Nature based solutions for contaminated land remediation and brownfield redevelopment in cities: A review

Science of the Total Environment 663 (2019) 568–579

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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Nature based solutions for contaminated land remediation and brownfield redevelopment in cities: A review Yinan Song a, Niall Kirkwood b, Čedo Maksimović c, Xiaodi Zhen d, David O'Connor a, Yuanliang Jin a, Deyi Hou a,⁎ a

School of Environment, Tsinghua University, Beijing 100084, China Graduate School of Design, Harvard University, 48 Quincy Street, Cambridge, MA 02138, USA Department of Civil Engineering, Imperial College, London SW7 2AZ, UK d School of Architecture, Tsinghua University, Beijing 100084, China b c

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• Reviewed pros and cons of nature based solution (NBS) in contaminated land remediation • Summarized contaminant removal and risk reduction by nature based technologies • Summarized planning and redevelopment methods integrating natural components • Additional research is needed to enhance the feasibility or efficacy. • Provided policy implications and suggestions for future studies

a r t i c l e

i n f o

Article history: Received 22 December 2018 Received in revised form 25 January 2019 Accepted 26 January 2019 Available online 28 January 2019 Editor: Damia Barcelo Keywords: Nature inspired NBS City planning Clean up Reclamation Soil pollution

a b s t r a c t Urban industrialization has caused severe land contamination at hundreds of thousands of sites in cities all around the world, posing a serious health risk to millions of people. Many contaminated brownfield sites are being left abandoned due to the high cost of remediation. Traditional physical and chemical remediation technologies also require high energy and resource input, and can result in loss of land functionality and cause secondary pollution. Nature-based solutions (NBS) including phytoremediation and conversion of brownfield sites to public greenspaces, holds much promise in maximizing a sustainable urban renaissance. NBS is an umbrella concept that can be used to capture nature based, cost effective and eco-friendly treatment technologies, as well as redevelopment strategies that are socially inclusive, economically viable, and with good public acceptance. The NBS concept is novel and in urgent need of new research to better understand the pros and cons, and to enhance its practicality. This review article summarizes NBS's main features, key technology choices, case studies, limitations, and future trends for urban contaminated land remediation and brownfield redevelopment. © 2019 Elsevier B.V. All rights reserved.

1. Introduction

⁎ Corresponding author. E-mail address: [email protected] (D. Hou).

https://doi.org/10.1016/j.scitotenv.2019.01.347 0048-9697/© 2019 Elsevier B.V. All rights reserved.

The United Nations 2030 Agenda for Sustainable Development calls for “making cities and human settlements inclusive, safe, resilient, and sustainable” (Sustainable Development Goal [SDG] 11). World leaders have adopted the New Urban Agenda, which demands cleaner cities,

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less greenhouse gas emission, and more green public space (UN, 2018). Striving toward this goal, a new concept known as nature based solutions (NBS) has drawn much attention in recent years, as evidenced by growing number of academic publications (see Fig. 1). The number of academic literature published each year incorporating “nature based solutions” has increased by 1200% over the last 5years. The European Commission Research Council devoted €185 million, for the period of 2014 to 2020, on research and development of NBS in its flagship research program Horizon 2020 (EPRS, 2017). An editorial article published in Nature magazine stated that “the concept it represents is of vital and urgent significance” and compared this emerging term to “sustainable development” and “biodiversity” (Nature, 2017). NBS refers to actions that are “inspired by, supported by, or copied from nature” (van den Bosch and Sang, 2017). The European Commission defines NBS as “solutions that are inspired and supported by nature, which are cost-effective, simultaneously provide environmental, social and economic benefits and help build resilience. Such solutions bring more, and more diverse, nature and natural features and processes into cities, landscapes and seascapes, through locally adapted, resource-efficient and systemic interventions” (European Comission, 2017). NBS may offer environmental, social, and economic benefits for a wide variety of applications. Many existing studies have focused on frameworks and theoretical knowledge (Faivre et al., 2017; Raymond et al., 2017). More knowledge about its actual implementation is needed in order to further direct this concept (Nesshover et al., 2017). The term NBS is traditionally used among the nature conservation community in natural environment (forest, river basins, wetlands) which then “extrapolated” to urban environment in the narrow area of communal urban gardens (van der Jagt et al., 2017). Nature based solutions offers great potential for application in the field of contaminated land remediation and brownfield redevelopment. This is an area of huge significance. For instance, in the United States, there are 450,000–600,000 registered brownfield sites (USEPA, 2017a), with the actual number likely to be closer to 1 million; in Europe, ~342,000 contaminated sites have been identified (EEA, 2014); and, in China, there are tens of millions of hectares of contaminated land that need to be managed (Hou and Li, 2017; MEP, 2014). Sites contaminated with potentially toxic elements and organic compound pose a risk to human health and the wider environment (Jin et al., 2019; Peng et al., 2019; Zhang et al., 2019). Conducting remediation on such a large scale with traditional technologies that heavily depend on chemical reagents, thermal energy, and electricity, renders huge social, economic, and environmental costs (Hou and Al-Tabbaa, 2014; O'Connor and Hou, 2018; USEPA, 2008). Due to the high cost associated with remediation activities, some brownfield sites can remain

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vacant and derelict for decades (Donaldson and Lord, 2018). Many governments have policies to promote brownfield redevelopment. For instance, in 2016 the UK government launched a pilot program of granting planning permissions at 90% of suitable brownfield sites, to facilitate the building of 1 million new homes (MHCLG, 2016). Under the Paris Agreement, each country has ambitious goals on greenhouse gas (GHG) emission reduction. Developing brownfield sites and vacant urban land holds great promises for global climate change mitigation. A study conducted in San Francisco indicates that brownfield redevelopment offers the mitigation equivalent to 14% of the city's annual GHG emissions (Hou et al., 2018b). Using nature based remediation technologies, such as phytoremediation and bioremediation, can offer a great variety of benefits, ranging from less energy usage and higher material efficiency to increased resilience to global environmental change (Chi et al., 2017; Liang and Wang, 2017). However, these technologies have only been used where they offer project cost savings. The wider socioeconomic and environmental benefits have not always been included in technology appraisal, thus limiting their utilization potential. Emphasis was often placed on contaminant treatment efficiency, lacking a holistic approach that maximizes the overall net benefits in achieving social, economic, and environmental sustainability (O'Connor et al., 2018a; Zhang et al., 2018). The emerging concept of NBS offers an umbrella framework for the assessment and promotion of this group of greener technologies. The many intangible benefits of these technologies can thus be manifested. Different types of nature based solutions can be suitable for various types of contaminants and site conditions. To promote the usage of NBS in contaminated site remediation and redevelopment, it is imperative to provide systematic guidance in selecting appropriate technologies for specific sites, and to offer a technological means for determining optimum design parameters and the integration of these solutions into broader planning framework. However, to our knowledge, no existing studies have systematically identified technological solutions fitting with the definition of NBS for the purposes of contaminated land remediation and brownfield site redevelopment. The present review intends to summarize both traditional and emerging technologies, which can not only meet the goal of site cleanup and redevelopment, but also realize the benefits of NBS. 2. Social, economic, and environmental benefits of NBS This section describes the social, economic, and environmental benefits of nature based remediation technologies. 2.1. Social benefits

Fig. 1. Temporal trend of academic literature on NBS, based on Google Scholar search of the full term “nature based solutions”.

NBS at brownfield sites can provide multiple social benefits. Though theses social benefits are hard to quantify, the following aspects can be summarized. Firstly, NBS can increase human well-being (Faivre et al., 2017) by providing space for play and recreation, thus improving people's physical and psychological states (O'Brien, 2005). Large redeveloped brownfield sites like the Sydney Olympic Park, have been used to host a variety of social activities, such as schooling in cultural heritage and conservation, cycling and walking, bird watching, and art events (Davidson, 2013). NBS can improve air quality, reduce noise and the heat-island effect, thus benefiting public health. Furthermore, if tree species, used in brown filed field remediation and redevelopment are selected and positioned, their beneficial effects properly designed, and quantified, additional multifunctional benefits can be achieved such as adiabatic cooling, energy efficiency improvements, creating space for socializing, pluvial flood reduction etc. The promotion of NBS was found to be favored by European citizens: 83% of survey participants were in favor of the EU's policy in promoting NBS (Faivre et al., 2017).

