991

Environmental Toxicology and Chemistry, Vol. 21, No. 5, pp. 991–998, 2002q 2002 SETAC

Printed in the USA0730-7268/02 $9.00 1 .00

IDENTIFICATION OF POLYCHLORINATED DIBENZO-p-DIOXIN, DIBENZOFURAN,AND COPLANAR POLYCHLORINATED BIPHENYL SOURCES IN TOKYO BAY, JAPAN

YUAN YAO,†‡ SHIGEKI MASUNAGA,*†‡ HIDESHIGE TAKADA,§ and JUNKO NAKANISHI†‡#†Graduate School of Environment and Information Sciences, Yokohama National University, 79-7 Tokiwadai, Hodogaya,

Yokohama 240-8501, Japan‡CREST, Japan Science and Technology Corporation, 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan

§Faculty of Agriculture, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu, Tokyo 183-8509, Japan# Research Center for Chemical Risk Management, National Institute of Advanced Industrial Science and Technology, 16-1 Onogawa,

Tsukuba, Ibaraki 305-8569, Japan

(Received 23 February 2001; Accepted 31 October 2001)

Abstract—A dated sediment core collected from Tokyo Bay, Japan, was used to assess the historical inputs of polychlorinateddibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and coplanar polychlorinated biphenyls (Co-PCBs) frommultiple sources. The levels, patterns, and profiles of these compounds in the core were congener-specifically investigated, and theresults show that the PCDD and PCDF (PCDD/F) and the Co-PCB inputs increased abruptly from the late 1950s and peaked duringthe period 1967 to 1972. From 1972 to 1981, the inputs decreased continuously and then generally leveled off. Using principalcomponent analysis, two herbicides widely used in the past, pentachlorophenol (PCP) and chloronitrofen (CNP), as well as com-bustion processes were identified as the major dioxin sources in Tokyo Bay. The PCB formulations and combustion processes wereestimated to be the major sources of Co-PCBs. Furthermore, multiple regression analysis was performed for dioxin-source appor-tioning, and it was found that the herbicides PCP and CNP have mainly contributed to the PCDD/F burdens since the late 1950s.This study suggests that herbicide-derived PCDD/Fs remaining in agricultural land will continue to run off and pollute the aquaticenvironment in Japan for a long time.

Keywords—Dioxins Coplanar polychlorinated biphenyls Sources Source contribution Sediment core

INTRODUCTION

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofu-rans (PCDFs), and biphenyls (PCBs) constitute a group ofpersistent, bioaccumulative, and toxic contaminants in the en-vironment. Several PCDDs and PCDFs (PCDD/Fs) and co-planar PCBs (co-PCBs) have been shown to cause toxic re-sponses similar to those caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD), the most potent congener withinthese groups of compounds. These toxic responses includedermal toxicity, immunotoxicity, carcinogenicity, and adverseeffects on reproduction, development, and endocrine functions[1]. To conduct a comprehensive dioxin risk assessment forhumans and the ecosystem, the toxic equivalent (TEQ) ap-proach has been developed and is now used worldwide. InJapan, the tolerable daily intake was revised in June 1999 to4 pg TEQ/kg/d for the sum of PCDD/Fs and Co-PCBs tocontrol the exposure to these compounds. For this purpose, afull understanding of the key sources of PCDD/Fs and Co-PCBs and the relative contributions of these sources is re-quired.

Olie et al. [2] first found PCDD/Fs in fly ash and flue gasof some municipal incinerators in The Netherlands in 1977.Since then, many PCDD/F sources have been identified, andthese can generally be divided into three categories [3]: In-dustrial processes [4–6], thermal processes [7–9], and sec-ondary sources or reservoirs. The contribution of dioxins fromdifferent sources is a topic of intense discussion. In Europe,incineration is generally thought to be the primary source, and

* To whom correspondence may be addressed(masunaga@ynu.ac.jp).

atmospheric emissions of PCDD/Fs are reported to have de-creased following the strong regulatory control of such pro-cesses [10,11]. On the other hand, a Canadian study foundthat pentachlorophenol (PCP), which was used extensively asa wood preservative, was one of the most significant sourcesof dioxins in that country [12]. In addition, Baker and Hites[13] recently noted that the photochemical synthesis of oc-tachlorodibenzo-p-dioxins (OCDD) from PCP in atmosphericcondensed water might be the most significant source ofOCDD to the environment.

