Using the mehlich-3 soil test as an inexpensive screening tool to estimate total and bioaccessible lead in urban soils

Soil Microbiome Influences on Seedling Establishment and Growth of Prosopis chilensis and Prosopis tamarugo from Northern Chile

Prosopis chilensis and Prosopis tamarugo, two woody legumes adapted to the arid regions of Chile, have a declining distribution due to the lack of new seedling establishment. This study investigated the potential of both species to establish in soil collected from four locations in Chile, within and outside the species distribution, and to assess the role of the root-colonizing microbiome in seedling establishment and growth. Seedling survival, height, and water potential were measured to assess establishment success and growth. 16S and ITS2 amplicon sequencing was used to characterize the composition of microbial communities from the different soils and to assess the ability of both Prosopis species to recruit bacteria and fungi from the different soils. Both species were established on three of the four soils. P. tamarugo seedlings showed significantly higher survival in foreign soils and maintained significantly higher water potential in Mediterranean soils. Amplicon sequencing showed that the four soils harbored distinct microbial communities. Root-associated microbial composition indicated that P. chilensis preferentially recruited mycorrhizal fungal partners while P. tamarugo recruited abundant bacteria with known salt-protective functions. Our results suggest that a combination of edaphic properties and microbial soil legacy are potential factors mediating the Prosopis establishment success in different soils.

Exchange of Adsorbed Pb(II) at the Rutile Surface: Rates and Mechanisms

The dynamics of Pb(II) at mineral surfaces affect its mobility in the environment. Pb(II) forms inner- and outer-sphere complexes on mineral surfaces, and this adsorbed pool often represents a large portion of the bioaccessible Pb in contaminated soils. To assess the lability of this potentially reactive adsorbed Pb(II) pool at metal oxide surfaces, we performed Pb(II) isotope exchange measurements between dissolved Pb(II) enriched in ²⁰⁷Pb and natural isotopic abundance Pb(II) adsorbed to rutile at pH 5, 6, and 7. We find that ∼95% of the adsorbed lead is exchangeable. An initially fast exchange (<1 h) is followed by a slower exchange that occurs on a time scale of hours to days. Pb L_III-edge extended X-ray absorption fine structure spectra indicate that similar binding mechanisms are present at all pH values and Pb(II) loadings, implying that differences in exchange rates across the pH range examined are not attributable to changes in the coordination environment. The slower exchange at pH 5 may be associated with interparticle and intraparticle diffusion resulting from particle aggregation. These findings demonstrate that the dissolved Pb(II) pool can be rapidly replenished by adsorbed Pb(II) if this pool is drawn down incrementally by biological uptake or a shift in chemical conditions.

The effects of biochar and redox conditions on soil Pb bioaccessibility to people and waterfowl

Biochar can reduce lead (Pb) bioavailability to plants in metal-contaminated soil, but the ability of biochar to reduce the bioavailability of soil Pb to people and wildlife remains unknown. In this study, 17 biochars were evaluated as in situ amendments for three soils with distinct sources of Pb contamination (smelter emissions, ceramics waste, mining waste), hydrology (upland, well-drained soil vs submerged wetland soil), and biological receptors (human vs waterfowl). Biochars were made from blends of 30% manure (poultry litter or dairy manure) and 70% lignocellulosic material (wheat straw or grand fir shavings) and pyrolyzed at 300, 500, 700, and 900 °C. Soils were amended with 2% biochar (w/w) and incubated for 6 months. A suite of standard (e.g., EPA Method 1340) and experimental soil Pb bioaccessibility assays were used to assess the impact of the treatments. The results showed that biochar amendments to upland soils resulted in modest reductions in gastrointestinal Pb bioaccessibility (maximum reduction from 78 to 68% bioaccessibility as a percent of total, EPA Method 1340 at pH 2.5). In the wetland soil, sample redox status had a greater impact on Pb bioaccessibility than any amendment. Low-solubility Pb sulfides in this soil oxidized over the course of the study and no treatment was able to offset the increase in Pb bioaccessibility caused by this oxidation. The impact of redox status on Pb bioaccessibility was only evident when soil bioaccessibility assays were adapted to preserve sample redox status. This result highlights the importance of maintaining in situ redox conditions when processing/analyzing samples from low-oxygen environments and that soil remediation efforts should consider the role of redox conditions on Pb bioaccessibility.

