Effect of incineration, co-incineration and combustion on TSE hazards in category 1 animal by-products
EFSA Panel on Biological Hazards (BIOHAZ), Ana Allende, Avelino Alvarez-Ordóñez, Valeria Bortolaia, Sara Bover-Cid, Alessandra De Cesare, Wietske Dohmen, Laurent Guillier … See all authors
First published: 28 May 2025
Adopted: 23 April 2025
The declarations of interest of all scientific experts active in EFSA's work are available at https://open.efsa.europa.eu/experts
Abstract
The European Commission requested EFSA to assess the effect of incineration, co-incineration and combustion of Category 1 animal by-products (ABP) on the BSE/TSE hazards in ash resulting from these treatments. The presence of residual TSE hazards is assessed by detection of prion infectivity or seeding activity. TSE agents or prions are challenging to inactivate completely using heat-based methods. Different TSE strains exhibit varying degrees of thermoresistance. Based on available studies at temperatures 120–134°C, the C-BSE strain is more thermoresistant than other evaluated strains. The vast majority of Category 1 ABP is rendered into 'meat and bone meal' prior to incineration/co-incineration/combustion. Scenarios involving co-incineration for cement production do not need to be considered because all ash is incorporated into the cement. It is not possible to generalise the time/temperature combinations to which Category 1 ABP are subjected across all processes. Due to the challenges in precisely measuring the temperature and residence time in industrial systems, and the wide range of system designs and operating conditions, it can only be assumed that Category 1 ABP are exposed to at least the legal requirements as determined by the conditions of the gas produced or injected into the process: 850°C for 2 s or 1100°C for 0.2 s. The limited sensitivity of the method used in a study involving C-BSE at 1000°C for 20 min prevented a conclusive exclusion of residual C-BSE prions.. Therefore, it is not possible to exclude – with high certainty (> 99%) – the presence of residual BSE/TSE hazards in ash produced from the incineration, co-incineration or combustion of Category 1 ABP. It is recommended to generate data on the actual reduction of infectivity in 'meat and bone meal' spiked with thermoresistant TSE field strains after treatment with the time/temperature combinations required by the legislation or specific industry processes.
SUMMARY The European Food Safety Authority (EFSA) was asked by the European Commission to deliver a scientific opinion by 30 April 2025 on the effect of incineration, co-incineration and combustion of Category 1 material referred to in Article 8 Regulation (EC) No 1069/2009 on the BSE/TSE hazards in the ash resulting from these treatments (ToR1). If the outcome of ToR1 is that there is no residual TSE/BSE infectivity, then EFSA will have to assess the effect of incineration, co-incineration and combustion on the biological hazards other than the BSE/TSE and on the chemical hazards in the ash resulting from these treatments (ToR2).
The requestor elucidated the necessity for a high level of certainty that no residual TSE hazards remain following the processes, and that the threshold applied to applications on alternative processing methods of Category 1 animal by-product (ABP) (6 log10 reduction of TSE agents) is not relevant for this mandate. The presence of residual TSE hazards was assessed by the detection of TSE agent (or prion) infectivity or seeding activity and for the most thermoresistant animal TSE field strain as a worst-case scenario. Multiple data sources were used. Relevant literature was selected on the thermal inactivation of TSE agents. Different stakeholders from the industry were approached to gain insight into the practices for rendering, processing and disposal of Category 1 ABP in Europe. Previous EFSA scientific opinions and Scientific Steering Committee (SSC) minutes and opinions were reviewed, as well as a number of documents submitted by a stakeholder (European Sustainable Phosphorus platform (ESPP)), including scientific papers, old and ad hoc recent risk assessments.
