The state-of-the-art in the soil pollution and restoration domain will be further reviewed during the next phase of the project. In this chapter, we lay down the principles and methods to develop a comprehensive overview of the domain, and provide a first summary of relevant available knowledge and literature.
2.1 System-approach and conceptual framework
A system-approach was developed to comprehensively tackle all aspects of the soil pollution and soil restoration/remediation domain by using the above-mentioned documents as a starting point, literature review listed under Reference and the feed-backs from our stakeholders, as explained under domain 3 below. The following studies provided more input for the development of the system-approach framework shown in Fig. 1: Adhikari and Hartemink 2016, Babí Almenar et al. 2021, Bouma 2014, Greiner et al. 2017, Jónsson and Davíðsdóttir 2016, Lacalle et al. 2020, O'Riordan 2021, Pulleman et al. 2012, Stolte 2016, Vári et al. 2021, Velasquez and Lavelle 2019, Villa et al. 2014, Stavi et al. 2016, Dushkova et al. 2021, Wade 2022, JRC and Maes 2020, Ponge 2015, Wood and Blankinship 2022. Putting soil health into the centre of the system-approach allows us to highlight all elements that are relevant for reaching the Soil Mission objectives of 2050, to demonstrate the complexity of pollution issues including the intertwined nature of policies and to provide a framework for assessing the state-of-the-art, the knowledge gaps and to identify key research questions. A schematic overview of this system approach and the components of the system are presented in Fig. 1. Three main domains were identified as pollution relevant during the scoping process along with the principles that should be integrated into all domains, since they reflect on pollution relevant social and economic aspects.
The four domains:
Soil pollution: identification and assessment of the extent of polluting agricultural and non-agricultural human activities and pollutants including (i) inorganic, (ii) organic) (also living organism) based on (i) soil descriptors and (ii) criteria reflecting on soil health
Effects of pollution: identification and assessment of extent of the impact of soil pollution on i) soil properties and conditions including linkages with other polluting pathways, ii) ecosystem services, soil functions and biodiversity and iii) human livelihoods. Negatively affected (directly or indirectly), (ii) Beneficiaries of polluting activities (e.g. polluters and clean-up companies)
Solutions to soil pollution: Identification of availability of and need for both solutions focused on (i) pollution prevention and (ii) restoration and remediation, as well as the assessment of the role of different stakeholders and policy decisions/frameworks in view of (implementation of) solutions. Negatively affected (directly or indirectly), (ii) Beneficiaries of polluting activities (e.g. polluters and clean-up companies), (iii) Stakeholders influencing decision making (scienes, business, civil society, consumers), (iv) Decision makers. Individual stakeholders or groups of stakeholders can belong to one or to all of mentioned categories.
The Principles for reaching soil pollution reduction targets (2030 and 2050):
Fairness and equality: distribution of and access to natural resources should be fair providing equal opportunity to everyone
Intergenerational justice: refers to the close relationship between generations and mutual respect (Rockström et al. 2023)
Precautionary Principle: allows measures to be taken to avoid risk of environmental harm, even in the face of scientific uncertainty
Prevention Principle: allows preventive measures to prevent the occurrence of environmental damage
Polluter Pays Principle: costs related to environmental damage should be born by those who caused it
Public Participation: the public is involved and is given early and effective opportunities to participate in all stages of their elaboration, when all options are still open
Eco-Economic Decoupling: breaking the links between economic growth and environmental pressure
2.2 Summary of State of the Art on Soil Pollution and Restoration
This part provides a first summary of relevant available knowledge and literature in the domain of soil pollution and restoration, based on a first set of relevant literature and inputs of stakeholders gathered so-far. The state-of-the art will be further developed during the next phase of the project. Specifically, the state-of-the art will be strenghtened with a further review of key relevant grey and scientific literature, as well as with information and outcomes from relevant projects, including the SMS, Prep Soil and EJP soil project.
2.2.1 Sources and scope of soil pollution
In this section, a first overview is given of important factors contributing to soil pollution. This overview will be extended and further elaborated during the following phases of the project. In section 2.2.2 and 2.2.3, a first summary of important impacts of soil pollution is provided. Two main types of soil pollution are mostly considered in literature: point-source soil pollution and diffuse soil pollution.
