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, . ...... i>.g<.Mvmor 8) (2) where the numerical coefficients arc taken from equation , 1V Similarly, the tree-growth anomaly pattern correspond ing *o the year following a high percentage of aibacore caught north of San Francisco can be represented as: map b=8.56(eigenvector 4)-6.17 (eigenvector 9) 4 11.54 eigenvector 10) (3) These maps arc presented in Fig. 4. The ring-width data were mostly from trees sited in arid localities, so that a wide ring would generally he associated with anomalously cool, cloudy weather and above normal precipitation whereas a narrow ring would reflect warm, sunny and dry conditions. Below normal tree growth in the Pacific North-west (Fig. 4) is indicative of dry conditions associated with below normal cyclonic activity during the fishing season. Sunny and mild weather would favour aibacore fishing ' in adjacent waters, as would above normal insolation regard less of weather. The resulting excess of stored heat in the ocean would be given up through evaporation during the following autumn and winter and lead to increased cyclonic activity and precipitation along the coast north of San Francisco. These conditions would lead to increased tree growth during the following growing season (Fig. 4). Autumn and winter climatic anomaly features, com bined with spring climate and the year-to-year autocorrela tion of tree-ring widths, produce the other ring-width anomaly features in Fig. 4 for the following growing season. Narrow ring widths south of San Francisco, for example, imply below normal precipitation--an expected feature since winter precipitation in the Pacific North-west is negatively correlated with winter precipitation in southern California*. The reconstructed values of aibacore catch distribution data (Fig. 3) and inferred population distribution also seem to exhibit long term changes over intervals of 100 yr or more, which suggest the possibility that long temi fluctua tions in the ocean-atmosphere system may be involved. The success of (he calibration of tree rings with aibacore catch indicates the possibility of relating tree-ring varia tions to any type of biological variations which are affected by large scale climatic fluctuations. Such relationships may be quantified and used to reconstruct objectively other climatically-caused biotic variations in the past. N. E, Clark National Oceanic and Atmospheric Administration, National Marine Fisheries Service, Southwest Fisheries Center, La Jolla, California 92037 T. J. Blasing H. C, Fritts Laboratory of Tree-Ring Research, University of Arizona, Tucson, Arizona 8572/ Received December 3. <974; May 6. 1975. < UMarthr. V. O. Sth-rur, 183. I04M048 (1974). 7 Narnia*. ) . Mon, Wvtuh. tfev.. U.S. fhp. April.. 97, 173-192 (1969). 7 l.uurs, R. M., t'f of., Report of Joint Kiajonnl Marine Fisheries Service-American tiiltcnhrr.'i Feseorth f'oiwtfutwn Aihmorc Sttuh'cs CnmUuWit During 1973 (Nations) Murine fiklieriej Service. Southwest t'lvbeiiv^ CenleT, La Jolla. 1973). 9 Ormcm, M. B., and Crafg, W. L., Cntlf. Dept f ish ami Came, Fish Dull., 128 f|96<|. 5 Stile, O. L-. Cotif. Coop. Oiconh Fi\h. Invest. Rept, 7, I8I-J94 (I960). * 1`yke. C. I*., An InustiRufinn of some precipitation pnUen.s in Cufiforhia anti (htjitfcnt reflow (Um'vcrvtly of California SVolcf Rcsourtey Center, 1966). may grow better in water depleted in oxygen 18 and deuterium While growing oats at different temperatures in waicr of different ,sO and deuterium (D) abundances, wc noliccd that oats grown in Antarctic water in which is depleted in '*o and D by -- 49%u and - 400%,, relative to standard mean ocean water (SMOW used as a comparative reference in hydrogen and oxygen isotope studies), showed initial growth 1-2 weeks sooner than did oats grown in water containing greater '"O and D concentrations. The oats seemed to grow better in water which was most depleted in the stable isotopes throughout the growth period. The oats were grown from the same batch of seeds in two sealed glass-covered glass jars (approximately 10 1). Twenty- five oat seeds were added to each jar, containing the same- amount of vermiculite and 500 ml water to which 5.0 g Bapid- Gro, a commercial fertiliser, had been added. One jar contained melted glacial ice from the Antarctic with isotope concentrations of --49%,, 6,eO (SMOW) and -400%,, 6D (SMOW). The other jar contained distilled ocean water with +1.0%. 