Agricultural activities impact on soil and sediment fluorine and perfluorinated compounds in an endemic fluorosis area

https://doi.org/10.1016/j.scitotenv.2020.144809Get rights and content

Highlights

  • Agricultural activities resulted in an elevation of soil fluorine and ΣPFCs levels.

  • PFNA, PFTeDA and PFOA were the dominant PFCs with high concentrations in the soils.

  • Long chain PFCs were dominant in soil, but opposite in sediment.

  • PFCs contributed little to soil total fluorine and their correlation was weak.

  • Soil organic matter had a significant positive correlation with PFBA and PFPeA.

Abstract

Perfluorinated compounds (PFCs) are organo-fluorine compounds which have been identified at significant levels in soils due to their widespread usage in industrial and commercial applications. However, few studies are available regarding the occurrence of PFCs in the environment of endemic fluorosis areas. To address the issue, soils collected from an endemic fluorosis area of southwestern China were analyzed for the distribution of fluorine and 21 kinds of PFCs. The average water-soluble fluorine concentration in cultivated soil (4.87 mg kg−1) was significantly higher than that in uncultivated soil (3.15 mg kg−1), which mainly ascribed to the utilization of fluorine-enriched fertilizers during agricultural practices. Concentrations of ΣPFCs in all soils ranged from 0.508 to 6.83 ng g−1, with an average of 2.81 ng g−1, dominated by perfluorononanoic acid (PFNA) and perfluorooctanoic acid (PFOA). Highest ΣPFCs was found in the soil samples collected from cropland with intensive agricultural activities. Long-chain PFCs, including four perfluoroalkylcarboxylic acids (PFCAs, C ≥ 8) and one perfluoroalkylsulfonic acids (PFSAs) (perfluorooctane sulfonate (PFOS), C8), exhibited high levels in soils, probably due to their higher hydrophobicity and lower water-solubility than short-chain PFCs. While in sediments, short-chain PFCAs were the dominant compounds. Based on correlation analysis, the relationship between total fluorine and PFCs was insignificant, and soil organic matter was a relevant factor affecting PFCs distribution in soils. This study is expected to present a more comprehensive information about fluorine contamination under the influence of agricultural activities in an endemic fluorosis area.

Introduction

Perfluorinated compounds (PFCs) are anthropogenic organic pollutants which have been widely used in industrial and commercial applications such as surfactants, lubricants, fire retardants, wetting agents and polymer additives (Xu et al., 2020). Currently, PFCs are ubiquitously detected in various environmental compartments and biological samples, including surface water (Pan et al., 2018), groundwater (Bräunig et al., 2017), sediment (Lin et al., 2020), soil (Brusseau et al., 2020), atmosphere (Zhao et al., 2020), as well as wildlife (Jouanneau et al., 2020) and human body (Kim et al., 2020). Due to the chemical inertness and resistance to hydrolysis, enzymatic degradation, and oxidation processes of PFCs in natural environments, they may produce long-term and extensive harm to human health and the environment, which have received considerable scientific and public attention in recent years (Du et al., 2014; Lu et al., 2014). Environment studies about PFCs mainly concentrated on low-molecular-weight surfactants perfluoroalkylcarboxylic acids (PFCAs) and perfluoroalkylsulfonic acids (PFSAs), in which all the carbons are bonded to fluorine atoms, and composing of homologous series of molecules with varied length of carbon chain (Castiglioni et al., 2015). In particular, great attention has been given to the long-chain PFCAs and PFSAs, which are highly persistent and capable of bio-accumulation and biomagnification through the food chain, exerting adverse consequences on animals and humans (Jin et al., 2015; Shi et al., 2018; Li et al., 2019).

As an essential component of terrestrial ecosystems, soil has become a prominent sink for PFCs (Cai et al., 2019; Lan et al., 2020). So far, most of the existing researches on soil PFCs mainly conducted in the soils affected by nearby point sources, such as fluorochemical manufacturing park (Liu et al., 2019; Fang et al., 2020), wastewater treatment plants (Washington et al., 2010; Shigei et al., 2020), and firefighting training ground (McGuire et al., 2014; Baduel et al., 2015). Different with point source contaminated soils, the soils in remote areas are also susceptible to the effects of non-point sources of PFCs, such as agriculture land uses where pesticides have been used or recycled wastewater has been applied for irrigation (Li et al., 2018). The application of biosolids in agricultural practices is a critical way for PFCs to enter the soil (Chen et al., 2020). Greater levels of perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were observed in samples collected near areas of intensive agricultural activities where a large amount of pesticides are applied every year (Wang et al., 2011). Besides, the employment of sewage sludge as manure in some agriculture areas can be a direct source of PFCs contamination in soils (Castiglioni et al., 2015). The PFCs in farmland soils can migrate from soil to crops through roots and to invertebrates by direct contact, posing a serious environmental threat to wildlife and humans (Cai et al., 2019; Liu et al., 2019). Therefore, it is critical and valuable to investigate the PFCs concentrations in farmland soils for health risk control.

