Soil lead testing at a high spatial resolution in an urban community garden: a case study in relic lead in Terre Haute, Indiana.
In many cities, community gardens have become popular among urban dwellers. These urban gardeners wish to grow their own produce, but they might be renters or might not have sufficient space for a garden. Community gardens provide access to low-cost, local food resources some users might not have access to otherwise. Community gardens are generally located on a single piece of land and managed by a community member (Holland, 2004; Kingsley, Townsend, & Henderson-Wilson, 2009; Pudup, 2008). For some families, participating in a community garden provides increased food security and healthy practices (Alaimo, Packnett, Miles, & Kruger, 2008; Corrigan, 2011; Langellotto & Gupta, 2012; Litt et al., 2011; George, Rovniak, Kraschnewski, Hanson, & Sciamanna, 2015; Teig et al., 2009). Gardens developed in urban areas where there is likely the greatest need, however, also often have a history of pollution that may increase gardeners' exposure to environmental contaminants (Clark, Hausladen, & Brabander, 2008; Leake, Adam-Bradford, & Rigby, 2009; Mitchell et al., 2014). Unfortunately, these gardens can be susceptible to relic or legacy pollution from previous land use, traffic, and industry (Filippelli, Laidlaw, Latimer, & Raftis, 2004). In many cases, community gardens develop on empty or abandoned plots of land (Drake and Lawson, 2014; McClintock, Cooper, & Khandeshi, 2013). The potential exposure to environmental contaminants, such as lead, may be a serious concern that needs to be evaluated prior to full development of the garden (Leake et al., 2009). The purpose of this research was to evaluate high-resolution surface soil lead variability across the Indiana State University (ISU) Community Garden on the garden plot level to determine whether individual plots were safe for gardening and to identify areas in need of remediation. This project provided an opportunity to discuss safe urban gardening practices in the community and serves as a model for collaboration between academic and community partners. These partnerships can immediately reduce exposure to soil lead while also providing a community service.
Terre Haute and Lead
Terre Haute in Vigo County, Indiana, has a long history of industry and high traffic volumes while also being characterized by older housing stock, with 40% of the homes built before 1950 (U.S. Census Bureau, 2012, 2014). The county is also plagued by high rates of childhood lead poisoning, with a rate of 11% in 2012 (Vigo County Health Department, 2013). In 2013, the rate dropped to 4%; however, only an estimated 20% of the children under six were tested for lead poisoning (Vigo County Health Department, 2013). Lead is a neurotoxin that has been linked to behavioral disorders in children, such as attention deficit-hyperactivity disorder, as well as lowered IQs (Koller, Brown, Spurgeon, & Levy, 2004; Manton, Angle, Stanek, Reese, & Kuehnemann, 2000).
In 2013, the Centers for Disease Control and Prevention (CDC) lowered the threshold for suggested environmental intervention to reduce lead exposure from 10 [micro]g/dL to 5 [micro]g/ dL, although medical intervention via chelation is not required if blood lead levels are below 45 [micro]g/dL (CDC, 2013a). Environmental intervention can include evaluating the home and yard to reduce potential exposure to lead in an effort to prevent blood lead levels from increasing. Unfortunately, the results of a considerable volume of research suggests there are no safe blood lead levels for children, and even low levels can have permanent impacts on behavior and academic achievement (CDC, 2013b; Koller et al., 2004; Manton et al., 2000).
While lead paint is a commonly recognized hazard in homes, lead in soils is an exposure route for lead that is less well known, despite the extensive documentation of elevated lead concentrations in urban soils (Filippelli et al, 2004; Laidlaw and Filippelli, 2008; Mielke, 1999; Mielke, Gonzales, Powell, & Mielke, 2008; Mielke & Reagan, 1998). Lead in soils comes from a variety of sources that includes deteriorating or improperly removed lead paint, lead solder, and leaded fuel, as well as atmospheric sources that might originate from industry or the burning of coal. Once anthropogenic lead is in soil, it is relatively immobile and stays near the surface (Filippelli et al., 2004). The lead will stay at the surface unless it is covered or disturbed. Lead is also often associated with the finest particle sizes. During dry times, lead can be mobilized as dust, thus distributing across neighborhoods from areas of higher lead concentrations to areas that previously did not have elevated lead (Laidlaw & Filippelli, 2008; Laidlaw, Zahran, Mielke, Taylor, & Filippelli, 2012; Zahran, Laidlaw, McElmurry, Filippelli, & Taylor, 2013). Since lead in paint and fuel additives have been eliminated in the U.S., the occurrence of childhood lead poisoning has decreased significantly (Berney, 1993; Crocetti, Mushak, & Schwartz, 1990). Unfortunately, children living in urban areas continue to have rates of lead poisoning greater than children living in suburban and rural areas (Filippelli et al., 2004; Mielke et al., 2008; Mielke, Dugas, Mielke, Smith, & Gonzales, 1997). This observation has led to the suggestion that cities have a relic lead burden in soils that includes sources such as leaded paint, solder, and past industrial emissions, but also particulate lead from vehicle exhaust (Berney, 1993; Filippelli et al, 2004; Mielke et al., 1997; Mielke et al, 2008; Zahran et al, 2013).
