Archives of Environmental Contamination and Toxicology https://doi.org/10.1007/s00244-018-0526-x
Seasonal Variation and Exposure Risks of Perchlorate in Soil, Indoor Dust, and Outdoor Dust in China Yiwen Li1 · Ruoying Liao1 · Zhiwei Gan1 · Bing Qu1 · Rong Wang1 · Mengqin Chen1 · Sanglan Ding1 · Shijun Su1 Received: 25 December 2017 / Accepted: 12 April 2018 © Springer Science+Business Media, LLC, part of Springer Nature 2018
Abstract A total of 97 paired soil, outdoor dust, and indoor dust samples were collected in the national scale of China in summer, and the perchlorate levels were compared with those in soil and outdoor dust samples collected in winter in our previous study. The median perchlorate concentrations in the outdoor dust, indoor dust, and soil samples were 8.10, 11.4, and 0.05 mg/kg, respectively, which were significantly lower than those in the winter samples due to the natural factors and human activities. No significant differences in perchlorate concentrations were found between Northern and Southern China in the dust samples, whereas the difference was obtained in the soil samples. In the terms of possible source, the perchlorate levels in the outdoor dust exhibited strong correlation with S O42− (r2 = 0.458**) and NO3− (r2 = 0.389**), indicating part of perchlorate in outdoor environment was likely from atmospheric oxidative process in summer. The perchlorate, S O42−, and C l− levels in the indoor dust were significantly related to those in the outdoor dust, suggesting that outdoor contaminants might be an important source for indoor environment. Furthermore, the human exposure to perchlorate was under relatively safe state in China except for special sites or periods with high perchlorate levels. Dust made an unexpected contribution of 41.3% to the total daily perchlorate intake for children, whereas 2.46% for adults in China based on biomonitoring, which deserves more attention. Perchlorate has attracted considerable attention in recent years referred as a new emerging environmental contaminants. It is widely used in aerospace, military, pyrotechnic, and other industrial manufacturing applications as strong oxidant or additives (Motzer 2001; Urbansky 1998). Perchlorate has been not only detected in various environmental medium, such as surface water, groundwater, airborne particle, soil, and dust at high levels, but also in some human bodily fluids (Her et al. 2011; Kannan et al. 2009; Kosaka et al. 2007; Pearce et al. 2010; Vella et al. 2015; Wan et al. 2015; Zhang et al. 2015). The irregular and extensive distribution of perchlorate in environment is mainly due to its
Yiwen Li and Ruoying Liao have contributed equal to the study. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00244-018-0526-x) contains supplementary material, which is available to authorized users. * Zhiwei Gan
[email protected] 1
College of Architecture and Environment, Sichuan University, Chengdu 610065, China
stability, natural occurrence, and anthropogenic discharge (Ye et al. 2013). Because of the similar ionic radius with iodide, perchlorate can inhibit iodide uptake and seriously interrupt the normal function of the thyroid gland (Domingo 2012; Kirk 2006). The thyroid hormone insufficiencies may potentially affect growth on children and neurodevelopment in infants (Wolff 1998). Therefore, human exposure to perchlorate has been a focus around the world, especially for sensitive groups, such as infants, children, and pregnant woman (Blount et al. 2009; Pearce et al. 2010). In general, diet and drinking water ingestion were regarded as the primary perchlorate exposure pathway for human, while indoor dust was found to make an unexpected contribution (28%) to total daily intakes (DI) for Children (Zhang et al. 2015). Compared with the reference dose (RfD = 700 ng/kg/day) established by the U.S. Environmental Protection Agency (EPA) in 2005, the total DI of perchlorate via diet, drinking, and indoor dust for Chinese people was below the RfD value (EPA 2005; Gan et al. 2015). Natural perchlorate could be formed by atmospheric processes (Catling et al. 2010; Dasgupta et al. 2005; Urbansky et al. 2001) and then came into land and ocean by dry
