Urban gardening: managing the risks of contaminated soil

Urban vegetable contamination - The role of adhering particles and their significance for human exposure

While urban-grown vegetables could help combat future food insecurity, the elevated levels of toxic metals in urban soils need to be met with measures that minimise transfer to crops. This study firstly examines soil/dust particle inclusion in leafy vegetables and its contribution to vegetable metals (As, Ba, Cd, Co, Cr, Cu, Ni, Pb, Sb, and Zn), using vegetable, soil and dust data from an open-field urban farm in southeastern Sweden. Titanium concentrations were used to assess soil/dust adherence. Results showed that vegetables contained 0.05-1.3 wt% of adhering particles (AP) even after washing. With 0.5 % AP, an adult with an average intake of vegetables could ingest approximately 100 mg of particles per day, highlighting leafy vegetables as a major route for soil/dust ingestion. The presence of adhering particles also significantly contributed to the vegetable concentrations of As (9-20 %), Co (17-20 %), Pb (25-29 %), and Cr (33-34 %). Secondly, data from an indoor experiment was used to characterise root metal uptake from 20 urban soils from Sweden, Denmark, Spain, the UK, and the Czech Republic. Combining particle adherence and root uptake data, vegetable metal concentrations were calculated for the 20 urban soils to represent hypothetical field scenarios for these. Subsequently, average daily doses were assessed for vegetable consumers (adults and 3-6 year old children), distinguishing between doses from adhering particles and root uptake. Risks were evaluated from hazard quotients (HQs; average daily doses/tolerable intakes). Lead was found to pose the greatest risk, where particle ingestion often resulted in HQs > 1 across all assessed scenarios. In summary, since washing was shown to remove only a portion of adhering metal-laden soil/dust particles from leafy vegetation, farmers and urban planners need to consider that measures to limit particle deposition are equally important as cultivating in uncontaminated soil.

Potential Policy and Community Implications of Equitable Organic Waste, Compost, and Urban Agricultural Systems in the United States

BACKGROUND

Urban organic waste diverted from landfills for use as compost feedstock may help mitigate and adapt to the effects of our changing climate. Yet, compost produced from urban food and yard waste is often a source of contaminants harmful to human and environmental health. Efforts by multiple municipalities are increasing residential and commercial food and yard waste collection; however, finished, tested compost is typically unavailable to those contributing the waste and whose gardens would benefit.

OBJECTIVES

This commentary evaluates the relative equity and safety of U.S. organic waste cycles in relation to urban and peri-urban agriculture (UA) and waste stewardship. We a) explore historical structures that have led to siloed food and waste systems and b) provide recommendations to promote safer compost production from urban organic waste inputs. The engagement of intersectional partners in the creation of equitable policies and contracts that integrate food and waste justice is crucial to this work.

METHODS

A 15-y relationship between community, academic, and government partners in Boston, Massachusetts, has increased access to health-promoting community gardens. Historical concerns raised by gardeners resulted in improvement to the quality of compost sourced from municipal organic waste and motivated a case study of Boston and three other cities (Seattle, Washington; San Francisco, California; New York, New York). This case study provides the approaches used to source, collect, process, test, and deliver urban organic waste as compost for UA. It informed recommendations to improve the safety and equity of organic waste-to-compost cycles.

DISCUSSION

Strict feedstock regulation and required compost safety testing are essential to produce safe, city-sourced compost. Balancing the needs of landfill diversion with equitable distribution to all contributors, particularly low-income and food-insecure people, will help concentrate UA benefits within marginalized communities. Adoption of a public health lens may help ensure the safety of nutrient-rich compost available for urban growers through legislation at state and local levels, along with explicit industry contracts. https://doi.org/10.1289/EHP12921.

Managing health risks in urban agriculture: The effect of vegetable washing for reducing exposure to metal contaminants

A common, yet poorly evaluated, advice to remove contaminants from urban vegetables is to wash the produce before consumption. This study is based on 63 samples of chard, kale, lettuce and parsley that have grown near a heavily trafficked road in the third largest city in Sweden, with one portion of each sample being analysed without first being washed, and the other portion being subjected to common household washing. Concentrations of 71 elements were analysed by ICP-SFMS after a sample digestion that dissolves both the plant tissues and all potentially adhering particles. The results show that the washing effect, or the fraction removed upon washing, varies significantly between elements: from approximately 0 % for K to 68 % for the ∑REEs. Considering traditional metal contaminants, the efficiency decreased from Pb (on average 56 % lost) to Co (56 %) > Cr (55 %) > As (45 %) > Sb (35 %) > Ni (33 %) > Cu (13 %) > Zn (7 %) > Cd (7 %), and Ba (5 %). A clear negative correlation between the washing effect and the different elements' bioconcentration factors shows that the elements' accessibility for plant uptake is a key controlling factor for the degree to which they are removed upon washing. Based on the average washing efficiencies seen in this study, the average daily intake of Pb would increase by 130 % if vegetables are not washed prior to consumption. For the other contaminant metals this increase corresponds to 126 % (Co), 121 % (Cr), 82 % (As), 55 % (Sb), 50 % (Ni), 16 % (Cu), 8 % (Zn), 7 % (Cd) and 5 % (Ba). The advice to wash vegetables is therefore, for many elements, highly motivated for reducing exposure and health risks. For elements which are only slightly reduced when the vegetables are washed, however, advising should rather focus on reducing levels of contamination in the soil itself.

