By Cynthia Lee Riskin
With drought predicted for the west, southwest, and south through June 2015 (National Weather Service March 2015), many conscientious vegetable gardeners will try to conserve water by using soaker-hoses, those bumpy black hoses that weep water onto the soil through tiny pores.
Soaker hoses are made from fine-crumb rubber, usually recycled from vehicle tires. Research strongly establishes that tire particles leach heavy metals, carcinogens, and mutagenics, among other toxins. Yet soaker hoses have not been studied for potentially increasing the toxicity of edible plants. Are they really safe to use safe on our edible plants?
Soil in the City
Urban soils already contain high levels of heavy metals (Murray et al. 2011) from years of household runoffs—chemicals from pesticides, cars, painting, cleaning, and more. Adding soaker hoses made of crumb tires might exacerbate the problem.
Whether plants take up enough heavy metals to be toxic, however, is a complex equation, depending on a slew of interrelated factors, including:
• Soil pH (Costello 2003) and texture (Singh and Kumar 2006; Murray et al. 2011)
• Temperature (Murray et al. 2011; Lim and Walker 2009)
• The size of the rubber particles (Gaultieri et al. 2004)
• Chemical composition of irrigation water (Singh and Kumar 2006)
Furthermore, the plant species and even the cultivar can affect a plant’s uptake of zinc and other heavy metals (Murray et al. 2009 and 2011).
Growing Healthy Food
If you’re looking for the key to ensuring that your vegetable patch grows healthy food, however, I’m sorry to disappoint you. Too many factors are involved to predict the toxicity of what we grow in our gardens.
A good way to get more information is to contact your local extension agent for a list of laboratories that test soils not only for nutrient composition but for heavy metals. Although this information won’t guarantee you’ll be able to grow heavy-metal-free produce, it’s a step in the right direction while we wait for more research to be done.
Cindy Riskin is a Master of Environmental Horticulture and freelance journalist raising edible plants, an unkempt ornamental garden, and elderly mutts in Seattle, Washington.
NOTE: This article is excerpted from a longer one soon to appear in Cindy Riskin’s upcoming blog, tentatively named Muddy Fingers Northwest. Please contact Cindy Riskin at cindyri@q.com for an advance copy or the blog’s web address.
REFERENCES
1. Costello, Laurence Raleigh. 2003. Abiotic disorders of landscape plants: A diagnostic guide. Oakland, Calif.: University of California, Agriculture and Natural Resources. P. 117.
2. Gualtieri M., M. Andrioletti, C. Vismara, M. Milani, and M. Camatini. 2005. Toxicity of tire debris leachates. Environment International 31 (5): 723–30.
3. Lim, Ly, and Randi Walker. 2009. An assessment of chemical leaching releases to air and temperature at crumb-rubber infilled synthetic turf fields. Albany, N.Y.: New York State Department of Environmental Conservation. http://www.dec.ny.gov/docs/materials_minerals_pdf/crumbrubfr.pdf.
4. Murray, H., T.A. Pinchin, and S.M. Macfie. 2011. Compost application affects metal uptake in plants grown in urban garden soils and potential human health risk. Journal of Soils and Sediments 11 (5):815–829.
5. Murray, Hollydawn, Karen Thompson, and Sheila M. Macfie. 2009. Site- and species-specific patterns of metal bioavailability in edible plants. Botany 87:702–711.
6. National Weather Service Climate Prediction Center. March 19, 2015. U.S. Seasonal Drought Outlook. NOAA/National Weather Service National Centers for Environmental Prediction. http://www.cpc.ncep.noaa.gov/products/expert_assessment/sdo_summary.html.
7. Singh, S., and M. Kumar. 2006. Heavy metal load of soil, water and vegetables in peri-urban Delhi. Environmental Monitoring and Assessment 120 (1-3):1–3.
There are two other types soaker hoses. They don’t seem to use rubber. I wish an article would discuss them. Soaker hoses do seem to be very useful here in New Mexico — it would be nice to know if they were harmful in some way.
Thank you for providing this column.
Wow! Thanks for this information. As a Master Gardener I’ve been telling folks for years that soaker hoses were one of the best ways to water their veggie patch. Guess I’ll have to change that and add the “we don’t know” caveat. I wish I could go back to all those people I advised and tell them to get their soil tested.