8II,0 (SMOW; and +17%,, 8D (SMOW). Both jars were placed in the chamber at the same time. The experiment was repeated three times with new materials: once thegrovvthchamberwas maintained between 1.7 and 3.3 C; once between 24 and 26.6 'C; and once the temperature fluctuated between 1.7 and 26.6 eC. Each time the oats in the jar containing water depleted in the heavy isotopes showed germination 1-2 w>ceks earlier and seemed to grow better throughout the growth period, than oats grown in distilled ocean water. Using oats grown at 15 C, the first sign of germination in the jar containing water depleted in the heavy isotopes was 4 d after planting. On the day 6, eight plants (out of 25) had attained a height of 6 cm. The first sign of germination in the jar with water containing the heavier isotope concentration, w>as after 17 d. By the time five plants had attained a height of 6 cm in this jar, in that with water depleted in the isotopes, 23 plants that had reached the top of the jar (approximately 25 cm). Kashutin' observed that snow-water depleted in D increases the yield of cucumbers, radishes and spring wheat compared w'ith controls grown in ordinary water of unspecified isotopic composition. He cites experiments on the egg productivity of hens and (lie weight gain of suckling pigs. In both cases water depleted in D was especially efficient in promoting productivity. Although much has been done on the effect of D-enriched water on biological systems, w>e suggest that research on the effect D-depleted water on plant and animal growth may prove fruitful. A major source of water depleted in D by over 400%, (40%) compared with SMOW is snow and ice from the Antarctic polar plateau. Water depleted by 150- 180%,, is readily available in the USA from Rocky Mountain snow precipitating above 10,COO feet elevation, Jim D. Gleason Irving Friedman US Geological Survey, Denver, Colorado 80225 Received February 10; accepted June 3, 1975. 1 Kuthulfn, K., Priroda (USSR). 58, 107 (1969). Identification of chlorinated dibenzofurans in American polychlorinated biphenyls Mortality of embryos has contributed to the reproductive failures of several bird species, including the sparrow haw ks (Accipiter nist/s) of southern Scotland1, the white-tailed eagles (Haiiueetus afbicilla) of Schleswig Holstein2, and the herring 306 pulls {Lams argentatus) of Lake Ontario3. Suspected causes include p,p'-DDE (2,2-6/.v-(/>-chloropbeny!)-l,l-dichloroeibykne), oilier clilorinated biocides and/or their derivatives, and the polychlorinated biphenyls (PCUs), all of which are present as contaminants in the eggs'-3. PCBs are present in high concentrations in the bird populations which suffer embryonic mortality'-3. Other organochlorine compounds which nitty be present in food webs include the chlorinated dibenzodioxins and the chlorinated dibenzofurans (Fig. 1), which are toxic to embryos in amounts'-' less than 1 pg. They are therefore among the most toxic substances known and are possible causes of the observed mortality. The chlorinated dibenzodioxins and chlorinated dibenzo furans, however, have proved exceedingly difficult to detect in environmental samples in the concentrations at which they are expected to be cmbryotoxic8-10. The chlorinated dibenzodioxins enter the environment as contaminants in preparations of the herbicide 2,4,5-T (refs 5 and II) and the fungicide pcntachlorophenol15-13. Chlorinated dibenzofurans have been found in a French (Phenoclor DP6) and a German (Clophen AuO) PCB and were shown to be the active cmbryotoxic agent in these preparations8. The techniques used, however, did not detect chlorinated dibenzofurans in an American PCB, Aroclor 1260. We report here the presence of chlorinated dibenzofurans in Aroclor PCB, widely used in North America