SIM 03/2010/11 – previously 03/2003/58
FOD inspectors covering manufacturing and service industries dealing with waste management and recycling and in particular composting activities.
Specialist inspectors
This Sector Information Minute (SIM) specifically covers issues related to bioaerosols generated at composting sites. It provides background information, outlines the conclusions of recent research, discusses the issues and advises inspectors of actions and lines to take when responding to enquiries.
There is an obligation on the UK Government to reduce the amount of waste going to landfill. Under the European Landfill Directive (Council Directive 1999/31/EC), the UK must reduce the quantity of biodegradable municipal solid waste sent to landfill to 35% of 1995 levels by 2020. Consequently, the composting of organic waste has become an important component part of the waste management industry.
As an expanding industry, there has been growing interest in the potential of this activity to create a health risk to both workers and members of the public. Microbiological activity is fundamental to the composting process, but the mechanical handling of compost, for example to aerate it and encourage composting, can generate aerosols of dust and micro-organisms, commonly referred to as bioaerosols. Inhalation of these bioaerosols in large concentrations may trigger the immune system leading to asthma or extrinsic allergic alveolitis (similar to farmer’s lung disease).
In 2003 a review of published data on the potential health risks arising from composting concentrated on the health risks to workers from composting but also dealt with health risks to the public residing outside composting sites. More recently in 2008 and 2010 separate studies reviewed the bioaerosol components from waste handling and their potential to cause harm and bioaerosol emissions from waste composting and the potential for workers’ exposure as well as downwind dispersion of those emissions.
These reports drew the following main conclusions:
Composting on a major scale is still a relatively new and expanding industry. Although evidence does not currently exist to cause major concern, there remains the potential for chronic ill health, which may not yet have had time to manifest itself.
If you make compost from waste materials or store compost made from waste materials you must have:
The regulator in England and Wales is the Environment Agency (EA). In Scotland it is the Scottish Environment Protection Agency (SEPA).
Based on scientific evidence that bioaerosol levels from waste composting are reduced to background levels within 250 metres from source the EA in England and Wales currently operates a '250 metre limit' rule around composting sites to minimise the potential of bioaerosol exposure to nearby residents. This is entirely a precautionary approach and although under review is likely to remain.
In summary, in England and Wales, the current position is that all aerobic composting facilities (closed and open) will need to operate under an environment permit issued by the EA unless exempt (e.g. composting small volumes up to 60 or 80 tonnes depending upon place of production and place of use). ‘Standard rules’ permits are available for composting facilities that meet certain criteria: otherwise a ‘bespoke’ permit will be required. The criteria for a ‘standard rules’ permit include that the facility will handle no more than 75,000 tonnes per annum and that the composting operation is located more than 250 metres from sensitive receptors (i.e. dwellings or workplaces). For those operations that handle greater quantities a ‘bespoke’ permit will be required. A ‘bespoke’ permit will also be required for facilities where the composting operations (open or contained) are within 250 metres of sensitive receptors. In such cases, the applicants will have to provide a site-specific bioaerosol risk assessment (SSBRA) which shows that bioaerosols from the composting operation can and will be maintained at acceptable levels at the sensitive receptors. If the SSBRA produced is inadequate in the opinion of the EA, a permit will not be granted. In particular, the EA indicate that permits are unlikely to be granted for medium to large scale composting operations within 250 metres of sensitive receptors unless they are enclosed or operate using negative aeration with bio filters.
In Scotland, SEPA although they do not have a stated position in the same way as the EA, the issue of bioaerosols is a consideration when licensing sites.
Inspectors should:
A briefing document for inspectors headed "Compost Bioaerosols - Frequently Asked Questions" is found at Appendix 2. It should assist when dealing with enquiries.
The Association for Organics Recycling (AfOR), previously known as the Composting Association, has produced a safety guide designed to help minimise the health and safety risks on site. Aimed at composting site operators, it includes advice on reducing health problems caused by airborne micro-organisms (bioaerosols) 'Health and Safety at Composting Sites - A Guidance Note for Site Managers' is available from AfOR as a priced publication. Copies for inspectors' reference can be obtained from Redgrave Court Information Centre and the Sector.
Other useful data on waste handling, including composting, can also be found in the Research Report RR609 Collecting, transfer, treatment and processing household waste and recyclables, which provides an assessment of the occupational health and safety risks of systems for collection, transfer, treatment and processing of household waste and recyclables and includes a risk comparator tool.
