Document 5D4rraZoxZN1nboD71OO5Bn7J

Reprinted from BioScienee Polychlorinated Biphenyls Another L^ng-Life Widespread Chemical in the Environment David B. Peakall and Jeffrey L. Linoer The recent finding last pelagic birds dying on the coasts of C real Brltian had polychlorinated biphenyli (^CBs) in their liven in concentrations of several hun dred pans per million (Bourne and Mead, 1969) shows that these compounds ere prceent in the ecoeystcm in targe emounu. Thus, it seems worthwhile to summarize and evaluate our current knowledge of theee compounds. Structural and Phyak|al Properties The picture is complicated by the fact that wc are not dealing w th a single com pound. The basic structure of PCBs is shown in Figure I. Any!of the positions marked with an m can m substituted by chlorine. Widmark (196a) lias calculated that of the 210 possible eorfibinationt 102 art probable. His criteria for these lim itations ere those compounds containing five to eight chlorine atom) per molecule end the number of chlorine atoms per ring differing by not more than one The commercially avkilgble Aroclors (Monsanto Company Trademark) are des ignated by numbers (Mojistnio Technical Bulletins). The first two digits represent the molecular type: 12 [ Chlorinated bi phenyls: 2$ end 44 blenks of chlorinated biphenyls end chlorinated tcrphenyls (75% biphenyl end 60% biphenyl, re spectively): $4 - chlorinated tcrphenyls. The last two digits givcj the weignt per cent of chlorine. Thus, Arcelor 1242 is chlorinated biphenyl containing 42% chlo rine. The biphenyls commercially avail able from Monsanto range from 21% to 61% chlorine. Mass specMographic studies of Arodor 1260 (KocmCn et el.. 1969a) show the presence of 11 ilofners: five con taining six chlorine storm, five containing seven chlorine atoms, injl One containing eight. Begley at el. (1970). studying Aro* dor 1254. found Ik compounds: one con taining three chlorine atoms, four contain ing four chlorines, four containing five chlorines, five containing six chlorines, und four containing seven chlorines. Thus, Ttw m* i Hu UtHemt), hhKt. N.Y UtorawC*<W1 I the number of compounds present is, for tunately, much smaller than la theoretical ly possible. PCBs are chemically inert, are not hy drolysed by water, end resist alkalies, adds, and corrosive chemicals. They have low volatility, their boiling points ranging from 271 C for Arodor 1221 lo4IS C for Arodor 1261 (Penning, 19)0). All are stable to prolonged heating at ISO C, and the lower Arodors can be distilled at atmospheric pressure without appreciable decomposition. PCBs are described as in soluble in water and very soluble in hydro carbon solvents, although no exact figures appear to be available. Nothing is known about the biological decomposition of PCBs, but it is likely that they arc more stable than DOT and its metabolites since they lack the ethane component between the aromatic rings, which is the site of action of most of the transformations of DDT. Thus, PCBs have the necessary physical and chemical characteristics for persistence end accumulation up the food chain. Use ol PCBs Polychlorinated biphenyls were first de scribed in the literature in (881 (Schmidt and Shultz, 1881), and the successful com mercial production was achieved by the Swann Company in 19)0. In that year the physical characteristics and commcncul possibilities of these materials was de scribed by Penning (19)0). PCBs arc now manufactured by Monsanto in the United States (Trade name Aroclor). Prodddc m France (Phenochlor), end Bayer in Ger many (Colphen). Other manufacturers arc located in Japan and the Soviet Union No figures of the amount of these mate rials produced annually are available, but to judge from the usee listed ia Table I they may be very large. The uses listed in the table are only suggested applications taken from Technical Bulletin 306 of the Monsanto Chemical Company, and again there is no