Twenty-Two-Year Observation on Urinary Cadmium and <i>ß</i><sub>2</sub>-Microglobulin in Inhabitants after Cessation of Cadmium-Exposure in Japan

doi:10.4236/ojneph.2013.34035

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Open Journal of Nephrology, 2013, 3, 205-210

Published Online December 2013 (http://www.scirp.org/journal/ojneph)

http://dx.doi.org/10.4236/ojneph.2013.34035

Open Access OJNeph

Twenty-Two-Year Observation on Urinary Cadmium and

ß2-Microglobulin in Inhabitants after Cessation of

Cadmium-Exposure in Japan*

Reiko Sato1#, Teruhiko Kido1, Hideaki Nakagawa2, Muneko Nishijo2,

Ryumon Honda2, Etsuko Kobayashi3, Yasushi Suwazono3

1Graduate School of Medical Science, Kanazawa University, Kanazawa, Japan

2Kanazawa Medical University, Uchinada, Japan

3Graduate School of Medical Science, Chiba University, Chiba, Japan

Email: #[email protected]

Received October 22, 2013; revised November 20, 2013; accepted December 15, 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Obje ctive: This is an epidemiological survey that was conducted for 22 years to investigate the physical effects on in-

habitants who had been exposed to cadmium (Cd) from processing of remnants discharged at the time of copper re-

finement. It was possible to obtain findings on physical effects 27 years after Cd exposure. Materials and Methods: Of

the inhabitants who were 50 years old or younger in 1981 and who were living in the most contaminated area in the

Kakehashi River basin, 68 (32 males and 36 females) who underwent all of the 5 screenings during the 22-year period

were extracted as subjects. Early morning urine was collected for urinalysis, and Cd and ß2-MG concentrations were

determined. Results: 27 years after cessation of Cd exposure, it was shown that urinary Cd concentrations were signifi-

cantly decreased and urinary ß2-MG concentrations were significantly increased. Conclusion: Once exposed to Cd, it

takes about 30 years for the Cd that remains in the body to decrease by half. Once renal tubular dysfunction occurs after

Cd exposure, irreversible aggravation is inevitable.

Keywords: Twenty-Two-Year Observation; Urinary-Cadmium; Urinary-ß2-Microglobulin; Itai-Itai Disease;

Biological-Half-Life

1. Introduction

A long-term follow-up survey was conducted to investi-

gate the effects of Cd exposure on the health of inhabi-

tants who had been living in a contaminated region con-

tinually in Japan with regard to the following: 1) Cd that

remained in the body as determined based on changes in

urinary Cd concentration [1], and 2) renal tubular disor-

der [2], a typical consequence of Cd exposure, based on

changes in urinary ß2-microglobulin (ß2-MG) [3,4] con-

centration.

Once exposed to Cd, about 30 years [5,6] are required

to reduce by half the Cd that remains in the body regard-

less of the amount of exposure. Even after a long period

of time, ß2-MG, an index of renal tubular dysfunction

caused by exposure, continues to irreversibly increase

[7-10] instead of decreasing. It has therefore been sug-

gested that with larger exposure volumes, the risk of de-

velopment of distressing Itai-itai disease [11-13] may in-

crease infinitely.

The Kakehashi River basin located in Komatsu City,

Ishikawa Prefecture, Japan, was contaminated with Cd

waste water from the former Ogoya Cupper Mine [14]

from 1882 to 1971. The inhabitants of the region were

orally exposed to Cd [15] for a long time because they

cultivated and consumed rice as a staple food with con-

taminated water used for irrigation in rice paddies. How-

ever, the Ishikawa Prefecture government conducted an

health impairment investigation only afterward, in the

1970s.

The physical effects of Cd exposure include renal tu-

bular dysfunction, osteomalacia, osteoporosis, hepatic

disorder, hypertension [16], and others. The most severe

consequence is Itai-itai disease. The name of this disease

*The authors declare no competing financial interests.

#Corresponding author.

R. SATO ET AL.

206

is Japanese, and literally means “ouch-ouch” because

even small movements result in fractures due to ad-

vanced osteomalacia, making the patient cry (According

to autopsy reports, 42 fractures were observed in some

cases.).