In Japan, incineration has been deemed by many to con-tribute the greatest portion of PCDD/Fs to the environment,and dioxin-control measures have been focused only on in-cineration until now. Recently, however, Masunaga et al. [14]reported that a significant portion of dioxins in Japanese sur-face sediments originated from agrochemicals, especially PCPand chloronitrofen (CNP), which were widely used as paddy-field herbicides in the past. Furthermore, Masunaga and Nak-anishi [15] investigated the dioxin impurities in agrochemicalsused in the past in Japan, and they proposed that the annualemission of dioxins from agrochemicals was far greater thanthat from combustion sources during the 1960s and 1970s. ForCo-PCBs, commercial PCB mixtures such as Aroclor, Ka-nechlor, and Clophen are known to contain Co-PCB congeners[16,17]. Several recent studies have indicated that municipalwaste incineration may result in Co-PCB formation [8,9,18].

The time course of dioxins and PCBs in the environmentprovides an important clue regarding the sources of these com-pounds [19,20]. The objective of this study was to reconstructthe historical trends and to further elucidate the key sourcesof PCDD/Fs and Co-PCBs in the Japanese aquatic system to

992 Environ. Toxicol. Chem. 21, 2002 Y. Yao et al.

Fig. 1. Location of sampling site in Tokyo Bay, Japan.

provide useful information for the establishment of compre-hensive dioxin and PCB control measures in Japan.

MATERIALS AND METHODS

Study area

Tokyo Bay is a typical closed inner bay located southeastof Tokyo, Japan. It has a surface area of 980 km2; maximumand mean depths of 50 and 15 m, respectively; and a hydraulicresidence time of 1.6 months. The catchment area is 7,600km2, in which 25.6 million people reside, corresponding tonearly one-fifth the total population of Japan. Tokyo Bay waschosen because it is considered to be one of the water systemsmost affected by human activities in Japan. For example, manyindustrial plants are located along the shoreline. Municipalsolid-waste incinerators in the area burn more than 6 milliontons/year. Furthermore, herbicides have been used in paddyfields and other agricultural fields, which comprise approxi-mately 20% of the catchment area [21]. Environmental pol-lution of Tokyo Bay proceeded intensively from the late 1950sand peaked in the 1970s, but contamination by organic com-pounds and heavy metals continues to date [22].

Sampling and dating

Details of the field sampling program and sediment datingmethods are given by Sanada et al. [22]. Brief descriptions areprovided here.

A sediment core of approximately 60 cm in length wascollected from Tokyo Bay with a Matsumoto gravity corer(Rigo, Tokyo, Japan) in September 1993. The coring site (F2)is in the middle of Tokyo Bay at 358339 N latitude and 1398559E longitude (Fig. 1), with a water depth of 18 m. The corewas sliced into 1-cm disks on board, and the sediment of eachdisk was immediately transferred to polypropylene containers.All disks were then freeze-dried and kept frozen until required.

To estimate the sedimentation rate, vertical distributions ofexcess 210Pb and 137Cs activity concentrations in the core wereinvestigated. The total 210Pb and 137Cs activity concentrationsin each disk were determined by g-spectrometry using a high-purity germanium detector (Ortec, Oak Ridge, TN). Supported210Pb was obtained by indirectly determining the activity con-centration of the supporting parent 226Ra. The 226Ra was mea-sured by analyzing its decay product, 214Pb, on the assumptionthat the two were in equilibrium. The excess 210Pb activityconcentration was plotted on a logarithmic scale against thecumulative mass per unit area. A regression line was fitted to

the data, and the slope of the regression line gave a 210Pb-derived average sedimentation rate. The distribution of 137Csactivity concentration in the core was related to fallout fromnuclear weapons testing. The 137Cs-derived average sedimen-tation rate was obtained by assigning the peak in 137Cs de-position to 1963. Although some distraction was observedfrom the obtained excess 210Pb and 137Cs activity profiles ofthe sediment core, trends of molecular markers such as PCBs,linear alkylbenzenes, and tetrapropylene-based alkylbenzenesmatched the use of these chemicals in the area, indicating thatthe sediment core was suitable for our historical study [22].

