by: b. ;> I970i; i :t silivt i somt.i. h Situ- .hi PlauNlei mceli;"' l`>59). | 1969). 1 U-rc render t maxinu artefacti paiticul. i of many example Parof, I known. (I cfeint amino a in 41 abnorii., Pitskata for instance, :o food, c might call tountablc in * concerned ! authorities to-dny. The nit, And the criticism or ut by Weis* n Pesticides .'oinmission in effects of >lemncc for lip by fern s toe concept nc exists in v produced : of hugely ontogenesis arefts nuto.1, should it mins under f udmimsleal IlSIlll, .*! :;:tog.rncsis reduction, Js in these arciiiogen, t prcHl tin* thematical d to stiess ven with a ;tics study ut, Klein, x*cil, 1969, dent study dminislta* ic nodules . Met how, ndmoiinry I) TRACE CHEMICAL CONTAMINANTS JN FOOD 67 The insistence on administration of a `maximum tolerated dose' may also he misleading if this is the only dose tested, as in the Dionctics study (Ilines cf al. 1969). No justification is forthcoming for abrogating the need to establish a dose-response relationship, which is fundamental to nil toxicological endeavour. Furthermore, the route of administration is allimportant in tests for carcinogenesis or tcratogencsis. We arc told that "parenteral adminis tration is an appropriate test route for pesticides to which humans arc exposed by inh.il.ition, or for pesticides which arc systcmically absorbed, following ingestion" (Commission on Pesticides, 1969, p. 660). Alas, the lessons of yesteryear arc so readily forgotten! The pro duction of subcutaneous malignant tumours by water, sail, glucose and a host of other common nutrients (Grasso & Golbcrg, 1966a) seems not to act as a deterrent to undis criminating experimentation by this route, despite the demons! ration that physical properties of a compound, such ns the surface activity, lipid solubility, amphipalhic character or hypcrosmolarity of the solution injected determine the neoplastic outcome in many instances (Grasso k. Golbcrg, 1966b; Gangolli, Grasso &. Golbcrg, 1967). It is safe to predict that, by appropriate choice of dose, concentration of solution and frequency of administration by the subcutaneous route, any chemical agent can be shown to be a carcinogen in the rat and probably also in other species of laboratory jodent. Tcratogenesis In cheeking on the potential teratogenicity of trace chemical contaminants in food, the height of absurdity is achieved by the combination of a maximum tolerated dose, a paren teral route of administration and the application of zero tolerance on the basis of the results. In this area we know full well that any one of a host of adverse influences on the mother is reflected in foetal deaths, resorptions and/or abnormalities. Teratogenic effects arc elicited by: transport of mice by air on days 12 and 13 of pregnancy (brown, Johnston & Niswandcr, 1970); fasting, for 24 hr or less at a critical stage of gestation (Kallcr k Warkany, 1959), a situation which may be brought about inadvertently or unsuspectingly by inducing somnolence, lethargy, muscle weakness or ataxia; a diet of raisins for l day (Peters & Strassburg, 1969); severe limitation of movement or avoidance behaviour (Rosen/weig. k Illaustcin, 1970); and many other non-specific factors probably acting through a sties* mechanism, as well as hyper- or hypothermia and endocrine influences (Kalter k Warkany, 1939). hven subcutaneous sodium chloride is teratogenic in mice (Nishimuta k Miyamoto, 1969). Here above all is a situation that demands the utmost care in selecting doses that do not render the mother sufficiently ill to produce even transient inappclanco. The use of a .maximum tolerated dose overlooks the possibility of non specific toxic stress. Apait Horn artefacts that arise by (his means, attention should be directed to the mechanism by which particular teratogenic effects arc elicited. 7 he. production of even transient deficiency of one of many vitamins or minerals suffices to induce reproductive failure or malformations. An example is the ease of J-D'J'A, which is teratogenic in mice (Tuchmann-Duplesds k McrcierParol, 1956). The production of congenital malformations by an excess of \ itair.in A is \u il known. A tenfold excess of nicotinamide is cmbryotoxic in the pantothenate-deficient rat (Lcfcbvrcs-Hoixsclot, 1951). Maximum tolerated doses of other H vitamins or of must amino acids have not been studied. A single injection of 2 mg leucine elicited abnormalities in 41% of chick embryos in an experiment in which 4 mg thalidomide brought about abnormalities in 22%, against an incidence of 2% in the control group (UngMrdm, 1 nl;i k Pirskanen, 1967). MQN5 085400 () ) 68 L. GOLBITRG These considerations arc provided ns n background to recent developments that led to the withdrawal of a petition lo establish negligible residue tolerances for 2,4,5-trichlorophcnoxyacclic acid (2,4,5-1). The petition would have set tolerances of 0 2 ppm for 2,4,5-T from the application of the acid form or certain salts or esters in or on a variety of food stuffs. Subsequently it was announced that the use of 2,4,5-T on food crops would be cancelled. This interesting ease study began with the observation that 2,4,5-T was teratogenic and foctocidal in two strains of mice when administered either subcutaneously or oially and in one strain of rats when administered orally (Courtney, Gaylor, Hogan, Falk, Dates & Mitchell, 1970). Analyses of the specimen of 2,4,5-T that had been tested revealed the presence of approximately 30 ppm 2,3,7,8-te(rachlorodibcn70-p-dioxin (referred to licncefoilh ns dioxin). Subsequent study of standard 2,4,5-T containing less than 1 ppm dioxin, given to rats by gavage in doses up to 24 mg/kg daily, failed to reveal evidence of teratogenic or cmbryolnxic effects (Emerson, Thompson, Gerbig & Robinson, 1970). Under similar conditions, (he dioxin produced no discernible effect at a dose of 0-03 /tg/kg/daify, while doses of 0-125 /o'./kg/day or. greater manifested toxicity to the foetus and, at 8-0 pg/kg/day, to the mother also (Spaischu. Dunn Cl Rowe, 1970). Finally in evidence picscmcd before Senator Hart's subcommittee, samples of 2,4,5-T containing less than 1 ppm dioxin were repelled lo have been tested by the oral route in rats nt levels lip lo 150 mg/kg, with negative results. In three strains of mice, levels of 100150 mg/kg/day, given subcutaneously in dimethyl sulphoxidc, proved teratogenic; so did the dioxin in both species tested (loot/ Chemical News, 1970). Even assuming that doses of 100 mg/kg daily did not servo lo introduce sufficient dioxin to account for the observed effects, it should be realized that such quantities of 2,4,5-T arc ill-folctafcd by mice. 