information on the extent to which theee recommendations ere acted upon by the manufacturers ol plastics and resins. The use of highly chlorinated Aroclors for extending the kill-life of formulations containing chlordane. sldrin, and dieldnn are mentioned under miscellaneous appli cations of Aroclors. This possibiliiv hat been considered in a number of papers. Sullivan and Hornstein (1953), Homatein and Sullivan (1953), and Tsaoat al. (1953) found that the chlorinated terphenyl Aro clor 5460 increased the residual persis tence of lindane. Tsao et ai. (1953) consid ered that there was some indication that chlorinated polypheny! may have a syner gistic effect with lindane. Duda (1957) 0O' x muau NMnroa luasmunoH os cxomc (a) OIO Q-C-0 I HONS 083917 Q7 uccusanmai OOa MMLOMOWMCWfl O o-c-o T| nit a XMKALS ft) Fig. I. Bask Mruciertol PCPs(A) eat gomlMe reacileesol PCBa(i). 958 BioScisnco Vet. 20 No 17 prayed elm saplings with a lindane Arodor MdO mixture (1:4) hn;d then tested the residual effect on the leaves to infes tation with elm leaf basic {GaltructHa jonftomrfer**). He found that leaves treated with lindane plus Aroclor were protected longer and that the Insecticidal effect was more rapid thW with lindane alone. Peaks corresponding to Aroclor MOO have not been detected in the envi ronment. However, under conditions of temperature and flow-rate commonly used lor |as chromatographic Analysis these compounds would not be detected (Reyn olds, 1970). I Nearly 25 years s|o it! was noted thst Aroclor 1242 was one of 175 compounds out of WOO tested tha was effective against mosquito \Atgyp ) larvae (Deonitr el el., 1946). lichtens eift el el. (1969) tested the effect of addi >g a variety of biphenyls and terphenyls o DDT and di eldrin with respect to t ie|r toxicity to house end fruit flies. It w*s found that PCBs had very low toxici y to house flies when given alone but PC Is increased the toxicity ol dieldrin and I >PT, especially the latter. The effcctivenc s pf these com pounds decreased as the i hlorinau-d level increased. For example. / .rOclor 1224 in creased the mortality of fruit flies from 59% to 92%, whereas Arojclor 1268 in creased it to only 77%. Analytical Mr hods I) MtnUfication. Sine Various com pounds with electron-cap! >ir|ng properties have been tentatively identified in atmo spheric samples in the pm t (Abbott ct si.. 1966), and some pesticide, tire capable of hybridi/fng in (he soil to form a new com pound (ftarlha, 1969), it i important that the presence of PCBs in ie|d samples be proven beyond doubt. I lehlification by means of a combination o high resolution gas chromatography and m|m spectrom etry his been carried ou< ty three inde pendent laboratories in Sweden (Widmark, 1967), Holland (Coeman et al.. 1969a), and the United States (Bagley et al. l970).Widmark`s repirt states that ail peaks were identified by mhss spccirom etry (although no data wefe given), but Koemen end co-workers gave full experi mental details, and Bagley et al. (1970) demonstrated that most chemicals in the eagle samples examined were components of Aroclor 1254. Thus, despite a recent statement by the Montaijito Chemical Compuay (in Risebrough| 1970) that the case for labeling the peeks In question as PCBs was not proven, there is enough evidence to convince an qn^aii ttienti- fic jury. September I. 1970 2) Sfpsrotio*. The chemical techniques preliminary to quantitation of residues in samples containing both PCBs and chlo rinated hydrocarbon pesticides fall into two group*--those necessitating the de struction or alteration of one or more of the compounds, and those which do not. Included in the first group is nitration. Treatment with a 1:1 mixture of sulfuric acid nitric acid at 0 C for 5 min destroys or alters aldrin, p.p'-DDE. p.p'-DDD (TDE), p.p'-DDT, and dieldrin such that they can no longer be detected at the original position on the chromatogram. This procedure leaves unaffected PCB, lindane, and BHC (Jensen and Widmsrk, 1967). A more rigorous nitration with a 1:1 mixture of sulfuric acid-fuming nitric add for 15 min at room temperature re moves, in addition to DDT and its related products, aldrin, heptachlor, Kellhane, Penhanc, Tedion, Telodrin, and Trithion while lindane, heptachlor epoxide, toxaphene, and Strobsnc are not removed (brroctal., 1967). Risebroughecal.