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Creating new green space for recreational purposes in urban areas can also enhance social equality by improving environmental conditions for people living in deprived communities (Mitchell et al., 2015). Land contamination has strong implications for environmental justice: such sites often represent locally unwanted land uses, and they are often associated with deprived/neglected communities where disadvantaged or marginalized people reside. The systemic cleanup and environmental upgrade of these sites could create new jobs and reduce social/behavioral problem, thus greatly improve the long-term livability and environmental quality of such local communities. For instance, as sites become remediated and redeveloped, often high-end commercial and residential buildings with green spaces are built, leading to wealthier residents moving in and the local community being displaced. This so-called “green gentrification” represents a concern for environmental justice (Anguelovski, 2016). A holistic approach to remediation with prudent decision-making based on green and sustainable remediation principals may help provide nature based solutions that work for all. 2.2. Economic benefits Ecosystem adaptation can help improve the resilience of urban systems, thus offering socioeconomic benefits in the long term. Traditional real estate developments, including brownfield sites, often narrowly focus on site-specific engineering concerns (e.g. remediation and construction) and the marketability of on-site properties. New developments are often enclosed by fences or buffer zones that prevent the spillover of market or financial benefits to surrounding properties. This design strategy can reduce the overall societal benefit of new developments. The use of NBS and the relevant “blend-in” concept of interactions with neighborhood can better balance the social and economic needs of the various different stakeholders, resulting in an integration of the new development with surrounding communities and a healthier local economy (Dagenhart et al., 2006). Further strategies can be used to enhance the economic viability of NBS. For instance, in phytoremediation, which makes use of the uptake, accumulation and breakdown of contaminants in plants, seedlings, grasses or shrubs may only be planted at strategically selected small areas, which can nurse subsequent plant succession in surrounding areas (Adamo et al., 2015). Many countries have put in place various financial and regulatory incentives to encourage contaminated brownfield regeneration (Thornton et al., 2007). For example, England had 79% of all new dwellings built on previously used land in 2008, driven by a public policy mandating that 60% of new housing developments should be built on brownfield land (DCLG, 2009). Converting large spaces of brownfield land to greenspace by NBS can also be effective in promoting urban regeneration in declining former industrial centers

(Hou et al., 2015), which renders huge economic benefits due to increased employment opportunities and local tax revenues. It should be noted that to date, very few cost benefit analysis have been conducted on NBS (Faivre et al., 2017). The cost effectiveness of NBS in general requires more research. However, for specific technological solutions that can meet the NBS definition, and have been used in a contaminated land remediation and brownfield redevelopment setting; there is a wealth of knowledge about their economic benefits. 2.3. Environmental benefits Life cycle assessment (LCA), one of the most widely used tool for the environmental impact assessment, has generally shown NBS to have lower environmental footprints than traditional methods for brownfield remediation such as chemical or thermal techniques. For example, in situ bioremediation, which takes advantage of the contaminant degrading ability of certain microorganism cultures, renders significantly lower global warming potential, air pollutant emissions, and ecotoxicity under most hydro-geochemical conditions than physical or chemical groundwater remediation techniques such as pump and treat or chemical oxidation (Hou et al., 2014a). Other NBS, such as phytoremediation (Hou et al., 2018a), stabilization with biochar (Hou et al., 2016; O'Connor et al., 2017), and nanoremediation based on green synthesis (Zhang et al., 2018) also tend to have lower environmental footprints due to lesser consumption of materials and energy, as well as often incorporating carbon sequestration potential. Redevelopment of sites with NBS can often be effective at protecting, providing or enhancing ecological features. Many brownfield sites lack meaningful ecological habitats, despite the ecological risk posed by contaminants often being low; however, large NBS sites can form valuable ecological habitats, such as wetlands, breeding areas, and designated wilderness areas (Fishman and Reinert, 2000), providing habitats for wildlife production and protection (Davidson, 2013). NBS can also render resilient urban infrastructure that mitigate climate induced impacts (Kabisch et al., 2016). Moreover, green infrastructure strategies can help regulate storm water runoff and reduce the energy footprint of urban sewer systems, reduce negative impact of UHI (urban hear islands, reduce noise and air pollution, enhance biodiversity etc. 3. Contaminant removal and risk reduction by nature based technologies This section discusses some of the social, economic, and environmental benefits of using nature based remediation technologies and nature based brownfield redevelopment methods for contaminant removal and risk reduction (Table 1).

Table 1 Social, economic, and environmental benefits of using nature based remediation technologies and nature based brownfield redevelopment methods. Nature based remediation technologies

Advantages

Disadvantages

Social benefits

Economic benefits

Environmental and ecological benefits

Constructed wetland

Improve aesthetics; create meeting/socializing space

Enhance flood control; ease drainage system burden;

Phytoremediation

Improve aesthetics; bring in health benefit;

Enhance flood control;

In-situ bioremediation

Fast removal of contaminants; Reduce use of toxic chemicals; fast removal of contaminants; Eliminate waste; improve aesthetics;

Lower capital expenditure;

Create a healthy ecosystem; low life cycle Challenges in operation; Slow time environmental footprint; reduce flood risk period for remediation; require space Slow contaminant removal or Create a healthy ecosystem; improve air sequestration quality; low life cycle environmental footprint; Low life cycle environmental footprint; Potential toxic byproducts;

Lower operating expenditure;

Low life cycle environmental footprint;

Difficulty in large-scale manufacturing;

Lower operating expenditure; enhance flood control; dust suppression;

Low life cycle environmental footprint; improve air quality;

Risks in contaminants release with time goes and soil condition change

Green synthesis for nanoremediation Stabilization with biochar, green mulch and compost

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3.1. Constructed wetlands

3.2. Phytoremediation

Urban areas, including brownfield sites, are often covered with impervious hard standing surfaces, which inhibit rainfall infiltration, thus increasing peak storm water runoff, and higher flooding risk. Constructed wetlands can incorporate both zones of dense vegetation and zones of deep open water, thus allowing both contaminant degradation by plant-microbial systems and water retention (Kadlec and Wallace, 2008). Constructed wetlands at brownfield sites are suitable for treating groundwater and surface water contaminated by low concentrations of easily biodegradable contaminants (USEPA, 2006). Contaminants that are more recalcitrant may also be treated, depending on the types of substrates used, (e.g. limestone, compost, gravel), and the chemical and microbial processes involved (e.g. anaerobic or aerobic processes). Constructed wetlands can provide successful NBS at brownfield sites when properly incorporated into the overall remedial design and aspects of site planning and landscape design. In Brisbane, Australia, two constructed wetlands were created in a brownfield setting, combining boardwalks, pathways, and signage posts (Greenway, 2017). Converted from concrete drainage channels, the constructed wetlands were populated with water lilies, aquatic creepers, and submerged pondweed (Fig. 2). The NBS provided a number of environmental, social, and economic benefits, including: 1) rainwater harvested by the wetlands was reused for landscape irrigation; 2) the constructed wetlands provided habitats for various macroinvertebrates, increasing species richness by N50%; 3) the NBS also greatly enhanced landscape amenity, providing recreational and educational opportunities for bird watching and bushwalking enthusiasts. In Michigan, USA, a historical development resulted in the loss of ~97% of coastal wetland in a river, and brownfield remediation included the construction of 6.5 ha of wetlands. The short- and long-term ecological success was tracked and monitored (Hartig et al., 2012). In a wetland with Pb contamination, Typha latiolia (cattail) grown in an industrial wetland was found to have minimal Pb translocation. Moreover, Fe formed a plaque outside of the roots, sequestering Pb in the rhizosphere, and preventing Pb from relocating to aboveground tissue. This mechanism can reduce ecological risk by preventing trophic transfer of Pb to insects, birds, and other wild animals (Feng et al., 2013). In the Franche-Comté region of France, an artificial wetland consisting of four shallow ponds was constructed for landfill leachate treatment. The performance was monitored for sixteen years (Aleya et al., 2019). Overall, leachate contaminants were effectively eliminated via precipitation and microbiological reactions, with the efficiency reaching 75–90% removal. However, a significant drawback was the level of maintenance needed. Also, when using wetland for remediation, the bioavailability of the contaminants to aquatic insects needs consideration (Gimbert et al., 2018).

Phytoremediation uses native or imported plant species, or even genetically modified species to address contaminated land issues. In recent years, phytoremediation plants have also been proposed as a potential feedstock source for bioenergy (Andersson-Sköld et al., 2014; Schreurs et al., 2011; Schroeder et al., 2018). Because a large areas of arable land are required to reach renewable energy targets set by governments (Timilsina et al., 2012), utilizing contaminated sites to produce biomass can reduce competition for land with food production (Andersson-Sköld et al., 2014) while contaminants are removed (Meers et al., 2010). Phytoremediation systems in an urban setting can help address urban challenges in water management. Rehabilitation of bare soil with plants can also prevent the migration of contaminated soil via water erosion or wind erosion. Contaminants may also adsorb to plant roots, thus rendering them immobilized in the environment (Feng et al., 2013). Researchers have also applied chelating reagents to facilitate heavy metal extraction with phytoremediation (Di Gregorio et al., 2006). Revegetation of brownfield sites may be achieved by spontaneous plant growth or seeding techniques. Specific species with deeper growth of root can bring additional benefits. The former practice is cheaper and naturally selects flora that is suitable for the local environmental conditions although some may be invasive species banned by local government authorities. However, it is slow to achieve full revegetation. A more active strategy is to initiate certain seeding techniques, and then allow the flora to evolve under the specific climatic and contaminant conditions. At sites where contaminants are potentially toxic to plant growth, imported soil cover or soil amendments may be needed, or the selection of contaminant resistant plant species. A key in successful revegetation is to engineer the right site conditions to enable vegetation to reach maturity (Adamo et al., 2015). Besides phytoextraction techniques, which aim to remove contaminants, phytoremediation can also entail phytostabilization techniques, which intend to minimize the uptake of contaminants. Enell et al. conducted field trials to demonstrate that willow trees can grow in heavy metal contaminated soil with low to moderate uptake, thus rendering a solution that both minimizes ecological risk and offers a biomass source for bioenergy production (Enell et al., 2016). Foucault et al. found that some plants grown as green manure, including borage and white mustard, could improve soil respiration and reduce heavy metal bioavailability and ecotoxicity. Lead and antimony contamination was addressed by phytoextraction with storage in shoots and phytostabilization with storage in roots (Foucault et al., 2013).