The U.S. Environmental Protection Agency (U.S. EPA) suggests that garden soil lead concentrations <100 parts per million (ppm) are safe. U.S. EPA further suggests that garden soils with lead concentrations between 100-400 ppm pose a potential risk. When garden soil has lead concentrations >400 ppm, precautions need to be taken to reduce exposure (U.S. EPA, 2014). At the time of this study, U.S. EPA recommendations for garden soils were not available. For this reason, 200 ppm was used as the upper limit for garden soils, which is within the lower limit U.S. EPA recommends for a potential risk. Lead does not appear to be readily taken up by most garden vegetables, but contaminated soil that is not adequately removed from produce and/or carried into homes does pose a risk of exposure. Using an exposure model, Clark and co-authors (2006) suggest that only 3% of lead exposure for children occurs as a result of eating homegrown vegetables, but that 82% of their exposure comes from the ingestion of fine-grained soil.
Foxx (2014) studied the spatial distribution of lead across Terre Haute using samples collected from public properties, right of ways, and residential properties. Similar research in other cities (e.g., Indianapolis, Syracuse, Dayton, and New Orleans) has highlighted the relic lead in soils from the use of leaded gasoline. While Terre Haute has several historic roads and past high traffic volumes, one of the most significant findings of Foxx (2014) is that the highest lead concentrations in Terre Haute are found in residential areas. In fact, 25% of the residential samples collected (n = 355) have lead concentrations higher than 200 ppm (the safe threshold used in this study of garden soils), and 49% have lead concentrations greater than 100 ppm, which is the safe threshold for gardening according to U.S. EPA (Foxx, 2014).
ISU Community Garden
The ISU Community Garden was established in 2006 near the ISU campus. The garden is located on a half block of property that was formerly residential. The original eight houses located on this land were constructed in the 1920s. All but one house was razed when the university acquired the property. The area was originally converted to green space by planting grass. The single house that remains on the site has become the offices of the Institute for Community Sustainability (ICS), which provides many resources to the local community including space for canning, sustainable cooking seminars, and gardening assistance. Gardeners are not allowed to use pesticides, herbicides, or fungicides; are allowed to plant only annuals; and are asked to donate 10% of their harvest to local charities. ISU Facilities Management maintains the garden property and a volunteer coordinator who is a member of the Wabash Valley Master Gardiners Association oversees activities. The initial garden site was tested for lead and found to have concentrations that were low and of no concern. This is largely because the area needed to be leveled and fill material was used for this purpose. In 2011, the garden expanded significantly, and extensive sampling of the community garden plots for lead contamination occurred beginning in May 2012 (Figure 1).
In 2012, the ISU Community Garden was approximately 1.25 acres and consisted of 128 plots that could be used by members of the local community to grow produce and other annuals. To understand the spatial variability of lead in garden soils at the community garden on the plot level, more than 1,000 surface soil samples were collected beginning in May 2012 and continuing throughout the summer. All samples were collected using a trowel to collect the top several inches of soil and stored in Whirl-Pak sample bags. Lead is not readily taken up by traditional garden plants; therefore, the concern about lead exposure was focused on dust and dirt that might be attached to produce or carried into homes on shoes, gloves, or clothing; because of this, only surface soil samples were collected.
Available garden plots can be small (10 x 10 [ft.sup.2]), medium (10 x 15 [ft.sup.2]), or large (20 x 20 [ft.sup.2]). Four samples were collected from each small plot, and eight samples were collected from each medium and large plot. Soil samples were initially analyzed with a Thermo Nitro handheld X-ray fluorescence (XRF) analyzer without sample processing. Samples were later dried and re-analyzed with the XRF because the presence of moisture and sample heterogeneity can impact the accuracy of XRF results significantly (Figure 2; Foxx, 2014). Even though wet and dry samples have a strong positive correlation, most dry sample concentrations determined by XRF are higher than the concentrations determined on wet samples. On average, the relative error associated with wet/dry measurements is >30% (Figure 2). In addition, for concentrations <100 ppm, the difference between wet and dry samples is on average 10 ppm, but the differences between wet and dry samples increases with increasingly higher concentrations (Foxx, 2014).