and Great Britain, and in the same Aroclor 1260 preparation examined previously with negative findings*. Samples of PC B examined include: Aroclor 1248, 1254, and 1260 (1969); Aroclor 1254 (1970); Aroclor 1016 (1972); and the same three preparations studied by Vos el alJ: Aroclor 1260, lot No. AK-3; Clophen A-60, lot No. 912434; and Phenoclor DP-6, lot not specified. The latter three PCBs were obtained from Dr Vos, the others from the Monsanto Company in the years indicated in parentheses. PCBs extracted from environmental samples most often have gas chromatographic profiles similar to those of PCB formula tions containing approximately 48, 54 or 60% chlorine. In the Aroclor series, the former two PCBs are equivalent to Aroclor 1248 and Aroclor 1254, respectively. Aroclor 1260, Phenoclor DP6, and Clophen A60 all contain approximately 60% chlorine. Chlorinated dibenzofurans were identified in all Aroclor preparations except Aroclor 1016, as well as in Clophen A60 and Phenoclor DP6. Aroclor 1016 is a PCB mixture containing Fig. 1 Skeletal structures of: a, chlorinated biphenyl, x~-y --1-10; b, chlorinated dibenzofurans, x-l y - 1-8; c, chlorinated dibeii/oclioxins, x -\ y 1-8. 3 <A O Cl Nature Vol. 256 July 2J 1975 Table I Chlorinated dibenzofuran concentrations* in Aroclor. Clophen and Phenoclor* 1 PCB 4-CI 5-CI 6-OI '1 otal Aroclor 1248 (1969) Aroclor 1254 (1969) Aroclor 1254 (1970) Aroclor 1260 (1969) Aroclor 1260 (lot. AK3) Aroclor 1016 (1972) Clophen A-60 Phenoclor DP-6 0.5 (25) 0.1 (6) 0.2(13) 0.1 (10) 0.2 (25) ND 1.4 (17) 0.7 (5) 1.2 (60) 0.3 (15) 0.2 (12) 1.4 (82) 0.4 (27) 0.9 (60) 0.4 (40) 0.5 (50) 0.3 (38) 0.3 (38) ND ND 5.0(59) 2.2 (26) 10.0 (74) 2.9 (21) 2.0 1.7 1.5 1.0 0.8 8.4 13.6 Expressed as pg g~' PCB. Values in parentheses represent quantity as percentage total dibenzofuran. ND, not detected (<0.001 pg g~'). Amounts of PCB ranging from 1.0 to 2.0 g were dissolved in 400 ml hexane, placed on a Elorisil column (180 g. internal diameter 31.5 mm), and eluted with: an additional 1,600 ml hexane, and successive 800 ml volumes each of 5% diethyl-clher-hexanc, 25% diethyf-ether-hexanc and acetone, at a rate of approximately 7 ml min~'.Thcmajor portion of thePCB was eluted in the hexane fraction, which was discarded. On addition of the 5% mixture, the cluates were collected in six successive 4(0 ml volumes. To eliminate the polar solvents, each cluate was evaporated twice just to dryness and taken up each time in a minimal amount of hexane. Each fraction, in 1 ml hexane, was placed on a microalumina column" and eluted with 10 ml each of 1 % and 20% methylene chloride in hexane. These were also taken twice just to dryness and made to up a volume of 1 ml in hexane to eliminate the methylene chloride before gas chromato graphic analysis. Aliquots of all fractions obtained before and after partitioning on alumina were injected into a six foot glass column containing 2% OV1 on 100-120 mesh Supelcoport in Tracor MT220 and Hewlett-Packard 5700 gas chromatographs equipped with t3Ni electron-capture detectors. PCBs were found to be present in each fraction eluted from the Elorisil column in amounts sufficient to interfere with the detection of trace contaminants. Partitioning on the alumina columns separated most of the PCB interference into the 1 % methylene chloride fractions. On removal of this interference, different peak patterns appeared in the chromatograms of the 20% methylene chloride fractions. Compounds eluting in the 20% methy lene chloride fraction were collected for mass spcctrometric analysis using a 20:1 effluent splitter, and a trap consisting of a capillary lube (1 mm internal diameter, 100 mm long) bent to a U shape, immersed in a liquid nitrogen bath. Methylene chloride (20%; 4 pi) in hexane was injected into the capillary as a rinse, removed with a 1.0 pi microptpelle, and placed directly on the mass spectrometer probe. The probe was inserted into a GEC AE1 MS902 high resolution mass spectrometer and the solvent removed by the force pump. 1 he probe was rapidly inserted into the ion source and multipie scans were recorded in the on-line