Fig. 2. Constructed wet land in a brownfield sitting; source: (Greenway, 2017).

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3.3. Bioremediation Bioremediation utilizes microbial activity to remove contaminants in soil and/or groundwater. It is achieved by delivering a microbial culture that is capable of degrading contaminants to the contaminated media, or by providing substrates that can stimulate the growth of native microorganisms (Pelaez et al., 2013). The microbial degradation of contaminants depends on the availability of nutrients, favorable geochemical conditions, and the abundance of microorganisms (Megharaj and Naidu, 2017). Bioremediation can be achieved either in situ or ex situ. In situ bioremediation has become the most widely used groundwater treatment technology in recent years (see Fig. 3), because of lower capital expenditure requirements than most other traditional remediation techniques, and due to rendering smaller life cycle environmental footprints (Hou et al., 2014a). Bioremediation can be considered a NBS because it is based on natural microorganisms. However, unlike most other NBS, it does not render landscape or aesthetic features because of the microorganisms not being visible by eye. 3.4. Green synthesis of nanoremediation materials Engineered nanoparticles have shown unprecedented performance for degrading various contaminants, such as chlorinated hydrocarbons, dyes, and polychlorinated biphenyls (PCBs) in soil and water. This is associated with properties such as their large specific surface area and high reactivity (Williams-Johnson et al., 2001; Zhang et al., 2017). However, the use of nanoparticles for remediation can result in a considerable burden on the environment as a result of their manufacture (Higgins and Olson, 2009). Due to this concern, the use of nature based greener synthetic approaches has seen growing interest and should be further developed (Varma, 2012; Virkutyte and Varma, 2014). Recent advances in nanotechnology have looked to natural materials in the production of green nanomaterials for environmental remediation (Wang et al., 2019; Zhang et al., 2018). Compared with conventional methods, green nanotechnology is dedicated to the creation and improvement of nanoparticles in a costeffective, biocompatible, non-toxic, and eco-friendly manner. Plants extracts can serve as both reducing and capping agents in their assembly, attributed to the antioxidant properties of polyphenol and caffeine molecules existing in plant extracts (Hoag et al., 2009; Weng et al., 2013). Green tea has been one of the most widely used source materials as a reducing agent for green nanoscale ZVI synthesis (Huang et al., 2015). The

use of microbes has also emerged as a novel technique for the synthesis of various inorganic metal/metal oxides nanoparticles. For example, microbial mediated synthesis of TiO2 nanoparticles using Lactobacillus sp. (Jha et al., 2009) and Bacillus sp. (Kirthi et al., 2011) has been reported. Bansal et al. (2005) also synthesized silica and TiO2 nanoparticles using fungus species. 3.5. Stabilization using biochar, green mulch and compost In the Solidification/Stabilization (S/S) approach to remediation, contaminants are bound in a solidified mass (solidification), or stabilizing agents are added to reduce the mobility of contaminants (stabilization). S/S can be an low-cost and efficient way in dealing with wide spread heavy metal contamination (Hou et al., 2017a). In the context of NBS, stabilization maybe achieved by using reagents derived from biological waste, such as biochar, mulch and compost (O'Connor et al., 2018b). The main purpose is to reduce contaminant mobility to receptors, thus mitigating the human health and ecological risks posed by the soil contaminants. Biochar is produced by the combustion of biomass under a limited supply of oxygen in a controlled environment (Zhao et al., 2018). It has widely been reported that biochar treatment of soils can reduce the bioavailability of certain contaminants such as heavy metals (Shen et al., 2019; Shen et al., 2018). Currently, the use of biochar for the remediation of polluted land is in the early stages of development. Many studies have been conducted in laboratory or greenhouse settings, but there have been only limited applications in the field. Organic amendments such as green mulch and compost have been found to be an effective stabilization agent due to various mechanisms including adsorption, complexation, precipitation, and redox reactions (Huang et al., 2016; Wu et al., 2017). There is also contradictory evidence regarding the stabilization effect of greenwaste compost (Clemente et al., 2010), because compost can release soluble phosphorus (Rainbow and Wilson, 2002) and humic and fulvic acids (Adani and Spagnol, 2008), both of which can displace heavy metals such as arsenic from binging sites. Adding peat to soil can significantly increase the organic carbon content which can easily bind with certain contaminants, but also reduces the soil pH which has implications for contaminant solubility (Adamo et al., 2015). Consequently, the addition of these materials may be advantageous for stabilizing certain types of contaminants, but may enhance the mobility of other types of contaminants. Phytostabilization of contaminated soil with plants can potentially be

Fig. 3. Adoption rates of in situ bioremediation and in situ chemical treatment, sources: (Hou et al., 2014b; USEPA, 2017b).

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enhanced by the application of soil amendments (Clemente et al., 2010). Adamo et al. monitored the colonization of spontaneous vegetation in polluted soils, with and without organic amendments. It was found that organic amendments reduced contaminant availability and phyto-toxicity, and enhanced plant growth (Adamo et al., 2015). 4. Planning and redevelopment integrating natural components This section discusses some of the social, economic, and environmental benefits of using nature based remediation technologies for city planning and redevelopment (Table 2). 4.1. Revegetation at contaminated sites and integration with landscape architecture and urban planning Former industrial sites often have environments that are unfavorable for plant growth, such as impermeable land surfaces, toxic contaminants in soil and groundwater, and a lack of seeding plants in the nearby environment. Attention to landscape architecture at such sites may serve two purposes: (1) to improve the aesthetic characteristics of the site; and, (2) to transform the site to a stable ecosystem. Depending on the temporal trend of site contamination levels, the abundance of either remediating or non-remediating flora may change, thus creating a successional landscape (Boroş and Micle, 2015). A field trial reported by Dickinson revealed that sustainable woodland can be established in heavily contaminated soil, with copper concentrations up to 9100 mg/kg and zinc concentrations up to 28,800 mg/kg (Dickinson, 2000). Spontaneous revegetation is environmentally friendly in that it reduces weeding, watering, and soil amendment requirements. It is affected by both pollution patterns and environmental effects. A study in Quebec, Canada, showed that up to 61% of variance in spontaneous plant distribution was explained by the distribution of soil contaminants (Desjardins et al., 2014), indicating that soil pollution was the primary driver. However, there is also conflicting evidence showing that other environmental effects are more influential. At a former steelworks brownfield site, Adamo et al. tested revegetation by spontaneous plant colonization. The site was contaminated by heavy metals (As: 45.9 mg/kg, Sn: 14.7 mg/kg, Pb: 286 mg/kg) and polycyclic aromatic hydrocarbons (benzo[a]pyrene: 1.74 mg/kg, total PAH: 18.37 mg/kg). Plant colonization was conducted in two series of twelve 0.3 m3 pots to test the effects of environment (e.g. brownfield site vs nearby park site), soil contamination (different pots containing different levels of contamination), and the addition of organic material. Over a five-year testing period, 20 species were recorded in the pots located at the

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brownfield site and 52 species were recorded in the pots located at the nearby park site. The average number of species per pot was 20% higher at the park site compared to that at the brownfield site, and the plant cover was nearly 100% higher. In contrast, there was no significant difference between the pots with different levels of soil contamination. It demonstrated that environmental effects can play a more important role than soil contamination level in determining plant diversity and abundance (Adamo et al., 2015). Integrating revegetation of contaminated soil with landscape architecture can be an effective NBS for brownfield redevelopment. For this, designers must understand the spatial distribution of soil contaminants and soil properties like pH and organic matter content. Contaminant enriching plant species may be used for contaminant removal at heavily polluted areas; whereas native species tolerant of contaminant toxicity can be used to cover the majority of moderately polluted areas. Institutional or engineered controls can be put in place to limit public site access in order to prevent the risk of direct contact, i.e. dermal and ingestion related exposure. For instance, raised pathways maybe used to separate human activities from the contaminated media (see Fig. 4[a]). 4.2. Converting brownfield sites into greenspace In many cases, city governments need to design and build new greenspace, to create a more enjoyable urban environment and to fulfill sustainability goals. Since the 1980s, scholars and designers have made efforts to convert large brownfield sites into parks and greenspaces (Dagenhart et al., 2006). Some notable examples include Parc de la Villette and Parc de Citroen in Paris, France; Landscape Park DuisburgNord in the Nord/Ruhr District, Germany; Westergasfabriek Culture Park in Amsterdam, Netherlands; Queen Elizabeth Olympic Park in London, UK; and Freshkills Park in New York City, US. Converting brownfield sites in downtown areas into greenspace is beneficial in that these sites tend to have a large number of residents living within walking distance, and they can greatly benefit from the aesthetic improvement and recreational space provision (Atkinson et al., 2014). Green parks provide a space for people from diverse backgrounds to interact, thus improving social relations (Peters et al., 2010). The development is often conducted in phases. For the 5–10 years following initial tree planting, intensive care such as irrigation, protection of young trees, and tree restocking may be required, which renders not only extra cost, but also limitations to public access (e.g. site fencing) (Atkinson et al., 2014). There are many challenges associated with this NBS strategy. One major challenge is the financial burden associated with the remediation

