8 Sep 2017

Is colored mulch potentially toxic?

Moving to the US way back in 2001 I was eager to continue with my love for gardening, and set about establishing flower beds with an array of perennials and some annuals. I was intrigued by the habit of applying a layer of mulch on the soil to maintain moisture, but mainly to reduce weed growth, and my own sweat labor.

What a cool solution!

Fast forward a few years, and a whole lot of life experience, education and resulting eye-opening awareness later, I was forced to confront this habit from a different point of view.

Is this cool solution possibly adding to my body’s toxic burden?

Having just had a dog pass away from super aggressive lung cancer, I had been wondering what else, besides exposure to the lawn pesticide treatments in our neighborhood on our daily walks, could possibly have contributed to any toxic body burden.

I know what some of you may be thinking now: I have used this stuff for years, and never had anyone in my family be affected by it.

I hear you. And my point is not to say that everyone will get diagnosed with x-y-z when using mulch.

But we need to be mindful of ALL the factors that can potentially CONTRIBUTE to weakening our body’s ability to ward off rogue cells that may become malignant, or that suppress the immune system to such a degree that it struggles to deal with normal protective mechanisms.

Let’s look at mulch a little closer, in particular, colored mulch, as this has been a subject of some controversy.

You may tend to think the problem lies in the dyes used, and that non-dyed mulch is a much safer option. Not so. Of concern should be the SOURCES of wood chips used, as these may possibly be contaminated with toxic substances. It’s the SUPPLIER of the mulch we need to scrutinize.

In my research, I came across the following explanation published by the UMASS Amherst’s Center for Agriculture, Food and the Environment:

Most of the wood used for making colored mulch comes from recycled wood, i.e. wood scraps, wood pallets, and wood reclaimed from construction and demolition (C&D) waste.  

Besides the benefits of recycling waste wood materials, the reason why these wood materials are used for colored mulches is that they are very dry and readily absorb or adsorb coloring agents. With their high moisture content, fresh wood chips do not easily absorb or adsorb the dyes commonly used for coloring.  

Nevertheless, it has been found that some of the recycled waste wood used for making landscape mulch products is contaminated with various chemicals, such as creosote and CCA (chromated copper arsenate).

CCA is the chemical that was used in the manufacture of pressure-treated wood. With bans on arsenic-based wood preservatives in recent years, this may become less of a problem, though there is still plenty of CCA preserved wood to be found in older decks and fences.

Sometimes wood pallets that have been used in the transport of chemical agents can become contaminated by spills of these chemicals. 

The bottom line is that CCA and other toxic chemicals have been found to be contaminating soil where colored wood chip mulch has been applied.

The most egregious source of the contamination appears to CCA treated wood recycled from C&D waste.

 

WHAT ABOUT THE ACTUAL DYES?

UMASS continues…
“The dyes used in coloring wood mulch are primarily of two types: carbon-based dyes and iron oxide based dyes.

Iron oxide, the most commonly used dye, is a compound of iron and oxygen. As the compound oxidizes, iron is released to the soil but is not considered to be toxic. Iron oxide dyes are often used in the floriculture industry to dye flowers.

Dyes that are not absorbed by or adsorbed to the wood would come off with contact, especially if the mulch is wet. There are some carbon-based dyes used on mulch. These carbon-based colorants are similar to those used in ink and cosmetics. At this time, there is no evidence that the dyes used to color wood chip mulch are toxic.”

 

In my personal opinion, even though there is no evidence of potential toxicity (maybe as yet), I still prefer to err on the side of caution. No more colored mulches for us. Besides running and sometimes lying on it on a daily basis, our pup Max will even occasionally chew on some, although thankfully as he is getting older this undesirable habit is waning!

The bottom line is this: there is no need to assume that all colored mulches are possibly contaminated. If you are planning to use colored mulch however, it would be prudent to find out:

  1. Who the supplier is
  2. What the source of wood being used to make the mulch is
  3. What dyes were used in the production
  4. Is there a private environmental testing laboratory in my area (in case you want to take it even further)?
  5. Is the packaged mulch you are considering certified by The Mulch and Soil Council? Back in 2004 the MSC was developed through an initiative by the Mulch and Soil industry who wished to adopt standards that would prohibit the use of CCA-treated wood in consumer products. A Product Certification program was set up to enable consumers to find mulches and soils that complied with these new industry standards.

Wood recycling should be viewed as an environmentally friendly practice, and the result should be non-contaminated wood chips that can safely be used as mulch for our gardens.

For our own garden, I called around to locate a mulch supplier who is local to the area and could elaborate where he received his mulch from, namely from natural wood or bark of trees that had died or needed to be removed, rather than from recycled industry wood. If you are needing a larger delivery of loose mulch, ask for composted, triple shredded bark and leaf mulch or aged, composted bark, both are much safer, natural mulch options.

Final note: Most park and school playgrounds in the US are mulched. Again, it pays to ask the right questions. Generally, if a green-certified EWF (Engineered Wood Fiber) mulch product is used, it comes with a guarantee that it is made from 100% virgin (rather than used and industrial) wood.

 

RESOURCES

 

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