high resolution mode". approximately 42% chlorine and has replaced Aroclor 1242 in many applications, principally as the dielectric fluid in capacitors'*. Values reported in Table 1 represent the total of those compounds found in 400ml Elorisil fractions 2-6. A total of 10-12 isomers was identified in each PCB. Two chlorin ated dibenzofuran contaminants have been reported for the Clophen and Phenoclor previously*; our first analyses of the Clophen revealed an additional five chlorinated dibenzofurans*. The structures contained fourtosixchlorineatoms.Otherdibenzofurans including those chlorinated to a lesser extent may have been present in the first 400 ml fraction but this was not examined in detail as it contained substantial PCB interference. Recently synthesised 2,3,7,8-tetra-, 2,3,4,7,8-penta- and 2,3,4,6,7,8hexachlorodibenzofuran were used to quantify tetra-, penta-, and hexachlorodibenzofurans, respectively. The former two authentic standards had retention times on the OV1 column the same as those of two dibenzofurans isolated from the PCB. Vos et al." detected no chlorinated dibenzofurans in an Aroclor 1260 preparation at a detection limit of 1 p.p.m. Fractionation and examination of the identical Aroclor 1260 in our study confirm their findings based on the stated limit, but reveal the presence of 11 chlorinated dibenzofurans in the preparation, having a tola! concentration of 0.8 pg g -' PCB (Table 1). The same workers also found diethyl ether extracts of the Clophen A60 and Phenoclor 1)1*6 to be much more toxic to chick embryos than diethyl ether extracts of Aroclor 1260. Our study confirms those findings on the basis of chlorinated STLCOPCB4009169 Nature Vol. 256 July 24 1975 b f- T-.- 150 200 250 300 350 Fig. 2 a. Gas chromatogram or a fraction of Aroclor 1254 containing a mixture of chlorinated biphenyls, dibenzofurans, and naphthalenes. Identities of peaks arc given in the text. b. Mass spectrum of peak 2, a tetrachlorodibcnzofuran. dibenzofuran content: the identical Clophen and Phenoclor contain 11 and 17 times more total chlorinated dibenzofurans, respectively, than the Aroclor 1260. A gas chromatogram showing components derived from the Aroclor 1254 obtained in 1969 is represented in Fig. 2. The components were eluted in the Second 400 ml Florisil fraction and recovcied from the alumina column in 20% methylene chloridc-hexanc. Fach of the numbered peaks was trapped as described here, and identified by mass spcctrometric analysis. A nominal mass plot of the high resolution mass spectrum of peak 2 is shown in Fig. 2. The plot includes all the ions with elemental compositions ranging to the maximum empirical formula The molecular ion cluster at nominal mjc 304- 310 fragments by successive losses of C'l lo yield the ions at mjc 269-275 and CO to the ions at ntle 241- 245. A minor loss of Cl from the peaks at m/e 269 -275 also occurs to yield the ions at mjc 234 -238, followed by CO elimination to mfe 206 210. The group of peaks at m/e 152- 154 arc the doubly charged molecular ions. An identical spectrum was obtained from an authentic standard of 2,3,7,8-tctrachlorodihenzofuran. This latter compound has a rctenlion time identical to that of peak 4. Peak 2 is, therefore, a positional isomer. The accurate mass measurements for the characteristic ions are within 2 p.p.m. of the calculated exact masses. Peaks identified on this chromato gram and their retention times relative to dieldrin areas follows: a mixture of tetra- and pcntachlorobiphenyl (1.02); tclrachloro- dihenzofuran (1.30); pcntachlorobiphenyl (1.46); tctrachlorodi- benzofuran (1.57); hcxachloronnphthalenc (1.75); penta- chlorobiphcnyl (1.86); hcxachloronaphthalenc (2.00); and hcptiichloronaphthalcne (3.46). An aliquot of combined fractions derived from the. same Aroclor 1254 was treated with dia/omethane to assess whether any chlorinated ortho-hydroxy- biphenyls (pre-furans) were present. Gas chromatographic analysts of the sample before and after Ucatnient resulted in identical chromatograms. As large quantities of PC'Bs have entered the global environ- nient,:'!", il may be