Towards a quantitative risk assessment for BSE in sewage sludge

Abstract

Aims:The aim is to determine the risk of transmission of BSE to humans and cattle through the application of sewage sludge to agricultural land. Methods and Results: A quantitative risk assessment based on the Source±Pathway±Receptor approach is developed. Central to the model is the estimation of the arithmetic mean concentration of BSE agent in sewage sludge. The main sources of uncertainty in the risk assessment are the degree to which sewage sludge treatment destroys BSE agent, whether there is a threshold dose for initiation of BSE infection in cattle, and most importantly, the amount of brain and spinal cord material which enters the sewer from the abattoir. Assuming 1% of brain and spinal cord is lost to the sewer from abattoirs, the model predicts a risk of BSE transmission of 7á1´10 ±5 cow ±1 year ±1 for cattle grazing on land to which sewage sludge has been applied. Conclusions: The risks to humans through consumption of vegetable crops are acceptably low. Although the risks to cattle are higher, because of higher exposure to soil and greater susceptibility, the model demonstrates that sewage sludge alone cannot sustain the BSE epidemic in the UK cattle herd. Furthermore, the model suggests that recycling of BSE agent through sewage sludge will not sustain endemic levels of BSE in the UK cattle herd. Signi®cance and Impact of the Study: The conclusions are consistent with the ®ndings from epidemiological studies which so far have not detected horizontal transmission of BSE (which would include transmission from contaminated pastures). The model demonstrates the importance of containment of brain and spinal cord within the abattoir.

Evaluation of Bovine Spongiform Encephalopathy (BSE) Infection Risk of Cattle via Sewage Sludge from Wastewater Treatment Facilities in Slaughterhouses in Japan

“…The authors concluded that, although they recognized the potential for risk of BSE infection via sludge-derived fertilizer, scientific data in support of the hypothesis was insufficient. Gale and Stanfield [1] conducted quantitative evaluations of the risk of BSE infection in humans and cattle via sludge-derived fertilizer route in the United Kingdom. They estimated that the BSE infectious value ingested by one head of cattle per year was 7.07 × 10 -4 bovine oral ID 50 , when the sludge from 700,000 cattle, including 3,780 infected cattle was applied to pastureland per year and implied that 49.5 cattle per year could become infected by BSE.…”

“…In the report on slaughterhouse sewage contamination in the United Kingdom, Gale and Stanfield [1] estimated that the risk posed by SRM contamination of sewage by tissue derived from stunning, pithing and splitting passing through 4-mm mesh filters installed along sewage drains was likely to be a maximum of 1% of the total SRM from one infected animal. While many slaughterhouses in Japan have removed spinal cord before splitting or installed filters into the drains with mesh sizes of 4 mm or less, the removal efficiency of these measures has not yet been clearly demonstrated.…”

“…Qualitative evaluation of the risk from slaughterhouse sludge was performed by the Agence Française de Sécurité Sanitaire des Aliments (the French Agency of Sanitary Security of Food) and a quantitative evaluation was undertaken by Gale and Stanfield [1]. Quantitative evaluation of the risk of slaughterhouse wastewater to cattle has also been conducted by the Bureau of Rural Science (BRS) of the Australian Government Department of Agriculture, Fisheries and Forestry as a precautionary measure.…”

Supercritical Water Gasification of Municipal Sludge: A Novel Approach to Waste Treatment and Energy Recovery

“…The pathogens are a result of normal, human metabolic wastes as well as additional loading from medical effluents (Arthurson, 2008;Deblonde et al, 2011;Lewis et al, 2002;Mathney, 2011;Reilly, 2001;Straub et al, 1993;USEPA, 2009;Verlicchi et al, 2010). There are fewer than two dozen pathogens (e.g., fecal coliforms, Salmonella, enteric viruses, and parasites) monitored in sewage sludge (Mathney, 2011;NASNRC, 2002;Reilly, 2001;Snyder, 2005;USEPA, , 2002bUSEPA, , 2003, and many dangerous pathogens (e.g., prions) are neither affected by sewage treatment nor detected by standard analytical methods (Gale & Stanield, 2001;NASNRC, 2002;Peterson et al, 2008b;Saunders et al, 2008;Smith et al, 2011;Snyder, 2005).…”

Methods and microbial risks associated with composting of animal carcasses in the United States

“…68 The investigation included assessment of BSE, foot-and-mouth disease, African swine fever, and classical swine fever by use of a quantitative MRA developed for assessment of BSE in sewage sludge. 39,73 It was concluded that the important factors governing risk were sources of composted animal parts, the efficiency of composting, and the decay and dilution in soil when compost was spread on pasture. The net pathogen destruction was heavily influenced by the degree of bypass, which is the compost that does not reach critical temperature because of its location in the pile.…”