Document gaxmZa1DdqBQ7yZNo5zeD7bbG

onion nated nvdrocarbons and the environment G. McConnell, D. M. Ferguson, and C. R. Pearson In recent years there has been concern about the potential toxic hazards of chlorinated orgamr compounds used as insecticides. It has come to be assumed that similar hazards arc present by chlorinated hydrocarbons generally, many of which are manufactured and used in lar~e quitntiiies. The evidence reviewed in this article indicates that while a number of C, and C. chlori nated aliphatic compounds are widely distributed, they do not accumulate to the same extern as the chlorinated insecticides nor do they have their extreme persistence in the environment. In recent years concern ha* been shown over the environmental effects, on both wildlife and man himself, of the organo-chlorine iniecticides \of which DDT is a familiar example) and the pohchlorinated biphenyls fPCH). This concern has extended to all `chlorinated hydrocarbons': consequently they have been included in the class of chemicals banned bv the Oslo ar.d Paris Conventions to regulate the discharge of waste into the sea. We have made a study of the potential environ mental impact of those chlorinated aliphatic hydro carbons that are manufactured no a large scale. Several surveys relevant to such a study have been published recently, either as review articles or in government or intergovernmental reports: a useful discussion has been presented by G. T. Gooum.ui [il. The following factors must all be considered. 'a> What quantities are produced; bow, where, and in what form the materials are released to the environment; ^b; how they are distributed, and in what concentrations thev occur in the atmosphere, in fresh and marine waters, and in soil sediments; fe) at what levels they exhibit toxic effects to man or wildlife; (d) whether they accumulate in living organisms, and, in particular, Isecome concentrated up food chain*; (e) how stable they are in the environment, and whether any of the products of degradation are themselves likely to have ill-effects. Im(a*ln and distribution pathways World production capacities for all the major chlorinated hydrocarbons are shown in Table t. Of the compounds in column (a) die fluoroehlriromeihaiie* are extensively used as aerosol propellants, and are therefore almost completely lost to the atmosphere after use. The others are employed principally as solvents in industrial or . McConnell. M.4., MJt. Was bom in Copland in Id* educated at ttia CclltQiate School. Liverpool, and Uio < Oior0. wnare no graduated m eRanuatry in H41. In IMS tto |0<nad in* ftataarch Deoartmant of mo in*" Oanorei CDoimcaia Division ot ICI (tinea moijod into Mono Division). Ho nas Soon involves in a ronfo ol Induilnel rosvarch ofoeiema. mainly in tho Aold of organic Bhomlcole and since l*M Nee Had e nmtor .mortal in tho environmental Impact of IM halo-ora.mie comoounoe. D. M. Foreueon. t.Sc.th.O. Woo bom m> Sceiland -n ied. He omdvm*o (in aRysiMoer) from AOerdeon Umvorattp n* 1MJ anO olit.nnsO n< goctoreie from (dmBurgh University m tW. In ISM. be lomod ICI ) mansion' Hygione ftcsearcti lanoretonoi (novr Conirsi Tosicolooy Laborcioryl wn>o no has been concerned ilh ihe lacicolaeicol evoiwaiien ol * v`de '*Qs el industrial and agricultural dwmicaia. C. It Peered". M l. Woo tern in fngisnd .n its*. Rood Natural Sciences at the University of Catnbndee. sosci.vutmo m tiotuerMsitj. Ms )>ntd 1C' >n 1VS3. .it (Ho iliiham Leboratur, m Cr.on. Ho has Usen involved in eniv rand* of etuOies ossocieied >in eom ntsetamenl end prevention el vrelcr OOlluUon. domestic applications. Although industrial solvents irr ;> a large extent recovered, the production nf these sol-. >*-cs represents the need to replace the handing luiies ncui. in their use. The quantities in column a, therefore trprrsent the annual losses to the environment. Tins loss t.iii arise from a multiplicity of sources, correlated mth li. .,) factors such as population densitv and industrial actn . The products in column (b) serve primarilv as ciien:cal intermediates. The amount of them that enters the environment is a very small fraction of the total produc tion, and is limited to relatively few '.aimcal manufac-. turing