SHORT COMMUNICATION

J For Res (2006) 11:137–142 © The Japanese Forest Society and Springer-Verlag Tokyo 2006DOI 10.1007/s10310-005-0196-1

Yuko Itoh · Satoru Miura · Shuichiro Yoshinaga

Atmospheric lead and cadmium deposition within forests in the Kantodistrict, Japan

Received: September 21, 2005 / Accepted: November 29, 2005

Y. Itoh (*) · S. YoshinagaSoil Geochemistry Laboratory, Forestry and Forest ProductsResearch Institute, 1 Matsunosato, Tsukuba 305-8687, JapanTel. +81-29-873-3211 (ext. 363); Fax +81-29-874-3720e-mail: yuko106@ffpri.affrc.go.jp

S. MiuraTohoku Research Center, Forestry and Forest Products ResearchInstitute, Morioka, Japan

Abstract Atmospheric lead and cadmium deposition inbulk precipitation and throughfall was investigated at fourforests in the Kanto district, Japan, to assess the impact ofhuman activities on the environmental health of forests.Annual lead and cadmium depositions in bulk precipitationranged from 8.9 to 25.7gha−1 year−1 and from 0.77 to1.30gha−1 year−1, respectively. Lead and cadmium deposi-tion increased in the summer at every forest due to largeamounts of rainfall. At one of the forests, the depositionswere also high in the winter due to heavy snowfall. Thesedepositions were similar to recent depositions observed atother rural and urban sites in Japan and several forests inEurope and North America after 1990. These results indi-cate that although anthropogenic lead and cadmium aredeposited at these rates over wide areas, depositions are stillhigher than in remote areas.

Key words Lead · Cadmium · Deposition · Bulk precipita-tion · Forests

Introduction

Human activities have resulted in emission of huge amountsof trace metals, which has drastically altered the naturaldistribution of these metals and biogeochemical cycles interrestrial and aquatic ecosystems (Borg and Johansson1989; Nriagu 1990). Lead and cadmium are toxic to livingorganisms even at low levels. Lead and cadmium are emit-ted to the atmosphere from various anthropogenic sources:

mining, smelters, industrial processes, fossil fuel combus-tion, automobiles, and waste incinerators (Pacyna andPacyna 2001). Atmospheric deposition is a major pathwayof lead and cadmium influx to forest ecosystems (Gallowayet al. 1982). Numerous studies on atmospheric deposition oftrace metals in forest ecosystems have been conducted inEurope and North America since the 1970s (e.g. Heinrichsand Mayer 1977; Smith and Siccama 1981; Bergkvist 1987).In these studies, both the forest floor and mineral soil wereimpacted by atmospheric deposition of lead and cadmium.The accumulated lead and cadmium in forest ecosystemsare likely released to surface water. Most studies ongeochemical dynamics of these elements in Japan havemainly focused on the emission and behavior of airborneparticulate matter in urban areas and on the distribution insediments or soils at heavily polluted sites (e.g. Mukai et al.1993; Asami 2001; Taki et al. 2001). The objective of thisstudy was to evaluate the atmospheric lead and cadmiumdeposition in bulk precipitation at four forests in the Kantodistrict, Japan.

Materials and methods

Site descriptions

Bulk precipitation and throughfall samples were collectedfrom 2001 to 2003 from three rural forests; GT, IT, and IK,and at one urban forest; TN, in the Kanto district, Japan(Fig. 1 and Table 1). GT (36°51′ N, 139°1′ E) is mountainousand is the headwater area for the Tone River, and is situ-ated 160kmNNW of Tokyo and 60kmSE of the Japan Seacoastline. IT (36°20′ N, 140°18′ E) is on the periphery of theKanto plain, which is 60kmNE of Tokyo and 50kmNW ofthe Pacific Ocean coastline. IK (36°32′ N, 140°18′ E) is hillyand 110kmNE of Tokyo and 30kmNW of the PacificOcean coastline. TN (35°44′ N, 139°32′ E) is located withinthe Tokyo metropolitan area, is densely populated, and20kmNW of the Pacific Ocean coastline. This site wasselected to compare atmospheric deposition with rural for-

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ests. No significant anthropogenic lead and cadmium emis-sion points were found in the study areas. IT, IK, and TNhave less precipitation in the winter than GT, where theaverage winter annual snowfall depth is over 3m at thesampling site.

Sampling

Bulk precipitation, which includes wet and dry deposition,was collected (one collector per site) monthly in an openarea within each forest. The sampler, consisting of a poly-ethylene funnel (210mm diameter) and tank (10 l), wasplaced 1.2m above ground level. The collection tank wascovered with a shade mat for protection from light and heat.At GT, the bulk precipitation sample was collected monthlyduring the snow season (December to May) with a snow-rainfall collector with an electric heater (Sun Techno,Toyama, Japan). The collector consisted of a Teflon-coatedpolyethylene funnel (210mm diameter) connected to a tank(30 l) within a box.