Ah, well, even if the soil has toxic levels of heavy metals, depending on numerous factors, such as pH and species grown (and many more), plants could be perfectly fine. On the other hand, in soil with acceptable levels of heavy metals, under certain circumstances, some plants will bioaccumulate toxic levels.
I don’t think there’s any way to predict, and few of us have the resources to test each of our plants.
*Do* have your soil tested for pH, nutrients, and other, fixable factors so that you don’t add something it doesn’t need. When you do that, the excess nutrient can run off into the groundwater and cause algal blooms in lakes, which kill the fish.
To a certain extent, I think we live in an age of risk, although some potential risks in the garden are from unseen factors rather than polio or a troop of Huns coming at us with axes.
If you want to garden, go for it. I’m guessing that getting outdoors and getting moving could offset any potential for harm. That’s my 2 cents, anyway.
My husband installed a homemade soaker hose watering system in our back yard veggie garden last year. We used to have a lush, green garden with large plants and good production. Ever since he installed the watering system, not so much.
Ah, well, even if the soil has toxic levels of heavy metals, depending on numerous factors, such as pH and species grown (and many more), plants could be perfectly fine. On the other hand, in soil with acceptable levels of heavy metals, under certain circumstances, some plants will bioaccumulate toxic levels. I don’t think there’s any way to predict, and few of us have the resources to test each of our plants.
Unless you have a particular reason for suspecting especially high levels of heavy metals in your soil, I’m not sure I would go through the effort and expense of having it tested for heavy metals. For example, I live on what used to be an apple orchard (arsenic) next door to a guy who had pesticides banned for the past 25 years when he died. The house with all its contents were crushed by a two-story trackhoe to make way for a minimansion. I might get *that* soil tested for heavy metals, although it still is unlikely (or at least unknown) whether the fruits on my grapevines would be at all toxic. Linda Chalker-Scott says not to worry about it, and she knows more about it than I do.
*Do* have your soil tested for pH, nutrients, and other, fixable factors so that you don’t add something it doesn’t need. When you do that, the excess nutrient can run off into the groundwater and cause algal blooms in lakes, which kill the fish.
To a certain extent, I think we live in an age of risk, although some potential risks in the garden are from unseen factors rather than polio or a troop of Huns coming at us with axes. But now we’re straying into philosophy.
If you want to garden edibles, go for it. I’m guessing that getting outdoors and getting moving could offset any potential for harm. That’s my 2 cents, anyway.
If he used a soaker hose made out of recycled tires (if black probably so) zinc present at high levels in tires (among other things) has been shown to inhibit plant growth (and toxic to aquatic organisms btw not so much to humans). Try pulling it up to prevent further leaching- I am not sure how long zinc stays in the soil though.
Zinc is an element. It stays in the soil forever unless taken up by something that is then removed from the site.
Can you comment on drip systems? Are they also made of recycled materials and do they have the same issues?
Connie, therein lies the rub. I studied only zinc, only recycled crumb-rubber soaker hoses, so I can’t say whether the risk is any greater from other materials or from your municipal water system.
I know some hoses are labeled in California as leaching potential carcinogens. I have a friend who mail orders $70 hoses rated for drinking use. But I don’t know about drip systems.
No, I mean, I really don’t know about drip systems. I’ve been trying to install one all summer. I finally realized I was trying to install a half-inch hose on a 5/8-inch fitting.
Also on the subject beware of the recycled tire rubber “mulch” sold for ornamental plantings. That too leaches zinc and toxins not good for plants (and avoid it’s uses on playgrounds! Many other human toxicants in tires too- see. http://www.ehhi.org and search on tires or rubber for reports)
I’ve written a fact sheet on rubber mulch. You can find it here: http://cru.cahe.wsu.edu/CEPublications/FS163E/FS163E.pdf
For urban or former ag and former lawn areas might the best advice be to create a raised bed garden with good compost and tested soil you know is heavy metal and toxin free and don’t use recycled rubber hoses?
What an eye-opening read! It’s crucial to stay mindful of our gardening practices, especially during times of drought. While this article raises important questions about soaker hoses, here’s a tip: consider using a layer of organic mulch over your soil. It not only helps retain moisture but also acts as a protective barrier, potentially reducing any leaching from the hoses.
I’m curious if anyone has tried alternative watering methods or has more insights on minimizing heavy metal exposure in garden produce? Thanks, Matt