Bioaccessibility and health risk assessment of arsenic in soil and indoor dust in rural and urban areas of Hubei province, China
Introduction
Soil and indoor dust are important components in the living environment of the general population in both rural and urban areas, and among all environmental materials, they are the most significant in terms of human health effects (Ibanez et al., 2010). Indoor dust is a heterogeneous mixture of particles derived from numerous sources, including soil particles, atmospherically deposited particulates, cooking and heating residues, paint particles, fibres, skin particles, and building and furnishing materials from both outdoor and indoor environments (Paustenbach et al., 1997, Paustenbach, 2000). Concentrations of many metals and metalloids in indoor dust are commonly higher than those in soil in ordinary urban environments (Ibanez et al., 2010). Arsenic (As) is a carcinogenic metalloid found in soil and dust and may pose a risk to human health. Exposure to As may result in serious harmful effects to humans, such as skin lesions, cardiovascular diseases and metabolic disorders. As in soil and indoor dust could enter the human body through dermal contact, inhalation, and ingestion (Reeder et al., 2006). Ingestion is the most important exposure route and may account for 90% of all arsenic entering the human body (Ruby and Lowney, 2012). Compared with the incidental soil ingestion rate of adults, the rate among children is higher; children intake more soil and indoor dust each day as a consequence of their frequent playing on the ground and frequent hand-to-mouth and object-to-mouth behaviours during outdoor and indoor activities (Fillol et al., 2013). Additionally, the less developed enzymatic metabolism and lighter body weight of children makes children more sensitive to arsenic poisoning than adults (Carrizales et al., 2006, Ramirez-Andreotta et al., 2013, Zhang et al., 2013).
Total As concentrations in soil/indoor dust have generally been utilised to determine potential As exposure in previous human health risk assessments, under the assumption that the entire amount of As present in the soil/indoor dust is available for uptake into the gastrointestinal tract. However, whether As poses a human health risk depends on the potential of As to dissolve in gastrointestinal fluid, reach the central (blood) compartment and cause adverse health effects. Therefore, the potential health risks may be overestimated by assessments based on total As concentrations in soil/indoor dust. As bioaccessibility, defined as the fraction of an administered dose that is soluble in the gastrointestinal environment and available to be absorbed by the gastrointestinal tract (Ruby et al., 1999), is an essential measure for more accurate assessments of health risks associated with oral ingestion of soil and dust. Bioaccessibility is calculated by in vitro simulations of digestive fluid using different extractants (Wragg and Cave, 2002). Many in vitro methods are developed to mimic the biochemical conditions in the human gastrointestinal tract (Bruce et al., 2007, Schroder et al., 2004). The physiologically based extraction test (PBET), for instance, is essentially a two-stage sequential extraction using various enzymes to simulate both gastric and small intestine compartments. A simplified bioaccessibility extraction test (SBET) is a simplified form of the PBET and has been used extensively to estimate the bioaccessibility of metals and metalloids in soil exposure studies (Das et al., 2013, Juhasz et al., 2007). This method uses a one-step extraction to simulate gastric conditions, making it a time efficient and reproducible method that is therefore more applicable to large batches of samples (Kelley et al., 2002, Wragg and Cave, 2002).
Soil and indoor dust have been extensively investigated separately on exposure and health risk assessments via ingestion route, for instance, soil contaminated by human industrial activities such as mining, smelting and coking (Cao et al., 2014, Lin et al., 2014, Martinez-Sanchez et al., 2013), and urban soil/dust contaminated due to the extensive effects of traffic and living activities (Hu et al., 2011; Li et al., 2014b; Xia et al., 2011). Indoor dust and normal soil (such as soil in playgrounds and courtyards in residential and school locations) are important exposures for the general population, especially for children, who spend a great deal of time playing on the ground and have high levels of contact with both indoor dust and soil in gardens or playgrounds at schools and nearby homes. Therefore soil and indoor dust are both important components to As ingestion exposure, and health risk assessment based on soil or indoor dust separately cannot represent the real heath risk caused by incidental ingestion properly. Unfortunately, few studies paid attention to the comprehensive health risk caused by ingestion of both soil and indoor dust.
This study is focused on the soil and indoor dust in residential locations and schools where children mainly live and play in rural and urban areas in Hubei Province, central China. The main objectives of this study are to: (1) quantify both the total and the bioaccessible As (determined by SBET method) in the soil and indoor dust of residential and school locations in rural and urban areas; (2) explore the relationships between total As content, bioaccessible As content, As bioaccessibility and physicochemical properties of soil/indoor dust to identify factors which may influence the bioaccessibility of As in soil and indoor dust; and (3) estimate comprehensive potential health risks due to As exposures via incidental ingestion of soil and indoor dust by children during daily indoor and outdoor activities.
Section snippets
Study sites and sampling
The study sites are situated in Yuyang Guan and Wuhan (typical rural and urban areas, respectively) in Hubei province of central China. Yuyang Guan is a typical rural town in north western Hubei province located between 30°03′ N and 30°15′ N and between 110°08′ E and 111°08′ E and experiences an average annual precipitation and temperature of 1215 mm and 16.9 °C, respectively. Wuhan is the capital city of Hubei province located between 29°58′ N and 31°22′ N and between 113°41′ E and 115°05′ E and
Physicochemical properties of soil and indoor dust
Selected physicochemical properties for soil and indoor dust of the <250 µm particle size fraction of samples collected in residential and school sites are presented in Table 2. The soil samples had weakly basic pH values; the mean values at different sampling sites ranged from 7.60 to 7.75, showing that the pH did not differ significantly within sampling sites (Table 2). The mean SOM (soil organic matter) values of residential and school soils from rural areas were 8.39% and 10.87%,
Conclusions
Bioaccessibility is a key factor in the performance of health risk assessments of children’s exposure to arsenic via ingestion of soil and indoor dust. Health risk assessment based on soil or indoor dust separately could not represent the real heath risk caused by incidental ingestion properly. However, few studies have paid attention to the comprehensive health risk caused by ingestion of both soil and indoor dust.
A Pearson's correlation analysis showed negative correlations between As
Acknowledgements
This work was supported by the Special Environmental Research Funds for Public Welfare Project (No. 201309044). The authors are grateful to all the people who helped with the sampling and questionnaire survey.
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