Community-Engaged Assessment of Soil Lead Contamination in Atlanta Urban Growing Spaces

Urban agriculture is emerging as a method to improve food security and public health in cities across the United States. However, an increased risk of exposure to heavy metals and metalloids (HMM) exists through interaction with contaminated soil. Community-engaged research (CEnR) is one method that can promote the inclusion of all partners when studying exposures such as HMM in soil. Researchers and community gardeners co-designed this study to measure the concentrations of lead (Pb), using X-Ray Fluorescence (XRF) verified with Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in soils from 19 urban agricultural and residential sites in the Westside of Atlanta and three rural sites in Georgia. Seventeen other HMM were measured but not included in this study, because they did not pose risks to the community comparable to elevated Pb levels. Pb concentrations were compared to the Environmental Protection Agency (EPA)'s regional screening levels (RSLs) for residential soil and the University of Georgia (UGA) extension service's low-risk levels (LRLs) for agriculture. Soils from the majority of sites had levels below EPA RSLs for Pb, yet above the UGA LRL. However, soil Pb concentrations were three times higher than the EPA RSL on some sites that contained metal refining waste or slag. Our findings led to direct action by local and federal government agencies to initiate the cleanup of slag residue. Studies involving exposures to communities should engage those affected throughout the process for maximum impact.

Key considerations for assessing soil ingestion exposures among agricultural workers

BACKGROUND

Soil ingestion is a critical, yet poorly characterized route of exposure to contaminants, particularly for agricultural workers who have frequent, direct contact with soil.

OBJECTIVE

This qualitative investigation aims to identify and characterize key considerations for translating agricultural workers' soil ingestion experiences into recommendations to improve traditional exposure science tools for estimating soil ingestion.

METHODS

We conducted qualitative in-depth interviews with 16 fruit and vegetable growers in Maryland to characterize their behaviors and concerns regarding soil contact in order to characterize the nature of soil ingestion in the agricultural context.

RESULTS

We identified and discussed four emergent themes: (1) variability in growers' descriptions of soil and dust, (2) variability in growers' soil contact, (3) growers' concerns regarding soil contact, (4) growers' practices to modify soil contact. We also identified environmental and behavioral factors and six specific agricultural tasks that may impact soil ingestion rates.

SIGNIFICANCE

Our investigation fills an important gap in occupational exposure science methodology by providing four key considerations that should be integrated into indirect measurement tools for estimating soil ingestion rates in the agricultural context. Specifically, a task-based framework may provide a structure for future investigations of soil contact that may be useful in other populations.

Children's exposure to environmental lead: A review of potential sources, blood levels, and methods used to reduce exposure

Lead has been used for thousands of years in different anthropogenic activities thanks to its unique properties that allow for many applications such as the manufacturing of drinking water pipes and its use as additives to gasoline and paint. However, knowledge of the adverse impacts of lead on human health has led to its banning from several of its applications, with the main goal of reducing environmental pollution and protecting human health. Human exposure to lead has been linked to different sources of contamination, resulting in high blood lead levels (BLLs) and adverse health implications, primarily in exposed children. Here, we present a summary of a literature review on potential lead sources affecting blood levels and on the different approaches used to reduce human exposure. The findings show a combination of different research approaches, which include the use of inspectors to identify problematic areas in homes, collection and analysis of environmental samples, different lead detection methods (e.g. smart phone applications to identify the presence of lead and mass spectrometry techniques). Although not always the most effective way to predict BLLs in children, linear and non-linear regression models have been used to link BLLs and environmental lead. However, multiple regressions and complex modelling systems would be ideal, especially when seeking results in support of decision-making processes. Overall, lead remains a pollutant of concern and many children are still exposed to it through environmental and drinking water sources. To reduce exposure to lead through source apportionment methods, recent technological advances using high-precision lead stable isotope ratios measured on multi-collector induced coupled plasma mass spectrometry (MC-ICP-MS) instruments have created a new direction for identifying and then eliminating prevalent lead sources associated with high BLLs.

Nature-based cooling potential: a multi-type green infrastructure evaluation in Toronto, Ontario, Canada

The application of green infrastructure presents an opportunity to mitigate rising temperatures using a multi-faceted ecosystems-based approach. A controlled field study in Toronto, Ontario, Canada, evaluates the impact of nature-based solutions on near surface air temperature regulation focusing on different applications of green infrastructure. A field campaign was undertaken over the course of two summers to measure the impact of green roofs, green walls, urban vegetation and forestry systems, and urban agriculture systems on near surface air temperature. This study demonstrates that multiple types of green infrastructure applications are beneficial in regulating near surface air temperature and are not limited to specific treatments. Widespread usage of green infrastructure could be a viable strategy to cool cities and improve urban climate.