Point-source soil pollution
Point-source soil pollution is associated with ‘contaminated sites’, which include sites where accidental or intentional spillage took place, and current or former industrial, waste disposal, mining, transport infrastructure and storage sites. Inorganic and organic pollutants, heavy metals, Persistent Organic Pollutants (POPs) and Polycyclic Aromatic Hydrocarbons (PAH) are pollutants often involved in point-source soil pollution. Point-source pollution also frequently involves historic contamination. Current available data on the number and the areal extent of contaminated sites in the EU are characterised by large knowledge gaps. The JRC estimated in 2018 that EU-28 counted about 2.8 million potentially polluted sites: sites where polluting activities are taking place or took place (Paya Perez and E.N. 2018). An EEA report published in 2022, based on national registries, showed that in 2016 1.38 million potentially contaminated sites were registered. About two third of contaminated sites could be potentially historic (e.g. brownfields) (EEA 2022). In 2016, 115 000 contaminated soils were estimated to be remediated in the EU; about 8.3% of the currently registered potentially contaminated sites . It is estimated that at least 166 000 additional sites are in need for remediation or measures which reduce risk (EEA 2022, European Commission 2023a) . Historic contaminated sites don’t fall under current legislation regarding industrial pollution prevention, such as for example the Industrial Emissions Directive. The proposal of the European Commission for the SML, currently under negotiation in the EU Parliament and Council, does include provisions on identification, assessment and management of contaminated sites, and aims to at least partly fill this policy gap. Also data on remediation of contaminated sites are scarce/limited.
Diffuse Soil Pollution
Diffuse soil pollution involves soil pollution whereby matter is transported under a gradient of chemical potential, activity or concentration that often spreads over large areas, and in general doesn’t originate from an easily identifiable, single source. These characteristics cause important challenges in assessing the full scope of diffuse soil pollution. Diffuse pollution often leads to chronic exposure to lower concentrations of pollutants, while the health and ecotoxicological impact of chronic exposure are more difficult to assess, and have been less researched. Agro-chemicals, fertilizers and manure are important contributors to diffuse soil pollution, as well as road traffic and the diffusion of point-source pollution. Often, diffuse soil pollution is further transported by air and water. Important diffuse soil contaminants are listed below (Paya Perez and E.N. 2018,IUNG 2019, Rodríguez-Eugenio et al. 2018).
Pesticides
Agro-chemical soil pollution, including pesticides, has been identified as a major soil threat (Stolte 2016). Different studies, among more by Orton et al. (2013), Pose-Juan et al. (2015), Qu et al. (2016), Chiaia-Hernandez et al. (2017), Hvezdová et al. (2018), have already provided data on the distribution of currently approved or banned pesticides in soils. However, a comprehensive overview on pesticide residues in the soils in the EU has been lacking due to different methods and analyte lists, and different sampling periods and strategies used among different studies. On the contrary, data on pesticide residues in surface water are more abundant, through monitoring in framework of the Water Framework Directive, and additional monitoring in some member states. For example, in the Netherlands pesticide spills in surface water have been monitored for many years (Institute of Environmental Sciences (CML), Leiden University and Royal HaskongingDHV 2024.
An important source of information on the presence of pesticide residues in European soils is the work of Silva et al. (Silva et al. 2022, Silva et al. 2019, Silva et al. 2023, Silva 2022). A large-scale study analyzing 76 pesticide residues in 317 EU agricultural top soils showed that 83% of soils contained 1 or more residues, while 58% of soils contained mixtures of different pesticides (Silva et al. 2019). A large scale study in framework of the H2020 SPRINT project umbrella assessed the presence and levels of 209 pesticide residues in 625 environmental samples in different matrices (soil, crop, outdoor air, indoor dust, surface water and sediment), across 10 study sites (Silva et al. 2023). In 86% of the complete set of samples at least one residue was measured, and in 76% of samples mixtures of different pesticides residues were found. 201 of the samples were taken in soils, and revealed 100 different pesticides. In soils of conventional farms, 99% of the samples contained pesticides, while 96% contained mixtures of at least two pesticide residues. For soils of organic farms, these numbers were 95% and 79% respectively. Total concentrations of pesticides in conventional fields reached a max value of 28.678 ug/kg, and 5.458 ug/kg in organic soils. The study of Silva et al. (Silva et al. 2019) made use of 317 samples from the 2015 LUCAS survey (Land Use and Coverage Area frame Survey). The 2018 LUCAS program included a pesticide module, which will probably be extended (Orgiazzi et al. 2022, Vieira et al. 2023).