In order to answer the ToR1, the mandate was translated into four assessment questions (AQ): AQ1: What is the most thermoresistant animal TSE field strain identified?; AQ2: What are the relevant/actual scenarios used by the industry in the EU for the processing and/or disposal of Category 1 material?; AQ3: What are the overall heat treatment (time/temperature) profiles of incineration, co-incineration or combustion processes before and after the gas is raised to the minimum legal requirement of 850°C for at least 2 s or 1100°C for 0.2 s?; AQ4: Can the presence of prions be excluded with more than 99% certainty in ash produced from Category 1 ABP after applying the time/temperature combinations of the relevant/actual scenarios identified in AQ2?
TSE agents are difficult to fully inactivate using heat-based methods. Different TSE strains exhibit varying degrees of thermoresistance. The matrix in which the prions are found and pretreatments (e.g. fixation or drying) can significantly influence their resistance to heat. Such variability compromises the possibility of extrapolating findings from one specific set of conditions to another.
Studies on the thermoresistance of EU TSE field strains are limited. Most research has concentrated on wet heat conditions at low temperatures relevant to cleaning and sterilisation, rather than the extreme dry heat conditions used in incineration. Evidence suggests that, among the evaluated strains at these lower temperatures, the C-BSE strain is more thermoresistant than other evaluated strains.
For practical reasons, the vast majority of ABP waste is rendered into 'meat and bone meal' (MBM) prior to incineration, co-incineration or combustion. It is acknowledged that the rendering of Category 1 ABP with method 1 provides a reduction of infectivity in the order of 3 log10, while method 4 (both methods as defined in Chapter III Annex IV of Commission Regulation (EU) No 142/2011), the second most applied method to Category 1 material in Europe, would provide an unknown reduction of infectivity, assumed to be lower than that achieved by method 1.
It has not been possible to determine accurately the relative amounts of Cat 1 ABP entering each scenario. It appears that rendering followed by co-incineration in cement plants and rendering followed by incineration in rotary kilns are currently the most common methods for the disposal of Category 1 ABP. During the process of co-incineration in cement plants, all the ash is incorporated into cement. Any scenario involving co-incineration results in cement production, and it does not need to be considered further because it does not result in ash as a by-product.
There are many different types of incineration, co-incineration and combustion systems in place in installations across Europe. These systems vary in design, size, capacity, structure and methodology. Consequently, the time/temperature combinations – and therefore the level of TSE agent reduction achieved – can vary significantly between systems. Given the wide range of system designs and operational conditions, it is not possible to generalise the time/temperature combinations to which Category 1 ABP are subjected across all processes.
Due to the challenges in precisely measuring the temperature and residence time in industrial systems, it can only be assumed that Category 1 ABP is exposed, during ash production, to at least the minimum legal requirements as determined by the conditions of the gas produced or injected into the process, namely, 850°C for 2 s or 1100°C for 0.2 s.
Only four TSE inactivation studies have examined conditions approaching those used in incineration, and none precisely replicate the time/temperature profiles specified in the regulation or achieved in industrial processes. While a treatment at 1000°C for 15 min has been demonstrated to completely inactivate the 263K hamster strain in tissues, no evidence is available for treatment durations of 0.2s or 2s. In the only study involving C-BSE at this temperature (1000°C) for 20 min, the limited sensitivity of the method used prevented a conclusive exclusion of residual C-BSE prions.
There is not sufficient relevant experimental data on the actual thermoresistance of TSE agents and on industrial operating conditions. Therefore, it is not possible to exclude, with high certainty (> 99%), the presence of residual BSE/TSE hazards in ash produced from the incineration, co-incineration or combustion of Category 1 ABP material.
It is recommended to collate and summarise actual time/temperature combinations to which MBM derived from Category 1 ABP is subjected during industrial processes; to conduct experimental studies comparing the thermoresistance of all animal TSE field strains identified in the EU under temperatures and processing conditions that reflect industry practices; to carry out experimental studies in which MBM is spiked with a thermoresistant TSE field strain (using C-BSE in the absence of any alternative data) and then treated at the minimal time/temperature combinations required by the legislation or specific industry processes; and to evaluate the extent of the reduction of TSE agent infectivity achieved by processing methods other than method 1 (pressure sterilisation).