Immobilization of lead by amendments in a mine-waste impacted soil: Assessing Pb retention with desorption kinetic, sequential extraction and XANES spectroscopy

Chemical stabilization is an in-situ remediation that uses amendments to reduce contaminant availability in polluted soils. Rates of phosphate, lime, biochar, and biosolids were evaluated as affecting Pb speciation and mobility in soil samples of a mining area located in Vazante, state of Minas Gerais, Brazil. Chemical and mineralogical characterization, desorption kinetics, sequential extraction, leaching evaluation in columns and speciation using X-ray absorption near edge structure were performed. Pb adsorbed on bentonite and on anglesite were the predominant species in the unamended soil. The treatments with phosphate and lime transformed part of the Pb species to pyromorphite. Conversely, part of Pb species was transformed to Pb adsorbed on citrate in the soil amended with biochar, while PbCl₂ was formed in soil samples amended with biosolids. Phosphate and lime increased the Pb extracted in the residual fraction, thus showing that more recalcitrant species, such as pyromorphite, were formed. Biosolids and biochar treatments decreased the Pb in the residual fraction, and the fraction associated to organic matter increased after the addition of biosolids. Phosphate and lime were effective to immobilize Pb and to decrease Pb desorption kinetics, but the organic amendments increased the desorption kinetics of Pb in all rates applied. The soil amended with phosphate decreased the Pb leached in the experiment with leaching columns.

Correlating soil nutrient test lead with bioaccessible lead in highly-contaminated soils receiving lead-immobilizing amendments

Lead (Pb) is one of the most common metals exceeding human health risk guidelines for soil concentrations worldwide. Pb bioaccessibility is known to vary depending on soil physiochemical characteristics and, as a result, in vitro and in vivo tests exist that are used to estimate bioaccessible Pb in contaminated soils. Although in vitro tests such as the relative bioaccessibility leaching procedure (RBALP) present simpler and more cost-effective risk assessments than in vivo methods, soil tests such as Mehlich-3, Modified Morgan, and ammonium bicarbonate-diethylenetriamine pentaacetate (AB-DTPA) extractions are extremely routine and even more cost-effective. Currently, there are few comparisons examining the viability of common soil nutrient tests for assessing Pb bioaccessibility in soils from contaminated sites with extremely high total Pb concentrations or for sites that have received amendments, such as those containing compost, iron, and/or phosphorus, intended to immobilize Pb. Here, we examine the correlation between RBALP Pb and Pb as determined using three commonly utilized soil tests, Mehlich-3, Modified Morgan, and AB-DTPA, in archived samples from one Pb-contaminated site receiving compost amendment (Seattle, WA, USA) and one extremely Pb-contaminated site receiving mixtures of compost, P, and Fe (Joplin, MO, USA). At both the Seattle and Joplin sites separately, RBALP Pb was significantly correlated with all three soil nutrient test values, regardless of soil amendment. However, RBALP was only significantly correlated with Modified Morgan and total Pb when examining the Joplin and Seattle data together, likely resulting from different factors controlling Pb solubility at the two sites. These findings suggest that a diverse suite of relatively inexpensive and accessible soil nutrient test methods correlate with bioaccessible Pb at a specific site, regardless of whether Pb-immobilizing amendments have been used.

Characterizing copper and zinc content in forested wetland soils of North Carolina, USA

Wetlands are often located in landscape positions where they receive runoff or floodwaters, which may contain toxic trace metals and other pollutants from anthropogenic sources. Over time, this can lead to the accumulation of potentially harmful levels of metals in wetlands soils. To assess the potential risk of Cu and Zn buildup in wetland soils in North Carolina, soil data from 88 wetlands were analyzed. In a subset of 16 wetlands, more intensive sampling was conducted. Samples were analyzed for Mehlich 3 Cu and Zn, and a subset of the samples was analyzed for total Cu and Zn. Overall, Mehlich 3 Cu and Zn were low, with mean values of 0.9 mg/kg for Cu and 3.2 mg/kg for Zn. Warning levels for Mehlich 3 Zn were only exceeded in three of the 88 sites; elevated Mehlich Cu was not observed. Total Cu and Zn were also low, with only a few sites having elevated levels; however, there was not a strong linear relationship between Mehlich 3 and total metals. Mean levels of Mehlich 3 Cu and Zn in wetlands were much lower than for human-impacted upland soils and background threshold concentrations that might be indicative of disturbance were much lower than warning levels for agricultural soils. The very low mobile Zn and Cu in most of these wetlands indicated that these metals do not pose a risk to the biota in most North Carolina wetlands, but wetlands with a direct and significant anthropogenic source of metal contamination could be exceptions.