sites. At these sites smaller amounts of by-product will also be produced; these range from other chlor.ua-.ea C, hydrocarbons to chlorinated hydrocarbons of lujf cr molecular weight and tarry residues. These residues iu\e in the past been dumped partly on land, but parncul.v h at sea; A. Jernelov and co-workers (2] l:a\e describ'd the effects of *EDC tar' dumped in the North Sea. The residues are now either incinerated under controlled conditions, or returned where possible as raw material to modified production plants, in particular lor manu facture of carbon tetrachloride. The products listed vn Table ( are characterized bv high volatility and low solubility in water; some of their physical properties are shown in Table 2. They enter the environment primarily by evaporation to the atmosphere. Some chlorinated hidrocarbons will, however, be lour.d in aqueous effluents from factories handling them, and even in household sewage, and so will pass into municipal drainage systems and riven. During the determination of the partition coefficients shown in (he last column <u Table 2, it was found that there is a rapid transfer of f.c chlorinated compound both from air to water, and from water to air. Irrespective of whether the initial lost ---I' chlorinated hydrocarbon is to the atmusphcic ur ! o hydrosphere, the transfer processes will lead to a w:_e distribution of these compounds, wnli aerial uatwpur: playing a major part. Such processes e.volam the occur rence of some chlorinated hydrocarbon m rainfail and upland waters. Ttbl# 1 Csiimaled world eroduct.nn eaeacitlea (1973) of ma/or chlorinated hyo/ccarboni. m 10* font year (a) (b> Triehloroathylane 1010 Perehloioethtyana 1030 1.1,1-TrichloroetRana 480 Melhylont cMond* 400 Trichlorofluoromathane 433 Oiehlonjditluoromoitidn 370 Vinyl chlorida 1.2-OlchioroaiRana Carbon tairachlonda Chloroform Maihyl Chlorida 10 3v0 13 500 1000 243 no MOMS 064550 Occurrence in the invironmint tetrachloride ;uc widely distributed .it the pg;kg level or I rr s Ji>r the I'-.I.ibon. idmtificnrinn, and measure* lower, hi nddiimn some samples of sea water from mem <>f 1H) l ami Pt'll hx\r been extensively studied and Liverpool Bay. which rcceis i s large solumcs of Indus; rial dr-enbrd. Almost .ill depend nn solvent extraction, and domestic diluents. contain traces (less than 1 ug.kg) careful clean-up l>y rolumn rlnouiatoqiMphy, and measurement by c-u-liquid chromatography (GLC) unmi .m electron capture detector W'licrc possible, of tciracltlornrihane. priw.arlilorocth.uic, pciua. and hrx.'ichlnrobut.uJienc ^HCllD,, hcxadtlorobenzcne, and y-bfiuenc hcxuchlnridc. identification is rnnfirmecl by a linked m.ass-spcctrnmeter Samples of marine sediment from Liverpool Bay con MS . Altlumeb the same basic methods can be applied tained llic same compounds as the nverlsing waters, but to the oiltrr indiiMiiallv import.mi chlorinated hydro there was no correlation between the chloro-orgamc carbons. then hi?b volatility introduces considerable content of the sediment and that of the mid-depth water dnitcuhirs at die sampling, extraction, and GLC from the same point on die sampling grid. It appears that , separation stares. In addition the response of the electron coarse gravels have little adsorptive capacity for these capture detector '.tries widrlv according to the number compounds, whereas sediments rich in organic detritus of chlorine atoms in the molt-rule. and this results in very base a much higher adsorptive capacity. Averaged over considerable ditTerenrcs in the sensitivity and accuracy all samples, the concentrations of chlorinated Ct/Ct oJ determinations of different compounds. But these compounds in the sediments were similar to those in-tlie difficulties ha\e been overcome. . water; hexachlorobutadiene with its higher molecular Initial observations of the occurrence of chlorinated weight does, however, show concentration factors up to h'drocarhons in die atmosphere have been made by a hundredfold. J. P. Riley [j]. J. E. Lovelock [4], P. E. H'ilkniif (5], and P. G. Simmonds [6], Our own observations in the Occurrence In animal tissue atmosphere of north-w estern England, as well as a much Details of the distribution of