This difference is likely because samples that have been dried and powdered are more homogenous than soil samples collected and analyzed in the field. Sample concentrations were verified for selected dried, crushed, and acidified samples following ashing at 550 [degrees]C and acidification with 1 M HCl using a Perkin Elmer 2100 DV inductively coupled plasma-optical emission spectrometer (ICPOES). Dry XRF lead concentrations agreed with ICP-OES values for this study within 10%. As the data were collected, the results were mapped using ArcGIS as points on a map (Figure 1) of the garden, but also using multiple indicator Kriging (Gaussian process regression) to predict the spatial variability between samples of known concentration (Figure 3). As the data became available, they were shared with the gardeners and posted at the ISU Community Garden immediately, allowing for real-time assessments of potential lead hazards that could be communicated to the gardeners.
Results and Discussion
The results shown in Figures 1 and 3 highlight the variability seen across the garden. The southern portion of the garden has uniformly low lead concentrations. This is the location of the original garden plots established in 2006. When the plots were initially established, a significant amount of fill material was needed to level the ground surface after a rat colony was removed. This area is the only one within the garden that has been treated with fill material. Most of the garden plots have soil with concentrations below 400 ppm, but there are areas within the garden that are of concern. The northern portion of the garden has higher concentrations than the rest of the garden. In particular, plots 88, 111, and 116 have lead concentrations >600 ppm, and several other plots have lead concentrations that exceed 400 ppm. The maximum concentration (>800 ppm) is found in plot 116, and many concentrations were below instrumental detection limits; however, highly variable concentrations are seen within individual plots. Many studies have pointed to roadway sources of lead in urban soils (Filippelli et al., 2004; Mielke & Reagan, 1998), but the highest concentration of lead found in the ISU Community Garden are located near an alley, rather than adjacent to the road.
Concentrations that are low and within safe ranges are frequently found within the same plot as concentrations of concern, for example plots 67, 88, 111, 116, and 127. Foxx (2014) found that the highest lead concentrations in residential areas are often found beneath the gutter driplines of homes in Terre Haute; however, this pattern is not apparent at the ISU Community Garden based on estimating where the former homes might have been. Once all of these results were known, two things became clear: Areas of the garden needed to be remediated and lead concentrations are highly variable across a residential block with values that are safe immediately adjacent to values of concern.
The ISU Community Garden was established on a series of previously residential lots near the ISU campus. These lots were not unusual or different than other residential properties in Terre Haute. Soil lead concentrations can be highly variable, but the variability seen across this residential block is very high. A different sampling scheme may not have identified the areas of concern within the garden and some gardeners could have been at risk for exposure to lead as a result. For example, if one sample was collected from each plot or a gridded sampling scheme was used, these approaches might have failed to identify areas with lead concentrations greater than 600 ppm.
While mulch is heavily used at the ISU Community Garden, its use is not always the case and not always possible. In addition, many gardens are tilled annually. No-till practices and using ground cover decreases the risk for the mobilization of lead, if present, within the garden and decreases the production of lead dust.
Furthermore, the spatial pattern of elevated lead concentrations (Figure 3) would not have been readily predicted based on the proximity to the road or approximate locations of the homes that were once present. Perhaps the spatial distribution has been altered by the demolition of homes or even the initial construction of the garden itself. The spatial distribution observed demonstrates that the areas of concern with respect to lead concentrations on residential properties are not always where you might expect to find them. This observation has implications for other urban neighborhoods and the selection of properties or locations for gardens within individual yards.
Communicating the Results to the Gardeners
As the data became available, all gardeners were provided with a letter that described the findings at the garden, instructed about safer gardening practices, and provided a map of the lead results. The results were also posted at the garden and the coordinator was available to discuss the results and safer gardening practices with concerned individuals. Gardeners were told that soils with lead concentrations >200 ppm required the practice of better habits, such as wearing gloves, removing gardening gloves or shoes before entering the home, peeling vegetables, and not allowing children to play near the garden.
When soil lead exceeds 400 ppm, gardeners are encouraged to consider using raised beds or increase the use of soil amendments and covers, such as phosphate fertilizers and mulch. The use of mulch was already an established practice in the ISU Community Garden, but it was further encouraged. Above 400 ppm, it is also recommended that root vegetables and leafy green vegetables not be grown. For gardens with lead levels above 600 ppm, it is recommended that gardens be relocated. Gardeners did not have the option to immediately switch to raised beds, so they were urged to begin changing their behaviors to reduce exposure. Gardeners were also given the option to move to an unoccupied garden plot.