Enabling Nature-Based Solutions to Build Back Better—An Environmental Regulatory Impact Analysis of Green Infrastructure in Ontario, Canada

The application of green infrastructure in the built environment delivers a nature-based solution to address the impacts of climate change. This study presents a qualitative evidence synthesis that evaluates policy instruments which enable the use and implementation of green infrastructure, using Ontario, Canada as a case study. Unpacking the elements of the policy landscape that govern green infrastructure through environmental regulatory impact analysis can inform effective implementation of this nature-based solution and support decision-making in public policy. This environmental regulatory impact analysis is based on a systematic review of existing policy instruments, contextual framing in a continuum of coercion, and identification of alignment with relevant UN SDGs. Enabling widespread usage of green infrastructure in the built environment could be a viable strategy to build back better, localize the UN SDGs, and address multiple climate change impacts.

Appraising Agroecological Urbanism: A Vision for the Future of Sustainable Cities

By the mid-century, urban areas are expected to house two-thirds of the world’s population of approximately 10 billion people. The key challenge will be to provide food for all with fewer farmers in rural areas and limited options for expanding cultivated fields in urban areas, with sustainable soil management being a fundamental criterion for achieving sustainability goals. Understanding how nature works in a fast changing world and fostering nature-based agriculture (such as low-input farming) are crucial for sustaining food systems in the face of worsening urban heat island (UHI) effects and other climatic variables. The best fit for the context is transformative agroecology, which connects ecological networks, sustainable farming approaches, and social movements through change-oriented research and action. Even though agroecology has been practiced for over a century, its potential to address the socioeconomic impact of the food system remained largely unexplored until recently. Agroecological approaches, which involve effective interactions between researchers, policy makers, farmers, and consumers, can improve social cohesion and socioeconomic synergies while reducing the use of various agricultural inputs. This review presents a timeline of agroecology transformation from the past to the present and discusses the possibilities, prospects, and challenges of agroecological urbanism toward a resilient urban future.

One map: Using geospatial analysis to understand lead exposure across humans, animals, and the environment in an urban US city

Environmental lead contamination negatively impacts human, animal, and ecosystem health, yet there is a lack of research in this area that incorporates a One Health framework - examining co-exposures among species through their shared environment. The purpose of this study was to integrate human and animal data with public soil lead levels to better understand lead exposure patterns across species in an urban US city. Over 200 soil samples were collected, analyzed for lead, and mapped in combination with other risk factors pulled from the literature to identify areas of highest risk. Human socio-demographic data, dog, and house sparrow density data were mapped to investigate the association between these variables and soil lead levels. Geospatial analysis software was used to visualize the geospatial distribution of soil lead levels and known risk factors for environmental lead contamination, and a block group risk score was calculated and mapped. Associations between human and animal-associated variables and soil lead levels and block risk scores were assessed using Spearman's correlations. Positive, statistically significant associations were found between soil lead levels and higher population density, higher education levels, and higher median household income. Areas with higher soil lead levels and lead exposure risk scores were associated with greater dog density and greater house sparrow density. This study fills an important knowledge gap on the risk of environmental lead exposure to humans, domestic animals, and wildlife.

Nature-Based Equity: An Assessment of the Public Health Impacts of Green Infrastructure in Ontario Canada

The built environment is a physical determinant of health essential to the planning and development of a more equitable society. Communities face growing challenges due to environmental stressors such as climate change, with vulnerable communities experiencing a disproportionate burden of adverse health outcomes. The interdependencies between urban planning and public health outcomes are inextricable, with respect to improving access to healthier built environments for vulnerable and marginalized groups. Widespread implementation of nature-based solutions, such as green infrastructure, provides a multi-functional strategy to support sustainable development, increase climate resilience, enhance ecological connectivity, and create healthier communities. A Health Equity Impact Assessment presents the findings of a participatory research study utilizing key informant interviews of public health unit professionals (eight) and a survey of green infrastructure volunteers and workers (36) on the impact of green infrastructure on individual and community mental and physical well-being, service use, and perceived unmet needs, using Ontario, Canada as a case study. Study findings indicate that where green infrastructure is both productive and publicly accessible, the benefits were significant for vulnerable populations. These benefits include increased social connectivity, skills development, and food security. Green infrastructure could be a viable strategy to address environmental stressors, improve health equity, and support localization of the UN Sustainable Development Goals (SDGs).