'I hey lie within the range of closes studied by Sos A Kcrlni (1958) and, later, by Fiorsliciin A Velcolf (1962) and Florshcim, VclcofT & Williams (1963) in the case of 2,4-<lichloi'ophenox>acctic arid (2,4-D). In experiments on rats, 2,4-D was shown to produce a striking reduction in the scrum level of protein-bound iodine, as a consequence of the displacement of thyroxine from scrum proteins into (lie liver and to a lesser extent into the kidney. In this way a characteristic 'hyperthyroid' state is created in these organs. Ethyl cbloi'ophcnoxyisobutyrnlc acts In a manner similar to 2,4-D, though some differences in detail may be observed (Kuegamei*, Ryan, Richer! A Wcslcrfeld, 1969). 'lhc profound effect exercised by 2,4-D, and presumably also by 2,4,5-T, may not be iclnlcd in any way to the observed teratogenic action of 2,4,5-T in mice. Nevertheless Die metabolic and other actions exercised by massive doses on the mother, the foetus, or both, Should be taken into consideration in extrapolating from 100 mg/kg/day in mice to residue levels below 0-2 ppm associated with a limited number of foods in the human diet--a ratio possibly exceeding 5000. The possibility of introducing dioxins into the environment has been pul forwnul as a further reason for taking action against 2,4,5-T. This aspect of polychlorinated compounds is dealt with below. Quite apart from concern with mechanisms of action, or the avoidance of artefacts due to non-specific stress, the metabolism of a test compound is a highly relevant consideration in teratogcncsis brought about by drugs or food contaminants. If the metabolic pathway in the. test nuimul differs radically from that in man, the results are unlikely to be useful for the assessment of hazaul arising from trace contaminants. The finding of cmbryotoxicity only has meaning in an apptopriatc animal model. There is a further aspect that has been insufficiently stressed in the past: the fact that the i i j ! j | Jl I i j ! j . ' J { j MONS 085401 use of a ms abnormal i pathway tl nml/oi nbi situation-* i levels of c' While the . his |i )><" liases. Cilr dose. nvF chaiiMcii- Mutagi-m-s The i i pteat and i diet within tests arc piavliiMl. : rcliMamv result in ;i. until piu.v Munu, is i agents, sir chekdors . ivnstihien; Chelating c It i` not than the g we dither iavailable a potential i of the lest body. I fai hai i.i of h alkjlating In the n. on IV,licit' too fat ren mulaeeme mediated ; thioiigh lit animal tre developin'. systems. A cnee ami | compound Hint led to 5-tricliloroi for 2,4.5-T qy of food 's would be logcnic mid ally mid in I;, IJntes A rvcAlrd the d to Jicnccpm dioxin, teratogenic do similar laity, while pn/l;p,/dfiy, of 2,4,S-T al route in els of 100 nic; so did init dioxin 2,4,5-T arc (1958) and, in Mu' ease f.lio\vn fo .qnenee of extent into airs. 1 thyl Icicnres in jay not he tireless the ov both, to residue cl - a latio ninent has aspect of tefacts due .'idertition utlnvay in fill I'tu I lie \icity only cl that (he TRACE CHEMICAL CONTAMtNANTSJN FOOD 69 use of n maximum tolerated, dose involves risks of artefacts, among them those arising from abnormal metabolism--either qualitatively or quantitatively, or both. There is no metabolic pathway that cannot be overloaded, with consequent diversion into other metabolic routes and/or abnormally prolonged retention or excretion of the unchanged compound. Such situations may be totally unrepresentative of the body's handling of the test compound at levels of exposure approaching more realistically the practical conditions of intended use. While the object of the toxicologist is to seek out target-organ effects elicited by high doses, his purpose in doing so is to provide guidance to informed searching for effects at lower doses. Grossly aberrant pathways and rates of metabolism that may exist at exaggerated doses make it imperative not to assume that effects observed at these doses arc neccssanly characteristic of the changes occurring at lower levels of exposure. Mutagenesis The risk of mutagenic effects to future generations of mankind is now thought to be so great And imminent that no chemical agent may be regarded as acceptable for use in the diet without being subjected to a battery of tests for mutagenicity. We ate assured that these tests arc "entirely practical and feasible . .. precise, efficient and relatively inexpensive ... practical, sensitive and relevant" (Commission on Pesticides, 1969, p. 572). Why then the reluctance to apply tests of this sort to ail food contaminants? Presumably any positive result in any one lest al any dose makes it necessary to consider ihc compound as dangerous until proved Snfc---though how such proof of safety can ever be achieved in these circum stances is not dear. On this basis, for example, it becomes necessary to dispose of chelating agents, since all those tested so far arc mutagenic (Kihlrmm, 1966). The problem is that chelators me plentifully present in food and throughout the body. Adenine, a common constituent of food, breaks chromosomes; that is it acts as a 'clastogen' (Shaw, 1970) by chelating certain bivalent metal ions. It is not my intention to convey the impression that as a toxicologist 1 am less concerned than the geneticists over the possibility of mutagenic effects of food contaminants. Wliuc we differ is on priorities for testing and possibly on the degree of satisfaction with the tests available al present. The range of compounds tested so far for mutagenic and cla-.to'vme potential is so limited (T able 1) that in effect we know virtually nothing about the u>pomr of Ihc test systems to the multitude of common chemicals