Throughfall (three collectors per site) was collectedmonthly at each forest where Japanese cedar (Cryptomeriajaponica) stands were dominant, but the stand age and den-sity were different at each site. The collector consisted of apolyethylene funnel (300mm diameter) and a tank (20 l).At GT, throughfall samples were collected only during

the snow-free period (May to November) due to heavysnowfall.

To minimize contamination by local debris (e.g., insectsand litterfall), a nylon mesh and a Teflon riddle plate wereplaced between the funnel and collection tank for bulkprecipitation and throughfall. All sampling equipment wasreplaced monthly with laboratory-cleaned apparatus thathad been washed with nitric acid and rinsed with high-purity water.

Chemical analyses

The bulk precipitation and throughfall samples were acidi-fied with ultra-pure nitric acid (0.1M HNO3) after filtrationwith a 0.45-µm membrane filter. The concentrations ofdissolved lead and cadmium were determined by induc-tively coupled plasma-mass spectrometry (Platform ICP,Micromass, UK). Spikes of indium (1µg l−1) were addedto the calibration solutions and samples as an internalstandard.

Results

Bulk precipitation and throughfall chemistry

Tables 2 and 3 show the volume-weighted mean values ofpH, electrical conductivity (EC), and lead and cadmiumconcentrations in bulk precipitation and throughfall atstudy sites. Bulk precipitation was acidic (pH < 5.6) at allsites, and the pH values were lowest at TN. The lead con-centration at GT, IT, IK, and TN ranged from 0.18 to 4.52,0.30 to 7.97, 0.09 to 3.51, and 0.22 to 14.54µg l−1, respectively.The maximum lead concentration was observed at TN andthe minimum was at IK. The mean concentration was high-est at TN. The cadmium concentration at GT, IT, IK, andTN ranged from 0.01 to 0.31, 0.01 to 0.43, 0.02 to 0.38, and0.02 to 0.38µg l−1, respectively. The maximum cadmium con-centration was observed at IT and the minimum was ob-served at GT. The mean concentration in bulk precipitationwas also highest at TN.

The pH values of throughfall were also acidic, althoughthey were higher than those of bulk precipitation at eachsite. The mean concentrations of lead and cadmium in bulkprecipitation and throughfall followed the same pattern:TN > IT > GT > IK. The mean concentration of lead in bulkprecipitation was higher than in throughfall (Tables 2, 3).

Fig. 1. Location of the sampling sites (diamonds) in the Kanto district,Japan

Table 1. General description of sampling sites

Site Location Age (years) Vegetation Altitudea (m) Mean annual rainfall (mm) Mean annual temperature (°C)

GT Rural 52 Cryptomeria japonica 816 2134 8.3IT Rural 49 Cryptomeria japonica 380 1373 14.1IK Rural 39 Cryptomeria japonica 220 1507 13.0TN Urban 22 Cryptomeria japonica 50 1300 15.5a Altitude of bulk precipitation sampling point

GT

TN

ITIK

TOKYO

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The mean concentration of cadmium in bulk precipitationwas higher in throughfall at GT and IK, while the meanconcentration of cadmium in throughfall was slightly higherthan in bulk precipitation at IT and TN (Tables 2, 3). Ap-proximately 70% of the bulk precipitation samples weregreater than throughfall samples, regardless of location(Fig. 2).

Annual lead and cadmium deposition

The annual lead and cadmium deposition in bulk precipita-tion was calculated as the product of the volume-weightedmean concentration multiplied by the precipitation amountfor each study period, expressed on an annual basis. Theannual lead deposition in bulk precipitation at GT, IT, IK,and TN was 19.1, 16.9, 8.9, and 25.7g ha−1 year−1, respectively(Fig. 3). The annual cadmium deposition in bulk precipi-tation at GT, IT, IK, and TN was 1.30, 0.95, 0.77, and1.28gha−1 year−1, respectively (Fig. 3). The annual leaddeposition was highest at TN, and the annual cadmiumdeposition was highest at GT.

The annual lead deposition at IT, IK, and TN inthroughfall was 11.3, 5.3, and 13.3gha−1 year−1, respectively.The annual cadmium deposition at IT, IK, and TNin throughfall was 0.96, 0.38, and 1.37gha−1 year−1,respectively.

Monthly lead and cadmium deposition in bulk precipita-tion increased in summer, due to the onset of the rainyseason and the occurrence of typhoons at each forest (Fig.4). In winter, the relatively high deposition of lead andcadmium was found at GT, as a consequence of heavysnowfall (Fig. 4).

