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<p>Representative batches of waste materials including biosolids, waste wood shavings, PSA, PLA and meat and bonemeal ash (MBMA) will be analysed and selected for inclusion in the study on the basis of their chemical characteristics. Dairy cows will be investigated because monitoring contaminant levels in milk from cows in mid-lactation will provide a relatively rapid and sensitive method for detecting and assessing 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.</p>
The dairy module will be carried out under highly controlled conditions using housed cattle fed specially prepared diets containing either:
<ul><li>bedding materials, to simulate incidental ingestion of bedding; or</li>
<li>waste-derived soil conditioners (eg PSA, PLA, MBMA, biosolids and/or biocompost) to mimic realistic rates of incidental ingestion of soil from waste-amended pasture</li></ul>
<p>For each exposure scenario, groups of four cows will be fed the specially prepared diets for three weeks and matched groups of control cows will be fed diets without added waste 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 during and after dietary exposure for each scenario.</p>
<p>Carrots represent a worst-case for potential uptake of POPs from waste-amended soil. Carrots grown under controlled experimental conditions in sandy loam amended with waste-derived soil conditioners will be used to examine uptake of organic contaminants.</p>
<p>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. </p>
<p>Background: There is pressure to use suitable recycled waste materials in agriculture either as animal bedding, or as soil conditioner. This has the benefit of minimising the use of virgin materials for bedding and of efficiently recycling increasingly scarce plant nutrients by using waste materials such as sewage sludge (biosolids) or poultry litter ash (PLA) as fertilisers. Paper sludge ash (PSA) is an effective desiccant in bedding for cattle. It is also used as a liming agent on land. However, the various waste streams currently used in agriculture can contain a range of chemical contaminants, including various emerging persistent organic pollutants (POPs).</p>
This project aims to generate robust scientific evidence that the following will not compromise food safety:
<ul><li>rearing dairy cattle on bedding made from recycled waste</li>
<li>using waste-derived fertiliser or liming agent for grassland or for arable land used for root crops or cereals</li></ul>
The project also aims to identify or validate control measures needed to protect the food chain.