Test Your Soil to Keep Your Poultry Safe
Know What Metals and Minerals Your Flock is Digesting
At first, we thought maybe our duck had hurt her leg when we weren’t looking.
Eight months old and full of energy, Puff, an adorable Buff Orpington, never seemed to mind when my middle-schooler carried her around or plopped her into the coop. That must have been when it happened, I told the vet, but the doctor thought we should run tests anyway. Just in case. It’s true our hen hadn’t been her usual perky self for a few weeks. Her feathers looked bedraggled and her eyes not quite as bright. A newbie duck owner at the time, I didn’t have much basis for comparison but, new or not, I had raised this bird from 2 days old and she really did seem off. No reason to call a vet, though, until she started limping.
The lab ran a panel of blood work for the usual signs of infection. We figured it might be a bug or even a vitamin deficiency. We were wrong. It was lead poisoning.
Welcome to Post-Industrial America
Sadly, we’re all familiar with the impacts of heavy metal pollution on cities like Flint, Michigan, and Boyle Heights, California, but, in reality, any inhabited area of the United States probably contains at least trace levels of these and other contaminants.
For centuries, the world has produced many millions of pounds of synthetic chemicals, causing significant noxious impacts on our air, water, and topsoil. Of the tens of thousands of compounds marketed since World War II, those with heavy metals have been particularly pervasive and have caused some of the most troubling effects.
The Natural Resources Defense Council’s On Earth magazine reports that an estimated seven million tons of lead were burned in gasoline in the 20th century before its ban in 1996. Added to that toxic burden, leaded paints were used for more than a century before sales stopped in 1978. Since it took many years for existing stockpiles to be depleted, buildings constructed before the mid-80s or even later are likely to have legacy pollution, inside and out. If you have an older home or one sited where an older structure used to stand, you may have residual lead in the nearby soil. This goes for ground near heavily traveled roadways as well.
Is this true even in the countryside? The short answer is, it depends. While agricultural land is usually far from the largest sources of point pollution, if a barn or coop once had lead-paint (or if something lead-painted stood on that site), there may still be particles and chips in the surrounding soil. A story in the New York Times cited a study on lead in chicken eggs from a small flock in Iowa. In this particular case, the poultry had ingested paint chips from a farm structure and the animals were then taken to Iowa State University at Ames for analysis. After examining blood, egg and tissue samples, the researchers concluded that chickens and their eggs with “significant” amounts of lead are “a potential human health hazard, especially to young children.”
And the problem goes beyond paint and gasoline. The Iowa study also mentions other potential sources of heavy metals including such everyday products as fishing sinkers, car batteries, and even drapery weights. Pesticides like some cadmium-based fungicides formerly used on golf courses and lawns, as well as sprays made of lead arsenate once used in orchards or sodium arsenate on potatoes, could also pose potential long-term risks. Many of these products were delisted decades ago, so why are we still concerned today?
The Once and Future Risk
Many of us may assume that by exposing these ubiquitous products to water, air or sunlight that, over time, they”ll eventually be rendered harmless. Unfortunately, this is not always the case. Some synthetic compounds break down into even more persistent or dangerous metabolites, and heavy metals, such as lead, arsenic, and cadmium, can’t break down further since they’re already in their elemental form. Although they do occur naturally, most of these metals came to our backyard in various chemical combinations. Those compounds can break down, sometimes releasing toxic residues into the environment.
Lead, in particular, poses daunting health challenges to both people and livestock. As I can attest from my own experience with waterfowl, the metal is dangerous to poultry, and a the Iowa State researchers describe, can be found not just in a bird’s eggs but also in her blood, meat, and bones.
Birds are often attracted to shiny objects, which they sometimes ingest as they forage. If those objects contain lead and if they lodge in the internal organs, the element can leach and wreak systemic havoc. Of course, soils often contain far less visible pieces that are no less problematic despite their size. These tiny particles can be taken up into the roots of plants, including some that we grow for food.
The Secret Soil Life of Plants
As in many things toxicity-related, there’s a lot of variation in how individual living organisms are affected, plants included. With agents such as herbicides, which are designed to harm, it’s easy to see the toxic effect. But heavy metals do not always reveal their presence in obvious ways. Lead, like cadmium, can be phytotoxic (poisonous to plants) but the degree of uptake depends on factors such as the overall amount of the element, soil pH, and levels of phosphorus and organic matter, all of which can impact the bioavailability of the contaminant. The Healthy Soils, Healthy Communities guidelines from the New York State Department of Health and Cornell University point out that some “metals may not harm the health or growth of the plant, even thought they may be a concern for human health.” This means the presence of a heavy metal in a growing medium is not always visually detectable in the plant. A hearty plant, therefore, can give false assurance to a grower who might expect to see symptoms from their tainted crops.