Discussion

Bulk precipitation and throughfall chemistry

The differences in annual lead and cadmium depositionbetween bulk precipitation and throughfall have followedseveral patterns in other forest ecosystems (Stahr et al.1980; Avila and Rodrigo 2004). Although concentrations ofmajor elements generally increase during passage throughthe tree canopy (Wu et al. 1996), the lead and cadmiumconcentration in the current study revealed negligible en-richment in throughfall. This result suggests that leaching oflead and cadmium from vegetation would be a minorprocess.

Atmospheric lead and cadmium deposition

In North America, Europe, and Japan, serious air pollutionoccurred from the 1960s to the early 1980s due to variousanthropogenic emissions. The high concentrations of leadand cadmium in bulk precipitation at an urban area in Eu-rope were reported to be 190µgl−1 and 19µg l−1, respectively(Galloway et al. 1982). At a forest site in central Germany,lead and cadmium concentrations in bulk precipitationwere reported to be 38µg l−1 and 1.2µg l−1, respectively, withresultant depositions of 405g ha−1 year−1 and 13gha−1 year−1,respectively (Heinrichs and Mayer 1977). These concentra-

Table 3. Throughfall chemistry at study sites

Site pH EC Pb concentration Cd concentration(µS cm−1) (µg l−1) (µg l−1)

GT 4.72 27.6 0.82 0.05IT 5.19 47.9 1.01 0.09IK 5.20 32.6 0.50 0.04TN 4.66 53.7 1.05 0.11

Table 2. Bulk precipitation chemistry at study sites

Site pH EC Pb concentration Cd concentration(µS cm−1) (µg l−1) (µg l−1)

GT 4.53 22.4 1.06 0.07IT 4.64 24.2 1.35 0.08IK 4.90 20.5 0.66 0.06TN 4.40 33.6 1.73 0.09

Pb in bulk precipitation (m g L-1)

Pb

in th

roug

hfal

l(m

g L

-1)

1:1

100.00.1 1.0 10.0

100.0

10.0

1.0

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Cd in bulk precipitation (m g L-1)

1:1

Fig. 2. Relationship of lead(left) and cadmium (right)concentrations between bulkprecipitation and throughfall.Closed circles, concentrations atGT, IT, and IK; open circles,concentrations at TN

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tions and deposition rates from other studies are consider-ably higher than those found in this study. Since the mid-1970s, stringent environmental controls have resulted indecreased emissions of trace metals from major pointsources in North America, Europe, and Japan (Mukai et al.1993). Due to these controls, the annual lead deposition atthe Hubbard Brook Experimental Forest (USA) decreaseddrastically from 396gha−1 year−1 in 1976 to 12.7gha−1 year−1

in 1989 (Johnson et al. 1995). The annual lead and cadmiumdeposition in the current study was similar to that recordedafter 1990 at rural forests in North America and Europe,indicating obvious improvement in the atmospheric envi-ronment (Table 4).

A few recent studies have presented lead and cadmiumconcentrations in precipitation at urban and rural areas inJapan (Kobayashi 2001; Tsumura and Yamasaki 1998). Inaddition, Takeda et al. (2000) reported that the annualdepositions of lead and cadmium at a rural site in Japanwere 17.8gha−1 year−1 and 0.90g ha−1 year−1, respectively. Theconcentration and input of lead and cadmium in these stud-ies coincide with those found in the current study (Table 5)and the values were very similar. These results suggest thatatmospheric lead and cadmium deposition are similar overa wide area in Japan, regardless of habitat type (forest,rural, or urban area). On the other hand, atmospheric leadand cadmium depositions at a remote site in Greenlandwere reported to be 0.08gha−1 year−1 and 0.003g ha−1 year−1,respectively (Sherrell et al. 2000). The lead and cadmiumdepositions in Japan were substantially greater (greaterthan three orders of magnitude) than those at the remotesites (Table 4). These differences indicate that various an-thropogenic emission sources of these metals are still wide-spread, with urbanization and an increase in automobilesand waste incinerators, in spite of reductions in emissionsfrom large point sources.

Seasonal variation in lead and cadmium deposition

The lead and cadmium deposition increased in summer atevery forest in this study, due to rainfall and the occurrenceof typhoons (Fig. 4). At GT, the deposition of lead andcadmium was high in winter (December to April) as a resultof snowfall. Conversely, lead and cadmium deposition inHiroshima (western Japan) had no clear seasonal variation(Takeda et al. 2000). In contrast, Bellis et al. (2005) re-ported higher lead deposition in winter and spring (Novem-ber to May) in Niigata, which is 140kmNNE of GT and onthe west coast. This trend is a result of long-range transportof air masses from continental Asia. The lead isotope ratiosin rime ice collected in winter at Mount Tanigawa (about8km from GT) were similar to those of urban airborneparticles from northeast China, Russia, and Korea, andwere different from those found in airborne particles inJapanese urban areas (Mori et al. 2002). The northwestwinter monsoon causes heavy snowfall on the Japan Seacoast. These reports suggest that the winter deposition oflead and cadmium at GT might be influenced by the long-range transport of air pollution from continental Asia.

