Science of the Total Environment 442 (2013) 189–197
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Science of the Total Environment
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Sedimentary records of metal deposition in Japanese alpine lakes for the last
250 years: Recent enrichment of airborne Sb and In in East Asia
Michinobu Kuwae a,⁎, Narumi K. Tsugeki a, b, Tetsuro Agusa c, Kazuhiro Toyoda d, Yukinori Tani e,
Shingo Ueda f, Shinsuke Tanabe c, Jotaro Urabe b
a
Senior Research Fellow Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
Graduate School of Life Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
Center for Marine Environmental Studies, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan
d
Graduate School of Environmental Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan
e
Institute for Environmental Sciences, University of Shizuoka, Suruga-ku, Shizuoka 422-8526, Japan
f
College of Bioresource Science, Nihon University, Fujisawa 252-8510, Japan
b
c
H I G H L I G H T S
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►
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First report on historical trends in Sb and In enrichment in East Asian atmosphere
Sedimentary records show a marked increase of Sb and In depositions since 1980.
Sb/Pb ratios suggest coal combustion in East Asia as an important source of Sb.
Atmospheric pollution of Sb and In intensified in East Asia during recent decades
a r t i c l e
i n f o
Article history:
Received 18 April 2012
Received in revised form 19 September 2012
Accepted 9 October 2012
Available online 22 November 2012
Keywords:
Antimony
Indium
Alpine lake sediments
Historical trends
Pollution
East Asia
a b s t r a c t
Concentrations of 18 elements, including Sb, In, Sn, and Bi, were measured in sediment cores from two pristine
alpine lakes on Mount Hachimantai, northern Japan, representing the past 250 years. Vertical variations in
concentrations are better explained by atmospheric metal deposition than by diagenetic redistribution of Fe
and Mn hydroxide and organic matter. Anthropogenic metal fluxes were estimated from 210Pb-derived accumulation rates and metal concentrations in excess of the Al-normalized mean background concentration before
1850. Anthropogenic fluxes of Sb and In showed gradual increases starting around 1900 in both lakes, and
marked increases after 1980. Comparison of Sb/Pb and Pb stable isotope ratios in sediments with those in
aerosols of China or northern Japan and Japanese source materials (recent traffic- and incinerator-derived
dust) suggest that the markedly elevated Sb flux after 1980 resulted primarily from enhanced long-range
transport in aerosols containing Sb and Pb from coal combustion on the Asian continent. The fluxes of In, Sn,
and Bi which are present in Chinese coal showed increasing trends similar to Sb for both study lakes. This
suggests that the same source although incinerators in Japan may not be ruled out as sources of In. The sedimentary records for the last 250 years indicate that atmospheric pollution of Sb and In in East Asia have intensified
during recent decades.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
Antimony (Sb) and indium (In) are important industrial metals whose
worldwide production is growing. Antimony is used in automobile brake
pads, batteries, ceramics, glass, plastics, and flame retardants (Filella et al.,
2002; Krachler et al., 2005). Indium use has increased dramatically due to
new applications in the rapidly growing electronics, photovoltaic, and
LED industries (White and Hemond, 2012). Some chemical compounds
containing Sb are considered to be hazardous to human health at very
low concentrations (Gebel, 1997), and In compounds are potentially
⁎ Corresponding author. Tel./fax: +81 89 927 9654.
E-mail address: [email protected] (M. Kuwae).
0048-9697/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.scitotenv.2012.10.037
pulmonary toxins, carcinogens, and teratogens (White and Hemond,
2012). These metals are present in the atmosphere as a result of human
activities as well as natural processes such as volcanic eruptions (Filella
et al., 2002; White and Hemond, 2012). Major anthropogenic airborne
sources of Sb are coal combustion, metal mining and smelting, and
waste incineration (Filella et al., 2002). Coal combustion and metal
mining and smelting are also important sources of In emissions (White
and Hemond, 2012). Large emissions of these metals to the atmosphere
(Filella et al., 2002; Tian et al., 2012; White and Hemond, 2012) and
their enrichment in sediments (Grahn et al., 2006) and Arctic ice cores
(Krachler et al., 2005) in recent decades suggest that anthropogenic
contamination of these metals is extensive (Grahn et al., 2006; Shotyk
et al., 2005). However, there are very few relevant historical data from
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well-dated natural archives to assess the modern extent and intensity of
these pollutants on a global scale.
East Asia plays an important role in global anthropogenic emissions
of Sb (He et al., 2012; Krachler et al., 2005; Pacyna and Pacyna, 2001),
but little is known about changes in the extent and intensity of atmospheric pollution during its rapid population and socioeconomic growth
of recent decades. Today Chinese mines account for almost 80% of the
world's Sb production (Piper and Nokleberg, 2002), and atmospheric
Sb emissions derived from coal combustion in China increased fourfold
from 1980 to 2007 (Tian et al., 2012). In Japan, domestic supplies of Sb
compounds began to increase significantly around the beginning of this
century as their use as a flame retardant for plastic products increased
(Tsunemi and Wada, 2008). A high enrichment factor of Sb in airborne
particulate matter was reported for 1995–2004 (Furuta et al., 2005).