chlorinated hydrocarbons fuller ranee of measurements in water, sediments, and in the tissues of marine plants and animals arc being marine organisms ate given elsew here (7]. All the authors published [). The compounds found in sea water are agree that ftuorochloromethane, in* and perchloro- also found in marine animals. Concentrations vary from ethvlene. chloroform, and carbon tetrachloride are found 1 ygkg or less in invertebrates, to 10 ug.kg in the Mesh universally in the atmosphere at concentrations normally of fish, to a maximum of 30 ug kg in the eggs ofsea birds in the range between 1 and to ng l; we ourselves also and (he blubber of seals. Special attention was paid to found 1.1.1-trichloroethane at a similar concentration. the fatty tissues of sea birds and mammals, as these The distribution of fluorochloromethane* and of tri- represent the highest trophic level* in which DDT and chlororth' lene. prrciiioroethylene. and trichloroethane, PCB are found to accumulate. As man occupies a which are major solvents. is consistent with their usage. similar position at the head of a series of food chains, The concentrations of chloroform and carbon tetra analyses of a wide range of foods, of both animal and chloride. which are chemical intermediates with limited vegetable origin, have been made: the results are shown lones. is somewhat surprising, and led Lovelock to in Table 3. Finally, it has been possible to carry out suggest that they mav arise naturally by reaction between some analyses of post-mortem human tissue; results are chlorine and methane in the atmosphere. presented in Table 4. During the early stages of these Analyses of rain-water, riven, municipal water sup investigations it was not possible to distinguish analyti plies, and the sea [7] again show that tri- and per- cally between carbon tetrachloride and trichloroethane, chtoroethylene, trichloroethane, chloroform, and carbon but improved technique allowed this later. A summary of the results from this and the previous section is presented Table 9 Physics/ 0'ODtrVft of some aliphatic chtarlnatad hydrocarbons in Table 5. From these results we draw two main conclusions: fa) The S.p. CC) Vapour pressure (mm Hg/2Q*C) Solubility in water al 20*C (parts/10* w/w) Partition coefficient water'air at 20*C (w/v per concentrations of DDT ar.d PCB in fatty tissues are at least three orders of magnitude greater than those of the industrial solvents, lb) Chloro form and carbon tetrachloride are w/v) very widely distributed, and at un Methyl chloride -24-2 3736 7250* 3-3 expectedly high concentrations. Methylene chloride Chloroform Ceroan tetrachloride Ethylene dichloude 1,1.1-Trlchlofosthen# Vinyl chloride Vinylidwe chloride Trichloroethylene PercMoioChylene Fiuoroinehloiomeihane Oifluo.'i'Ct loromsthana Heiacr.ioro butadiene 40 1 ft! 3 7(1 ue 71-1 -- 13-9 11 t 7-0 121-2 231 -- 29-1 21S 362-4 ISO-5 04 04 2320 406-9 574 744 667-4 4306 0-19 13 200 (2S*C) eoo 7*9 moo 490 m (i8*o* 400 two 190 1100 200 (25*5* --2 1 6 11 26-4 0-71 042 (IVC) 410 2-74 122 043 046 0-97 Passible hazard to human health The ubiquitous distribution of the chiorinatrd hydrocarbons means that a population may breathe air, drink water, and consume food containing trace quantities of these m.ifciials. In many instances, the cooking of a food*iu/T will reduce these levels still further. There is. mnrrovvr, evidence for the presence of ihee compounds in human tissue, again at extremely * Uncar 76(1 mm outturn ol orQanocfttonna compound low- concentrations (Table 4). 14 MGNS 06*551 Table 3, which summarizes all (he analytical data, demonstrates that there is no evidence for significant accumulation in human tissue of any of (lie materials under discussion. Rather, they indicate a general back ground, at the parts in to* level, which pervades the whole ecosplicrc--atmosphere, hydrosphere, and bio sphere. These results are in sharp contrast to those reported for DDT or PCB, where accumulation in tissues of several orders of magnitude has been observed [0). It is interesting to compare in Table 6 tlte threshold limit value* iTLV; set by the American Conference of Governmental and Industrial Hygienists with the maxi mum atmospheric concentrations