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), Hvězdová 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 (Cycoń 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.

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 (Cycoń 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.

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.

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.

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.

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.

1 Need for clear definitions regarding soil pollution

A clear definition of soil health, including a clear set of parameters and monitoring approaches is essential. In general, across different studies, projects and policy frameworks, there are different definitions and understandings of ‘soil pollution’. In view of policy frameworks, setting targets and progressing towards targets, there is a need for clear agreements on definitions. For example, the term ‘pollutant’ should be clearly defined, as there is a need to differentiate substances which are causing harm/negative impacts, from those which are present without causing harm. For example substances added to the soil which are causing no harm could be considered contaminants. Substances that are causing negative impacts could be described as pollutants. There should also be made a distinction between naturally present and human introduced pollutants, especially in terms of solutions related to prevention and legislation. However, also naturally present pollutants, such as heavy metals, can occur at hazarouds concentrations (e.g. radon from bedrock in mountainous regions). A clear definition on a ‘clean soil’ is lacking (FAO 2020): there is no clear understanding on what is considered a clean soil and a polluted soil. For example, should the definition of a clean or healthy soil entail the absence of pollutants/the lack of exceedance of defined concentration thresholds, or the absence of negative impacts on certain soil health descriptors and ecosystem functioning? The thresholds from which certain pollutants are considered harmful depend on the soil characteristics, and are hence often country/region specific.

In view of policy frameworks and projects, there also is a need to define which soil pollutants are considered (e.g. pesticides, potassium, nitrate, mineral oil hydrocarbons, pharmaceuticals, microplastics, PFAS, newly emerging contaminants). A clear classification and prioritization approach is needed, in view of monitoring, setting targets and implementing management practices. In this regard, we also refer to the knowledge gaps on monitoring, indicators and thresholds/criteria.

2 Data gaps on soil pollution in soils and lack of systemized monitoring

A clear lack of data on soil pollution exists, linked to a lack of systemized monitoring frameworks, which are needed to assess the scope and possible impacts of soil pollution, and to develop management and policy tools.

In this regard, it is also a needed to (further) develop classification frameworks for contaminants in combination with prioritization methodologies. A classification framework (e.g. decision tree) should take into account:

• The (eco)toxicity of contaminants and impact on soil health, ecosystem functioning and human health, determined by risk assessments. The interaction of the contaminant with other soil substances (e.g. other contaminants, organic matter, clay content) and living organisms. Mixture, synergistic and cumulative effects should be considered

• The prevalence of the contaminants

• Origin of contaminants

• Their persistence (short/medium/long term) and bioaccumulation

• Prevention and Bioremediation solutions

• Possible migration, evaporation and chemical phase change of contaminants of pollutants

• Risk for exposure

• ...

The above criteria should also be considered to develop a set of soil pollution indicators. A contamination framework is essential for improved monitoring and remediation of soil contaminants, and should be taken into account when designing monitoring frameworks, performing risk assessments and setting policy and management priorities.

Also the difficulty of monitoring substances should be taken into account. There is much diversity and complexity in the monitoring of different pollutants. For example, microplastics are very challenging to monitor. Also newly emerging pollutants present an important challenge. It is key to include newly emering pollutants in monitoring frameworks, for example through generic chemical screening methodologies. Although prioritization approaches and practical feasibility are prerequisites for effective gathering of data and monitoring, it is overall essential to monitor as many soil components/contaminants as possible. Materials which are currently not considered pollutants, could pose extensive problems in the future. Past experience has shown a long delay between substances ending up in soils, and the realisation of their negative impacts, resulting in far-reaching, long-term challenges for ecosystems, their services and human health. Currently there is a lack of understanding of the scope of contaminants/pollutants, including newly emerging contaminants, and their possible (future) impact on soil functioning. Large data gaps exist regarding the presence of emerging pollutants (e.g. pharmaceuticals, endocrine disruptors, hormones, micropollutants (e.g. microplastics) in soils, their behaviour in the environment and their toxicity, transport and bioaccumulation properties in humans. Available research shows that emerging pollutants can raise pollutants of concern, involving high risks for the environment and human health (Rodríguez-Eugenio et al. 2018,Covaci et al. 2011). Enhancing and implementing methodologies to measure and predict the presence and impact of newly emerging contaminants are needed. Concluding, there is a significant need for the development of the appropriate monitoring frameworks and the standardisation of methodologies for the measurement of emerging pollutants.