Table 2 Social, economic, and environmental benefits of using nature based brownfield redevelopment methods. Nature based redevelopment technologies

Advantages

Revegetation and integration with landscape architecture

Improve aesthetics; provide leisure and recreational opportunities

Converting brownfield sites into greenspace

Improve public health, aesthetics, social interaction; increase area for public recreation Education; culture preservation; increase area for public recreation

Converting brownfield sites into green industrial heritage park Ground source heating and cooling Nature Preserves

Social benefits

Meet the community heating and cooling demand; Improve aesthetics; provide leisure and recreational opportunities

Disadvantages Economic benefits

Environmental and ecological benefits Create a healthy ecosystem;

Enhance flood control; Reducing costs of building envelopes Improve local economy; low remediation cost; Improve life cycle cost Lower heating and cooling costs; eligible for government subsidy;

Low life cycle environmental footprint; create a healthy ecosystem; Low life cycle environmental footprint; Enhance evaporative cooling Low life cycle environmental footprint; Maintain urban biodiversity;

Extra cost for maintenance; Slower time period No income, extra cost for maintenance; High maintenance cost;

High construction cost due to below ground excavation No income, extra cost for maintenance;

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Fig. 4. An integrated nature based solution for brownfield remediation and redevelopment designed for Amsterdam-Noord in the Netherlands: a) raised path to limit access to a phytoremediation area; b) street channel integrated with purifying landscape (Source: (Wilschut et al., 2013)).

of contaminated media (soil, groundwater, and sediments), and the construction and maintenance of greenspaces. Unlike other typical brownfield redevelopments, which can generate revenue by developing commercial or residential buildings, the conversion of brownfield into greenspace does not generate direct financial return. Therefore, private investors are unlikely to take such actions without external involvement. City governments have to sponsor these projects; and the extra cost associated with remediation must be justified in order to secure public funding. Besides the socioeconomic benefits (e.g. improved public well-being) discussed in Section 2, creating greenspaces from brownfield land can also have significant spillover effects. For instance, the property values of adjacent buildings can increase significantly. City governments may foresee indirect socioeconomic gains and thus justify the use of public spending with projected increases in property tax revenue, or the selling/leasing of vacant government owned land. The funding model may vary depending on socioeconomic and cultural contexts. For the Central Park in New York City, donations from individuals, corporations, foundations, and public bodies cover 85% of the park's $27 million annual budget; and for the Royal Parks in London, a registered charity was founded to help finance the £30 m annual budget (Davidson, 2013). Health and safety concerns are another big challenge. The remediation community traditionally relies upon health risk assessment (HRA) to derive cleanup standards that are suitable for future use. When a brownfield site is planned for greenspace, as long as surficial soil is replaced or capped with a thin layer of clean soil, exposure pathways associated with ingestion and dermal contact can be managed. Because greenspace is usually an open field, any volatile contaminants released from the soil would be rapidly attenuated by atmospheric movement, resulting in minimal inhalation risk. Consequently, HRA could show that residual contaminants pose no health risk. On the other hand, such residual contaminants would pose a risk if intrusive work (i.e. digging for utility work) is undertaken, or there is enclosed structure (e.g. housing or office building) which allows for vapor intrusion and accumulation. Therefore, where residual contaminants may potentially cause unacceptable health risks, institutional controls must be enforced to prohibit uncontrolled intrusive work and the building of enclosed structures at the site. A lack of effectiveness of such institutional controls (e.g. caused by antisocial behavior by certain site users) and potential public anger are of concern. At the Lansdowne Park site in the City of Ottawa, Canada, integrated risk management strategies were used to alleviate this concern: 1) park features and grading were designed to allow certain contaminated soils to remain in place and to accommodate soil excavated from other parts of the park; 2) both hard and soft caps were placed above the contaminated soils; 3) shallow rooting tree species were used to avoid penetrating the soil cap. These innovative risk management strategies rendered a cost saving of over $8 million (Carew et al., 2015).

4.3. Green Industrial Heritage Park The discussion of brownfield redevelopment is often limited to narrow technical considerations, with little attention to the historical and cultural significance of these sites (Bliek and Gauthier, 2007). On the other hand, brownfield sites can be developed into green industrial heritage parks, offering significant socioeconomic benefits. In the City of Duisburg, Germany, a 20 ha former industrial site was developed into a public park, with the intension of remembering rather than rejecting the industrial past (see Fig. 5). The contaminated site was divided in different zones, with concrete bunkers converted into gardens, historical gas tanks converted into a pool for scuba divers, concrete walls converted to rock climbing walls, etc. (https://www.landschaftspark.de/ en/visitor-information/landscape-park/). Earlier examples of this approach are Gasworks Park in Seattle, Washington State, USA by the landscape architect Richard Haag. This park opened in 1975 and used the derelict remnants of the former coal gasification manufacturing plant on site as a major site element, cultural relic and visual identity. Although it was fenced off to public access it contributed to a change in the mindset of city administrators and the visitors to the park about the role of industrial processes in shaping the modern green park space. In other parts of the park, waste material found on site is placed and capped to form gently sloping hills for visitors to use as an amphitheater for outdoor music and community performances. Other more recent examples of this approach that attempt to leave elements of the industrial and manufacturing past intact for cultural and social use is the collection of former wastewater treatment complexes in the capital city of Seoul, South Korea. One of the more famous is the 26 acre Seonyudo Park by the landscape architects Seo Ahn Total Landscape of Seoul next to the Han River where the layout of former concrete tanks becomes connected ponds and pools of wetland plants and grasses. Opened in 2002 it produces an intense natural experience for the visitor of the integration of old industrial infrastructure of the waste treatment with green intimate spaces of water plants, insects and pond life in the center of a large city. 4.4. Ground source heating Space heating accounts for N50% of total energy consumption in the domestic sector in the UK (Donaldson and Lord, 2018). Many households are unable to provide sufficient energy service at b10% of their income, rendering a “fuel poverty” status. Donaldson et al. reported that as the amount of social housing and brownfield sites are correlated (R2 = 0.51), the use of ground source heating on brownfields as a renewable energy source could heat 43,735 properties, or 47% of those in fuel property in the city of Glasgow. In the Netherlands, researchers coupled groundwater remediation with a heat-cold storage (HCS) technique (Slenders et al., 2010). A recirculation system was used to create a

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Fig. 5. Pre- (a, b) and post- (c, b) development of a former steelworks: from debris to industrial heritage park in Germany (Source: thyssenkrupp, Corporate Archives, Duisburg; Jürgen Dreide; Michael Latz; and, needpix.com).

constant flow so that heat and cold could be exchanged with groundwater, which had a near constant temperature of 12–13 °C. Such a strategy offers great synergy, enabling faster contaminant degradation as well as low-cost air conditioning. Results showed 30%–50% reduction in CO2 emission, and 30%–40% reduction in project cost. 4.5. Nature reserves Depending on the perception of risks by the public and other stakeholders, brownfield sites may be converted to nature reserves with human access (Levi and Kocher, 2006). At such sites, woody biomass can be effective in stabilizing contaminants such as As, Pb, Cu, and Ni (French et al., 2006). Most plant species have certain levels of tolerance to toxic chemicals, and vegetation can be developed at brownfield sites after appropriate soil amendment or cover is added. Brownfield sites in coastal areas are particularly suitable for this type of NBS. Historically, many coastal sites were used for industrial usage because of convenience for sea transport and wastewater discharge. As environmental regulatory standards and people's living standards were raised, the use of coastal areas shifted toward recreation, tourism, and residence. Converting coastal brownfield sites to nature reserves can achieve multiple environmental, social, and economic benefits. Nature reserves can support urban biodiversity and resilience (Kattwinkel et al., 2011), which has been successfully implemented at some large contaminated sites in the US. One of the largest examples is the National Environmental Research Parks around the US DOE's nuclear facilities. These parks are open to the public for environmental research, environmental education, and outdoor recreation, but only for a limited number of days per year (Levi and Kocher, 2006). At another brownfield site in Michigan, USA, restoration and redevelopment activities were conducted to incorporate the brownfield with a national wildlife refuge (Hartig et al., 2012). A number of nature-based strategies

were used: an underground culvert was converted to a surface creek; a retention pond and emergent wetland were constructed to treat surface runoff; coastal wetland and upland habitats were restored; and facilities were built to allow for wildlife-compatible public uses. The design of this type of NBS requires conservatively assessing the effect of soil contamination on site visitor's health, as well as ecological systems. Human health protection can be achieved by designating segregation areas and using guided hiking trails. Stress imposed on the ecological system needs to be addressed in both planning and maintenance. Studies have shown that the environmental stress gradient caused by site contaminants can result in distinctive vegetative assemblages, as well as uncertainties in the end point of assemblage development (Gallagher et al., 2011). 5. Implications and conclusions 5.1. Outlook for NBS in managing contaminated land Nature based solutions offer many socioeconomic and environmental benefits when properly applied. There are constraints of NBS such as slow contaminant attenuation rates, health risk posed by residual contaminants, and reduced land area for housing development; and cannot fully replace active remediation technologies. However, there is no doubt that NBS offers a valuable option for brownfield redevelopment. Whether it is appropriate to apply NBS depends on the extent and fate of contaminants, site-specific risks, and the intended future land use. Brownfield transformation processes are significantly influenced by a city's future vision (Duzi and Jakubínský, 2013). A European survey indicated that a lack of financial resources and a lack of political will, are the main barriers to NBS (Faivre et al., 2017). Initially, brownfield redevelopment was once directed toward public parks and open space creation, due to public pressure and a weak housing market. However, as

