UN Enviroment Programme

Chapter 14. Summary of key findings and way forward


Background concentration. The concentration of an element or a substance in the soil above natural background concentration due to diffuse atmospheric deposition caused by anthropic activities and not point source discharges (ISO, 2018), in a given place and time. See Natural background concentration definition.

Background value. Statistical characteristics (e.g. a numerical value calculated from a set of observed values of a variable of a selected parameter of the population) of the total (natural pedo-geochemical and anthropogenic) content of a substances in soil (ISO, 2018).

Bio-accessibility. The fraction of the total quantity of a chemical/substance that desorbs from its particle matrix (e.g., soil dust, wood) (Paustenbach, Bruce and Chrostowski, 1997) inside an organism and thus can be metabolized by the organism (ISO, 2015; Semple et al., 2004). Bio-accessibility results from chemical transfer between the particle matrix to the internal environment of the organism, and it depends in a complex way on the internal chemical environment of the organism, the chemical/substance and its matrix, and the reaction kinetics.

Bio-availability. The portion of the total quantity of a chemical/substance that is ‘freely available’ to cross an organism’s cellular membrane from the medium the organism inhabits at a given time (Semple et al., 2004), and which can be metabolically active in a living organism (Klaassen, Casarett and Doull, 2013).

Bio-accumulation. The net result of all processes of absorption and loss, such as respiratory absorption and through food ingestion, and loss by egestion, passive diffusion, metabolism, transfer to offspring and growth (Borgå, 2013). It comprises the specific processes of bioconcentration and biomagnification.

Bioconcentration. The process by which organisms take up chemical/substances from all sources including water, air, soil and diet, and their concentration is enriched within the organisms relative to their concentration in the surrounding environment (Sijm, Kraaij and Belfroid, 2000). In soil organisms, the degree of bioconcentration of a chemical/substance in a given soil organism (e.g. earthworms) at a given time, t, can be determined by:

  1. The bio-accumulation factor (BAF), which is calculated as the ratio between the concentration of a chemical/substance in the organism (Cc(t)) and its concentration in the surrounding medium (Cs(t)), and it is expressed as kg soil*kg-1 organism (OECD, 2010).

  2. The biota-soil-accumulation factor (BSAF), calculated as the ratio between the lipid-normalised concentration of the chemical/substance in the organism and the carbon-normalised concentration of the chemical/substance in the soil

where Cc(t) is the contaminant concentration in a particular compartment/organ of the organism under study at the time of sampling (t), ∫lipid is the lipid content of the organism, Cs is the contaminant concentration in soil at the time sampling (mg kg−1 soil) and ∫SOC is the content of soil organic carbon (Wang et al., 2014).

Biological indicator. An organism, part of an organism, the product of an organism (e.g., enzyme), collection of organisms or biological process that can be used to obtain information about the quality of all or part of the environment (Killham and Staddon, 2002), through measurable responses (i.e., biomarkers). Biological indicators are used to monitor environmental changes, to assess the efficacy of management practices and to provide warning signals for impending ecological shifts (Siddig et al., 2016).

Biomagnification. The enrichment of a chemical/substance in an organism relative to the chemical/substance in the organism’s food, when the major exposure route occurs from the organism’s diet (Drouillard, 2008). Biomagnification leads to increased chemical/substance concentration with higher trophic position in the food web (Borgå, 2013).

Biomonitoring. The use of living organisms to assess environmental contamination or pollution by measuring accumulation of chemicals in organism tissues or by assessing biomarkers of exposure on indicator species.

Carcinogenicity. The ability of a physical phenomenon (e.g. radiation), or of a chemical or biological agent to cause cancer or increase its incidence (United Nations, 2011).

Contaminant. A substance, compound or chemical element present in the soil as a result of human activity and at a concentration that exceeds natural background concentrations (Chapman, 2007; ISO, 2015). The presence of a contaminant does not necessarily indicate harmful or deleterious effects. The term is often used as a synonym for pollutant.

Diffuse pollution. Presence in soil of contaminants that do not have a single point of origin (point-source), often resulting from land runoff, precipitation, atmospheric deposition, drainage, seepage or hydrologic modification (US EPA, 2017). It occurs where emission, transformation and dilution of contaminants in other media have occurred prior to their transfer to soil, or where the pollution is spread over very wide areas due to the source being mobile (e.g., cars, trucks, airplanes, ships, trains, etc.). Diffuse pollution can be distributed over large areas, including globally.