Harnessing the Four Horsemen of Climate Change: A Framework for Deep Resilience, Decarbonization, and Planetary Health in Ontario, Canada

Widespread implementation of nature-based solutions like green infrastructure, provides a multi-functional strategy to increase climate resilience, enhance ecological connectivity, create healthier communities, and support sustainable urban development. This paper presents a decision-support framework to facilitate adoption of green infrastructure within communities using the Climate Change Local Adaptation Action Model (CCLAAM) developed for this purpose. It also presents an ecosystems-based approach to bridging the gap between climate change mitigation and adaptation actions in Ontario, Canada. Green infrastructure could be a viable strategy to address multiple climate change impacts and support the implementation of the UN Sustainable Development Goals (SDGs).

Soil Lead Concentration and Speciation in Community Farms of Newark, New Jersey, USA

Farmed urban soils often bear legacies of historic contamination from anthropogenic and industrial sources. Soils from seven community farms in Newark, New Jersey (NJ), USA, were analyzed to determine the concentration and speciation of lead (Pb) depending on garden location and cultivation status. Samples were evaluated using single-step 1 M nitric acid (HNO3) and Tessier sequential extractions in combination with X-ray absorption fine structure spectroscopy (XAFS) analysis. Single-step extractable Pb concentration ranged from 22 to 830 mg kg−1, with 21% of samples reporting concentrations of Pb > 400 mg kg−1, which is the NJ Department of Environmental Protection (NJDEP) limit for residential soils. Sequential extractions indicated lowest Pb concentrations in the exchangeable fraction (0–211 mg kg−1), with highest concentrations (0–3002 mg kg−1) in the oxidizable and reducible fractions. For samples with Pb > 400 mg kg−1, Pb distribution was mostly uniform in particle size fractions of <0.125–1 mm, with slightly higher Pb concentrations in the <0.125 mm fraction. XAFS analysis confirmed that Pb was predominantly associated with pyromorphite, iron–manganese oxides and organic matter. Overall results showed that lowest concentrations of Pb are detected in raised beds, whereas uncultivated native soil and parking lot samples had highest values of Pb. As most of the Pb is associated with reducible and oxidizable soil fractions, there is a lower risk of mobility and bioavailability. However, Pb exposure through ingestion and inhalation pathways is still of concern when directly handling the soil. With increasing interest in urban farming in cities across the USA, this study highlights the need for awareness of soil contaminants and the utility of coupled macroscopic and molecular-scale geochemical techniques to understand the distribution and speciation of soil Pb.

Inaction on Lead Despite the Relevant Knowledge: Predictors, Covariates, and Outreach Implications

Testing residential soil and paint for lead provides actionable information. By showing where and how much lead exists on the residence, it allows one to quantify risk and determine the best ways to reduce exposure along with the corresponding health and financial costs. For these reasons, several federal and state programs offer outreach to audiences on the benefits of testing residential soil and paint for lead. Not all individuals who know about lead’s adverse health effects, however, test their residence for lead, potentially limiting the actionable information that could have helped to reduce their exposure. Such individuals represent a challenge to outreach programs and the broader public health objectives. There is, thus, a need to understand who such individuals are and why they behave this way, allowing us to develop a specialized outreach program that addresses the problem by targeting the relevant sub-population. Using survey data, we quantitatively determine the profiles of individuals who, despite knowing about lead’s adverse health effects, are unlikely to test their residence for lead, finding statistically significant socio-economic predictors and behavioral covariates. We also find a geographic component to it, further helping outreach professionals learn how to allocate their limited resources.

Urban soil health: A city-wide survey of chemical and biological properties of urban agriculture soils

The integration of urban green spaces into modern city planning is seen as a promising tool to offset the drawbacks of ever-expanding cities. Urban agriculture is a common method to implement such strategies and to increase urban sustainability with a special focus on food security. Due to their location, urban farms are highly influenced by past and present anthropogenic activities which can threaten both soil health and food safety. This study includes 12 urban agriculture sites in the metropolitan area of Adelaide, Australia. It is the first of its kind to focus on soil health in urban agriculture systems with a further emphasis on mycorrhizal fungi. Descriptive information about each site, the biodiversity of the selected plots and soil samples from different depths and locations were collected and analysed for chemical and biological parameters. Seven metals, total and plant-available (Colwell) phosphorus and available nitrogen were measured in soils. A glasshouse bioassay was also conducted to determine the abundance of beneficial arbuscular mycorrhizal fungi in the soils and the change of root colonization after inoculation with the mycorrhizal fungus Rhizophagus irregularis. Results showed a generally high biodiversity of plants that correlated with site activity (commercial or community garden) and which could potentially be used for urban biodiversity conservation. Metal concentrations in soils were below national guidelines levels for all samples, although sites with previous industrial history showed elevated levels when compared to sites without industrial history. The use of raised beds with introduced soils eliminated differences in previous land-use history, thereby providing a good option to support cleaner production. Gardening soils were considered highly fertile, with plant-available (Colwell) P concentrations exceeding recommended levels for most horticultural crops, while soils were adequately supplied with nitrogen. Most plant nutrients were derived from freely available urban waste streams and integrated via composting. Various urban waste streams could be used to counter-act imbalanced soil nutrients. Arbuscular mycorrhizal fungi were present in all sites, indicating that the practiced soil management is sustainable from a microbial perspective. Given their important role in supporting plant nutrition, and potential to reduce the need for external nutrient inputs, they provide an important focal point for achieving clean and sustainable urban food production. The results were incorporated into a framework for the management of urban soil health.