(i969) reported that this nitration alto removed the chromatograpllic peaks ol PCBs. Rey nolds (1969) reported that his attempts to nitrate samples were not fully successful in that there appeared to be loss of some of the more volatile PCBs while peaks with longer retention limes appeared. Armour and Burke (1969) reported that complex chromatograms resulted after nitration which could not be related to (he unrcacted DDT-PCB mixture, and nitra tion was not pursued as a practical means of separating DDT and PCB for further tests. Saponification with alcoholic NaOH or KOH will dehyrodrochlorinsu Perthsne. Tox*phene. DDD. and DDT to their re spective olefins (Archer and Crosby. 1966; Klein and Walts, 1964). Risebrough et al. (1969) reported that PCI peaks are not removed or displaced but gave no data. The second, and in some instances more desirable, group ol analytical tech niques allows the special separation of many chlorinated hydrocarbon pesticides from PCBs. Reynolds (1969, 1970) re ported on an activated Florisil column technique which separated heptachlor, uldrin, DDE. and PCB with the first elu tion (60 ml n-hexane) from lindane: hep tachlor epoxide, DDD, and DDT with the second elution (40 ml 50% ethyl ether in hexane). Armour and Burke (1970) devel oped a method utilising a silicic acidCelile column eluting aldrin and PCB with the first fraction (250 ml petroleum ether), and lindane, heptachlor. heptachlor epoxide, dieldrin. endrin. p.p'DDE. o,p*-DDT, p.p' DDT. and p.p'DDD with the second fraction (200 ml acetonitrile hexane methylene chloride 1:19:80). Koeman et al. (1969a). using an activated Florisil column, eluted the apoiar compounds including DDE and PCB with hexane, and then dieldrin and endrin with 10% diethyl ether in hexane. Mulhern (1968) reported on a method which utilised silica gel-coated thin-layer plates I/ >m osmi MM IW IW IMS MM MM MQNS 083918 959 Ml bexanc/eibyl ether (91.2) rolvent system. The plates were developed, preyed with e silver nitrate solution, aed exposed to UV light. The plates were (hen divided into five horizontal suctions. Di- eldrin, endow. y-BHc, tiepuchlor epoxide, p,p'-DDD, p.p'-DDT, o,p`DDT. end p,p`-DDE (In 0iet order) were found le the fim four fractions, while meet of the interfering compounds found in wildlife lamplea were found in the fifth tone, Begley el al. (1970) Lied this meth od hut mentioned that zpnes three and four contained practically all unknown components as well ai p'p'-DDT (zone three) end p,p'-DDE (zom fpur). Armour and Burke (1969) used j*#coaied (alu minum oalde) sheets and n-heptane and 2% acetoae/n-hepune for solvent sys tems. PCBs (Aroctors I2M and 1260) and DDE were not separated,' hut p.p'-DDT and p.p'-DDD were completely sep arated from fCI by both Wvoit systems. Another poaaihle means oi separating in terfering substances is to use a series ol differing polarity columnsjin the gas chro matograph at the time off determination. TMa is leas time consuming and may be useful whan operating conditions can be selected such that PCB peaks are absent in the region where sought pesticides emerge (Simmons end Tejton, 1967). 