Last year, for example, I grew ornamental squash in a test plot made from a section of former lawn. The previous season I’d begun preparing the site by tossing vegetable compost on the prepared ground. Some of the compost included excess grape tomatoes and garlic from our kitchen garden, which then became vigorous volunteers the following summer. There were no signs of phytotoxicity in the tomatoes, garlic or squash but mindful of the possible presence of lead, we didn’t eat any of the produce. Later, I took a soil sample under the bed and found a hot spot where lead readings were high, lower than what’s found in urban areas but still over recommended values. To make it even more complicated, a sample taken five feet away measured under New York State median levels. A previously tested spot 15 feet in the other direction and under a raised bed showed no lead at all.
It is, perhaps, this heterogeneity that makes soil testing so challenging. I describe the process as thinking about your garden or farm as a whodunit where the farmer must play the detective. She or he must attempt to figure out what happened and where, usually with no reliable witnesses to interrogate.
If the property’s former owner had washed lead-covered paintbrushes in the lawn or if they had a few apple trees sprayed with heavy metal pesticide, there may be no outward indication of these hazards. If you test your soil and get good results, great. If you don’t test, though, you may never know what’s really going on inside your plants, your animals and possibly yourself. As Cornell University’s Jonathan Russell-Anelli recently said at an OFA workshop on managing urban soils, “The assumption is that it’s contaminated, not that it’s clean.”
Even in suburban and rural areas, this is not bad advice.
Good Plants, Bad Places
In addition to variable concentrations in soil, there are also differences in lead uptake depending on the type of plant. Leafy greens and root vegetables such as carrots, beets and potatoes are most often cited as crops to avoid in compromised soils. Furthermore, a 2014 study in Environmental Pollution showed that herbs had the highest concentration of lead, more than the other greens or root crops that were tested. In contrast, fruiting plants have been shown to be less likely to transfer lead into edible parts of the plant. This group includes tree fruit but also plants such as tomatoes and peppers.
To add to the complexity, the uptake profile of plants with other metals can be different than those with lead. For example, according to a study published last year in Water, Air & Soil Pollution, lettuce “had the strongest ability to accumulate As [arsenic],” even more than lead. Factors such as the source of the metal (pesticides vs. mining), pH and clay levels appear to play a role.
As I said, it’s very complicated.
Be aware, too, that even if you’ve isolated your crop by using containers or raised beds, soil particles can splash on plants in heavy rains or transfer in dust from foot traffic or wind. You should still remove outer leaves, wash thoroughly and peel root vegetables. Also, mulch or otherwise cover all bare soil, including pathways. These strategies are called “Best Management Practices” or simply, “best practices” (see sidebar) and have been developed by scientists and public health institutions as guidelines for dealing with challenged soils.
Experts, in fact, often emphasize that it’s the soil itself that’s the concern, even more than the plant uptake. Presuming you choose the right crops and grow them in the right places, you still need to avoid ingesting or inhaling tainted particles when working in the soil. A factsheet from Brooklyn College’s Environmental Sciences Analytical Center emphasizes that it’s “what you do with the soil” that “determines the risk.” Avoid bringing it into the house on your clothing and shoes and wash your hands thoroughly, especially under your nails.
Despite these precautions, there are limits. Some soil is regarded as just too contaminated for growing even fruiting vegetables. Guidance values vary but I follow recommendations from Brooklyn College and the University of Connecticut Soil Nutrient Analysis Laboratory, which indicate, for example, that soil with high levels of lead (more than 400 ppm) should not be used for growing food plants at all.
Back at the Homestead
Making good choices with plant selection and following best practices can minimize your family’s exposure to heavy metals but it’s not that easy when you’re also raising livestock. In one of those ironies of 21st-century ag life, free-range poultry can be more susceptible to toxic exposures than caged birds.
This is not an endorsement of battery systems but a wake-up call to those of us who let our ducks and chickens roam. If the soil is tainted, birds can take up contamination when they dig or dust bathe or consume smaller organisms that live in it. For the sake of our waterfowl, we try our best to manage the soil, but it’s impossible to stop the girls from doing what nature programmed them to do. You can control plants (mostly), ducks (somewhat) but when it comes to worms and arthropods, not at all. The living creatures that ingest lead and travel through the subsoil simply can’t be contained.