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the real estate market strengthened, brownfield redevelopment became favored for housing, retail, and office space creation (Dagenhart et al., 2006). Therefore, planners will need to pay greater consideration to long-term future visions for cities, and how NBS could provide a means to achieving that goal, rather than simply using brownfield redevelopment as a way to plug a short term housing shortage. Conventional remediation is often independent from other sites in a city; however, the use of NBS at a brownfield site may depend on the choices made at other brownfield sites in the same city, or metropolitan area. For instance, if a given brownfield site is converted into a greenspace for public access; it may discourage the same choice for other sites. For conversion of brownfield sites into industrial heritage parks, it depends on whether the metropolitan area has other industrial heritage parks, and whether the nation has other facilities of similar nature, i.e. originated from the same industrial sector and maintained with similar historical features. For governments who own a large number of brownfield sites, policy makers may use GIS and index methods to screen a large numbers of sites over wide areas, to select the most suitable sites for redevelopment, including application of such NBS strategies. Chrysochoou et al. (2012) used a three dimensional approach for such an assessment: socioeconomic variables including population density, property values, and unemployment; smart growth variables including intersection density, utility service area, job housing balance, and public transportation transit access; and environmental variables including potential source of contamination, pathway of exposure, and receptors (Chrysochoou et al., 2012). 5.2. Synergy with green and sustainable remediation Current state-of-art practice in contaminated land remediation is the risk-based land management approach. However, risk-based thresholds are often arbitrary and the establishment of regulatory guidance values often does not rigorously take into account the amount of remediation work versus environmental benefit at individual sites (Hou et al., 2017b; O'Connor and Hou, 2018). In recent years, the green and sustainable remediation (GSR) movement has emerged, which calls for the maximization of “net environmental benefit” and simultaneous consideration of social and economic benefits (Hou and Al-Tabbaa, 2014; Song et al., 2018). The NBS approaches align with GSR in several aspects: (1) NBS can minimize usage of non-renewable energy and resource; (2) NBS avoids landfilling, which has long-lasting secondary environmental impacts; (3) NBS allows designers to take into account bioavailability and ecotoxicity, thus better reflecting the net environmental benefit; 4) NBS improves the local environment and can render substantial socioeconomic benefits. 5.3. Lessons learned for designers and policy makers There are several constraints posed by brownfield sites when applying NBS. Besides the toxicity of site contaminants limiting plant growth or a general lack of fertile soil, there are often limited diaspores which can reach such isolated urban sites (Gallagher et al., 2011). Early colonization of metal-tolerant plant species may delay or inhibit the colonization by other species (Sänger and Jetschke, 2004). The remediation approach used at the Sydney Olympic Park generated significant demand for long-term management and maintenance cost, particularly due to concerns regarding leaching of contaminants from soil (Davidson, 2013). It was found that brownfield redevelopment designers tend to focus on aesthetics, leaving other social considerations as secondary concerns. On the other hand, the redevelopment process itself is driven more by economic and sociocultural forces rather than design considerations (Loures, 2015). Both factors pose a challenge for sound redevelopment of brownfield sites. For example, at development at large brownfield sites, it is important to take into consideration the pedestrian friendliness, which may be achieved by subdividing the large scale development (Dagenhart et al., 2006). Lafortezza et al.

compared remediation scenarios with various types of tree coverage, by using cost-surface modeling (CSM) and visual preference assessment (VPA). Modeling results showed that visually preferable remedial scenarios were also more ecologically functional for forest bird species dispersal (Lafortezza et al., 2008). For urban areas undergoing economic and population decline, vacant brownfield sites may cause problems for community aesthetics and increase the perception of being run-down (Rall and Haase, 2011). In Leipzig in eastern Germany, the city implemented an “Interim Land Use (ILU)” policy to fight against urban blight in the late 1990s. An “authorization agreement” was signed between city government and private owners, to allow for public use of private land while maintaining the owners' building rights. The city created new greenspace for public use on such private land, and more importantly, connected fragmented greenspaces. In return, private owners obtained subsidized land clearance and development, and exemption of property taxes. The ILU was considered successful; however, it was suggested that public acceptance and support should be strengthened to achieve greater socioeconomic benefits (Rall and Haase, 2011). 5.4. Limitations of existing research Even though the use of technologies which fit the definition of NBS are used seen in various industrial sectors, the implementation of NBS remains mostly experimental (Kabisch et al., 2016). Metal uptake by plants is influenced by environmental factors such as soil pH, oxidation-reduction potential and organic content, because these factors affect the bioavailability of heavy metals such as As, Cr, Cu, and Zn (Qian et al., 2012). However, there is a general lack of research on the relationship between environmental factors under field conditions and the effectiveness of full-scale phytoremediation. Green synthesis of nanomaterials in the laboratory is able to deliver small amounts of products; however, large-scale production can result in inconsistent characteristics such as size, shape, and stability. It remains challenging to design scalable synthesis protocols for practical application. Challenges also remain for the selection of surfactants solvents and reducing agents, which affect not only the stability of nanomaterials but also environment pollution deriving from the synthesis process. Nature based solution may prove to be well-suited to developing countries such as China, where there are tens of millions of hectares of contaminated land to be managed (Hou and Li, 2017; MEP, 2014). However, little research has been conducted for NBS specifically in this context. As NBS is a relatively new concept, there is a general lack of technical standards and guidelines for implementation (Kabisch et al., 2016) and there is a lack of research quantifying the benefits of NBS remediation in different settings. For example, under complex site conditions, the effectiveness of NBS becomes more questionable. Roy et al. found that phytoextraction became less effective when soil contaminated by heavy metals is comingled with organic contaminants (Roy et al., 2005). Laval-Gilly et al. found that besides toxic heavy metal species, the accumulation of other elements like potassium in biomass grown on brownfield could also cause problems such as fouling and slagging in combustion units (Laval-Gilly et al., 2017). One of the biggest concerns for applying NBS at brownfield sites is that they tend to leave residual contaminants in situ at the site. Residual contaminants pose long-term uncertainty and liability; however, risk can be kept low by post remediation long-term management. At a site in the UK, 20 cm of acidic colliery spoil was used to ameliorate high alkalinity of alkali waste. A thin layer (5 cm) of soil and fertilizer was applied in 1980, and the site seeded as an amenity grassland. After 28 years, arsenic concentrations remained extremely high, but it was strongly adsorbed to soil and had low mobility, posing no immediate risk to human receptors or the ecological system (Hartley et al., 2009). Nevertheless, because the original reclamation design was conducted at a much less stringent regulatory standard compared to what would