The average sedimentation rate was estimated to be 0.27g/cm2/year by the 210Pb method, with a range of 0.20 to 0.40g/cm2/year. On the basis of the 137Cs method, the average sed-imentation rate was estimated to be 0.26 g/cm2/year (range,0.18–0.29 g/cm2/year). In addition, a molecular stratigraphyapproach was also performed using PCBs as a molecular mark-er, and the average sedimentation rate was then estimated tobe 0.27 g/cm2/year (0.26–0.29 g/cm2/year) by assigning thepeak in PCB deposition to 1970 [22]. All these estimates aresimilar, and the 210Pb-derived average sedimentation rate wasused for dating in this study [23].

Extraction and cleanup

A related study on the historical trends of endocrine dis-rupters in Tokyo Bay was previously reported by Okuda et al.[24], using the same sediment core, in which they compositedthe individual 1-cm core disks into 16 subsamples at 3- or 6-cm intervals. In the present study, the disks were subsampledto make up 13 samples at various depths (0–3, 3–6, 6–9, 9–15, 15–20, 20–25, 25–30, 30–35, 35–40, 40–45, 45–50, 50–55, and 55–58 cm) for our PCDD/F and Co-PCB analysis.

After the addition of 16 13C-labeled PCDD/F and 14 13C-labeled Co-PCB internal standards (Wellington Laboratories,Guelph, ON, Canada), each sample (5–10 g) was Soxhlet(Millville, NJ, USA) extracted with toluene for 20 h. Theextracts were hydrolyzed with aqueous potassium hydroxidesolution at room temperature, treated with concentrated sul-furic acid, washed with n-hexane-extracted water, and thentreated with activated copper. Sample cleanup included chro-matography on silica gel, alumina, and activated carbon col-umns [25]. The silica gel column was packed with 2 g of silicagel (Wakogel S-1; Wako Pure Chemical Industries, Osaka,Japan) heated at 1308C for 3.5 h, and 120 ml of n-hexane wasutilized for eluting PCDD/Fs and PCBs. The alumina columnwas packed with 5 g of basic alumina (Aluminium oxide 60,Activity I; Merck, Darmstadt, Germany) heated at 1908C for3 h. This column was first eluted with 30 ml of n-hexanecontaining 2% (v/v) dichloromethane and then with 30 ml ofn-hexane containing 50% (v/v) dichloromethane. The last frac-tion was loaded onto the activated carbon column packed with0.5 g of activated carbon-impregnated silica gel (Wako PureChemical Industries). This column was first eluted with 20 mlof n-hexane containing 25% (v/v) dichloromethane, and theeluate was added to the initial fraction of the alumina columnchromatography for collecting mono-/di-ortho and normalPCBs. Then, 200 ml of toluene was used for eluting PCDD/Fs and nonortho PCBs. The final PCDD/F and nonortho PCBfractions were concentrated to 25 ml, whereas the mono-/di-ortho and normal PCB fractions were concentrated to 1 ml.All these fractions were spiked with two 13C12-labeled recoverystandards (Cambridge Isotope Laboratories, Andover, MA,

Major PCDD/F and Co-PCB sources in Tokyo Bay, Japan Environ. Toxicol. Chem. 21, 2002 993

USA) for high-resolution gas chromatography/high-resolutionmass spectrometry (HRGC-HRMS) analysis.

HRGC-HRMS analysis

Both PCDD/Fs and Co-PCBs were analyzed by HRGC(HP6890; Hewlett-Packard, Wilmington, DE, USA)-HRMS(AutoSpec; Micromass, Manchester, UK). Both DB-5 and DB-17 columns (length, 60 m; inner diameter, 0.25 mm; film thick-ness, 0.25 mm; J&W Scientific, Folsom, CA, USA) were usedto separate seventeen 2,3,7,8-substituted PCDD/F (2,3,7,8-PCDD/F) congeners, in which the congeners being interferedon DB-5 were quantified with DB-17. The DB-5 column wasutilized for the analysis of other PCDD/F and Co-PCB con-geners. An autosampler (gas chromatography system injector;Hewlett-Packard) was employed for injection (2 ml, splitless).

