>> Under certain temperature and moisture conditions, some micro-organisms present during the composting process can turn out to be pathogenic, either spontaneously or because of the production of spores or the secretion of toxins.

>> In compost, we can distinguish:

• Micro-organisms (bacteria, viruses, intestinal parasites) of faecal origin which are present in the original waste.
• Pathogenic or allergenic organisms (thermophilic actinomycetes, fungi) develop during composting or storage.
• Toxis and allergens released by bacteria and fungi.

According to a working document of the European Commission (February 2001), optimal conditions for hygienising compost are as follows:

	Temperature	Duration of treatment	Turning
Windrow composting	= 55°C = 65°C	2 weeks 1 week	5 2
Composting in a closed system	= 60°C	1 week	No instructions

UMIC probes allow you to ensure that the thermophilic phase is performing the funciton of hygienising the compost as it should.

The concentrations of dust measured in the ambient air of composting plants rarely exceeds the recommended threshold value for the workplace in France (10 mg/m³), and are in fact often considerably lower.

Organic dust contains animal, vegetable and microbiological particles. Their size may vary and they can accumulate at any point within the respiratory system, from the nose to the pulmonary alveoli.

Higher concentrations of aerobic bacteria and thermophilic fungi are detected during compost mixing operations.

The risks posed by the various dust components involve 3 processes:

>> >> Infection caused mainly by Aspergillus

>> >> Inflammation caused by endotoxins, glucans and mycotoxins

>> >> Allergy caused by actinomycetes and fungi

Types of response associated with the inhalation of organic dust	Diseases
Inflammation (non-allergic)	Irritation of the mucous membrane of the eye and airways Acute bronchoconstriction Chronic bronchitis Toxic pneumonitis Non-allergic or intrinsic asthma
Allergy	Extrinsic allergic alveolitis or hypersensitivity pneumonitis Allergic rhinitis Allergic asthma
Infection	Necrotising pneumonia (invasive, systemic) Pulmonary disease (invasive, non-systemic)

Little is known about the risks posed to employees. Considering the data available, the risk seems to be confined mainly to allergens or toxins affecting the respiratory system and skin, but high exposure levels are needed in order to reach the threshold for sensitization to Aspergillus or actinomycetes.

Moreover, Aspergillus does not tend to cause serious infections in people with immunodepression or those bearing residual lung cavities.