Atlanta Residents' Knowledge Regarding Heavy Metal Exposures and Remediation in Urban Agriculture

Urban agriculture and gardening provide many health benefits, but the soil is sometimes at risk of heavy metal and metalloid (HMM) contamination. HMM, such as lead and arsenic, can result in adverse health effects for humans. Gardeners may face exposure to these contaminants because of their regular contact with soil and consumption of produce grown in urban areas. However, there is a lack of research regarding whether differential exposure to HMM may be attributed to differential knowledge of exposure sources. In 2018, industrial slag and hazardous levels of soil contamination were detected in West Atlanta. We conducted community-engaged research through surveys and follow-up interviews to understand awareness of slag, HMM in soil, and potential remediation options. Home gardeners were more likely to recognize HMM health effects and to cite health as a significant benefit of gardening than community gardeners. In terms of knowledge, participants were concerned about the potential health effects of contaminants in soil yet unconcerned with produce in their gardens. Gardeners’ knowledge on sources of HMM exposure and methods for remediation were low and varied based on racial group.

Safe Community Gardening Practices: Focus Groups with Garden Leaders in Atlanta, Georgia

Although best management practices have been recommended by government agencies and non-profit organizations to reduce community gardeners' potential exposure to soil contaminants such as lead, some gardeners do not perform these practices. Understanding gardeners' beliefs and motivations is critical for effective promotion of safer gardening practices. This study, grounded in the Theory of Planned Behavior (TPB), employed five focus groups to investigate Atlanta community garden leaders' perspectives concerning three gardening practices: composting, hygiene behaviors, and mulching. These general practices are also considered safe gardening practices in that they can reduce exposure to toxicants in urban gardens. Qualitative analysis identified advantages and disadvantages; supporters and non-supporters; and barriers and facilitators that might influence gardeners' opinions regarding these behaviors. Gardeners expressed that more funding, volunteers, and training are needed to promote these behaviors. Gardeners noted that mulch and compost provided advantages such as improving soil quality, but a primary barrier was concern about contamination of source materials. Focus group participants did not directly associate composting and mulching with reduction of exposure to soil contaminants. Behavioral challenges related to hygiene included concerns about decreased exposure to salubrious bacteria, inadequate access to potable water, and limited availability of gloves and wipes. These study findings characterize factors that community garden stakeholders should consider when promoting safe gardening practices and interventions.

Atmospheric Concentrations and Wet/Dry Loadings of Mercury at the Remote Experimental Lakes Area, Northwestern Ontario, Canada

Mercury (Hg) is a global pollutant released from both natural and human sources. Here we compare long-term records of wet deposition loadings of total Hg (THg) in the open to dry deposition loadings of THg in throughfall and litterfall under four boreal mixedwood canopy types at the remote Experimental Lakes Area (ELA) in Northwestern Ontario, Canada. We also present long-term records of atmospheric concentrations of gaseous elemental (GEM), gaseous oxidized (GOM), and particle bound (PBM) Hg measured at the ELA. We show that dry THg loadings in throughfall and litterfall are 2.7 to 6.1 times greater than wet THg loadings in the open. GEM concentrations showed distinct monthly and daily patterns, correlating positively in spring and summer with rates of gross ecosystem productivity and respiration. GOM and PBM concentrations were less variable throughout the year but were highest in the winter, when concentrations of anthropogenically sourced particles and gases were also high. Forest fires, Arctic air masses, and road salt also impacted GEM, GOM, and PBM concentrations at the ELA. A nested GEOS-Chem simulation for the ELA region produced a dry/wet deposition ratio of >5, suggesting that the importance of dry deposition in forested regions can be reasonably modeled by existing schemes for trace gases.

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.

Comparative Optimism: Relative Risk Perception and Behavioral Response to Lead Exposure

Despite their true exposure, individuals with Comparative Optimism consider themselves less prone to the adverse health effects of pollution. Since individuals' response to a given environmental risk is affected by their appraisal of the risk, those with Comparative Optimism may be less likely to engage in prescribed behaviors or to do so at the urgency required of the given risk. Such limited or delayed response can amplify the risk instead of reducing it. Thus, there is a need to understand if Comparative Optimism applies to pollutants with irreversible adverse health effects as it would impose a higher burden. There is also a need to know which segments of the population are prone to Comparative Optimism and how it manifests in terms of activities that can enhance exposure. Doing so will allow public health professionals address gaps in risk communication and management efforts and help improve environmental health outcomes. Using survey data, we assess the presence, behavioral and socioeconomic predictors, and implications of Comparative Optimism for communicating and managing lead exposure risk in an urban setting. Our results indicate that a large share of the population has Comparative Optimism for lead exposure, despite living in a city that has a relatively higher lead poisoning burden. We also found that ethnicity, income, length of stay at residence, among others, predict Comparative Optimism, suggesting that Comparative Optimism may predict elevated blood lead level.