Exposure to high levels of fluorine can cause health impacts called fluorosis, which remains a prominent problem in many regions such as Afghanistan, Japan, Iraq, Turkey and India (Singh et al., 2018). China is also a high incidence area of endemic fluorosis, with more than 200 million people being currently threatened by fluorosis (Wang et al., 2019a; Gan et al., 2021). It has been reported that high fluorine regions in southwestern China overlap with phosphorus-containing strata regions (Liu et al., 2020b). As a consequence of phosphate rocks extraction, the fluorine content in the local environment is relatively high. Moreover, the volatilization and transfer of fluorine in thriving phosphate chemical production process often lead to a high level of fluorine in the final produced fertilizers (Yu et al., 2020).The utilization of these fluorine-enriched fertilizers in endemic fluorosis areas significantly increased the fluorine levels in surface soil (Wang et al., 2019b). Therefore, the fluorine contamination in soils is co-affected by natural and anthropogenic sources. Unlike soil fluorine, PFCs are a family of synthetic compounds, which mainly derive from anthropogenic factors in various consumer products during industrial and agricultural processes. Previous studies focused merely on the distribution of inorganic fluorine response to agricultural activities in endemic fluorosis areas, including the total fluorine and water-soluble fluorine (Wang et al., 2019c; Yang et al., 2020), but did not identify whether the use of the high fluorine-enriched fertilizers and other agricultural practices would lead to the occurrence of PFCs in farmland soil. Therefore, a deeper insight into the distribution of the PFCs in soils under the influence of agricultural activities in endemic fluorosis area is necessary. In addition, we are urgently want to know whether there is a correlation between the concentrations of total fluorine and PFCs in soil media.

The present study investigated the contamination of fluorine and 21 kinds of PFCs in agricultural soils and sediments near farmland in an endemic fluorosis area in southwest China. The objectives were to (1) determine the levels and distribution of total fluorine and water-soluble fluorine in soils and sediments under the influence of agricultural activities; (2) characterize the composition and distribution of PFCs in farmland soils as well as sediments; and (3) analyse the correlation among surface soil pH, organic matter (OM), total fluorine, water-soluble fluorine and PFCs. The results of our study might be used to determine potential sources of fluorion in soil and provide references for further management and remediation of contaminated soil in endemic fluorosis areas.

Section snippets

Study area and sample collection

The study area, Shifang City, is located in Sichuan Province, Southwestern China (Fig. 1). The average annual temperature and rainfall of Shifang are 16.8 °C and 338 mm in 2018, respectively, and 77% of the rainfall is in summer (SMPG, 2019). Soils in Shifang City are mainly classified as alluvial soil according to Chinese Soil Genetic Classification System, and there are calcareous alluvial soil, gray-brown alluvial soil and purple alluvial soil in this region. The dominant texture of the

Fluorine in soils

In uncultivated soils, the total fluorine concentration ranged from 416 to 731 mg kg−1, with arithmetic mean and median values of 542 and 538 mg kg−1 (Fig. 2a). The total fluorine concentration in cultivated soils was in range of 360–2001 mg kg−1, with arithmetic mean and median values of 729 and 621 mg kg−1, respectively, showing greater variation of total fluorine concentration in cultivated soils than uncultivated ones, though no statistically significant difference (p > 0.05) was observed

Conclusions

The occurrence of total fluorine, water-soluble fluorine and PFCs in soils and sediments was investigated in an endemic fluorosis area of southwestern China. The level of soil water-soluble fluorine appeared significantly higher in cultivated soils than that in uncultivated soils, suggesting that agricultural activities had a remarkable impact on bioavailable fluorine in farmland. The application of phosphate fertilizer or phosphorous compound fertilizer with high fluorine content was an

CRediT authorship contribution statement

Chun-dan Gan: Conceptualization, Investigation, Methodology, Validation, Writing – original draft, Writing – review & editing. Zhi-wei Gan: Conceptualization, Methodology, Writing – review & editing, Resources, Supervision. Si-fan Cui: Investigation, Resources, Methodology, Supervision. Rui-jun Fan: Investigation, Methodology, Validation. Yuan-zhou Fu: Investigation, Resources, Supervision. Mu-yi Peng: Data curation, Investigation, Resources. Jin-yan Yang: Investigation, Methodology,

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the Strategic Cooperation Project Between Sichuan University and Yibin Municipal Government [2019CDYB-19] and the Chengdu Science and Technology Project [2018-YF05-00760-SN].

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