Urban Sb sources from megacities of East Asia are suspected as a
cause of recent enrichment of Sb in Canadian Arctic ice core samples
(Krachler et al., 2005). These observations imply enrichment of Sb in
the East Asian atmosphere during recent decades.
Although there are no reports of In emissions to the East Asian
atmosphere, enrichment of In in the atmosphere during recent decades
is plausible. World production of In has increased tenfold over the past
30 years, and China is the largest producer (White and Hemond, 2012).
Coal consumption in China, which results in In emissions (White and
Hemond, 2012), increased roughly fourfold from 1980 to 2008 (Tian et
al., 2012). For its part, Japan consumes more than 50% of the worldwide
In output for products such as semiconductors and electronics, and In
consumption within Japan has risen more than tenfold during the past
decade (The Economics of Indium, 1999). Increasingly, these products
are being disposed of and incinerated (White and Hemond, 2012).
To assess the potential Sb and In enrichment in the East Asian
atmosphere in recent decades, well-dated natural archives are required
in the area. Two alpine lakes, Hourai-Numa and Hachiman-Numa on
Mount Hachimantai in northern Honshu Island, Japan (Fig. 1) have
been protected from anthropogenic impacts as national parks after
1957 and there are no facilities that directly supply pollutants to these
lakes. Multiple-element analysis of sediments in these pristine lakes
can provide natural archives of the deposition of anthropogenic metals.
Undisturbed lake sediments have been widely used for the assessment
of historical trends of atmospheric metal deposition (e.g., Renberg et al.,
1994; Thevenon et al., 2011). Analysis of multiple elements can give
useful information to identify sources of aerosols (Furuta et al., 2005;
Iijima et al., 2009; Kusunoki et al., 2012; Mukai et al., 1990; Okuda et
al., 2006; Wang et al., 2006) and to relate stratigraphic and temporal
variations of element concentrations to anthropogenic or lithogenic
sources and diagenetic redistributions (Lavilla et al., 2006). In this
study, we analyzed concentrations of multiple elements in sediments
of the two alpine lakes to reconstruct historical changes in atmospheric
deposition of metals during the last several centuries; in particular, we
focused on historical variations in anthropogenic Sb and In enrichment
in the East Asian atmosphere during recent decades.
2. Study sites
To elucidate trends of regional-scale deposition of metals, we chose
two lakes, Hachiman-Numa (1560 m asl) near the top of Mount
Hachimantai and Hourai-Numa (1305 m asl) southeast of the summit
(Fig. 1). The lakes are only 2 km apart, but their drainage areas and
limnological properties differ. Hachiman-Numa is on a plain (Fig. 1B)
surrounded by numerous peat bogs and wet moors, and its pH is slightly acidic (pH = 5.1 in July 2005; pH= 5.2 in August 1979, Ministry of the
Environment, 1979). It is 22.4 m deep, and it has an area of 0.060 km2
and a watershed of 0.54 km2. Hourai-Numa is on a slope (Fig. 1B)
surrounded by forest, and its pH is neutral (pH = 6.8 in July 2005;
pH= 6.4 in August 1979, Ministry of the Environment, 1979). It is
5.2 m deep, and it has an area of 0.0065 km2 and a watershed of
0.12 km2.
Fig. 1. Location map showing the study area (Mount Hachimantai) and aerosol sampling
sites of previous studies (A) and map of the study area showing the two alpine lakes
yielding sediment cores (B).
3. Materials and methods
3.1. Sediment core acquisition and dating
Sediment cores were collected in August 2007 in Hourai-Numa (water
depth 4 m; 39°56′23.8″N, 140°52′13.9″E) and Hachiman-Numa (water
depth 12 m; 39°57′24.0″N, 140°51′40.1″E) using a gravity corer installed
with acrylic tube with an inner diameter of 10.9 cm (model HR, RIGO Co.
Ltd., Saitama, Japan). Each core was sampled within a few hours after the
collection every 1 cm for analyses of chronology, elemental concentrations, grain size, and Pb stable isotopes. Thickness of an oxic layer of
each core collected from both lakes was not altered during the core processing, indicating no change of redox properties of surface sediments
in the sampling processes. Age models of the sediments based on
unsupported 210Pb (210Pb derived from the 222Rn decay that occurs in
the atmosphere and the water column) and the constant rate of supply
(CRS) model of unsupported 210Pb (Appleby and Oldfield, 1978), as described in detail by Tsugeki et al. (in press), were used in this study. Sediments were dated back to 1760s for both lakes by the CRS age models,
but dates before 1850 were tentative because 210Pb is generally not useful
for dating materials beyond ~150 years due to its half-life of 22.3 years.
Age error estimations for the Hachiman-Numa core were ±44 at 1858
(16 cm core depth), ± 6 years at 1905 (11 cm depth) and less than
± 1 year after 1957 (6 cm depth). For the Hourai-Numa core, age errors
were ±42 years at 1870 (17 cm depth), ±9 years at 1898 (14 cm
depth) and less than ±1 year after 1964 (6 cm depth). Increasing trends
in unsupported 210Pb (Tsugeki et al., in press) in the surface layers indicate that vertical mixing of surface sediments due to core collection and
bioturbation was minor for each core.
