How soil pollution works
Soil acts as a filter and buffer for contaminants, but its potential to cope is finite. If the capacity of the soil to mitigate the effects of pollutants is exceeded, the contaminants pollute other compartments of the environment.
Unsustainable agricultural practices that reduce soil organic matter can facilitate the release of pollutants into groundwater or make them available for plant uptake and entry into the food chain.
Pollutants accumulate in plant tissues, passing to grazing animals, birds that eat fruits and seeds, or to humans that consume them. Many pollutants become more concentrated as they rise up the food chain, increasing the potential for harm to human health. Soil dwelling organisms such as earthworms can also absorb pollutants.
Soil pollution causes a chain reaction that starts with reduced soil biodiversity, alters organic matter incorporation rates, and then weakens soil structure and ability to resist erosion.
The nitrification process that occurs after excessive nitrogen fertilizers are applied to soils can produce significant and rapid acidification, which only occurs over hundreds to millions of years under natural conditions. Acidification affects bioavailability of contaminants and can lead to metal toxicities in plants.
Nitrates also accumulate and can easily leach to groundwater. Nitrous oxide (N2O), a major greenhouse gas, contributes to climate change when it is released from excessively fertilized soils.
What we can do about it
- Combatting soil pollution requires a sustained effort to prevent further issues and to mitigate existing pollution. Promoting sustainable agricultural practices, asking governments to develop policies to reduce the use of harmful chemicals and to prevent and control soil pollution are actions that can be taken now.
- In many farm settings significant reductions could be made in the use of agro-chemical inputs while preserving yields and profitability, with benefits to soil health and water quality.
- Integrated Pest Management policies have been mandated in the European Union, and similar practices are now promoted in many parts of the world.
- The Voluntary Guidelines for Sustainable Soil Management, developed by the Intergovernmental Technical Panel on Soils through FAO’s Global Soil Partnership, also include integrated or organic pest management as an important best practice.
- The International Code of Conduct on Pesticide Management provides internationally recognized management and mitigation strategies for the safe use of pesticides.
- Integrated land management practices at scale, such as the landscape approach, also have benefits for limiting the use of pesticides or the transfer of residues to waterbodies.
- At the individual level, composting can reduce the amount of waste that enters landfills and improve soil health when applied to the soil. Proper composting reduces pathogen loads and produces a product that is easy to handle, has high levels of stable carbon, and has low contaminant concentrations.
- Soil pollution has high economic costs due to the loss of soil, the reduction of crop yields and quality, and the expense associated with remediation. Therefore, the prevention of soil pollution should be a top priority worldwide.
- The consensus achieved by more than 170 countries during the last UN Environment Assembly is a clear sign of global determination to tackle pollution and its causes.
Impacts on Agriculture and Human Health
- Soil pollution affects food security by reducing crop yields and quality;
- Global production of municipal solid waste was approximately 1.3 billion tonnes per year in 2012. Waste production is expected to rise to 2.2 billion tonnes by 2025. Between 60 and 80% of items in landfills can be recycled, but are not;
- In China, 19% of arable land is polluted with heavy metal, including cadmium, nickel and arsenic but is nonetheless used to grow grain for human consumption;
- Each year around 700,000 deaths are attributable to antimicrobial resistant bacteria. By 2050, if not tackled, it will kill more people than cancer, and cost, globally, more than the size of the current global economy.
- 7 tablespoons of lead can contaminate up to 1ha of soil or 200 thousand litres of water.
- Over 3 million people are hospitalized due to pesticide poisoning every year, resulting in a quarter of a million premature deaths.