Mortality and causes of deaths of inhabitants with renal dysfunction induced by cadmium exposure of the polluted Jinzu River basin, Toyama, Japan; a 26-year follow-up

Cadmium body burden and health effects after restoration of cadmium-polluted soils in cadmium-polluted areas in the Jinzu River basin

BACKGROUND

Itai-itai disease is caused by environmental cadmium (Cd) pollution in the Jinzu River basin in Japan. To reduce the Cd contamination of rice, soil restoration of paddy fields was carried out. We evaluated the effect of soil restoration on the health status of residents of the former Cd-polluted area.

METHODS

Participants were 1,030 men and 944 women who lived in the area of restoration of Cd-polluted rice paddies. First morning urine was collected and urinary Cd, β2-microglobulin (β2MG), and N-acetyl-β-D-glucosaminidase (NAG) levels were measured. Associations among age, years of residence before and after soil restoration, and urinary Cd, β2MG, and NAG levels were evaluated by multiple regression analysis.

RESULTS

The geometric mean (interquartile range) of urinary Cd (µg/g Cr) was 1.00 (0.58-1.68) in men and 1.67 (1.02-2.91) in women. The geometric means of urinary β2MG (µg/g Cr) and NAG (U/g Cr) were 174.6 (92.6-234.2) and 1.47 (0.72-3.14) in men, and 217.6 (115.3-28.7) and 1.48 (0.73-2.96) in women, respectively. Urinary Cd, β2MG, and NAG were significantly positively correlated (p < 0.01 all). Age and duration of residence in the Cd-polluted area before soil restoration were independently associated with urinary Cd, β2MG, and NAG. Among the 916 participants who had resided in the area before the soil restoration, urinary Cd concentrations were significantly higher, thus by 1.03-fold (95% CI, 1.01-1.04) in men and 1.03-fold (95% CI, 1.01-1.05) in women, when the years of residence before soil restoration by each 5-years increment. By contrast, urinary Cd concentrations were significantly lower, thus 0.97-fold (95% CI, 0.96-0.99) lower in men and 0.97-fold (95% CI, 0.95-0.99) lower in women, by each 5-year increment of residence after soil restoration. A similar association was observed for urinary β2MG concentration, and no significant association was observed for urinary NAG levels in men or women.

CONCLUSIONS

Cd exposure and associated renal tubular dysfunction in residents of a former Cd-polluted area were influenced by Cd exposure from the environment prior to soil restoration. Soil restoration in Cd-polluted areas reduced the Cd exposure of local residents.

The Relationship between the Urinary Cadmium Concentration and Cause-Specific Mortality in Subjects without Severe Renal Damage: A 35-Year Follow-Up Study in a Cadmium-Polluted Area of Japan

We evaluated the association between urinary cadmium concentration (uCd, μg/g Cr) and risk of cause-specific mortality according to urinary β2-microglobulin (MG) concentration. Participants were 1383 male and 1700 female inhabitants of the Cd-polluted Kakehashi River basin. The uCd and β2-MG were evaluated in a survey in 1981–1982, where those participants were followed-up over 35 years later. Among the participants with a urinary β2-MG < 1000, the hazard ratios (HRs) (95% confidence interval) for mortality were significantly higher in those with a uCd of ≥10.0 compared with <5.0 for cardiovascular disease [HR 1.92 (1.08–3.40) for men, 1.71 (1.07–2.71) for women], pneumonia or influenza [2.10 (1.10–4.00) for men, 2.22 (1.17–4.19) for women], and digestive diseases [for men; 3.81 (1.49–9.74)]. The uCd was significantly associated with mortality from heart failure in women and digestive diseases in men, after adjustment for other causes of death using the Fine and Gray competing risk regression model. For participants with a urinary β2-MG of ≥1000, no significant association was observed between uCd and any major cause of death. In the absence of kidney damage, Cd may increase the risk of death from cardiovascular disease, pneumonia, and digestive diseases.

