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Is Mulch Toxic to Humans? (Potential Hazards of Mulch to Human Health)

Is Mulch Toxic to Humans? (Potential Hazards of Mulch to Human Health)

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For centuries, mulch has been regarded as a gardener’s best friend. It does practically everything to support the growth and health of plants. It retains moisture, suppresses weeds, and enriches the soil with organic matter, among others.

However, discussions about its potential danger to humans are rarely brought up in conversation. I aim to change that.

Mold growth in mulch can trigger allergies or respiratory issues in some people, especially those with pre-existing respiratory conditions. Mulch also provides favorite conditions for pests like ants, ticks, and spiders, which can compromise the comfort and safety of outdoor spaces.

In this article, I’ll discuss the dangers and potential toxicity of mulch to humans. I’ll also share some essential safety tips and considerations when using this gardening resource.

Is Mulch Toxic to Humans?

As a long-time gardener, I’ve come to realize that mulch is much like a double-edged sword. While it offers incredible benefits to a garden, its potential dangers shouldn’t be underestimated.

Here are some factors that may contribute to the dangers of mulch:

1 – Chemically-Treated Mulch

Chemically-treated mulch, such as those treated with chromate copper arsenate (CCA), has the potential to be toxic to humans.

In the past, CCA-treated mulch was used to resist decay and pests.

Environmental and health concerns led to the discontinuation of the practice, but CCA-treated mulch can still be found in some areas as a formal was never imposed.

Direct and prolonged contact with CCA-treated mulch, as well as accidental ingestion, poses great health risks.

CCA-treated mulch releases arsenic emissions when burned, which can lead to diseases including skin cancer, cardiovascular disease, and respiratory cancer among others.

To avoid potential exposure to these emissions, it’s best to opt for untreated or naturally decay-resistant mulches. I recommend natural cedar mulch and cypress mulch for their anti-rot and antimicrobial properties.

2 – Mold and Fungi

Mulch can be a hotbed for mold and fungi, especially when placed in damp or humid areas. Mold spores can trigger respiratory issues or allergies in some people.

Mold in mulch can take on different appearances, ranging from white rings to orange, brown, and yellow-colored patches.

Shotgun fungus, slime mold, and bird’s nest fungus are among the most common types of fungi you’ll find in mulch.

Proper mulch maintenance, including regular ventilation and replacement, can help reduce mold growth and potential health risks.

3 – Bacteria

Gardeners that handle a lot of mulch may be at risk of inhaling Legionella, a pathogenic bacteria that can cause a severe respiratory illness called Legionnaires’ disease.

Legionella bacteria are typically found in natural water environments, but they can also be present in certain man-made environments like plumbing systems, water heaters, and the like.

If the mulch is sourced from areas near environments that contain Legionella bacteria, there’s a possibility that the bacteria could be present in the mulch.

The same is said when contaminated water is used during the mulch production process.

Legionella bacteria come in two primary variations: Legionella pneumophila and Legionella longbeachae.

Legionella pneumophila is found in water systems, where it can grow on wet surfaces. On the other hand, Legionella longbeachae is found in compost, garden soil, potting mix, and—you guessed it—mulch.

Legionnaires’ disease can be fatal. Initial symptoms include headache, muscle ache, and fever, which then progresses to coughing (sometimes with blood-streaked phlegm), chest pain, vomiting, shortness of breath, and diarrhea.

According to the Centers for Disease Control and Prevention, Legionella bacteria affects more than 10,000 US citizens a year.

To reduce any potential risk, thoroughly wash your hands after handling mulch and avoid direct inhalation of aerosols and dust near mulched areas.

Additionally, source your mulch from reputable suppliers to reduce the likelihood of bacterial contamination.

4 – Pest Infestation

Poorly maintained mulch can attract pests such as ticks, termites, ants, and spiders. While not inherently dangerous to humans, these pests can cause discomfort or trigger allergic reactions in some people.

Termites are particularly attracted to wood mulch, as it serves as both food and a conducive environment for their colonies.

Ticks and spiders are drawn to the cover and humidity of mulch, while slugs and snails creep in mulch due to its damp and cool environment.

To minimize pest infestation, keep mulch away from builds and structures to discourage insects from accessing indoor spaces.

You should also maintain an appropriate mulch depth to prevent the development of excess moisture in the mulch.

Can Mulch Have Fungus?

Fungus is a natural part of the decomposition process, so the presence of fungal growth in mulch is a common occurrence.

Organic mulches, such as wood chips, straw, bark, and compost, create a favorable environment for fungi to thrive.

As mulch breaks down, it imparts an abundance of nutrients for fungi to feed on, leading to the growth of various fungal species.

Is Mulch Fungus Harmful to Humans?

Most fungi aren’t harmful to humans. However, certain types of molds can produce mycotoxins, which may cause allergies or trigger respiratory issues when inhaled.

For this reason, good hygiene is crucial when working with mulch.

Avoid direct contact with moldy areas and wash your hands thoroughly after handling. Gloves can reduce the risk of exposure to mold spores.

Final Thoughts

Understanding the potential dangers can mitigate the risks and hazards associated with using this resource.

Instead of using chemically-treated mulch, opt for untreated or naturally decay-resistant mulch to avoid chemical inhalation.

It’s also wise to source your mulch from reputable supplies to ensure the mulch is free from potential contaminants, bacteria, or harmful substances.


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