3.2. Bulk metal concentrations and Pb isotope ratios
Bulk concentrations of 18 elements (Sb, In, Sn, Hg, Bi, Cd, Ag, As,
Se, Mo, V, Cr, Mn, Co, Cu, Zn, Tl, and Pb) were determined using the
following method (Amano et al., 2011; Ha et al., 2009). Each dried
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sediment sample was digested in a mixture of 69 wt.% HNO3 (6 mL)
and 50 wt.% HF (1 mL) using a microwave system (Ethos D, Milestone
S.r.l., Sorisole, BG, Italy). The microwave digestion program was 2 min
at 250 W, 3 min at 0 W, 5 min at 250 W, 5 min at 400 W, 5 min at
500 W, 5 min at 400 W, and 5 min for ventilation. The digested sediment solution was evaporated by heating to remove HF, and then
the residue was dissolved in HNO3.
Metal concentrations were measured three times with an inductively coupled plasma-mass spectrometer (ICP-MS; Agilent 7500cx,
Agilent, Palo Alto, CA, USA). Rhodium was used as an internal standard for correction of matrix effects and instrumental drift. Concentration of Hg was determined with a cold vapor-atomic absorption
spectrometer (HG-450, Hiranuma Sangyo Co. Ltd., Mito, Japan).
Analytical accuracy was assessed using the National Institute for
Environmental Study (NIES) standard reference materials NIES no. 2
(pond sediment) and NIES no. 12 (marine sediment), and the recoveries of metals were 80–119% based on three replications.
Lead isotope ratios ( 207Pb/ 206Pb and 208Pb/ 206Pb) were determined with ICP-MS in a previous study (Tsugeki et al., in press)
using 1000 scans per measurement and 10 s integration time. Each
sample was measured five times, and the average and relative standard deviation for Pb isotope ratios in the sample were calculated.
The relative standard deviation of measurements was less than 0.1%.
The obtained Pb isotope ratios were normalized to their absolute
values by comparison with the National Institute of Standards and
Technology standard SRM981 (Gaithersburg, MD, USA).
3.3. Analysis of Fe, Mn, and Pb concentrations in
acid/reductant-extracted fraction
The chemical extraction method has been widely used for characterization of many trace metals associated with the precipitation–
dissolution–diffusion–reprecipitation cycle of iron and manganese
hydroxides. It is useful in assessing the effects of diagenesis that
could influence the vertical distribution of trace metals in sediment
profiles (e.g., Chen et al., 2003; El Bilali et al., 2002). We analyzed
Fe, Mn, and Pb concentrations in the acid/reductant-extracted fraction and its residue fraction by the following procedure. All dried
samples (0.1–0.5 g) were leached with 0.5 mL of 1 M NH2OH and
12 mL of 1 M HCl at 85 °C for 80 min (Kawashima, 2009; Toyoda
and Masuda, 1991). The leaching condition was defined to minimize
dissolution of amorphous clay and to complete leaching of hydrogenous iron oxide minerals (Marchig and Gundlach, 1982; Tessier et al.,
1979), which was shown to be incomplete by the conventional
Tessier method (Toyoda and Masuda, 1991). As carbonate contents
were negligible in these sediments, this extraction procedure separated
the samples into two fractions: (1) an extract fraction consisting of
mainly iron and manganese oxyhydroxides and exchangeable cations
in clays and organic matter and (2) a residue fraction consisting of
mainly aluminosilicates and organic matter. The concentrations of
these fractions were measured using inductively coupled plasma atomic emission spectroscopy (ICP-AES) at Hokkaido University (Seiko Co.
Ltd. model SPS7700). The residue was decomposed by 25 M HF, and a
mixture of 16 M HNO3 and 6 M HClO4 and dissolved into 0.5 M HCl
solution for ICP-AES measurement. Total concentrations of Al and Ti
were determined by the same procedure and reported as the sum of
the extracted and residual concentrations. Analytical error in the ICP
measurement ranged between 1% and 3% for Al, Ti, Fe, Mn, and Pb.
3.4. Grain size analysis
Although changes in physical erosion in watersheds can alter
metal concentrations in sediment due to dilution by clastic materials,
dilution can be estimated from changes in grain size data (Horowitz,
1985; Lin et al., 2002). We measured the median and mode grain size
of sediment samples using a laser diffraction particle size analyzer
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(SALD-2100, Shimazdu Co.). As a pretreatment to remove organic
matter, 10 cm 3 of 10 wt.% H2O2 was added to approximately 1 g of
dry sample in a beaker; this was left to settle at room temperature
for 24 h. Immediately before analysis, distilled water was added and
grains were ultrasonically dispersed for 3 min. During analysis,
4 mL of 0.1 mol/L (NaPO3)6 aqueous solution was added to the samples to maintain dispersion.