Soil management is key to maintaining soil moisture in urban gardens facing changing climatic conditions

Urban gardens are vital green spaces, providing food for residents and space for engaged citizenry and community development. In California, climate change conditions (heat and drought) are becoming more extreme, threatening the resilience of urban gardens. Water use restrictions limit the timing and amount of water that gardeners can access, exacerbating these climate challenges for urban food production. Together with volunteer gardeners, we examined how ambient temperature, water use, vegetation, ground cover, and soil management affect rates of soil moisture gain and loss in urban gardens for a six-week period in the summer of 2017, during the hottest part of the growing season. We found that plot-level management of soils is essential for creating urban garden plots that maintain stable levels of water within garden soils. Although plots with better soil quality (i.e. water holding capacity) experienced slower rates of soil moisture gain after a watering event, they also experienced slower rates of soil moisture loss after the event, leading to soils with more stable, less fluctuating moisture profiles over time. This may benefit gardeners because under extreme climates (such as heat and drought) and water use restrictions, maintaining more stable soils for their plants means that the soils will retain water over a longer period after each watering event. Overall, such results highlight that better soil management that improves soil quality measures such as water holding capacity are potential solutions for maintaining soil moisture and reducing water use under changing climate conditions.

Mapping the Urban Lead Exposome: A Detailed Analysis of Soil Metal Concentrations at the Household Scale Using Citizen Science

An ambitious citizen science effort in the city of Indianapolis (IN, USA) led to the collection and analysis of a large number of samples at the property scale, facilitating the analysis of differences in soil metal concentrations as a function of property location (i.e., dripline, yard, and street) and location within the city. This effort indicated that dripline soils had substantially higher values of lead and zinc than other soil locations on a given property, and this pattern was heightened in properties nearer the urban core. Soil lead values typically exceeded the levels deemed safe for children's play areas in the United States (<400 ppm), and almost always exceeded safe gardening guidelines (<200 ppm). As a whole, this study identified locations within properties and cities that exhibited the highest exposure risk to children, and also exhibited the power of citizen science to produce data at a spatial scale (i.e., within a property boundary), which is usually impossible to feasibly collect in a typical research study.

Assessment of soil metal concentrations in residential and community vegetable gardens in Melbourne, Australia

Gardening and urban food production is an increasingly popular activity, which can improve physical and mental health and provide low cost nutritious food. However, the legacy of contamination from industrial and diffuse sources may have rendered surface soils in some urban gardens to have metals value in excess of recommended guidelines for agricultural production. The objective of this study was to establish the presence and spatial extent of soil metal contamination in Melbourne's residential and inner city community gardens. A secondary objective was to assess whether soil lead (Pb) concentrations in residential vegetable gardens were associated with the age of the home or the presence or absence of paint. The results indicate that most samples in residential and community gardens were generally below the Australian residential guidelines for all tested metals except Pb. Mean soil Pb concentrations exceeded the Australian HIL-A residential guideline of 300 mg/kg in 8% of 13 community garden beds and 21% of the 136 residential vegetable gardens assessed. Mean and median soil Pb concentrations for residential vegetable gardens was 204 mg/kg and 104 mg/kg (range <4-3341 mg/kg), respectively. Mean and median soil Pb concentration for community vegetable garden beds was 102 mg/kg and 38 mg/kg (range = 17-578 mg/kg), respectively. Soil Pb concentrations were higher in homes with painted exteriors (p = 0.004); generally increased with age of the home (p = 0.000); and were higher beneath the household dripline than in vegetable garden beds (p = 0.040). In certain circumstances, the data indicates that elevated soil Pb concentrations could present a potential health hazard in a portion of inner-city residential vegetable gardens in Melbourne.

Challenges in assessing the health risks of consuming vegetables in metal-contaminated environments

A great deal of research has been devoted to the characterization of metal exposure due to the consumption of vegetables from urban or industrialized areas. It may seem comforting that concentrations in crops, as well as estimated exposure levels, are often found to be below permissible limits. However, we show that even a moderate increase in metal accumulation in crops may result in a significant increase in exposure. We also highlight the importance of assessing exposure levels in relation to a regional baseline. We have analyzed metal (Pb, Cd, As) concentrations in nearly 700 samples from 23 different vegetables, fruits, berries and mushrooms, collected near 21 highly contaminated industrial sites and from reference sites. Metal concentrations generally complied with permissible levels in commercial food and only Pb showed overall higher concentrations around the contaminated sites. Nevertheless, probabilistic exposure assessments revealed that the exposure to all three metals was significantly higher in the population residing around the contaminated sites, for both low-, median- and high consumers. The exposure was about twice as high for Pb and Cd, and four to six times as high for As. Since vegetable consumption alone did not result in exposure above tolerable intakes, it would have been easy to conclude that there is no risk associated with consuming vegetables grown near the contaminated sites. However, when the increase in exposure is quantified, its potential significance is harder to dismiss - especially when considering that exposure via other routes may be elevated in a similar way.

