Public summary of the working group meeting on 24th May 2001

A specially convened SEAC Working Group met on 24 May. It was chaired by Professor Peter Smith, Acting SEAC Chairman. Other SEAC members who attended were Professor Roy Anderson, Professor Christopher Bostock, Mr Ray Bradley and Mr Peter Jinman as well as experts from the Department of Health, Food Standards Agency, Environment Agency, MAFF's Joint Co-ordination Centre, HSE and DNV Consulting. The following issues were considered:

(a) the potential TSE risks arising from carcases from cattle over 5 years of age buried prior to the revised EA advice issued on 26 March;
(b) the relative BSE risks from the various possible disposal routes for ash from FMD pyres; and,
(c) the re-use for food and feed transportation of lorries and containers used to transport FMD carcases.

Buried bovine carcases over 5 years of age

The Working Group was advised that up to 10,000 cattle aged over 5 years could have been buried between the start of the FMD outbreak and the SEAC, and revised EA, advice received in late March. Work was continuing to improve these estimates. Assuming a 0.4% prevalence of late stage BSE infected carcases, this equated to a total of about 40 infected carcases. On the basis of returns received so far from regions, at least 55 sites were involved.

- the Environment Agency were carrying out specific risk assessments on all affected sites. In many cases, these would probably show that there was no need for action. At the other extreme, there might be sites where pollution was occurring and where immediate action would be needed which could include digging up the carcases, removing authorisation for a private water supply, or creation of a barrier to prevent pollution. TSE aspects were an important part of these risk assessments but not the only one.

- even on a worse case scenario, we were dealing with relatively small risks to public health. Digging up the carcases and transporting them elsewhere was likely to involve a significant engineering feat which could potentially involve a greater risk than the one being avoided.

- a recent unpublished scientific paper indicated that most body fluids could have leaked out from the carcases within around two months.

The SEAC Working Group noted that, although there were both animal and public health issues to be considered, this particular meeting was concerned primarily with public health issues. The Group agreed with the Environment Agency that the sites where over 5 year cattle may have been buried would need to be examined on a case by case basis, and appropriate risk assessments carried out. It was likely that most body fluids would already have leached out of the carcases which would no longer be intact. Digging up the remains would itself create significant risks - for example of bringing deep soil to the surface - that would need to be taken into account in any assessment. Overall, the number of BSE infected carcases across all sites - let alone any particular site - would be small. The risk from any individual site would, normally, be small and should be kept in perspective.

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Disposal routes for ash

The Working Group was advised that:

- incomplete returns indicated that there were at least 400 locations where pyres had been used to burn carcases of cattle over 5 years old, including at least 200,000 cattle of which at least 50,000 would have been aged over 5 years. Work was in hand to improve these estimates.

- Where the Environment Agency had carried out risk assessments and issued groundwater authorisations for these sites, the assumption had generally been that the ash would be buried on site, which was their preferred disposal option and which had been assumed in the generic risk assessments. In many cases, this is what had happened in practice. However, where for example the groundwater table was high or particularly large numbers of carcases had been burnt, the Agency had advised against on site burial, and the best offsite method of disposal for this ash now had to be found.

- Ash from pyres was being analysed for residual protein content to give an indication of the extent to which prion protein infectivity had been destroyed. So far, only 3 analyses had been carried out. Two of these indicated at least 99% destruction of protein; the other had indicated at least 80% destruction. This limited data broadly supported the 90% destruction of infectivity assumption in the recent risk assessments on burning and burial of over 5 year cattle.

- Previous SEAC opinion, e.g. the SEAC Statement of 7 June 1996, in relation to parallel but not exactly equivalent situations had been that incineration would ensure greater destruction of any residual TSE infectivity, and was the preferred disposal option. However, burial in landfill sites had also been judged to present no significant risk.

- Given available incineration capacity, initial indications were that up to 8-10 years might be required to dispose of the estimated 100,000 tonnes of ash currently unburied. The recently imported air curtain incinerator destructors could help reduce this period, but were currently unproven for burning ash. If all the ash had to be incinerated, therefore, some would have to be stored for several years which would require double handling given that it could not safely be left where it currently lay. The worker safety risks of multiple movement of the ash could be much bigger than the relative TSE risks of different disposal options and needed to be taken into account in any risk assessments.

- Calculations indicated that the currently unburied ash would contain infectivity equivalent to roughly 60 BSE infected animals, which equated to 0.01 infective units per tonne - a very low level.

- The likely relative levels of infectivity would vary according to the number of over 5 year cattle from which the ash was derived, and the incidence of BSE in the area in question. Approximate relative risk rankings could be calculated relatively quickly in relation to the location aspect.

In the light of these considerations, the Working Group noted that, in general, the preferred method for disposing of ash from pyres was on site burial, as assumed in general risk assessments and in line with the policy adopted by the Environment Agency. Where on site burial was not possible, site specific risk assessments should be carried out. It would be useful if these could take into account both the origin of the ash and the geographic incidence of BSE to obtain broad relative risk bandings. Incineration would ensure the greatest destruction of any residual infectivity in the ash and was SEAC's generally preferred disposal option. However, the risks from landfilling ash were also very small, and certainly smaller than leaving the ash where it currently lay. Where incineration capacity was limited, the risks from greater handling and storage of the ash, if it all had to be incinerated, also had to be taken into account in the risk assessments.

Use of transporters of FMD carcases

The Working Group was told that, during the FMD crisis, hauliers had been transporting the carcases of animals slaughtered under either the FMD or the Welfare Cull. Such vehicles might now be returning to other uses, which might include transport of foodstuffs or feedingstuffs. The Working Group was invited to advise on the risks to human and animal health from possible contamination with TSE infected material arising from subsequent use for food or feed of vehicles which had been used to transport FMD cull carcases; and whether the requirements under food safety legislation for effective cleaning/thorough washing and disinfection, which reflected the existing SEAC advice on transport of specified risk materials, would adequately reduce any such risk.

The Working Group was told that, in practice, only a small proportion of the trucks used for carcase transport had been grain trucks. Calculations indicated that, in all probability, no more than 1 or 2 infected carcases, but not showing clinical signs, may have been carried in these trucks. Each truck would have been lined with plastic (liner or sheet) and sawdust and scrubbed and disinfected between each load. In any case, it would have been unlikely that any specified risk material from infected animals would have come into contact with the trucks trailer.

 The SEAC Working Group considered that rigorous washing down of the vehicles would be a reasonable precaution. They saw no need to change SEAC's earlier view in June 1996 in relation to transport of SRM (Specified Risk Materials) that, provided vehicles were thoroughly washed and disinfected, subsequent use for carrying food was acceptable. The Working Group emphasised the importance of thorough cleansing and did not consider specific anti prion treatment to be necessary.

Conclusion

The Working Group agreed that its conclusions should be put on the agenda of the next full SEAC meeting on 27 June.