Assessing the risks of cattle waste disposal

The first of the new animal carcase incinerators for disposing of cattle under the Government's cull programme, the Over Thirty Month Scheme (OTMS), is now ready for operation in Nottingham, pending the Environment Agency's go-ahead. But before authorising any new incinerators, the Agency intends to publish the results of its risk assessment work on facilities managing wastes contaminated with prions - the BSE infective agent. As well as incinerators, the work has covered landfill sites, power stations burning meat and bone meal (MBM) and rendering plants.

The BSE crisis is a major test of the Agency's resolve in standing up to Whitehall pressure and maintaining public credibility. "There's an overriding desire in the Agency to fully grasp the extent of the problem," according to the Agency's Stuart Stern - and publishing the risk assessment is intended to ensure that no pathways have been missed.

The Nottingham incinerator, to burn 400 carcases per week, is the first fruit of WRE Services, a joint venture between Yorkshire Water and Evans Universal set up to win contracts from the Intervention Board.

The new plant will barely scratch the surface of the cattle waste mountain the Government is creating. Up to 40 such facilities, costing around £1 million apiece, would be required to match the expected rate of future slaughter. But so far Cornwall, Manchester, Lincolnshire, Northamptonshire and Staffordshire planning authorities have refused consent for proposed carcase incinerators.

In February, John Prescott, now Environment Secretary, published a "BSE map of Britain" showing all the coal-fired power stations that could be used to burn rendered cattle remains. Since substantial new incineration capacity appears beyond reach, the Government's options are limited, and negotiations with the power generators are continuing.

The only significant disposal activity to date is the incineration of MBM at Rechem's chemical waste incinerator in Hampshire, which has a contract for 15,000 tonnes per year - far less than the rate at which MBM is accumulating in Government stores.

If the power station route is not followed, the Government may have to consider an alternative, large-scale incineration proposal by Yorkshire Water. In April, the company submitted a £30 million bid to the Intervention Board to burn a total of 150,000 tonnes of MBM per year in three rotary kiln incinerators. Each plant, including heat recovery and gas cleaning facilities, would be demolished after the cull is completed. Another option is to permit the rendering industry to burn MBM in its existing plants (see main article ).

By mid-May - one year into the cull - more than 1.4 million cattle had been killed under the OTMS, and a further 800,000 dairy cattle aged over 30 months will follow each year until the scheme ends - which is unlikely to be before 2002. The Government does not expect BSE to be eradicated before 2001.

Almost all the animals culled to date have been rendered, with the resulting MBM and tallow sent for storage. Some 200,000 tonnes of MBM and 115,000 tonnes of tallow are currently in store, under a one-year exemption from waste management licensing permitted under emergency regulations laid last year (ENDS Report 256, p 34 ). One year on, the first stores used by the Intervention Board have now applied to the Agency for a licence.

In addition, the Government stored 68,000 tonnes of frozen carcases, 2-3,000 tonnes per week of which are now being taken out and rendered.

The OTMS cull does not include animals suspected of having BSE, which are incinerated in separate facilities. The cull was billed as a measure to increase consumer confidence, but it also serves to remove unwanted meat from the British market following the beef export ban.

  • Landfill risks: Despite its relatively low risks, waste from the OTMS cull falls under stricter regulatory controls than any other animal waste. Under an EC Regulation, all the material must be "incinerated or rendered and destroyed" - a definition now taken to exclude landfill.

    By contrast, specified bovine material (SBM) from younger cattle - which has been banned from human or animal consumption since 1989 because it can contain the BSE infective agent - can be landfilled after rendering.

    For the past year, however, rendered SBM has not been sent to landfill. Instead, it is mixed with carcases from the OTMS cull in the same rendering plants, and all this rendered material is stockpiled by the Intervention Board. A revision of the OTMS now being negotiated will allow landfilling of the rendered SBM from younger cattle to resume, reducing demands on Intervention Board storage.

    The Environment Agency's work on assessing risks from landfill, incineration and rendering will be published shortly along with comments from SEAC. Last June, however, before any such risk assessment had been conducted, SEAC's initial advice on waste management concluded that landfilling MBM produced from SBM "presented no significant risk". The Committee did not regard incineration of MBM and tallow as necessary on scientific grounds, and added that there was no reason to believe there was a significant problem from landfilling whole carcases from BSE-infected cattle, as practised in the early 1990s.

    However, SEAC did not investigate landfill degradation processes in reaching its conclusions. And it was not until March this year that the full extent of landfilling came to light.

    Whereas all BSE suspects have been incinerated since 1991, roughly 6,100 infected cattle, with their heads removed, were disposed of by landfill in the early years of the epidemic. More than 1,000 went to Everleigh Tip near Pewsey, a Wiltshire County Council landfill that has now closed.

    Over the past few months, the Agency has been conducting a risk assessment for wastes containing prions. The "broad thrust" is that landfill comes out "satisfactorily low", according to Stuart Stern. Pathways considered include possible leachate contamination of groundwater and landfill gas emissions.

  • Incineration: The Agency has also prepared reports on risks from incineration and combustion in power stations. SEAC's advice last June was that combustion at 850°ree.C or above - in power stations, cement kilns or incinerators - would be "sufficient to ensure that there was no risk".

    But subsequent trial burns of MBM in power station test rigs have found traces of amino acids - protein building blocks - surviving incineration. It is impossible to say whether prions were among the amino acids detected, but, for the risk assessment work, the Agency has assumed that they are present. Even so, "the risks do come out jolly low indeed," said Dr Stern.

  • Rendering:
    The risk of prions leaching into drinking water supplies was the focus of public concern at a recent planning inquiry into a proposed effluent treatment system at Thruxted Mill rendering works near Canterbury. As a statutory consultee and regulator of wastewater discharges, the Agency commissioned a risk assessment of the proposal. The works, which currently discharges effluent directly to the land surface, plans to install primary and secondary effluent treatment followed by disposal underground through a soakaway.

    The Agency's methodology uses techniques for assessing risks developed in the nuclear industry. The study, by DNV Technica, considered four wastewater management options - discharge to sewer, tankering off-site and the historical and proposed disposal methods. It concluded that "all options present extremely low risks of exposure to BSE infectivity and would be considered negligible in comparison to established risk criteria." The tankering option represented the lowest risk, but the advantages would be "more than negated by the risk of fatal accidents due to the tanker movements".

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