International Archives of Occupational and Environmental Health

, Volume 86, Issue 8, pp 865–873

High cadmium and low lead exposure of children in Japan

Authors

  • Takao Watanabe
    • Department of EducationTohoku Bunkyo University
  • Haruo Nakatsuka
    • Department of NursingMiyagi University
  • Shinichiro Shimbo
    • Department of Food and NutritionKyoto Women’s University
  • Kozue Yaginuma-Sakurai
    • Environmental Health SciencesTohoku University Graduate School of Medicine
    • Kyoto Industrial Health Association (Main Office)
Original Article

DOI: 10.1007/s00420-012-0821-1

Cite this article as:
Watanabe, T., Nakatsuka, H., Shimbo, S. et al. Int Arch Occup Environ Health (2013) 86: 865. doi:10.1007/s00420-012-0821-1

Abstract

Background

Cadmium (Cd) is a wide-spread environmental pollutant with insidious toxicity to kidneys, and children are considered to be a high-risk group. Lead (Pb) is suspected to induce retardation in mental development in children. Daily foods are an important source of both Cd and Pb exposure for general population. Nevertheless, data on dietary exposure of children to Cd and Pb are still scarce in Japan.

Objectives

This study was initiated to clarify the extent of exposure of children to Cd. Exposure to Pb, another environmental pollutant element, was also studied in combination.

Methods

Twenty-four-hour food duplicates and the first morning urine samples were collected from 296 children (159 boys and 137 girls at the ages of 3–6 years) in 15 kindergartens in Miyagi prefecture on the Pacific coast in north-east Japan; no environmental pollution with Cd has been known in the prefecture. Cd, Pb and iron in food duplicates and Cd in urine were analyzed by inductively coupled plasma-mass spectrometry. α1-Microglobulin (α1-MG) in urine was measured by the latex method. Log-normal distributions were confirmed for these analytes.

Results

The geometric mean (GM) values for dietary intake of Cd and Pb were 11.8 and 2.28 μg/day, or 4.20 and 0.84 μg/kg body weight/week, respectively, for total children studied. No significant difference was detected in dietary Cd and Pb intake between boys and girls of the same age (except for Pb on a μg/day basis at 6 years) as well as of all ages in combination. Trends of increase in Cd and Pb intake were observed parallel to age when calculated on a daily intake basis, but the trends disappeared after correction for body weight. No age-dependent increase was observed in α1-MG, despite there was an age-dependent increase in Cd.

Conclusions

The dietary intake of Cd and Pb for children studied were 4.20 and 0.84 μg/kg body weight/week, respectively. International comparison of the present results with values reported in literature suggested that exposure of children in Japan was higher with regard to Cd, and lower regarding Pb, reproducing the observation in adult Japanese populations. For better health of children, efforts may be necessary to reduce high dietary exposure to Cd.

Keywords

CadmiumChildrenFood duplicatesJapanKindergartenLeadUrine

Introduction

Cadmium is a wide-spread environmental pollutant with insidious toxicity on kidney and bone typically after long-term exposures even at low levels (International Programme on Chemical Safety 1992). It is been considered that children are among populations with a high risk to Cd toxicities. Namely, children need more foods than adults on a body weight basis, because additional nutrients are necessary for growth (Ministry of Health, Labour and Welfare, Japan 2010). More food intake inevitably increases intake of Cd in foods. Cd absorption may be elevated when iron (Fe) storage in the body is in short (Åkesson et al. 2002; Gallagher et al. 2011; Kippler et al. 2007; Turgut et al. 2007) whereas dietary Fe supply is only barely sufficient among general Japanese population (Ministry of Health, Labour and Welfare, Japan 2011) and insufficiency of Fe supply to children is a matter of additional concern in relation to Cd exposure.

With regard to Pb, concern has been expressed since last century (e.g., Needleman and Gatsonis 1990) that elevated level of Pb in blood may cause retardation of mental development (e.g., US Agency for Toxic Substances and Disease Registry 2007). As for sources of exposure to Cd and Pb sources in Japan, daily foods are almost exclusive for Cd, and about a half of daily exposure to Pb comes from foods (Ikeda et al. 2000a).

Nevertheless, data on the dietary exposure of children to Cd and Cd levels in urine are still scarce for Japanese populations as compared with adult people for whom substantial data are currently available (e.g., Ikeda et al. 1999, 2000b; Watanabe et al. 1996, 2000). The gap in information is also the case for dietary exposure to Pb.