found in 'natural' food oi in the body. 1 fail to see how, lacking such background experience, we can assess the potential for harm of trace contaminants in food by equating Ihcm with cateinogcns and with paucilul Alkylating agents used in cancer chemotherapy. In the months that have elapsed since Ihc publication cf the Mi.il; Report (Coiunuv.ion on Pesticides, 1969) the view Inis gained wider acceptance that non-mammalian systems aic too far removed from the areas of concern to be adequate lest systems for assessing potential mutagenic ha/aid to man. Unfortunately, for the detection of point mutation*, the hostmediated assay still employs micro-organisms; but this situation will no doubt be remedied through the use of mammalian cells maintained in tissue cull me ami implanted into the lu\.t animal treated with the test compound. A variety of intcioMinr approaches aie under development, based on in vivo cytogenetics, the dominant lethal test and in vitro cell-culture systems. All these tests call for careful evaluation and the acquisition of substantial experi ence and perspective before being applied indiscriminately for picdictivc purposes u> new compounds. MONS 085402 70 L. GOLMiRG Tabic I. Food clnstopens (cfaomosome-breaking o$entt; C) ond iiutfn^cm (A/) I. C or M In non-mnmmrtlimi organisms Acetate Amyl Alcohol Acetophenone Cyanide Iitlumol Formate K* (excess) Cnptan Ethylene oxide Ethylene bromohydrin litbylenc chloiohydrin Ethylene dibromidc DDT Nitiito Pyiophosphnies II. C in mammalian organisms llcxamcthylcnctciiamific III. C in human cells in vitro or in vivo Adenine AHatoxin Arsenates Bisulphite Caffeine Cyclamatc Cyclohcxylamine Lead (excess) Meihylmcrcnry Theobromine Theophylline IV. Suspected of being M or C Acetone' )Un/o(n)pyicnc Ethyl acetate Methanol Methyl ncclnto 1'iopanol Monosodium glutamate Toluene Mainly front Shaw (1970). I'ollulnnts derived from environmental sources Many and varied arc the possibilities for the entry into foot! of chance contaminants whose exigence in the cmiionmcnl was unrecognized or whose harmful potential was not fully realized. Id recent years contamination of food with persistent chlorine-containing pesticides, principally DDT, aldrin ami tliekJrin, has commanded increasing attention. The environmental and other problems presented by these compounds have bam discussed in numerous publications and reviewed most comprehensively in the report of the Commission on Pesticides (15769). On the basis of this report, action has been taken to eliminate the use of DDT mid DDD and, progressively, the uses of aldrin, dicldrin and other compounds that "cause or can cause contamination of the environment and damage to various life forms within it". A price of unknown magnitude, possibly involving serious future reper cussions, has thus been paid for the protection of wildlife and the environment. As far as trace contamination of human food is concerned, the report states clearly that no evidence has ever been produced of harm to man stemming from this source. The sole known consequence of human cxposuic to traces of DDT in food is the acquisition of measurable levels of DDT and DDT in blood, body fat and other tissues. No harmful cfl'ccl has been found to follow such storage (Mayes, 1967). Essentially similar conclusions were reached in n British report on persistent orgunochlorinc pesticides (Advisory Committee on Pesti cides and Other Toxic Chemicals. 1969), and again tire recommendations have been followed by restriction of the use of these materials. Uy n remarkable coincidence the present age of ferment has witnessed the discovery of the presence of polychlorinated biphenyls in a wide range of organisms (Risebrough, Kicchc, Pcakall, Merman A Kirven, 1968) as well as further recognition of the evil potentialities of chlorinated naphthalenes and dioxins (Friedman A Shibko, 1969; Bauer, Sclui!/. A Spicgclberg, 1961; Jones & Krizck, 1962; Higginbotham, Huang, Firestone, Vcrrctl, Ress & Campbell, 196S). To eliminate such materials from the food supply or from the environ ment is a more complex undertaking than might appear at first glance. 2,4-Dichlorophcnol, A potential precursor of chlorinated dioxins, is synthesized by a strain of I'cnicillium from soil (Ando, Kato A Suzuki, 1970). A diligent search will probably reveal a variety of MOMS 085403 cblorinat 1969). 2 Ronncl, 1 he d apparent (1970) h phenyls fmar.r. c tenfold product' under;.:.) lives (M In an poilutan a'.ion at. imihid'? that pa-. prc'CiU are hruu 1 he II has Kr ahead) organic can be r in. thanism> by inlrodm almo't i fi'h and allev.p. imiLnvi Fiiip!. preferca Faro A nerves, damage TatclMi, periphet De,him capacity concern I t ItfttfiliMC) f.litlamnK' itNininnnls ial whs not containing iilion. 'I'hc iscussed in ommission ate the use nmpoumls aiimis life lure reper. As fill ns o evidence ole Known oeiiMirnNc I has been ic reacbed e on 1'estihavc Iwcii very of the h, Kicrlic, itlialilics of A Spicgel;t, Kcsv A: ic environ* oiophenol, Ilium from variety of `: . ) TRACE CHEMICAL CONTAMINANTS IN FOOI> 71 chlorinated compounds of this sort synthesized in Nature (Wylin, Sponger & Gunther, 1969). 2,4,5-Trichlorophcnol, formed as a metabolite of the organophosphatc pesticide Ronncl, is stored in body fat and other animal tissues (Menzie, 1969). The distinction between polychlorinated biphenyls and polychlorinated dioxins is more apparent than real. Thus Vos, Kocninn, van der Maas, ten Noever dc Drauw & dc Vos (1970) have demonstrated that the striking toxicity of commercial polychlorinated bi phenyls is associated with the presence of tetrachloro- and pcntachlorodibenzofurans. These furans closely mimic the toxic properties of 2,3,7,8-lclrachlorodibcnzo-/>-dioxin but at tenfold dosage. Attention should also be directed to the question of photo-oxidation products, several of which, In the ease of pcntachlorophcnol, arc potentially capable of undergoing further cyclizalion to tricyclic and pcntacyclic polychlorinated dioxin deriva tives (Munnkatn & Kuwahma, 1969). In an era of increasing concern about lead as an atmospheric pollutant as well as a food pollutant, there