Edaphoclimatic conditions. Set of moisture and temperature conditions prevailing within a soil. It depends on the climate of the site, water movement in the soil, drainage type and biological activity, among other factors. It varies according to the depth within the soil (SECS and IEC, 2021).

Emerging contaminants (ECs). Synthetic or naturally occurring chemicals that are not commonly monitored in the environment, for which no regulatory guidance values are available, but which have the potential to enter the environment and cause known or suspected adverse ecological and (or) human health effects (UNESCO, 2015). ECs are not necessarily new chemicals. They are substances that have often long been present in the environment but whose presence and significance are only now being elucidated, as new detection methods are developed (Huerta-Lwanga et al., 2017).

Endocrine disruptor. An exogenous substance or mixture that alters function(s) of the endocrine system and consequently causes adverse health effects in an intact organism, or its progeny, or (sub)populations (IPCS, 2002).

Environmental Risk Assessment (ERA). An ERA is a process to characterize the nature and magnitude of a risk to environmental health and ecological receptors (e.g. wildlife and soil-dwelling organisms) from chemical contaminants and other stressors that may be present in the environment (US EPA, 2013). ERA integrates chemical and ecotoxicological assessments. A tiered approach is typically used, whereby chemical concentrations in soil are first compared with soil quality guidelines (screening/ warning/ trigger/ target/ intervention/ cut-off values) relevant to the receptor of concern (e.g., human, soil biota, and groundwater).

Eutrophication. The excessive enrichment of surface waters with plant nutrients, primarily N and P (FAO, 2019).

Genotoxicity. The ability of any contaminant to damage the genetic information in a cell, causing changes in chromosomes or DNA and gene mutations that are not necessarily transmissible from cell to cell or generation to generation (Stammberger, Czich and Braun, 2013).

Hazard. The inherent properties of a substance or agent having the potential to cause undesirable consequences or adverse effects to organisms or the environment, depending on the magnitude and duration of exposure (Duffus, Nordberg and Templeton, 2007).

Heavy metals. See trace elements definition (Duffus, 2002).

Inorganic contaminants. The term encompasses elements of natural origin, which are released into the environment by mineralisation of parent material, from unusual rock types, like serpentinite, black shale or alkaline intrusions; or may be caused by human activities, such as emissions from different types of industries, mining, batteries recycling, superphosphate fertilisers, sewage sludge, atomic weapons manufacture, testing and use, nuclear power generation, and radioactive waste disposal. This category includes elements that have diverse behaviours in contact with the soil matrix and have various toxic effects on human health and the environment, e.g. trace elements (TEs), macronutrients such as nitrogen and phosphorous, radionuclides or naturally occurring asbestos.

Land. A delineable area of the earth’s terrestrial surface, encompassing all attributes of the biosphere immediately above or below this surface including those of the near-surface climate, the soil and terrain forms, the surface hydrology (including shallow lakes, rivers, marshes and swamps), the near-surface sedimentary layers and associated groundwater reserve, the living organisms communities, ecological and hydrological processes that operate within the system, the human settlement pattern and physical results of past and present human activities. See soil definition.

Monitoring. The process of repetitive observation and/or measurements for defined purposes of one or more chemicals and chemical, physical and ecological characteristics of the environment, according to pre-arranged schedules in space and time using analytical comparable methods.

Mutagenicity. The ability of any contaminant to damage the genetic information in a cell, producing transmissible genetic alterations to other cells and progeny (Gupta, 2016).

Natural (geochemical) background concentration. The concentration of an element or a substance in the soil that is derived solely from natural sources (geological and pedological processes), commonly expressed in terms of average or a range of values (Reimann and Garrett, 2005), in a given place and time, the origin and presence of which is not the result of human influence (ISO, 2015; Tian et al., 2017). Natural soil background concentrations are variable depending on the mineralogical composition of the soil parent material and on the pedogenetic (soil-forming) processes (Kabata-Pendias and Pendias, 2001; Wilson et al., 2008).