2) Quomiftion. Koemln et el. (1969a) tcmiquanliielively measured the residues in Japanese quail fed phepochlor DP6 by using one of the peeks in phenochlor DP6 mixture as a standard- Risebrough (1969) quentUeted relativ| levels of PCBs by essuming that each PCS compound produced the seme peek height with the electron capture dc(ecto| ms the seme mount by weight of pip'-DDE. After summing the heights of the individual paaks. the total was multiplied by a factor derived from measurements of standard solutions with electron capture and microooulometric detectors. Jensen et et. (1969) reported PCB amounts as the sum of ail PC9 components and baked the estimate on a combination of mass spectrometry and microcoulomctric and electron cap ture detection. Even with this elaborate approach, thcae investigators suggest that the method is still rough and may be cor rect only within factor of 2- Anderson et I. (1969) devised a method for obtaining a crude estimate of PCB residues as Aro- cior 1254 from chromatograms where sep aration Had not been attempted. On.on empirical heals, it was found that Aroclor 1254 could be quantitate^ by considering peek 10 as p.p'-DDT and multiplying that value by 10. Since this peak had originally been quantitated as p,p-DDT, and in Otf | fact many of the original samples con tained little or no p,p' DDT, it was pos sible to eatimete relative PCB values. Anderson and his co-workers also saponi fied saniplee to remove interfering p.p'DDT and p,p'-TDE and then quantitated PCBs as Aroclor 1254 by relating sample peeks 9 and 10 to the corresponding peaks of an Aroclor 1254 standard. Reynolds (1970) employed a method similar to Koemen et al. (1969a) but basetf'hii quan titation on an average of two or more peaks, (a addition, his results were re ported as Aroclor 1254 or 1260 depending on (he overall pattern of the chroma tographic peak profile. It is clear that we arc still relatively unsophisticated in our PCB quantitation methodology and will continue to animate only relative amounts of PCBs in field samples until we synthe size the individual PCB components com monly found in the ecosystem end are able to speak in terms of these individual peaks as we do for most pesticide residues. However, it has been kindly pointed out (Risebrough, pers. comm.) that, with ref erence to biological significance, the cor rect order of magnitude and aocurate rela tive amounts of PCB give the essential information. This is because biological effects, such as enzyme induction, are re lated to degree of chlorination, and the existing methods give some indication of this activity. Therefore, that information would be lost if stress were placed only upon quantitating individual peaks. 4) Magnitude e/ Error. Ever since PCB peaks were recognized for whet they are, residue chemists and other researchers interested in pesticide residues have asked whet magnitude of error is likely to result from ignoring the presence of PCBs. Only recently have studies either directly or indirectly resulted in an esti mate of this error. Anderson et al. (1969) quantitated p,p'-l>DE, p.p'-DDD, end p,p'-DDT in five egg samples before end after saponification. There was no appre ciable change in the p,p'-DDE, but ap parent p,p*-DDD was reduced by ap proximately 56% and p.p'-DDT by 90%. Reynolds (1970) looked at a large number of samples before end after his PCBF1o{isil separation and found that the actual p,p'-DDD residue (relative to the apparent residue) represented from 0 to 7% in California gull {Lana occidtniaiit) fat, 0% in cormorant (Fholocrocomx ouritut) eggs, 10% in ID pooled mallard {Aitot pforyrAyorfo*) duck eggs, and from 0 to 104% in great blue heron (Ardee cinerta) eggs. Respective values for p.p'-DDT wereOto $3%. 13 to 41%. 