Perceived Benefits of Participation and Risks of Soil Contamination in St. Louis Urban Community Gardens

Community gardens are credited for promoting health within neighborhoods, by increasing healthy food intake and exercise frequency. These benefits, however, are potentially undermined as urban soils are often contaminated from industrial legacies. The purpose of this study was to examine the perceived benefits of participation and risks of soil contamination within urban community gardens, and factors associated with soil contamination concerns. Ninety-three gardeners were interviewed across 20 community gardens in St. Louis, Missouri between June and August 2015. Surveys included questions on demographics, gardening practices, and perceptions of community gardening. Multilevel logistic models assessed how gardener demographics, gardening practices, and garden characteristics were associated with soil contamination concerns. Common perceived benefits of community gardening were community building (68.8%), healthy and fresh food (35.5%), and gardening education (18.3%). Most gardeners (62.4%) were not concerned about soil contamination, but nearly half (48.4%) stated concerns about heavy metals. Black race was significantly associated with soil contamination concerns (OR 5.47, 95% CI 1.00-30.15, p = .04). Community gardens offer numerous social and health benefits. Although most gardeners were not concerned about soil contamination, black gardeners were more likely to have concerns. Garden leaders should provide resources to gardeners to learn about soil contamination and methods to manage their risk, particularly in minority neighborhoods.

Lead (Pb) Bioaccessibility and Mobility Assessment of Urban Soils and Composts: Fingerprinting Sources and Refining Risks to Support Urban Agriculture

While the presence of legacy lead (Pb) in urban soil is well documented, less is known about the bioaccessibility, transport, and exposure pathways of urban soil Pb. We study Pb bioaccessibility in Roxbury and Dorchester, MA, urban gardens to assess exposure risk and identify remediation strategies, applicable locally and in urban gardens across the country. We work in partnership with The Food Project, which brings the goals and perspectives of local farmers to the center of the research process and enables efficient local application of results to reduce Pb exposure. We measure changes in Pb bioaccessibility as a function of growing material, grain size, and Pb source. In comparison to soils, compost has lower total Pb concentrations, has lower Pb solubility in gastric fluid, and limits fine particle resuspension. The mean bioaccessible Pb concentration of compost is 265 mg/kg, nearly an order of magnitude lower than that of soils, and compost contains 14% higher carbon content than soils, which may account for the observed 19% lower Pb bioaccessibility in compost. For all matrices (soil, raised bed fill, and compost) grain sizes <37 μm contain a disproportionate fraction of the total pool of bioaccessible Pb. Furthermore, the isotopic composition of Pb in the size fractions linked with resuspension and elevated blood lead levels is indicative of leaded gasoline and leaded paint even decades removed from the primary deposition of these sources.

Urban Green Space and the Pursuit of Health Equity in Parts of the United States

Research has demonstrated that inequitable access to green space can relate to health disparities or inequalities. This commentary aims to shift the dialogue to initiatives that have integrated green spaces in projects that may promote health equity in the United States. Specifically, we connect this topic to factors such as community revitalization, affordable housing, neighborhood walkability, food security, job creation, and youth engagement. We provide a synopsis of locations and initiatives in different phases of development along with characteristics to support effectiveness and strategies to overcome challenges. The projects cover locations such as Atlanta (GA), Los Angeles (CA), the District of Columbia (Washington D.C.), South Bronx (NY), and Utica (NY). Such insight can develop our understanding of green space projects that support health equity and inform the dialogue on this topic in ways that advance research and advocacy.

Accumulation of trace elements in edible crops and poplar grown on a titanium ore landfill

Urban gardening has recently experienced rapid development; however, the risk of the transfer of toxic elements from neighboring industry needs to be evaluated. We performed a multi-elemental analysis with several common edible crops (cucumber, pepper, cabbage, and lettuce) and poplar grown directly on a titanium ore landfill as a maximized scenario of exposure. Despite elevated concentrations of soil Ca, Fe, Mn, and Ti resulting from the industrial process, we did not register higher accumulation of these elements in the edible parts of crops or in poplar leaves grown on red gypsum compared with the control soil. Only S concentrations were higher in plants grown on the red gypsum, especially for cabbage. The principal component analysis among elements for plants grown on red gypsum indicated that S and Mn were accumulated by different plant species than Cd, Cu, and Zn. The poplar clone had a significantly higher transfer of S and Cr than the control and is a suitable tree species for monitoring element transfer to vegetation in this industrial context. By comparing our data with tolerable daily intake (TDI) recommendations, we demonstrated the low risk of cultivating edible crops directly on an industrial substrate in a maximized scenario of exposure, except for Cr, for which the toxicity depends on the bioavailable form. However, we did not consider the cumulative effects of the various elements because there are no current guidelines, and further research is needed to address this question.

