Three-year field experiment on the risk reduction, environmental merit, and cost assessment of four in situ remediation technologies for metal(loid)-contaminated agricultural soil

https://doi.org/10.1016/j.envpol.2020.115193Get rights and content

Highlights

  • Turnover and attenuation data show the highest efficiency of risk reduction.

  • Phytoextraction costs the most due to expensive sporelings of hyperaccumulator.

  • Remediation target set by national food standard doesn’t meet the risk reduction requirement.

Abstract

The traditional assessment of agricultural soil remediation technologies pay limited attention to sustainability and only considers the decrease in contaminant concentrations and cost, even though the sustainability of these technologies has been prioritized. This 3-year field study comprehensively assessed the sustainability of four commonly used agricultural soil remediation technologies in terms of metal(loid) removal efficiency, environmental merit, and cost. The farmland was contaminated by previous sewage irrigation with excessive amounts of As, Cd, and Pb. The four selected remediation technologies used were phytoextraction, intercropping of hyperaccumulators and cash crops, chemical immobilization, and turnover and attenuation (T&A). A risk reduction–environmental merit–cost model was utilized to compare these four technologies. Results showed that T&A reduced the health risks posed by excess metal(loid)s by ∼47% and yielded the highest risk reduction and lowest cost. Phytoextraction achieved the highest environmental merit because it produced the least interruption to the environment. A simplified assessment frame for soil remediation technology was established from a retrospective aspect using data from a real soil remediation project. Environmental merit is a less considered factor and more difficult to quantify than risk reduction or cost, thus requiring increased attention.

Introduction

Soil contamination with heavy metal(loid)s is a major environmental issue worldwide. In Europe, approximately 1,170,000 pieces of potentially contaminated soils have been identified, in which heavy metal(loid)s and mineral oil contribute to approximately 60% of soil contamination (Panagos et al., 2013). In the United States, 1335 sites are on the Superfund National Priorities list of pollution hotspots (USEPA, 2020). In China, the national survey on soil environmental quality found that 16.1% of the investigated soil was contaminated, and inorganic contamination accounted for 82.8% (MEEP and MNRP, 2014).

Farmland contamination by heavy metal(loid)s poses a serious threat to human and environmental health because of the non-biodegradability, toxicity, persistence, and bioaccumulation of heavy metal(loid)s in food chains (Gong et al., 2018). Heavy metal(loid)s are difficult to remove once they enter soil (Zhou et al., 2018). Therefore, feasible soil remediation technologies have been established. These technologies can be classified into two categories: the first one decreases heavy metal(loid) concentrations in soil, while the second one transforms heavy metal(loid)s to less harmful forms (Ashraf et al., 2019).

Phytoextraction and turnover and attenuation (T&A) are two most commonly used technologies in the first category. Phytoextraction uses hyperaccumulators to extract heavy metal(loid)s from soil and then gradually remove them by harvesting metal(loid)-enriched aboveground biomass (Luo, 2009). Phytoextraction is easy to operate but requires long remediation time and depends on the regional adaptability of hyperaccumulators. T&A mixes contaminated topsoil with clean soil from deeper layers to rapidly and easily lower the total concentration of contaminants; however, this technology is costly and may negatively affect crop growth (Chen and Chiou, 2008). Phytoextraction ceases income generation during the remediation period; thus, hyperaccumulator and cash-crop intercropping emerged as an alternative to remove contaminants from soil while ensuring safe production of cash crops (Wang et al., 2015). Intercropping also requires a long remediation period and suffers from the other shortcomings of phytoextraction. Chemical immobilization belongs to the second category. This method does not remove metal(loid)s but reduces the bioavailable fraction of heavy metal(loid)s. It is currently the most widely used technology because of its low cost and easy operation (Wang et al., 2019). However, this method is limited by its variable efficiency and the need for long-term monitoring (Shen et al., 2018).

Considering the advantages and disadvantages of existing farmland remediation technologies, the comparison of different technologies and the subsequent decision-making become increasingly difficult tasks (Agostini et al., 2009). Previous comparison of soil remediation technologies often focused on the cleanup level, the time required for remediation, and cost (Cappuyns et al., 2011). Even though these technologies aim to improve the environmental quality, they could bring in negative environmental effects during remediation practice. The concept of a sustainable remediation strategy for contaminated sites (mostly industrial) was recently proposed to focus on the negative environmental effects brought by soil remediation (Rizzo et al., 2016). However, the environmental merits of agricultural soil remediation technologies are rarely considered. Assessments that consider risk reduction, environmental merits, and cost are even less reported.