conics, as a final blow, the recognition that hazards of mercury coiilaminRtion arc not confined to fish from remote Swedish lakes, but, as forecast so accimitcly by Dcrglund (1969), are here on the American continent. F.nch of these problems has its own individual characteristics, yet there is a common thread running through them all: (he fact that past ignorance or disregard of ecological implications is only now being overcome ns present-day methods of analysis, in all their tremendous sensitivity, specificity and accuracy, arc brought to bear on the complex questions at issue. The mercury problem is typical in this respect. An excellent account of its various facets has been presented by several authors in a volume edited by Miller A: Berg (1969). An already difficult environmental situation, stemming from treatment of seed grain with organic mercury compounds, has been confounded by the discovery that inorganic mcicnry can be methylated by anaerobic micro-organisms (Jensen & Jcrncldv, 1969), specifically by methanogcnic bacteria (Wood, Scott, Kennedy & Kosen, 1968). The existence of mechan isms by which, mclhxleobalnmin can readily transfer its methyl group to mcrcmic ion introduces a new dimension into the problem, since we are now concerned exclusively, or almost exclusively, with mclhylmcrcury residues far more than with inorganic meremy in fish and olhci foods. Such a transfer of interest has far-reaching implications, in \inv o! allegations of subliminal neuronal damage, potential for icralogcnesix and olvctvcd mutagenic effects in lower organisms. Emphasis on the accumulation of mclhylmcrcury in the central nervous system, with preferential injury to certain groups of neurones, such as the cerebellar granule cells (Ivin land, Faro & Sicdlcr, I960; Miyakawa A: Deshimaru, 1969), has been extended to the peripheral nerves, where the initial impact of methylmcicury was found to elicit specific s.lcctne damage to sensory fibres (Miyakawa, Deshimaru, Sniniyoshi, Tcraoka, Udo, 1 [allot i A: Talctsu, 1970). Accounts of human poisoning with mcllnlinereuiy also jcfcr to initial petiphcral sensory disturbances, ataxia and polyneuritis (Kurland ci a!. 1960; Miyakawa Ac Deshimaru, 1969; Tsubaki, 1968), The suggestion that accumulated mclhylmcrcuiy has the capacity to "pick off individual neurones raises three questions that arc the core of the issue concerning nictliylmercury; 1. Is the natuie of local binding sites for methxImcrcury in contain individual neurones such that selective accumulation occurs within these cells, more, or less independently of the rate of intake of mclhylmcrcury, the resulting total body burden and the nature and extent of redistribution of the mcthylmercury that ocems MQNS 085404 ) 72 L. coi-8tf; within the body with the passage of time, and, finally, irrespective of the rate of excretion of the mcthylmcrcury and the resulting decrease in total body burden? 2. Docs localized selective damage to individual neurones or groups of neurones represent n permanent and ii replaceable loss which may not necessarily become apparent, at least initially, as a functional deficit? 3. If such loss docs indeed occur, what is the extent of the damage that must be sustained before clinical signs and symptoms arc manifest? In other words, how useful is clinical evidence ns a means ofestablishing a threshold or `noilJ-c/Tcct' dose for nicthylnicrcury in food? Consideration of the accumulation of mcthylmcrcury must also lake into account excretion fiom the brain and from the body (Bcrglund & Berlin, 1969). The body burden, expressed as the concentration of mcthylmcrcury per gram of brain, docs bear a direct relationship to intake and to the appearance of neurological signs. The brain content of mcthylmcrcury, however, may not reflect adequately the extent of irreversible damage to susceptible neurones or other structures. Despite the elegant studies of distribution of organic mercury in mice (Osthmd, 1969) ami men (Aberg, kmun, Talk, Greity, Persson A Snihs (1969), we have as yet no means of knowing the amount of mcthylmcrcury needed to cause a critical degree of long-term irrcvcrnblc damage to the foetal nervous system, which is said to be mote susceptible than that of an adult (Bcrglund A Berlin, 1969). Equally, possibilities of effects on germ cells cannot as yet be gauged by measuring body burdens. The p.cnerally-accepted value for the biological half-life of mcthylmcrcury is about 70 days. According to Atvrg c( al. (1969), a weekly intake of unit amount of mcthyhnereuric nitrate will result in a total body burden of 15-2 units of mercury at infinite lime. The longterm consequences of such storage remain to be determined, particularly in man. The oppoilunily for epidemiological study of exposed populations must not be missed. l'icorcupation with those problems that arc currently the most pressing must not cause us to lose sight of traditional, yet increasingly serious contaminants like lead, or environmental contaminant hazards of uncertain magnitude like cadmium or asbestos. Ihc dimensions of (he lead problem in food and drink arc still not accurately comprehended. A recent series of analyses of basic foodstuffs in Germany (Lehnert, Stadelmann, Schuller & S/adkowski, 1969) revealed an average intake of lead tlnough food of 0-518 nig/dny, with giccn vegetables contributing a major proportion. Undoubtedly some of litis lead otiginalcs as an air pollutant (P.vcrclt, Day & Reynolds, 1967; Danielson, 1970). Also, unsuspected lead hazards abound, particularly for children, as exemplified by the conscqucttces of intrauterine and neonatal exposure of the offspring of mothers consuming tintaxed whiskey in the southeastern United States (Patmisano, Sneed & Cassady, 1969). The complexities of biological interrelationships of trace minerals, both commonplace and rare, in food and water arc attracting increasing attention on the part of those interested in hypertension and cardiovascular disease (Mnsironi, 1969), cancer (Rose, 1968; Kanisawa A Schrocdcr, 1969) and dental caries (Loscc & Adkins, 1968; Jenkins, 1969). With each passing clay it becomes more difficult to disentangle polentmlly-harmful from potentially* beneficial effects of tunny trace metal contaminants of food. Interactions between contaminants Concern has often been expressed that, among the thousands of chemical contaminants present in food, some subtle forms of interaction with one another or with food components | j ! ; ! { ! j , \ j ! * j j ; I > ! . ! ` } ! ; ! j ; ! j J j J j j ( i j j j I MQNS 085405 will be m, past (Go*' placates. that c\. 