The present study was initiated to fill this information gap by studying dietary Cd and Pb exposure of children in kindergartens in Miyagi prefecture. It should be added that the intensity of Cd exposure in this prefecture was just on average with regard to adult women population exposure to Cd (Ezaki et al. 2003; Koizumi et al. 2010; Watanabe et al. 2000).

Materials and methods

Ethical issues

The study protocol was approved by the Ethics Committee of Miyagi University, Japan. Informed consents were obtained from the guardians of the children (i.e., parents) in writing.

Survey design

The survey was conducted in winter seasons (December to March) in 2001–2004 in Miyagi prefecture on the Pacific coast in north-east Japan; there is no known environmental pollution with Cd in the prefecture. In total, 296 children (159 boys and 137 girls) in 15 kindergartens participated in the study by offering food duplicate samples (for details, see below). In addition, 255 children among the 296 offered also the first morning urine samples. The kindergartens were located in an urban area (two kindergartens), rice-producing (6), orchard-farming (2), rice- and vegetable-producing (1) and fishing villages (4). Participation of kindergartens was on a voluntary basis, whereas all children in the volunteering kindergartens participated in the survey.

Mothers were requested to prepare a food duplicate sample (Watanabe et al. 1985, 1996) by cooking for a hypothetic child in their families. The same food items at the same amounts her child consumed on the entire study day (i.e., three meals and any snacks including energy-free tea, water and other drinks) were saved in plastic containers which were made metal leakage free by dipping in dilute nitric acid baths followed by rinsing with de-ionized water to remove acidity (Watanabe et al. 1987). After manual separation for each food item by use of bamboo chopsticks and weighing of separated food items (weight being recorded), a total homogenate was prepared, of which a part was subjected to element analysis after wet digestion (Watanabe et al. 1987). Energy intake was estimated from the food weight by use of the latest version of food composition tables (Ministry of Education, Culture, Sports, Science and Technology, Japan, 2010).

Analyses for Cd, Pb and Fe in food homogenates, Cd in urine samples and Fe in food homogenates were conducted by inductively coupled plasma-mass spectrometry under the conditions previously detailed (Sakurai et al. 2008 for Fe; Shimbo et al. 2001 for Cd and Pb). Limits of determination were 0.1, 1 and 2 μg/kg food for Cd, Pb and Fe, respectively, as previously observed. α1-Microglobulin (α1-MG) was measured by the latex method with the LX reagent kit, ‘EIKEN’ α1-M-III G, from Eiken Chemical Co., Tokyo, Japan.

Creatinine in urine and urine specific gravity were measured by colorimetry (Jaffé) and refractometry, respectively. Urinary analyte levels were expressed as observed, or after correction for creatinine concentration (Jackson 1966) or for a urine specific gravity of 1.016 (Rainsford and Lloyd Davies 1965), as, for example, Cdob, Cdcr and Cdsg, respectively.

Distribution patterns and statistical analysis

Age, height, weight and intakes of energy and Fe were distributed normally. A log-normal distribution was confirmed for Cd in food and urine, and Pb in food. Accordingly, the distributions of former five items were presented as arithmetic means and arithmetic standard deviations (i.e., AM ± ASD), whereas the latter three items were presented as geometric means and geometric standard deviations [GM (GSD)]. In calculating GM and GSD, the value below the corresponding limit of determination (LOD) was assumed to be half the LOD. Unpaired t test, analysis of variance (ANOVA) followed by post hoc test (Scheffe) and χ2 test were used to detect possible significance in difference between or among groups.

Results

Populations surveyed

The subjects studied were 296 children (159 boys and 137 girls) in 15 kindergartens (Table 1). The ages were in a range of 3–6 years, with a majority at 5 years (45 %) followed by those at 6 years (29 %), and then at 4 years (21 %). The number of three-year-old children was small, that is, <5 %. There was no significant difference in age distribution between boys and girls (p > 0.05 by χ2 test).
Table 1

Height, weight and daily energy intake of boys and girls by age

 

Age (years)

No.