For PCDD/F determination, the following temperature pro-grams were used: for DB-5, 1608C for 3 min, 408C/min to2008C, hold for 2 min, and 28C/min to 3108C; and for DB-17,1608C for 3 min, 408C/min to 2208C, hold for 2 min, 28C/minto 2808C, and hold for 33.5 min. In the case of Co-PCBs, thetemperature programs used were as follows: for nonorthoPCBs, 1208C for 1 min, 408C/min to 2008C, hold for 2 min,68C/min to 3208C, and hold for 5 min; and for mono-/di-orthoPCBs, 708C for 1 min, 408C/min to 1908C, 18C/min to 2408C,108C/min to 3108C, and hold for 9 min. The temperatures ofthe injector and the ion source were 2808C and 2508C, re-spectively. The interface temperature was set at the maximumvalue of each temperature program. The carrier gas was he-lium, and the electron-impact ionization energy was 40 eV.

The mass spectrometer was operated at a resolution of10,000–13,000 (5% valley) and in a selected ion monitoringmode. Tetra- to octachlorinated PCDD/Fs and 14 Co-PCBsInternational Union of Pure and Applied Chemistry 77, 81,126, 169, 105, 114, 118, 123, 156, 157, 167, 189, 170, and180) were analyzed by congener-specific analysis [25]. Toxicequivalent concentrations were calculated based on the toxicequivalency factors (TEFs) for humans and mammals estab-lished by the World Health Organization, Paris, France, in 1998[1]. The accuracy and reliability of the analytical method usedin the present study were previously approved by analyzingtest samples including harbor sediment, industrial sludge, andfortified industrial soil extract in the fourth round of the In-ternational Intercalibration Study on PCDDs, PCDFs, andmono-ortho and planar PCBs [26]. Method blanks generallycontained OCDD, but in concentrations no more than 2.5 pg/g. Some other congeners detected were present in much smallerconcentrations. The average recoveries for 2,3,7,8-PCDDs,2,3,7,8-PCDFs, and Co-PCBs were 88 6 26%, 77 6 21%, and84 6 20%, respectively.

Data analysis

In this study, Statistica software (Statistica 2000, Ver 5.5;StatSoftt, Tulsa, OK, USA) was used for statistical analysis.Source identification was performed using principal componentanalysis (PCA). The PCA is a multivariate technique that canbe used to reduce the dimensionality of complex data. It hasbeen applied to PCDD/F and PCB data by many researchers[12,19,27,28]. For our PCDD/F congener-specific data set, eachcongener or congener cluster was considered as a variable,whereas each sediment sample was treated as a case. Becausethe number of cases was smaller than that of variables, congener-specific data were transformed into a correlation matrix, and thematrix was utilized as input data for PCA. Principal components

(PCs) were obtained by varimax rotation, and the major PCswere determined based on the cumulative proportion (.95%).The characteristic congeners of each major PC were then ex-tracted based on their factor loadings, and they were comparedwith those of known sources for source identification. Further-more, multiple regression analysis (MRA) was applied for di-oxin source apportioning. The congener-specific data of PCDD/F concentrations in PCP, CNP, and atmospheric deposition wereused to estimate the historical contributions of different sourcesto dioxin pollution in Tokyo Bay. Both PCA and MRA werenot carried out for Co-PCB source identification and appor-tioning, because our Co-PCB congener-specific data set was toosmall and Co-PCB congener-specific information on the esti-mated sources was lacking.

RESULTS AND DISCUSSION

Trends in PCDD/Fs

Because congener profiles (including the non-2,3,7,8-sub-stituted constituents) reflect the characteristics of dioxin sourc-es, we conducted congener-specific analysis for our sedimentcore samples. Consequently, nearly all the tetra- to octachlor-inated PCDD/Fs were detected in the samples examined. Partof the results are given in Table 1. The SPCDD/F level in-creased during the period 1935 to 1972, in which a drasticincrease occurred from the late 1950s that peaked around 1970(SPCDD/Fs, 45,000 pg/g). During 1972 to 1981, the totaldioxin concentration decreased continuously to 22,000 pg/gand then generally leveled off. The SPCDD/F concentrationwas found to be 620 pg/g in the deepest sediment layer, datedat approximately 1937, which provides the information on thePCDD/F background level before World War II in Tokyo Bay.Combustion of coal and wood as well as metal productionmight be responsible for the pollution level at that time. Forinstance, on average, 35 million tons of coal were producedeach year in Japan from 1930 to 1937. Using the concentrationof SPCDD/Fs in the surface sediment layer and the averagesedimentation rate estimated by the 210Pb method, the presentflux of PCDD/Fs to Tokyo Bay sediment was estimated to be5,100 pg/cm2/year [29].

