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)

Visit the Food Standards Agency (FSA) site to learn more about our funder.


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.

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The dairy module will be carried out under highly controlled conditions using housed cattle fed specially prepared diets containing either:

  • bedding materials, to simulate incidental ingestion of bedding; or
  • waste-derived soil conditioners (eg PSA, PLA, MBMA, biosolids and/or CLO) to mimic realistic rates of incidental ingestion of soil or contaminated foliage from waste-amended pasture.

For each exposure scenario, groups of four cows will be directly fed the specially prepared diets for three weeks and matched groups of control cows will be fed diets without added waste materials. The ingestion rate of amended soil, biosolids or bedding, equivalent to 5% of the dry matter intake, represents a reasonable worst-case for diary cattle. These approaches allow for much greater control of the experimental variables and precision than is possible in a comparative field study or by relying on voluntary incidental ingestion of bedding materials. Milk samples will be monitored prior to dietary exposure, during exposure and four weeks after exposure ceases to determine how contaminant concentrations in milk vary for each scenario.

Carrots represent a worst-case for potential uptake of POPs from waste-amended soil. Carrots grown in a plant growth chamber under controlled experimental conditions in sandy loam amended with waste-derived soil conditioners will be used to examine transfer of organic contaminants to carrot roots.

The potential uptake of selected organic contaminants into cereal plants grown in waste-amended soil will initially be screened under laboratory conditions using a controlled 5-leaf-stage barley bioassay. Any organic contaminants from waste that are found to transfer to the barley shoots will then be investigated further for crop transfer to wheat grain in a replicated field trial on plots of sandy loam amended with the selected waste materials.

The outputs from the experimental work will feed into the development of an Assessment Methodology to determine the suitability of waste products for agricultural utilisation.