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deposition and wet deposition. Rajagopalan et al. (2009) obtained a representative concentration of perchlorate (14.1 ± 13.5 ng/L) by investigating on wet deposition over the 3-year period in the United States. Andraski et al. (2014) showed that dry deposition can be a significant contributor of total deposition. But these concentrations of natural perchlorate were always much lower than the detected results in actual environmental samples due to the anthropogenic source. As a primary source for perchlorate, anthropogenic pollution deserves to be mentioned. Perchlorate level was found to increase dramatically in outdoor dust, municipal lake, and air aerosols after fireworks displays (Wilkin et al. 2007; Shi et al. 2011; Yao et al. 2015). Recent studies from Malta compared perchlorate concentration in frequent pyrotechnic activity period to off-festival-period in urban environments, the results inferred that human activities played a pivotal role in perchlorate levels (Vella et al. 2015). Thus, the perchlorate concentration detected during fireworks occurrence or shortly thereafter did not reflect the real situation of perchlorate contaminations to environment. In China, there are more celebration activities in winter than summer, but until now less information about the impact of seasonal variation on the perchlorate concentration could be found. Dust and soil in an outdoor environment could be regarded as carriers of perchlorate contaminations from atmospheric deposition or human activities (Christoforidis and Stamatis 2009; Shi et al. 2011). Therefore, the purposes of this study were: (1) to estimate perchlorate levels in 97 paired soil samples and outdoorindoor dust samples collected from mainland China, and Hong Kong, Macau, and Taiwan; (2) to describe the distribution and analyze the seasonal variation for perchlorate levels in China based on extensive data combined with our previous studies; (3) to shed light on the possible source of perchlorate in indoor-outdoor dust by determining related ions and doing statistical analysis; and (4) to perform human exposure assessment via soil, indoor dust, and outdoor dust in winter, summer, and the whole year.
Materials and Methods Chemicals Perchlorate was purchased from Sigma-Aldrich (St. Louis, MO). The 18O-labeled perchlorate used as internal standard (IS) was obtained from Cambridge Isotope Laboratories (Andover, MA). HPLC-grade methanol and formic acid were obtained from J.T. Baker (Phillipsburg, NJ) and CNW Technologies GmbH (Germany), respectively. The standards of SO42−, NO3−, and Cl− were purchased from Fluka and Sigma-Aldrich, respectively. Milli-Q water was used throughout the study.
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Sample Collection A total of 97 paired outdoor-indoor dust and soil samples were collected in China during April to July in 2015. There are fewer grand festivals and celebrations during this period. The sampling sites covered all regions of China, including mainland, Hong Kong, Macau, and Taiwan. The sampling locations are shown in Fig. 1 and Table S1. According to the geographical conditions, China is divided into northern and southern cities along the Yangzi River. Settled indoor dust was collected from 97 homes using a hand-held brush, paper, and a precleaned glass bottle from the top and bottom of furniture in bedrooms and living rooms. Outdoor dust and soil were sampled around the indoor dust sampling site simultaneously. Four subsamples of the topsoil (0–3 cm) were collected and then mixed to obtain bulk samples. All the hand-held brush, paper, glass bottle, and pp tubes were used only once to avoid contamination. All samples were stored at − 20 °C in the laboratory until analysis.
Sample Preparation Before accurately weighing, the organic material in the sample, such as hair and fur, were removed by forceps, and the pebbles was sieved from the soil samples. Dust sample (50 mg) and soil sample (100 mg) were extracted in 15-mL PP tube with 5 mL of Milli-Q water. Each sample was spiked with labeled internal standard (10 ng/mL), and other extract procedures were the same as our previous study (Gan et al. 2014). To ensure enough sample for ion chromatography measurement, 2 mL of the extraction was diluted with 6 mL of Milli-Q water, then filtered through 0.22-μm filter membrane, and the filtrate was collected.