The Ministry of Health and Welfare of Japan recog-

nized Itai-itai disease as the first mining-related illness in

April 1968 [17] and subsequently enacted a law to im-

prove the polluted soil. Based on this law, in 1981 Ishi-

kawa Prefecture improved the soil of the Kakehashi Riv-

er basin district that was contaminated with Cd. Since the

Ogoya Mine had already been closed by this time and its

operation suspended, it was declared that Cd exposure

had discontinued in this region [18]. At the same time in

1981, the prefectural government investigated health ef-

fects [19] only among inhabitants of the Kakehashi River

district who were 50 years old or older at that time and

also believed to be severely exposed to Cd. In the survey,

findings of ß2-MG of 1000 µg/g·Cr [20,21] or higher

were judged abnormal. The incidence of abnormal values

was 14.3% in males and 18.7% in females who lived in

the polluted area, and 6% and 5%, respectively, in those

who lived in non-polluted areas, clearly demonstrating a

significant difference (p < 0.01) [22] between the pol-

luted and non polluted areas. However, the inhabitants

who were 50 years of age or younger and assumed to be

moderately exposed to Cd were not investigated by Ishi-

kawa Prefecture even though they lived in the same pol-

luted Kakehashi River area. During 22 years from 1986,

5 years after the declaration on the discontinuation of

exposure, up to 2008, Kido et al. who were concerned

about the pollution, conducted a survey 5 times (1986,

1991, 1999, 2003 and 2008) [23,24] to investigate health

effects using only excluded inhabitants who were 50

years of age or younger at the time of the former survey.

Our study summarizes these investigations.

The objectives of the studies were 1) to investigate the

changes in urinary Cd and ß2-MG concentrations in

males and females over the 22-year period to determine

the excretion of these substances and 2) to determine the

relationship between Cd exposure and renal tubular dys-

function on the basis of the correlation of urinary Cd

with ß2-MG in males and females over the 22 years. The

following methods were used.

2. Materials and Methods

Of all the inhabitants who were 50 years old or younger

in 1981 and who were living in the commune, which was

one of the most contaminated areas in the Kakehashi

River basin, 68 (32 males and 36 females) who un-

der-went all of the 5 screenings during the 22-year period

were included as subjects. Inhabitants who neither par-

ticipated at least once due to their illness or moving were

excluded. Early morning urine was collected for urinaly-

sis, and Cd and ß2-MG concentrations were determined.

The measured Cd and ß2-MG concentrations were cor-

rected with Cr. As methods of determination, RIA (Ra-

dioimmunoassay), flameless atomic absorption spectro-

photometry [25] and the Jaffe method were used to de-

termine ß2-MG concentration, Cd concentration, and Cr

concentration, respectively. A questionnaire was also

used to investigate gender, age, and duration of resi-

dence.

ß2-MG is a plasma protein of low molecular weight

(11.800 Daltons) and is produced from immunologically

competent cells, the liver, and other tissues. Almost

100% of ß2-MG is filtered through the glomeruli of the

kidneys and 99.9% of that is reabsorbed in the renal tu-

bules [24-26]. Accordingly, ß2-MG was used as an index

of renal tubular dysfunction. Currently, new indexes of

renal tubular dysfunction are being described. However,

the newest and the most sensitive index as of 1986 was

urinary ß2-MG [24,25]. In a long-term follow-up epide-

miology survey, it was necessary to employ the same

investigation method in the same subjects for 22 years.

Therefore, urinary ß2-MG was continuously used as an

index of renal tubular dysfunction for the 22-year period.

The results were statically analyzed using analysis of

covariance (ANCOVA), Bonferroni and Pearson correla-

tion coefficient. The software used for analysis was

SPSS12 OJ for Windows.

The inhabitants participated in the survey of their own

free will. The survey in 2008 was granted approval by

the Ethics Committee of Kanazawa University (2008, ap-

proval No. 166).

3. Results and Discussion

The mean ages of subjects in 2008 were 65 years and 68

years in the case of males and females, respectively. The

mean years of residence were 53 years and 46 years, re-

spectively (Table 1).

The scales of Figures 1-3 show concentrations con-

verted to logarithmic values.

Figure 1 shows a graph of average urinary Cd con-

centrations of 32 males and 36 females during the

22-year period. On t-testing of the difference in average

Cd concentrations of male and female urine specimens in

1986 and 2008, the levels of significance were females p

= 0.001 and males p = 0.001, indicating a significant

decrease in 2008. The average actual measurements in

1986 were males 6.0 μg/g·Cr and females 8.20 μg/g·Cr,

while the 2008 average actual measurements were males

2.30 μg/g·Cr and females 5.70 μg/g·Cr. This graph reflects

the biological half-life of Cd, which is about 30 years,

though the results also suggest long-term residue of Cd in

the body even 27 years after exposure. In addition, the

Open Access OJNeph

R. SATO ET AL.

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207

Table1. Information on tested subjects (Males = 32, Females = 36).

1986 1991 1999 2003 2008

M F M F M F M F M F

Average age 43 46 48 50 56 59 60 62 65 68

Average period of residence 31 24 36 29 44 37 48 41 53 46

M: Males; F: Females.