7!nt>, srnitic.i Among r dangctt. . eido on food Co front t; . as todi-, r.C'iieit. lurK r, comfit . Knifin' 'lh.-.(Men., StfCll'.* . (ii-cn* Cc'vir _ (I'.V. food, t c.dcid. int > 3n i:.. Atro. . Sag m, that 1* * dire.:;;. An . Ih:: q. - ' If.(tv . . do-c i. i.id IrmN'i . utc of : pi up - . 1'if ; expo Cunlio high Ivhn. . Cficc;' . n.ituf.i.' if the rate or ly burden? of neurones arily become Ihnt must be words, bow ll-cfl'cct* dose into account l*ody burden, bear a direct in content of le damage to i&tribution of rcitz, Perwon rctiry needed vous system. >69). Equally, ly burdens. . y is iibout 70 .iliylmei curie ne. Tire longin man. *1 he nissnl. uM qI.cause I, <n environ* .sbestos. 'flic >mph hended. lann, Schaller KS1K mp/dny, of tins lead 1970). Also, by the consc* onsuming tin* ly, l%9). commonplace -osc interested 68; Kanisuwa '>). With each n> potentially* eonlatuinants lil components f) TRACU CHEMICAL CONTAMINAS W I'OOO 7J will be manifested as unexpected toxic cfTccts. Instances of this sort that have arisen in the past (Golbcrg, 1967; Friedman & Shibko, 1969) indicate that there is no room for com placency. On the other hand, one must be rational in assessing the extent of real hazard that exist s in practice. Thus, in the ease of pesticides, a masterly analysis of possible interactions and their significance has been presented in the Mrak report (Commission on Pesticides, 1969). Among many topics covered, this account places in proper perspective the rather miniscule dangers, under current conditions of use, that arc presented by interactions between pesti cides on (he one hand and mclhylcncdioxyphcnyl synergists and mclhylcncdioxyphcnyl food components on the other. Several attempts to unearth other forms of hazard arising from mixtures of pesticide residues have yielded so little evidence of biological interaction as to discourage further exploration of such possibilities. Suggestive indications of cocarcinogcnicity with afiatoxin can be obtained when cyclopropenoid fatty acids arc tested (Sinnhuber, Wales & Lee, 1966). The results, however, probably have little relevance to the conditions that obtain in human or animal diets. Radioisotopes The issue of "Fallout, Food and Man" was thoroughly aired in a Symposium held in 1963 (Menzel, 1963; Comar, 1963; Eisenbud, 1963). Among more recent developments, the strenuous efforts that have been made to achieve acceptability of irradiated foods will be discussed Inter in this Symposium in connexion with contaminants arising from food pro cessing. A new controversy has recently arisen over the suggestion put forward by Sierngkiss (1969a) who states in effect that nuclear fission products and oilier forms of radiation in food, particularly *Sr in milk, arc the primary cause for the interiuption in the decline of foetal and infant mortality at the jucsent time. The possibility exists that gonad dose calculations made in the past and based largely on ,57Cs were grossly in error, by not taking into account *wSr and its yttrium daughter product as well as radioisotopes such as ,4C and Hi that "seek out specific critical sites in the mammalian eel!" (olerngiass, 1969b, e). Attempts to refute the allegations concerning foetal and infant mortality (Tnmplin, 1969; Sagan, 1969; Lindop it Kolblat, 1969) have only partially succeeded in restoring confidence that both the total level of radioactivity in food, as well as that portion of it that most directly a fleets the gonads, arc well within acceptable limits. An attack from a different quarter has been launched by Gofman & Tamplin (1969) on the question of tritium levels in water issuing from nuclcai-fucllcd power stations (Wcavci, ) forward & Peterson, 1969). Here the substance of the charge is that Ihc existing allowable dose of whole-body ionizing radiation laid down by the Federal Radiation C ouncil (017 rnds/ycar), is too high by n factor of 10. The practical implications, in terms of public health and of the design of power stations to conform with these higher safety standards, are of such magnitude ns to demand critical consideration of (lie Ciofman & famplin proposals (Holcomb, 1970). Fundamentally the problems that arise over the assessment of hazard from prolong'd exposure to low levels of radioactivity in food and water are exactly analogous to tho>c that confront us in the case of carcinogens. T hey involve extrapolation from known effects m high levels of exposure to presumed potential effects at very low levels, levels that mv often below the natural background of radiation or of carcinogens from other sources. Hie effects on the body arc in both instances regarded as strictly addithc, despite evidence that natural food stock ration contains one or more factors that protect against X-in.idiutioii MONS 035406 \ 74 . L. GOLM-RG carcinogenesis in mice (Prshoff, Bajwa, Field & Bnvettn, 1969) and that nnticarcinogenic factors and mechanisms abound (Shamberger, 1970). Among the few voices to dispute the rigid orthodoxy of the majority, lludineci (1970) hns pointed to dose rate, rather than total dose, ns the determining factor which, at low values, may permit recovery and repair mechanisms to operate with exquisite sensitivity. From all sve know of the systems involved, the likelihood that effective thresholds do exist at low dose rales seems greater than the prophets of doom will admit. This statement applies to cancer, genetic effects and chromosomal aberrations induced by exposure to radiation. Residues of drugs mid feed additives Trace contaminants present ns residues in foods of miinud origin constitute another critical area. In an era of increasingly intensive production of animal foods, the use of