Height (cm)

Weight (kg)

Energy (kcal/day)

RDAc for energy

%RDA

AMa

ASDb

AMa

ASDb

AMa

ASDb

Boys + girls

 

296

        

Boys

3

9

101.9

4.0

16.6

1.0

1,382

351

1,300d

106.3

4

32

104.8

6.0

18.1

2.9

1,368

308

1,300d

105.3

5

71

110.8

4.2

20.0

3.7

1,427

307

1,300d

109.7

6

47

117.3

4.8

23.2

3.8

1,529

313

1,500e

101.9

Total

159

        

Girls

3

4

97.3

3.3

14.2

1.0

1,140

253

1,250d

91.2

4

31

105.0

5.4

17.9

2.9

1,361

220

1,250d

108.9

5

62

109.9

5.9

19.8

3.8

1,243

211

1,250d

99.5

6

40

113.2

4.3

20.7

3.1

1,332

211

1,450e

91.8

Total

137

        

No difference (p > 0.05 by unpaired t test) in energy intake was observed between boys and girls at the same age

aAM, arithmetic mean

bASD, arithmetic standard deviation

cRecommended dietary allowance for energy by Ministry of Health, Labour and Welfare, Japan 2010

dFor 3- to 5-year-olds

eFor 6- to 7-year-olds

Body stature and energy intake

AM height and AM weight of children are shown by age in Table 1. As expected, the body size was larger for elder children in reflection of the growth, and the size was somewhat greater for boys than for girls. Of particular interest was the energy intake estimated from food duplicate samples. The AM values were in a range of 1,382–1,529 kcal/day for boys and 1,140–1,332 kcal/day for girls with no significant difference (p > 0.05) between boys and girls of the same age. When energy intake by age was compared with corresponding recommended daily allowance (established by Ministry of Health, Safety and Welfare, Japan 2010), the observed values met with the recommendations by 92–109 %. It should be noted that the recommendations were for three- to five-year-olds and six- to seven-year-olds, and lower percentages (typically six-year-old boys and girls) were attributable at least in part to the gap between the age range of the recommendation (i.e., 6–7 years of age) and actual age of children (6 years). In overall evaluation, energy intake was sufficient, which meant that food duplicate collections were adequately conducted on average.

Dietary intake of cadmium (Cd), lead (Pb) and iron (Fe)

Instrumental analyses of food duplicate samples showed that the amounts of dietary intake of Cd and Pb were 11.8 and 2.28 μg/day, respectively, as GM for total children (Table 2). For both elements, there was a trend that boys took more than girls, but the difference was statistically insignificant (p > 0.05) except for Pb at 6 years (i.e., more for boys than for girls). It appeared that there was a trend of age-dependent increase in GM both in boys and girls for Cd as well as for Pb. In Cd, however, ANOVA detected no significant differences (p > 0.05) possibly due to small number of cases available (typically for three-year-olds in both boys and girls) and wide variations (GSD > 1.64) (Table 2). ANOVA with regard to Pb showed significant difference (p < 0.01 for boys and < 0.05 for girls) among four age groups. In boys in particular, Pb for three- and four-year-old groups (1.45 and 1.86 μg/day as GM, respectively) were significantly smaller (p < 0.05 and < 0.01) than the value for six-year-old group (3.38 μg/day).
Table 2

Dietary intake of cadmium (Cd), lead (Pb) and iron (Fe)

 

Age (years)

Dietary intake

No. of cases

Cd

Pb

Fe

EARe

%EAR

GMa (μg/day)

GSDb

GMa (μg/day)

GSDb

AMc (mg/day)

ASDd

Boys + girls

 

296

11.82

1.80

2.28

2.21

3.55

1.54

  

Boys

Total

159

12.04

1.81

2.41

2.18

3.64

1.63

  

3

9

8.66

2.15

1.45f

2.08

3.51

1.30

4.0g

87.8

4

32

12.29

2.05

1.86f

2.11

3.29

1.76

4.0g

82.2

5

71

11.27

1.74

2.30

2.15

3.72

1.80

4.0h

92.9

6

47

13.97

1.66

3.38

2.03

3.78

1.29

4.5h

84.0

p by ANOVA

 

>0.05

 

<0.01

 

>0.05

   

Girls

Total

137

11.58

1.79

2.14

2.25

3.46

1.43

  

3

4

9.31

1.64

0.95

2.11

1.73

1.47

4.0g

43.3

4

31

11.26

1.76

1.60

2.52

3.74

1.36

4.0g

93.5

5

62

11.50

1.80

2.28

2.34

3.37

1.21

4.0h

84.1

6

40

12.22

1.82

2.62

1.71

3.56

1.68

4.5h

79.1

p by ANOVA

 

>0.05

 

<0.05

 