Pb

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ar-1

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0.00

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1.000

1.50

GT IT IK TN

0.00

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0.08

0.10Cd Cd conc.

Fig. 3. Lead (upper) and cadmium (lower) annual deposition and meanconcentration at the four study sites. Columns show lead and cadmiumdeposition (left axes); diamonds show mean concentration (right axes)

Pb

depo

siti

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m g

m-2

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400

600

800

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Fig. 4. Temporal variations of lead (upper) and cadmium (lower)deposition in bulk precipitation at four forests; diamonds, GT; tri-angles, IT; circles, IK; crosses, TN. Lines are not connected for analysesnot completed due to small amount of sample

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Thus, GT would have been more susceptible to the influ-ence of local, regional, and transboundary sources than theother study sites.

Conclusions

The annual lead and cadmium depositions at GT, IT, IK,and TN ranged from 8.9 to 25.7gha−1 year−1, and from 0.77to 1.30gha−1 year−1, respectively. There were slight differ-ences in deposition among sites, and at all sites the deposi-tion was lower than that of heavily polluted areas. However,the deposition showed much higher rates than remote ar-eas. Lead and cadmium deposition increased in the summerat every forest due to rainfall. At GT, high deposition oflead and cadmium was also observed in winter due to heavysnowfall. Anthropogenic lead and cadmium deposit con-tinuously from the atmosphere over wide areas in Japan, as

well as in forests in Kanto, and the sources of atmosphericlead and cadmium deposition require elucidation.

Further studies on the behavior of atmospherically de-rived lead and cadmium in forest ecosystems are needed toreveal chronic effects or the migration to stream water andgroundwater. The study of input–output balances in water-sheds, metal chemical form and speciation, and lead isotopeanalysis might be useful tools in evaluating trace metal bio-geochemical cycling.

Acknowledgments The authors express their sincere appreciationto Dr. D. Sakaue and Mr. N. Iwamoto (Tanashi Experimental Station,Tokyo University) for their continued support and Dr. K. Baba(NIAES) for the ICP-MS analysis. We also thank Mr. S. Yoshinoand our many colleagues (FFPRI) for their field sampling, and Dr.M. Takahashi for his useful comments. This study was, in part,financially supported by the research project “Integrated ResearchProgram on Effects of Endocrine Disrupters on Agriculture, Forestry,and Fisheries and their Mechanisms of Action on Domestic Animalsand Fishes” of the Ministry of Agriculture, Forestry, and Fisheries,Japan.

Table 4. Comparison of lead and cadmium deposition in precipitation at rural forests and remoteareas

Location Period Site Annual deposition Reference(gha−1 year−1)

Pb Cd

Rural 1960s–1980s Germany 405.0 13.0 Heinrichs and Mayer (1977)Europe 220.0 4.0 Jeffries and Snyder (1981)UK 150.0 2.6 Durand et al. (1994)USA 150.0 5.0 Lindberg and Harriss (1981)

1990s– Japan 8.9–19.1 0.8–1.3 This studyUK 10.0–24.0 0.1–0.4 Lawlor and Tipping (2003)Canada 26.1 2.7 Gelinas and Schmit (1998)Finland 8.0–9.5 0.2 Ukonmaanaho et al. (2001)Spain 6.3 5.4 Avila and Rodrigo (2003)Sweden 14.3 0.4 Aastrap et al. (1995)USA 9.7 1.2 Lawson and Mason (2001)Czech 21.5 1.2 Bendl and Skrivan (1997)RepublicNorway 2.3–68.0 0.3–2.0 Berg et al. (1994)

Remote 1990s– New Zealand 0.1–0.4 0.01–0.04 Halstead et al. (2000)Greenland 0.1 0.003 Sherrell et al. (2000)

Table 5. Comparison of lead and cadmium concentrations in rainfall in Japan

Site Location Pb (µg l−1) Cd (µg l−1)

Meana Range Meana Range

Higashi Hiroshimab Rural 1.24 0.02–25.15 0.06 0.006–1.23Kanazawac Urban – <0.42–8.50 – <0.006–13.15Tokyo, Tsukubad Urban, rural 0.56e 0.06–10.78 0.06e 0.004–3.75This study Rural/forests 1.02 0.09–7.97 0.07 0.01–0.38This study Urban/forest 1.73 0.22–14.54 0.09 0.02–0.38a Volume-weighted meanb Takeda et al. (2000)c Kobayashi (2001)d Tsumura and Yamasaki (1998)e Median value

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