Final report for GNE19-209
Project Information
Agricultural soils may be contaminated with chemicals that pose risks to farmers. Ensuring safe and sustainable agricultural practice necessitates knowledge of farmers’ activities and behaviors that drive soil contact as well as data regarding the concentrations of contaminants in agricultural soils. Filling these knowledge gaps requires a mixed methods approach and involves innovation through updating of existing soil contact tools to collect data specific to this context.
Little is known about the specific activities and behaviors that dictate soil contact among agricultural workers. Typically, behavioral data used in safety assessments would be drawn from default assumptions from the US EPA Exposure Factors Handbook (which provides estimates of inhalation, ingestion and dermal contact rates for soil for adults and children in the general US population). These estimates are unavailable for farmers, who would be expected to have greater rates and frequency of soil contact (US EPA 2011a). Researchers have estimated dermal exposure to soil while engaging in several soil-related activities, but these estimates are highly uncertain, based on limited data, and likely irrelevant to the agricultural context (Holmes et al. 1999; Kissel et al. 1996; Kissel et al. 1998; Kissel 2011). The nationally-representative Soil Contact Survey (Garlock et al. 1999; Wong et al. 2000) was used to estimate the frequency and duration of soil contact among the US population, but was not designed to characterize direct soil contact among farmers.
This research used in-depth interviews analyzed via a framework approach to identify key considerations and factors that may impact rates of soil exposure among agriculture workers. Using an innovative meso-activity-approach, we also administered a semi-structured questionnaire longitudinally to collect time-activity-pattern data about growers’ activities and behaviors for 6 meso-activities and derived exposure factors describing soil contact over one year. Our interviews reveal 18 factors that may impact soil exposure in the agricultural context and 4 considerations for exposure scientists to consider in the refinement of indirect exposure assessment tools. We also derive several exposure factors demonstrating variability in growers’ soil exposure and behaviors (e.g., glove use, handwashing) across tasks and seasons. Growers’ estimation of their own soil ingestion on a typical day suggests current ingestion rates intended for non-agricultural workers may underestimate exposure for the most highly exposed agricultural workers. Through the development of an innovative approach for collecting time-activity pattern data focused on meso-activities, this research has enhanced our understanding of soil exposure in the agricultural context and generated novel exposure factors for agricultural workers’ soil contact that can be used to inform occupational health guidelines for contaminants in soils to protect agricultural workers.
Objective 1. Describe the activities and behaviors of rural farmers that impact soil exposure.
Objective 2. Quantify the activities and behaviors of rural farmers that impact soil exposure.
Objective 3. Estimate farmers' soil exposures and the contribution of farmers' activities and behaviors that impact soil exposure across seasons.
Objective 4. Measure and compare concentrations of soil contaminants on urban and rural farms in Maryland
The purpose of this project is to investigate and contextualize environmental health risks associated with exposure to potential soil contaminants among urban and rural farmers. Most occupational investigations of health risks among agricultural workers have focused on accidents, injuries, and exposure to pesticides in rural locations (Alavanja et al. 1996; Alavanja et al. 1999; Racine et al. 2012). For farmers, direct soil contact is an important, but poorly characterized source of exposure to potential soil contaminants. Urban soils may be contaminated with heavy metals (e.g., lead and arsenic) due to their natural occurrence, as well as current and historical industrial activity (e.g., fossil fuel combustion and waste incineration), and legacy uses of lead-based paint and leaded gasoline (Mielke et al. 1983; Mielke and Reagan 1998; Mielke et al. 2011; Schwarz et al. 2012; Yesilonis et al. 2008). The increased interest in and practice of urban agriculture (Palmer 2018) has raised concerns about risks stemming from farmers’ exposure to soil contaminants and exposures resulting from consumption of urban-grown fruits and vegetables (Kim et al. 2014). Rural soils may be contaminated with heavy metals due to current and historical and applications of persistent pesticides (e.g., lead arsenate) or from previous land uses or contamination events unknown to the farmer (Hood 2006; McBride et al. 2015). Given increased interest in local, sustainable food production, and the simultaneous loss in agricultural land (particularly in the Northeastern US) to other non-agricultural land uses (America’s Farmland Trust 2018), new and younger farmers may take on rehabilitation of land for which the previous land uses are unknown.