>0.05

   

No significant difference (p > 0.05) was observed in Cd and Pb (after logarithmic conversion) between boys and girls of the same age (except for Pb at 6 years; p < 0.05) as well as all ages in combination

aGM, geometric mean

bGSD, geometric standard deviation

cAM, arithmetic mean

dASD, arithmetic standard deviation

eEstimated average requirement for iron by Ministry of Health, Labour and Welfare, Japan (2010)

fDifference from 6-year-old group was significant (p < 0.05) by post hoc test (Scheffe)

gFor 3- to 5-year-olds

hFor 6- to 7-year-olds

No age-dependent difference was detected in daily intake of Fe. When the observed amount of dietary Fe intake was compared with the estimated average requirement (EAR) for Fe (Ministry of Health, Labour and Welfare, Japan 2010), the sufficiency by percentage was 43.3 (3-year-old girls) to 93.5 % (four-year-old girls). Very low percentages for three-year-old girls might be due to small number of cases studied (i.e., four cases) and should be taken less reliable. Over all, dietary Fe intake was considered sufficient although barely, and no Fe-deficiency anemia (to induce elevation in Cd absorption) should be expected.

Body weight (BW)-corrected intake of Cd, Pb and Fe

To examine whether apparent age-dependent increase in Cd intake (Table 2) was associated with growth of children, dietary intake of both Cd and Pb was recalculated as the intakes by kg BW (BW for body weight in short) (Table 3). It turned out that there was essentially no age-dependent increase in Cd or Pb intake (p > 0.05 by ANOVA), suggesting that the apparent increase should be attributable to BW-related increase in food intake.
Table 3

Daily dietary element intake by body weight

 

Age (years)

Daily dietary intake by body weight

No. of cases

Cd

Pb

Fe

GM

GSD

GM

GSD

AM

ASD

(μg/kg/day)

(μg/kg/day)

(mg/kg/day)

Boys + girls

 

296

0.60

1.81

0.12

2.18

0.19

0.08

Boys

Total

159

0.60

1.83

0.12

2.14

0.19

0.08

3

9

0.52

2.14

0.09

2.05

0.21

0.08

4

32

0.69

2.08

0.10

2.15

0.19

0.08

5

71

0.57

1.79

0.12

2.22

0.19

0.08

6

47

0.61

1.68

0.15

1.97

0.17

0.06

Girls

Total

137

0.60

1.79

0.11

2.22

0.19

0.08

3

4

0.66

1.67

0.07

2.02

0.16

0.06

4

31

0.64

1.70

0.09

2.51

0.21

0.08

5

62

0.59

1.82

0.12

2.35

0.18

0.07

6

40

0.60

1.84

0.13

1.72

0.18

0.09

No significant (p > 0.05) difference was detected by ANOVA

Age-related increase in urinary Cd levels

When Cd levels in urine were compared among boys and girls of increasing ages (Table 4), trends of age-dependent increase were detectable both in boys and girls. For example, GM Cdob was 0.75 μg/l for three-year-old boys and the GM values gradually increased to reach 2.51 μg/l for the boys at the age of 6 years. The values for six-year-old group were significantly (p < 0.01 or 0.05) greater than the values for younger groups (Table 4). A similar trend of increase was observed even after correction for urine density both in boys and girls. Levels of α1-MG in urine were, however, relatively unchanged when compared across age groups (p > 0.05 by ANOVA; Table 4).
Table 4

Cadmium (Cd) and α1-microglobulin (α1-MG) levels in urine

 

Age (years)

Cd in urine

α1-MG in urine

No.

Cdoba

Cdcra

Cdsga

No.

α1-MGoba

α1-MGcra

α1-MGsga

GM (μg/l)

GSD

GM

GSD

GM (μg/l)

GSD

GM (mgl)

GSD

GM

GSD

GM (mgl)

GSD

(μg/g cr)

(mg/g cr)

Boys + girls

 

255

1.74

2.36

2.45

2.19

1.23

2.28

254

0.60

1.74

0.84

1.82

0.42

1.80

Boys

Total

136

1.77

2.33

2.46

2.24

1.20

2.31

135

0.59

1.76

0.82

1.82

0.40

1.77

3

8

0.75

1.74

1.23

1.90

0.54

1.94

8

0.51

1.41

0.83

1.42

0.36

1.58

4

29

1.47

2.10

2.12

2.04

0.99

2.07

29

0.63

1.98

0.90

1.99

0.42

1.92

5

60

1.73

2.33

2.47

2.19

1.18

2.24

59

0.58

1.76

0.82

1.81

0.39

1.76

6

39

2.51b

2.26

3.16c

2.33

1.67b

2.35

39

0.61

1.67

0.77

1.80

0.40

1.73

p by ANOVA

 

