What is the Project About
Study Duration: February 2014 to March 2016
Project Lead: Professor Stephen Smith, Imperial College London
Consortium Members: Imperial Consultants (Lead) University of Reading The Food and Environment Research Agency (FERA)
A variety of waste materials are recycled in agriculture with the benefit of reducing pressure on virgin resources. Recycled waste materials, such as untreated waste wood shavings or paper sludge from paper recycling mills, can be effectively used as animal bedding in livestock production. Nutrient-rich waste materials such as sewage sludge (biosolids) or outputs from the combustion of waste biomass (e.g. meat and bonemeal ash (MBMA) and poultry litter ash (PLA)) can be applied to land as agricultural fertilisers and soil conditioners in grassland and crop production, closing the nutrient loop and reducing the use of manufactured fertilisers.
Paper sludge ash (PSA) is an effective desiccant in bedding for cattle, and is also used as a liming agent on land. The management of municipal and commercial and industrial solid wastes by mechanical biological treatment is expanding as a means of waste valorisation and landfill diversion and the stabilised biodegradable output from such processes, described as compost-like-output (CLO), whilst not currently applied to agricultural land in the UK, has future potential value as a soil conditioner.
However, the various waste streams currently used in agriculture can contain a range of chemical contaminants, including emerging persistent organic pollutants (POPs). These include polychlorinated biphenyls (PCBs) and dioxins, which are by-products of combustion and some manufacturing processes. The health effects of dioxins and dioxin-like PCBs include carcinogenicity, immunotoxicity, reproductive and developmental effects. Other contaminant groups such as Polycyclic Aromatic Hydrocarbons (combustion by-products), phthalates (used as plasticisers), brominated flame retardants and musks (used in personal care products) may also be present.
This project aims to generate robust scientific evidence that the following will not compromise food safety:
- rearing dairy cattle on bedding made from recycled waste
- using waste-derived fertilisers or liming agents for grassland or for arable land used for root crops or cereals
The project also aims to identify or validate control measures needed to protect the food chain.
Research Approach: Representative batches of waste materials including biosolids, CLO, waste wood shavings, paper sludge, PSA, PLA and MBMA will be analysed and selected for inclusion in the study on the basis of their chemical characteristics.
Dairy cows have been selected for investigation because monitoring contaminant levels in milk from cows in mid-lactation provides a relatively rapid and sensitive method for detecting the transfer of contaminants to livestock from ingested waste materials. Research has shown that concentrations of POPs such as polychlorinated biphenyls (PCBs) in milk can reach steady state within two to three weeks in response to dietary exposure, whereas it takes much longer for these contaminants to reach steady state in body fat. Monitoring milk also has the advantage that samples can be taken at multiple time points in an individual animal, unlike meat samples.