Neurotoxicity. Any adverse effect on the structure and/or the normal activity of the nervous system after exposure to contaminants (neurotoxins) (Spencer and Lein, 2014).

Organic contaminants (OCs). The term includes a wide diversity of carbon-based compounds, with very different chemical properties; e.g., pesticides, polycyclic aromatic hydrocarbons (PAHs), halogenated solvents, petroleum hydrocarbons, polychlorinated biphenyls (PCBs), polychlorinated dibenzo-p-dioxins, and -dibenzofurans (PCDDs/DFs) and pharmaceuticals and personal care products (PPCPs). OCs reach soil mainly through industrial activities, agricultural practices, livestock use and manure storage, waste and wastewater treatments, atmospheric deposition and urban influence (Duarte, Cachada and Rocha-Santos, 2018). Once in soil, OCs may undergo several physicochemical processes (volatilization, leaching, runoff, sorption, plant and animal uptake, and biological and chemical degradation) that determine their persistence, fate and toxicity. Some OCs are Persistent, Toxic and Bio-accumulative (PBT criteria) (Matthies et al., 2016), and can be transported over long distances.

Persistence. The residence time a compound/substance, once introduced into the environment, stays before it is physically removed or chemically or biologically transformed.

Persistent inorganic contaminant (PIP). See trace elements (EVISA, 2003).

Persistent organic pollutant (POP). Organic chemical substance that: (i) possesses toxic characteristics to both humans and wildlife; (ii) remains intact for exceptionally long periods of time; (iii) accumulates in the fatty tissue of living organisms including humans, and bio-accumulates up the food chain; (iv) becomes widely distributed throughout the environment as a result of natural processes involving soil, water and, most notably, air; and (v) is likely to cause significant adverse human health or environmental effects near to and distant from their sources (adapted from Stockholm Convention, 2008). The Stockholm Convention on Persistent OPs was created to restrict or prohibit the production and use of certain POPs.

Pest. Any species, strain or biotype of plant, animal or pathogenic agent (microorganisms, including viruses) injurious to plants and plant products, materials or environments, including vectors of parasites or pathogens of human, animal, and plant disease, and animals causing public health nuisance (FAO and WHO, 2014) or other nuisance.

Pesticide. Any substance, or mixture of substances of chemical or biological ingredients intended for repelling, destroying or controlling any pest, or regulating plant growth. By nature, pesticides are potentially toxic to non-target organisms, including humans, and need to be used safely and disposed of properly (WHO, 2019).

Point-source pollution. Pollution arising from any discernible, confined and discrete source from which contaminants are discharged, including but not limited to any pipe, ditch, tunnel, conduit, well, discrete fissure, container, rolling stock, or concentrated animal feeding operation (US EPA, 2002).

Pollutant. Any contaminant present in the environment, which, due to its properties, amount or concentration causes adverse impacts on air, water, land, biota, humans, soil functions or soil use (adapted from ISO, 2015).

Potentially toxic elements (PTEs). See trace elements.

Predicted environmental concentrations. A modelled parameter to determine the indirect exposure to a certain contaminant via the environment (EC, 2003). It is used in ERA models to assess the environmental fate, distribution and potential effects of a contaminant released into the environment (Kullik and Belknap, 2017).

Radionuclides. Radionuclides are unstable isotopes of elements that undergo radioactive decay to give off minute quantities of radiation. Radionuclides occur naturally in soils but in small quantities, depending on the parent material and in turn, on soil physicochemical properties such as texture, cation exchange capacity and organic matter content. As a result of radioactive decay, an element can transmute into a different one.

Remediation. The process of removing contaminants from polluted soil, groundwater, or site to eliminate, control or reduce the risk to both the health of the population and the environment (Cooper, 2013; ISO, 2015).

Reclamation. Term especially used for mining areas. The process of restoring disturbed lands to a safe, stable, non-polluting and consistent with agreed post-mining land use (ISO, 2020).

Restoration. The process of returning an area to a state that corresponds as much as possible to its pristine condition which may include revegetation, soil enrichment, land and water decontamination, and proactive conservation processes (ISO and IWA, 2017).

Rehabilitation. Action taken to improve the capability of damaged or degraded soil to perform specified functions (e.g. addition of organic matter and nutrients to promote plant growth) (ISO, 2015). Normally, it does not refer to polluted soils, unless it is a post-remediation action, such as brownfield redevelopment (Meuser, 2013).