Cadmium and Lead Exposure, Nephrotoxicity, and Mortality

The present review aims to provide an update on health risks associated with the low-to-moderate levels of environmental cadmium (Cd) and lead (Pb) to which most populations are exposed. Epidemiological studies examining the adverse effects of coexposure to Cd and Pb have shown that Pb may enhance the nephrotoxicity of Cd and vice versa. Herein, the existing tolerable intake levels of Cd and Pb are discussed together with the conventional urinary Cd threshold limit of 5.24 μg/g creatinine. Dietary sources of Cd and Pb and the intake levels reported for average consumers in the U.S., Spain, Korea, Germany and China are summarized. The utility of urine, whole blood, plasma/serum, and erythrocytes to quantify exposure levels of Cd and Pb are discussed. Epidemiological studies that linked one of these measurements to risks of chronic kidney disease (CKD) and mortality from common ailments are reviewed. A Cd intake level of 23.2 μg/day, which is less than half the safe intake stated by the guidelines, may increase the risk of CKD by 73%, and urinary Cd levels one-tenth of the threshold limit, defined by excessive ß₂-microglobulin excretion, were associated with increased risk of CKD, mortality from heart disease, cancer of any site and Alzheimer's disease. These findings indicate that the current tolerable intake of Cd and the conventional urinary Cd threshold limit do not provide adequate health protection. Any excessive Cd excretion is probably indicative of tubular injury. In light of the evolving realization of the interaction between Cd and Pb, actions to minimize environmental exposure to these toxic metals are imperative.

Relationship between urinary β2 -microglobulin concentration and mortality in a cadmium-polluted area in Japan: A 35-year follow-up study

The relationship between urinary β₂ -microglobulin (β₂ -MG) and the risk of all-cause mortality and cause-specific mortality in a cadmium (Cd)-polluted area was investigated in 3139 inhabitants (1404 men and 1735 women) of the Kakehashi River basin in Japan at 35-year follow-up. The subjects had been participants in the 1981-1982 health impact survey that assessed Cd-induced renal dysfunction, as measured by the urinary β₂ -MG concentration. Hazard ratios were calculated to assess the risk of all-cause and cause-specific mortality according to the urinary β₂ -MG concentrations. Risk ratios (RRs) were assessed using the Fine and Gray regression model to account for competing risks of cause-specific mortality. The mortality rate was significantly higher in participants with urinary β₂ -MG concentrations >1000 μg/g creatinine (Cr) for men and >300 μg/g Cr for women. In the proportional hazard model, higher urinary β₂ -MG concentrations were associated with higher risks of circulatory disease, digestive system diseases, and kidney and urinary tract diseases in men and women, and with senility for women. However, when competing risk was accounted for, the RRs were significantly higher only for kidney and urinary tract diseases in men and women (RR for each increment of 1000 μg/g Cr [95% confidence interval]: 1.02 [1.00-1.04] for men, and 1.01 [1.00-1.02] for women). The long-term prognosis of participants with renal tubular dysfunction was poor, most likely due to kidney and renal tract diseases.

Identification of high cadmium-accumulating oilseed sunflower (Helianthus annuus) cultivars for phytoremediation of an Oxisol and an Inceptisol

Forty oilseed sunflower cultivars were screened in two soil types for phytoremediation of Cd coupled with maximum biomass yield and oil production. Several cultivars exhibited a significant difference in biomass and yield with enhanced uptake in shoots and low accumulation in roots from two Cd-contaminated soil types, an Oxisol and an Iceptisol. The Transfer Factor of Cd was >1 in several cultivars in both soil types, where as a significant difference in phytoextraction of Cd was observed in the Oxisol (acidic soil), greater than in the Inceptisol (alkaline soil). The results revealed that of the 40 cultivars, S9178, Huanong 667in the Oxisol and cvs. DW 667, HN 667, Huanong 667 and 668F1 in the Inceptisol showed a high biomass, better yield and enhanced accumulation of Cd in the shoots but a lesser accumulation in oil. The screened cultivar S 9178 produced the greatest amount of oil (55.6%) with 77% oleic acid, which makes it suitable for human consumption. Cultivar Huanong 667 was found to be the highest accumulating cultivar in both soil types. It is therefore suggested that some sunflower cultivars do exhibit phytoremediation potential together with agro-production potential.