Although still limited, the available data show that mixtures of pesticide residues are the rule rather than the exception. Large-scale, harmonized monitoring of mixtures of pesticides residues is urgently needed to evaluate risk for ecosystem and human health (Silva et al. 2023).
Limited data is available on the actual application of pesticides, which will change with the implementation of the Regulation on Statistics on agricultural inputs and outputs (European Commission 2022b). Pesticide sales data, a proxy for actual applications, show that pesticide use has increased from about 215 000 tonnes (2011) tot more than 345 000 tonnes (2017) (Eurostat 2022a).
Persistent Organic Pollutants (POPs)
Important sources of Persistent Organic Pollutants (POPs) are emissions from agriculture, combustion and industry, and from disposed commercial products (e.g. plastic containing POPs). The waste sector is relevant for the more recent POPs, for example through application of sludge. Data on POPs pollution of soils are very limited. For example, a EU study from 2011 (European Commission 2011) included only limited data on 4 POPs pollutants in soils. Under the Stockholm Convention, data on POPs for 2021 (UNEP 2021) were gathered, however important data gaps remain. Long-term POPs pollution trends have shown no decline in Benzo(a)pyrene (B(a)p) air pollution and high concentrations of polychlorinated dioxines and furans (PCDD/Fs) in Europe (TF HTAP 2021).
Also for emerging contaminants, such as the widely used Perfluoralkyl chemicals (PFASs), an important lack of data exists. PFASs resist degradation, and are easily transported over long distances. PFASs pollution is widespread, including in soils, water and waste. Remediation of sites polluted with PFASs is technically challenging and costly (Council of the European Union 2019).
Pharmaceuticals (including veterinary products) and personal care products
An estimated 5,507.4 tonnes of active substance of antimicrobial Veterinary Medicinal Products were sold in Europe in 2020 (EU-27, UK, Iceland, Norway and Switzerland). In the period 2011-2020, a decrease of 43.2% was reported in sales of the 25 countries providing annual data to the European Medicines Agency (European Medicines Agency 2021). Through manure application, veterinary products end up in the soil (Gros et al. 2019), while pharmaceutical and personal care products can pollute soils through sewage sludge application (Gworek et al. 2021). No comprehensive data exist on the scale of contamination of these contaminants in the EU. For example, the continuous release of antibiotics into the environmentan is of important concern. The majority of antibiotics are not completely metabolised in humans and animals, and a high percentage is discharged into water and soil through animal manure, municipal wastwater, sewage sludge and biosolids. Antimicrobioal drug resistance (AMR) poses an important challenge (Cycon et al. 2019).
Plastics and microplastics
Available data from Eurostat (Eurostat 2022b) indicate that the generation of plastic was increasing during the past years (9.5 million tonnes (2004) to 17.2 million tonnes (2018)). This entails important potential impacts for soils. For example, the use of plastic in agriculture (e.g. plastic mulching (estimated rate of 100 000 tonnes per year in the EU), plastic in fertilizer products and pesticides, plastic used in greenhouses, crop protection nets, irrigation systems, sports fields with artifical grass,…)) contributes to soil pollution (EIP AGRI 2020). Microplastics waste has also been increasing due to the use in e.g. cosmetics, leading to the widespread presence of microplastics in the environment and in food. Comprehensive data on microplastics are limited. A study (Lofty et al. 2022) estimated that the contribution of microplastics to soils in Europe through sewage sludge is about 31 000 to 42 000 tonnes yearly. Also tyre wear is estimated to be an important source of microplastic pollution, resulting in about 57 3000-65400 tonnes yearly in soils near roads in Germany (Baensch-Baltruschat et al. 2021.)
Nutrients
About 67% of ecosystem areas in Europe are estimated to be exposed to excessive nitrogen. The primary cause is fertiliser use, livestock densitity and degraded soils in agriculture (European Environment Agency 2018, European Environment Agency 2019, Velthof et al. 2011). Also phosphorus has accumulated in agricultural soils in Europe, after the introduction of phosphorus-containing fertilizers in addition to manure. Manure can also be a source of antibiotics from veterinary medicines (Antikainen et al. 2008, Panagos et al. 2022).