Bioaerosol is the term used to describe micro-organisms (bacteria, fungi/moulds or viruses) or their products that are airborne. Bioaerosols are naturally present in the air, mainly soil borne micro-organisms in airborne dust, so everyone is constantly exposed to them. Concentrations change depending on the weather, season and whether indoors or outdoors. Typical bioaerosol concentrations are greater in rural areas, because of nearby vegetation, than in urban areas. Bioaerosols can result from any process that makes microbially contaminated material airborne. Examples in the workplace include contaminated industrial process water. In agriculture, bioaerosols may be created from handling dusty contaminated material such as grain or animal feed, or from animal housing.
Composting is a natural process in which micro-organisms (fungal/mould spores and certain types of bacteria called actinomycetes) are encouraged to grow to break down waste material. As a result, very large numbers of micro-organisms are present in compost and any handling of the material that generates dust will create a bioaerosol. To encourage efficient composting, the piles of material (called windrows) have to be well aerated and therefore are turned regularly. At the end of the process, often the compost is screened (sieved) to produce a quality soil supplement. Both of these activities will create bioaerosols.
The UK Government has an obligation, through EU legislation, to reduce the amount of waste going to landfill. Challenging targets have been set and ways to achieve these targets include recycling of waste materials. Composting of organic waste is an important part of the recycling initiative and as a result composting sites have proliferated. Because bioaerosols are generated from composts, concerns have been raised mainly by residents in the vicinity of composting sites, that exposure to the bioaerosols can affect health.
As part of the planning and permitting procedure, new composting sites must assess the impact their business may have on the surroundings, including the risks that may be associated with bioaerosols generated from composting activities. The EA in England and Wales issued a position statement in 2007 which was updated in 2010 which stipulated that if new composting sites or new activities on existing sites, are less than 250 metres from a sensitive receptor such as a nearby residential property, they must assess any health risk and if necessary control potential exposure of that sensitive receptor to bioaerosols. The 250 metres distance was estimated from previous studies which indicated that by this distance any bioaerosols associated with commercial composting would disperse in the atmosphere and concentrations would be reduced to background levels.
The study undertaken by Health and Safety Laboratory (HSL) and the Composting Association in 2003 on behalf of HSE critically reviewed the available literature to provide a single source of information to assess worker exposure to bioaerosols and potential health risk and also to identify gaps in relevant information. The Institute of Medicine (IOM) review in 2008) commissioned by Defra added further to this knowledge. In the more recent HSL study (2010) , bioaerosol measurements were taken at various locations on a number of compost sites near to and downwind of compost handling, as well as outside vehicle cabs and in workers’ breathing zones inside cabs, with upwind samples providing background measurements. This provided a comprehensive data set on typical bioaerosol levels associated with waste handling, and the dispersion and dilution effects of distance from source. The overall conclusion from the reviews and measurement studies is that compost bioaerosols are potential respiratory sensitisers and could pose a health risk to unprotected exposed workers, but that composting sites are unlikely to pose a significant risk to the health of residents in the vicinity of composting sites.
If you work with compost, potentially you will be exposed to bioaerosols, because of the large number of micro-organism present in the compost. As with other workers exposed to organic dust and large numbers of airborne micro-organisms (e.g., in certain agricultural activities and in waste handling) if you breathe in those micro-organisms in large numbers over a long period they can trigger an allergic reaction. This can range from a short term flu- like reaction (inhalation fever) to longer term ill health such as asthma or bronchitis. Once a person has become sensitised, subsequent exposure to even a smaller quantity can trigger the allergy.
The key is to assess risk and control exposure, which is an obligation placed on employers by the Health and Safety at Work etc. Act 1974 and relevant statutory provisions such as the COSHH Regulations. Potential exposure can be controlled by changing the work process to minimise the generation of bioaerosols, or possibly by managing temperature and moisture levels in the compost to reduce dustiness. Introducing control measures may also be applicable, such as exhaust ventilation to prevent exposure, using adequate filters on the air intakes of vehicles such as tractors used to move compost, or using personal protective equipment such as adequate and suitably fitted respiratory protective devices when working in areas close to where bioaerosols are generated.
The greatest risk of exposure, justifying the control measures described above, are when in close proximity to compost being handled i.e. within 30 metres. Further away when working outside exposure levels will be greatly reduced and require less stringent control, but may still be above background levels. If site specific measurements indicate elevated bioaerosol levels beyond 30 metres then it may be appropriate to provide respiratory protection especially if working in those areas for extended periods.
In more traditional composting, the material is composted outdoors in heaps (open windrows) that are turned frequently to aerate the compost and it is this turning process that generates most bioaerosols. In some composting systems known as in-vessel composting systems (IVC), also used to compost material potentially containing animal by-products, the composting process is enclosed and sometimes uses forced aeration, but the material is not turned. Bioaerosols will still be generated particularly when the material is being handled to load and unload the vessel, and during post-vessel maturation of the compost.
