Heavy metals in food crops, soil, and water in the Lihe River Watershed of the Taihu Region and their potential health risks when ingested
Graphical abstract
Introduction
Heavy metal environmental pollutants of all kinds have received much attention in recent years because of their persistence, bioaccumulation, and high toxicity (Liu et al., 2010, Liu et al., 2017, Ma et al., 2016, Singh and Kumar, 2017, Xu et al., 2016). Some heavy metals are essential for biological systems in the human body, acting as both structural and catalytic components of proteins and enzymes, but may be toxic when safe concentrations are exceeded. These include Zn, Cu, and Ni. Other metals, such as Cd, Pb, and Cr, are harmful contaminants even at low concentrations (Bermudez et al., 2011, Gall et al., 2015, Zheng et al., 2015).
Generally, the consumption of foodstuffs and water, as well as the ingestion of soil particles, from contaminated areas can contribute to human exposure to heavy metals. Studies have demonstrated that, except for occupational exposure, dietary intake through contaminated foods has become the main route of heavy metal intake by humans (Bermudez et al., 2011, Ji et al., 2013, Khan et al., 2008). However, the contamination of drinking water with heavy metals in some heavily polluted areas, such as mining areas, metal industry clusters, and so on, also significantly affects human health (Brännvall et al., 2016, Liu et al., 2010). The oral ingestion of heavy metals in soil cannot be ignored and may also pose a health risk to humans. For example, soil ingestion has been implicated in a number of case studies in which it was the main source of Pb exposure in children with elevated blood Pb levels in some areas (Hu et al., 2011, Kumar et al., 2007, Laidlaw and Filippelli, 2008).
In recent years, heavy metal pollution has become increasingly serious (Ran et al., 2016, Singh and Kumar, 2017, Yu et al., 2017). The effective assessment of the health risks to residents is imperative, so that any adverse effects can be avoided to the maximum extent. Although the health risk of heavy metals has been extensively studied (Cai et al., 2015, Chen et al., 2015, Liu et al., 2017), most researchers have only considered the potential health risks of their ingestion via a single pathway (Ahmed et al., 2015, Huang et al., 2008, Lei et al., 2015). Little attention has been paid to the potential integral health risk resulting from ingesting food or soil, and drinking water. Consuming two important cereal crops (rice and wheat), drinking water, and ingesting soil are all important routes by which heavy metals can enter the human body through the mouth. Previous studies have simply calculated the health risk values at specific sampling points, or have averaged the health risk values for different sampling points in a study area (Ahmed et al., 2015, Huang et al., 2008), but no prediction of the health risk posed in a whole study area has been made. Therefore, the IR posed by these four pathways and the proportion of the accumulative risk (AR) posed by each pathway contributing to IR in the study area were quantified. We also predicted the IR spatial distribution pattern in the whole study area using the inverse distance weighting method.
The primary objectives of this study were: (1) to assess the heavy metal pollution levels in the soil, wheat, rice, and drinking water in the Lihe River watershed; (2) to calculate the hazard quotient (HQ) for individual heavy metals, the AR for multiple heavy metals, and the IR for the local residents caused by the ingestion of rice, wheat, soil, and water; and (3) to predict the values of HQ, AR, and IR throughout the study area and analyze their spatial distribution patterns by the inverse distance weighted interpolation method. The results of our study should provide insight into the pollution levels of heavy metals and health risk assessment of human in the Lihe River watershed, and serve as a basis for comparison to other regions both in China and worldwide.
Section snippets
Description of the sampling sites
The sampled zone is called the Lihe River watershed, and is located to the west of Taihu Lake. Taihu Lake is the largest lake in the China Eastern Coastal Area and the second largest freshwater lake in China. It acts as the control center of regulation and allocation of water resources, and has many functions such as flood protection, water supply, shipping, aquaculture, tourism, and climate regulation in the Taihu Basin. However, the Taihu Basin is located in the south of the Yangtze River
Heavy metals in tap water samples
The heavy metal concentrations in the tap water at each site are listed in Table S3 of supplementary materials. The concentrations of Pb at six sampling sites and Cd at three sampling sites were unavailable because their concentrations were below the detection limit. Only the Zn concentration in one sample exceeded the standard limit set by the Drinking Water Health Standards (GB 5749-2006), suggesting that the drinking water for the local inhabitants is safe and poses no risk to the health of
Conclusions
The average IR values for the heavy metals to which local residents in the Lihe River watershed are exposed via the ingestion of rice, wheat, soil, and water were 3.53 for adults and 3.91 for children, indicating that these adults and children may experience adverse health effects. The spatial distribution patterns of the IR values for the different exposed populations in the study area were high in the eastern and middle parts, with a maximum value > 5, and low in the western part, with a
Acknowledgements
This work was supported by Key Technology Support Program of Jiangsu Province (grant number BE2015708).
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