Instrumental Analysis Perchlorate analysis was performed on LC–MS/MS (Agilent Technologies, USA) using the method represented in our previous study (Gan et al. 2014). The water-soluble ions (SO42−, NO3−, and C l−) were analyzed by ion chromatography (Dionex, USA) using the method described by Qu et al. (2016).
Quality Assurance and Quality Control Quantification was performed with internal calibration, and the internal standard concentration was 10 ng/mL. The limit of quantification (LOQ) for perchlorate in the aqueous solution was 0.15 μg/L corresponding to a signal-to-noise ratio of 10, and the detection limits of S O42−, NO3−, and − Cl are 0.40, 0.80, and 0.35 mg/L, respectively. Matrix-spike
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Fig. 1 Map of the sampling sites
recoveries were determined for each type of the samples with spiking of perchlorate standard in different concentration by triplicate. The high spiked concentration for dust and soil samples was 100 and 10 ng/mL, whereas low concentration was 50 and 5 ng/mL, respectively. Satisfactory recoveries (91.2–111.6%) were achieved for the tested samples, and the results and relative standard deviation (RSD) are shown in Table S2. To ensure accuracy and check for any cross-contamination in reagents and memory effect during pretreatment and instrumental analysis, a standard solution (20 μg/L) of perchlorate, procedural blank, and reagent blank (Milli-Q water) was injected with each batch of 40 samples. None of the target chemical was found in the blanks.
Exposure Evaluation The detailed assessment method and calculation parameters can be found in supplementary materials and Table S3 (Gan et al. 2014). The DI of perchlorate for different age group (children and adults) was calculated in two different scenarios (A and B). Scenario A represents mean exposure level using median perchlorate concentration, mean ingestion, and inhalation rates in evaluation models. In the case of scenarios B, 95th percentile perchlorate concentration and high ingestion and inhalation rates were used, which represents
high exposure level. Many previous studies did exposure assessment to perchlorate only based on a simplex sampling season, which might overestimate or underestimate the real situation. Thus, the average concentration of perchlorate in summer and winter was used for exposure assessment in this study. The total DI of perchlorate was calculated by summing the exposure amount via ingestion, inhalation, and dermal contact.
Statistical Analysis Statistical analyses were conducted using SPSS 21.0 software program. Date sets of perchlorate concentrations and three ions concentrations were normally distributed when natural logarithm transformed (Kolmogorov–Smirnov test), and In-transformed data were used in the parametric statistical analysis. Person correlation coefficient was calculated to assess the potential relationship between the indoor and outdoor dust perchlorate and ions levels. An independent sample t test was applied to analyze the difference between winter and summer seasons in both soil and outdoor dust perchlorate concentrations. The paired-sample t test was used to analyze the difference in perchlorate levels among the paired soil, indoor, and outdoor dust samples. Statistical tests were considered significant when p 0.05) in perchlorate concentrations between these two areas, and the same result could be found in outdoor samples that were collected in winter (Table S4) (Gan et al. 2014). The median concentration of perchlorate in outdoor dust samples were approximately 1.3 times lower than those in Malta (Vella et al. 2015), where numerous activities celebrated with fireworks. In general, 12 and 21 of the 97 outdoor dust samples detected at high concentrations (> 100 mg/kg) and at
Fig. 2 Nonparametric probability distribution of the perchlorate levels in the soil,outdoor dust and indoor dust samples in summer (the top and bottom of each box represent 75th and 25th percentiles, respectively; the top and bottom of each whisker represent 90th and 10th percentile, respectively; line across inside of each box represents median; the small square represents the mean value). A: Soil in Northern (n = 41); B: Soil in Southern (n = 56); C: Outdoor dust in Northern (n = 41); D: Outdoor dust in Southern (n = 56); E: Indoor dust in Northern (n = 41); F: Indoor dust in Southern (n = 56)
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relatively low concentrations (
