Influence of paint chips on lead concentration in the soil of public playgroundin Tokyo
Environmental Process Engineering 36646 Michie TAKAOKA
1. INTRODUCTION
Recently, it has been suggested that declined IQ score was found among children with blood Pblevel lower than 10 µg/dL, the action level of Center for Disease Control and Prevention (CDC) ofthe US (1,2). These results suggest the necessity of lowering Pb exposure level as much as possible.
It is well known that soil is an important medium of Pb exposure for children (3). As sources ofsoil Pb, two products, i.e., lead-based paint (LBP) and leaded gasoline, have been widely
recognized (3). Fortunately, in Japan, phase-out of leaded gasoline was started in early 1975, andmarket share of non-leaded gasoline reached 100% in 1980 (4). Moreover, the LBP has not beenused for interior/exterior decoration of houses in Japan. Therefore, Pb exposure level ofcontemporary Japanese people has long been considered insignificant in the past two decades.
Aung et al.’s estimation revealed that Pb exposure level of Japanese children could reach
Provisional Tolerable Weekly Intake set by FAO/WHO, and soil and dust appreciably contributed
to the intake (5). They found gasoline Pb, that was emitted before 1980s and had been thereafter
settled in the surface soil, as one of the sources of Pb in the soil (6). Besides gasoline Pb, paintchips can be another significant source of Pb in surface soil of public playground. It is often thecase that paint chips peeled off from playing equipments are scattered on the surface soil in thepublic playground in Japan. Lead concentration in these paints was reported to be high (7).
In this study, the effect of paint chips peeled off from the playing equipments to Pb content in
the surface soil was evaluated for a number of public playgrounds in Tokyo.
2. MATERIALS AND METHODS
Soil sampling and preparation
Playgrounds where the present samples were taken were located in a ward in Tokyo. Two types ofsoil sampling were carried out. Sampling method 1. The area of a playground (12 m × 28 m) wasdivided into 68 (2 m × 2 m) grids. Surface soil (top 0.5 cm) at the center of each grid was collected.
Sampling method 2. Each of 31 playgrounds was divided into 10 m × 10 m grids. Five sampling
points were selected in each grid and soil sample was taken. Soil samples were collected from 91grids (455 individual points) in 31 playgrounds.
The soil sample was air-dried and sieved through a 150 µm mesh. Five samples collected bysampling method 2 for each grid were mixed in equal weight to represent the grid.
Paint sampling
The paint chips, which were peeled-off from the playing equipments and had scattered on thesurface soil, were collected. Sixteen samples were collected from 5 playgrounds; swings (4), slides(2), a sandpit (1), a rail (1), a maze (1), flowerbeds (3), and benches (4).
Analysis of Pb concentration
Approximately 300 mg of soil sample was digested with HNO3/HClO4/HF in a Teflon beaker on ahotplate. Around 10 mg of paint chips was digested with HNO3 using a double vessel digestion
bomb for 4 h (8). Lead concentrations and isotope ratios of Pb (207Pb/206Pb and 208Pb/206Pb) in thesamples were determined by ICP-MS.
For analytical quality assurance, NIST SRM 2709 and 2711 were analyzed NIST SRM 981
was used for the calibration of isotope ratios.

Calculation of the degree of peeling-off of paint from surface of playing equipments
Cross-section paper (2 cm × 2 cm per grid) was applied to an appropriate surface of playing
equipments and the peeling-off index (POI) was calculated as follows:

POI = {(number of grids all of paint is peeled-off) × 1 + (number of grids
a part of paint is peeled-off) × 0.5} / total number of grids
When more than 2 playing equipments were present in a playground, POIs for all of theequipments were averaged to represent the playground.
3. RESULTS
Lead concentration in paint chips scattered on surface soil
A maximum of 8.5% of Pb was
Table 1. Lead concentration in paint chips
contained in the paint chips (Table 1).
Park No. source
Pb(%)
Park No.
sourcePb(%)
Lead concentration in the paint chips
collected from surface soil underneath
No.1
bench 1.66±0.03
No.3
swing
5.69±0.06
No.1
bench
2.58±0.05
No.4
swing
3.12±0.01
wooden benches in the playgroundNo.1
Slide 4.58±0.09
No.4
sandpit0.45±0.01
No.2 was low as compared with those
No.1
swing 4.61±0.08
No.4
flowerbed 8.49±0.10
underneath playing equipments madeNo.2
bench 0.003±0.000
No.4
flowerbed 6.85±0.08
No.2
bench
0.003±0.001
No.4
flowerbed 5.51±0.08
of metals. This result is consistent withNo.2
Slide 0.77±0.01
No.5
swing
0.26±0.01
my notion that anticorrosive paint is
No.2
maze 3.00±0.03
No.5
rail
2.90±0.03
the major contributor to elevated Pb
Average ± SD, n=3
concentration in paint chips scattered on the surface soil.