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.

Does intake of trace elements through urban gardening in Copenhagen pose a risk to human health?

This study investigates the potential health risk from urban gardening. The concentrations of the trace elements arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), and zinc (Zn) in five common garden crops from three garden sites in Copenhagen were measured. Concentrations (mg/kg dw) of As were 0.002-0.21, Cd 0.03-0.25, Cr < 0.09-0.38, Cu 1.8-8.7, Ni < 0.23-0.62, Pb 0.05-1.56, and Zn 10-86. Generally, elemental concentrations in the crops do not reflect soil concentrations, nor exceed legal standards for Cd and Pb in food. Hazard quotients (HQs) were calculated from soil ingestion, vegetable consumption, measured trace element concentrations and tolerable intake levels. The HQs for As, Cd, Cr, Cu, Ni, and Zn do not indicate a health risk through urban gardening in Copenhagen. Exposure to Pb contaminated sites may lead to unacceptable risk not caused by vegetable consumption but by unintentional soil ingestion.

Metal uptake by homegrown vegetables - the relative importance in human health risk assessments at contaminated sites

Risk assessments of contaminated land often involve the use of generic bioconcentration factors (BCFs), which express contaminant concentrations in edible plant parts as a function of the concentration in soil, in order to assess the risks associated with consumption of homegrown vegetables. This study aimed to quantify variability in BCFs and evaluate the implications of this variability for human exposure assessments, focusing on cadmium (Cd) and lead (Pb) in lettuce and potatoes sampled around 22 contaminated glassworks sites. In addition, risks associated with measured Cd and Pb concentrations in soil and vegetable samples were characterized and a probabilistic exposure assessment was conducted to estimate the likelihood of local residents exceeding tolerable daily intakes. The results show that concentrations in vegetables were only moderately elevated despite high concentrations in soil, and most samples complied with applicable foodstuff legislation. Still, the daily intake of Cd (but not Pb) was assessed to exceed toxicological thresholds for about a fifth of the study population. Bioconcentration factors were found to vary more than indicated by previous studies, but decreasing BCFs with increasing metal concentrations in the soil can explain why the calculated exposure is only moderately affected by the choice of BCF value when generic soil guideline values are exceeded and the risk may be unacceptable.

Urban agriculture: long-term strategy or impossible dream?: Lessons from Prospect Farm in Brooklyn, New York

Proponents of urban agriculture have identified its potential to improve health and the environment but in New York City and other densely developed and populated urban areas, it faces huge challenges because of the shortage of space, cost of land, and the lack of contemporary local food production. However, large portions of the city and metropolitan region do have open land and a history of agricultural production in the not-too-distant past. Local food movements and concerns about food security have sparked a growing interest in urban farming. Policies in other sectors to address diet-related illnesses, environmental quality and climate change may also provide opportunities to expand urban farming. Nevertheless, for any major advances in urban agriculture, significant changes in local and regional land use policies are needed. These do not appear to be forthcoming any time soon unless food movements amplify their voices in local and national food policy. Based on his experiences as founder of a small farm in Brooklyn, New York and his engagement with local food movements, the author analyzes obstacles and opportunities for expanding urban agriculture in New York.

Urban community gardeners' knowledge and perceptions of soil contaminant risks

Although urban community gardening can offer health, social, environmental, and economic benefits, these benefits must be weighed against the potential health risks stemming from exposure to contaminants such as heavy metals and organic chemicals that may be present in urban soils. Individuals who garden at or eat food grown in contaminated urban garden sites may be at risk of exposure to such contaminants. Gardeners may be unaware of these risks and how to manage them. We used a mixed quantitative/qualitative research approach to characterize urban community gardeners' knowledge and perceptions of risks related to soil contaminant exposure. We conducted surveys with 70 gardeners from 15 community gardens in Baltimore, Maryland, and semi-structured interviews with 18 key informants knowledgeable about community gardening and soil contamination in Baltimore. We identified a range of factors, challenges, and needs related to Baltimore community gardeners' perceptions of risk related to soil contamination, including low levels of concern and inconsistent levels of knowledge about heavy metal and organic chemical contaminants, barriers to investigating a garden site's history and conducting soil tests, limited knowledge of best practices for reducing exposure, and a need for clear and concise information on how best to prevent and manage soil contamination. Key informants discussed various strategies for developing and disseminating educational materials to gardeners. For some challenges, such as barriers to conducting site history and soil tests, some informants recommended city-wide interventions that bypass the need for gardener knowledge altogether.