No public or occupational health agency is responsible for surveillance and routine monitoring of contaminants in agricultural soils. Soil contaminant testing is highly recommended by the US EPA before establishing any urban agriculture project (US EPA 2011b), but comparable guidance is not available for rural farms. Interpretation of contaminant results is difficult because current health-based guidelines for contaminants in soil can vary widely by jurisdiction and designated land use (Jennings 2013a, b). No guidance values for soil contaminants exist for agricultural land that are intended to protect farmers. To inform evidence-based guidelines for contaminants in soil, research is needed to understand the nature and extent (e.g., the frequency, duration, and intensity) of soil contact among farmers in urban and rural contexts. The conduct of this research will provide participating farmers with soil contaminant testing services. These individual results can be used to inform soil conservation and management decisions in the short term. The long-term impacts of this research will improve the health and well-being of farmers by increasing our understanding of farmers’ interactions with soil contaminants as a potential contributing factor to acute and chronic illness and disease. More importantly, this research will generate information about farmers’ soil contact necessary to inform evidence-based recommendations to reduce exposure that are practicable for farmers in both urban and rural contexts and can be used to improve the quality of life for farmers and their employees.
Cooperators
- (Researcher)
- (Researcher)
Research
Objective 1. In January - February 2020, we conducted in-depth interviews with 16 farmers in Maryland about their soil contact activities and behaviors. Interview recordings were transcribed verbatim using nVivo and analyzed using a framework approach.
Objective 2. To comply with CDC recommendations and university restrictions on in-person contact for research due to the COVID-19 pandemic, the administration of a seasonal soil contact activity questionnaire was conducted via phone, beginning in May 2020. Between May 2020 and January 2021, we administered 130 soil contact activity questionnaires to 38 farmers in Maryland. Twenty-two growers (58%) completed the questionnaire in all 4 seasons; seven (18%) completed the questionnaire in three seasons; six (18%) growers completed the questionnaire in two seasons; three growers completed the questionnaire in one season (8%).
Objective 3. Using the novel exposure factors derived from the soil contact activity questionnaire (Objective 2), we used EPA models to estimate soil exposures via dermal and incidental ingestion pathways.
Objective 4. The collection of soil samples from farms was postponed until spring 2021 due to the COVID-19 pandemic. In May 2021, soil sampling kits were sent via US mail to 24 farmers who had previously completed questionnaires and agreed to provide a soil sample. 18 farmers provided a soil sample. All soil samples were analyzed for the concentrations of 12 metals (6 harmful to human health: As, Ba, Cd, Cr, Pb, and Ni; and 6 not harmful to human health: Ca, Co, Fe, Mn, K, Zn) using Inductively Coupled Plasma- Mass-Spectrometry (ICP-MS). Farm-specific results and interpretations were returned directly to each farmer in September 2021.
Objective 1. Our interviews identified four emergent themes relevant to soil exposure in agricultural context: 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. These considerations were incorporated into the soil contact activity questionnaire that was administered for Objectives 2-3.
Objective 2. Growers generally spent the greatest number of days per month irrigating (median = 6 days per month in the fall to 20 days per month in the summer), and the greatest number of hours per day preparing beds (medians: ≥3 hours). Across all seasons, growers reported transplanting and weeding as the most soil contact-intensive meso-activities – i.e., their hands were in contact with soil on average 87% of the time while transplanting and 72% of the time while weeding.
Objective 3. Estimates of soil exposure varied across meso-activities and seasons. We observed no consistent pattern in the relative contribution of meso-activities to total annual exposure. Spring and summer generally accounted for the largest shares of exposure, particularly for the dermal pathway.
Objective 4. Because there are soil concentrations were compared to Maryland Residential Soil Standards and background levels in Maryland and returned via email directly to farmers. All concentrations were below the soil safety standard for Ba, Cd, Pb and Ni. All but one sample had As concentrations greater than the residential soil standard but were within or below background levels for the state of Maryland. Concentrations of all not harmful metals were below the residential soil standards (Cu, Fe, Mg, Zn).
This research has enhanced our understanding of soil exposure in the agricultural context. Our qualitative data provided a rich context for better understanding the growers’ experiences and laid the foundation for designing a soil-contact activity questionnaire for a more nuanced collection of quantitative information describing soil exposure in the agricultural context. We generated novel exposure factors to quantify the meso-activities and behaviors of fruit and vegetable growers. Application of these exposure factors to existing US EPA exposure models improved our ability to understand the degree to which behaviors may contribute to soil exposures, across both across and within meso-activities and seasons.
Our focus on behavior provided the information necessary to develop more appropriate behavior-based interventions. For example, tasks where reported soil contact is highest, but the prevalence and/or frequency of exposure reduction behaviors (like handwashing) is low could be a starting point for designing more effective behavioral interventions for reducing soil exposures that are most easily adopted. Our qualitative findings also provide additional context for how soil exposure may compare to growers’ other health and safety concerns.
