Currently, waste water from premises handling Specified Risk Materials (SRM) can be applied to pasture land (land grazed by farm animals or land cropped for forage) with or without prior pre-treatment by filtration in accordance with Annex II of Regulation (EC) No. 1774/2002. Within these regulations, there is a requirement for filtration of materials with a 6 millimetre filter prior to treatment and direct spreading to land. These regulations aim to address the environmental impact of spreading waste water but do not specifically consider the animal health impacts. It is aimed within this project, therefore, to assess the risk of livestock becoming infected with a Transmissible Spongiform Encephalopathy (TSE) from waste water that has been directly spread onto pasture land both with and without prior treatment by filtration in accordance with the Regulations. The results from this assessment will be used to inform policy decisions in this area.
To assess this risk, the OIE framework for risk assessment of release, exposure and consequence assessment, will be used. Following this framework, firstly, the release of TSEs (BSE, atypical and typical scrapie) from premises handling SRM will be considered. This will include an estimate of the amount of TSE being released in waste water from Category 1 and 2 rendering plants and abattoirs. As the size of each of these premises will impact on the amount of waste water produced, the amount of TSE released will be estimated for both small and large throughput premises. Secondly, the amount of TSE to which livestock (cattle and sheep) are exposed in waste water spread onto pasture land will be estimated. Different scenarios will be considered investigating the efficiency and likelihood of by-passing the filters, and the effect of an additional post-filtration step. Lastly, the number of new TSE infections resulting from exposure to TSEs in the waste water will be quantified taking into account the dose-response relationship of ingestion and infection of TSE in livestock. The end result of the risk assessment, therefore, will be a quantitative estimate of risk (the number of new TSE infections). A sensitivity analysis will also be undertaken to ascertain the impact that any uncertain parameters have on the final output of risk. In doing so, those parameters which have a large impact on the results can be identified and further research undertaken to assist in reducing the uncertainty in the model inputs. In summary, the risk assessment model proposed will follow a similar approach to that produced by Cummins & Adkin (2007).
The risk assessment model will be parameterised with the most recently available data from the scientific literature, VLA studies, and in colloboration with contacts in the Meat Hygiene Service (MHS). It is likely that there may be gaps in knowledge for some model parameters in which case expert opinion will be sought. The resulting model framework, data, model assumptions, results and sensitivity analysis will be written within a peer-reviewed scientific paper and subject to review by Defra and other scientific bodies (e.g. SEAC).