Environment

Fertilizer-derived heavy metals in the environment

The use of fertilizers in agricultural production can induce increases in toxic elements like heavy metals (see the Heavy Metals section for more information) in soils and affect, in the long term, soil fertility or impact crop and ground water quality. Concentrations of heavy metals vary depending on the fertilizer used, such as manures, organic waste, bone meal, guano, or mined phosphate rock. Mineral fertilizers from certain types of phosphate rock are particularly known to contain elevated levels of heavy metals, such as arsenic, cadmium, lead and uranium. The principles affecting the variation in concentrations of heavy metals in the rock depend, among others, on the texture of the host rock, leaching, and weathering. Given the different geological forming and reforming conditions, heavy metal concentrations can vary greatly in and between rock deposits, and therefore in phosphorus acid and fertilizer end products.

Heavy metals from fertilization accumulate in the top soil. Among the more frequently discussed elements are arsenic, cadmium, lead, mercury, and uranium. Cadmium contained in fertilizers in particular is known to be mobile and bioavailable to crops. However, the level of uptake depends on a number of factors, including crop type, fertilizer regime, climate, and soil characteristics. Soil accumulation processes depend on specific fertilizer and heavy metal properties, site-specific biogeochemical characteristics, and plant species. Numerous studies have investigated the distribution of heavy metals in fertilizers to soils and air, as well as into the human food chain by crop uptake or ground water leaching, potentially affecting drinking water quality. Scientific and regulatory interest in this matter has increased over the last decade or so due to greater concerns about environmental pollution and potential health risks.

The Global Soil Partnership postulates the prevention of soil contamination as the best way to maintain healthy soils and food safety, thus contributing to the Sustainable Development Goals [5]. To use fertilizers containing as little heavy metals as possible is a meaningful approach to reduce the social and environmental risks that arise from the redistribution of heavy metals in the aquatic and terrestrial environment. Another effective measure to prevent dispersion is the recovery of trace elements from mineral fertilizers such as cadmium or uranium. For the European Union, it was recently found that most of the agricultural land is currently sufficiently safe for food production given their heavy metal concentrations [6]. However, precautionary measures should be taken for large areas with high heavy metal concentrations.

Water quality and fertilizers

Since the middle of the 20th century, human activity has impacted biogeochemical cycles at an unprecedented rate, including the essential water and phosphorus cycles [7]. Growing human activity has also lead to intensified agricultural production in many regions of the world. In parallel to this, ecosystem integrity has come under increasing stress. As a result, water pollution from nutrient runoff into waterways has become an increasingly urgent issue. The World Resources Institute considers human-induced eutrophication and hypoxia a leading cause for water quality impairment around the world [8]. Well-known affected and large areas are the Gulf of Mexico, the Baltic Sea, the Mississippi river and Lake Erie.

As one of the most important nutrients for crops, phosphorus (P) is a key focus with regards to the balance between sustainable resource management and environmental quality. On the one hand, high levels of P in inland waters, estuaries and coastal waters causes eutrophication and dead zones. On the other, phosphate rock reserves are non-renewable. A rational use is therefore required. The challenge is to find the balance between too little and too much.

1. IFA (2014). Soil & Fertilizer: Expert Views. Available online: http://www.fertilizer.org/en/images/Library_Downloads/2014_ifa_soil_expert_views.pdf [return]
2. Source: IPNI [return]
3. OECD (2013). OECD Compendium of Agri-environmental Indicators. Nutrients: Nitrogen and phosphorus balances. OECD Publishing. [return]
4. IFA (2016). Nutrient Management Handbook. Available online: http://www.fertilizer.org/en/images/Library_Downloads/2016_Nutrient_Management_Handbook.pdf [return]
5. FAO (2017). Voluntary Guidelines for Sustainable Soil Management. Food and Agricultural Organization of the United Nations, Rome, Italy. Available online: http://www.fao.org/documents/card/en/c/5544358d-f11f-4e9f-90ef-a37c3bf52db7/ [return]
6. Toth, G., Hermann, T., Da Silva, M.R. & Montanarella, L. (2016). Heavy metals in agricultural soils of the European Union with implications for food safety. Environmental International, 88, 299-309. [return]
7. Sutton et al. (2013). Our nutrient world. The challenge to produce more food and energy with less pollution. Global overview of nutrient management. Centre for Ecology and Hydrology, Edinburgh on behalf of the Global Partnership on Nutrient Management and the International Nitrogen Initiative. [return]
8. Water Resources Institute (2013). About Eutrophication. Available online: http://www.wri.org/our-work/project/eutrophication-and-hypoxia/about-eutrophication [return]