chemical agents as feed additives serves to improve clliciency of feed utilisation directly, or indirectly by preventing disease. Residues derived from these additives are augmented by Race contaminants resulting from the use of chemotherapeutic agents and pesticides applied directly to the animal, as well ns the pesticide residues forthcoming indirectly from con sumption of Iced of plant origin. Detailed consideration of the implications of the use of drugs in animal feeds has been presented in a Symposium (National Academy of Sciences, 1969), Munio & Morrison (1970) have also dealt with this topic. The most crucial issue at present is (hat of antibiotic residues, a subject dealt with at length in the report of the Joint Committee on the Use of Antibiotics in Animal Husbandry and Veterinary Medicine (1969). This UK. committee (the `Swann Committee*) has arrived at far-reaching conclusions. Despite the fact that present antibiotic residues in food were not considered by the Committee to constitute a toxic or allergic hazard to the consumer, evidence of potential risks resulting from admin istration of antibiotics to farm livestock was deemed sufficiently great to justify prompt legislative action. This evidence related to a marked increase in the number of strains of enteric baetciin of animal origin that showed resistance to one or more antibiotics and were able to transmit this resistance to other bacteria; to the observation of human infection with cnlctic bacteria derived from animals as a result of consumption of foods of animal origin; and to the possibility (hat antibiotic resistance could thereby be introduced into organisms that arc highly pathogenic to man. 7 he sweeping recommendations of the Committee, and the resulting legislative measures applied in the UK have given authorities in other countries much food for thought. Without entering here into the detailed data supporting these actions, one can decide that there arc grounds for reasonable suspicion of hazard but as yet little conclusive epidemiological information. In this situation, as in so many others involving food contaminants, one is left with the alternatives of drastic action on a slender basis of fact or the introduction of limited precautions during the period of grace needed to try to establish the reality or other wise of the presumed hazards. The crucial issue seems to be our increasing doubts as to the usefulness, if any, of antibiotic growth supplements in well-conducted animal husbandry. 7 bis, more than any other factor, militates against continued acceptance of the hazards of what has been termed a ``potentially explosive situation". Migrants from food-contact materials Here we have a vast heterogeneous group of some 5000 chemical agents which for the most part arc present in food in small numbers and in minute amounts at uny one time. i i i \ i } HONS 085X07 Detennin foods fun such infoi regarded . l aved v simulatin' (Uritixb I' Health Ol by the m migration Statutory ably xind In an e, Sumer, l'i chcmivn!,. 1 lie ba'.ie function,d level ia IV. A furth taken by t! Commute. y.eiv/v </'( nlion of (2 culminate At this ( doubt it ix jp cater thcneour.i-e- In (lie i' area of lo namely g:a of tile atm i (logic, I(V 4,.r-tlm'br paUiculuih Another achnimxtcri minute. I'r glycol (I t. soi vc sever other speci (Rowe. I9f gives rixe t> of 'c.iieino the rat Idajtloml, I lh tolerated f< I licarcinogaiic idinfcr (1970) +vhigh, at low ;lc sensitivity, fields do exist *mcni Applies iio radiation. lute Another >, I he use of ji directly, or igmcnlcd by rides applied y from con- ds Jins been H Moriisoi) nf antibiotic i the Use of . committee te fact that constitute it rout adminil'y piompt T Minins of biolics and ni infection of animal laced into v measures 't. Without i thi'ie are miolojuYal ms, one is durlion of ' or other* ' as to the msbandry. hazards of Mi fov the. one time. ,, TRACE CHEMICAL CONTAMINANT' y I`OOD 7S Determination of the precise nature and quantities of compounds migrating into various foods from any single packaging material often presents formidable obstacles. Nevertheless, such information is necessary if the components of the package extractable into food are regarded in essence as food additives (McCollistcr, 1964). Faced with these difficulties, the extent of migration has been assessed by means of food- simulating solvents and various schemes have been devised for broad flexible approval (lhitish Plastics Federation; Golbcrg, 1963), recipe-type approval (West German Federal Health Office) or approval by end use (US Food and Drug Administration.) A recent report by the UK Food Additives and Contaminants Committee (1970) recommends that a total migration limit should be laid down, based on the use of specified food-simulating solvents. Statutory control would be exercised by drawing up permitted lists of ingredients, inestim ably similar to the German lists. ' In an effort to rationalize various approaches on the basis of likely hazard to the con sumer, Fr.iwlcy (1967) elaborated a general plan, based on experience of no-cfl'ccl levels of chemicals (other than pesticides and heavy metals) deduced from lifespan studies in animals. The basic conclusion drawn from this experience was that any material suitable for use as a functional component in food packaging at a level of 0-2% or less could not attain an unsafe level in food contained in such packaging material. A further step in the process of bringing common sense to bear on these problems was taken by the National Academy of Sciences- National Research Council's Food Protection Committee (1969) in a report entitled Guidelinesfor Estimating Vosicologically Insignificant levels of Chemicals in food. There was every reason to believe that some logical implement ation of these approaches by the US Food and Ding Administration would at long last culminate jn a rational method of regulating food contact materials ((Her, 1969). At this point, unfortunately, progress has been halted and in the prevailing climate of doubt it is haul to foresee whether any fresh solution will emerge. The need for action is greater titan ever, for