3 Behaviour/transportation and fate of soil pollutants and link of soil pollution with water and air

Extensive knowledge gaps exist concerning the partition of pollutants in different physical phases, and the behaviour, transportation and fate of many soil pollutants in soil, water and air. For example, transport of pollutants via air, water and soils is a major factor in (diffuse) soil pollution. These three compartments hence need to be adequately assessed to evaluate (the impact of) diffuse soil pollution, demanding complex analyses (Geissen et al. 2021). Soil pollution is a major cause of groundwater and surface water contamination, and NOx soil emissions can have important impacts on air quality. Local pollution (e.g. contaminated sites) is via transportation processes also often linked to diffuse pollution. At the same time, pollutants found in water bodies and in the air can be transported to soils, through precipitation or deposition processes. The interlinkages of the different matrices entail important consequences for management of pollution. For example, when groundwater is contaminated, the costs and complexity of bioremediation of soils are greatly increased.

Processes of transportation (e.g. wind erosion) and air-water-soil interactions are highly dependent on soil characteristics and climatic conditions. Hence, a global approach is challenging, and site-specific evaluations are needed.

4 Impact of soil pollutants (individual and mixtures, short-term and long-term) on soils and soil ecosystem services

Significant knowledge gaps exist concerning the impact of soil pollutants on soil characteristics, including on soil biodiversity, soil functioning, other living organisms and the delivery of ecosystem services.

For the majority of pollutants, there are no comprehensive (eco)toxicity data, and hence risk assessments, available (e.g. microplastics). When data on toxicity and risk are available, they are often limited to the impact of a single pollutant on a small set of organisms during a short time frame, often in controlled (laboratory) conditions. However, it is essential that cumulative and synergistic effects and long-term effects of pollutants in field conditions are taken into account, to assess the probable impacts of soil pollution on long term soil health and ecosystem functioning. Although available research clearly shows the extensive impacts and possible impacts of soil pollution on soil characteristics, biodiversity and the delivery of ecosystem services, large data gaps remain. The high complexity of soil and interactions of soil compounds, organisms and contaminants provides a large challenge in assessing the full impact of soil pollution on the delivery of ecosystem services.

Again, it is important to note that the impacts of soil pollutants are site specific, as they depend on soil characteristics and environmental conditions.

5 Overall impact of soil pollution on wider ecosystem functioning (beyond soils)

On the one hand, soil pollution impacts the ecosystem services directly linked to soils, such as soil biodiversity at all levels (from micro- to macro-organisms), structure, aeration, control of erosion, nutrient cycling, water retention and buffering, crop health and growth, … On the other hand, soil pollution and transportation of soil pollutants also impact ecosystems far beyond soils, e.g. aquatic systems, vegetation, insects (links between belowground and aboveground biodiversity: many insects have a life phases below- and aboveground), mammals and other fauna dependent on soil health and biodiversity, pollination, …The full scope of these impacts is estimated to be extensive, but not comprehensively understood or assessed.

6 Baseline, Indicators/descriptors and quality thresholds/criteria

Connected to the knowledge gaps related to the need for clear definitions, there is a need to set a clear baseline for the assessment of progress towards targets. Currently, knowledge gaps remain on how to set the baseline(s). This while baseline(s) are needed to define among more policy targets. For example, the baseline could be based on a set of soil descriptors and accompanying criteria. A lack of soil monitoring data regarding required parameters and exisiting concentrations lies at the base of this knowledge gap. Setting up the baseline at EU level, and assessing different local contacts, is a prerequisite to effectively set targets, impemenent actions to achieve them, and effective mechanisms to monitor progress towards targets,

Different indicators/descriptors and accompanying quality thresholds/criteria for assessing soil health have been described in scientific literature and applied by policy frameworks (European Environment Agency 2020). Pollution is one of the many aspects which can make a soil unhealthy: a polluted soil is considered an unhealthy soils. However, a lack of understanding and agreement remains on which indicators and criteria to apply to define and assess (the progress towards) healthy soils, levels of soil degradations, and identify soils which need restoration. In order to efficiently set targets, and make progress towards targets, a clear understanding of baselines, indicators and quality thresholds are all key.

7 Impact of soil pollutants (individual and mixtures, short-term and long-term) on human health

Available research clearly shows that soil pollution poses severe risks to human health. People are throughout their life exposed to soil pollutants through different routes (ingestion, inhalation, skin exposure). The measure of all the exposures throughout a lifetime is referred to as "the exposome". Drinking water contamination, food contamination, transport of pollutants via dust to places frequented by people (paths, playgrounds, houses, gardens, …), ingestion of soil particles, … are a few important exposure pathways, how soil pollution can impact human health. In accordance with the knowledge gaps regarding the full impact of soil pollution on soil characteristics, biodiversity and ecosystem functioning, extensive knowledge gaps remain on the impacts of soil pollution on human health. For example, many uncertainties remain on the full impact of diffuse pollutants on human health.