3.5. Calculations of anthropogenic metal concentration and flux
To express the anthropogenic contribution to the metal inventories in the cores, we calculated lithogenic metal concentrations
according to the formula of Shotyk et al. (2004), based on the Al concentration of a sample ([Al]sample) and the ratio of the metal of interest and the background Al concentration:
½metallithogenic ¼ ½Alsample ð½metal=½AlÞbackground :
We used Al as the conservative lithogenic metal because it has
been widely used for the normalization of lithogenic metals to their
anthropogenic counterparts (Lantzy and Mackenzie, 1979; Mikac et
al., 2011; Ravichandran et al., 1995). We defined the background
metal/Al ratio as the mean value for the bottom four or five samples,
in which lithogenic metal was assumed to be dominant because of the
very low concentrations of Sb, In, and other anthropogenic metals
(see Results section). Anthropogenic metal concentration in a sample
was then calculated as the difference between the total and lithogenic
metal concentrations:
½metalanthropogenic ¼ ½metaltotal –½metallithogenic :
Because background samples were dated before 1850 (see Results
section), the anthropogenic metal concentrations presented here are
metal concentrations in excess of the Al-normalized mean metal concentration before 1850.
Furthermore, to minimize any effect of dilution by lithogenic materials on trends in anthropogenic metal deposition, we calculated
anthropogenic metal flux (μg cm −2 year −1) as
Flux ¼ ½metalanthropogenic AR
where AR is the dry mass accumulation rate (g cm−2 year−1) obtained
from the 210Pb-based CRS model (Appleby and Oldfield, 1978).
3.6. Data analysis
To characterize the vertical variations in metal concentrations, the
constrained incremental sum of squares cluster-analysis (CONISS) was
conducted using program available in TILIA version 1.7.16 (Grimm,
1987). Analysis was performed using stratigraphically constrained
method and standardized Euclidian distance used for calculating dissimilarity coefficient. We used data of concentrations in metals (this
study), and Al, Pb, extracted Fe, Mn, and Pb, residual Fe and Mn, total
carbon (carbonate is negligible in the total carbon), and sum of chlorophyll a plus its derivatives (Tsugeki et al., in press). Furthermore, in
order to obtain major patterns of variations in the concentrations and
to examine differences between the major patterns and patterns of
diagenetic redistribution-inducing materials (Fe/Mn hydroxides and
organic matter), we performed principal component analysis (PCA)
using the data employed for CONISS in the upper clusters (upper
zones) of two lake cores (details as shown below). PCA computations
were performed on centered and standardized data using CANOCO for
Windows 4.5 (Ter Braak and Šmilauer, 2002).
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4. Results
4.1. Concentrations of metals
Cluster analysis revealed two dissimilar zones in the concentrations
of metals, total carbon, and chlorophyll a and derivatives, which were
divided by around 1910 (13 cm depth) for Hourai-Numa (Fig. 2) and
around 1940 (8 cm depth) for Hachiman-Numa (Fig. 3). In the lower
zone, the concentrations of Sb, In, Sn, Hg, Bi, and Cd in the core from
Hourai-Numa were constantly low before 1870 (below 17 cm depth in
core), started to slightly increase after around 1890 (15 cm). Higher
concentrations were measured in the upper zone and the highest values
were measured around 1980 (above 6 cm) (Fig. 2). Concentrations in the
lower zone of Hachiman-Numa core were constantly low before 1860
(16 cm depth), then started to slightly increase (Fig. 3). Conspicuous
increase occurred after around 1940 (8 cm), and maintained high levels
after the 1960s (6 cm). Concentrations of acid/reductant-extracted Pb in
both cores (Figs. 2 and 3) were comparable to those of bulk Pb, indicating
that most of the vertical variations of Pb were derived from nonaluminosilicate components.
Unlike the above metals, V, Cr, Mn, and Co in both lakes and Mo in
Hourai-Numa showed slight decreasing trends in the upper zone.
Concentrations of Cu, Zn, and Tl were almost constant with small
fluctuations. Concentrations of Al (data from Tsugeki et al., in press)
and Ti in both lakes were also almost constant (Fig. 2). Because concentrations of Al and Ti of residual fraction in both lake sediments
accounted for more than 70% of their total concentrations (data not
shown), constant vertical/temporal trends of these metals may reflect
trends of lithogenic materials.
Concentrations of Fe obtained by acid/reductant extraction (Tsugeki
et al., in press), which include Fe hydroxides, were enriched in the upper
3 cm of the Hachiman-Numa core (Fig. 3), but not in the Hourai-Numa
core (Fig. 2). The downcore decreasing trend of unsupported 210Pb
(Tsugeki et al., in press) in Hachiman-Numa suggests that this surface
enrichment of extracted Fe is not be due to instant deposition of Fe
hydroxides in the water column.
The results of the multidimensional PCA for the concentration data
of the upper zone of the cores Hachiman-Numa and Hourai-Numa are
illustrated as an ordination diagram (Fig. 4). For the Hachiman-Numa
core, the first two PCA axes (PC1 and PC2) cumulatively explained
75% of the total variation in concentration data, with eigenvalues of
0.47 (PC1) and 0.28 (PC2). PC1 was highly correlated with Sb, Ag, In,
Sn, Bi, and Cu. In contrast, extracted Fe and Mn showed relatively low
loadings on PC1. Total carbon and chlorophyll a and derivatives also
showed relatively low loadings on PC1. For the core Hourai-Numa, the
first two PCA axes cumulatively explained 65% of the total variation in
concentration data, with eigenvalues of 0.39 (PC1) and 0.26 (PC2).
PC1 was highly correlated with Sb, In, Sn, Bi, Hg, and Zn. Compared to
these metals, extracted Mn, total carbon and chlorophyll a plus derivatives showed relatively low loadings on PC1. Extracted Fe showed no
loading on PC1.