Heavy metals
European countries have a number of approaches to define risk levels associated with different concentrations of heavy metal in soil (Carlon et al., 2007; Ferguson, 1999). The Finnish standard values represent a good approximation of the mean values of different national systems in Europe (Carlon et al., 2007) and India (Awasthi, 2000) and they have been applied in an international context for agricultural soils as well (UNEP, 2013).
About 6.24% of EU agricultural area is estimated to contain high concentrations of heavy metals (concentration above the guideline value set by the Finnish legislation for contaminated soils in agricultural areas) (Ministry of the Environment, Finland 2007). Copper, lead and zinc are estimated to be accumulating in EU soils, while for cadmium a net decline is estimated (De Vries et al. 2022). High concentrations of copper are found in vineyards and orchards in humid climates, because of a high use of fungicides (Ballabio et al. 2018). Ballabio et al. 2021 found that EU hotspots of mercury are located close to mine areas, coal-fired power plants and chlor-alkali industries.
Beyond agricultural soils, data on heavy metals are limited. Panagos et al. (2021) estimated that the average concentration of mercury in EU top soils amounted to 103 g/ha. About 6 tonnes per year would be transferred downstream via transport of sediments (EU27 + UK). Tóth et al. (2016) indicated that heavy metal concentrations in soils are very unevenly distributed through the EU, with many sites of highly concentrated pollution.
Pourret and Hursthouse (2019) (Pourret and Hursthouse 2019) have suggested to use the term 'Potentially Toxic Elements' instead of 'heavy metals' when reporting environmental research. During our further work within the Tink Thank, we will explore this option.
Waste management and disposal
Waste management and disposal (e.g. sewadge sludge, water purification, (urban) compost has a direct and important link with soil pollution. In the futher development of the scoping document, this topic will be further elaborated on in both the state of the art as the knowlege gaps.
2.2.2 Impacts of soil pollution on biodiversity and ecosystems
Different studies have indicated important negative impacts of soil pollution on ecosystems and their services (water purification, water retention, food production, biodiversity, etc.) (Morgado et al. 2018, Rodríguez-Eugenio et al. 2018).
For example, pesticide residues in soil hold risk for biodiversity, ecosystems and their services, and get transported to/taken up by other matrices (water, air, indoor dust, food, microorganisms/microbiota, animals, humans, …). Many pesticide residues are persistent, bioaccumulative or toxic to non-target species (Silva et al. 2019, Silva et al. 2023.) Pesticide residues in soil are shown to negatively impact soil macroorganisms microbiota and the microbiome, as described in a review of Gunstone et al. 2021 on the negative impacts of pesticides on beneficial soil-dwelling invertebrates. Pesticide pollution in soils can alter processes in the rhizosphere, impact plant growth and resistance against pests, alter the composition of soil microorganisms, and can lead to an increase of pathogens and decrease of beneficial organisms. Also changes in nutrient composition in roots, leaves, grape juice and xylem sap have been observed after pesticide applications (Klátyik et al. 2023, Mandl et al. 2018, Zobiole et al. 2010, Zaller et al. 2018, Brühl and Zaller 2021, Ruuskanen et al. 2023). Negative effects on soil organisms also impact fauna dependent on soil organisms, e.g. farmland birds (Rigal et al. 2023).
The excess of fertilizer and manure cause extensive negative impacts on waterways and biodiversity. E.g. mycorrhizal fungi, essential for many soil functions and services, are negatively affected by excessive nutrients (Origiazzi 2016). The multifunctionality of soils, and the trade-offs between for excess nutrients and other soil functions, are assessed by Vazquez et al. 2020.
Pharmaceuticals, such as anbitiobitcs, can affect soil microorganisms, for example by changein their enzyme activity and ability to metabolize different carbon sources, and by altering the overall microbial biomass and releative abundance of different groups (Cycon et al. 2019).
Microplastics can impact soil physicochemical properties (e.g. increase bulk density, decrease porosity and water holding capacity), soil microorganisms, macro-organisms, plant growth and can leach toxic chemicals (Lofty et al. 2022).