A comparative study of cadmium levels in blood from exposed populations in an industrial area of the Amazon, Brazil

Chemical pollution from industrial sources is one of the main problems affecting the environment. In urban areas, the emission of toxic gases and particulates to the atmosphere can damage human health. Cadmium (Cd) is one of the most ecotoxic metals among these pollutants, even at low concentrations. In this study, environmental exposure to Cd was evaluated from the Cd blood levels (CdB) of the human populations living in two Amazonian districts. The first was Bairro Industrial (BIN), which is located next to the industrial complex in Barcarena City, while the second was Vila do Beja (VBJ), a control group located in the farthest area from industrial activities in Abaetetuba City. Sectional and comparative studies were applied for both districts. Sampling (N = 469) occurred in 2012 and 2013. Gender, age, residence time, drinking water source, alcohol consumption, and smoking were used as independent variables. CdB levels were analyzed by induced coupled plasma mass spectrometry (ICP-MS). In BIN, geometric mean and median CdB levels were 0.27 and 0.43 μg∙L^-1, respectively (range: ≤0.03-17.49 μg∙L^-1), while in VBJ these were 0.19 and 0.23 μg∙L^-1 (range: ≤0.03-2.38 μg∙L^-1). The higher CdB concentration in the blood of people from BIN was similar to levels previously found in people living near other industrial areas, and showed that the BIN residents were more exposed to Cd pollution. The studies showed the need for surveillance actions to evaluate possible routes of exposure, avoiding the future worsening of the health of the population living next to industrial areas in the Amazon.

Antioxidant response to cadmium exposure in primary skeletal muscle cells isolated from humans and elephant seals

Cadmium (Cd) occurs naturally; however, its concentration can increase with anthropogenic activities. Excess Cd increases reactive oxygen species (ROS) production and oxidative damage, which can lead to pathological conditions. Marine mammals accumulate Cd in the liver and the kidney; yet, there are no reports of Cd-associated tissue damage in whales, seals or dolphins. Response to Cd exposure (0-5.0 μM CdCl₂ for 1-12 h) was analyzed and compared in primary skeletal muscle cells isolated from northern elephant seals (Mirounga angustirostris) and humans (Homo sapiens). Antioxidant enzyme activities (glutathione S-transferase, glutathione reductase, glutathione peroxidase), glutathione concentration, and protein carbonyl levels (an indicator of oxidative damage) were quantified. Glutathione levels were higher in northern elephant seal than in human cells. Protein carbonyl content in cells exposed to Cd was lower and had a smaller variability range in elephant seals than in humans. Generalized linear models (GLIM) identified Cd exposure and antioxidant defenses as significant contributors to protein carbonyl variability in human but not in elephant seal cells. These results suggest that the previously observed differences in circulating and tissue glutathione levels between marine and terrestrial mammals are maintained under cell culture conditions and that northern elephant seal and human muscle cells respond differently to Cd exposure. The results also suggest that the observed differences could potentially be associated with the protective mechanisms that allow northern elephant seals to tolerate extreme conditions that result in increased ROS generation (e.g. diving, sleep apnea, fasting) with no oxidative damage.

Risk factors for chronic kidney disease of non-traditional causes: a systematic review

OBJECTIVES

To evaluate the potential associations between chronic kidney disease of uncertain or non-traditional etiology (CKDnT) and agrochemicals, heat stress, heavy metals, and other factors identified in the literature in any region of the world and at any time.

METHODS

This was a systematic review of the most frequent exposures suspected to be possible causes of CKDnT. A search was conducted of PubMed, LILACS, World Wide Science electronic databases, among other sources. Only medium- and high-quality studies were included. The synthesis of evidence included a narrative synthesis, meta-analysis, and meta-regression.