Phytostabilization of a contaminated military site using Miscanthus and soil amendments

Military activities can contaminate productive land with potentially toxic substances. The most common trace metal contaminant on military bases is lead (Pb). A field experiment was begun in 2016 at Fort Riley, KS, in an area with total soil Pb concentrations ranging from 900 to 1,500 mg kg^-1 and near-neutral pH. The main objectives were to test the potential of Miscanthus sp. for phytostabilization of the site and to evaluate the effects of soil amendments on Miscanthus growth, soil-plant Pb transfer, bioaccessibility of soil Pb, and soil health. The experimental design was a randomized complete block, with five treatments and four replications. Treatments were (a) existing vegetation; (b) Miscanthus planted in untilled soil, no amendments; (c) Miscanthus planted in tilled soil; (d) Miscanthus planted in tilled soil amended with inorganic P (triple superphosphate applied at 5:3 Pb:P); and (e) Miscanthus planted in tilled soil amended with organic P (Class B biosolids applied at 45 Mg ha^-1 ). Tilling and soil amendments increased dry matter yields only in the establishment year. Total Pb uptake, plant tissue Pb concentration, and soil Pb bioaccessibility were significantly less in the Miscanthus plots amended with biosolids than the Miscanthus plots with no added P across all 3 yr. Enzyme activities, organic carbon, and microbial biomass were also greater in biosolids-treated plots. Results show that planting-time addition of soil amendments to Pb-contaminated soil supported Miscanthus establishment, stabilized and reduced bioaccessibility of soil Pb, reduced concentration and uptake of Pb by Miscanthus, and enhanced soil health parameters.

Engineered biochars from catalytic microwave pyrolysis for reducing heavy metals phytotoxicity and increasing plant growth

Pb, Ni, and Co are among the most toxic heavy metals that pose direct risks to humans and biota. There are no published studies on biochars produced at low temperatures (i.e., 300 °C), which possess high sorption capacity for heavy metal remediation and reclamation of contaminated sandy soils. This research studied the effect of catalytic microwave pyrolysis of switchgrass (SG) using bentonite and K₃PO₄ to produce biochar at low temperature (300 °C) with high sorption capacity for reducing the phytotoxicity of heavy metals, and investigated the synergistic effects of catalyst mixture on biochar sorption capacity. The quality of the biochars was examined in terms of their impacts on plant growth, reducing phytotoxicity and uptake of heavy metals in sandy soil spiked with Pb, Ni, and Co. All catalysts increased the micropore surface area and cation-exchange capacity of biochars, and resulted in biochars rich in plant nutrients, which not only decreased heavy metal phytotoxicity, but also boosted plant growth in the spiked soil by up to 140% compared to the sample without biochar. By mixing bentonite and K₃PO₄ with SG during microwave pyrolysis, the efficacy of biochar in reducing phytotoxicity and heavy metals uptake was further enhanced because of the highest micropore surface area (402 m²/g), moderate contents of Ca, Mg, K, and Fe for ion-exchange and moderate concentration of phosphorus for the formation of insoluble heavy metal compounds. Generally, the biochar created at 300 °C (300-30KP) showed similar performance to the biochar created at 400 °C (400-30KP) in terms of reducing heavy metal bioavailability.

Perspectives on Heavy Metal Soil Testing Among Community Gardeners in the United States: A Mixed Methods Approach

Community gardens offer numerous benefits, but there are also potential risks from exposure to chemical contaminants in the soil. Through the lens of the Theory of Planned Behavior, this mixed methods study examined community gardeners’ beliefs and intentions to conduct heavy metal soil testing. The qualitative component involved five focus groups of community garden leaders in Atlanta, Georgia. Qualitative analysis of the focus group data revealed that heavy metal soil contamination was not frequently identified as a common gardening hazard and several barriers limited soil testing in community gardens. The focus group results informed the development of a questionnaire that was administered to 500 community gardeners across the United States. Logistic regression analysis revealed that the soil testing intention was associated with attitude (aOR = 2.46, 95% CI: 1.34, 4.53), subjective norms (aOR = 3.39 95% CI: 2.07, 5.57), and perceived behavioral control (aOR = 1.81, 95% CI: 1.10, 2.99). Study findings have implications for interventions involving community garden risk mitigation, particularly gardens that engage children and vulnerable populations.