Although negative (potential) impacts of different soil pollutants on biodiversity and ecosystem functioning have been shown by a variety of studies, the complete and long-term impact of the cumulative effects of different soil pollutants on the variety of different organisms exposed remains unknown. In general, there is a lack of long-term studies that also evaluate the impact of mixtures and cumulative effects on a wide range of organisms and ecosystem services.
In the next phase of the development of this scoping document, an overview table of the main described (potential) impacts of soil pollutants on biodiversity and ecosystems described in literature will be summarised.
2.2.3 Impacts of soil pollution on stakeholders
Different studies have indicated that soil pollution directly affects human health. Soil pollution can contaminate food, which can pose risks for human health. Many links have been described between increased risks for a variety of illnesses and health impacts, and pollutants frequently found in soils, such as arsenic, lead, and cadmium, organic chemicals such as PCBs (polychlorinated biphenyls), PAHs (polycyclic aromatic hydrocarbons), pharmaceuticals such as antibiotics, pesticides and micro-plastics (Rodríguez-Eugenio et al. 2018, Cox et al. 2019, European Commission 2019, Lim 2021). Rodríguez-Eugenio et al. 2018 underline the potential risks of contaminated soil for human health, including uptake from dust and vapours by farm workers, skin contact and ingestion of soil.
Tolerable daily intake values for pesticide residues are likely to underestimate the risk to consumers, as they don’t account for mixture effects (Silva et al. 2019). Pathways other than ingestion or food, such as inhalation or skin contact, are seriously underestimated. Soil pollutants, such as pesticide residues, can accumulate in the lighter top layer of the soil, and easily get transported by the wind and inhaled by animals and humans. Pesticide residues have also been shown to accumulate in indoor dust (Silva et al. 2019, Silva et al. 2023, Silva et al. 2022,Navarro et al. 2023). A recent paper by Matsuzaki et al. 2023 highlights the potential links between pesticide exposure and the microbiota-gut-brain axis.
Overall, there is an important lack of research on the potential long-term impacts of mixtures of soil pollutants people are exposed to. Here the "exposome" is relevant: the measure of all the exposures of an individual throughout a lifetime and how those exposures relate to health. There is also an important link between the impact of soil pollutants on (soil) biodiversity and human health, as soil pollutnats can lead to the selection for harmful taxa and to an overall decrease in diversity of microbiota, also leading to effects on the human microbiome. More and more research also refers to the impacts of soil pollutants on the gut microbiome, and potential links with health conditions, including neurological illnesses. Soil pollutants can lead to advantages for harmful microbiota, for example through antibiotics resistance (Roslund et al. 2024).
Soil pollution is associated with important economic and social impacts and costs. For example, soil pollution can negatively impact health, land availability, water quality, water retention, crop growth/food production and other ecosystem services (Bouma 2014, Adhikari and Hartemink 2016, Greiner et al. 2017, Jónsson and Davíðsdóttir 2016, JRC and Maes 2020, Lacalle et al. 2020, O'Riordan 2021, Pulleman et al. 2012, Stavi et al. 2016, Stolte 2016, Velasquez and Lavelle 2019).
In the next phase of the development of this scoping document, an overview table of the main described (potential) impacts of soil pollutants on stakeholders described in literature will be summarised.
2.2.4 Solutions to soil pollution
Prevention of soil pollution
Agriculture
Different practices and management tools are available to decrease soil pollution. Integrated Pest Management (IPM), Integrated Crop Management (ICM) and agro-ecological practices have been shown to provide effective approaches to minimizing inputs of pesticides and fertilizers, and maximizing ecosystem functioning and services, such as biological pest control. These approaches are based on increasing the resilience of the crop, while agro-chemicals such as pesticides are only used as a last resort, if needed, instead of prophylactic or calendar-based practices (Rodríguez-Eugenio et al. 2018, IPM Works 2022) . Different EU legislations and initiatives are in force or in development which can contribute to reduction of soil pollution originating from agricultural activities. An assessment of these legislations, their expected impacts and limitations, will be carried out in the next phase of the project.
Non-agricultural soil pollution
Different EU legislations and initiatives are in force or in development which can contribute to reduction of soil pollution originating from industry, traffic and waste. An assessment of these legislations, their expected impacts and limitations, will be carried out in the next phase of the project.