A distinct homologue profile dominated by OCDD andsome interesting trends were found from the bottom to the topof the core. Figure 2 shows the PCDD/F homologue trends(without those of hexachlorodibenzo-p-dioxins [HxCDDs] andhexachlorodibenzofurans [HxCDFs] for clear illustration). TheOCDD, heptachlorodibenzo-p-dioxins (HpCDDs), octachlo-rodibenzofuran (OCDF), heptachlorodibenzofurans (Hp-CDFs), HxCDDs, and HxCDFs showed similar trends: Theyincreased dramatically during 1956 to 1972, decreased rapidlyduring 1972 to 1981, and then leveled off. On the other hand,TCDDs, pentachlorodizenzo-p-dioxins (PeCDDs), and tetra-chlorodizenzofurans (TCDFs), particularly 1,3,6,8-TCDD and1,3,7,9-TCDD, increased during 1962 to 1977, decreased rap-idly during 1977 to 1981, and subsequently leveled off. More-over, pentachlorodibenzofurans (PeCDFs) showed a differenttrend from those of other homologues mentioned above, in-creasing slowly to date. These characteristics indicate the ex-istence of different dioxin sources in the Tokyo Bay area.

Sources of PCDD/Fs

To identify PCDD/F sources, PCA was performed using acorrelation matrix calculated from the PCDD/F data set (83variables and 13 cases). Three major PCs with proportions of

994 Environ. Toxicol. Chem. 21, 2002 Y. Yao et al.T

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s.

Major PCDD/F and Co-PCB sources in Tokyo Bay, Japan Environ. Toxicol. Chem. 21, 2002 995

Fig. 2. Historical trends of polychlorinated dibenzo-p-dioxin/diben-zofuran (PCDD/F) homologues in the sediment core. Arrows in pa-rentheses indicate the corresponding axes (left or right). TCDFs 5tetrachlorodibenzofurans; PeCDFs 5 pentachlorodibenzofurans;HpCDFs 5 heptachlorodibenzofurans; OCDF 5 octachlorodibenzo-furan; TCDDs 5 tetrachlorodibenzo-p-dioxins; PeCDDs 5 pentachlo-rodibenzo-p-dioxins; HpCDDs 5 heptachlorodibenzo-p-dioxins;OCDD 5 and octachlorodibenzo-p-dioxin.

Fig. 4. History of pentachlorophenol (PCP), chloronitrofen (CNP) andpolychlorinated biphenyl (PCB) use in Japan. Arrows in parenthesesindicate the corresponding axes (left or right).

Fig. 3. Principal component loadings for the polychlorinated dibenzo-p-dioxin/dibenzofuran (PCDD/F) congener-specific data. PC 5 prin-cipal component; TCDD 5 tetrachlorodibenzo-p-dioxin; TCDF 5 te-trachlorodibenzofuran; PeCDD 5 pentachlorodibenzo-p-dioxin;PeCDF 5 pentachlorodibenzofuran; HxCDD 5 hexachlorodibenzo-p-dioxin; HxCDF 5 hexachlorodibenzofuran; HpCDD 5 heptachloro-dibenzo-p-dioxin; HpCDF 5 heptachlorodibenzofuran; OCDD 5 oc-tachlorodibenzo-p-dioxin; OCDF 5 octachlorodibenzofuran.

approximately 35%, 33%, and 28% were obtained. Becausethe cumulative proportion of these PCs was more than 95%,it was considered that the dioxin pollution in Tokyo Bay mainlycame from three sources (PC-1, PC-2, and PC-3). The factorloadings (.0.8) of the three major PCs are plotted in Figure3 [30].