Use of Routine Soil Tests to Estimate Pb Bioaccessibility

Soil lead (Pb) hazard level is contingent on bioavailability, but existing assays that estimate Pb bioavailability for human health risks are too expensive or otherwise inaccessible to many people that are impacted by Pb-contaminated soil. This study investigated the use of routine soil nutrient tests to estimate soil-Pb bioaccessibility as a surrogate measure of Pb bioavailability. A silt loam soil was spiked to a target concentration of 2000 mg Pb kg^-1 with Pb(NO₃)₂ and amended with H₃PO₄ (varying P-to-Pb molar ratios) and KCl (Cl-to-P molar ratio of 2:5) to generate soils with similar total Pb concentrations but a range of Pb bioavailability (and bioaccessibility). Soils were extracted using Mehlich 3, Mehlich 1, Bray P1, Olsen, and  micronutrient (DTPA) methods, and the results were compared to U.S. Environmental Protection Agency method 1340 data as well as to extended X-ray absorption fine structure (EXAFS) spectroscopy. The Mehlich 3 and method 1340 treatment effect ratios were well-correlated ( r² = 0.88, p ≤ 0.05), whereas Bray P1, DTPA, and Olsen results were more reflective of EXAFS data. Preliminary animal-feeding trials suggest that the Mehlich 3 is as effective as method 1340 at predicting the impact of P treatment on Pb relative bioavailability; however, both methods over-estimated the Pb hazard to mice in P-amended soil. Other routine soil tests that have heightened sensitivity to P amendment (e.g., Bray P1) may be promising candidates for Pb bioaccessibility assessment.

Point of zero charge: Role in pyromorphite formation and bioaccessibility of lead and arsenic in phosphate amended soils

Soluble lead (Pb) can be immobilized in pure systems as pyromorphite by adding sources of phosphorus (P), but uncertainties still remain in natural systems. Knowledge of PZC is important to predict the ionization of functional groups and their interaction with metal species in solution. This study utilized the Pb- and As-contaminated soils to determine the combined effect of pH with respect to PZC and different rates of P-application on pyromorphite formation, and Pb and arsenic (As) bioaccessibility as impacted by speciation changes. Solution chemistry analysis along with synchrotron-based Pb- and As-speciation, and bioaccessibility treatment effect ratios (TERs) were conducted. Results indicated no significant effect of PZC on pyromorphite formation in P-amended soils; however, the TER_Pb appeared significantly lower at pH>pH_PZC and higher at pH<pH_PZC (α = 0.05). In contrast, the TER_As was significantly higher at pH>pH_PZC, compared to the other two treatments, for the tested soils. The lack of conversion of soil Pb to pyromorphite may be attributed to presence of stable minerals limiting soluble-Pb availability and high organic matter content of the tested soils.

Lead Speciation and In Vitro Bioaccessibility of Compost-Amended Urban Garden Soils

In situ soil amendments can modify the Pb bioavailability by changing soil Pb speciation. Urban soils from three vegetable gardens containing different total Pb concentrations were used. The study evaluated how compost amendment and aging of soil-compost mixture in situ affected the following: (i) soil Pb speciation in the field and (ii) change of soil Pb speciation during an in vitro bioaccessibility extraction mimicking gastric phase dissolution at pH 2.5. X-ray absorption fine structure spectroscopy was used to determine Pb speciation in amended and nonamended soils and residues left after in vitro bioaccessibility extraction of those soils. Compost amendment and aging of compost in the field had a negligible effect on Pb bioaccessibility in the soils. Major Pb species in the soils were Pb sorbed to Fe oxy(hydr)oxide (Pb-Fh) and to soil organic C (Pb-Org). The fraction of Pb-Org was increased as soil-compost mixture aged in the field. During the in vitro extraction, the fraction of Pb-Fh was decreased, the fraction of Pb-Org was increased, and hydroxypyromorphite was formed in both amended and nonamended soils. Freshly incorporated compost enhanced the dissolution of Pb-Fh during the extraction. As soil-compost mixture aged in the field, the dissolution of Pb-Fh was low, demonstrating more stability of the Pb-Fh during the extraction. Compost amendment showed potential to contribute to reduced bioaccessibility of Pb as compost aged in the soil by increasing Pb-Org fraction in the field and stability of Pb-Fh during the in vitro bioaccessibility extraction.