RESULTS

Four systematic reviews and 61 primary studies were included. Results of the meta-analysis suggest that exposure to agrochemicals and working in agriculture increase the risk of CKDnT, but this only reached significance for working in agriculture. When cross-sectional studies were excluded, agrochemical exposure became significant. However, there is substantial heterogeneity in the effect sizes.

CONCLUSIONS

Based on the existing evidence and the precautionary principle, it is important to implement preventive measures to mitigate the damage caused by CKDnT to both agricultural workers and their communities (i.e., improvement of working conditions, cautious management of agrochemicals, etc.). More high-quality research is needed to measure impact and to build the evidence base.

Increase of lifetime cadmium intake dose-dependently increased all cause of mortality in female inhabitants of the cadmium-polluted Jinzu River basin, Toyama, Japan

BACKGROUND

Exposure to cadmium (Cd) via food is supposed to affect life prognosis of inhabitants of Cd-polluted area in Japan. However, there have been few reports demonstrating a significant relationship between the amount of Cd intake and mortality. We aimed to investigate the relationship between mortality and individual lifetime Cd intake (LCd) in inhabitants of the polluted Jinzu River basin, Toyama, Japan.

METHODS

We conducted a 26-year follow-up survey in 2407 inhabitants (1208 men and 1199 women) who participated in health examinations for screening of renal dysfunction from 1979 to 1984. The calculation of LCd in each inhabitant was based on the formula of Nogawa (Nogawa et al., 1989): (mean Cd concentration in rice of the present hamlet × 333.5 g/day + 34 μg/day) × 365 days/year × number of years of residence in the present hamlet + 50 μg/day × 365 days/year × number of years living in Cd non-polluted regions. In this formula, 333.5 g/day is the 1970 average daily intake of rice in this area, 34 µg/day is the Cd intake from foods other than rice in this area, and 50 μg/day is the average intake of Cd in non-polluted areas in Japan. Mortality risk ratios of LCd for all and specific causes were estimated after adjustments for age at baseline, smoking status, and history of hypertension using a Cox hazard model or Fine and Gray competing risks regression model.

RESULTS

The mortality risk ratios of LCd (+ 1 g) for all causes in women were significantly dose-dependently increased (risk ratio: 1.08). Relative risk of LCd for kidney and urinal tract disease, renal diseases, renal failure and toxic effects of cadmium were significantly higher in women.

CONCLUSIONS

The present study documents that individual LCd dose-dependently decreased life prognosis over long-term observation in women. LCd was significantly related to the increased mortality for renal disease and toxic effect of Cd in women. The result provides clear evidence that life prognosis was adversely affected by Cd-exposure, especially in women.

A comprehensive study including monitoring, assessment of health effects and development of a remediation method for chromium pollution

Chromium (Cr) pollution caused by wastewater from tanneries is a worldwide environmental problem. To develop a countermeasure, we performed a comprehensive study using Hazaribagh, the tannery area in Dhaka City, Bangladesh, as a model. Our environmental monitoring indicated that the soluble form of Cr, but not barium or arsenic, in Buriganga River is derived from Hazaribagh. Our chemical analysis next showed that Cr, the primary pollutant in canal water at Hazaribagh, consisted of ≤0.7 μM hexavalent Cr [Cr(VI)] and ≤1705 μM trivalent Cr [Cr(III)]. Our biological study then showed that coexposure to Cr(VI) and Cr(III) at possible ratios in canal water at Hazaribagh synergistically promotes transforming activity of human non-tumorigenic HaCaT keratinocytes with activated MEK/ERK and AKT. Our environmental engineering study finally indicated that a magnesium and iron-based hydrotalcite-like compound (MF-HT), our original depurative, can maximally adsorb 9.0 mg/g Cr(VI) and 1041 mg/g Cr(III). Our results suggested the importance of removal of Cr(III) as well as Cr(VI) by showing that Cr(III), which is generally recognized as a chemical with low toxicity, synergistically promoted carcinogenicity of a low level of Cr(VI). Therefore, we propose the use of our original high-efficient and low-cost depurative as a countermeasure to address the worldwide problem of environmental Cr pollution.