Pb concentration in soils [mg/kgThe Pb concentration distribution in playgroundFigure 1 shows profile of surface soil Pb distribution within playground A. Lead concentration in
the 2 m × 2 m grid ranged from 15.9 mg/kg to 104 mg/kg (mean: 52.3 ± 19.4 mg/kg). As clearlyshown in this figure, Pb concentration was higher in the soil of the grid with painted playing
equipment (Fig. 1).
The mean Pb concentration each of the 31 playgrounds was 55.5 mg/kg (15.2-237 mg/kg)
indicating that soil in some of the playgrounds is contaminated with Pb because natural soil Pblevel in Japan was reported to be 20 mg/kg (9).

Slide

Swing

(painted)(painted)

Sandpit(noｔ painted)

Flowerbed(not pained)

Tile(Surface not soil)(not painted)

Bench

Bench

Bench

(panted)(panted)(painted)

350
300
250
200
150
100
50
0123

<20mg/kg 21-30 31-40

4567841-50 51-60 61-70 71-80 >80mg/kg

Fig. 1 Lead distribution profile of surface soil
within playground AWithoutWith playing
equipments

Fig. 2 Comparison of Pb concentration ingrids with/without playing equipments for
20 playgrounds in TokyoIn 17 playgrounds out of 20, where grids (10 m × 10 m) with and without painted playingequipments were present, Pb concentration was higher in the grid with painted playing equipment
than that without it (Z = -3.136, p = 0.002, Wilcoxon’s matched pair signed rank test) (Fig. 2).

150
100
50
0
0.0

0.1
0.2
0.3
0.4
Peeling-off index [POI]
Fig. 3 Correlation between Pbconcentration and POI

2.14
2.13Pb2.12206

Lead isotope composition of the playground soils
Figure 4 shows Pb isotope ratios of surface soils of theplaygrounds. Lead isotopic composition of theplayground soil distributed with rather wide range.
Although the predominant sources of Pb in surface
soil can be assumed to be native soil and atmosphericfallout, Pb isotopic compositions of some soil samples
were distinct from these sources indicating
contribution from gasoline Pb of the past. Figure 5shows the correlation between Pb concentration andisotopic ratio. This positive correlation was
statistically significant (Spearmanrank-correlation coefficient, 207Pb/206Pb and Pb
conc. r = 0.536, p = 0.002; 208Pb/206Pb and Pb
conc., r = 0.600, p < 0.001).

Pb concentration [mg/kgCorrelation with the Pb concentration in soil and the degree of peeled-off of paintFigure 3 shows the correlation between POI and soil
250
Pb concentration for 31 playgrounds. This positive
correlation was statistically significant (Spearman200
rank-correlation coefficient, r = 0.368, p = 0.041).

2.11

208

Pb/4. DISCUSSION
2.10
The results shown in Fig. 1 and Fig. 2 indicatedthat paint chips peeled off from the playing
2.09
equipments contributed to the elevated Pb
2.08
concentrations observed in playground soils inTokyo. It is possible that the paint chips are
2.07
reduced to smaller fragments and particles by
0.82 0.84 0.86 0.88 0.90
weathering and the fragments/particles will
207
206
Pb/ Pbeventually be mixed into the soil particles.
Fig. 4 Plot of Pb isotope ratios in
However, the correlation between the Pb
playground soil and other environmental
concentrations in playground soil (the average of allsamples
grids in playground) and POI of the playing※●This study, □Airborne particulatematter (11), ▲Ore (12),◆Bed rock andequipments in the playground was only marginallysoil(13), ＊Leaded gasoline (11)significant (Fig. 3). I can assume that there aretechnical inadequacies in this data analysis that could have led to marginal significance (e.g.,repainting). Besides these technical problems, large playground-to-playground variation in soil Pb
concentration can also be the reason of the marginal significance of POI-Pb concentrationrelationship. In fact, Pb concentrations of the surface soils of the grids in playgrounds without any
painted equipments (n = 37 grids from 31 playgrounds) ranged from 11.8 to 229 mg/kg. Thus thelarger variation of Pb concentration in surface soil might have masked relatively smaller variation
caused by paint chips when multiple playgrounds are involved in the comparison.