ISU Community Garden Remediation
In response to the lead concentrations that were identified within the garden, ISU decided to reconfigure the garden, including the creation of a mulching station, the conversion of some garden plots to permanent plantings, the addition of a greenhouse, and the construction of raised beds (Figure 4). Several garden plots were removed from circulation, and future plans include an orchard with permanent ground cover. The ISU Community Garden continues to expand each year, and new areas are tested prior to expansion. When the garden was expanded in 2013, for example, the soil was tested for lead prior to the expansion to ensure that the property was suitable. Those areas with elevated lead concentrations were not converted into garden plots.
Abandoned and empty lots can be converted to productive uses once again as public spaces, such as community gardens; however, these areas need to be tested for their suitability and safety prior to gardening. Testing is absolutely necessary because the spatial patterns of lead concentrations across a former residential block cannot be predicted based on previously known relationships between elevated lead concentrations near roads or homes, and is likely due to disturbances of soil during the demolition process or subsequent construction.
Community gardens are important resources in urban areas for local, inexpensive produce; however, to be most effective, gardeners need to be aware of safe gardening practices and potential hazards associated with gardening. Whenever possible, lead testing needs to be completed prior to the establishment of an urban community garden. The relationship between ISU and the community gardeners is a model example of how universities can have a positive impact on local, sustainable resources. This project demonstrates how universities can work with the community to increase awareness of public health issues and environmental literacy.
Most community gardens do not have significant resources to pay for extensive soil lead testing or subsequent remediation. In addition, most public health departments are often overwhelmed with existing work. Many universities, environmental consultants, and government groups, however, have handheld, portable XRFs that could be used at little to no cost in collaboration with community groups prior to development of their community gardens. Even though wet and dry soil lead concentrations differ, the initial measurements provide insight into areas of concern. If these groups worked with local communities to assess potential lead hazards by providing real-time data that could have immediate influence over the placement of gardens, the types of produce planted, and safer gardening techniques that should be employed, then potential exposure could be reduced in many urban communities.
Approaching this problem of elevated soil lead in the ISU Community Garden from multiple directions (i.e., soil geochemistry and outreach education), we were able to increase awareness of lead exposure via contaminated soil and ultimately remediate a valuable resource to the local community. While lead in soils is a serious environmental concern, it is also one of the most manageable. Unfortunately, lead in urban soils is also a ubiquitous environmental issue that needs attention and low-cost community-based solutions.
Jennifer C. Latimer, MS, PhD
David Van Halen
Department of Earth and Environmental
Systems, Indiana State University
James Speer, MS, PhD
Department of Earth and Environmental
Systems, Indiana State University
Institute for Community Sustainability
Stephanie Krull, LA
Facilities Management, Indiana
Wabash Valley Master
Joseph Pettit, MS, PhD
Department of Earth and Environmental
Systems, Indiana State University
Institute for Community Sustainability
Heather Foxx, MS
Department of Earth and Environmental
Systems, Indiana State University
Acknowledgements: The authors wish to thank Dr. Gabriel Filippelli and Jessica Adamic for their invaluable insight related to lead in urban soils and community gardens. We also thank Ashley Burkett and Kyle Burch for their assistance collecting samples at the ISU Community Garden, as well as Nicole Terrell, Kevin Hardin, and Melanie Johnson for their assistance preparing samples for analysis via ICPOES. The ISU Center for Student Research and Creativity (CSRC) and Department of Earth and Environmental Systems (EES) provided support for the students involved in this research project. ICS, CSRC, EES, and College of Arts and Sciences provided support for the purchase of the handheld XRF. Support was also provided for instrumentation and laboratory renovations by NSF award numbers 0963289 and 0651431.
Corresponding Author: Jennifer C. Latimer, Associate Professor of Geology, Department of Earth and Environmental Systems, Indiana State University, 600 Chestnut Street, Terre Haute, IN 47809.
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Please note: Some tables or figures were omitted from this article.
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|Title Annotation:||ADVANCEMENT OF THE SCIENCE|
|Author:||Latimer, Jennifer C.; Van Halen, David; Speer, James; Krull, Stephanie; Weaver, Patricia; Pettit, Jo|
|Publication:||Journal of Environmental Health|
|Article Type:||Case study|
|Date:||Oct 1, 2016|
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