assumed llral the contaminant dibcnz.ofurans 307 also have been released in proportional amounts. Their per sistence, effects, and significance remain to be determined. We thank J. A. Buikc, M. L. Porter and J. G. Vo-, for discussions; A. S. Kende for standards of chlorinated di benzofurans; and F. C. Walls for assistance with the mass spectrometry. This work' was supported by the Canadian Wildlife Service, National Science Foundation, and NASA. Gerald W. Bowes* Canadian Wildlife Service, Michael 3. Mui.vnm.i. Toxic Chemicals Section, Ottawa, Canada KJA OH3 Bernd R. T. StMOMir Space Sciences Laboratory, A. L. Burlingame University of Californio, Berkeley, California 94720 Bodega Marine Laboratory, R. W. Risfbrough University of California, Bodega Buy, California 94923 Received February 13; accepted May 28, 1975. Present address; California Water Resource* Control Board, Division of Planning end Research, 1416 Ninth Street. Sacramento, California 95814. * Newton, 1., and Bogan, J., Xantrc% 249. 582-583 (1974). 2 Koemrm, J. M,, Hotldcringri, R. II., and BiilcNeld, M. F. J. J., Blot. Consav,, 4, 373-377 (1972). 5 Gilbertson. M., and Hale, R., Can. Flit Not.. 88. 354 -356 (1974), 4 Hiccinboihftni, G. R., et at., Nature. 220, 702-703 (1968). 5 Spnrschu, G, L., Dunn, F. L., and Rowe, V. K., Food Contact. Toxic., 9. 405 412 0971). 6 Vos, J. G.,Koeman J. H.. Van der Maas. H. L... ten Noever dc Brauw, NT. C.. and dc Vos, R. H., Food Cosma. Toxic., 8. 625-633 (1970). 7 Vos, 3. G., Environ, Hllh Persp., 1, 105-117 t!972). 8 Bowes, G. W., Srrnoncit, B. R., Burlingame, A- L., de t.appe, B. W., and Risc- brougt), R. W., Emiton. filth Pcrsp.,5. 191-198 (1971). v Baughman, R. and Meselson, M., Environ, fifth Pcnp,,$t 27-35 (1973). *0 Baughman, R., and Mcselson, M., Adv. Chem.. 120, 92-104 (1973). l * Repot ton 2.4,5-T (F-xeembe Office of the President, Science Advisory Committee, Office of Science and Technology, March. 1971). *7 Jensen, S., and Renberg. L., Arabia, !, 62-65 (1972). 15 Firestone, D., Ress, J.. Broun, N. L., Barton. R. P., and Damico, J. N., J. Ass. OJ)\ Anofyu Chem., 55, 85-92 U9T2;. 14 Porter, M. L.,and Burke. J. A..J. Ass. Of. Arufyt. Chan., 54, 1426- M2R (1971). 15 Burlingame, A. 1... Olsen, R. W. and MePherron, R. V., Adv. Moss Spear., 6. 1053-1059 0971). HNisbet, 1. C. T.,end SaroBm. A. T., F.miron, Wth PenpI, 21-38 (1972). 17 Bowes, G. VV., and Jonkcl. C. ).,J. Fish Rrs. fuf Can. (in the press). 18 Jensen. S.. Johnels. A. G., OKson, M., and 0trrlmt1f G., Nature, 224, 247--250 (1969). 19 Koeman, J. H.. ten Noc'fr dc Brauw, M. C., and dc Vos, K. H., .Nutate, 221, II26-J!28 (1969). 29 Risebrotich, R. W,, Reiche. P., Peakall, D. B., Herman, S. G., and Kirven, M. N-, Nature. 220, 1098-1102 (1968). IBM Niche breadth in.Bryozoa as a test of competition theory Competition theory predicts that intraspecific and inter specific competition should often have opposite effects on the use of resources by a population, the former increas ing, the latter decreasing, the range of resource actually used''*. Field data supporting these predictions are well known for the interspecific case*'1 but are scarce for the inlraspecific condition, and we have been unable to find any reference demonstrating both effects within a single species. We therefore report here the verification of both predictions in respect of competition for space by the epiphytic bryozoan Atcyonidium hirsutum; less extensive data suggesting the same effects within other bryozoans arc also reported. ' Intraspeeific competition should result in an increase in the range of a resource spectrum used by a species, as at high population levels the advantages to any individual of being at the competition-free optimum of a resource gradient are offset by the intense intraspecific competition found there (Fig. lo); this is the `principle of equal oppor tunity' of MacArthur'. Interspecific competition, on the other hand, should tend to restrict the range of the resource spectrum used by a species, as individuals attempting to exploit marginal resources cannot do so as efficiently as DSW 025215 STLCOPCB4009170