Figure 1. Changes in urinary cadmium concentration

(μg/g·Cr) over 22 years in 32 males (Blue) and 36 females

(Red).

Figure 3. Scatter-plot of correlation between urinary Cd

and ß2-MG concentrations for 36 females (○) and 32 males

(△) in 2008 (r = 0.55: Pearson correlation coefficient, p =

0.000).

concentrations in male and female urine specimens in

1986 and 2008, levels of significance were females p =

0.001 and males p = 0.019. The level significantly in-

creased in both males and females.

These results indicate that, once renal tubular dysfunc-

tion occurs after Cd exposure, no cure can be expected

and irreversible aggravation is inevitable over time. For-

tunately, however, the subject group consisted of those

moderately exposed rather than severely exposed to Cd.

Since the mean ß2-MG concentration at the time of initial

screening in 1986 was 1000 µg/g·Cr or less [18], these

individuals had not suffered renal tubular dysfunction,

with the exception of several individuals, even though a

significant increase in the ß2-MG concentration was not-

ed after 22 years (see Figure 3).

Figure 2. Changes in urinary ß2-MG concentration (µg/g·Cr)

over 22 years in males (Blue) and females (Red).

mean concentration in females was clearly higher than

that in males, since Cd absorption rate depends on the

metallic ion. In conditions of iron deficiency in particular,

the absorption rate increases by 20 to 30% compared

with normal. The higher incidence of iron deficiency

anaemia observed in females [26,27] due to menstruation,

giving birth, etc. is cited as a reason why Cd concentra-

tion was higher in females than males.

In addition, the downward trend in average concentra-

tion shown in Figures 1 and 2 in 1999 is interpreted as

the result of physiologically fluctuation, since all values

were within normal [24].

To adjust the effects of age or period of residence on

the trend in average concentrations of urinary Cd and

ß2-MG, analysis of covariance (ANCOVA) analysis was

performed and results were shown from Tables 2-5. Ta-

ble 2 shows the change of urinary Cd concentration dur-

ing 22 years adjusted by age in males and females. Pre-

liminary parallel tests showed a positive result for fe-

males and a negative result for males. Hence, the

Figure 2 shows a graph of average urinary ß2-MG

concentrations of 32 males and 36 females during 22

years. The average actual measurements in 1986 were

males 181.0 μg/g·Cr and females 199.0 μg/g·Cr, while

the 2008 values were males 224.0 μg/g·Cr and females

268.0 g/g·Cr. On t-testing of the difference in average Cd

R. SATO ET AL.

208

Table 2. The change of urinary Cd concentration during 22 years adjusted for age in females.

Urinary Cd (μg/g·Cr)

Year Females (N = 36)

GM SE p

1986 0.968 0.48

p = 0.002

1991 0.857 0.046

p = 0.027

1999 0.615 0.045 p = 0.001

p = 0.001

2003 0.601 0.045 p = 0.000 p = 0.049

2008 0.419 0.048

GM: Geometric Mean; SE: Standard Error; p: p-value; A Parallel test for males was negative and positive for females. Hence, a further Bonferroni multiple

comparison in ANCOVA analysis was performed for females.

Table 3. The change of urinary Cd concentration during 22 years adjusted for period of residence in males and females.

Urinary Cd (μg/g·Cr)

Males (N = 32) Females (N = 36)

Year GM SE p GM SE p

1986 0.670 0.058

p = 0.001 0.925 0.050 p = 0.039

1991 0.563 0.056 p = 0.0000.824 0.048

1999 0.343 0.055 p = 0.038 0.626 0.047 p = 0.000 p = 0.038

2003 0.430 0.056 p = 0.000 p = 0.0120.622 0.048 p = 0.000

2008 0.170 0.057 0.464 0.049

GM: Geometric Mean; SE: Standard Error; p: p-value; Parallel tests for males and females showed a positive result. Hence, a further Bonferroni multiple com-

parison in ANCOVA analysis was performed.

Table 4. The change of urinary ß2-MG concentration during 22 years adjusted for age in males and females.