The PC-1 includes OCDD, HpCDDs, OCDF, most Hp-CDFs, some HxCDDs and some HxCDFs as its characteristiccongeners. These higher chlorinated PCDD/Fs correspond wellwith the impurities of PCP [3,15], and their trends noted aboveare consistent with the history of PCP use in Japan as shownin Figure 4. The annual PCP usage increased rapidly from1957 and reached a maximum of approximately 16,000 tonsin 1967. It decreased by a factor of 55 during 1967 to 1975and then generally leveled out until 1986. Based on these

comparisons, PC-1 was judged to be the dioxin impurity ofPCP.

In the case of PC-2, many PeCDFs and HxCDFs are thecharacteristic congeners. Based on the homologue pattern ofa typical combustion process reported by Hutzinger and Fiedler[3], in which PeCDFs and HxCDFs are the main components,it was assumed that PC-2 corresponds to combustion processesin which incineration is the main factor.

The characteristic congeners of PC-3 include some TCDD,PeCDD, and TCDF congeners, particularly 1,3,6,8-TCDD,1,3,7,9-TCDD, 1,3,6,9-TCDD, 1,2,3,6,8-PeCDD, 1,2,3,7,9-PeCDD, and 2,4,6,8-TCDF. These lower chlorinated PCDD/Fs correspond with the primary impurities of CNP, which wasused as the replacement of PCP [15]. Their trends mentionedabove are consistent with the history of CNP use in Japan;that is, the annual CNP usage increased steadily from 1965,reached a maximum of approximately 5,500 tons in 1974, andstopped in 1995 (Fig. 4). Based on these comparisons, weidentified PC-3 to be the dioxin impurity of CNP.

Considering the separate periods of time during which PCPand CNP were used in Japan, the observed trends among thehigher and lower chlorinated homologue classes in differenttime frames seem to reflect the difference in period of PCPand CNP inputs. On the other hand, it should be noted thatour source identification approach mentioned above is basedon the assumption that variance in the congener space of thesediment profile is forced only by source variation. Other pos-sible causes of variance such as environmental breakdownwere neglected, because PCDD/Fs are reported to be resistantto microbial attack in the environment [31] and because theirphotodegradation in sediment is not considered to be signifi-cant.

Contributions of different sources to dioxin pollution

After dioxin source identification, MRA was carried outfor source apportioning based on the congener-specific data ofPCDD/F concentrations in such sources. Because of the largevariability in dioxin congener profiles from different samplesof each source, we used average congener profiles for thesesources, and this may cause uncertainty in our estimation. Thedioxin congener profile used for PCP was the average profileof four Japanese PCP formulations [15] with slight modifi-cation to adjust its homologue pattern. That is, the congener-specific concentrations of HpCDDs, OCDF, and HpCDFs inthe average profile were modified based on the typical ho-

996 Environ. Toxicol. Chem. 21, 2002 Y. Yao et al.

Fig. 5. Historical contributions of different sources to total polychlor-inated dibenzo-p-dioxin/dibenzofuran (SPCDD/F; left bar) and totalPCDD/F-derived toxic equivalent (STEQ [PCDD/Fs]; right bar) con-centrations in Tokyo Bay, Japan. Arrows indicate the correspondingaxes (left [SPCDD/Fs] or right [STEQ (PCDD/Fs)]). CNP 5 chlo-ronitrofen; PCP 5 pentachlorophenol.

Fig. 6. Historical trends of coplanar polychlorinated biphenyl (Co-PCB) congeners in the sediment core. Arrows in parentheses indicatethe corresponding axes (left or right).

mologue ratios of HpCDDs, OCDF, and HpCDFs to that ofOCDD in PCP reported by Hutzinger and Fiedler [3] to reducecalculation error. The congener profile of CNP was determinedbased on the average of five CNP formulations [15]. For com-bustion processes, the average congener profile of atmosphericdeposition obtained in the Kanto area (including Tokyo Bay)[32] was used.