<0.01

 

<0.05

 

<0.01

  

>0.05

 

>0.05

 

>0.05

 

Girls

Total

119

1.70

2.39

2.44

2.14

1.26

2.24

119

0.60

1.72

0.86

1.82

0.44

1.83

3

3

0.98

1.28

1.50

1.66

0.73

1.91

3

0.62

1.76

0.96

2.56

0.47

2.38

4

28

0.96

1.83

1.59

1.64

0.77

1.61

28

0.60

1.84

1.00

2.06

0.49

1.96

5

53

2.14d

2.29

2.90d

2.07

1.52d

2.19

53

0.63

1.75

0.86

1.68

0.45

1.76

6

35

2.02d

2.57

2.75e

2.39

1.46e

2.47

35

0.56

1.57

0.76

1.78

0.41

1.82

p by ANOVA

 

<0.01

 

<0.01

 

<0.01

  

>0.05

 

>0.05

 

>0.05

 

aob, cr and sg indicate that the values are as observed (i.e., without correction), after correction for creatinine concentration or after correction for a specific gravity of 1.016

bp < 0.01 for the difference from 3-year-old group

cp < 0.05 for the difference from 3-year-old group

dp < 0.01 for the difference from 4-year-old group

ep < 0.05 for the difference from 4-year-old group

Discussion

The present study made it clear that the children surveyed had dietary Cd exposure of 0.6 μg/kg BW/day (Table 3) or 4.2 μg/kg BW/week (Table 5). The latter value is 72–75 % of the provisional monthly intake of 25 μg/kg BW (roughly equal to 0.81–0.83 μg/kg BW/day or 5.6–5.8 μg/kg BW/week) established by the Joint FAO/WHO Expert Committee on Food Additives (Joint FAO/WHO Expert Committee on Food Additives 2011). With regard to dietary Cd intake by adult women, Ikeda et al. (2000b) observed 32 μg/day and Watanabe et al. (2000) found 25.5 μg/day. Assuming that the average BW for adult women is about 53 kg (Ministry of Health, Labour and Welfare, Japan 2011), the former and the latter values are equivalent to 0.60 and 0.48 μg/kg BW/day. Overall, the present observation in children appears to be equal to or somewhat more than the value for adult women.
Table 5

Dietary intake and concentrations in urine and blood; Cd and Pb levels in children reported for various areas in the world

 

Authors

Years

Age of children (year)

B/Ga

Area of study

Elements in foodb

Elements in urinec

Elements in bloodd

Cd

Pb

Cd

Pb

Cd

Pb

Asia

The present studyh

 

3–6

C

Japan

4.20

0.84

1.74 (ob)

   

   Ibid.h

 

3–6

B

Japan

4.20

0.91

1.77 (ob)

   

   Ibid.h

 

3–6

G

Japan

4.20

0.77

1.70 (ob)

   

Moon et al.i

2003

4–10

C

Korea

3.20

2.36

1.33 (ob)

5.44 (ob)

1.51

38.0

   Ibid.i,j

2003

Adults (AM = 35.1)

W

Korea

2.10

2.32

    

Aung et al.k

2006

5

C

Japan

4.66e

2.02f

    

Wang et al.

2009

AM = 4.1

B

China

 

15.3

    

   Ibid.

2009

AM = 4.4

G

China

 

12.7

    

Liu et al.l

2010

2–7

C

China

0.65e

12.09e

    

   Ibid.l

2010

Adults

C

China

1.01

7.68

    

Shah et al.

2011

1–5

B

China

  

1.1 (ob)e

41.5 (ob)e

3.2

130.3

   Ibid.

2011

 

G

China

  

0.7 (ob)e

40.5 (ob)e

2.6

121.4

Europe

Schery et al.m

2000

AM 3.9

C

Germany

2.67

2.01

    

Beneš et al.

2000

AM 9.9

B

Czech Rep.

    

0.25

36

   Ibid.

2000

AM 9.9

G

Czech Rep.

    

0.23

31

Wilhelm et al.

2002

AM = 1.8

C

Germany

1.7

     

   Ibid.