100%. and 16 to 102%. Actual residue levels of heptachlor epoxide generally represented a majority of the apparent valuta. Before tad after values for p.p'-DDE and diddria were not significantly different. Obviously, the magnitude of error may very depending on the trophic level sampled end certainly with the area from which sample is col lected (Risebrough al., 1966, Jensen et al., 1969). Sinoc the publishing of edequate separation techniques, there is no reason why there should be any arror in pesticide quantitation contributed by PCBs. Tnkfbgy Despite some recent studies, the toxi cology of PCBs remains rather poorly known as compared to that of the chlo rinated hydrocirboa pesticides. For ex ample, no definite work has been done to tstaWilh LDS0 values for the various formulations of PCBs. 1) Acute, single dote experiment/ Tucker and Crabtree (1970) found that a single dose of 100 mg/kg Aroclor 1254 (stomach tubed in oil) wns fatal to two out of three rats, while 500 mg/kg was not fatal to throe rats. Aroclor 1266 killed one rat out of throe at 300 mg/kg, 1000 mg/ kg, 2000 mg/kg. and 4000 mg/kg. Smyth (1931) found that a 4 g/kg (degree of chlo rination not stated) was nomoxic to guinea pigs and rabbits, but this appears to be due to the fact that malarial which was given as a paste passed through the intes tine unabsorbed. Tucker and Crabtree (1970) found that Aroclor 1242. 1254, 1260, and 1266 at a dose of 2000 mg/kg was not fatal to mallard ducks (four groups of three birds etch). 2) Acme, feeding experiment!. Mon santo Bulletin 306 statm that 100 ppm diet hsd no effect on rats, although no details of the studies were given. The ex periments of Bennett el el. (1936) in which 0.05 g/rat of 65% chlorine biphenyl was given orally every other day led to 50% mortality. If one assumee a body weight of 200 g. then the alternate day dose is roughly 250 mg/kg, which can he com pared to oral LD50 for DDT of 113 mg/kg (Frcar, 1966). Miller (1944) found that two oral doses of 69 mg of 42% chlorine biphenyl a week apart were fatal te guinea pigs. At an satimnted body weight of 400 g. this gives a dose of 170 mg/kg. Tucker end Crabtree (1970) fed rots diets coalmin ing 10 and 1000 ppm Aroclor 1254. One rat out of six oa the low dose died; ibis mortality was considered le be due to other causes. Four out of four of the high group died within 53 days end the cal culated intake was IJXM520 mg/kg. The BioSowwc Vet. 20 No 17 HONS 0 8 3 9 1 9 food intake of the 1000 |ppm group was only W4 of the control group. ' Preset el at. (1970) hafe examined the toxicity of Aroclor 1254 to Bengalese finches (Lottekura zfriettl. this is a diffi cult speeies for which jo cnlrolaic the dietary intake. Doe to tMr dependence upon umhetled food, it Is oply possible to present the PCd-laden fopd for a few hour* a day (iefferies. 1947). Lou by evaporation and lou by spillage must be allowed for. and increase if weight by def ecation must be kept to a minimum. Thus, the calculated dietary intake is (.ob ject to more error than is Lsjually the case. Presst et al. < 1970) also measured the con centration of PCBs in the liver; they found that the range waj large (i.c., 70 697 ppm in birds that died compared to 3-6.14 ppm in those that survived). These authors conclude that Afoclor 1254 has only 1/13 the toxicity of (DDT, although the different shape oL the mortality curves steep with DDT, gradual with PCB -makes comparison (difficult. Jef feries and Walker (1966) sound good cor relation between calculated dietary intake and liver concentrations jor pp'-DDI in the Bengalese finch. However, other workers (Dale et al.. I96J; Stickel et al.. 1966; Slickel and Stickel, 1969) have con sidered that levels in the brain are a more reliable index of toxic levils than those in the liver or whole carcass' Dc Vos and Kocman (1970) fed Phenodor DP6. Ciophen A60, a|td Aroclor 1260 to chickens at a dosage of 400 ppm. Mor tality was complete (20/20) for those birds on Phenoclor in I2-5S days and in 13-29 days for Ciophen. The mdrtplity for Arodor was only 3/20 for a 60-day period. This differential effect is unexplained and is surprising in view of Ute fact that all three formulations contain 00% chlorine. These workers measured thp residue lev els in the liver, and. for somp birds, in the hrain, for chickens dying dpring the ex periment. Although there! das consider able variation, most of Ok brain levels were between 210 and 420 ppm, which can be compared to 5040 ppm for DDT (Stickel