In the MRA, the three sources and the 13 sediment sampleswere regarded as independent and dependent variables, re-spectively, whereas congeners or congener clusters in thesevariables were treated as cases. For each sediment sample, theregression coefficients of the three sources were obtained sep-arately on the basis of the least squares. Then, source appor-tioning was performed using the obtained regression coeffi-cients. Based on the calculated apportionment of each source,the historical contributions of PCP, CNP, and atmospheric de-position to SPCDD/F concentration in Tokyo Bay were esti-mated, and the results are expressed as the left bars (corre-sponding to the left axis) in Figure 5. Furthermore, these resultswere transformed into TEQ using the TEQ:PCDD/F ratio ineach source. The historical contributions of different sourcesto STEQ (PCDD/Fs) concentration in Tokyo Bay are alsoshown in Figure 5 (right bar and axis).

It can be seen that the herbicides PCP and CNP have mainlycontributed to the PCDD/F burdens since the late 1950s (Fig.5). Pentachlorophenol has been the greatest contributor to bothSPCDD/F and STEQ (PCDD/Fs) concentrations in Tokyo Bay.The contribution of PCP peaked around 1970, decreased during1972 to 1981, and then leveled off. Chloronitrofen has playeda minor role in SPCDD/F concentration since 1967. The con-tribution of CNP reached its maximum around 1975, decreasedduring the period 1977 to 1986, and subsequently leveled off.Combustion processes are the secondary contributor to STEQ(PCDD/Fs), but their proportion has been generally increasingto date. The contributions of PCP, CNP, and combustion pro-cesses to the SPCDD/F concentration in the surface sedimentlayer were estimated to be 76%, 15%, and 9%, respectively.In the case of STEQ (PCDD/Fs), their contributions were 62%,4%, and 34%, respectively. The inputs originating from PCPand CNP did not significantly decrease even after the declinein their use. This suggests that herbicide-derived PCDD/Fsremaining in agricultural land will continue to run off and topollute the aquatic environment in Japan for a long time.

Trends in Co-PCBs

For Co-PCBs, the 14 congeners were detected in nearly allthe sediment layers examined. The obtained data are presentedin Table 1. The SCo-PCB concentration in the oldest sedimentlayer, corresponding to approximately 1937, was found to be94 pg/g. It increased drastically from 1956 to 1972, reachinga peak of 26,000 pg/g in approximately 1970. Thereafter, adecrease occurred by a factor of 2.7 during 1972 to 1986, afterwhich the total concentration generally leveled off. The PCB-118 had been the dominant congener, contributing more than39% (up to 59%) of the SCo-PCB concentration throughoutthe core, followed by PCB-105, -180, -77, and -170. The con-tributions of PCB-118, -105, -180, -77, and -170 to the SCo-PCB concentration in the surface sediment layer were 42%,17%, 16%, 8.0%, and 7.7%, respectively. Based on the con-centration of SCo-PCBs in the surface sediment layer and theaverage sedimentation rate of 0.27 g/cm2/year, we calculatedthe present flux of Co-PCBs to Tokyo Bay sediment to be2,300 pg/cm2/year [29]. On the other hand, the STEQ (Co-PCBs) was dominated by PCB-126, contributing more than66% (up to 88%) of the STEQ (Co-PCBs) throughout the core.This can be explained by its having the largest TEF withinthe Co-PCB group. The other important TEQ contributors werePCB-118, -105, -156, and -77. The contributions of PCB-126,-118, -105, -156, and -77 to the STEQ (Co-PCBs) concentra-tion in the surface sediment layer were 71%, 12%, 4.8%, 4.8%,and 2.2%, respectively.

Also, the STEQ (PCDD/Fs and Co-PCBs) level increaseddrastically from the late 1950s and reached its maximum of83 pg/g in approximately 1970. It then declined to 49 pg/gover the next 9 years, after which it generally leveled off. ThePCDD/Fs contributed more than 90% of the STEQ (PCDD/Fs and Co-PCBs) throughout the sediment core, thus indicatingthat PCDD/Fs have played a major role in the toxic burden inTokyo Bay since the late 1930s (Table 1).

From the historical trends of individual Co-PCB congenersas shown in Figure 6 (without those of PCB-114, -123, -156,-157, -167, -189, -170, and -180 for clear illustration), it wasfound that all the compounds, except PCB-169, showed verysimilar trends. They increased drastically during 1956 to 1972,then decreased quickly during 1972 to 1977. On the other hand,PCB-169 showed a different trend from those of the othercompounds; the PCB-169 level has generally been increasingslowly to date. These characteristics suggest that different Co-PCB sources are present in the Tokyo Bay area.