Risk. The probability or likelihood of an adverse effect on human health or on the environment occurring due to exposure to a hazard.

Risk assessment. A qualitative and quantitative evaluation performed in an effort to define the risk posed to human health or the environment by the presence or potential presence and use of specific pollutants. The identification, evaluation, and estimation of the levels of risks involved in a given situation, their comparison against benchmarks or standards, and determination of an acceptable or tolerable level of risk. It consists of hazard identification, hazard characterization, exposure assessment, and risk characterization (Van-Camp et al., 2004).

Site. Area of land related to a specific ownership or activity, which is the focus of a given assessment.

Soil. Upper layer of the Earth’s crust transformed by weathering and physical/chemical and biological processes and composed of mineral particles, organic matter, water, air, and living organisms organized in generic soil horizons (ISO, 2015).

Soil contamination. Presence of chemical or biological contaminant(s) in the soil (Knox et al., 1999). Contamination can be directly evaluated by analytical procedures. See soil pollution definition.

Soil ecosystem functions. Description of the roles that soils play in ecosystems, and the significance of soils to humans and the environment. Examples are: (1) Biodiversity, genetic resources, cultural services; (2) Food web support; (3) Biodegradation of pollutants; (4) Nutrient cycling (for example N, and P); (5) Pest control and plant growth promotion; (6) Carbon cycling and sequestration; (7) Greenhouse gas emissions; (8) Soil structure affecting soil water, gas balance and filtration function; and (9) Control of energy cycles.

Soil ecosystem services. The capacity of natural processes and soil components to provide goods and services for the well-being of humans and for the environment (Groot, 1992). According to the Common International Classification of Ecosystem Services (CICES) (Haines-Young and Potschin, 2018), there are three major groups of ecosystem services (Millennium Ecosystem Assessment, 2005):

  1. provisioning services: supply of food, water, timber, fibre and other raw materials;
  2. regulation and maintenance services: regulating water, heat and nutrient cycles, contaminants buffering, filtration and detoxification, and disease regulation;
  3. cultural services: those that provide nonmaterial benefit to humans, including recreation, aesthetic and spiritual experiences, or preservation of artefacts;

Supporting services such as photosynthesis, primary production, or soil formation are essential for ecosystem functioning, however, are no longer considered in international frameworks due to their intermediate status (sometimes described as ‘intermediate services’), which operate alongside more basic ecological structures and processes, to underpin the output of final services (Potschin-Young et al., 2017).

Soil health. The capability of the soil to sustain the productivity, diversity, and environmental services of the terrestrial ecosystems (ITPS, 2020).

Soil pollution. Presence of contaminant(s) in the soil whose nature, location, or quantity produces undesirable effects in the environment or human health (UN Statistical Division, 1997). It cannot be directly quantified by only a laboratory analysis, but depends on the assessment of a contaminant’s bioavailability, the environmental fate and risk analysis, and the exposure and risk assessment for human health. See soil contamination definition.

Soil quality. The capacity of a specific kind of soil to function, within natural or managed ecosystem boundaries, to sustain plant and animal productivity, maintain or enhance water and air quality, and support human health and habitation (ISO, 2012; Karlen et al., 1997).

Trace elements (TEs). Elements that are generally found in soil at low concentrations, less than 100 mg/kg, that are biologically significant in some fashion. Biological significance would include elements that are essential or toxic to any organism where some elements can be both, depending on their concentration. Many of the TEs of importance are metals, while others are metalloids, non-metals, actinoids, and halogens occurring a variety of chemical states (elemental, cations, anions, oxyanions, methylated, etc.). This category can overlap or be used synonymously with terms such as potentially toxic elements, heavy metals, persistent inorganic contaminants, and inorganic contaminants (Hooda, 2010). For the clarity of this document, only the term trace elements will be used.

Xenobiotic. Synthetic chemicals foreign to the human body or living organisms (ISO, 2006). They contain structural elements that are unknown or rare in nature and/or are assembled in a structure that is not of natural occurrence (Knapp and Bromley-Challoner, 2003) and do not fit the enzyme systems of living organisms.