measured m our lurvey (7]. The threshold limit values define permissible atmo spheric concentrations applicable only to an 8-hour working day and a 3-day week. In the United Kingdom, maximum allowable ground level concentrations to which the public might continuously be exposed are set in the range of 1/25th-1,40th of the TLY. It can be seen that the environmental concentrations are less by some orders of magnitude. If we examine the possibility of poisoning by swallow ing, we find from tests on rat* and mice (ho-i^l that al! five aliphatic compounds of Tabic 6 have low tnv.cinci with LD50 values varying between 2 and i;- kc. IT.e LD50 value is the dc.se that will kill 30 per cent nf j group of experimental animals.) The corresponding LD50 value lor DDT with rats was 013-04 2 );g. Clearly the presence of a few pans per 10* of thrse substances in food or water will not give rise to acme poisoning. The acceptable daily intakes 'ADI', of subitance? 1:1 foodstulVs are set by bodies such as the FAO WmI.t.j Party of Experts and the WHO Expert Group on Pesticide Residues. They are generally calculated applying safety factors (of 100-20001 to the maximum no-eflect levels observed in long-term feeding studies i.n animals, taking into account the absorption, metaboUm. and excretion of the substance. Absorption, metabolism, and oxerstion Published reports indicate that most of the chemical* are moderately lo ..ell absorbed from the gastrointestinal tract after oral administration (20, 21, 22]. Tvpicalh, a very large fraction of the administered dose i> excretes unchanged in the expired air. It has been established Table a Chtotinstod hydrocarbons in foodstuffs (Concentrations in 9. *ft) Foodstuff Chloroform airy product Froth milk Choahfrs chssso English butter Hana sggs Moal English bosf (tissh) English bool (fat) Fig's llvsr Offs snff fsts Margarine OtWo oil (Spanish) Cod llvor oil VogoloMo eooking oil Cootor oil Beveregsa Connod fruit drink Light slo Cannod orangs )uieo Instant ceffoo Taa (packs!) Wlno (Yugoslav) Fruit and vegetables Fotatoss (S. Woios) Fototoos (N. W. England) Appios Fopra Tomotooa* 9 a El 1-4 4 9 1. 9 19 1 NA 1 04 1 10 NA 10 4 1 0 t Carbon tetrachloride oft-t 14 04 7 a o to to 0-7 NA o-s 0-2 ft ft 4 os 0 a 9 4 44 Trlchloro' TtieWoro- Porenioro- othono sthylano othylono 04 0-3 9X 10 13 04 NO ft9 19 0-9 1! 14 4 89 97 10 0 7 9 10 1 ft 7 041 NO 3 92 0-7 NO NO NO 43 7 60 3 0-01 NO 4 NO NO 1 9 0-7 39t t4a 1-7 1-2 Mock gtapos (importd) Frooh braod MO 1 10.7 9t *4 NO 7t * Tomato plants wore grown on a reclaimed lagoon at Runcorn Works of ICJ. t HCBO is still usad in soma countries as an insecticide for vineyards. 1 TCE, PCS -- T<<!-, pentacniorosihano; HCBO " Hosachlorobutedieno; HC8 * Heaachlorobrnzsns NA No Analysis; NO - Not Ostsclcd Others HCBO 9-00 KCS 1 NO HCBO 2 NO NO NO TCE 0-1 PCE0 4 PCI 0 9 NO TCE 2 HCBO02HCBO7 NA PCC 04 HCBO 02 NO NO NO NA NL TCE 0-7 NO NO HCBO 09 HC301 TCE 10 HCBO 3-r NO 13 HONS 064552 Taita 4 Occurrence of cMormatad hydrocarbont in human iitsua. Co-'emlrat'ont m ug.*9(**i Uttua) Age ol subfact Sax 76 F 7S r KF 48 M UM 78 M 86 M 74 F Tlaaua Body fat Kidney Uver Brain Body fat Kidney Uvar Brain Body tat liver Body fat Llvar Body fat Uvar Body fit Uvar Body fat Body fat Chloroform Carbon tatrachloridt-r trichloroethane Trichloro* athyiana IS 2 8 4 9 9 t 2 87 8-7 87 1! . 84 8<6 88 10-0 88 sa 24 1 t <1 4 9 4 2 16 39 21 . 34 11-0 3-9 73-8 8*1 14 II 32 <1 9 t 2 3 2 <1 14 32 84 38 34 82 1M 9-8 48 44 Perchtoro* thylana 8 <81 <0-9 <0 9 1 8 2 <5 04 1-2 04 0-7 21 34 MI 41 Q-S 4 HC80 __--___ 04 12-1 18 9-7 14 11-8 0-8 13-7 14 4 Others _ _ __ ____ TCE <0-5 y-BHC 24 y-BHC 7-9 y-BHC 22 that metabolism mult* in the formation of trichloro acetic acid (from trichloroethylene and perchloro* ethylene , mchloroeihanol (from trichloroethylene), chloroform (from carbon tetrachloride), and CO, (from carbon tetrachloride and chloroform) [20-03). Some of the compounds have non-industrial uses and it is possible to compare permitted use concentrations with the maximum concentrations found in the survey described above. The relevant data are summarized in Table 7. This table demonstrates that, with one exception, there are enormous differences between