208

206

Pb/ PbLead isotopic composition of our playground2.14
soil samples distributed with rather wide range (Fig.
2.134). According to the list of Pb isotope ratios in a
number of environmental media in Japan (10), no2.12
other sources than gasoline Pb distribute to
2.11
significantly less radiogenic direction beyond theatmospheric particles. Thus it can be reasonable to
2.10
assume that playground soil with isotope ratios
2.09
close to gasoline Pb does contain gasoline Pb. In
addition, there was a significantly positive
2.08
correlation between the isotopic ratios and Pb
0100
200
300
concentration showing that playground withPb concentration in soil [mg/kg]
gasoline signature had higher Pb concentration.
Thus my isotopic result was consistent with Aung etFig. 5 Correlation with Pbal.’s in that gasoline Pb emitted in the past was theconcentration and 208Pb/206Pb
major source of excess Pb in the surface soil ofplaygrounds in Tokyo (6).
The correlation coefficients between Pb concentration and isotopic ratios indicate thatapproximately 30-40% of playground-to-playground variation in Pb concentration can beexplained by isotope ratio, i.e., by the contribution from gasoline Pb. On the other hands, paintchips can explain additional 10% of the variation. The playground with greater contribution fromgasoline, consequently with higher Pb concentration, was constructed prior to 1970s, when leaded
gasoline was still in use in Japan, hence the year of construction of playground was certainly one of
the factors of the variation.
5. CONCLUSION
My analysis indicated that there were at least two factors that contributed to variation in the Pb
concentration in surface soil of public playground in Tokyo: gasoline Pb and paint chips fromplaying equipment. The correlation coefficients indicated that gasoline Pb exhausted fromautomobile before 1980s influenced more to Pb concentration in public playground soil than did
paint chips peeled off from playing equipments, the contribution of which was relatively small but
still statistically significant. In order to decrease Pb concentration in the surface soil of publicplayground in Japan, consequently to reduce Pb intake of children, it is necessary to replacesurface soil to remove excess Pb due to the past gasoline Pb as well as to use lead-free
anticorrosive pigment to playing equipments to reduce Pb from paint chips.
LITERATURE CITED(1)(2)

Lanphear, B. P. ; Dietrich, K. ; Auinger, P. ; Cox, C. Public Health Reports 2000, 115, 21-529.
Canfield, R. L. ; Henderson, C. R. ; Cory-Slechta, S. A. ; Cox, C. ; Jusko, T. A. ; Lanphear, B. P. N. Engl. J. Med. 2003, 348,1517-1526.
(3) Mieke, H.W. ; Reagan, P. L. Environ. Health Perspect. 1998, 106 (Suppl.1), 217-229.
(4) Yoshinaga, J. Organolead compounds in the environment. In “Organometallic compounds in the environment” Edited byCraig P., Wiley, Chichester 2003, pp. 151-194.
(5) Aung, N. N. ; Yoshinaga, J. ; Takahashi, J. Environ, Health Prevent. Mad. 2004, 9, 257-261.
(6) Aung. N. N. ; Yoshinaga, J ; Tanaka, A. J. Environ. Chem. 2004, 14, 545-553.
(7) Irie, K. ; Maeda, N. ; Yoshida, K. ; Kaniwa, M. Nihon Kashei Gakkai-shi 1997, 48, 1103-1109. [in Japanese](8) Okamoto, K. ; Fuwa, K. Anal. Chem. 1984, 56, 1758-1760.
(9) Asami, T. Heavy metal pollution in soils of Japan. Asami T. ed: Japan Scientific Society Press, Tokyo [in Japanese](10) Aung, N.N. ; Uryu, T. ; Yoshinaga, J. Anal. Sci. 2004, 20, 195-198.
(11) Mukai, H. ; Furuta, N. ; Fujii, T. ; Ambe, Y. ; Sakamoto, K. ; Hashimoto, Y. Environ. Sci. Technol. 1993, 27, 1347-1356.
(12) Sato, K. Econ. Geol. 1975, 70, 800-805.
(13) Murozumi, M. ; Nakamura, S. ; Yochida, K. Nihon Kagakukai-shi 1982, 9, 1479-1484. [in Japanese]