And so, it’s been quite an education. Today, Puff and her flock mates are regularly blood tested, and when necessary, given chelation therapy for lead exposure. Although their eggs generally test within safe ranges, I’m hesitant to eat any because it’s difficult to know the exact levels in any given egg, on any given day. Luckily, we don’t count on our hens for meat. Like an unwanted guest, lead can leave the blood but stick around in an animal’s tissues and bones. And that, I think we can all agree, is hardly the best recipe for a good dinner.
How to Get Your Soil Tested
When we first decided to grow food on our property, I knew I wanted to test the soil but I had lots of questions. What should we test for? Where and how should we test? Where do we take the samples?
I started looking around and discovered that many labs are set up for institutional and commercial testing only. Our local extension office offered nutritional evaluation but wouldn’t tell us how to test for contaminants. Eventually, an organic landscaper told me to try the soil-testing center at Brooklyn College. This facility provides affordable and user-friendly services for residential and community gardeners in the New York City area.
After that first round, I began a long-term study of lead contamination in suburban soils with Dr. Joshua Cheng, chair of the Department of Earth and Environmental Science, a partner organization of the NYC Urban Soils Institute. In four years of soil, plant and egg testing, I’ve learned a lot about what, how and where to get samples tested.
What to Test for
Soil testing is a bit wonky but even if you haven’t looked at a periodic table since high school, don’t despair! Each lab has its own submission procedure with a list of tests such as these:
• pH • Soil class • Soluble salts • Organic content • NPK • Basic lead (Pb) test • Heavy metals — lead (Pb), chromium (Cr), arsenic (As), cadmium (Cd), nickel (Ni), cobalt (Co), copper (Cu), zinc (Zn) and mercury (Hg) • Major and minor nutrients • Particle analysis
Where to Get Your Soil Tested
Many local extension offices will handle heavy metal testing or can refer you to a lab that can. If not, try your state department of environmental conservation for a referral. A local or state facility will probably have the best understanding of the region’s soil (i.e., some areas have higher levels of naturally occurring elements than others).
In addition, if you know something about your property’s history that suggests there may be legacy residues, you may want to specifically test for those as well. Please note that testing for chemical compounds is more expensive and can be difficult to obtain.
How to Read the Results
Depending on the facility, you may get slightly different interpretation guidelines, but results should come with a guide and resource. Either way, it’s a good question to ask the testing center before you submit your soil samples. Here are a few other good places to start:
New York State Department of Health/Cornell University —“Understanding Your Test Results: Metals in Garden Soils and Vegetables” www.cwmi.css.cornell.edu/UnderstandingTestResultsMetalsSoilsVeg.pdf
Brooklyn College/NYC Urban Soils Institute —“How to Read the Numbers: Heavy Metals in Garden Soils” www.brooklyn.cuny.edu/web/aca_centers_esac/110901_Soil_HeavyMetalInterpretations_March10.pdf
University of Vermont Extension —“Interpreting the Results of Soil Tests for Heavy Metals” www.uvm.edu/vtvegandberry/factsheets/interpreting_heavy_metals_soil_tests.pdf
Understanding Lead Levels in Soil
The University of Connecticut Cooperative Extension’s interpretation guidelines explain that “No federal standard for soil lead has been determined for soils where vegetables will be grown.”
Without this standard, guidelines differ among states and institutions on what actions you should take. The chart below incorporates recommendations from the University of Connecticut Cooperative Extension* and the Environmental Sciences Analytical Center at Brooklyn College.
What Are Best Practices?
Here are some best management practices when dealing with challenged soils:
• Use raised beds or other containers. Make sure you fill them with clean soil and amendments from trusted sources.
• Avoid planting in pressure-treated or previously painted wood, railroad ties, telephone poles or tires since these materials can transfer contaminants into the soil.
• Site your growing area away from roadways and buildings that may have deteriorating painted surfaces.
• Maintain healthy soil with proper nutrients, with appropriate phosphorus levels and pH between 6.5 & 7.
• Minimize access to bare soil. Cover planting soil with mulches to protect from splash and wind. Keep walkways covered, too.
• Wash hands well and consider using gloves. Be careful not to bring soil into the house on tools, clothing, and shoes.
• Wash plants well, remove outer leaves and peel root vegetables.
• Watch children carefully while in the garden.
Sources: Environmental Sciences Analytical Center at Brooklyn College, New York State Department of Health/Cornell University, University of Connecticut Cooperative Extension, University of Vermont Extension.
Lori Fontanes is a freelance writer who lives in New York. She regularly contributes a humor column to Backyard Poultry.
Originally published in the June/July 2016 issue of Backyard Poultry and regularly vetted for accuracy.