Cancer Mortality in Residents of the Cadmium-Polluted Jinzu River Basin in Toyama, Japan

After 26 years, we followed up 7348 participants in a 1979-1984 health screening survey in the Jinzu River basin, the heaviest cadmium-polluted area in Japan. We assessed the associations of cadmium exposure levels and mortality from cancer and renal damage, indicated by records of proteinuria and glucosuria in the original survey. Mortality risks (hazard ratios) were analyzed using the Cox proportional hazards model, stratified by sex, after adjusting for age, smoking status, and hypertension, as indicated in the original survey records. In men, the adjusted hazard ratio for mortality from lung cancer was significantly lower in individuals residing in an area of historically high cadmium exposure and in subjects with a historical record of proteinuria, glucosuria, and glucoproteinuria. The risk of mortality from prostate cancer was borderline higher in cadmium-exposed men. In women, historical cadmium exposure was not associated with an increased risk of mortality from malignant neoplasms, but the adjusted hazard ratios for death from total malignant neoplasms or from renal and uterine cancers were significantly higher in exposed subjects with a historical record of proteinuria, glucosuria, and glucoproteinuria. These findings suggest that women residing in cadmium-polluted areas who exhibit markers of renal damage may be at risk of dying of cancer.

Urine cadmium levels and albuminuria in a general population from Spain: A gene-environment interaction analysis

BACKGROUND

The interaction of cadmium with genes involved in oxidative stress, cadmium metabolism and transport pathways on albuminuria can provide biological insight on the relationship between cadmium and albuminuria at low exposure levels.

OBJECTIVES

We tested the hypothesis that specific genotypes in candidate genes may confer increased susceptibility to cadmium exposure.

METHODS

Cadmium exposure was estimated by inductively coupled plasma mass spectrometry (ICPMS) in urine from 1397 men and women aged 18-85years participating in the Hortega Study, a representative sample of a general population from Spain. Urine albumin was measured by automated nephelometric immunochemistry. Abnormal albuminuria was defined as urine albumin greater than or equal to 30mg/g.

RESULTS

The weighted prevalence of abnormal albuminuria was 6.3%. The median level of urine cadmium was 0.39 (IQR, 0.23-0.65) μg/g creatinine. Multivariable-adjusted geometric mean ratios of albuminuria comparing the two highest to the lowest tertile of urine cadmium were 1.62 (95% CI, 1.43-1.84) and 2.94 (95% CI, 2.58-3.35), respectively. The corresponding odds ratios of abnormal albuminuria were 1.58 (0.83, 3.02) and 4.54 (2.58, 8.00). The association between urine cadmium and albuminuria was observed across all participant subgroups evaluated including participants without hypertension, diabetes or chronic kidney disease. We observed Bonferroni-corrected statistically significant interactions between urine cadmium levels and polymorphisms in gene SLC30A7 and RAC1.

CONCLUSIONS

Increasing urine cadmium concentrations were cross-sectionally associated with increased albuminuria in a representative sample of a general population from Spain. Genetic variation in oxidative stress and cadmium metabolism and transport genes may confer differential susceptibility to potential cadmium effects.

Causes of death in patients with Itai-itai disease suffering from severe chronic cadmium poisoning: a nested case-control analysis of a follow-up study in Japan

OBJECTIVE

To clarify the causes of deaths among patients with Itai-itai disease and severe cadmium (Cd) poisoning.

DESIGN

Nested case-control analysis of a population-based cohort study.

SETTING

Database of patients with Itai-itai disease and residents of Cd-polluted areas, maintained by the Ministry of Environment, Japan.

