| Cadmium is a toxic heavy metal naturally present in the earth’s crust. In the process of mining and smelting, various wastes containing cadmium can escape into the surrounding environment and cause cadmium pollution in soil and water. Cadmium in the environment can be enriched in the crops, and enter the body through the food chain. Large number of studies have demonstrated that dietary cadmium exposure has become the main way of non-occupational population exposure to cadmium. Renal dysfunction is the most critical early harmful effect caused by cadmium exposure.In epidemiological studies, the level of rice cadmium, soil cadmium, vegetable cadmium may reflect the cadmium levels in the environment where the study population lives. Moreover, the level of urinary cadmium is generally used as the indicator of chronic cadmium exposure. The effect biomarkers of renal function such as urinary β2-MG and NAG were widely used as indicators for monitoring early renal dysfunction.Epidemiological investigation were carried out in an environmental cadmium exposure area and a control area to obtain the level of dietary cadmium exposure in local population(the indicator of environmental cadmium external exposure), the level of urinary cadmium(the indicator of cadmium body burden) and the level of urinary NAG and β2-MG(the indicator of renal dysfunction). This study analyzed the relationship among environmental cadmium external exposure, environmental cadmium internal exposure and renal dysfunction. Classification tree analysis model were using for investigating the key factors for renal dysfunction and identifying the characteristics of the people who have the high risk of renal dysfunction. Thus, we provide the epidemiological evidence of the early renal dysfunction caused by environmental cadmium exposure.ObjectiveTo explore the relationship between environmental cadmium exposure and renaldysfunction, investigating the key factors for renal dysfunction and identifying the characteristics of the people who have the high risk of renal dysfunction as well as providing the epidemiological evidence of the early renal dysfunction caused by environmental cadmium exposure.Methods(1)Epidemiological studyselection and grouping of study subjectsThis study used epidemiological method, and selecting one cadmium polluted area and one non-polluted area as survey areas in Guangdong Province, where the local residents taken the locally produced rice and vegetables as the main food. Stratified random sampling and cluster sampling method were used to chose residents who lived in investigating sites for more than 15 years, aged above 40. QuestionnairePersonal health questionnaires were conducted to acknowledge the subjects’ general health and living habits; Dietary survey were conducted to acknowledge the subjects’ dietary consumption data of main food. ExaminationThe examinations including height, weight, dental examination, bone examination, and so on.Collection, transportation and storage of the specimensOne rice and one vegetable locally produced from each family were collected, and 2 or 3 water samples were collected from each survey town, numbered and recorded. All the samples were refrigerated after collection at 0 ~ 4 ℃ refrigerator, and complete the test within three days.The morning urine from each subject was gathered and sent to the laboratory with a cold-chain transportation, and finished the relevant analysis within 2 hours; The testing work of NAG and β2-MG should complete the detection within 6 h after collection.(2)Laboratory testingThe indicators of external environmental cadmium exposureWe use the levels of cadmium in rice and vegetables as the indicators of external environmental cadmium exposure and the ICP-MS was employed for detecting.The indicators of internal environmental cadmium exposureWe use the level of urinary cadmium as the indicator of internal environmental cadmium exposure and the ICP-MS was employed for detecting. The biomarkers of renal dysfunctionWe use the urinary NAG and β2-MG as the biomarkers of renal dysfunction that were related to cadmium exposure. The urinary creatinine was detected by use of Jaffe’s assay, and the urinary NAG as well as β2-MG were detected by immunoturbidimetric test. NAG and β2-MG were corrected for creatinine concentration and were expressed as U/ g·cr as well as μg/ g·cr.(3)Statistical analysisThis study used correlation analysis to explore ①The impact of dietary cadmium exposure(external environmental cadmium exposure) on the level of urinary cadmium(internal environmental cadmium exposure); ② The impact of the level of urinary cadmium(internal environmental cadmium exposure) on the level of the urinary NAG and β2-MG(the biomarkers of renal dysfunction); ③The impact of dietary cadmium exposure(external environmental cadmium exposure) on the level of the urinary NAG and β2-MG(the biomarkers of renal dysfunction);④Classification tree analysis model were using for investigating the key factors for renal dysfunction and identifying the characteristics of the people who have the high risk of renal dysfunction.Results(1)The demographic characteristics of the subjectsA total of 360 subjects were recruited, including 180 subjects in the control group and 180 subjects in the exposed group. The difference of sex ratio, agedistribution, years of residence, smoking status distribution of residents between two groups was insignificant. However, the self-discomfort rate of muscle pain in exposed group(12.2%) were significantly higher than that of the control group(2.8%), P<0.05. Also, the self-discomfort rate of bone pain in exposed group(10.0%) were significantly higher than that of the control group(0.0%), P<0.05. There were no significant difference in other physical condition between two groups(P>0.05).