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be enforced today; additional assessment is needed to ensure the longterm sustainable management of the site. When using NBS in an urban setting, there may be trade-offs between ecological values and social inclusiveness; but there is a lack of conceptual and theory-oriented research on the subject to date (Haase et al., 2017). This dilemma needs to be resolved in order to make NBS in urban areas socially inclusive and sustainable. 5.5. Suggestions for future studies Remediation practitioners tend to consider contaminated site remediation solely as an engineering problem. In order to promote NBS, it is imperative to produce stronger scientific evidence regarding the suitability of NBS, as well as to raise awareness among interdisciplinary stakeholders. Gallagher et al. showed that elevated heavy metal concentrations at brownfield sites can result in alternative steady states in vegetative assemblages development, raising uncertainties in its endpoints (Gallagher et al., 2011). Therefore, in the process of revegetating brownfield sites, it may be more effective to define endpoints that are more flexible. However, this may contradict with traditional landscape design procedures. Interdisciplinary research studies crossing ecology, landscape architecture, and environmental engineering fields are needed to enhance both scientific knowledge and design tools. Keesstra et al. classified NBS into soil solutions and landscape solutions (Keesstra et al., 2018); however, contaminated land remediation involves both soil and landscape. Future studies need to identify opportunities and methodologies to simultaneously enhance ecological attributes and visual preferences, which require interdisciplinary collaboration between ecologists, planners, landscape architects, and engineers (Lafortezza et al., 2008). The effect of heavy metal toxicity on photosynthesis maybe masked by varying nutrient level and other environmental factors (Radwanski et al., 2017). More research is needed to examine the optimum environmental conditions for effective phytoremediation. The long-term effectiveness of NBS also needs to be further explored. Salisbury et al. investigated the long-term effectiveness of stabilization of spontaneously vegetated urban brownfield contaminated by As, Cr, Cu, Pb, and Zn. It was found that after 48 years of site abandonment, Cu, Pb, and Zn remained stable, while As and Cr mobilized from the top 5 cm to the 5–25 cm horizon (Salisbury et al., 2017). For engineered NBS such as phytostabilization, there is a general lack of research on the longterm effectiveness of phytostabilization. Therefore, more research is needed to provide stronger scientific evidence and guidance. There is a need to study the full life cycle of brownfield redevelopment and how to incorporate the social, economic, and environmental considerations along the full life cycle. At the Sydney Olympic Park, the initial design to establish a sustainable park was progressively eroded by the desire to enhance revenue-generating urban development (e.g. V8 Supercar racing). Phytoremediation is a muchresearched technology; however, the disposal of biomass from phytoremediation is a far less frequently studied topic. Biomass combustion has been proposed as a viable disposal method and has been applied at a pilot scale (Kovacs and Szemmelveisz, 2017). The commercial viability of large-scale application of phytoremediation plus biomass combustion still needs to be tested. More research is also needed to identify economic solutions for controlling environmental emission of toxic elements during biomass combustion. If it is not adequately managed, biomass combustion processes may cause secondary pollution that is worse than leaving the contaminants in place. There are also environmental complexities that need to be addressed in implementing NBS. For instance, existing research on phytoremediation at brownfield sites tend to focus on single plant species. However, at actual sites, there are strong variations of soil conditions and biological contexts. More research is needed to develop genetic variations to deal with changes in soil conditions (e.g. high

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sodium and chloride contents or unusual pH values), insect and disease outbreak, and other unfavorable plant-environment interactions (Roy et al., 2005; Zalesny Jr. et al., 2016). 5.6. Conclusions Hundreds of thousands of contaminated sites in cities around the world await remediation and redevelopment. However, traditional physical and chemical remediation technologies require high energy and resource inputs, and may result in loss of soil functionality and secondary pollution. In recent years, The European Commission has actively promoted nature based solutions (NBS). The use of NBS at brownfield sites holds much promise because it has a number of beneficial sustainability implications, including the following: 1. Increased human well-being by providing space for play, cycling, walking, bird watching, education, and social activities; 2. It tends to be more cost effective and more resilient to social and environmental changes; 3. Improved air quality, reduced noise, protection or reclaiming ecological habitats, and lowered life cycle environmental footprint of remediation operation. Some of the NBS discussed in the present study have been widely used in commercial applications, e.g. phytoremediation, bioremediation, converting brownfield sites into greenspace. Other NBS have only been used in rare cases or on an experimental basis, e.g. biochar-based remediation, green industrial heritage parks, using ground source heating in remediation. In both cases, additional research is needed to enhance their feasibility or efficacy. Acknowledgment This work was supported by China's National Water Pollution Control and Treatment Science and Technology Major Project (Grant No. 2018ZX07109-003), and the National Key Research and Development Program of China (Grant No. 2018YFC1801300). References Adamo, P., Mingo, A., Coppola, I., Motti, R., Stinca, A., Agrelli, D., 2015. Plant colonization of brownfield soil and post-washing sludge: effect of organic amendment and environmental conditions. Int. J. Environ. Sci. Technol. 12, 1811–1824. Adani, F., Spagnol, M., 2008. Humic acid formation in artificial soils amended with compost at different stages of organic matter evolution. J. Environ. Qual. 37, 1608–1616. Aleya, L., Grisey, E., Bourioug, M., Bourgeade, P., 2019. Performance assessment of Etueffont (France) lagooning treatment system: report from a 16-year survey. Sci. Total Environ. 648, 518–529. Andersson-Sköld, Y., Hagelqvist, A., Crutu, G., Blom, S., 2014. Bioenergy grown on contaminated land–a sustainable bioenergy contributor? Biofuels 5, 487–498. Anguelovski, I., 2016. From toxic sites to parks as (green) LULUs? New challenges of inequity, privilege, gentrification, and exclusion for urban environmental justice. CPL Bibliography. 31, pp. 23–36. Atkinson, G., Doick, K., Burningham, K., France, C., 2014. Brownfield regeneration to greenspace: delivery of project objectives for social and environmental gain. Urban For. Urban Green. 13, 586–594. Bansal, V., Rautaray, D., Bharde, A., Ahire, K., Sanyal, A., Ahmad, A., et al., 2005. Fungusmediated biosynthesis of silica and titania particles. J. Mater. Chem. 15, 2583–2589. Bliek, D., Gauthier, P., 2007. Mobilising urban heritage to counter the commodification of brownfield landscapes: lessons from Montréal's Lachine Canal. Can. J. Urban Res. 16, 39. Boroş, M.-N., Micle, V., 2015. Study on Soil Decontamination by Phytoremediation in the Case of Former Industrial Sites. ProEnvironment. Carew, B., Pilgrim, S., Hicks, K., Bailey, S., Miller, J.D., 2015. Integrating Risk Management into Redevelopment of an Urban Brownfield Site. Chi, T., Zuo, J., Liu, F., 2017. Performance and mechanism for cadmium and lead adsorption from water and soil by corn straw biochar. Front. Environ. Sci. Eng. 11. Chrysochoou, M., Brown, K., Dahal, G., Granda-Carvajal, C., Segerson, K., Garrick, N., et al., 2012. A GIS and indexing scheme to screen brownfields for area-wide redevelopment planning. Landsc. Urban Plan. 105, 187–198. Clemente, R., Hartley, W., Riby, P., Dickinson, N.M., Lepp, N.W., 2010. Trace element mobility in a contaminated soil two years after field-amendment with a greenwaste compost mulch. Environ. Pollut. 158, 1644–1651. Dagenhart, R., Leigh, N., Skach, J., 2006. Brownfields and urban design: learning from Atlantic Station. WIT Trans. Ecol. Environ. 94.