et al., 1966). On thp basis of this work, PCB Is 1/4-1/5 as toxic as DDT. Little difference was noted between the three different PCB fojmulationr, al though the numbers of determinations involved was rather small^ If this finding is borne out by subsequent work, it would suggest that differential eotprption from the gut or differential penetration of the blood bnin barrier is involved. The liver values wart more verisblj. There w#s a considerable number in the 200-400 ppm range, but there were several values in excess of 2000 ppm. This finding is in agreement with the findings of Dele, Stickel. and co-workers that the brein levels are the best indication of acute toxic levels. MoCune et at. (1962) found no mor tality with chickens fed 100 or 200 ppm Aroclor 1242 in their diet fur a 4-week period. On diets of 400 ppm and 800 ppm, the mortalities over a 4-week period were, respectively, 50% and 90%. During the first 3 weeks, the mortality figures were 10% and 50%, rcepectivcly. Flick et al. (1965), using the same material at 400 ppm in the diet, had three birds out of 24 die in a 3-week period. Kocman et al. (1969a) found that a diet containing 2000 ppm Phenoclor DP6 caused complete mortality with Japanese quail (5/S) in 5 13 days and rats (S/6) in 1-56 days. Schoettger (unpublished) found that the 96-hr TLm for Aroclor 1221 using cut throat trout was 1.2 mg/1 and for Aroclor 1260 was 60.9 mg/I. In general, they lound that the toxicity of Aroclon was inversely proportion^ to their percentage chlorination and directly proportional to their solubilities. These figures suggest that PCBs are two to three orders of mag nitude less toxic to fish than DDT. Work by Lichtenstein et al. (1969) on house and fruit flies found that PCBs were 40-300 times less toxic than DDT. the toxicity decreasing as the chlorine content in creases. Thus, it appears that the lower vertebrates and invertebrates are much less susceptible then mammals to direct toxicity from PCBs 3) Subleihal fjjects. As with the chlo rinated hydrocarbon pesticides, the most important effects are long-range sublethal effects. The pathologic changes In various organs are summarized in Table 2. The table shows some interesting differences between mammals and birds. The most striking finds in mammals are alterations to the liver, whereas fluid in the peri cardial sac, kidney damage, and reduced spleen was found in birds. McLaughlin et al. (1963) found that 2$ mg Aroclor 1242 injected into the yolk aac of chicken eggs caused complete mor tality, whereas 10 mg caused 9$% failure and teratogenetic effects were noted among the young that hatched (beak deformity, edema, and growth retardant). Induction of hepatic hydroxylating en zymes hat been demonstrated in the pi geon (Risebrough et al., 1968), rat (Street et al.. 1969), and American kestrel (Falco tpanvrUu) (Linear and Peakall, 1970). Street and co-workers studied the effects of a diet of 50 ppm and 100 ppm on sleep ing time induced by a standard dose of hexobarbital, in vitro rales of aniline bydroxylation and demetbyiation of p-uitroanisole. and the rate of excretion of dieldfin. These workers studied 10 com pounds ranging in chlorine content from 21% to 61% and found that all the effects increased with increasing chlorine con tent. Fur example, 50 ppm of Aroclor 1221 reduced hexobarbital sleeping lime by 11%, wherens for Aroclor 1241 and 1266 the figures were, respectively, 33% and 48%. Thus, the suMethal effects have direct correlation with chlorine content, while the lethel effects appeor to be in versely correlated (Tucker and Crabtree, In press). Llncer and Peakall (1970) noted an increase of the in vitro rate of metabo lism of estradiol in keatrels fad 0.5 and 5 ppm Aroclor 1254 in their diet and also demonstrated increased levels of cytoplas mic RNA with the higher dietary level using a cytophotomttrk technique. Tucker (unpublished) found that a sin gle oral dose