Biological and Chemical Health

Composters are exposed to the resident organisms involved in decomposition, and their components (e.g. spores, endotoxins), plus the volatile compounds and dusts generated during composting. When these biological and chemical elements become airborne (usually with dust particles and mists), they are referred to as bioaerosols. The bad news is that both acute and chronic adverse health effects could potentially arise from these biological and chemical agents if ordinary safety practices are ignored. The possible health effects range from short term symptoms, like skin or eye irritations, to more worrisome allergic reactions and illnesses. The good news is that workers, compost users or neighbors rarely experience adverse health effects because of the body’s ability to defend itself and because these biological elements are present most everywhere in the environment. 

While these potential health concerns are real and merit attention, it is unclear if they make composting a risky occupation. Compost workers are an underresearched group and research results to-date are inconclusive, if not contradictory. Some of the potential adverse effects depend to a great extent on the susceptibility of the individual. Again, there is little evidence to suggest that compost workers -- the group most exposed to the hazards -- have any greater incidence of health problems than the population at large. Ordinary safety practices and the body’s inherent defenses are apparently effective in keeping the risks low.

Routes of Entry 

The first step in minimizing the risks from biological and chemical substances is understanding their potential routes of entry into the body. Chemicals and biological agents enter or make contact with the body through eye contact, skin absorption, injection through the skin, or ingestion and inhalation.  Common sense, hygiene and personal protective equipment (see following section) block these routes of entry. 

Eye contact

hen present in high concentrations, water-soluble gases such as ammonia and hydrogen sulfide, volatile fatty acids and aldehydes can dissolve in eye moisture and produce eye irritation. Dusts and aerosols can also enter via eyes and produce irritation, while microorganisms in the eyes could produce infection. Defense mechanisms for eyes, including tears and blinking, exclude or remove most airborne hazards. However, eye protection is still recommended to lower the risks from bioaerosols, dust, and chemicals (in high concentrations) as well as flying particles. Hand-toeye contact (e.g. rubbing eyes) is another pathway for irritation and infection, which is minimized by frequent hand-washing and wearing gloves.

Skin contact or absorption

The skin is an incredibly effective barrier to microorganisms and most chemicals. While rare, irritation or burns may result from skin contact with a few abrasive chemicals that may be used at some composting facilities, such as cleaning acids or caustics or laboratory chemicals. Skin reactions to plant toxins, such as poison ivy or poison oak, are more likely. Protection practices include appropriate clothing and gloves and awareness of the hazardous chemicals and plants that might be present.

Injection

Chemicals and organisms are much more likely to cause infection or injury once they penetrate the fortress of the skin. Damaged skin (punctures, cuts, abrasions) can become infected, as well as serve as an entrance to the bloodstream. There are numerous opportunities for composting workers to acquire cuts and scrapes while walking near or handling materials containing sharps (e.g. glass fragments), scrap metal and wood with protruding nails and while working with equipment and tools. Cuts and scrapes should be cleaned and treated immediately and then kept protected with bandages and washed frequently. Existing wounds must remain protected and cleaned. Appropriate gloves and footwear (e.g. steel soles) should be worn, and sharp, protruding objects should be removed promptly from harm’s way.

Ingestion

Assuming that you are not taste-testing compost nor drinking the compost tea, dusts and particles carrying microorganisms landing on lips can be inadvertently swallowed. In addition, hand-to-mouth transfer can occur by eating food or smoking cigarettes without first washing hands. If the microorganisms proceeded to the digestive tract, some may be killed by stomach acid and some may survive to infect the intestine or other body systems. Good hygiene greatly reduces hand to mouth ingestion. Respirators and masks worn in dusty situations minimize inadvertent ingestion.

Inhalation

The atmosphere carries small to microscopic bioaerosols that people routinely inhale including gases, dusts, mists, vapors, bacteria, fungal spores, viruses and protozoa. At composting sites (and other locations where organic materials are disturbed; e.g. raking leaves), bioaerosols are present at concentrations that are much higher than normal and thus present greater health risks. Most bioaerosols are removed before reaching the lungs by fluids in the nose, throat and bronchial tubes (Figure 10.2). Particles that are not water soluble or smaller are more likely to be carried into the air sacs of the lungs. Here white blood cells, called macrophages, engulf and destroy many bioaerosols and guard against infection. As with ingestion, most organisms that are inhaled die inside the body, while some may persist. Respirators and masks should be used in dusty situations to reduce inhalation of bioaerosols. In addition, fewer bioaerosols become airborne when materials are kept moist.