The role of tailored biochar in increasing plant growth, and reducing bioavailability, phytotoxicity, and uptake of heavy metals in contaminated soil

Microwave-assisted catalytic pyrolysis was investigated using K₃PO₄ and clinoptilolite to enhance biochar sorption affinity for heavy metals. The performance of resulting biochar samples was characterized through their effects on plant growth, bioavailability, phytotoxicity, and uptake of heavy metals in a sandy soil contaminated with Pb, Ni, and Co. The produced biochars have high cation-exchange capacity (CEC) and surface area, and rich in plant nutrients, which not only reduced heavy metals (Pb, Ni, and Co), bioavailability and phytotoxicity, but also increased plant growth rate by up to 145%. The effectiveness of biochar in terms of reduced phytotoxicity and plant uptake of heavy metals was further improved by mixing K₃PO₄ and clinoptilolite with biomass through microwave pyrolysis. This may be due to the predominance of different mechanisms as 10KP/10Clino biochar has the highest micropore surface area (405 m²/g), high concentrations of K (206 g/kg), Ca (26.5 g/kg), Mg (6.2 g/kg) and Fe (11.9 g/kg) for ion-exchange and high phosphorus content (79.8 g/kg) for forming insoluble compounds with heavy metals. The largest wheat shoot length (143 mm) and lowest extracted amounts of Pb (107 mg/kg), Ni (2.4 mg/kg) and Co (63.9 mg/kg) were also obtained by using 10KP/10Clino biochar at 2 wt% load; while the smallest shoot length (68 mm) and highest extracted amounts of heavy metals (Pb 408 mg/kg, Ni 15 mg/kg and Co 148 mg/kg) for the samples treated with biochars were observed for soils mixed with 1 wt% 10Clino biochar. Strong negative correlations were also observed between biochar micropore surface area, CEC and the extracted amounts of heavy metals. Microwave-assisted catalytic pyrolysis of biomass has a great potential for producing biochar with high sorption affinity for heavy metals and rich nutrient contents using properly selected catalysts/additives that can increase microwave heating rate and improve biochar and bio-oil properties.

Management Options for Contaminated Urban Soils to Reduce Public Exposure and Maintain Soil Health

Soil management in urban areas faces dual challenges of reducing public exposure to soil contaminants, such as lead (Pb) and polycyclic aromatic hydrocarbons, and maintaining soil function. This study evaluated three management options for an urban lot in Cleveland, OH, containing 185 to 5197 mg Pb kg and 0.28 to 5.50 mg benzo(a)pyrene kg. Treatment options included: (i) cap the site with a soil blend containing compost and beneficially reused dredged sediments, (ii) mix compost with the soil, and (iii) mix compost and sediments with the soil. The soil blend cap reduced surface soil Pb to 12.4 mg Pb kg and benzo(a)pyrene content to 0.99 ± 0.41 mg kg. Aggregate stability for 2- to 0.25-mm aggregates in the soil blend cap was 13% compared with the 38% aggregate stability in the urban soil. Mixing compost with the soil reduced benzo(a)pyrene content, but sample variability indicated that elevated spots likely remained exposed at the surface. Compost addition diluted soil Pb and increased aggregate stability to 60%. Mixing compost and sediments with the soil was the only management option accomplishing both management goals of reducing surface soil contaminants and maintaining soil health. For this combined mixing option, aggregate stability was 37%, soil Pb was 15 mg kg, and benzo(a)pyrene was 0.99 ± 0.09 mg kg. Food-grade oil addition did not increase benzo(a)pyrene degradation. Future studies should evaluate how incorporating soil blends in different soil types with a range of contaminants may offer a suitable long-term management option for urban soil contaminants.

Alterations of lead speciation by sulfate from addition of flue gas desulfurization gypsum (FGDG) in two contaminated soils

