Before we get started, let me get this disclosure out of the way:

I love compost.

From peeing on my garden mulch to composting the waste from my house move, I've written prolifically about my adventures in rotting biomass.

I never fail to be amazed how nature’s regenerative powers can take dead, rotting waste, and cycle it back into life-enhancing black gold.

Is compost the enemy?

As an enthusiast, I've always been confused by the idea that anyone could not love compost. Yet these people exist. In fact, a quick search of the Internet will find those who don’t just “not love” compost — they actively hate it.

Some even see it as a threat to our health, well-being and way of life.

Take this impassioned, if grammatically challenged, article warning of Danger Mulch & Compost Environmental Danger [sic]:

"DANGER: Environmental Organic, Gardening with Mulching Composting Can Kill You! While enviro friendly web articles pitches you on organic gardening they forget to tell you about the dangers of going organic.  […] Mulching & Composting is a lot like cooking, but our unfriendly brain dead environmental recyclers forget to tell you is some of the micro- organisms developing in the pile can be deadly to humans."

So what’s the deal?

Is my beloved compost pile really just a deadly source of contagion, ready to claim its next victim?

Yes ... and no.

Aspergillus spores, fungus, mold and meningitis

The fact is that fungal spores, mold and bacteria can, on rare occasions, present a health risk — especially to young children, the elderly, pets or those with compromised immune systems. In one much-blogged-about incident in 2008, a U.K. man died after breathing in Aspergillus fungal spores from his leaf mulch pile. Similarly, molds caused by bread, meat or cooked foods in compost piles can cause illness in pets that dig around in the pile. And there are concerns that Legionella longbeachae, a rare form of meningitis, can be transferred through exposure to potting compost. (This risk seems to be predominantly a problem in Australia.)

But these rare instances have given rise to vocal howls of protest over the dangers of composting, most notably when residents oppose industrial-scale composting facilities in their neighborhoods.

From increased truck traffic to noise pollution or land use issues, as with any industrial development, there may be good reasons why a composting plant is inappropriate for a certain site. But the evidence of airborne health risks from fungal spores seems tenuous at best.

AspergillusAspergillus risk overblown

A fact sheet on aspergillus spores from the Minnesota Pollution Control Agency suggests that everyday activities, such as mowing grass, mulching the garden, or walking on a wood chip-covered trail expose people to more A. fumigatus spores than living near a compost facility.

Citing a study by Millner et al. (1980), the fact sheet goes on to demonstrate that while there may be temporary increases in airborne spores immediately adjacent to a compost heap after it is turned, spore counts quickly return to normal after turning has stopped. The agency suggests that simple, commonsense measures should be put in place to ensure that risks are minimized:

"To be a good neighbor and to minimize risks, the Minnesota Pollution Control Agency (MPCA) recommends that all compost facilities spray water on the compost on dry or windy days and refrain from turning the piles on windy days. This minimizes not only A. fumigatus spores, but also litter and fugitive odors that may escape the site. A buffer zone between the facility and a residential area is also recommended for the same reasons."

Composting industry safety

Fungal spores are not, of course, the only danger posed by large-scale compost facilities. Like any industry, composting operations carry with them inherent risks, and occasionally things will go wrong. In the fall of 2011, two brothers died at a composting facility in Kern County, California. Ellen Widess, chief of the state Division of Occupational Safety and Health, later described the deaths as “completely avoidable.”

Due to the high temperatures generated in large-scale composting, fire is also an ongoing risk. Indeed, major fires have broken out at composting facilities, sometimes spreading to nearby buildings. But here too, sensible measures can head off trouble before it happens.

Brian Rosa, organic recycling specialist at the N.C. Department of Environment and Natural Resources, puts it this way:

"The industry has grown increasingly sophisticated at managing risks and preventing problems. There are specific guidelines that limit the height of compost heaps, and cover everything from how often you turn it to when and how much you damp it down with water. If you have a fire at your facility, it’s your own damn fault."

Sensible composting precautions

Ultimately, the health risks from composting — both on an industrial scale and in home compost heaps — can be minimized, and almost eliminated, through sensible precautions. Whether it’s buffer zones and frequent spraying at commercial facilities, or hand washing and avoiding composting materials that cause mold at home, these measures are neither rocket science nor particularly complicated to implement. When using potting soils and commercial composts, gardeners would do well to damp down the compost to avoid inhaling spores. And the elderly, the severely asthmatic, or those with allergies or immune deficiencies might want to wear a mask when handling compost.

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