At some sites, composting may be done in enclosed facilities. While this may reduce bioaerosol emissions downwind to comply with EA permit conditions if the facility is within 250 metres of a sensitive receptor, the enclosure may increase bioaerosol concentrations to which workers are exposed by reducing the potential for open air dilution and dispersion of emissions, including bioaerosols. In such cases, operators should ensure that suitable ventilation systems (forced or otherwise) are provided that ensure suitable dilution of bioaerosols and biogases such as carbon dioxide (as well as provision of sufficient oxygen). Other hazards which should also be considered including thermal discomfort due to excessive heat and moisture. High moisture content in the atmosphere could also lead to poor visibility. Monitoring of contaminants such as bioaerosols and carbon dioxide will demonstrate if the systems are effective.
Most published studies on compost bioaerosol exposure and health have focussed on the exposure of workers on sites handling the material, because their exposure will be greatest. Some studies have looked at the effect of composting activities on surrounding bioaerosol concentrations. A limited number of studies have looked at the health of nearby residents. While it is recognised from these studies that under certain conditions composting activities nearby may raise bioaerosol concentrations above background levels, these concentrations are much lower than would occur on a composting site near to compost material being handled. There is no reported evidence of significant increase in ill health in residents near composting sites in these situations. The lungs of a healthy person are capable of being exposed to relatively large concentrations of micro-organisms without ill effect.
Bioaerosols are always present in the atmosphere. These may be considered as the background level of exposure we constantly experience. The recent HSL study (2010) has confirmed previous published studies which showed that by 250m distance from composting activity in most cases the bioaerosol concentrations will be reduced to background levels. In some studies, however, bioaerosol concentrations above background have been recorded. Consequently, although there is no evidence of ill health for nearby residents, it would be difficult to justify changes to the 250 metre limit set by the EA on the strength of current evidence. It should be noted that other activities locally, such as farming activities, or even the presence of large areas of vegetation, can also raise the background bioaerosol concentration.
Composted material may have a distinctive smell, depending on the feedstock, for example if it contains a large proportion of pine branches there will be the characteristic resin smell. The volatile chemicals responsible for smells are gases, which are smaller in size and lighter than particles of dust, and bioaerosols (mould spores and bacterial cells in the air) behave like small particles of dust. Consequently, gases can travel further in the air than the heavier particles, which drop from the air under gravity. Some odorous gases can be smelled at extremely low concentration. Sometimes, if composting activities are poorly managed, the compost becomes 'anaerobic' (oxygen starved) which causes the bacteria in the compost to create different chemicals with unpleasant smells. In many cases, this can be avoided: if it occurs you should complain to the compost site or bring it to the attention of the local authority. HSE inspectors will refer complainants commenting on smell and other public nuisance issues to the appropriate local authority Environmental Health Department or EA (or SEPA in Scotland).
Bioaerosols, including those from compost, are like any other small dust particles in the air. They can move and be carried along in air currents before falling to the ground under gravity. If the wind direction and strength is known, it is possible to predict in what direction and how far a bioaerosol will travel away from the source of its release. As it is carried by air currents from that source, it will be dispersed and therefore diluted in concentration as it mixes with the surrounding air. Local conditions will affect this; for example, the warmth from a compost pile will make the bioaerosol rise higher in the air, and nearby buildings, trees, fences etc will also push the air current higher into the air, causing more mixing with the surrounding air and dilution of the bioaerosol. It is possible to use computer models (dispersion models) to predict these movements, and such models may be a useful tool to predict the movement of bioaerosols around and away from composting sites.
In addition to the hazards associated with inhalation of bioaerosols on composting sites, there may be other biological hazards depending on the feedstock. If sewage sludge is being used, there may be infectious bacteria and viruses present. If vermin on the site are not controlled, there is the risk of workers contracting leptospirosis (Weil's disease), a bacterial infection caused by exposure to contaminated rat urine. Good hygiene, including provision of adequate hand washing facilities, can reduce these risks.
Other hazards on a composting site include potential exposure to any chemicals used on site, and physical hazards such as slips and trips, moving vehicles and machinery. In enclosed buildings, other hazards include the build-up of biogas (carbon dioxide, hydrogen sulphide etc.) from the biodegradation process and exhaust gases from the mobile plant and delivery and collection vehicles. If these are allowed to build up sufficiently they may cause an asphyxiation hazard. Increased dust and volatile organic compounds (VOCs) exposure, potential thermal discomfort from excessive heat and humidity, poor visibility due to high moisture content in the atmosphere and odour may also result in enclosed buildings. It is the responsibility of the site operator to identify potential hazards, make a suitable risk assessment and to provide adequate protection to their work force to control such risks.