2002

AM = 3.8

C

Germany

3.9

     

   Ibid.

2002

Adults (AM = 40.9)

C

Germany

2.9

     

Wilhelm et al.

2005

4–6

C

Germany

2.1

4.8

    

Leblanc et al.

2005

3–14

C

France

0.40g

2.9g

    

Friedman et al.

2006

3

C

Ukraine

  

0.21 (ob)

   

Schulz et al.

2007

6–14

C

Germany

  

0.071 (ob)

   

USA

Thomas et al.n

1999

0–7

C

USA

2.73e,g

1.82e,g

    

Gulson et al.o

2001

6–11

C

USA

 

1.61

    

Arora et al.

2008

6–7

C

USA

  

0.086 (cr)

   

Values in the table are geometric means (GM)

aB and G are for boys and girls, respectively. M and W are for adult men and adult women. C is for the combination of either boys and girls or men and women

bIn the unit of μg/kg body weight/week

cIn the unit of μg/l (ob) g cr (cr); ob and cr for observed and creatinine-corrected values

dIn the unit of μg/l

eGM values were estimated by use of the moment method (Sugita and Tsuchiya 1995) from original AM and ASD for uniformity in presentation

fA single value estimation

gMedians

hValues in Table 3 are on a daily basis and multiplied by 7 for a weekly basis

iFood values were originally on a daily basis and multiplied by 7 for a weekly basis

jMothers of children studied

kOriginal reported values were per day basis and divided by 18.5 (kg; estimated body weight for 5-year-old children), and then multiplied by 7 for a kg body weight and weekly basis)

lOriginal reported values were per kg BW and per day basis and multiplied by 7 for a weekly basis

mOriginal reported values of 6.1 and 4.6 μg/day were divided by the reported AM body weight of 16 kg and then multiplied by 7 for a weekly basis

nOriginal reported values (medians) were per kg body weight per day basis, and multiplied by 7 for a kg body weight and weekly basis

oOriginal reported values for a day was divided by 28 kg as an estimated body weight of 8-year-old boys and girls in combination, and then multiplied by 7 for a weekly basis

Literature survey revealed that several reports are available on dietary intake of Cd and Pb by children in Asia (Aung et al. 2006; Liu et al. 2010; Moon et al. 2003; Wang et al. 2009), in Europe (Friedman et al. 2006; Leblanc et al. 2005; Schrey et al. 2000; Schulz et al. 2007; Wilhelm et al. 2002, 2005), as well as in the USA (Arora et al. 2008; Gulson et al. 2001; Thomas et al. 1999). Values for adult populations (Liu et al. 2010; Moon et al. 2003; Wilhelm et al. 2002) in the same sites where children were studied were also cited for comparison purpose. In addition, reports were available on Cd or Pb levels in urine (Arora et al. 2008; Friedman et al. 2006; Moon et al. 2003; Schulz et al. 2007; Shah et al. 2011) or in blood (Beneš et al. 2000; Moon et al. 2003; Shah et al. 2011). It should be noted that dietary Cd is almost an exclusive source of Cd burden with very limited contribution of exposure via respiration, and therefore Cd in foods is a full estimate for daily Cd exposure (Ikeda et al. 2000b), whereas contribution of exposure via respiration can be substantial depending on the extent of air pollution with Pb (Ikeda et al. 2000a).

The values for dietary intake of Cd for children in Japan is about 4–5 μg/kg body weight/week (μg/kg BW/week, in short), and values for Korea (2.10–3.20 μg/kg BW/week: Moon et al. 2003) are close to the values for Japan. In contrast, much lower values (0.7–1.0 μg/kg BW/week: Liu et al. 2010) were reported for China. The values for Europe and the USA (0.4–3.9 μg/kg BW/week: Arora et al. 2008; Friedman et al. 2006; Gulson et al. 2001; Leblanc et al. 2005; Schrey et al. 2000; Schulz et al. 2007; Thomas et al. 1999; Wilhelm et al. 2002, 2005) were distributed in a wide range, but appear to be somewhat lower than the value for Japan. The reverse is the case for Pb. The present survey gives <1 μg/kg BW/week for Japan (although Aung et al. reported 2 μg/kg BW/week), whereas the values for Europe and the USA are in a range of 1.6–4.8 μg/kg BW/week. Much higher values (13–15 μg/kg BW/week) are reported for China (Wang et al. 2009). Thus, it may be prudent to conclude that dietary Cd intake is higher for Japan as compared with the levels for other countries, whereas it is the reverse with regard to Pb intake. Such is as a whole in agreement with findings for adults (Ikeda et al. 2000b). Higher Cd dietary intake should be a matter of child health concern.

