Cadmium exposure pathways in a population living near a battery plant☆
Introduction
Cadmium (Cd) is a toxic metal, widely spread in the biosphere in spite of restrictions for its use. When evaluating human Cd exposure, it is important to consider all routes of exposure, smoking in particular, along with factors influencing the uptake such as, dietary habits and nutritional factors (e.g. iron status).
Food is the most important source of Cd exposure in the general non-smoking population (WHO, 1992). Cadmium is present in virtually all food, but the concentrations vary to a great extent, depending on the type of food and the Cd load in the food production environment (Jorhem and Sundström, 1983, Olsson et al., 2005). Natural occurrence of Cd in bedrock and soils as well as anthropogenic sources of Cd, such as industrial emissions and the application of soil amendments (e.g. lime, phosphorous-fertilisers and sewage sludge) to farm land, may lead to contamination of soil by Cd and increased uptake by cereal crops, vegetables and root crops (Andersson and Bingefors, 1985, Andersson, 1992, Erikson et al., 1996, Eriksson et al., 1997, Eriksson et al., 2000, McLaughlin and Singh, 1999). The uptake of soil Cd by plants is enhanced by a low pH (WHO, 1992, Erikson et al., 1996, Grant et al., 1999). In particular, the Cd concentration in potatoes and carrots has been shown susceptible to changes in soil pH during Swedish field conditions (Öborn et al., 1995), while salinity, i.e. Cl concentration, is the major factor influencing potato tuber Cd concentration in other climatic regions (e.g. McLaughlin et al., 1997). Thus, a decrease of soil pH due to environmental acidification, which is a well recognised problem in Sweden, may further increase the Cd concentration in foodstuff. While Cd levels in potatoes and carrots vary, clearly the contribution to the total dietary Cd intake in Sweden is substantial (Grawé et al., 2000).
In general, Cd in drinking water does not contribute much to the total intake. Drinking water contains very low concentrations of Cd, usually less than 1 μg l− 1 (WHO, 2004). The maximum limit for Cd in drinking water is set to 5.0 μg l− 1 in the European Union (EC Council Directive, 1998).
Cadmium concentrations in ambient air are generally low. In rural areas of Europe, an annual mean air Cd concentration of 0.1–0.5 ng m− 3 has been reported, but levels up to100 ng m− 3 can be found in the proximity of emission sources (WHO, 2000). Smoking is an important source of Cd exposure. One cigarette contains about 1–2 μg Cd and about 10% is inhaled during smoking (Järup et al., 1998). Approximately 50% of the Cd inhaled via cigarette smoke is absorbed, and if a person smokes 20 cigarettes per day it can be estimated that about 1–2 μg of Cd may be absorbed (Järup et al., 1998).
Cadmium in urine is known to be a good estimator of Cd body burden, whereas Cd in blood reflects more recent exposure (Järup et al., 1998). In general, non-smokers have urinary Cd (UCd) concentrations of 0.02–0.7 nmol Cd/mmol creatinine, slowly increasing with age in parallel with the accumulation of Cd in the kidneys (Berglund et al., 1994, Vahter et al., 1996). Smokers have about twice the urine concentrations as non-smokers (Järup et al., 1998).
Nickel–cadmium batteries have been produced in the community of Fliseryd in the southeast of Sweden, between 1910 and 1974, when the factory was closed. Occupational exposure to Cd during the first five decades of battery production was considerable, but exposure levels decreased gradually since the 1960s (Järup and Elinder, 1994). Cadmium contamination of the environment has been substantial in the vicinity of the plant. In order to assess the pollution, samples of moss and soil have been collected and analysed for Cd content on several occasions and found to be high near the former factory, decreasing with distance from the plant (Bergbäck and Carlsson, 1995). In a pilot study, we found increased levels of UCd in persons who had lived close to the plant for many years (Järup et al., 1995).
The purpose of this study was to investigate to what extent a population living near a battery plant was exposed to Cd and to assess different exposure pathways, in particular the contribution of locally produced vegetables and root crops.
Section snippets
Materials and methods
The present study population was a part of the OSCAR-study that included individuals between 16 and 80 years of age, who had lived in the community where the battery factory was situated for at least 5 years during the period 1910 to 1992 (Järup et al., 2000). Of these, only persons living in the county of Kalmar at the time of the study in 1995 were included. From the main study 513 environmentally exposed persons were identified after excluding individuals who had been occupationally exposed.
Statistical methods
Using logistic regression (STATISTICA StatSoft ®, Oklahoma, USA) on categorical data (for categorization see Table 2), the association between Cd in urine and gender, age, pack-years, environmental Cd-exposure-index and consumption of homegrown vegetables/potatoes were analysed. The prevalence of tubular proteinuria in the OSCAR study population was 10% at a urinary Cd level of 1.0 nmol/mmol creatinine (Järup et al., 2000). Therefore this UCd value was used as cut-off point in the analysis. The
Results
Age, urinary excretion of Cd, distance to battery plant, smoking index and environmental Cd-exposure-index in the study populations are shown in Table 1.
The geometric means of urine Cd concentration (nmol/mmol creatinine) did not differ between never smokers (0.35; 95%CI 0.32–0.38; n = 262) and ever smokers with less than 10 pack-years consumption (0.36; 95%CI 0.32–0.39; n = 99) and they were therefore combined into one group in the analysis. A total of 33 persons had increased urinary Cd
Discussion
We found statistically significant relationships between elevated Cd in urine and environmental Cd-exposure-indices and regular intake of homegrown vegetables.
We also found a statistically significant relation between urinary Cd and Cd in soil and carrots in individuals cultivating vegetables/potatoes at home. Although samples of soil, carrots and potatoes were rather few, these results indicate that consumption of locally produced vegetables and root crops grown on Cd contaminated soil may
Conclusion
The results show that consumption of locally grown vegetables and root crops was an important exposure pathway for individuals living near a nickel–cadmium battery plant, whereas direct exposure through ambient air was of less importance. Thus Cd exposure in contaminated areas may be prevented by reducing the intake of locally grown vegetables/potatoes or by replacing the contaminated garden soil.
Acknowledgments
We would like to thank all the participants in the study. Thanks also to Ann-Christin Palmqvist and Ann-Kristin Thunberg, who collected the data, Mariette Blomberg for entering the data into computer files. Kerstin Olsson Svalöf Weibull AB for carrot seed and advice in the carrot study, and Bo Bergbäck and Stina Larsson Kalmar University for their contribution to the soil and carrot study. We would also like to thank Dr Susan Hodgson, Imperial College London for language corrections. The study
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This work was performed at the Department of Environmental Medicine and Public Health, County Council of Kalmar, SE-572 32 Oskarshamn, Sweden.