Effects of Childhood Exposure to Lead and Cadmium on Physical Growth and Bone Calcium Metabolism in An E-waste Processing Area
|Keywords||E-waste lead,cadmium children physical growth bone metabolic biomarker calcium osteoporosis|
Background: Electrical and electronic equipments pervade modern lifestyles and their consumption is growing rapidly all over the world. Quick obsolescence and newer functionalities of these products are resulting in huge quantities of Waste Electrical and Electronic Equipment or electronic and electric waste (e-waste). Due to the contained hazardous substances, such as heavy metals and other chemicals, e-waste may cause a threat to the environment and human health during the management and processing. Guiyu in Southern China, is one of the biggest destinations of e-waste in the world and has nearly 20 years of disposal and recycling history. The processes and techniques used to recycle electrical waste in Guiyu are primitive. Various hazardous heavy metals are released into the environment threatening the health of local residents. Several studies conducted in Guiyu have reported the high levels of toxic heavy metals and organic contaminants in samples of dust, soil, river sediment, surface water and groundwater of Guiyu. Our previous studies showed that Children living in Guiyu had significantly higher blood lead levels (BLLs) and blood cadmium levels (BCLs)than those living in Chendian (a neighboring town) and other suburban areas. Lead and cadmium are toxic metals which have been considered as an environmental harmful pollutant of world wide concern. Lead and cadmium can cause toxicity on several organs in human. Lead and cadmium are most easily accumulated in human body. 90%-95% lead absorbed by human deposited over time in bone with a half-life of about 20 years. The half-life of cadmium in human body last for 10-30 years. Bone is target organ of Lead and Cadmium. Epidemiologic and animal studies have showed that as a result the effects of lead and cadmium on bone cell functions could persist for a lifetime eventually leading to osteoporosis and osteopenia.Objective: we aimed to investigate lead (Pb), cadmium (Cd), and bone metabolic biomarkers of children in an e-waste processing area. And the effects of lead and cadmium on childhood bone growth and bone and calcium metabolism.Methods: A total of 238 children aged 3~8 were investigated in a kidsgarden of Guiyu from November to December 2009. Blood lead levels (BLLs) and blood cadmium levels (BCLs) were determined by graphite furnace atomic absorption spectrometry with Zeeman background correction. Serum calcium, osteocalcin, bALP, u-DPD were used as biomarkers for bone and calcium metabolism. Osteocalcin, bALP, u-DPD were measured with ELISA methods. Urinary creatinine was determined by a colorimetric assay, using commercially available kit. uDPD was then adjusted to urinary creatinine to account for differences in dilution of the urine. The total serum calcium was determined by compleximetry and Automatic biochemistry analyzer. At the same time, self-designed questionnaire was carried out among the subjects. Spearman rank correlation (rs) was used to assess any univariate associations. Mann-Whitney U-test, t-test and Chi-quare test were used to compare the covariates between subjects by cumulative lead exposure status. We also investigated associations between biomarkers of effect and exposure using multiple linear regressions.Results: 1. The mean of the blood lead level of children was 7.30μg/dL with 16.4% of those≥10μg/dL and blood cadmium levels was 0.69μg/dL. Blood cadmium levels increased with age. House dwelling near or functioned as e-waste workshop was a risk factor contributed to high blood cadmium levels, consuming milk products and having a vitamin supplement were protect factors to children.2. We assessed the univariate associations between exposure and the various bone-related variables and covariates. There was a strong positive correlation between blood lead and u-DPD but not between osteocalcin and bALP. A positive association was found between serum calcium levels and bALP and uDPD. Serum calcium levels were higher in girls than in boys. We also found that uDPD levels was highest among children aged 4, and lowest among children aged 6.3. In a separate analysis the covariates between subjects by cumulative lead and cadmium exposure status (i.e., low vs. high), we found that subjects with high cumulative lead exposure had a higher uDPD and serum calcium than the subjects with low cumulative lead exposure.4. We evaluated further the associations between exposure and variables by adjusting for age and sex. In this adjusted model, BLLs showed a significant negative association with height and weight. However, the association between cadmium and physical growth indexes (height, weight, BMI) disappeared. Blood lead levels were associated with increases in the urinary excretion of DPD. No similar associations were found for cadmium exposure.Conclusions: Blood lead levels and cadmium level has decreased a lot compared with our previous studies. Our results show that Childhood lead exposure affected the physical development and increased bone resorption of children in Guiyu, which may eventually lead to osteoporosis. No statistical correlation was observed between cadmium and bone and calcium metabolic biomarkers. However, the accumulation of cadmium in childhood may pose a health risk later in life. Whatever, effective measures to decrease local children’s exposure is still necessary.