(2)The level of dietary cadmium exposure of the subjectsThe subjects’ dietary structure was relatively simple, mainly taken the locally produced rice and vegetables as the main food. The rice and vegetable intake of the subject accounted for more than 70% of the total intake. The levels of cadmium in rice and vegetables and abnormal detection rates in exposed group were much higher than that of in control group(P<0.05). Because the dietary structure was similar in two groups, so the main dietary cadmium exposure(rice and vegetables) in exposed group [(277.12±115.31)μg/day] were also higher than that of in control group [(39.32±13.86)μg/day](P<0.05). After stratified the total population by age and gender, there were no significant difference in level of dietary cadmium exposure among the subgroups(P>0.05).(3)The level of NAG and β2-MG of the subjectsThe median level of urinary cadmium in exposed group was 10.46(4.63~18.87) μg/ g·cr, higher than 1.76(1.31~2.42)μg/ g·cr in control group(P<0.05). After stratified the total population by gender, the median urinary cadmium level in female was 3.23(1.95~13.20)μg/g·cr, higher than 2.61(1.60~8.72) μg/g·cr in male(P<0.05). After stratified the total population by age, there were no significant difference in level of urinary cadmium between two groups(P>0.05).The median level of NAG and β2-MG 17.60(12.80~25.55) U/g·cr and 201.74(94.63~878.10)μg/g·cr in exposed group were higher than 5.51(4.16~7.34)U/ g·cr and 23.46(0.00~311.39)μg/ g·cr in control group(P<0.05).(4)Associations Among external environmental cadmium exposure, internal environmental cadmium exposure, and Renal DysfunctionCorrelation analysis showed that: 1) Dietary cadmium exposure and urinarycadmium The higher daily dietary cadmium expose, the subjects’ level of urinary cadmium were higher. The two independent variables, that were daily dietary cadmium expose and gender could explain the change of the levels of urinary cadmium in 57.9%, daily dietary cadmium expose was the most important factors for urinary cadmium(b’=0.756,P<0.001);2) Urinary cadmium and the biomarkers of renal dysfunction With the increase of the levels of urinary cadmium, the levels of NAG and β2-MG were also increased, the level of urinary cadmium could explain the change of the levels of NAG in 60.4%, and age as well as the level of urinary cadmium could explain the change of β2-MG in 22.8%. Age was the most important factors for β2-MG(b’=0.315,P<0.001), followed by the level of urinary cadmium(b’=0.295,P<0.001);3) Dietary cadmium exposure and the biomarkers of renal dysfunction The higher daily dietary cadmium expose, the subjects’ level of NAG were higher. The two independent variables, that were daily dietary cadmium expose and gender could explain the change of the levels of NAG in 57.6%, daily dietary cadmium expose was the most important factors for NAG(b’=0.758,P<0.001), however, it showed no correlation existed between the dietary cadmium exposure and β2-MG.The classification tree models using the abnormal rate of NAG as dependent variable showed that people whose the level of urinary cadmium higher than 4.51μg/g·cr or lower than 4.51μg/g·cr but dietary cadmium exposure higher than 41.13μg/day were the high risk group of renal dysfunction. The classification tree models using the abnormal rate of β2-MG as dependent variable showed that people whose the level of urinary cadmium higher than 13.43μg/g·cr or lower than 13.43μg/g·cr but male were the high risk group of renal dysfunction.Conclusion1. The level of dietary cadmium expose and body burden of cadmium(urinary cadmium) of residents in exposed area were high that should be attracted wide attention; Dietary cadmium exposure was the most important factor of increasing the body burden of cadmium.2.With the increase of the levels of urinary cadmium, the levels of renal dysfunction biomakers( NAG and β2-MG) were also increasing. The increase of dietary cadmium exposure was directly related to the increase of the levels of NAG, but no significant correlation was shown between dietary cadmium exposure and β2-MG.3.The classification tree models results showed people whose the level of urinary cadmium higher than 4.51μg/g·cr or people whose dietary cadmium exposure were higher 41.13μg/day were the high risk group of renal dysfunction, which were the key group in the health surveillance and should pay close attention. |
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