PARTICIPANTS

Subjects included 142 women with Itai-itai disease, 111 women with Cd-induced renal tubular dysfunction and 253 controls matched for sex, age and occupation. All subjects participated in a health impact survey between 1979 and 1984 and were followed until 30 November 2005.

MAIN OUTCOMES AND MEASURES

Adjusted HRs with 95% CIs for cause of death in women with Itai-itai disease and screened female cases with tubular dysfunction were compared with matched pair controls, using Cox's proportional hazard model. Vital statistics data were used to determine cause of death. Direct causes of death from autopsy records were used in 29 patients who died from Cd poisoning.

RESULTS

The most common cause of death among patients with Itai-itai disease was pneumonia, with a significantly increased adjusted HR of 4.54 (95% CI 2.65 to 7.76). Renal diseases were the most common cause of death in renal tubular dysfunction cases, with an increased HR of 12.0 (95% CI 3.92 to 36.8). The adjusted HR for renal diseases was also significantly increased in patients with Itai-itai disease (19.49 (95% CI 6.43 to 59.09)), with a greater impact on mortality of patients with Itai-itai disease than screened cases. The HR for gastrointestinal (GI) diseases was significantly increased (13.79 (95% CI 3.87 to 49.10)) in patients, especially in the first 10 years (37.1 (4.81 to 286.0)).

CONCLUSIONS

Among patients with Itai-itai disease, pneumonia and GI diseases contributed to increased mortality risk. Renal disease is also a significant mortality risk in patients with Itai-itai disease and women with renal tubular dysfunction.

Cadmium exposure and age-associated DNA methylation changes in non-smoking women from northern Thailand

DNA methylation changes with age, and may serve as a biomarker of aging. Cadmium (Cd) modifies cellular processes that promote aging and disrupts methylation globally. Whether Cd modifies aging processes by influencing establishment of age-associated methylation marks is currently unknown. In this pilot study, we characterized methylation profiles in > 450 000 CpG sites in 40 non-smoking women (age 40-80) differentially exposed to environmental Cd from Thailand. Based on specific gravity adjusted urinary Cd, we classified them as high (HE) and low (LE) exposed and age-matched within 5 years. Urinary Cd was defined as below 2 µg/l in the LE group. We predicted epigenetic age (DNAm-age) using two published methods by Horvath and Hannum and examined the difference between epigenetic age and chronologic age (Δage). We assessed differences by Cd exposure using linear mixed models adjusted for estimated white blood cell proportions, BMI, and urinary creatinine. We identified 213 age-associated CpG sites in our population (P < 10^-4). Counterintuitively, the mean Δage was smaller in HE vs. LE (Hannum: 3.6 vs. 7.6 years, P = 0.0093; Horvath: 2.4 vs. 4.5 years, P = 0.1308). The Cd exposed group was associated with changes in methylation (P < 0.05) at 12, 8, and 20 age-associated sites identified in our population, Hannum, and Horvath. From the results of this pilot study, elevated Cd exposure is associated with methylation changes at age-associated sites and smaller differences between DNAm-age and chronologic age, in contrast to expected age-accelerating effects. Cd may modify epigenetic aging, and biomarkers of aging warrant further investigation when examining Cd and its relationship with chronic disease and mortality.

Concentrations of Trace Elements in Organic Fertilizers and Animal Manures and Feeds and Cadmium Contamination in Herbal Tea (Gynostemma pentaphyllum Makino)