The US EPA’s current approach to pesticide regulations assesses risks to human health by considering exposures to pesticides via food, drinking water and occupational (application) pathways, but not via contact with soil. With evidence that some pesticides are persistent in the soils, soils may be an important and unaccounted-for source of exposure to pesticides for farmers. This project advanced methods for quantifying soil exposures among agricultural workers and generated preliminary data that could be used in regulatory risk assessment and decisionmaking andprompt the development of more stringent environmental and occupational health guidelines to protect farmers.
Education & Outreach Activities and Participation Summary
Participation Summary:
18 farmers participated in the soil testing component of this project and received individual reports regarding soil contaminants at their farms.
The COVID-19 pandemic hindered our ability to present at in-person sustainable agriculture conferences and local urban agriculture community events, but we presented the following at virtual meetings.
- Lupolt SN*, Nachman KE, Novel task-based exposure factors to assess soil exposure among fruit and vegetable growers. 2021 International Society for Exposure Science Annual Meeting, August 30-September 2, 2021, Virtual poster presentation, virtual due to COVID Pandemic.
- Lupolt SN*, Kennedy RD, Nachman KE, Understanding soil exposure experiences of fruit and vegetable growers for the exposure science community. 2020 International Society for Exposure Science Annual Meeting, September 21-22, 2020, Poster presentation, virtual due to COVID Pandemic.
- Lupolt SN*, Kennedy RD, Nachman KE, Contributors to soil exposure among fruit and vegetable growers: A framework for collection activity-pattern data to estimate soil ingestion. 2020 International Society for Exposure Science Annual Meeting, September 21-22, 2020, Poster presentation, virtual due to COVID Pandemic.
Project Outcomes
Our interviews reveal 18 factors that may impact soil exposure in the agricultural context and 4 considerations for exposure scientists to consider in the refinement of indirect exposure assessment tools. We also derive several exposure factors demonstrating variability in growers’ soil exposure and behaviors (e.g., glove use, handwashing) across tasks and seasons. Growers’ estimation of their own soil ingestion on a typical day suggests current ingestion rates intended for non-agricultural workers may underestimate exposure for the most highly exposed agricultural workers. Through the development of an innovative approach for collecting time-activity pattern data focused on meso-activities, this research has enhanced our understanding of soil exposure in the agricultural context and generated novel exposure factors for agricultural workers’ soil contact that can be used to inform occupational health guidelines for contaminants in soils to protect agricultural workers.
My advisor (Keeve Nachman) and I built upon the methods in my thesis work to pursue a funding opportunity (US EPA-G2020-STAR-D1, Estimating Children’s Soil and Dust Ingestion Rates for Exposure Science) to advance methods for estimating soil and dust ingestion rates for children. We are currently working on a 3 year, multi-disciplinary effort to improve methods for estimating children’s soil and dust intake. The methods we are developing and improving (e.g., improved time-activity pattern collection tools, computer vision, and non-targeted tracers) in our current work for estimating children's exposures to soil and dust will be transferrable to agricultural workers. In the future, I hope to apply these methods to agricultural worker populations to generate more refined (e.g., task-specific) and reliable estimates of soil and dust ingestion.
Dr. Nachman is also Co-Principal Investigator on an EPA-funded grant (US EPA R840247) to identify and prioritize chemicals in human biosolids intended for use in agriculture for human health risk assessment. Both the approach demonstrated and exposure factors derived from this work will be used to estimate exposure to chemicals in biosolids. Combined with advanced probabilistic modeling of exposure scenarios, we will characterize risks and develop a flexible prioritization framework suitable for multiple decision contexts
Information Products
- Key considerations for assessing soil ingestion exposures among agricultural workers (Peer-reviewed Journal Article)
- A qualitative characterization of meso-activity factors to estimate soil exposure for agricultural workers (Peer-reviewed Journal Article)
- Urban soil safety policies: The next frontier for mitigating lead exposures and promoting sustainable food production (Peer-reviewed Journal Article)
- The Safe Urban Harvests Study: A Community-Driven Cross-Sectional Assessment of Metals in Soil, Irrigation Water, and Produce from Urban Farms and Gardens in Baltimore, Maryland (Peer-reviewed Journal Article)
- The Safe Urban Harvests Study: An assessment of urban farms and community gardens in Baltimore City (Book/Handbook)