Hou et al. (2018) first proposed a framework of sustainability assessment for agricultural soil remediation technologies by reviewing the current agricultural soil remediation practices. Their study was innovative but only compared the sustainability of five different sites instead of different soil remediation technologies. They conducted an in-depth life cycle assessment of two soil remediation alternatives (biodegradation and stabilization, landfilling and importing topsoil). However, some most commonly used agricultural soil remediation technologies, such as phytoextraction, were not included. When developing new metal(loid) immobilizers or chelators, the environmental effects of soil amendments are recently considered (Gluhar et al., 2020; Wang et al., 2020), but the field-scale assessment and comparison of different agricultural soil remediation technologies remains few. A comprehensive assessment could provide essential parameters for further decision-making in farmland remediation technologies and indicate the future research direction of soil remediation technologies.

In this study, a comprehensive assessment of most commonly used in situ agricultural soil remediation technologies was conducted on the basis of the project data from a 3-year field experiment. These technologies included phytoextraction, intercropping, chemical immobilization, and T&A in China, Taiwan, and Japan (Wang et al., 2019). Such retrospective assessment is rarely reported but hypothesized to produce varied results from the prospective assessment.

The risk reduction–environmental merit–cost (REC) model proposed by Beinat and van Drunen (1997) was employed in the present study. The output of REC is a set of three indices for each cleanup alternative: risk reduction, environmental merit, and costs. These indices summarize the overall performances of each soil remediation alternative. The REC system has the advantages of being a systematic analysis of the pros and cons of remediation alternatives that highlight its strengths and weaknesses and streamline the multiple factors involved in cleanup management.

This study aimed to (1) compare the risk reduction, environmental merit, and cost in the four mainstream farmland remediation technologies from a retrospective aspect on the basis of the project data and (2) establish a feasible assessment frame for agricultural soil remediation technologies considering the three aspects.

Section snippets

Field site and experimental setup

Field experiment was conducted in a contaminated farmland (115° 45′ 27″–115° 45′ 30″ E, 38° 49′ 1″–38° 49′ 5″ N) in Anxin County, Baoding City, Hebei Province, Northern China (Fig. 1). Sewage irrigation was performed in this area in the early 1960s because of serious water shortage and stopped in the 2010s after food safety risks were identified. The main contaminant is As according to preliminary investigations (Yang et al., 2018).

Ten soil profiles were sampled randomly before the experiment

Total concentrations of metal(loid)s in soil

The results showed that the soil in the experimental site was mostly contaminated with As (40.5 mg kg−1) compared with the risk screening value for soil contamination of agricultural land (MEEP, 2018). The As contamination degree was nearly twice the recommended value (Table S1). The Cd and Pb concentrations in the studied site exceeded the background values (Cd: 0.002–0.474 mg kg−1; Pb: 19.93–35.89 mg kg−1) of the experimental area (CEMS, 1990; Lin, 1984) but did not exceed the risk-screening

Discussion

Agricultural soil remediation technologies have developed rapidly (Tang et al., 2016), but the field-scale comparison of different soil remediation technologies under the same environmental circumstances is still few. The current study compared the risk reduction, environmental merit, and cost of four widely used agricultural land remediation technologies on the basis of a real soil remediation project.

Conclusion

In this study, the 3-year field comparison of four soil remediation technologies demonstrated that T&A was the most effective technology in the experimental area. This technology could efficiently decrease As at a low cost and be considered the most appropriate technology when its requirements are satisfied. Fertilizer is necessary to support crops. Phytoextraction was the most expensive yet the most environment-friendly technology that could continuously remove As and Pb in soil. REC could be

CRediT authorship contribution statement

Xiaoming Wan: Conceptualization, Methodology, Writing - original draft. Mei Lei: Project administration, Funding acquisition, Writing - review & editing. Jun Yang: Investigation, Writing - review & editing. Tongbin Chen: Supervision, Writing - review & editing.

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.

Acknowledgment

Financial support was provided by the Innovation Academy for Green Manufacture of the Chinese Academy of Sciences(Grant No. IAGM-2019-A16-5), the National Key Research and Development Program of China (Grant No. 2017YFD0800900), the Guangxi Science and Technology Major Project (Grant No. GuiKeAA 17204047-2), and the Youth Innovation Promotion Association of the Chinese Academy of Sciences (No. 2017075).

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