578

Y. Song et al. / Science of the Total Environment 663 (2019) 568–579

Davidson, M., 2013. The sustainable and Entrepreneurial Park? Contradictions and persistent antagonisms at Sydney's Olympic Park. Urban Geogr. 34, 657–676. DCLG, 2009. Land Use Change Statistics (England) 2008 - Provisional Estimates (July 2009). DCLG. Department for Communities and Local Government, London, UK. van den Bosch, M., Sang, A.O., 2017. Urban natural environments as nature-based solutions for improved public health - a systematic review of reviews. Environ. Res. 158, 373–384. van der Jagt, A.P., Szaraz, L.R., Delshammar, T., Cvejić, R., Santos, A., Goodness, J., et al., 2017. Cultivating nature-based solutions: the governance of communal urban gardens in the European Union. Environ. Res. 159, 264–275. Desjardins, D., Guidi Nissim, W., Pitre, F.E., Naud, A., Labrecque, M., 2014. Distribution patterns of spontaneous vegetation and pollution at a former decantation basin in southern Quebec, Canada. Ecol. Eng. 64, 385–390. Di Gregorio, S., Barbafieri, M., Lampis, S., Sanangelantoni, A.M., Tassi, E., Vallini, G., 2006. Combined application of triton X-100 and Sinorhizobium sp Pb002 inoculum for the improvement of lead phytoextraction by Brassica juncea in EDTA amended soil. Chemosphere 63, 293–299. Dickinson, N.M., 2000. Strategies for sustainable woodland on contaminated soils. Chemosphere 41, 259–263. Donaldson, R., Lord, R., 2018. Can brownfield land be reused for ground source heating to alleviate fuel poverty? Renew. Energy 116, 344–355. Duzi, B., Jakubínský, J., 2013. Brownfield dilemmas in the transformation of postcommunist cities: a case study of Ostrava, Czech Republic. Hum. Geogr. 7, 53. EEA, 2014. Progress in Management of Contaminated Sites (CSI 015/LSI 003). European Environment Agency, Copenhagen, Denmark. Enell, A., Andersson-Skold, Y., Vestin, J., Wagelmans, M., 2016. Risk management and regeneration of brownfields using bioenergy crops. J. Soils Sediments 16, 987–1000. EPRS, 2017. Nature-based Solutions: Concept, Opportunities and Challenges. European Comission, 2017. Environment - Research & Innovation Policy Topics - Nature Based Solutions. Faivre, N., Fritz, M., Freitas, T., de Boissezon, B., Vandewoestijne, S., 2017. Nature-based solutions in the EU: innovating with nature to address social, economic and environmental challenges. Environ. Res. 159, 509–518. Feng, H., Qian, Y., Gallagher, F.J., Wu, M., Zhang, W., Yu, L., et al., 2013. Lead accumulation and association with Fe on Typha latifolia root from an urban brownfield site. Environ. Sci. Pollut. Res. 20, 3743–3750. Fishman, B.E., Reinert, K.H., 2000. Ecological considerations in brownfields redevelopment. Environ. Toxicol. Chem. 19, 257–258. Foucault, Y., Leveque, T., Xiong, T., Schreck, E., Austruy, A., Shahid, M., et al., 2013. Green manure plants for remediation of soils polluted by metals and metalloids: Ecotoxicity and human bioavailability assessment. Chemosphere 93, 1430–1435. French, C.J., Dickinson, N.M., Putwain, P.D., 2006. Woody biomass phytoremediation of contaminated brownfield land. Environ. Pollut. 141, 387–395. Gallagher, F.J., Pechmann, I., Holzapfel, C., Grabosky, J., 2011. Altered vegetative assemblage trajectories within an urban brownfield. Environ. Pollut. 159, 1159–1166. Gimbert, F., Petitjean, Q., Al-Ashoor, A., Cretenet, C., Aleya, L., 2018. Encaged Chironomus riparius larvae in assessment of trace metal bioavailability and transfer in a landfill leachate collection pond. Environ. Sci. Pollut. Res. 25, 11303–11312. Greenway, M., 2017. Stormwater wetlands for the enhancement of environmental ecosystem services: case studies for two retrofit wetlands in Brisbane, Australia. J. Clean. Prod. 163, S91–S100. Haase, D., Kabisch, S., Haase, A., Andersson, E., Banzhaf, E., Baro, F., et al., 2017. Greening cities - to be socially inclusive? About the alleged paradox of society and ecology in cities. Habitat Int. 64, 41–48. Hartig, J.H., Krueger, A., Rice, K., Niswander, S.F., Jenkins, B., Norwood, G., 2012. Transformation of an industrial brownfield into an ecological buffer for Michigan's only Ramsar wetland of international importance. Sustain. For. 4, 1043–1058. Hartley, W., Dickinson, N.M., Clemente, R., French, C., Piearce, T.G., Sparke, S., et al., 2009. Arsenic stability and mobilization in soil at an amenity grassland overlying chemical waste (St. Helens, UK). Environ. Pollut. 157, 847–856. Higgins, M.R., Olson, T.M., 2009. Life-cycle case study comparison of permeable reactive barrier versus pump-and-treat remediation. Environ. Sci. Technol. 43, 9432–9438. Hoag, G.E., Collins, J.B., Holcomb, J.L., Hoag, J.R., Nadagouda, M.N., Varma, R.S., 2009. Degradation of bromothymol blue by ‘greener’ nano-scale zero-valent iron synthesized using tea polyphenols. J. Mater. Chem. 19, 8671. Hou, D., Al-Tabbaa, A., 2014. Sustainability: a new imperative in contaminated land remediation. Environ. Sci. Pol. 39, 25–34. Hou, D., Li, F., 2017. Complexities surrounding China's soil action plan. Land Degrad. Dev. 28, 2315–2320. Hou, D., Al-Tabbaa, A., Luo, J., 2014a. Assessing effects of site characteristics on remediation secondary life cycle impact with a generalized framework. J. Environ. Plan. Manag. 57, 1083–1100. Hou, D., O'Connor, D., Al-Tabbaa, A., 2014b. Modeling the diffusion of contaminated site remediation technologies. Water Air Soil Pollut. 225, 1–6. Hou, D., Al-Tabbaa, A., Hellings, J., 2015. Sustainable site clean-up from megaprojects: lessons from London 2012. Proceedings of the Institution of Civil Engineers-Engineering Sustainability. 168. Thomas Telford Ltd., pp. 61–70. Hou, D., Gu, Q., Ma, F., O'Connell, S., 2016. Life cycle assessment comparison of thermal desorption and stabilization/solidification of mercury contaminated soil on agricultural land. J. Clean. Prod. 139, 949–956. Hou, D., O'Connor, D., Nathanail, P., Tian, L., Ma, Y., 2017a. Integrated GIS and multivariate statistical analysis for regional scale assessment of heavy metal soil contamination: a critical review. Environ. Pollut. 231, 1188–1200.

Hou, D., Qi, S., Zhao, B., Rigby, M., O'Connor, D., 2017b. Incorporating life cycle assessment with health risk assessment to select the ‘greenest'cleanup level for Pb contaminated soil. J. Clean. Prod. 162, 1157–1168. Hou, D., Ding, Z., Li, G., Wu, L., Hu, P., Guo, G., et al., 2018a. A sustainability assessment framework for agricultural land remediation in China. Land Degrad. Dev. 29, 1005–1018. Hou, D., Song, Y., Zhang, J., Hou, M., O'Connor, D., Harclerode, M., 2018b. Climate change mitigation potential of contaminated land redevelopment: a city-level assessment method. J. Clean. Prod. 171, 1396–1406. Huang, L., Luo, F., Chen, Z., Megharaj, M., Naidu, R., 2015. Green synthesized conditions impacting on the reactivity of Fe NPs for the degradation of malachite green. Spectrochim. Acta A Mol. Biomol. Spectrosc. 137, 154–159. Huang, M., Zhu, Y., Li, Z., Huang, B., Luo, N., Liu, C., et al., 2016. Compost as a soil amendment to remediate heavy metal-contaminated agricultural soil: mechanisms, efficacy, problems, and strategies. Water Air Soil Pollut. 227, 359. Jha, A.K., Prasad, K., Kulkarni, A.R., 2009. Synthesis of TiO2 nanoparticles using microorganisms. Colloids Surf. B: Biointerfaces 71, 226–229. Jin, Y., O'Connor, D., Ok, Y.S., Tsang, D.C.W., Liu, A., Hou, D., 2019. Assessment of sources of heavy metals in soil and dust at children's playgrounds in Beijing using GIS and multivariate statistical analysis. Environ. Int. 124, 320–328. Kabisch, N., Frantzeskaki, N., Pauleit, S., Naumann, S., Davis, M., Artmann, M., et al., 2016. Nature-based solutions to climate change mitigation and adaptation in urban areas: perspectives on indicators, knowledge gaps, barriers, and opportunities for action. Ecol. Soc. 21. Kadlec, R.H., Wallace, S., 2008. CRC press, Treatment wetlands. Kattwinkel, M., Biedermann, R., Kleyer, M., 2011. Temporary conservation for urban biodiversity. Biol. Conserv. 144, 2335–2343. Keesstra, S., Nunes, J., Novara, A., Finger, D., Avelar, D., Kalantari, Z., et al., 2018. The superior effect of nature based solutions in land management for enhancing ecosystem services. Sci. Total Environ. 610, 997–1009. Kirthi, A.V., Rahuman, A.A., Rajakumar, G., Marimuthu, S., Santhoshkumar, T., Jayaseelan, C., et al., 2011. Biosynthesis of titanium dioxide nanoparticles using bacterium Bacillus subtilis. Mater. Lett. 65, 2745–2747. Kovacs, H., Szemmelveisz, K., 2017. Disposal options for polluted plants grown on heavy metal contaminated brownfield lands - a review. Chemosphere 166, 8–20. Lafortezza, R., Corry, R.C., Sanesi, G., Brown, R.D., 2008. Visual preference and ecological assessments for designed alternative brownfield rehabilitations. J. Environ. Manag. 89, 257–269. Laval-Gilly, P., Henry, S., Mazziotti, M., Bonnefoy, A., Comel, A., Falla, J., 2017. Miscanthus x Giganteus composition in metals and potassium after culture on polluted soil and its use as biofuel. Bioenergy Res. 10, 846–852. Levi, D., Kocher, S., 2006. The use of coastal brownfields as nature preserves. Environ. Behav. 38, 802–819. Liang, D., Wang, S., 2017. Development and characterization of an anaerobic microcosm for reductive dechlorination of PCBs. Front. Environ. Sci. Eng. 11. Loures, L., 2015. Post-industrial landscapes as drivers for urban redevelopment: public versus expert perspectives towards the benefits and barriers of the reuse of postindustrial sites in urban areas. Habitat Int. 45, 72–81. Meers, E., Van Slycken, S., Adriaensen, K., Ruttens, A., Vangronsveld, J., Du Laing, G., et al., 2010. The use of bio-energy crops (Zea mays) for ‘phytoattenuation'of heavy metals on moderately contaminated soils: a field experiment. Chemosphere 78, 35–41. Megharaj, M., Naidu, R., 2017. Soil and brownfield bioremediation. Microb. Biotechnol. 10, 1244–1249. MEP, 2014. National Soil Contamination Survey Report. Ministry of Environmental Protection, Beijing, China. MHCLG, 2016. First Areas to Push for Faster Brownfield Land Development. Ministry of Housing, Communities & Local Government. Mitchell, R.J., Richardson, E.A., Shortt, N.K., Pearce, J.R., 2015. Neighborhood environments and socioeconomic inequalities in mental well-being. Am. J. Prev. Med. 49, 80–84. Nature, 2017. 'Nature-based solutions' is the latest green jargon that means more than you might think. Nature 541, 133. Nesshover, C., Assmuth, T., Irvine, K.N., Rusch, G.M., Waylen, K.A., Delbaere, B., et al., 2017. The science, policy and practice of nature-based solutions: an interdisciplinary perspective. Sci. Total Environ. 579, 1215–1227. O'Brien, L., 2005. Trees and Woodlands: Nature's Health Service. Forest Research, Farnham. O'Connor, D., Hou, D., 2018. Targeting cleanups towards a more sustainable future. Environmental Science: Processes & Impacts. O'Connor, D., Peng, T., Li, G., Wang, S., Duan, L., Mulder, J., et al., 2017. Sulfur-modified rice husk biochar: a green method for the remediation of mercury contaminated soil. Sci. Total Environ. 621, 819. O'Connor, D., Hou, D., Ok, Y.S., Song, Y., Sarmah, A.K., Li, X., et al., 2018a. Sustainable in situ remediation of recalcitrant organic pollutants in groundwater with controlled release materials: a review. J. Control. Release 283, 200–213. O'Connor, D., Peng, T., Zhang, J., Tsang, D.C., Alessi, D.S., Shen, Z., et al., 2018b. Biochar application for the remediation of heavy metal polluted land: a review of in situ field trials. Sci. Total Environ. 619, 815–826. Pelaez, A.I., Lores, I., Sotres, A., Mendez-Garcia, C., Fernandez-Velarde, C., Santos, J.A., et al., 2013. Design and field-scale implementation of an "on site" bioremediation treatment in PAH-polluted soil. Environ. Pollut. 181, 190–199. Peng, T., O'Connor, D., Zhao, B., Jin, Y., Zhang, Y., Tian, L., et al., 2019. Spatial distribution of lead contamination in soil and equipment dust at children's playgrounds in Beijing, China. Environ. Pollut. 245, 363–370. Peters, K., Elands, B., Buijs, A., 2010. Social interactions in urban parks: stimulating social cohesion? Urban For. Urban Green. 9, 93–100.