Urinary ß2-MG (μg/g·Cr)

Males (N = 32) Females (N = 36)

Year GM SE p GM SE p

1986 1.979 0.131

p = 0.16 2.306 0.121

1991 2.025 0.126 p = 0.005 2.510 0.116 p = 0.014

1999 1.394 0.124 1.983 0.113

2003 1.863 0.125 p = 0.001 2.212 0.114

2008 2.090 0.130 2.377 0.120

GM: Geometric Mean; SE: Standard Error; p: p-value; Parallel tests for males and females showed a positive result. Hence, a further Bonferroni multiple com-

parison in ANCOVA analysis was performed.

resulting Bonferroni multiple comparison in ANCOVA

analysis for females showed a significant decrease during

22 years (1986 - 2008), without involvement of age. In

Table 3 the change of urinary Cd concentration during

22 years was adjusted by period of residence in males

and females. Preliminary parallel tests showed a positive

result for both males and females. In the resulting in

ANCOVA and Bonferroni multiple comparison analysis,

there was a significant decrease in males and females

during 22 years (1986 - 2008), without the involvement

period of residence. As shown in Table 4 the change of

urinary ß2-MG concentration during 22 years was ad-

justed by age and preliminary parallel tests showed a

positive result in males and females. Hence, the resulting

Bonferroni multiple comparison in ANCOVA analysis

showed a significant decrease between 1986 to 1999 and

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R. SATO ET AL. 209

Table 5. The change of urinary ß2-MG concentration during 22 years adjusted for Period of residence in males and females.

Urinary ß2-MG (μg/g·Cr)

Males (N = 32) Females (N = 36)

Year GM SE p GM SE p

1986 1.935 0.130

p = 0.038 2.267 0.118

1991 2.008 0.126 p = 0.009 2.468 0.114 p = 0.038

1999 1.902 0.125 1.999 0.112

2003 1.877 0.126 p = 0.001 2,230 0.113

2008 2.129 0.129 2.424 0.117

GM: Geometric Mean; SE: Standard Erro; p: p-value; A Parallel test for males and females showed a positive result. Hence, a further Bonferroni multiple com-

parison in ANCOVA analysis was performed.

1991 to 1999, but there was significant increase during

1999 to 2008 in males, with no significant increase in

females. However, there was a tendency towards increase

during 22 years (1986 - 2008) for both males and females

without the involvement of age. Table 5 shows that uri-

nary ß2-MG concentration during 22 years was adjusted

by period of residence. A significant increase was ob-

served between 1999 and 2008 for males, but for females,

there was no significant increase without the involvement

of period of residence. However, during 22 years (1986 -

2008) there was a tendency to increase in males and fe-

males. Therefore, Significant increase were observed for

urinary ß2-MG concentration (µg/g·Cr) adjusted by age

and period of residence, for males and females. An in-

creasing tendency was observed during 22 years for fe-

males. It was revealed that once exposed to Cd, ß2-MG

occurs in the body and irreversible

Figure 3 shows a scatter-plot of the correlation be-

tween urinary Cd and ß2-MG concentrations for 36 fe-

males (○) and 32 males (△) in 2008 using the Pearson

correlation method. This figure indicates a significant

correlation of urinary Cd with ß2-MG in 2008 with a

Pearson correlation coefficient of r = 0.55 and a signifi-

cance level of p = 0.0001. The relationship of Cd expo-

sure to renal tubular dysfunction indicates that this dys-

function persisted even 27 years after Cd exposure and as

long as Cd remained in the body.

4. Conclusion

Our findings clearly indicate the following. Once ex-

posed to Cd, it takes about 30 years for the Cd that re-

mains in the body to decrease by half. Once renal tubular

dysfunction occurs after Cd exposure, irreversible ag-

gravation is inevitable. If the Cd exposure volume is lar-

ger, the renal tubular dysfunction will be more severe.

Therefore, measures to prevent mining pollution are re-

quired for mining development in the 21st century so that

the tragedy caused by Cd pollution that occurred as a

secondary effect of cupper mining development is never

repeated. In addition, the first measures to prevent min-

ing pollution is a process of gravel remaining emissions

during the refining process. The gravel that contain con-

taminants is discharged, and appropriate processing of it

is the first step in preventing pollution. However, we may

be able to find rare metals by carefully sifting this gravel,

which has been irresponsibly discharged.

5. Acknowledgements

The authors thank the inhabitants of the Kakehashi area,

who had to endure physical examinations over a period

of 22 years. Special thanks go to Mr. M. Iga, a historian

of Kakehashi town, who is currently 96 years of age. The

authors also thank Mr. M. Hino for environmental data

on the Kakehashi river stream (Komatsu Environmental

Partnership) and Mr. H. Hayashidera.

Finally, we sincerely wish the inhabitants of the Kake-

hashi area good health and long lives.

6. Author Contributions

Dr. Sato conducted the project. Dr. Nishijo, Dr. Kobaya-

shi, and Dr. Honda analyzed the urinary samples. Dr.

Kido and Dr. Nakagawa participated in several health

examinations. Dr. Suwazono calculated analytical data.

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