4.2. Grain sizes and accumulation rates
The median and mode grain sizes in the Hourai-Numa core were
higher than in the Hachiman-Numa core, where these values were
almost constant throughout the study period (Fig. 5). The values in
Hourai-Numa changed with time, being coarser between about 1960
Fig. 2. Temporal/vertical concentrations of metals, acid/reductant-extracted Fe (Fe-ext), Mn (Mn-ext), and Pb (Pb-ext), residual Fe (Fe-res) and Mn (Mn-res), total carbon (TC), and
chlorophyll a and derivatives (Chl) in sediment cores from Hourai-Numa and result of cluster analysis (dendrogram). Zonation (dashed line) was defined by a constrained incremental sum of squares cluster-analysis (CONISS) constrained by depth. Concentrations of Al, Pb, extracted and residual Fe/Mn, extracted Pb, total carbon, and chlorophyll a and
derivatives, in lake sediments were from Tsugeki et al. (in press).
M. Kuwae et al. / Science of the Total Environment 442 (2013) 189–197
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Fig. 3. Temporal/vertical concentrations of metals, acid/reductant-extracted Fe (Fe-ext), Mn (Mn-ext) and Pb (Pb-ext), residual Fe (Fe-res) and Mn (Mn-res), total carbon (TC), and
chlorophyll a and derivatives (Chl) in sediment cores from Hachiman-Numa and result of cluster analysis (dendrogram). Zonation (dashed line) was defined by a constrained incremental sum of squares cluster-analysis (CONISS) constrained by depth. Concentrations of Al, Pb, extracted and residual Fe/Mn, extracted Pb, total carbon, and chlorophyll a and
derivatives, in lake sediments were from Tsugeki et al. (in press).
and 1980 (6–9 cm depth) and between about 1870 and 1910
(13–17 cm). Accumulation rates in Hourai-Numa were almost constant
before 1940 (below 11 cm) and increased afterward; they also increased slightly in nearly the same intervals as the coarsening of grain
sizes (6–9 cm and 12–17 cm). In contrast, accumulation rates in
Hachiman-Numa were higher between 1810 and 1940 (8–19 cm)
than in other periods, but variations in grain-size values were not consistent with accumulation rates.
Fig. 4. Results of principal component analysis (PCA) for concentrations in metals, acid/reductant-extracted Fe (Fe-ext), Mn (Mn-ext), and Pb (Pb-ext), residual Fe (Fe-res) and
Mn (Mn-res), total carbon (TC), and chlorophyll a plus its derivatives (Chl) in the cores Hourai-Numa and Hachiman-Numa.
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two samples (2001 and 2006 for Hachiman-Numa and 2003 and
2006 for Hourai-Numa) coincided with Sb/Pb ratios of aerosols observed in the Tohoku region (Noshiro and Kashima) and Hokkaido
(Rishiri Island) (0.02–0.04 on an annual basis; Table 1) (Sakata et
al., 2006). The ratios in our study lakes were in agreement with
those of Lake Shinji (0.04 on the basis of Sb and Pb concentrations
in excess of those during 1890–1940; Kusunoki et al., 2012).
5. Discussion
5.1. Effects of diagenesis and dilution by lithogenic materials
Fig. 5. Temporal/vertical changes in median and mode grain size and mass accumulation rates derived from 210Pb-based CRS model (Appleby and Oldfield, 1978).
4.3. Anthropogenic fluxes of Sb, In, Sn, Bi, and Pb
Anthropogenic fluxes of Sb, In, Sn, and Bi (Fig. 6), whose metals
were highly correlated with PC1 for both lakes, increases starting
from around 1890 in Hachiman-Numa (12 cm depth) and around
1900 in Hourai-Numa (13 cm). The fluxes of these metals exhibited
their highest values after 1980. In particular, Sb, In, and Sn in both
lakes peaked around 2000. In the time since approximately 1930,
with small age errors (b 3 years for Hachiman-Numa and b4 years
for Hourai-Numa), anthropogenic fluxes of Sb increased by a factor
of 3.7 to 4.5 and fluxes of In increased by a factor of 1.9 to 4.5.
Fluxes of Pb in both lakes remain high from 1910 to the present
with large fluctuations.
4.4. Anthropogenic Sb/Pb ratios
Anthropogenic concentration ratios of Sb and Pb ([Sb]anthropogenic/
[Pb]anthropogenic) in the two records showed very similar increasing
trends beginning around 1900 and reaching maximum values in the
most recent years (Fig. 6). The mean ratios (0.02–0.03) in the top
The history of concentrations and fluxes for Sb, In, Sn, and Bi over
the last 250 years in the Mount Hachimantai area (Figs. 2, 3, and 6)
suggest an increase in deposition of these pollutants after 1900 with
highest values recorded after 1980. However, similar enrichment patterns in sediments may result from effects of diagenesis associated
with Fe hydroxides and adsorption of organic matter or from dilution
by lithogenic materials.