Major PCDD/F and Co-PCB sources in Tokyo Bay, Japan Environ. Toxicol. Chem. 21, 2002 997

Sources of Co-PCBs

Because the Co-PCB data set obtained from the sedimentcore is too small, it was difficult to apply PCA for sourceidentification. However, from the historical trends of Co-PCBcongeners described above, we found something interesting.The trends of all the congeners, except PCB-169, in the coreare consistent with the history of PCB production and use inJapan (Fig. 4). Commercial PCB production began under thetrademark of Kanechlor (KC) in 1954. The annual PCB usageincreased significantly by a factor of more than 50 from 1954(200 tons/year) to 1970 (10,120 tons/year), and the productionwas stopped in 1972 [33]. These trends are also in agreementwith that of SPCBs in the same sediment core previouslyreported by Okuda et al. [24]. In addition, the observed Co-PCB pattern with a predominance of PCB-118, -105, -180,-77, and -170 mentioned above can be explained by the char-acteristics of KC preparations. According to Takasuga et al.[34], PCB-118 and -105 are the major Co-PCB componentsin KC-500, -400, and -300. Both PCB-180 and -170 exist athigh levels in KC-600, whereas PCB-77 is an important com-ponent in KC-400 and -300. Kannan et al. [16] also reportedthat KC preparations contain PCB-77 as a characteristic non-ortho Co-PCB congener. Based on these comparisons, we be-lieve that PCB formulations were the greatest contributing Co-PCB source in Tokyo Bay. Thus, the phenomenon of the SCo-PCB concentration generally leveling off since 1986 is largelyattributed to the supply of formulation-derived Co-PCBs re-maining in the catchment area.

In the case of PCB-169, it was found to exist in trace orundetectable levels in PCB formulations. Its time trend men-tioned above is consistent with that of PeCDFs recorded inthe sediment core. As described previously, PeCDFs are con-sidered to be the main combustion-related dioxin components.Furthermore, combustion processes were reported by Ballsch-miter et al. [35] to be the source of PCBs, particularly manyhighly chlorinated congeners, including PCB-169. Brown etal. [36] studied the Co-PCB concentration profiles in Aroclorformulations, and they noted that the environmental burden ofPCB-169 was derived largely from non-Aroclor sources. Ac-cordingly, we infer that combustion processes were anothersignificant source of Co-PCB pollution in Tokyo Bay.

Our inference is consistent with the view of Ohsaki et al.[37]. They indicated that municipal waste incineration mightbe a minor Co-PCB source compared with commercial PCBpreparations. On the other hand, the presence of Co-PCBs inthe sediment layers corresponding to the period 1935 to 1951,the pre-PCB production era in Japan, might be attributed tothe PCB importation and use at that time [33]. Long-distanceatmospheric transport is another possible explanation [33].Further investigation is required to obtain more detailed PCBcongener-specific information for improved future source iden-tification.

CONCLUSIONS

Based on the obtained congener-specific data of PCDD/Fsand Co-PCBs in a dated sediment core, the historical trendsof these compounds in Tokyo Bay were reconstructed. Usinga statistical analysis approach, two herbicides, PCP and CNP,as well as combustion processes were identified to be the majordioxin sources, and contamination from the use of PCP andCNP followed by agricultural runoff was further shown to bethe primary factor for dioxin inputs in this watershed. For Co-PCB pollution, PCB formulations and combustion processes

were estimated to be the major sources, in which the formerwas considered to be the primary factor. These findings willassist remediation planning for and subsequent monitoring inthe Tokyo Bay area. Furthermore, our results are of signifi-cance for the establishment of comprehensive PCDD/F andCo-PCB control measures in Japan and would help in under-standing the global dioxin and dioxin-like PCB problems.

Acknowledgement—This work was conducted under the research pro-ject Establishment of a Scientific Framework for the Management ofToxicity of Chemicals Based on Environmental Risk-Benefit Analysis,supported by Core Research for Evolutional Science and Technologyof the Japan Science and Technology Corporation.

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