8 Effects (social, economic, cultural) of and on different stakeholders

A variety of different stakeholders are involved in and/or impacted by soil pollution and restoration: citizens, scientists, farmers, industries (e.g. pesticide producers), water companies, policy bodies, …). For example, soil pollution has a wide impact or possible future impact on stakeholders and land uses which directly or indirectly depend on ecosystem services delivered or supported by healthy soils, such as all citizens, farmers, drinking water producers, cultural heritage (landforms etc.) … A concrete example are farmers who engage in low-input/nature inclusive/restorative practices, and are confronted with residues from previous practices or transported residues from other fields. Although available information shows clear and extensive impacts of soil pollution on these different stakeholders, the full scope of economic, social and cultural impacts is not fully understood. Correspondingly, also the potential benefits of soil restoration across different regions have not been fully assessed (e.g. quantification of ecosystem services).

9 Urban Soil Pollution

Urban soil pollution has been documented through several cases, but has been overall poorly studied. Urban soil pollution is associated with specific challenges related to among other issues, t health, water quality (e.g. groundwater pollution) and risks for pollution of surrounding regions. Insights in the full impact of urban soil pollution have been lacking, as well as clear frameworks and initiatives to tackle urban soil pollution.

10 Technical/practical tools to prevent agricultural and non-agricultural soil pollution

Although many management practices and technologies, including Integrated Pest Management strategies, agro-ecological and regenerative practices, monitoring systems and precision farming and biocontrol, are available to reduce agricultural soil pollution, it is apparent that significant challenges remain in their uptake. Moreover, further research is still needed to develop and/or optimize these practices for more cropping systems in different climatic and environmental conditions. For example, the use of functional biodiversity in increasing natural pest control and decreasing dependence on pesticides is a highly complex field, which needs specialised adaptation to specific cropping systems and environments. Moreover, adequate risk assessment systems are needed to effectively and efficiently assess new technologies.

11 Technical/practical tools to remediate soil pollution and restore soils

Current available techniques to remediate soil pollution, such as management practices, crop use, the use of microbial technologies, are in need of further research and development to improve remediation effectiveness. Microbial technologies carry great potential, however still need further development regarding increasing efficiency. The process is highly time consuming, which is considered a significant bottleneck in the field of bioremediation.

12 Which policy tools are available to prevent soil pollution, and are they fit-for-purpose?

Different legislations related to soils are implemented at national level. However, there is a strong need to harmonize different legislations which relate to soils. Sometimes different laws conflict, even within the same jurisdiction (e.g. law on soil protection and law on fertilization in the Netherlands). At the same time, important gaps in legislation exist regarding large-scale monitoring and managing of soil pollution, and a EU level policy framework for soils has been absnet. The EU proposal for a Soil Monitoring Law, published in 2023, aims at addressing part of these challenges. However, the proposal is characterized by important gaps regarding e.g. soil biodiversity and soil pollution, namely diffuse pollution. Also clear binding and time bound targets remain absent in the proposal, as well as a clear link with groundwater and surface water pollution and relevant legislation. Important gaps remain in different policy frameworks with an impact on soil pollution. For example the revised Urban Wastewater Treatment Directive (UWWTD) does not address certain sources of diffuse pollution, such as settlements below 1000 P.E. (population equivalent). Both the existing policy landscape with focus on activities (e.g. agriculture, pesticide use, industrial emissions) should be integrated, as existing legislation regarding management of different resources (e.g. Water Framework Directive, Ambient Air Quality Directives) should be integrated. Important knowledge gaps exist regarding whether or not current legislation and legislation under development will comprehensively address policy needs regarding soil pollution.

13 Socio-economic and market tools to prevent soil pollution/fitness-for-purpose

There is a need for further assessment of available and needed socio-economic and market tools to prevent soil pollution and restore soils. These include incentives and financial support (public and private support), and business models based on soil health, decreasing the soil footprint, remuneration of ecosystem services and stimulating innovation. Public funds need to be directly linked to soil restoration, and not support activities polluting soils. Different market failures contribute to the problem of soil pollution, for example insufficient/heterogeneous internalisation of environmental costs in the EU and beyond, lack of soil data, and a lack of implementation of the polluter pays principle.

14 Which initiatives exist and are needed to involve farmers in soil restoration and prevention of soil pollution?

Different initiatives involving the reduction of soil pollution and enhancement of soil restoration by farmers have been developed, such as projects fostering the implementation of agroecological practices, Integrated Pest Management and organic agriculture. However, a comprehensive overview of all relevant initiatives is needed, as well as, if relevant, information on reasons for discontinuation. This information should contribute to an analysis on which initiatives and supporting conditions would still be needed to increase uptake of good practices throughout Europe.

15 Bottlenecks regarding the implementation and upscaling

Further insight is needed into the bottlenecks and also into enhancing conditions regarding the implementation and upscaling of relevant and valuable techniques to prevent soil pollution and enhance restoration. While many effective techniques to prevent and remediate soil pollution exist, a comprehensive, clear overview on what is preventing their uptake is needed.

16 Modelling

There is a need for further development of modelling tools to assess in an integrative way the impact of soil pollution and the impact of reducing soil pollution and restoring soils on ecosystems and ecosystems services, and associated economic impact.