Micronized Copper Azole #409600

Asked June 24, 2017, 9:54 PM EDT

I see micronized copper azole (MCA) treatment for wood advertising 90-99% less copper leaching than traditional pressure treated wood. Is this safe for building garden beds?

Wayne County Michigan

Expert Response


Research continues on the long-term affects of treated lumber products. I found a couple research-based articles that explain the risk of using MCA is very low, because plants die from lower levels of copper than humans do.  However, MCA is not approved for organic farms. There is some risk, especially when lumber is new, to skin exposure and breathing saw dust. Here is a discussion of these points from Dr. Steven Newman of Colorado State University:

"Micronized copper or copper azole treatment of wood is the modern replacement for chromiated copper arsenic treatment. Copper azole is a registered fungicide for treatment of wood. As with any fungicide treated materials, the lumber should be handled with gloves as well as a dust mask when sawing, sanding or machining the lumber. It can not be burned and not used where it may become a component of food, beehives, or animal feed. 

However, copper will not be taken up by plants in a significant volume as a human health risk, the plant will die first. Therefore the risk is minimal. Yet, if you are concerned about the use of micronized copper azole compounds, give your raised beds a good coat of paint. That will seal the wood. You might also consider topping your raised beds with redwood or some other wood as the copper compounds can rub off onto your skin and stain clothing when new. 

Here is some web-based information on micronized copper wood preservatives: ‘Treated wood” refers to the green-colored lumber that is widely available at hardware stores and building centers. In Tennessee , this wood is usually southern pine that has been impregnated at a factory with a copper-based wood preservative. The green color is from the copper. In the past, the copper was combined with chromium and arsenic. This “CCA” formulation was the standard for many years. About four years ago, CCA was withdrawn from residential use and replaced with alkaline copper quaternary (ACQ) and copper azole (CA). These preservatives are also copper-based but include organic co-biocides instead of chromium and arsenic. All of these formulations leave the wood green in color (unless a dye is added), clean to the touch, paintable, and protected from insect attack and rot. ACQ and CA are very corrosive to metal, however, so it is important to use only ceramic coated, stainless steel, or other approved screws and nails with treated wood. 

Copper azole-treated wood is greenish-brown and has little to no odor. Type A (also known as CBA-A) contains copper, boric acid, and tebuconazole. Type B (also known as CA-B) contains higher concentrations of copper and tebuconazole but no boric acid. Copper azole is registered for a variety uses above and below ground, as well as in freshwater and marine decking applications. Water-based preservatives like copper azole leave wood with a clean, paintable surface after they dry. Copper Azole is registered for treatment of millwork, shingles & shakes, siding, plywood, structural lumber, fence posts, building and utility poles, land and freshwater piling, composites, and other wood products that are used in above-ground, ground contact and fresh water as well as in salt water splash (marine) decking applications."

Steven Newman, Ph.D., A.A.F. Greenhouse Crops Specialist Colorado State University , April 2012

You can search 'MCA' here and you will find the studies done by the Environmental Protection Agency---

 This is a discussion of copper, how it binds to soil, and levels tolerated by plants and humans---

Following Dr. Newman's precautions, as mentioned above, you should be safe using MCA treated lumber if you aren't growing certified organic produce. Thank you for using our service.

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