pennitted-use concentrations of tlte chemicals, admittedly in some instances for discontinuous use, and the maximum levels found in food. The exception is carbon tetrachloride, where the suggested guidelines for grain residues are similar to the amount of this material in food; the grain Table 9 Ocrurftnct of chfonnefttf hydrocarbons m Iha environment. Typical concanlrahont (w w) of tha fire majornmpoundt (chloroform, carbon iairacMorida, triet1 faraalhyitfla. parcMotoathylana. trichbroaihanaf Air Rain wattr Surfaet wattr Potabfa watar Saa watar Marina aedimenta Marina Invartabrataa Fish Walerbfrds Marina mammals Fatty feeda Non-fatty feeds Human organa Human body fat Minimum Maximum IP-* 10-* IP" IP-* IP-" IP* 1P-" IP* IP-** IP* 18-" IP* tf* IP* IP-* IP* SP-* >1p* IP-* >p* IP* IP* IP- IP- * P* 10-* IP* IP* residues, however, do refer to regular daily intake. To put the remaining figures in perspective, some 500 kg of cheese would have to be consumed to give an intake of chloroform equivalent to one dose of the linctus described. Meets on wlldll* , So far only a few results are available for the levels of the C,/C, chlorinated hydrocarbons in land animals (other than marine and avian species) or plants. The indica tions are, however, that the levels in such species are not significantly different from the general background con centrations shown in Table 5. Hexachlorobenxene (HCBy and hexachlorobutadiene :'HCQD), of which we have found traces in fish and foodstuff samples, are used on a small scale as pesticides. J. G. Vo* [34] showed that toxic effects occur only in birds fed high dose rates of HCB, namely 30 mg/t over 3 months. At the end of the trials, the average HCB concentration found in the liver "" 35 nij/l. Our own study of effects on marine organisms has been described {*]. Acute toxicity levels for marine fish, barnacle nauplii, and a unicellular alga are reproduced Table I Thrathoid limit talua compared with maximum obiarrad eoneantrations fmg.t) Trichferealhyiant Parehloroathylena Tnchlereeihane Carbon tetrachloride Chloroform TIV 0-50 047 140 048 PIS Maa. observed concentration 0-00019 SIMM pooooi* 0-00008* P00004 * Not tfi.'Urer.tiatvd by analysis, tneitfora, tha concentration hewn t* tha maximum vatu*, assuming tha GlC peak represents wholly tnchtof&athant or earbon tetrachloride. HONS 064553 Tibia 7 Companion of obterrtd concentration* In fcod and pormUttd ut* co.'ictfl<ri(/on Chemical Uses Trichloroethylene Perchtoreethylena 1,1,1-TMehloroethana Carbon tetrachloride Chloroform An**thtlc Extraction advent Antlhtlminthic (veterinary and human medicine) 7 Grain fumigant Antithetic * US Food and Dmjq Admimatration (1973) Food Chemical Newt Guide * t Mertlndale'The Extra Pharmacopoeia' 20th Ed. (1972) t FAO/WNO Expert Committee*. WHO Pesticide Ra**du* Sails* 1,1971 (1979) Ptrmittad coneenttattont/dasa 10-2S mg/Vg decaffeinated coffee* 10-0 0 g,60 kg t (therapeutic do**) 7 90 ug/kg - (coohtd earaal preduets): 10-40 mg,dot* T (cough iinctua) Max. eoncrv measured (1.5 <gj 60 (packt coflea) 13 (butler) 20 (black grapai) 20 (black grapai) 33 (chaasa) in Table 8; companion with Table 5 shows that they are It has been suggested that low concentrations of at least three orders of magnitude higher than those chlorinated solvents could, however, inhibit mi'-robud found in xea water. There is no evidence that the bio degradation processes generally, especially in anaerobic accumulation up food chains, which is such a feature of environments. Particular concern has been expressed DDT and PCD, occurs to any significant extent with the over the effects on sewage treatment. Our observation, commercial solvents. There is some indication that in show that concentrations in raw sewage are uru!;v fish, by-product 'heavies' such as HC8D show some less than o-i ing,l; some of this is adsorbed on to primary bioaecumulation intermediate between the two former sludge, while most is lost to the atmosphere during classes, but this does not increase in birds and mammals biological oxidation, either by activated sludge or feeding on fish. trickling filters. Our initial experiments show that inhibition of aerobic Degradation in tfto environment oxidation does not occur