Assessment of risk to public health from exposure to BSE infectivity from the Rendac Bergum rendering plant

To identify and quantify the risks to the public health from the BSE infective agent arising from the activities at the Rendac Bergum rendering plant, a risk assessment study was performed. The flow of infectivity entering the rendering plant was modelled using an event tree approach. The model was evaluated using a probabilistic risk assessment approach to reflect the uncertainties in the input parameters. For input of fixed parameters, conservative values were used in order to present a worst case scenario. Selected variables were defined as a distribution of values and the result calculated many times using a Monte Carlo simulation tool. In 2001, in the Netherlands, a total of 20 animals were tested positive for BSE. It was assumed that all of these animals would have been processed at the Rendac Bergum plant as part of the SRM processing, and that they had the infectivity of a fully infected animal. The median value of the infectivity entering the process was estimated to be 3,620 human oral ID50 units per year, with a range from 36 to 408,000. It was estimated that 99% of the infectivity entering the plant would be inactivated by the rendering process. Of the remaining infectivity, most was found to end up in in the Meat and Bone Meal (MBM) product: 9 human oral ID50 units per year. At the current production level this would result in about 0.00008 human oral ID50 units per kg MBM. Currently all of this MBM was sent offsite for disposal by incineration. Infectivity from the plant could enter the environment through one of three routes, via sludge used in landfill or spread on the land as fertiliser, waste water discharged to the canal, or as particles released to the air. In all 3 cases the amounts of infectivity were found to be very small and could not pose any significant risk to the public health