This is the first study to evaluate the potential application of FGDG as an in situ Pb stabilizer in contaminated soils with two different compositions and to explain the underlying mechanisms. A smelter Pb contaminated soil (SM-soil), rich in ferrihydrite bound Pb (FH-Pb), cerussite and litharge with a total Pb content of 65,123mg/kg and an organic matter rich orchard soil (BO-soil), rich in FH-Pb and humic acid bound Pb with a total Pb content of 1532mg/kg were amended with 5% FGDG (w/w). We subjected the two soils to three leaching tests; toxicity characteristic leaching protocol (TCLP), synthetic precipitation leaching protocol (SPLP), kinetic batch leaching test (KBLT) and in-vitro bioaccessibility assay (IVBA) in order to evaluate the FGDG amendment on Pb stabilization. Solid residues of original and FGDG amended soil were analyzed using X-ray absorption spectroscopy (XAS) to identify changes in Pb speciation after each leaching test. The leachate Pb concentrations of FGDG amended soil were lower compared to those of in non-amended soil. The linear combination fitting analysis of XAS confirmed the formation of anglesite and leadhillite in FGDG amended soil. FGDG reduced the Pb desorption from ferrihydrite (FH), by forming FH-Pb-SO4 ternary complexes. FGDG decreased the Pb adsorption onto humic acid (HA) possibly due to the release of divalent cations such as Ca and Mg, which can compete with Pb to get adsorbed onto HA. The FGDG can successfully be used to remediate Pb contaminated soil. The efficiency of the treatment highly depends on the soil composition.

The effect of bullet removal and vegetation on mobility of Pb in shooting range soils

Lead (Pb) contamination at shooting ranges is a public health concern because Pb is a toxic metal. An experiment was conducted to determine the effect of two best management practices; bullet removal and vegetation, on bioavailability and leachability of Pb in three shooting range (SR) soils. St. Augustine grass was grown in sieved (2 mm) and un-sieved SR soils for 8 weeks after which leachates, soil and plant samples were analyzed. Bullet removal reduced total soil Pb, increased Mehlich-3 Pb in unvegetated soils and increased dissolved organic carbon (DOC) in all soils. Bullet removal increased leaching in two SR soils while grasses reduced leaching but increased water soluble Pb in two SR soils. The roots of the grasses were able to accumulate more Pb in the root (1893-5021 mg kg(-1)) than the aboveground biomass (252-880 mg kg(-1)) due to mobilization of Pb in the rhizosphere. Grasses had a higher plant biomass in unsieved soils suggesting tolerance to the presence of bullets in the unsieved soils. Results suggest that bullet removal probably increased microbial activity and Pb bioavailability in the soil. The leaching and bioavailability of Pb in shooting range soils depends on biological activities and chemical processes in the soil.

Phosphorus Amendment Efficacy for In Situ Remediation of Soil Lead Depends on the Bioaccessible Method

A validated method is needed to measure reductions of in vitro bioaccessible (IVBA) Pb in urban soil remediated with amendments. This study evaluated the effect of in vitro extraction solution pH and glycine buffer on bioaccessible Pb in P-treated soils. Two Pb-contaminated soils (790-1300 mg Pb kg), one from a garden and one from a city lot in Cleveland, OH, were incubated in a bench scale experiment for 1 yr. Six phosphate amendments, including bone meal, fish bone, poultry litter, monoammonium phosphate, diammonium phosphate, and triple superphosphate, were added to containers at two application rates. Lead IVBA was assessed using USEPA Method 1340 and three modified versions of this method. Modifications included using solutions with pH 1.5 and 2.5 as well as using solutions with and without 0.4 mol L glycine. Soil amendments were ineffective in reducing IVBA Pb in these soils as measured by pH 1.5 with glycine buffer. The greatest reductions in IVBA Pb, from 5 to 26%, were found using pH 2.5 extractions. Lead mineral results showed several soil amendments promoted Pb phosphate formation, an indicator of remediation success. A significant negative linear relationship between reduction in IVBA Pb and Pb-phosphate formation was found only for pH 2.5 without glycine extraction solution. A modified USEPA Method 1340 without glycine and using pH 2.5 has the potential to predict P soil treatment efficacy and reductions in bioavailable Pb.

Lead in Urban Soils: A Real or Perceived Concern for Urban Agriculture?

Urban agriculture is growing in cities across the United States. It has the potential to provide multiple benefits, including increased food security. Concerns about soil contamination in urban areas can be an impediment to urban agriculture. Lead is the most common contaminant in urban areas. In this paper, direct (soil ingestion via outdoor and indoor exposure) and indirect (consumption of food grown in Pb-contaminated soils) exposure pathways are reviewed. It is highly unlikely that urban agriculture will increase incidences of elevated blood Pb for children in urban areas. This is due to the high likelihood that agriculture will improve soils in urban areas, resulting in reduced bioavailability of soil Pb and reduced fugitive dust. Plant uptake of Pb is also typically very low. The exceptions are low-growing leafy crops where soil-splash particle contamination is more likely and expanded hypocotyl root vegetables (e.g., carrot). However, even with higher bioaccumulation factors, it is not clear that the Pb in root vegetables or any other crops will be absorbed after eating. Studies have shown limited absorption of Pb when ingested with food. Best management practices to assure minimal potential for exposure are also common practices in urban gardens. These include the use of residuals-based composts and soil amendments and attention to keeping soil out of homes. This review suggests that benefits associated with urban agriculture far outweigh any risks posed by elevated soil Pb.