In the Hachiman-Numa core, we found a sharp peak in concentration for almost all metals at 2 cm depth and enrichment of metals
such as Sb, In, Sn, and Bi above 8 cm depth (Fig. 3). The surface enrichment of these metals could occur from post-depositional redistribution through their release to pore waters by decay of organic
matter (Brooks et al., 1968; Duchart et al., 1973) and Fe and Mn hydroxide dissolution beneath the oxic/anoxic interface (Belzile and
Tessier, 1990). Extracted Mn (Mn oxides) from the Hachiman-Numa
core did not show a surface enrichment, while extracted Fe showed
this at a core depth of 0–3 cm. The surface enrichment of only Fe
does not explain the post-depositional redistribution because redistribution of Fe could not occur prior to that of Mn (Stumm and
Morgan, 1996). In addition, extracted Fe and Mn, total carbon, chlorophyll a and derivatives in the upper zone did not show high loadings
on PC1 which was highly correlated with Sb, In, Sn, and Bi. This result
implies that the enrichment of Sb, In, Sn, and Bi is not induced by their
post-depositional redistributions associated with Fe/Mn hydroxides
and decay of organic matter. Therefore, the surface enrichments of
Sb, In, Sn, and Bi most likely resulted from increased atmospheric
deposition.
In the upper layer (upper zone) of Hourai-Numa core, the vertical
concentration profiles of many metals and extracted Pb differed from
those of extracted Fe and Mn that showed almost constant values
(Fig. 2). It is thus reasonable to infer that vertical variations in most
Fig. 6. Anthropogenic flux records of Sb, In, Sn, Bi, and Pb, lead isotope ratios (Tsugeki et al., in press), Sb/Pb ratios derived from anthropogenic concentrations (see text for details),
and records of Chinese coal production (Dai et al., 2012) and consumption (Tian et al., 2012). Shaded zones within the Pb isotope panels denote ranges of isotopic ratios reported
from surrounding volcanic rocks from Nanashigure (Kimura and Yoshida, 2006; Yamamoto et al., 2008) and Zn and Cu mines in Tohoku (Oppu, Namariyama, Kosaka, Daira, Ani,
Washiaimori, and Taro mines) (Sasaki et al., 1982). Black bars on top of the Pb isotope panels denote ranges of isotopic ratios obtained from aerosols and outer bark (a good integrator of present air pollution) reported in Korea and Beijing, China (Åberg and Satake, 2009; Mukai et al., 1993, 2001). Black bar on top of the Sb/Pb ratio panel denotes ranges of
aerosol ratios reported from three sites in northern Japan (see Table 1).
M. Kuwae et al. / Science of the Total Environment 442 (2013) 189–197
metals presented here are not attributable to diagenetic redistribution by Fe/Mn hydroxides. From the observation of the surface enrichment of total carbon and chlorophyll a and derivatives (Fig. 2), one
might suspect that the enrichment of Sb, In, Sn, and Bi in the upper
zone resulted from diagenetic effect of organic matter decay. However, the surface enrichment of total carbon and chlorophyll a and
derivatives may result from a 3–6-fold increase in algal and herbivore
plankton biomasses in Hourai-Numa in recent decades in relation to
increased nutrient supply from atmospheric dust (Tsugeki et al., in
press). The concomitant surface enrichments of Sb, In, Sn, and Bi
and organic matter might be caused by direct or indirect effects of
the increased deposition of atmospheric dust to the lake and the
watershed during recent decades.
Sediments in Hourai-Numa were characterized by large variations in
grain size whereas Hachiman-Numa sediments were almost constant in
grain size (Fig. 5). The grain sizes in Hourai-Numa increased during the
period 1960–1980 (depth 6–9 cm), when concentrations of Sb, In, Sn,
Bi, and Pb were slightly lower than before and after this period
(Fig. 2). It is well known that grain size is a major factor controlling
sedimentary metal concentrations because coarse-grained particles
dilute these concentrations (Horowitz, 1985; Lin et al., 2002; Windom
et al., 1989). Thus the rise in grain size in Hourai-Numa in this interval
is compatible with dilution of metals by lithogenic materials. In fact,
the accumulation rate increased during this interval (Fig. 5). The decrease in metal concentrations at depths of 13 to 17 cm, coinciding
with coarser grain sizes in the Hourai-Numa core, may also result
from dilution. This may account for the fact that the initial rise in Sb,
In, Sn, Bi, and Pb concentrations in Hourai-Numa (around 1890) lagged
behind the concentration rise in Hachiman-Numa (around 1870).
Alternatively, the lags may reflect age uncertainties of the cores in the
late 19th century (1879 ± 18 for Hourai-Numa, and 1873 ± 15 for
Hachiman-Numa).
Because dilution effects can be suppressed by converting concentration to flux versus time (Norton, 2007), a metal flux record may represent more realistic trends of metal deposition than the concentration
record does. The excellent concordance between the trends in metal
fluxes of the two lakes (Fig. 6) is not easily explained by either diagenetic processes or local geological sources, implying that these lake sediments faithfully preserve the historical trends of pollution.
5.2. Historical trends of anthropogenic Sb and Pb flux and their sources
Anthropogenic fluxes of Sb in our study lakes increased starting
from around 1900. Similar enrichments in anthropogenic Sb from
around 1900 have been reported elsewhere in the world (Cloy et
al., 2005; Cooke and Abbott, 2008; Grahn et al., 2006; Krachler et al.,
2005; Kusunoki et al., 2012; Mikac et al., 2011; Shotyk et al., 2004).