the development of entirely new forms of food packaging needs to be encouraged if mankind is to solve its problems of vvaMc disposal. In the meantime, we have to recognize frankly some of the difficulties inhtu nl in this area of food contaminants. Considering the five major classes of food-packaging m.itcnak. namely glass, coated metal, paper, regenerated cellulose and plastics, om- lias to take account of the amounts of the same compound contributed to the diet fiom several of these smttces (Ingle, 1968), or the addition to food grade oils of what is, in effect, a food additive (lMT, 4,4Mhiobi.s-(W(vM-utyl /u-cresol or other antioxidant) derived from low-pressure or, ntoic particularly, high-pressure polyethylene (Woppon, Uhde <fc Zydek, 1968). Another problem often arises: how to dispel notions of hazard based upon the result-, of administning huge doses to animals, when the amounts migrating from food packaging are minute. Pjobably nothing can bcttci exemplify this absurdity than the ease ol ubskne glycol (KG) which, if permitted for use in food packaging, at rviiemcb low levels, would serve several important technical purposes. FCi suffers from two stigmata. In man. iat> and other species given large doses it produces renal calculi, calcification and tubulin damage (Rowe, 1963). picthylcnc glycol, which is probably metabolized along, lines similar to 1 (i, gives vise to bladder stones and bladder tumours. The attendant controversy over tins form of'carcinogenesis' has been resolved by evidence that implantation even of glass beads into the rat bladder produces bladder tumours (Weil. Carpenter & Smyth, 1965). In the monkey, Wood, Flliotl &. Wright (1%?.) showed that dietary levels of 0-2 ami 0 5% FG could be tolerated for up to 3 years without apparent died. Recently we have dcmonsliated the MUNS 085408 ) . ..... uft. .,v*vt.\ 76 L. COLOrRG capacity of rats and monkeys to excrete and metabolize small amounts of EG with great dispatch (McChcsncy, Golberg, Parckh, Russell & Min, 1971). This facility is shared by man (F. Coulslon, J. H. Wills, E. Golberg & J. C. Russell, in preparation, 1970). Finally, it now transpires that (he normal mammalian organism has EG among the `did lipid' components of its tissues (for references see Bachmann & Golberg. 1971). The consumer's organoleptic threshold for taint acts as a limiting factor to volatiles transferred from plastics and other packaging to food. With increasing complexity of packaging materials, for instance polyvinylidenc chloride-cellophane-polypropylene laminates, traces oTresidual sohents may be transferred to food. Toluene, a typical example, is probably innocuous at levels well above those that cause rejection of the food because of taint (Wilks & Gilbert, 1969). Similarly, in the case of polyvinyl chloride, the extent of migration of monomers and oligomers is so small as not to inllucncc consumer acceptability. Nevertheless, now that vinyl chloride has been reported to be "highly cancer ogenie"- admittedly by inhalation -in rats (Viola, 1970), other considerations enter into the picture. It will be interesting to see how `zero tolerance' is applied in this instance. In an age when problems of waste disposal loom large, the toxicity of pyrolysis products of materials like vinyl plasties assumes importance. Studies of polyvinyl chloride homopolymer and vinyl chloride vinyl acetate copolymer have established the presence of IK'l, CO, methyl and ethyl chlorides, benzene, toluene and a variety of short-chain alkanes among (he products formed (Lc Moan & Ctuigncau, 1969; Cornish A Ah*u\ 1969). A rapidly-increasing and advantageous use of plastics is in the transport of potable water. The Jive major types of thermoplastics in water pipes all contribute minute amounts of contaminants. In some countries the use of stabilizers containing lead or cadmium is Accepted practice; it is doubtful whether the amounts of these elements entering the water supply JVom tins source appreciably increase (he total intake into the body from the environment as a whole (l.efaux, I9GS). Conclusion 1 could cite many more groups of food contaminants that furnish examples of uncertainty as to what constitutes a safe level in food. Sufficient has been said, however, to establish (hat (he po(cn(ial for harm is not conlincd to any one class of compounds or to any one source of contaminants. In the picscnce of this multitude of trace chemicals entering into our food, what should the regulatory approach be? Should we strive to return food to its `natural' pristine state? ChemicaJly-iincontaminatcd food has never existed. Jn fact, if one includes nil forms of contamination, our present diet is Die least contaminated in human history. There arc, as I have indicated, many disturbing features in the present silunlion. The accumulation of complex issues and scientific imponderables makes it necessary to grapple with urgent practical necessities by adopting more limited objectives titan the establishment of levels or other conditions of use that ensure practical certainty of freedom from hazard. In many instances the most we can hope to do is to try to define as clearly ns possible the likely hazard associated with particular conditions of exposure; in other words the price, in terms of potential harm, that the consumer may be cxpcctctl to incur for a certain increment of contaminant level in bis diet. We should cease trying to assme the public that all food is safe and nutritions when we recognize that, in clinical terms, the capacity for harm of`natural' food is virtually unknown. All that (lie toxicologist can claim to acconiplish, or hope to do at picscnt, is to assess the degree to which particular levels of food j j ; ; ( ! , ; : ; ! ! ' ; ; i ' * ' ' ; ; ! J j J i I j j ! ; j : j j | HONS 0S5409 contamin: to the pro Given a food tout, measures ill-conside awaiting . fitulin-'. m facile solu demand (I product tl on the ni; We h:i\ Of food ,i; late ami \a:; the d d C Xl 11`IOCs coiiitn..ci. pre-sar.-., Alice-. Ic.l A (1m-.. iv ( C'.' An.li', U., cftecu. / Ji.MItT, l t , Pi"Ml-'i P.-nv-a.l, ' ;hm( (. i lt.