43. Sustainable Materials (part two)

We are talking again about sustainable landscape materials, another one of those big topics that gets bigger the more I learn about it.  I previously covered some key points on the best types of materials to use, now I want to dig deeper into some issues related to potential toxics in some landscape materials and then focus a bit more on wood and its alternatives.

Toxicity in Landscape Materials

Gardens are generally great things for the environment compared to parking lots, buildings or factories, but there are a few materials commonly used in landscapes that have toxic properties.  These properties include hazards to construction workers during installation, as well as unhealthy chemical emissions over time after things are installed.

An obvious example is the chemicals used to control weeds and pests (herbicides and pesticides).  I have written before about herbicides and won’t get into the specifics here, but in general these types of products should be avoided.  Use alternative natural methods where possible, and when they are necessary hire a professional with proper training and equipment to apply them.  Beyond that, there are a several commonly used materials that do have some potential toxic environmental effects that I want to discuss.

PVC

PVC (Poly Vinyl Chloride) is one of the more toxic landscape materials and is the main plastic used in the irrigation and drainage piping needed for almost every garden project.  PVC has negative environmental effects throughout its life cycle – in manufacture, installation, use, and disposal.  It has a high level of chlorine in it, which releases very toxic (carcinogenic) dioxins when manufactured.  Once installed, PVC will off-gas unhealthy chemicals that are especially dangerous in enclosed spaces.  With irrigation piping that is not such a big issue but over time PVC does emit toxic chemicals into the soil that will contaminate the groundwater.  Disposing of it is a big issue as well, it is not recyclable and again gives off toxic dioxin if burned.  I’m not very expert in the chemistry or other details of this issue, but see the references below for more detailed information.  Suffice it to say that we should be limiting the use of PVC as much as possible.  Unfortunately there is no good alternative for irrigation piping that I’m aware of.  Copper is of course a good irrigation piping material, but quite a bit more expensive, energy and resource intensive, and not without its own contamination problems.

Paints and Coatings

There are many different kinds of paints, stains, sealers, glues, etc. used in landscape construction and quite a few have negative environmental effects.  A common issue is the off-gassing of volatile organic compounds (VOC’s) that are toxic when inhaled and have serious long term health effects.  These VOC’s also contribute to general air pollution.  It is true that most landscape paints and coatings are applied to surfaces outdoors where there is plenty of ventilation to mitigate immediate health effects, but it is still a good idea to seek out “low VOC” paints and stains for the health of those doing the painting and for overall air quality.

Treated Wood

Wood that can resist rot, fungus and insects is essential in landscape construction, things like fence posts and vegetable beds need a wood that can be in contact with wet soil and not rot away in a few years.  Old growth heartwood from Redwood trees and other species meets this requirement, but gone are the days when that was plentiful or sustainably produced at competitive prices.  Therefore chemically treated wood is, as far as I can see, a necessary evil in the landscape.  The options for treated wood have gotten better in the last few decades as we have moved away from using things like chromium and arsenic.  However, it is still a confusing marketplace of different products and limited environmental information and I can’t say I found a clearly superior option in terms of sustainability.

One type of treated wood, CCA (chromated copper arsenic) is clearly bad for the environment, with likely leaching of these highly toxic chemicals into the soil over time.  My understanding is that CCA has been phased out for residential uses at this point in California.  The Wolmanized brand, stocked commonly at big box home improvement stores, seems to be a more benign product; their residential treated wood uses Copper Azole, without the chromium or arsenic.  It still comes with warnings on skin contact, inhalation of sawdust, potential leaching into the soil, and toxicity from burning, so I’m not sure it is a huge improvement.  It is also regulated in California as a hazardous material, it can only be disposed of in special waste facilities.  Because of this, it is important to only use treated wood when absolutely necessary, perhaps turning to plastic lumber for some of your landscape construction.

Plastic lumber

When compared to wood, plastic lumber it is at least as durable and it doesn’t get eaten by insects or rot when in contact with soil.  Many plastic lumber products are made from recycled plastic, and some are recyclable themselves.  But not all types of plastic lumber are the same, and some do in fact contain PVC or other plastics which have the toxicity issues mentioned above.   Others include a mix of ingredients such as wood fiber or fiberglass that make them more hazardous to work with and difficult to recycle.

The best plastic lumber products in terms of general sustainability are those with high post-consumer recycled plastic content (at least 50%), and a single plastic ingredient, typically polyethylene.  Polyethylene is thought to be a less toxic plastic, and it is one of the most recycled plastics, found in things like milk jugs and detergent bottles.  However, this type of plastic does not typically work well for structural uses like beams and posts – fiberglass and other materials are often mixed in to give the plastic lumber more strength.

I won’t get into specifics on different plastic lumber products but there are a wide range of options and it is important to look behind the “green” claims of the different companies to be sure the product is truly a positive for the environment.  Plastic lumber has come a long way from the early versions of the material that faded and warped, but take a close look at what it is made of and how easily it is to work with.  Trex, one of the most well-known plastic lumbers consists mostly of a wood plastic mix, with a coating of a different plastic.  It does have high recycled content and a nice finished look, but doesn’t actually recycle all that much plastic.  I don't know of any products that are useful for structural applications, so we are still stuck with a less environmentally friendly option in those cases.

Wood – the bad and the good

Wood is the traditional material for some of the most common landscape structures such as fences, decks and trellises.  We are now in an era where high quality wood that can last in contact with the ground is often expensive and/or coming from an environmentally questionable source.  Chemically treated wood and plastic lumber are able to replace wood in some cases, but they do have their disadvantages.

Ultimately wood is a renewable resource that will provide more supply over time, especially compared to the petroleum based products that go into plastics.  But our consumption of wood is much faster than the growth of Redwood forests can sustain, and the environmental damage of large scale clear-cutting is well known.  There are some responsible timber operations out there as well as independent certifiers of sustainably harvested wood such as the Forest Stewardship Council that can help inform wood choices.  Bamboo is a much faster growing plant that can be used to build some interesting structures, but is not yet very widely adapted to US building techniques.

In my opinion wood is still a great material to use, it just has to be used wisely.  A good sustainable designer should use high quality wood like old growth Redwood only for special situations where it can be appreciated.  Good design can also work with the known dimensions of wood to limit the amount of waste produced, for example adding a few inches here or there so that the standard 8 foot board doesn’t have to be cut.  Otherwise seek to use alternative materials with high recycled content and limited toxicity and save some of that wood for the next project!

References:

Bay Friendly Gardening Guide and Landscaping Guidelines

Bay Friendly Landscaping Guide to Recycled-Content and Salvaged Materials Sustainable Landscape Construction, by J. William Thompson and Kim Sorvig

PVC information resources:

http://www.eco-novice.com/2013/09/whats-so-bad-about-vinyl-plastic-pvc.htmlhttps://www.motherearthnews.com/green-homes/the-vinyl-debate

Blue Vinyl – an award winning documentary about PVC and the environment, released in 2002

Treated Wood information resources:

https://www.wolmanizedwood.com/https://www.epa.gov/ingredients-used-pesticide-products/overview-wood-preservative-chemicals

Plastic Lumber information resources:

The Healthy Building Network’s Guide to Plastic Lumber, June 2005: https://www.greenbiz.com/sites/default/files/document/CustomO16C45F64528.pdf

Trex information on eco-friendly processes: http://www.trex.com/why-trex/eco-friendly-decking/