Thailand is predominantly an agriculture-based country. Organic farming is enlisted as an important national agenda to promote food safety and international export. The present study aimed to determine the concentrations of trace elements in commercial organic fertilizers (fermented and nonfermented) composed of pig and cattle manures available in Thailand. Pig and cattle manures as well as animal feeds were also collected from either animal farms or markets. The results were compared to the literature data from other countries. Fermented fertilizer composed of pig manure contained higher concentrations of nitrogen (N) and phosphorus (P) than fertilizer composed of cattle manure. High concentrations of copper (Cu) and zinc (Zn) were also found in fertilizers and manures. Some organic fertilizers had high concentrations of arsenic (As), cadmium (Cd), and lead (Pb). The range of As concentration in these fertilizers was 0.50-24.4 mg/kg, whereas the ranges of Cd and Pb were 0.10-11.4 and 1.13-126 mg/kg, respectively. Moreover, pig manure contained As and Cd (15.7 and 4.59 mg/kg, respectively), higher than their levels in cattle manure (1.95 and 0.16 mg/kg, respectively). The use of pig manure as soil supplement also resulted in high Cd contamination in herbal tea (Gynostemma pentaphyllum Makino; GP). The Cd concentration in GP plants positively correlated with the Cd concentration in the soil. Therefore, the application of some organic fertilizers or animal manures to agricultural soil could increase some potentially toxic elements in soil, which may be absorbed by plants and, thus, increase the risk of contamination in agricultural products.

CKD of Uncertain Etiology: A Systematic Review

BACKGROUND AND OBJECTIVES

Epidemics of CKD of uncertain etiology (CKDu) are emerging around the world. Highlighting common risk factors for CKD of uncertain etiology across various regions and populations may be important for health policy and public health responses.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We searched PubMed, Embase, Scopus and Web of Science databases to identify published studies on CKDu. The search was generated in January of 2015; no language or date limits were used. We used a vote-counting method to evaluate exposures across all studies.

RESULTS

We identified 1607 articles, of which 26 met inclusion criteria. Eighteen (69%) were conducted in known CKDu-endemic countries: Sri Lanka (38%), Nicaragua (19%), and El Salvador (12%). The other studies were from India, Japan, Australia, Mexico, Sweden, Tunisia, Tanzania, and the United States. Heavy metals, heat stress, and dietary exposures were reported across all geographic regions. In south Asia, family history, agrochemical use, and heavy metal exposures were reported most frequently, whereas altitude and temperature were reported only in studies from Central America. Across all regions, CKDu was most frequently associated with a family history of CKDu, agricultural occupation, men, middle age, snake bite, and heavy metal exposure.

CONCLUSIONS

Studies examining etiologies of CKDu have reported many exposures that are heterogeneous and vary by region. To identify etiologies of CKDu, designing consistent and comparative multisite studies across high-risk populations may help elucidate the importance of region-specific versus global risk factors.

Both the concentration and redox state of glutathione and ascorbate influence the sensitivity of arabidopsis to cadmium

BACKGROUND AND AIMS

Cadmium (Cd) is a non-essential trace element that elicits oxidative stress. Plants respond to Cd toxicity via increasing their Cd-chelating and antioxidative capacities. They predominantly chelate Cd via glutathione (GSH) and phytochelatins (PCs), while antioxidative defence is mainly based on the use and recycling of both GSH and ascorbate (AsA), complemented by superoxide dismutase (SOD) and catalase (CAT). In addition, both metabolites act as a substrate for the regeneration of other essential antioxidants, which neutralize and regulate reactive oxygen species (ROS). Together, these functions influence the concentration and cellular redox state of GSH and AsA. In this study, these two parameters were examined in plants of Arabidopsis thaliana exposed to sub-lethal Cd concentrations.

METHODS

Wild-type plants and mutant arabidopsis plants containing 30-45 % of wild-type levels of GSH (cad2-1) or 40-50 % of AsA (vtc1-1), together with the double-mutant (cad2-1 vtc1-1) were cultivated in a hydroponic system and exposed to sub-lethal Cd concentrations. Cadmium detoxification was investigated at different levels including gene expression and metabolite concentrations.

KEY RESULTS

In comparison with wild-type plants, elevated basal thiol levels and enhanced PC synthesis upon exposure to Cd efficiently compensated AsA deficiency in vtc1-1 plants and contributed to decreased sensitivity towards Cd. Glutathione-deficient (cad2-1 and cad2-1 vtc1-1) mutants, however, showed a more oxidized GSH redox state, resulting in initial oxidative stress and a higher sensitivity to Cd. In order to cope with the Cd stress to which they were exposed, GSH-deficient mutants activated multiple alternative pathways.

