Content area
Full text
Introduction
It is widely recognized that soil contamination in China is of serious concern (Chen et al. 2014; Larson 2014; Yang et al. 2014). Unintentional soil ingestion is a potentially important route of exposure to soil contaminants, especially for children, who may ingest more soil than adults because of their frequent hand-to-mouth or hand-to-object behaviors (U.S. EPA 2011). Soil ingestion rate (SIR) is a prerequisite for assessing the health risk of contaminated sites to children (U.S. EPA 2011). However, a reliable SIR for Chinese children has yet to be determined.
Doyle et al. (2010), the U.S. EPA (2011), and Moya and Phillips (2014) comprehensively reviewed studies on SIR, showing that the metric was established in the 1970s. Early studies tried to quantify soil ingestion by employing qualitative or semi-quantitative methods, combining hand-to-mouth frequency with soil loadings on the hand (Day et al. 1975; Doyle et al. 2010; Duggan and Williams 1977; Hawley 1985; Kimbrough et al. 1984; Lepow et al.1974).
Since the 1980s, scientists have used the tracer mass-balance method to quantify SIR. Binder et al. (1986) modified the methods used in estimating the amount of soil ingested by ruminants to measure soil ingested by children, neglecting the tracers in food. Subsequent studies (Calabrese et al. 1989; Davis et al. 1990) improved the tracer method of Binder et al. (1986) to estimate a child’s SIR by including tracers in food and by increasing the number of tracers. The best tracer method (BTM) was further developed to estimate a child’s SIR (Calabrese and Stanek 1993; Calabrese et al. 1997; Stanek and Calabrese 1995). First, the BTM ranks tracer elements according to their food-to-soil (F/S) ratios, defined as the mass of the tracer element ingested from food over a 1-d period divided by the mass of the tracer element in 1 g of soil. Then, the SIR for each subject over the study period is calculated using the median of the SIRs estimated by four tracers with the lowest F/S ratios. Recently, Doyle and colleagues used a higher number of tracers, including radionuclides, to quantify a child’s SIR with the tracer mass-balance method (Doyle et al. 2012a; Irvine et al. 2014).
The biokinetic model comparison method (BMC) has also been used to estimate a child’s SIR. The...