These studies suggested that expansion of emissions from anthropogenic sources, such as mining and refining processes, enriched these
metals in peat bogs, ice caps, and lake sediments in pristine areas.
In the Mount Hachimantai area, since there have been no facility to
directly input any pollutants and no land use changes in the watershed
since its regulation as a national park starting from 1957. Because airborne supply of metals to aquatic systems seems to be important in
systems far from direct pollution sources (Filella et al., 2002), our
metal flux records from two pristine lakes after 1957 likely represent
temporal changes in atmospheric deposition.
Although enrichments of Sb after around 1900 have been widely
reported, anthropogenic Sb deposition in Europe and Peru has decreased in recent decades (Cloy et al., 2005; Cooke and Abbott,
2008; Shotyk et al., 2004). In contrast, our records as well as the ice
core record from the Canadian Arctic (Krachler et al., 2005) show
prominent increases after 1980. This evidence suggests that historical
variation of atmospheric Sb deposition in recent decades reflects
different regional sources.
195
Recently, a pronounced increase of Sb concentration after 1980 in
lake sediments has also been reported from Lake Shinji, in southwestern Japan near the Japan Sea coast (Kusunoki et al., 2012). They
suggested that this increase was attributed to aerosols transported
from the Asian continent. In fact, studies using aerosol Pb isotope ratios
as a tracer of aerosol source regions (Bellis et al., 2005; Mukai et al.,
1994; Nakano et al., 2006) concluded that Pb-containing aerosols
from the Asian continent have contributed substantially to Pb levels
in Japan, especially during the cold season (e.g., Bellis et al., 2005;
Nakano et al., 2006). Back-trajectory analyses during winter (Bellis et
al., 2005; Murano, 2006; Murano et al., 2000) suggest that the much
of air mass transporting aerosols in Japan is originated from Japan Sea
and Asian continent. In our study area, surface sediments (Fig. 6) have
also yielded Pb isotope ratios (208Pb/206Pb and 207Pb/ 206Pb) typical of
aerosols collected in China and Korea (Åberg and Satake, 2009; Mukai
et al., 1993, 2001), and did not show ratios of other domestic potential
sources such as fly ash from incinerators (2.106± 0.003 and 0.864 ±
0.001, respectively, Sakata et al., 2000), road sediments (2.110± 0.001
and 0.861 ± 0.002, Shinya et al., 2006), and aerosols in seven Japanese
cities (2.099 and 0.863, Mukai et al., 1993). The observed Pb isotope
ratios are different from values measured in the surrounding rocks
(Kimura and Yoshida, 2006; Yamamoto et al., 2008) or associated
with mines in Tohoku (Sasaki et al., 1982) and are similar to values
reported for aerosols of Asian continental origin during the last several
decades. In particular, Pb isotope ratios notably increased after 1950
and exhibited values close to or matching those of Asian continent
origin after 1980. This is consistent with the fact that production of
coal in China started increasing after 1950 (Dai et al., 2012) and the consumption dramatically increased after 1980 (Tian et al., 2012) (Fig. 6),
though Japanese mining activities in Tohoku diminished in and after
1970s. It should be noted that the increase of the flux in Sb after 1950
was concordant with the notable increase in Pb stable isotope ratios
(Fig. 6). This implies that the increase in Sb flux in the lakes of Mount
Hachimantai area after 1950 was also attributed to aerosols transported
from the Asian continent.
Major atmospheric Sb emissions in China are thought to be derived from coal combustion (Okuda et al., 2008; Tian et al., 2012).
Recent coal combustion in China (2000–2006) has emitted Pb together with Sb with a Sb/Pb ratio of approximately 0.05 (Table 1) (Tian et
al., 2012, 2011). Comparable Sb/Pb ratios (0.04–0.07, Table 1) have
also been reported in aerosols from China (Arimoto et al., 2004;
Okuda et al., 2008; Zheng et al., 2004). Similar ratios have been observed in aerosols collected from three locations in northern Japan
(0.02–0.04) as well as in our surface sediments (0.02–0.03) in the
early 21st century (Table 1). Considering the Pb isotopic evidence
showing the dominance of Asian continental aerosols in cold-season
air of north Japan and the lake sediments from Mount Hachimantai,
the consistent Sb/Pb ratios between China and north Japan suggest
that recent aerosols in Japan contain substantial Sb from the Asian
continent. Thus the markedly increased Sb fluxes after 1980 in our
records, as well as increased Sb/Pb ratios, may reflect the increased
intensity and extent of coal-derived Sb pollution in the East Asian
atmosphere in recent decades. This inference is supported by records
of sedimentary flux of inorganic ash spheres (the best tracer of
coal-derived particles) from Lake Akagi-konuma, 100 km northwest
of Tokyo, documenting the increase in transport of coal-derived particles from China since the 1970s (Nagafuchi et al., 2009).