-ij-lu.ld, | bctww.i J't'f il >/ / Iki" lii'in. elm U-n. ItiOO.I, b. 7.mV. il ltirmn. k. of isol.it Jliutmi'.cr, Oir.ir, (\ m.i'V /1 Cor.mir.u- n.c. C't'Miish, I P. tv CoiHll>'>'. lei-i'iv Jj.inii. ! on Nalm.b 1 with great it shared by 70). Finally, ' 'diol lipid' to volatiles unplcxity of lypropylcne cal example, d because of fc extent of unci acceptlily cancctoliter into the nee. sis products >ride homoncc oD IC1, lain alkanes 969). liable water, amounts of cadmium it ip, the water iy ftom the imceilainty to r.xtablisJi to any one niciinp into t food to its i fact, if one J in human nation, 'the v to grapplelablislimnil om hazard. possible the Is the price, 'i n certain - public that capacity for n to nccom* s ets of food i | 1 . i TRACE CHEMICAL CONTAMINANTS IN FOOD 17 contaminants, in designated foods consumed in defined amounts at defined intervals, add to the pre-existing potential Tor various sorts of harm that the diet already possesses. Given an indication that the increment in potential harm attributable to the presence of a food contaminant is unacceptably great, how much information is needed before preventive measures arc taken? Here we arc on o delicate tightrope, balanced between rushing in with ill-considered action before icsuJts have been adequately established and, on the contrary, awaiting detailed confirmation of every aspect of an experimental or epidemiological finding, in spite of mounting evidence that calls urgently for decisive intervention. Too numv facile solutions to this problem have been proposed. Least heed of all should be given to the demand that every straw in the scientific wind should prompt immediate withdrawal of the product thus impugned--with (he rather naive idea (hat the material can readily be restored on the market once its safety has been successfully re-established. We have had ample experience recently of the chaos, public alarm and confusion, waste of food and economic loss that can result when precipitate restrictions arc introduced too laic and without adequate warning, in place of measured and timely precautions instituted as the data develop. Neither neglect nor panic is the answer. Somewhere between these two extremes lies the course of reasonable action appropriate to each chemical-contaminant contingency. Given good science, good judgement and, above all, freedom from extraneous pressures, the right course can be found. m-.FF.UF.NCnS Ahcrp.lr., Hitman, I... l-'alk, R., Grritz.U., Pcrsxon.G. & Snihs.3.-0. (I960). Metabolism of methyl mercury compounds in mail, Fxciction and distribution. Archs enrir. Wth 19,478. Advisory Committee on Pesticides and Other Toxic Chemicals (1969). Further Kerim- of Certain 1`i-isisient OiftftHfch.WiKfi Fr.t/iride.t uwd in Ore/ti Jlrimin. Department of Ldiicaiion ami Screnec, j IMSO. London. Ando, K... Kato, A. A Suzuki, S. (1970). Isolation of 2,4-dicJilorophcno) from a soil luru-.usnmi its hic*lo,:ic.:l sii-nificance. Ih'ochcm. Itipphys. An. Common. 39, 1104. Hachmann, F. & Gollvrp, L. (1971). Reappraisal of the toxicolopy of ethylene glycol. 111. Kiiuvhondii i effects. I / Cosuu't. Toxieoi. 9. 39. Hauer, U., SchnU, K. 11. u. Spicovlbcrp, l). (1961). H.ruOiclie. Verpiftungen bci die Jleisicllun?. von C h oiphci<hVe*'biiuliinrcn. Arch. Ce.cn he/<ath. (iewrrhcliyy. 18, 538. Hcrphmd, J \ (1969). lit Chemical Fallout. Ctmeat Research on Persistent Pesticides. Ldilcd hy M W. Mi'.`c r and Cl. C. Herp. p. 90. C. ('. 1 hoims, Sprint-field, 111. Heri-.lund,F. A Heflin, M. (1969). Risk of inclhylnwicury cumulation in man and mammals and the iel.ition between body Inn den of mcthylmeicury and toxic effects. In Chemical lolhut. (..uncut Rc\ca>('. rr Persistent Pesticides, l'idilcd by M. W. Miller A; C>. Ci. Heig. p. 258. C. C. `1 homas, SpiiiuTiJJ. III. Herpstibm, K. M., J'rilii, T. A Pii>kancn, It. (1967). Terntopenic effects of the amino acid leucine m ;,.e chicken. Fycnrntui 23, 767. Hlood, ]'. R., FUiolt, C. A. A Wriphl, M. S. (1962). Chronic loxicily of ethylene p.lycol in the monkey. Tflxie. r//';>/. Pharmac. 4, 489. Hr own, K. S., Johnston, M. C. A Niswandcr, J. D. (1970). Lffects of transportation by air on Hie production of isolated cleft palate in mice. Absij\ 10th Annual Mn-tinp Teratology Society. p. 198. Hmlinrxr, T. P`. (1970). Frontal attack on radiation. Sricatc. /V Y. 168, 315. Comar, C. L. (J963). Factors inDueneitiy the biological availability of fallout radionuclides for animals I man. J'cdn Proe. I edit Am. Sort ex/>. Idol. 22, 1402. Commission on Pesticides (1969). Report of the Scereuvy s Commission on Pesticides and I heir Re\itir .V . to Fmiratuneniol Health. Parts 1 and 11. US. Department of I kaltli, l-'.ducation, and Wcllare, Wad an . \ DC. Cornish, 11. 11. A Abar, Tllcn L. (1969). Toxicity of pyrolysis products of vinyl plastics. Archs rn\it. II.' h 19, 15. Coniines*. K. Diane, Gaylor, D. \V., Horan, M. I).. Falk, If. L.. Hales, R. R. A Mitchell, I. (I9'0). Ic.a- lopenic evaluation of 2,4,5-T. Science, AM'. 16S, t!G4. Daniekon, (1970). Gasoline conlaininr. lead. Icolopical Research Comniillcc bulletin, no. 6. 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Hotshoim, W. II., Veleoll, Shit ley M. A Williams, A. I). (1963). Some cit'cctx of 2.4-dicltloioplwnoxyacclic acid on ihyioid function in the tat: l.Hects on peripheral thyroxine. hulocrinology 72, 327. Pood Additives and Contaminants Committee (1970). Report on the i.caching ofSubstances from Packaging Mm,rials into Food. Ministry of Agriculture, Fishctics and food, HMSO. London. land Chemical News (1970). 2,4.5-T cancellations, suspensions proposed by PRD. ibid 12(4), 7. Food Pi meet ion Commillcc (1959). Principles anti Piocedtircs for Pxiihiinnv the Safety of food Additives. National Academy of Sciences National Rcsc.mli Council Publication 7)0. Washington, D.C. Fond Protection Commillcc (1969). Guidelines for estimating Toxieo/ogitvlh h>\iemj:cant i.excise/ Chemicals In load. National Academy of Scicnces-National Research Council, Washington, D.C. I ia\sley, J. p. (1967). Scientific evidence and common sense ns a basis for food-packaging regulations. I'd Cosowt. Toxicol. 5, 293. 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