Application of Citizen Science Risk Communication Tools in a Vulnerable Urban Community

A public participatory geographical information systems (PPGIS) demographic, environmental, socioeconomic, health status portal was developed for the Stambaugh-Elwood (SE) community in Columbus, OH. We hypothesized that soil at SE residences would have metal concentrations above natural background levels. Three aims were developed that allowed testing of this hypothesis. Aim 1 focused on establishing partnerships between academia, state agencies and communities to assist in the development of a community voice. Aim 2 was to design and conduct soil sampling for residents of the SE community. Aim 3 was to utilize our interactive, customized portal as a risk communication tool by allowing residents to educate themselves as to the potential risks from industrial sources in close proximity to their community. Multiple comparisons of means were used to determine differences in soil element concentration by sampling location at p < 0.05. The results demonstrated that eight metals (As, Cd, Cu, Pb, Mo, Se, Tl, Zn) occurred at statistically-significantly greater levels than natural background levels, but most were below risk-based residential soil screening levels. Results were conveyed to residents via an educational, risk-communication informational card. This study demonstrates that community-led coalitions in collaboration with academic teams and state agencies can effectively address environmental concerns.

When Vacant Lots Become Urban Gardens: Characterizing the Perceived and Actual Food Safety Concerns of Urban Agriculture in Ohio

This study was intended to characterize the perceived risks of urban agriculture by residents of four low-income neighborhoods in which the potential exists for further urban agriculture development and to provide data to support whether any chemical hazards and foodborne pathogens as potential food safety hazards were present. Sixty-seven residents participated in focus groups related to environmental health, food security, and urban gardening. In addition, soils from six locations were tested. Residents expressed interest in the development of urban gardens to improve access to healthy, fresh produce, but they had concerns about soil quality. Soils were contaminated with lead (Pb), zinc, cadmium (Cd), and copper, but not arsenic or chromium. Results from our study suggest paint was the main source of soil contamination. Detectable polyaromatic hydrocarbon (PAH) levels in urban soils were well below levels of concern. These urban soils will require further management to reduce Pb and possibly Cd bioavailability to decrease the potential for uptake into food crops. Although the number of locations in this study is limited, results suggest lower levels of soil contaminants at well-established gardens. Soil tillage associated with long-term gardening could have diluted the soil metal contaminants by mixing the contaminants with clean soil. Also, lower PAH levels in long-term gardening could be due to enhanced microbial activity and PAH degradation, dilution, or both due to mixing, similar to metals. No foodborne pathogen targets were detected by PCR from any of the soils. Residents expressed the need for clearness regarding soil quality and gardening practices in their neighborhoods to consume food grown in these urban areas. Results from this study suggest long-term gardening has the potential to reduce soil contaminants and their potential threat to food quality and human health and to improve access to fresh produce in low-income urban communities.

Bioavailability-Based In Situ Remediation To Meet Future Lead (Pb) Standards in Urban Soils and Gardens

Recently the Centers for Disease Control and Prevention lowered the blood Pb reference value to 5 μg/dL. The lower reference value combined with increased repurposing of postindustrial lands are heightening concerns and driving interest in reducing soil Pb exposures. As a result, regulatory decision makers may lower residential soil screening levels (SSLs), used in setting Pb cleanup levels, to levels that may be difficult to achieve, especially in urban areas. This paper discusses challenges in remediation and bioavailability assessments of Pb in urban soils in the context of lower SSLs and identifies research needs to better address those challenges. Although in situ remediation with phosphate amendments is a viable option, the scope of the problem and conditions in urban settings may necessitate that SSLs be based on bioavailable rather than total Pb concentrations. However, variability in soil composition can influence bioavailability testing and soil amendment effectiveness. More data are urgently needed to better understand this variability and increase confidence in using these approaches in risk-based decision making, particularly in urban areas.