Remediation of soil pollution
Remediation techniques are often divided into in situ (on the site) and ex situ (off the site) remediation, and include physical, chemical and biological treatments. Physicochemical treatments are often characterized with high speed and efficiency, but also with high costs and labour, and potentional destruction of soil functionality. The field of remediation techniques has developed over time to a focus on effective restoration of soil quality and preservation of the environment, while minimizing the damage caused by clean-up interventions. Recent developments have also reflected the aim to promote clean-up strategies which also address climate change effects (Grifoni et al. 2022). Biological treatments provide eco-friendly features and larger social acceptance, but often require long periods. A wide variety of biological techniques have been developed and successfully applied.Lacalle et al. 2020 provide an overview of biological methods of polluted soil remediation for an effective economically-optimal recovery of soil health and ecosystem services. Methods include phytoremediation, phytoextraction, phytostabiliziation, phytomanagement, bioremediation and vermiremediation. Specific challenges are associated with soils contaminated with multiple pollutants. For example the interaction between organic and inorganic pollutants can change bioaccessibility and solubility of pollutants and their biotoxicity and biological metabolic processes. For pollutants that are relatively new to the environment, such as PFAS, important challenges remain due to unknown pathways of degradation. Also competition or joint-adsorption on binding sites poses a challenge. For mixed contaminated soils, successful combinations of chemical and biological remediation techniques have been discussed, although more research is needed (Aparicio et al. 2022, Lacalle et al. 2020). More research is needed on the potential of nature-based solutions and the use of microorganisms for bioremedation processes. In general, more research is needed to improve efficiency, feasibility, costs and time-efficiency of remediation techniques for a variety of different contaminants and soil conditions. As mentioned in the document, this is a significant knowledge gap (Grifoni et al. 2022, Aparicio et al. 2022, Huysegoms and Cappuyns 2017, Lacalle et al. 2020, Ministry of the Environment, Finland 2007, Mulligan et al. 2001, Smith 2010).
In the next phase of the development of this scoping document, an overview table of the main (potential) technical solutions (related to prevention and remediation) to soil pollution described in literature will be summarised.
2.2.5 Social and economic tools to prevent soil pollution/fitness-for-purpose
Important reoccurring aspects regarding socio-economic and market tools relevant to tackling soil pollution are the need for implementation of the polluter pays principle, as well as for the targeted use of public funds. For example, current agricultural legislation and funding doesn’t secure linkages between funding and protection of the environment and enhancement of ecosystem services (OECD 2023). The polluter pays principle is insufficiently included in legislation, while the loss of ecosystem services associated with soil degradation is not integrated into economic optimisation of economic actors. Historic soil pollution poses an additional problem, which challenges the implementation of the polluter pays principle. Who should cover remediation costs of historic pollution remains often a challenge (European Commission 2023a). An important potential instruments is a pollution levy, e.g. a pesticide levy, which is for example used in Denmark (Nielsen et al. 2023). Austria has, for example, a well-designed tax on landfill, incineration and other forms of waste disposal: the waste disposal tax (Altlastenbeitrag) (European Commission 2021c).
In the next phase of the development of this scoping document, an overview table of the main (potential) social and economic tools to reduce soil pollution and enhance restoration will be summarised.
2.2.6 Lock-in mechanisms of soil pollution
Soil pollution is associated with many "lock-in mechanisms". Lock-in mechanisms can be described as the barriers and underlying mechanisms that are holding back the transition towards decreasing or preventing soil pollution. For example, the lock-in mechanisms of pesticide use were analyzed elaborately in the framework of the Sprint project (Frelih-Larsen and Sprint project 2022). These lock-in mechanisms include factors related to farmer’s perceptions and views (Vanino et al. 2022), agronomy and research, economics, knowledge and awareness and policy and regulation. For example, lack of linkage between Common Agricultural Policy funding and the implementation of Integrated Pest Management (IPM)/Integrated Crop Management (ICM), lack of the Commong Agricultural Policy and soil health, lack of independent advisory systems, consumer awareness or market outlets for alternative crops contribute to lock-in mechanisms. Lock-in mechanisms contributing to soil pollution will be further explored during the analysis of ‘bottlenecks’ in reducing soil pollution and restoration.
In the next phase of the development of this scoping document, an overview table of the main lock-in mechanisms challenging reducing soil pollution and enhancing restoration will be summarised.