at concentrations Iselow 10 m? 1: Biachtmcdl dffradafwn. -Ai the major chlorinated hydro* this concentration will not normally he found in anv carbons are so widely distributed in the environment* sewage works. An extensive investigation of the erfecu they are exposed to a wide range of potential degradation on anaerobic digestion in sewage work-, particularly b1- routes. Although there is evidence that they can be chloroform, is given in (25]. metabolized by mammalian tissues, w do not know how Physic^cfumieoi degradation. There is evidence for the many other phyla have this ability. U is generally chemical breakdown of chlorinated hydrocarbons -n accepted, however, that micro-organisms, whether water, but in general these reactions are very slow: we aerobic or anaerobic, do not have it. Microbiological estimate the chemical half-life of perchlornenn lene m degradation, which is *0 important for the destruction of water to be about six yean. Exceptions to thu at.ic ur many organic compounds, therefore probably does not compounds which are easily dehydrochlormatcd: the have any significant direct pan to play in this case. reaction rate in such cases depends on the pH. An In mammals, the metabolic pathways of all the com important example of this is the dehvdroehloruuiion <>f pounds discussed so far lead to chlorinated acetic acids, the solvent i.t.i-trichlorocthane, which would have a either directly or via chlorethanob. Chlorinated acetic chemical half-life in sea water ;pH 0. 10'C) of about p acids have all been shown to be susceptible to further months. The decomposition product is vimlidene degradation by micro-organisms in sea water [7]. chloride, with (at environmental temperatures, oniv a minor amount of acetic acid armr.r Ttbhl Acuta torkity ofehhektatad hydrocarbon* to marina organism* (Concantrum* uprauad at mf-ti by hydrolysis. Rapid degradation ;n aqueous systems docs, how ever, occur in the presence of metallic iron. At Mh EC iato D* (Aat-ftah) a ft 1C iato Barnacle newplll EC ta to Unicalluiar alga* the present time die resulting degra dation products have not been iden tified, but this faster rate in tlie pre Trichloroethylene Porchloroethyiane Trichloroetnan* Chloroform Carbon tetrachloride NoaaeMofebutadlana Ethytano dlcMoride Propylene diehlowd* it 1 a a ~a MS 119 61 a M H -- -- MT as S3 0 tence of metals could be important. 10-i The current implication of our s work is that it is by tropupheric -- photo-oxidatinu that the cm inmtnen- -- tat aliphatic oigaim-cltlorinc com pounds are principally destroyed. 440 This will apply also to lltoie com 0 pounds present in the hydrosphere. HONS 064554 *ncc transfer reactions between hydrosphere and atmo sphere <rur rapidly (^Gl. Oxidation can easily l>e demon strated by introducing a few mg/I of die nnjanoclilormc compound into a sealed quartz Husk and exposing the latter out of doors. Monitoring the organic residue shows that the mean half-lives of the chlorine-substituted ethy* lenes lie in the range 6-ia weeks, and of the chlorinesubstituted methanes and ethanes in the range 10-33 weeks. These experiments are naturally influenced by diurnal ami climatic variations of temperature and inci dent solar radiation, and the half-lives are reproducible only to within =30 per cent. Nonetheless, they serve to thaw that tiic simpler aliphatic organochlorines do not have the high persistence associated with the chlorinated insecticides and PCD, nor on the other hand are they sulhcientlv reactive to give rise to photo-chemical smog, a view confirmed by the work of M. F. Brunelle tl at. [ay]. Similar experiments have been carried out exposing the flask to radiation front a xenon arc, suitably filtered to remove radiation below aqo nm, taken as the lower limit of tropospheric solar, radiation. Under these condi tions of constant radiation flux and temperature it has been found in a number of cases that the order of the reaction with respect to the halo-organic compounds is fractional, tending to zero at the higher (100 mg/1) initial concentrations and to unity at the lower concen trations (o'i mg/1). At the much lower concentration* fng I) found in the troposphere we can--at least to a first approximation--assume