of 500 mg/kg Aroclor 1254 caused regular egg laying of Japanese quail (CotumiM eotumix) to turn first to scattered egg production and then to stop completely for a week. The scattered eggs had shells 9% thinner than normal, but thickness returned to control values when regular laying was resumed. Mallard ducks dosed with 1000 mg/kg of Aroclor laid one or no eggs before stopping for I 2 weeks. The few eggs laid after the sin gle large dose of Aroclor had shells 11% thinner, and again eggshell thickness was normal after resumption of regular laying. The period before egg laying has been noted to be increased in the ring dove (Peakall, unpublished). It is possible that the mechanism involved is increased rale of metabolism of circulating estradiol in the liver (Peakall, 1970). Anderson et al. (1969) had suggestive evidence that PCBs affected eggshell thickness, al though to a less extent then DDL Pre liminary results with ring doves support this conclusion (Peakall, unpublished). Levels of PCBe Fmmd hi Nature Roburn (I96S). compering total chlorine (by concentration cell techniques) with results calculated from gas chromatog raphy, found that some unknown chlorine compounde were present in several tissue samples and eggs of wild birds in Great Britain. The first identification of these materials was by Jensen and it is stated (Anonymous, 1966) that residues in feath ers collected in Sweden go back to 1944. PCB residues have been reported in wild life from Canada (Holden and Marsden, 1967: Anderson el el., 1969; Reynolds, September I. 1970 MONS 063920 961 ue^tm* m M|Mf I* MiMit n.M,iiNp hMkll *'<* 9 Imm h A Hi pwl MphM HIpkM uuiiic mimm blilul wmIs W*. amto) HUpHtfWiM ,*f**l* Pm* * * tie pwi OMgaliM to M toy* mo*) <hnmphmp te Off* .. 1PII. uw mLl Utlm4 tm W*, Nni mm- nPi <N9twM l>wm mtt h mmmm* mm# m hUkUm *mtp*p mi *t*Oi 0 still prfp (MpA t *1). t*tm PmP Nm |144nM|l1M'lfH Mp . PatfaMM(ipMMf 1970), Germany (Fiuc/ynklki and Wand- lend, I960; Kocmen t a| 1967), Great w:Britain, (Holm* et al., 7; Pressi and Jcfferien, 1969: Prowl al 11970; Holden and Martden. IW). Nc|jlheriands (Koe* man at al., 1967; 1969), ^wUan (Anony- mows. 1966: Jensen at al 1969), and the United States (Andersori at al., 1969; Risebrough at al.. I96J; Risebrough, 1969).. Mfkd Mapdl No detailed studies. u<ich as those for DOD at Clear Lake (Hum and Bis:hoff, I960) and DDT and its metabolites in Luke Michigan (Hickey et al., 1966), Lave yet been made for PCBs. The most detailed sMies currently jjvuilable are those of Jensen et al- (t969). The figures (mean, range of values, and sample si/e) given in the table below are taken Irom their paper. PCfe ippm Ik tiiwtiM* l0 ath* StmkMm ^Khipdipo MwP, Htntag 4,){l.mi (40) 41(0.5-])) (II) 5.5(54-5 0) 5 I O J I 5) ImI 54(1444) ( J) 50(1454) OvtltoiMl^p. }$0(l4MOK 4) nopuPi 14000(1400'15.0001 ( 4) 410(4441500) 4 )) UP Htm 540(2)4100) 400 ( 5) ( I) The levels in three species of fish in Clear Lake in 1968 were 0.0J-0.O05 ppm (wet weight) compared to 0.098 ppm in the breast muscle of a western grebe (Risebrough et al., 1969). Anderson et al. (1969) found that in moat fish extracts the levels of PCBs ware leas than 0.1 ppm. whereas the levels in the eggs of cormorants (Pftaiacrocomx puritut) were 5-9 ppm. Press), Jefferies, and Moore (unpublished) found that the livers of fish-eating birds in the British fsias ranged up to a nutitmum of 900 ppm (wet weight), bird feeders up to 70 ppm, mammal eaters to 30 ppm. and insectivorcs to I ppm. Unfortunately, no average valuea or prey items were in cluded. The physical properties of PCB and ihe available residue data dearly indicate that these materials arc capable of bio logical magnification up the food chain. 962 MONS PioScience Vol 20 No. >7 Ratio at DDT m PCI Ritebrough i1.