Although composting is seen as a green alternative to conventional waste management and is certainly a 'natural' process, it may not be without its associated health hazards. Bioaerosols in composting facilities contain bacteria, fungi and other biological elements which could pose a risk of allergy and lung disease. Research into bioaerosols and their effects still have some way to go, and, in the meantime, it is important to adopt regulations that protect both the public and those who work at composting facilities from particulate pollution and chemical and gases, while not stifling the growing organic recycling industry.
An aerosol is a suspension of solid or liquid particles in a gas. Bioaerosol is short for biological aerosol and refers to the fact that the particles contain biological material, including:
A bioaerosol is usually a very complex mixture, whose particle range varies between 10 nanometres (0.01 microns) for viruses and 100 microns for pollen grains. Particles in a bioaerosol are subject to buffeting by air currents, which can carry them through relatively large distances, and to the force of gravity which pulls them downwards. The larger the particle is, the quicker it settles under gravity. Thus, pollen grains tend to remain airborne for just a few hours, while a virus will remain airborne almost indefinitely. Of course, one of the places bioaerosol particles can settle is in the human respiratory tract. Particles six microns or more in size will become trapped in the upper respiratory tract (nose and throat) but if they are 20 microns or more, they will be too big to penetrate to the lower respiratory tract (lungs).
Many of the microorganisms found in a bioaerosol are not actually viable (ie, alive). They cannot survive easily in the air because of the lack of the water they need (under conditions of higher humidity, however, more microorganisms may survive). Fungal spores, which have a tough outer coat, are more likely than most bacteria to survive in bioaerosol conditions and are found to be viable under conditions of low humidity and at extremes of temperature.
Bioaerosols are found around soil, particularly in woodland, around water and near sewage. Although bioaerosols tend to be an outdoor phenomenon, it is not uncommon to find them indoors under damp conditions. Bioaerosols are particularly associated with composting (the use of microorganisms to break down organic waste).
Organic recycling, or composting, has gone far beyond the creation of the modest garden compost heap from kitchen and garden waste. The UK compost industry has enjoyed strong growth in recent years, driven by the need to find alternatives to landfill to deal with domestic waste. Composting is seen as an environmentally friendly approach to waste management. In composting at its simplest, a pile of organic matter is simply left to rot, with bacteria and fungi present in the material transforming it into compost, a material rich in plant nutrients which has value as a fertiliser.
Modern industrial composting is a highly controlled process, with inputs of oxygen, and carbon and nitrogen nutrient sources for the microbes being carefully monitored. The material is turned often to allow for a more efficient composting process, which can create bioaerosol emissions. According to the Environment Agency, which has responsibility for giving composting companies permission to operate and for making sure they are safe, operations that may result in the uncontrolled release of high levels of bioaerosols include:
The fungus Aspergillus fumigatusis commonly present in bioaerosols in composting facilities and can cause a serious lung condition known as allergic bronchopulmonary aspergillosis (ABPA) if the fungal spores are inhaled. This is a particular problem for people with asthma and can lead to permanent lung damage. Exposure to bioaerosols in composting facilities can also lead to nausea, fatigue and headache. Pollen grains and other components of bioaerosols can cause allergic reactions in susceptible people.
However, there is much that we do not know about the health effects of bioaerosols, both on those working at composting facilities and those living in the surrounding area. According to the Environment Agency, there is some limited evidence suggesting that those who live close to a composting facility may be at increased risk of adverse health effects. It is generally accepted that bioaerosols generated from commercial composting decline rapidly within the first 100 metres from a site and have reached background levels within 250 metres.
In light of current knowledge, the Environment Agency quotes the following as being acceptable levels for bioaerosols:
A cfu is a recognised microbiological method for estimating the number of viable organisms in a sample.
In November 2010, the Environment Agency put out a new position statement on composting and the potential health effects of bioaerosols, which gives guidance to those applying for permits and discusses the legal limits of air pollution. This is part of an ongoing Government waste policy review. The Department of Environment, Food and Rural Affairs and the Welsh Assembly Government have agreed that these guidelines should apply, at least for now, in England and Wales to all composting operations located within 250 metres of a dwelling or workplace. These guidelines are summarised below:
When it comes to the SSBRA, these guidelines state that, in the current state of scientific understanding of bioaerosols, there is nosuitable methodology for carrying out an adequate quantitative risk assessment for new composting facilities. This means that the Agency, taking a precautionary approach, will not permit these new facilities where such an assessment would be required. This means that large facilities (more than 500 tonnes) carrying out operations in the open will not be allowed (unless, presumably, they can operate far from human habitation).
While the Environment Agency regulations protect people living or working near a composting site, the protection of those working there is the responsibility of the Health and Safety Executive (HSE). In recent years, HSE has carried out some monitoring at composting facilities and concluded that workers close to compost handling activities have been exposed to high levels of airborne bacteria and fungi, exceeding 100,000 cfu and even, on occasion, one million cfu per cubic metre of air sampled. There are a number of ways in which such exposures may be minimised, including:
If you are concerned about bioaerosols in your composting facility and the risk to your employees, then contact a member of our expert team who will be able to recommend the best solution for improving air quality and protecting your employees. Email us or call us on 020 3176 0524.
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Since the emergence of Covid-19 and global efforts to minimise the spread of infection throughout populations, there has been a renewed focus on determining what measures can be adopted to mitigate the risk of airborne transmission of respiratory viruses, including Covid-19, in a range of close proximity indoor settings.