It should be noted that the major dietary source for Cd is different depending on the local food habits. Thus, rice is the leading source of dietary Cd in most parts of Asia including Japan (Ikeda et al. 2000b). In contrast, potato in addition to cereals (for bread, pasta and pastry) is a major source of Cd in foods in Belgium (Vromman et al. 2010) and Sweden (Becker et al. 2011). Difference in sources might affect bio-availability of the pollutant elements, but this was not taken into account in the present comparison.

When the food duplicate samples were collected for children and adults in the same site, daily Cd intake per kg BW was larger for children than for adults in studies in Korea and Germany (Moon et al. 2003; Wilhelm et al. 2002) as in the present study (see above for details), although such was not always the case in another study conducted in China (Liu et al. 2010). Larger values for children than that for adult people when compared on a BW basis may imply higher risk for children. Nevertheless, such is quite conceivable as children need more energy/kg BW than adults as they need additional nutrients for their growth. According to Ministry of Health, Labour and Welfare, Japan (2011), for example, recommended dietary allowance (RDA) for 30–49-year-old adult Japanese men (68.5 kg in BW) and women (53.0 kg) is 2,650 and 2,000 kcal, respectively, or 38.7 and 37.7 kcal/kg BW, whereas corresponding values for three- to five-year-old boys and girls (both 16.2 kg) are 1,300 and 1,250 kcal, and therefore 80.2 and 77.2 kcal/kg BW, respectively. The values for children (77.2–80.2 kg BW) are more than two times greater than the values for adult people (37.7–38.7 kg BW) in agreement with the consideration that children need more nutrients than adults.

Cd in urine of children in the present study also seemed to be higher than the levels reported for children in other countries (Table 5). Urinary Cd tended to increase as age progressed (Table 4), suggesting that Cd started to accumulate in the body (in the kidneys in particular) early in life. Thus, it was of particular concern to know if such increase was associated with any tubular dysfunction. When α1-MG levels were compared, however, no age-dependent increase was detected (Table 4). In fact, α1-MG levels in about 66 % of urine samples (196 cases out of 255) were below the limit of determination of 0.9 μg/l, and the levels in children were well below the levels of about 2.5 μg/l as GM for adult women in non-polluted areas in Japan (e.g., Ezaki et al. 2003; Moriguchi et al. 2005). Thus, it is possible to conclude that the age-dependent increase in urinary Cd (Table 4) does not reach the level to affect α1-MG levels as a marker of tubular function.

It is of child health and public health concern if the children with urinary Cd higher than the levels for children in other parts of the world (but with no elevation in α1-MG in urine) may develop any Cd-induced health problem later in their life. It was observed that Cd exposure (almost exclusively from dietary sources) in Japan has been decreasing since the late 1960s (Ikeda et al. 2004). The adult women in Miyagi prefecture showed no tubular dysfunction in a study conducted in the early 2000s (Ezaki et al. 2003), although Cd exposure should be higher for these women in their childhood than that for the kindergarten children in the present study. These findings suggest that the risk should be very small for present time kindergarten children to have Cd-induced health problems in the future. Nevertheless, a survey is warranted to examine their health some half a century later to confirm whether the present time estimation is in fact validated.

It was not possible to make pH adjustment of urine samples [to prevent spontaneous decomposition of β2-microglobulin (β2-MG)] on the sites of urine sample collection and unfortunately no reliable data were available on the levels of β2-MG, the most popular marker of tubular dysfunction (e.g., Ezaki et al. 2003; Moriguchi et al. 2005). It should be added, however, that α1-MG could be a better marker of tubular dysfunction than β2-MG as it is less affected by urine density and more sensitive to changes in Cd levels in urine than β2-MG (Moriguchi et al. 2004, 2005).

Acknowledgments

The authors are grateful to the administration and staff of the Kyoto Industrial Health Association, Kyoto, Japan, for their interest in and support to this study. This work was mainly supported by grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant-in-Aid for Scientific Research B: 15406024) for financial year 2003–2005.

Conflict of interest

The authors declare that they have no conflicts of interest.

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© Springer-Verlag Berlin Heidelberg 2012