Accumulation of PTEs in agricultural soils: A Case Study showing the inability of the current legal order and legislation to ensure sustainable food production
Start date: 12 September 2018
Soil quality is fundamental for ensuring the future of all terrestrial life on earth, and although it is frequently overlooked, modern human society would not be able to function without it. Soil also plays a vital role in climate change mitigation through carbon sequestration, flood prevention, water storage and filtration, and ecosystem services and decomposition. There are over 700 different soil types identified for the UK and are categorized by the unique characteristics of each soil layer.
Healthy soils can be defined as a foundation of ecosystems supplying various benefits to humans, through providing food, clean air and water, resulting in a successful and prolonged human well-being. The term ‘soil health’ is used to represent the ideal state of soils, but it can be difficult to singularly define as soils have many different functions.
Soils in the UK are subject to degradation through a variation of processes, including sealing by infrastructure; compaction from machinery and vehicles; a loss of organic matter; erosion by wind and water; contamination from toxic elements; salinization; and acidification through fossil fuel burning.
Typically, contamination arises through aerial deposition of substances emitted into the atmosphere, the use of normal agricultural materials and the recycling\dumping of wastes to agricultural land. A wide variety of potentially toxic substances can contaminate soils by these routes. Whilst organic contaminants can be broken down by a variety of process such as photodegradation and microbial action, element contaminants such as trace metals cannot. Therefore, potential toxic elements (PTEs, i.e. trace metals) can have residence times in soils that can measured in centuries and natural re-equilibration of soil concentrations is typically measured in 1,000s of years.
Trace metals enter agroecosystems from many sources, but the use of organic by-products as fertilisers are the principle source. Trace metals added to soils in this way can cause toxicity to important organisms involved in the provision of ecosystem services. Whilst the use of sewage sludge is controlled to prevent the build-up of trace metals in soils to damaging levels, the use of other organic by-products is not. The lack of legal controls on the addition of PTEs to soil in forms other than sewage sludge clearly leaves soil health vulnerable. Amongst the PTEs, Cu and Zn are the least controlled and therefore have the greatest potential to affect soil health. Whilst organic by-products have a sufficient nutrient content can be used as organic fertilisers and replace lost organic carbon from the soil, they can also contain significant levels of Cu and Zn.
This paper critically examines the UK’s attempt to promote soil health and argues that the use of organic by-products other than sewage sludge can damage important constituents of agroecosystems. Furthermore, it is argued that there is a distinct lack of scientific, legal and investigative appreciation of the potentially serious threat to soil fertility and food security from PTE that requires urgent attention