Y. Song et al. / Science of the Total Environment 663 (2019) 568–579 Qian, Y., Gallagher, F.J., Feng, H., Wu, M., 2012. A geochemical study of toxic metal translocation in an urban brownfield wetland. Environ. Pollut. 166, 23–30. Radwanski, D., Gallagher, F., Vanderklein, D.W., Schaefer, K.V.R., 2017. Photosynthesis and aboveground carbon allocation of two co-occurring poplar species in an urban brownfield. Environ. Pollut. 223, 497–506. Rainbow, A., Wilson, F., 2002. Composting for soil improvement in the United Kingdom. Proceedings of the 12th International Soil Conservation Organization Conference. 67. Tsinghua University Press, Beijing. Rall, E.L., Haase, D., 2011. Creative intervention in a dynamic city: a sustainability assessment of an interim use strategy for brownfields in Leipzig, Germany. Landsc. Urban Plan. 100, 189–201. Raymond, C.M., Frantzeskaki, N., Kabisch, N., Berry, P., Breil, M., Nita, M.R., et al., 2017. A framework for assessing and implementing the co-benefits of nature-based solutions in urban areas. Environ. Sci. Pol. 77, 15–24. Roy, S., Labelle, S., Mehta, P., Mihoc, A., Fortin, N., Masson, C., et al., 2005. Phytoremediation of heavy metal and PAH-contaminated brownfield sites. Plant Soil 272, 277–290. Salisbury, A.B., Reinfelder, J.R., Gallagher, F.J., Grabosky, J.C., 2017. Long-term stability of trace element concentrations in a spontaneously vegetated urban brownfield with anthropogenic soils. Soil Sci. 182, 69–81. Sänger, H., Jetschke, G., 2004. Are assembly rules apparent in the regeneration of a former uranium mining site. Assembly Rules and Restoration Ecology: Bridging the Gap between Theory and Practice. SER Island Press, Washington, USA, pp. 305–324. Schreurs, E., Voets, T., Thewys, T., 2011. GIS-based assessment of the biomass potential from phytoremediation of contaminated agricultural land in the Campine region in Belgium. Biomass Bioenergy 35, 4469–4480. Schroeder, P., Beckers, B., Daniels, S., Gnaedinger, F., Maestri, E., Marmiroli, N., et al., 2018. Intensify production, transform biomass to energy and novel goods and protect soils in Europe-a vision how to mobilize marginal lands. Sci. Total Environ. 616, 1101–1123. Shen, Z., Zhang, J., Hou, D., DCW, Tsang, Ok, Y.S., Alessi, D.S., 2018. Synthesis of MgOcoated corncob biochar and its application in lead stabilization in a soil washing residue. Environ. Int. 122, 357–362. https://doi.org/10.1016/j.envint.2018.11.045, ISSN 0160-4120. Shen, Z., Hou, D., Jin, F., Shi, J., Fan, X., Tsang, D.C.W., et al., 2019. Effect of production temperature on lead removal mechanisms by rice straw biochars. Sci. Total Environ. 655, 751–758. Slenders, H.L.A., Dols, P., Verburg, R., de Vries, A.J., 2010. Sustainable remediation panel: sustainable synergies for the subsurface: combining groundwater energy with remediation. Remediat. J. 20, 143–153. Song, Y., Hou, D., Zhang, J., O'Connor, D., Li, G., Gu, Q., et al., 2018. Environmental and socio-economic sustainability appraisal of contaminated land remediation strategies: a case study at a mega-site in China. Sci. Total Environ. 610, 391–401. Thornton, G., Franz, M., Edwards, D., Pahlen, G., Nathanail, P., 2007. The challenge of sustainability: incentives for brownfield regeneration in Europe. Environ. Sci. Pol. 10, 116–134. Timilsina, G.R., Beghin, J.C., der Mensbrugghe, D., Mevel, S., 2012. The impacts of biofuels targets on land-use change and food supply: a global CGE assessment. Agric. Econ. 43, 315–332.

579

UN, July 1, 2018. The New Urban Agenda: Key Commitments. 2016. USEPA, 2006. In Situ and Ex Situ Biodegradation Technologies for Remediation of Contaminated Sites. USEPA, 2008. Green remediation: incorporating sustainable environmental practices into remediation of contaminated sites. EPA 542-R-08-002. USEPA. United States Environmental Protection Agency, Washington, DC. USEPA, 2017a. Overview of the Brownfields Program. 2017. USEPA, 2017b. Superfund Remedy Report 15th Edition EPA-542-R-17-001, Washington DC. Varma, R.S., 2012. Greener approach to nanomaterials and their sustainable applications. Curr. Opin. Chem. Eng. 1, 123–128. Virkutyte, J., Varma, R.S., 2014. Greener and sustainable remediation using iron nanomaterials. In: Sharma, V.K., Chang, S.M., Doong, R.A., Wu, C.H. (Eds.), Green Catalysts for Energy Transformation and Emission Control. 1184, pp. 1–21. Wang, Y., Li, Q., Zhang, P., O'Connor, D., Varma, R.S., Yu, M., et al., 2019. One-pot green synthesis of bimetallic hollow palladium-platinum nanotubes for enhanced catalytic reduction of p-nitrophenol. J. Colloid Interface Sci. 539, 161–167. Weng, X., Huang, L., Chen, Z., Megharaj, M., Naidu, R., 2013. Synthesis of iron-based nanoparticles by green tea extract and their degradation of malachite. Ind. Crop. Prod. 51, 342–347. Williams-Johnson, M.M., Ashizawa, A.E., De Rosa, C.T., 2001. Trichloroethylene in the environment: public health concerns. Hum. Ecol. Risk Assess. Int. J. 7, 737–753. Wilschut, M., Theuws, P.A.W., Duchhart, I., 2013. Phytoremediative urban design: transforming a derelict and polluted harbour area into a green and productive neighbourhood. Environ. Pollut. 183, 81–88. Wu, S., He, H., Inthapanya, X., Yang, C., Li, L., Zeng, G., et al., 2017. Role of biochar on composting of organic wastes and remediation of contaminated soils—a review. Environ. Sci. Pollut. Res. Int. 24, 1–18. Zalesny Jr., R.S., Stanturf, J.A., Gardiner, E.S., Banuelos, G.S., Hallett, R.A., Hass, A., et al., 2016. Environmental Technologies of Woody Crop Production Systems. Bioenergy Res. 9, 492–506. Zhang, P., Lo, I., O'Connor, D., Pehkonen, S., Cheng, H., Hou, D., 2017. High efficiency removal of methylene blue using SDS surface-modified ZnFe2O4 nanoparticles. J. Colloid Interface Sci. 508, 39–48. Zhang, P., Hou, D., O'Connor, D., Li, X., Pehkonen, S.O., Varma, R.S., et al., 2018. Green and size-specific synthesis of stable Fe-Cu oxides as earth-abundant adsorbents for malachite green removal. ACS Sustain. Chem. Eng. 6 (7), 9229–9236. https://doi.org/ 10.1021/acssuschemeng.8b01547. Zhang, Y., Hou, D., O'Connor, D., Shen, Z., Shi, P., Ok, Y.S., et al., 2019. Lead contamination in Chinese surface soils: source identification, spatial-temporal distribution and associated health risks. Crit. Rev. Environ. Sci. Technol. (In press). Zhao, B., O'Connor, D., Zhang, J., Peng, T., Shen, Z., Tsang, D.C.W., et al., 2018. Effect of pyrolysis temperature, heating rate, and residence time on rapeseed stem derived biochar. J. Clean. Prod. 174, 977–987.