a first-order reaction with respect to the halo-organic compounds. The kinetic pattern observed does not appear to arise from heterogeneous reactions, since packing the reaction vessel with quartz wool has a negligible effect on half life. It can, however, be explained in terms of initial attack on the halo-organic compounds by some Transient species present in the troposphere, possibly by active photolysis products of such species as nitrogen peroxide, os.one, or chlorine, known to be present in the tropo sphere at concentrations very similar to those of the halo-organic compounds. Deliberate addition of these inorganic species in the xenon arc experiments can accelerate the decay rate, even when the inorganic material is presrnt in murh levs ihan stoichiometric equivalence. 1 lie implication is that, because of ihe excess of lialo-orgame rnmpnimdf over trace nmrg.inic species present in the outdoor fl.xtk experiments, the latter do not repiesrni a true microcosm of live tropo sphere. In that case, the half-life ranges quoted above are probahly over-estimated. We have also identified the degradation products arising from xenon are exposure. For the most part these are simple inorganic species tCO. CO., II.O, MCI) already present in the atmosphere: in some cases {CCI4, CHjCCIj) molecular chlorine can also be formed. Only tri* and pcrcliloroethvlene \icld relatively stable chloroorganic intermediates, ihe di- and tricldoroacety] chlorides, with minor amounts of phosgene. The latter rapidly hydrolyses to CO. and HC1, but the chloro* acetyl chlorides will enter the hydrosphere as the di- and triehloroacetate anions, which have very long chemical half-lives at environmental temperatures. However, we have already noted the microbial breakdown in sea water of both these anions, complete oxidation occurring during a 20-day incubation period. It thus appears that not only are the simple chloroaliplunc compounds not particularly persistent, but their degradation products are simple species commonly found in the environment. Conclusion From evidence so far available we conclude that several chloroderivativesofmethane.ethane, and ethylene arevery widely distributed in the environment at a level ofconcen tration of the order of 1 part in 10'. The particular com pounds are chloroform, carbon tetrachloride, trichloro ethylene, perchloroethylene, and trichloroethanc. The as sumption that the last three occur as a result of chemical manufacturing processes is tenable, but the occurrence of the first two mav also be due to unidentified geochemical processes. All these compounds are fairly rapidly degraded in the environment to carbon dioxide, water, and chlor ide ion, and there is no evidence for their significant bioaccumuiation, via the food chains, to higher trophic levels. References [1] Goodman, G. T. Prat. R. St*. Zand.. 1, il), 107, 1974. {] Jsmelov, A, Rosenberg, R. sad Jensen, S. HW Au, 4, 1 if1, 197a. la) Riley, J. ?. end Murray, A. J. A'atsrs, Land., 24a, 97, 1973. (4] Lovelock, J. .. Magga, JL J. and Wade, R. J. /Sid., >41, >94, 973(il Wilkniu, P. C. 0 tl. /Sid., 14S, 43, 97J. [6] Simmchicu, f, Q., Kcrrin, S. L., Lovelock, J. E. end Shair, F. H. Alampk. Emimmmt, I, Mg, 1974. [7] Psanon, C. R. and McConnell, G. Aar. Jt. St*. Land. 8. (To be published.) [I) Kocman, J. H-, National Swedish Environment Protection Beard. PCB Conference 0, 1973. Il) Abbott, D. C., Collin*, G. I. and Cotslding, R. Mr, Alad. 3S3> >979. lie] Smyth. H. F., Carpenter. C. P., Weil, C. S., Poeaam, U. C* Suretgcl, J. A., and Nycum; J. S. Lilt Vll, Am. mi. fyg. Au. lo. 470, 1969. (||) Paribok. V. P. Farmaiai. Taknkal, so, 78, 1937. [il The Merck Index (19G8:, p. 1037. (13) Banoum, C. P. J. Phana, Labi., 7, 903, 1934. (14I Tori, lion, T. R.. 0>rn. F.. MtCollisier, D. O. and Rowe, V. K. Am. mi. Afjj. An. J., it, 333, 1938. IS [13] McColUiter. D. D-. Hollingsworth, R. L., Oyen. F. and Rowe, V. K. Arthi tmd. Wtk., tj, 1, >938. [16] Speaor, W. 5. In 'Handbook of Toxicology', Vol. 1, p. fie, W. B. 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TJtke. threnoi of Organic belvents m Photocltcmtesi 5nwg Formation'. Air Pollution Control Di.triet, Los Angeles, CaliCorota, *986. MGNS 064555