It is plausible that because domestic metal pollutants may be important in aerosols during the warm season in Japan (Nakano et al.,
2006), domestic sources may account for the recent increases of sedimentary Sb flux and Sb/Pb ratio presented here. However, candidate
substances (incinerator, road, airborne particulate matter, and residential dusts in megacities of Japan, coal and oil fly ash in Japan,
and automobile brake pad particulates) have very high Sb/Pb ratios
(0.12–610, Table 1) (Furuta et al., 2005; Iijima et al., 2009; Jung et
al., 2004). Today, the annualized Sb/Pb ratios of aerosols in northern
196
M. Kuwae et al. / Science of the Total Environment 442 (2013) 189–197
Table 1
Sb/Pb ratios of aerosols in northern Japan, potential Sb source materials in Japan, emissions from coal combustion in China, aerosols in China, and recent sediments of
Hachiman-Numa, Hourai-Numa, and Lake Shinji in western Japan.
Sample
Aerosols in north Japan
Aerosol in Rishiri Island
(dry deposition)
Aerosol
(dry + wet deposition)
from Noshiro
Aerosol
(dry + wet deposition)
from Kashima
Source materials in Japan
Incinerator fly ash
Incinerator fly ash from
Tokyo
Waste fly ash
Road dust (b200 μm)
Fine roadside dust
(0.5–0.7 μm)
Airborne particulate
matter
(b2 μm) from Tokyo
Airborne particulate
matter
(2–11 μm) from Tokyo
Airborne particulate
matter
(>11 μm) from Tokyo
Fine residential dust
(0.5–0.7 μm)
Coal fly ash in Japan
(NIST SRM 2689)
Oil fly ash
Brake pad
Brake abrasion dust
Emissions and aerosols in
China
Emission from coal
combustions in China
Aerosols in Beijing,
China
Aerosols in Zhenbeitai,
China (38.3°N, 109.7°E)
Aerosols in Shanghai,
China
Sediments in Japan
Hachiman-Numa
Hourai-Numa
Lake Shinji
Sampling year
Sb/Pb
Reference
2001–2003
0.03
Okuda et al. (2006)
2003–2004
0.02
Sakata et al. (2006)
2003–2004
0.04
Sakata et al. (2006)
manufacture are thought to be small compared to those sources (White
and Hemond, 2012). Therefore, emissions of In from Japanese manufacturers might be minor. However, incinerators in Japan are not yet ruled
out as sources of recent elevated In fluxes because their emissions of In
remain unknown (White and Hemond, 2012).
World production and industrial usage of In is predicted to expand
greatly over the next few decades (White and Hemond, 2012).
Enrichment of In in the East Asian atmosphere should be a concern,
and further studies of long-term archive data and aerosol concentrations of In are needed to certify its historical trend and source.
6. Conclusion
0.23
0.26
Jung et al. (2004)
Furuta et al. (2005)
2008
0.15
0.12
0.29
Iijima et al. (2009)
Furuta et al. (2005)
Iijima et al. (2009)
1995–2004
0.13
Furuta et al. (2005)
1995–2004
0.27
Furuta et al. (2005)
1995–2004
0.19
Furuta et al. (2005)
2008
0.21
Iijima et al. (2009)
0.14
Iijima et al. (2009)
0.13
610
Pb:
ND
Iijima et al. (2009)
Furuta et al. (2005)
Iijima et al. (2009)
To examine historical variations in anthropogenic deposition of Sb
and In from East Asia, we analyzed multiple elements in sediment
deposited in two alpine lakes in Japan over the last several centuries.
Vertical variations in concentration of these metals are better explained
by their temporal changes in atmospheric deposition than by diagenetic
redistribution of Fe/Mn hydroxides and organic matter. Anthropogenic
fluxes of Sb and In showed gradual increases after around 1900 in both
lakes. In the time since approximately 1930, when the fluxes started
increasing notably, fluxes of Sb and In increased by factors of 3.7–4.5
and 1.9–4.5, respectively. The markedly increased levels of Sb flux
after 1980, coinciding with rapid increases in coal production and
consumption in China, may result from enhanced long-range transport
of Sb-containing aerosols deriving mainly from coal combustion in the
Asian continent. Similar increasing trends in In, Sn and Bi that are
contained in Chinese coal suggest that the same mechanism controls
their deposition, although further studies on emissions of In, Sn, and
Bi from domestic incinerators are required to assess their main sources.
Our records for the last 250 years indicate that the greatest emissions of
metals, Sb and In, from East Asia have occurred in recent decades.
Acknowledgments
2000–2006
0.05
Tian et al. (2011, 2012)
2001–2006
0.07
Okuda et al. (2008)
Apr. 2001
0.05
Arimoto et al. (2004)
2001–2002 (winter) 0.04
Zheng et al. (2004)
2001–2006
2000–2003
2000
This study
This study
Kusunoki et al. (2012)
0.03
0.02
0.04
We thank Drs. M. Kawata, T. Suzuki, J. Yokoyama, and F. Kato for sampling assistance and Dr. F. Hyodo for his helpful discussions. This study
was funded by a grant-in-aid for scientific research A (no. 19207003)
from the Ministry of Education, Culture, Sports, Science and Technology
(MEXT) to Urabe, by a grant from the Ministry of the Environment
Government of Japan, Environment Research and Technology Development Fund (D-1002) to Urabe, and by the Global Centers of Excellence
programs from MEXT and the Japan Society for the Promotion of Science.
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