Soil pollution and ecosystems

Figure 14. Summary analysis: soil pollution and ecosystems

Note: Link to further data on LUCAS. 

Introduction

Soil is essential for all terrestrial ecosystems and their biodiversity. An active and healthy biological soil ecosystem with a diversity of soil animals and microbes is needed to make sufficient nutrients available, and to decompose, filter and/or immobilise pollutants. Soil’s biochemical capacity is key to allowing terrestrial ecosystems to thrive; it also largely determines how contaminants are transported to lower soil layers with the percolating soil water.

Pollutants can enter soil through various pathways, including atmospheric deposition (e.g. of heavy metals, nitrogen), direct application (e.g. of synthetic fertilisers, manure, pesticides, sludges, waste) and accidents (e.g. spills at industrial sites). These contaminants affect soil in four ways:

1. The diversity and activity of soil-dwelling organisms are affected, and plant species diversity is reduced. The soil ecosystem is directly affected by contamination; once toxic levels are reached, sensitive species are eliminated in favour of a few dominating ones.
2. Contaminants typically enter the food chain through soils. Plants and animals take up contaminants into their tissues and pass them on to organisms of higher trophic levels, including humans.
3. Drinking and irrigation water contamination depends on the soil passage and the soil’s filtering capacity. Contaminants pass through the soil into aquifers through leaching and subsurface run-off.
4. Flooding, water erosion, surface run-off and wind erosion redistribute contaminants. This affects urban as well as rural areas.
    

In Europe, the chemical contamination of soils is widespread. This takes place at local sites (mostly in urban areas), at mining locations and in larger areas, such as those under agricultural management or previously flooded land. The two main categories of pollutants affecting soil are heavy metals and organic contaminants. Recently, pollution by pharmaceuticals and plastics has become an emerging concern.

The intensity and impact of soil pollution vary significantly across Europe. This is due to the large differences across regions with respect to soil properties, land use, the type and number of agricultural inputs (fertilisers or manure) and climate.

The EU soil strategy for 2030 reiterates the general zero pollution ambition: by 2050, soil pollution should be reduced to levels no longer considered harmful to human health and the environment (EC, 2021). It also prioritises pollution prevention at source, aligning with the zero pollution hierarchy. Moreover, the European Commission is preparing to propose a soil health law with legally binding provisions, such as the requirement to identify and remediate contaminated sites.

Pollution of agricultural land through heavy metals

Plants growing in soils polluted with heavy metals may show a reduction in growth, performance and yield (Chibuike and Obiora 2014; Zhu et al., 2020). Evidence also suggests that metal pollution significantly reduces the diversity of bacterial communities by up to 90% (Gans et al., 2005).

The distribution of heavy metals in agricultural soils has recently been documented by the EEA (De Vries et al., 2022). While copper and zinc are essential plant micronutrients in trace amounts, high concentrations lead to an exceedance of critical levels — thresholds above which harm to soil ecosystems can occur. Such exceedances are seen across a significant proportion of Europe’s agricultural areas. Copper, for example, has been extensively used as a fungicide, especially in vineyards to combat mildew; this land use is considered a significant cause of soil copper pollution (Ballabio et al., 2018). Copper and zinc mainly reach the soil through animal manure (77% and 78%, respectively) (De Vries et al., 2022). Future zero pollution monitoring at the EU level will build on the Land Use and Coverage Area Frame Survey (LUCAS) soil module, through which heavy metals and other contaminants are now regularly being monitored.

Map 7. Critical limit exceedances for copper (left) and zinc (right) in the EU-27, 2010

Notes : In each map the colours represent the level of exceedance of the thresholds in units of mg of each metal per kilogram of soil. For values less than zero, there is no exceedance. Only values greater than zero indicate an exceedance of the critical limit in each case.

Source: De Vries et al. (2022).

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Map 7 shows the areas in which soil metal content exceeds critical levels in terms of ecotoxicological effects on soil organisms. Critical limits for copper and zinc are exceeded in 23% and 18% of the EU-27’s arable lands assessed, respectively. This means that the amounts of these metals in soils are too high in a significant area (De Vries et al., 2022).

Cadmium is a toxic heavy metal that largely contaminates soil via mineral fertilisers (which account for around 43% of contamination). It does not exceed critical limits (De Vries et al., 2022). However, soil cadmium levels are slightly increasing in areas with calcareous soils and/or low precipitation inputs (Map 8). This may lead to long-term negative effects on the quality of food, groundwater and surface waters.

Map 8. Cadmium accumulation in soils in the EU-27, 2010

Notes: The map shows areas where cadmium levels are accumulating (with values greater than zero) and depleting (with values less than zero). Accumulation rates have been slowing more recently as a result of lower application rates of inorganic fertilisers and lower levels of input from atmospheric pollution.

Source: De Vries et al. (2022).

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Pollution of agricultural land through organic pollutants

Persistent organic pollutants (POPs), which include many herbicides, fungicides and insecticides, are investigated in routine soil monitoring (Hvězdová et al., 2018). Additional data come from the 2018 LUCAS soil module, which monitored 3,470 sites for pesticides (JRC, 2022; Orgiazzi et al., 2022). While there is rich literature on POP prevalence in soils, knowledge about POP accumulation in larger areas — and the resulting environmental impact — is still limited (FAO and UNEP, 2021).

In a representative sample of European agricultural soils (monitored as part of the LUCAS soil module), more than 80% of the soils tested contained pesticide residues (Silva et al., 2019). Geissen et al. (2021) reviewed the risks of pesticides and possible cocktail effects on soil organisms. Considering that these substances are toxic, DNA damage in earthworms, changes in enzymatic activity and bacterial imbalances are possible. Soil composition can also influence how easily pesticides may find their way into water bodies, with the risk of pesticide movement being highest for coarsely textured soils (McGinley et al., 2022).

Nutrient pollution

Nutrient pollution sources and impacts are discussed in other parts of this zero pollution monitoring assessment and will not be repeated in detail here. This includes assessing progress towards targets to reduce nutrient losses by 50%, reducing air pollutant impacts on ecosystems by 25% and reducing the influence that excess nutrients can have on bathing water and drinking water.

It is clear that soil ecosystems play an important role in transporting these pollutants into waterways; for example, only 60-65% of the nitrogen applied to agricultural land in Europe is taken up by crops (De Vries et al., 2022). Nutrient deposition (primarily ammonia from agriculture) on land also harms a significant proportion of EU terrestrial habitats.

In addition, while sludges from wastewater treatment plants benefit crop growth because of their nutrient content, other contaminants can also be present in sludges. The use of sludges requires careful monitoring and assessment to prevent pollution as detailed in the zero pollution ‘Signal’ on assessment of the impacts of sewage sludge spreading. The ongoing evaluation of the Sewage Sludge Directive should help reduce pressure from emerging contaminants such as pharmaceuticals and plastics.

Indicator analysis – soil pollution and ecosystems

The zero pollution and health section assesses the EEA indicator on progress in the management of contaminated sites. No other formal indicators are currently available for soil pollution and ecosystems.

Cover image source: © Panagiotis Dalagiorgos, Well with Nature /EEA