(l96l) afid Ritebrough (1970) HoVe tomlMd tbe.raifo of total OPT, l.s., DDT and Hi meisbolites to Kl. Ha Hu found that tip rettio DDT/ PCI wa* 1*2 in San Francisco lay and 5 10 for aanbirda in ihc Pacific; in (He Oulf of California, a ration relatively remote from opalamlaatfon, the' ratio was 9-10. Vermont (gaoled in Reynolds. 1970) in western Canada found a jDpE/PCB ratio of 7 for California gull tissues and I) for grant blue Heron eg|t. In the Bailie (He ratio was 1-2 (Jansen pi., 1969), al though along the weal ^o|tt of Sweden the ratio wai a low et 0.1$. In grebes in the Iritish Islet the ritio was 0 4-0.1 (Preest and Jefferies, 1969). For sea-bird eggs, Prestt et al. (unpublished) found ratios of 0.06 to 0.5. I The overall impression is that (be amount of PCI in tissues fends to paral lel that of DDE, at least in local ecosys tems, and the DDE/PCI ratio Is lowest near industrial areas tuue*iing that PCI is not carried quite to readily to remote mas. Nevertheless, the'variation of the ratio is smell enough to suggest tnat the routes of dispersal ere similar. Since the evidence points to aerial fallout as the route of dispersal of tM chlorinated hy drocarbon pesticides (Ritebrough et el., 1961; Frost. 1969), it is Ugly that this is also the main route for PCB*. The path ways by which PCls escape into the eco system ere poorly known, although the possibilities have been rogntly discussed at some length (Rttebrajugh, 1970; Rey nolds 1970). Since a forge number of plastics and resins may contain PCls (Table t), the most liketyjrqutc is combus tion of those materials. This supposition remain* to be tested. The possibility that PCls could be derived frofo DDT should alio be considered. Tm possibility that this oonvaraion occurs m thane is most twalfkofy for two reasons, fim, H has never been detected deepile Up detailed work on the metabolism of DDt. Second, the only machanhm likely i o give ris* to a biphenyl h vie free rat kali and this is unlikely to oocur in tin ue However, in the atmosphere under hp Influence of UV light, ench a breakdown is more prob able. A poesiWt reaction is shown in Figure I. Tautomeric si ifl could lend to a variety of isomers oi ^ichlorophenyl, but it is difficult to envision the formation of more highly ehlorina ed biphenyls hy this route. Since PCBe' eatractod from biological material match rtll with higher Aroclon (i.e., 1254), it Moiftt unlikely that PCBs found in nature poiild be derived from other meterieli. ItremUr I ISW Slgnifleance of Carnot levels . jn view of the similarity of PCBe to DDT and its metabolitas, the addition of PCB residues to the environment is rough ly equivalent to an increase of DDE resi dues. However, since a synergistic effect of PCBs on DDT has been demonstrated in insects (Tsao et al.. 1955), this pos sibility should not be overlooked in higher organisms. The enzyme induction affects of PCBs have been well documented, and carbonic anhydrase inhibition is likely. The eflect of PCBs on photosynthesis is a critical experiment that hei not been done. Wursler** (1968) experiments with phytoplankton should be repeated with PCBs. The most critical area for research on PCBs is to discover the major source(s) of escape into the environment. Legislative control of a material escaping as a side effect of its use may have a different set of problems than the control of pesticides which are broadcast as a function of their normal use. The evidence suggests that it is important to find the leak and stop it. Acknowledgments We are grateful to Dr. Kecman (Uni versity of Utrecht). Drs. Preset and Jef feries (Ntture Conservancy, Great BritianK Dr. Reynolds (Ontario Research Foundation). Dr. Street (Utah State Uni versity), and Dr. Tucker (U.S. Fish and Wildlife Service) for advance copies of important material. Some of the work prteentod here was carried out under N1H Orant ES00306. Dr. T. J. Cade. Principal Investigator. The review was written while one of us (D.B.P.) was an Established Investigator, American Heart Association. 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