CONCLUSIONS

Our observations indicate that GSH and AsA deficiency differentially alter plant GSH homeostasis, resulting in opposite Cd sensitivities relative to wild-type plants. Upon Cd exposure, GSH-deficient mutants were hampered in chelation. They experienced phenotypic disturbances and even more oxidative stress, and therefore activated multiple alternative pathways such as SOD, CAT and ascorbate peroxidase, indicating a higher Cd sensitivity. Ascorbate deficiency, however, was associated with enhanced PC synthesis in comparison with wild-type plants after Cd exposure, which contributed to decreased sensitivity towards Cd.

Additional Burden of Diseases Associated with Cadmium Exposure: A Case Study of Cadmium Contaminated Rice Fields in Mae Sot District, Tak Province, Thailand

The cadmium (Cd) contaminated rice fields in Mae Sot District, Tak Province, Thailand has been one of the major environmental problems in Thailand for the last 10 years. We used disability adjusted life years (DALYs) to estimate the burden of disease attributable to Cd in terms of additional DALYs of Mae Sot residents. Cd exposure data included Cd and β₂–microglobulin (β₂-MG) in urine (as an internal exposure dose) and estimated cadmium daily intake (as an external exposure dose). Compared to the general Thai population, Mae Sot residents gained 10%–86% DALYs from nephrosis/nephritis, heart diseases, osteoporosis and cancer depending on their Cd exposure type and exposure level. The results for urinary Cd and dietary Cd intake varied according to the studies used for risk estimation. The ceiling effect was observed in results using dietary Cd intake because of the high Cd content in rice grown in the Mae Sot area. The results from β₂-MG were more robust with additional DALYs ranging from 36%–86% for heart failure, cerebral infarction, and nephrosis/nephritis. Additional DALYs is a useful approach for assessing the magnitude of environmental Cd exposure. The Mae Sot population lost more healthy life compared to populations living in a non- or less Cd polluted area. This method should be applicable to various types of environmental contamination problems if exposure assessment information is available.

Urinary cadmium and mortality from all causes, cancer and cardiovascular disease in the general population: systematic review and meta-analysis of cohort studies

BACKGROUND

Cadmium is a toxic heavy metal distributed in the environment. We conducted a systematic review and meta-analysis to examine the association between urinary cadmium concentration and mortality from all causes, cancer and cardiovascular disease (CVD) in the general population.

METHODS

Studies were identified by searching PubMed and Embase (to 30 March 2015) and the reference lists of retrieved articles. We included prospective studies that reported hazard ratios (HR) with 95% confidence intervals (CI) for the association between urinary cadmium concentration and all-cause, cancer or CVD mortality. A random-effects model was used to combine study-specific results.

RESULTS

Nine cohort studies, including 5600 deaths from all causes, 1332 deaths from cancer and 1715 deaths from CVD, were eligible for inclusion in the meta-analysis. The overall HRs for the highest vs lowest category of urinary cadmium were1.44 (95% CI, 1.25-1.64; I(2 )= 40.5%) for all-cause mortality (six studies), 1.39 (95% CI, 0.96-1.99; I(2 )= 75.9%) for cancer mortality (four studies) and 1.57 (95% CI, 1.27-1.95; I(2 )= 34.0%) for CVD mortality (five studies). In an analysis restricted to six cohort studies conducted in populations with a mean urinary cadmium concentration of ≤1 µg/g creatinine, the HRs were 1.38 (95% CI, 1.17-1.63; I(2 )= 48.3%) for all-cause mortality, 1.56 (95% CI, 0.98-2.47; I(2 )= 81.0%) for cancer mortality and 1.50 (95% CI, 1.18-1.91; I(2 )= 38.2%) for CVD mortality.

CONCLUSIONS

Even at low-level exposure, cadmium appears to be associated with increased mortality. Further large prospective studies of cadmium exposure and mortality are warranted.