edited by
MALCOLM M. RENFREW Unwer~ityof Idaho MOSCOW, l d a b 83843
Benzene, A Familiar Hazard? Roger M. Smith University of Technoloov, Loughborough, Leicestershire LE 11 3TU
OSHA regulations in the U S . and Health and Safety Acts in the United Kingdom have brought a positive inducement for better safety practices to the teaching laboratory. The more obvious dangers, such as flammable solvents, hydrogen cyanide, etc., have commonly been treated with care. However, other hazards, although recognized and widely reported, have been largely ignored in the past and now, because of familiarity, are uften forgotten. "Familiarity breeds contempt" is as true here as in other fields. Benzene is a particularly prominent example, and this review attempts to point out
just how frequently and widely its uneontrolled use appears in laboratory manuals and exercises. The dangers of benzene as a toxin of the hematopoietie (blood forming) system have been recognized for aver 75 years. Benzene can beahsorbed both by inhalation or via the skin, the toxic level being about 20,000 ppm in air although effects can be observed at 400-500ppm. However, as with mercury, its principal danger is as a chronic poison. The 1971 OHSA limit, based on toxicity, was 10ppm over an 8-hr day (and how many teaching laboratories acted on those limits?) A recent morestrineent OSHA orooosal(1). b a e d on a soecific i n k betweenbenzene and Irukmia, hol heen pulhihrd, redwin:: the limit 10 1 ppm over nn A-hr day ur 5 ppm i m a 15-minute period; this requires monitoring of exposure and other precautions. The passibility that these levels may be unrealistically severe, as judged by court action blocking enforcement of the new OSHA standard (Ib). does not affect our areuments
ample in this column (10)) but not of toxicity, and the need to use fume cupboards or take other precautions. It can be argued, but only weakly, that benzene is a necessary reactant if only to produce a simple reaction mixture. The second frequent use of benzene in organic manuals, as the chemical of choice to introduce distillation (6,8,9, I I ) , can surely have no justification. Some manuals warn of flammability, none of toxieity. Thus the familiarity with benzene as a common chemical (and by implication innocuous) is introduced a t the very start of the course without any indication of its danger. Benzene can also be found in experiments in column chromatography (8,11,12),and as a typical aromatic compound in spot tests (7, 13).One example of the synthesis of benzene includes the instruction to note the odor and compare it with the smell from an authentic benzene bottle (14). Organic laboratory manuals are not alone in these failines: in a recent analvtical text
plied. The hazards have been well documented in safety manuals, for example, "Dangerous Properties of Industrial Materials," by Sax (2)."It (benzene) is a recognised carcinogen of bload-forming tissues," and the excellent manual by Muir, "Hazards in the Chemical Laboratory" (3),specifies a threshold limit value for skin of 10 ppm (the same as for hydrogen cyanide) and warns, "Extremely flammable. Gives off poisonous vapour. Danger of cumulative effects." A recent column in This Journal makes the same point (41,and a t least one chemical supplier (5)lists benzene as "CANCER SUSPECT AGENT."
Journal recommended benzene as a sample t o test resolution (16). The introductory course in Nuffield Chemistry contained in the index a number of experiments involving benzene, ranging from solubility to freezing point (17), slthough in a number of cases the text doesnot actually use benzene. Of a number of manuals examined only one (18) (from 1970) gave a warning about toxicity. When benzene was used as a tlcsolvent the student was instructed "carry out this experiment in a fume cupboard because benzene vapaur is toxic." Although there may be more recent editions of man" of these manuals and im-
elementary examples introducing the concepts of aromaticity and substitution reactions. This has resulted in a logical, but careless, tendency t o use benzene as a reactant in laboratory courses to demonstrate nitration (6, 7, a'), Friedel Crafts (7, 9) reactions, etc. These laboratory manuals often warn of flammability (also see a recent ex-
many authors used benzene unnecessarily and without warning, even though the toxicity was known a t the time. Secondly, as manuals can he in use in the laboratory or as reference works for more than 10 years,
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l ) r . i i , , g t , ~\'I. Smith g a i d a n I b nwtw rlpgrre i n rhwristry at the ilni-
versitv (11' Manchester in 1964. After completing a Master's degree a t Mancheater, he moved to the Australian National University where he was awarded a PhD degree in 1968. He carried out postdoctoral research with Profesaa Kupchan at the Universities of Wisconsin and Virginia and with Pmfessor ,Johnson at the University of Sussex. He was appointed as a lecturer at the University of the South Pacific in Fiji, in 1972,and has recently taken up a lectureship a t Loughborough University of Technology. His research interests are in the structure of natural products and chemotaxonomy and he is currently concentrating on the analytical use of glc and hplc.
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(Continued on page A861 Volume 57, Number 3, March 1980 1 A85
Safety
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(23j. But why was benzene used in the first place, and why didn't the notice of withdrawal point out the reason for this action so that existing booklets could be amended? Clearly writers of articles and textbooks used in chemical education are not as aware of the prohlem as the author of a recent article on waste disposal (24). "It is hoped that all laboratories nowadays treat aromatics with the carp they deserve and in particular that benzene is regarded not as a solvent hut as a reagent to be used under the strictest control, only when absolutely necessary," (my italics).
teachers and instructors need to be aware of the omissions and hazards that may be present in alder works (note in particular the f o o t n ~ t a s 'in . ~this paper on carcinogens used in two of these texts). Specific warnings to schools have not been hidden in the past; in the U.K. teachers were warned in 1973 (19):"Renzene is dangerous as a chronic poison." "It should neither be kept nor handled on an open bench. I t should not be used as a solvent."; and again (20), "Asbestos wool and benzene should not (my emphasis) he used in schools either in laboratories or elsewhere." For more advanced and experienced students in further education some use of benzene is permissible, but Literature Cited "The use of benzene should be reduced to the ahsolute minimum" (21). Individual uni(1) (a1 F e d ~ r o Reeider, l 42,22516 (19771 and references versities have gone further, and the use of therein. lbi Carter. L. J., Science. 203. 3324 benzene is often controlled as a carcinogen i1919). and thus effectively banned from under121 Sax, N.l.,"DangerusPropenip4of Industrial Mnterials,"4th Ed., Reinhold Publishing Corp. graduate laboratories (22). 13) Muir. G. D. "Hazards in tho Chemical I.ahsrat,ry." T h e hazard needs to he mare widely pubChemical Society, I.ondon, 1977. licized. A eood start could be bv editorialac141 Lowry,G.G..J. CHEM. EDUC.,SS,A263 11978). &m TIM J m r n o l , ~ t ~ t I ~ t , r ~ ~ ~wmg i a r ~ : ~ l(51 e sAldiieh Chemiral Catslo~ue,977173. (6) Holmksmp, G. I