See full report;
EFSA Panel on Biological Hazards (BIOHAZ), Ana Allende, Avelino Alvarez-Ordóñez, Valeria Bortolaia, Sara Bover-Cid, Alessandra De Cesare, Wietske Dohmen, Laurent Guillier … See all authors
First published: 28 May 2025
Adopted: 23 April 2025
The declarations of interest of all scientific experts active in EFSA's work are available at https://open.efsa.europa.eu/experts
Abstract
The European Commission requested EFSA to assess the effect of incineration, co-incineration and combustion of Category 1 animal by-products (ABP) on the BSE/TSE hazards in ash resulting from these treatments. The presence of residual TSE hazards is assessed by detection of prion infectivity or seeding activity. TSE agents or prions are challenging to inactivate completely using heat-based methods. Different TSE strains exhibit varying degrees of thermoresistance. Based on available studies at temperatures 120–134°C, the C-BSE strain is more thermoresistant than other evaluated strains. The vast majority of Category 1 ABP is rendered into 'meat and bone meal' prior to incineration/co-incineration/combustion. Scenarios involving co-incineration for cement production do not need to be considered because all ash is incorporated into the cement. It is not possible to generalise the time/temperature combinations to which Category 1 ABP are subjected across all processes. Due to the challenges in precisely measuring the temperature and residence time in industrial systems, and the wide range of system designs and operating conditions, it can only be assumed that Category 1 ABP are exposed to at least the legal requirements as determined by the conditions of the gas produced or injected into the process: 850°C for 2 s or 1100°C for 0.2 s. The limited sensitivity of the method used in a study involving C-BSE at 1000°C for 20 min prevented a conclusive exclusion of residual C-BSE prions.. Therefore, it is not possible to exclude – with high certainty (> 99%) – the presence of residual BSE/TSE hazards in ash produced from the incineration, co-incineration or combustion of Category 1 ABP. It is recommended to generate data on the actual reduction of infectivity in 'meat and bone meal' spiked with thermoresistant TSE field strains after treatment with the time/temperature combinations required by the legislation or specific industry processes.
SUMMARY The European Food Safety Authority (EFSA) was asked by the European Commission to deliver a scientific opinion by 30 April 2025 on the effect of incineration, co-incineration and combustion of Category 1 material referred to in Article 8 Regulation (EC) No 1069/2009 on the BSE/TSE hazards in the ash resulting from these treatments (ToR1). If the outcome of ToR1 is that there is no residual TSE/BSE infectivity, then EFSA will have to assess the effect of incineration, co-incineration and combustion on the biological hazards other than the BSE/TSE and on the chemical hazards in the ash resulting from these treatments (ToR2).
The requestor elucidated the necessity for a high level of certainty that no residual TSE hazards remain following the processes, and that the threshold applied to applications on alternative processing methods of Category 1 animal by-product (ABP) (6 log10 reduction of TSE agents) is not relevant for this mandate. The presence of residual TSE hazards was assessed by the detection of TSE agent (or prion) infectivity or seeding activity and for the most thermoresistant animal TSE field strain as a worst-case scenario. Multiple data sources were used. Relevant literature was selected on the thermal inactivation of TSE agents. Different stakeholders from the industry were approached to gain insight into the practices for rendering, processing and disposal of Category 1 ABP in Europe. Previous EFSA scientific opinions and Scientific Steering Committee (SSC) minutes and opinions were reviewed, as well as a number of documents submitted by a stakeholder (European Sustainable Phosphorus platform (ESPP)), including scientific papers, old and ad hoc recent risk assessments.
In order to answer the ToR1, the mandate was translated into four assessment questions (AQ): AQ1: What is the most thermoresistant animal TSE field strain identified?; AQ2: What are the relevant/actual scenarios used by the industry in the EU for the processing and/or disposal of Category 1 material?; AQ3: What are the overall heat treatment (time/temperature) profiles of incineration, co-incineration or combustion processes before and after the gas is raised to the minimum legal requirement of 850°C for at least 2 s or 1100°C for 0.2 s?; AQ4: Can the presence of prions be excluded with more than 99% certainty in ash produced from Category 1 ABP after applying the time/temperature combinations of the relevant/actual scenarios identified in AQ2?
TSE agents are difficult to fully inactivate using heat-based methods. Different TSE strains exhibit varying degrees of thermoresistance. The matrix in which the prions are found and pretreatments (e.g. fixation or drying) can significantly influence their resistance to heat. Such variability compromises the possibility of extrapolating findings from one specific set of conditions to another.
Studies on the thermoresistance of EU TSE field strains are limited. Most research has concentrated on wet heat conditions at low temperatures relevant to cleaning and sterilisation, rather than the extreme dry heat conditions used in incineration. Evidence suggests that, among the evaluated strains at these lower temperatures, the C-BSE strain is more thermoresistant than other evaluated strains.
For practical reasons, the vast majority of ABP waste is rendered into 'meat and bone meal' (MBM) prior to incineration, co-incineration or combustion. It is acknowledged that the rendering of Category 1 ABP with method 1 provides a reduction of infectivity in the order of 3 log10, while method 4 (both methods as defined in Chapter III Annex IV of Commission Regulation (EU) No 142/2011), the second most applied method to Category 1 material in Europe, would provide an unknown reduction of infectivity, assumed to be lower than that achieved by method 1.
It has not been possible to determine accurately the relative amounts of Cat 1 ABP entering each scenario. It appears that rendering followed by co-incineration in cement plants and rendering followed by incineration in rotary kilns are currently the most common methods for the disposal of Category 1 ABP. During the process of co-incineration in cement plants, all the ash is incorporated into cement. Any scenario involving co-incineration results in cement production, and it does not need to be considered further because it does not result in ash as a by-product.
There are many different types of incineration, co-incineration and combustion systems in place in installations across Europe. These systems vary in design, size, capacity, structure and methodology. Consequently, the time/temperature combinations – and therefore the level of TSE agent reduction achieved – can vary significantly between systems. Given the wide range of system designs and operational conditions, it is not possible to generalise the time/temperature combinations to which Category 1 ABP are subjected across all processes.
Due to the challenges in precisely measuring the temperature and residence time in industrial systems, it can only be assumed that Category 1 ABP is exposed, during ash production, to at least the minimum legal requirements as determined by the conditions of the gas produced or injected into the process, namely, 850°C for 2 s or 1100°C for 0.2 s.
Only four TSE inactivation studies have examined conditions approaching those used in incineration, and none precisely replicate the time/temperature profiles specified in the regulation or achieved in industrial processes. While a treatment at 1000°C for 15 min has been demonstrated to completely inactivate the 263K hamster strain in tissues, no evidence is available for treatment durations of 0.2s or 2s. In the only study involving C-BSE at this temperature (1000°C) for 20 min, the limited sensitivity of the method used prevented a conclusive exclusion of residual C-BSE prions.
There is not sufficient relevant experimental data on the actual thermoresistance of TSE agents and on industrial operating conditions. Therefore, it is not possible to exclude, with high certainty (> 99%), the presence of residual BSE/TSE hazards in ash produced from the incineration, co-incineration or combustion of Category 1 ABP material.
It is recommended to collate and summarise actual time/temperature combinations to which MBM derived from Category 1 ABP is subjected during industrial processes; to conduct experimental studies comparing the thermoresistance of all animal TSE field strains identified in the EU under temperatures and processing conditions that reflect industry practices; to carry out experimental studies in which MBM is spiked with a thermoresistant TSE field strain (using C-BSE in the absence of any alternative data) and then treated at the minimal time/temperature combinations required by the legislation or specific industry processes; and to evaluate the extent of the reduction of TSE agent infectivity achieved by processing methods other than method 1 (pressure sterilisation).
See full report;
