Occupational health research in agriculture often focuses on injuries and pesticide exposure via inhalation and dermal contact. However, soil ingestion may be a significant route of contaminant exposure. Soils used for food production can be contaminated through various sources, including industrial activity, legacy pollutants, and pesticide applications. Agricultural workers, especially those directly involved in crop cultivation (growers), have frequent soil contact and may face increased health risks due to soil ingestion. While dermal contact, inhalation, and ingestion are all potential routes of exposure to soil contaminants, ingestion is hypothesized to be the most significant. Traditional dietary assessment methods are inadequate for estimating soil ingestion because it's usually unintentional. Existing research on time activity factors for soil ingestion has limitations, focusing on broad activities in the general population or on children's hand-to-mouth behaviors, with little focus on adult workers. This study uses qualitative methods to address these gaps and provide insights into growers' experiences and beliefs about soil contact to improve the accuracy of exposure science tools.

The literature review highlights the gap in understanding soil ingestion as a significant exposure pathway for agricultural workers. While traditional dietary assessment methods are insufficient for estimating unintentional soil ingestion, existing studies on time activity factors lack specificity regarding agricultural tasks and adult behaviors. Previous research primarily focuses on general populations or children, neglecting the unique context of adult agricultural workers. The existing literature emphasizes the need for improved exposure assessment tools that account for the complex interplay of environmental, behavioral, and occupational factors influencing soil ingestion in agricultural settings. This lack of targeted research makes it difficult to accurately estimate and manage the health risks associated with this exposure route.

This qualitative study used purposive sampling to recruit 16 fruit and vegetable growers in Maryland. Recruitment strategies included using online farm databases and direct networking. Eligible participants were current farm owners/managers, employees, or community gardeners who had engaged in food production activities within the past year. Informed consent was obtained, and in-depth interviews (IDIs) were conducted at the participants' farms between January and February 2020. The IDIs were audio-recorded and transcribed verbatim. A semi-structured interview guide explored growers' work activities, soil contact experiences, and practices to modify soil contact. An adapted framework approach was used for data analysis, combining inductive and deductive coding methods. The first round involved deductive coding based on the interview guide's questions. The second round involved inductive coding to identify emergent themes. Data were then mapped onto key exposure science concepts to develop analytical frameworks. The analysis process was iterative, with transcripts reviewed and refined by all co-authors to ensure thoroughness and accuracy.

Four main themes emerged from the interviews: (1) Variability in growers' descriptions of soil and dust: Growers used “soil,” “dirt,” and “dust” interchangeably, creating challenges in aligning their descriptions with scientific definitions. The EPA's definition distinguishes between soil, outdoor settled dust, and indoor settled dust, but growers' usage often blurred these lines. The study found that 'soil' often carried positive connotations associated with life and cultivation, while 'dirt' and 'dust' had more negative associations. (2) Variability in growers' soil contact: The study revealed that soil ingestion is just one component of a broader multi-route exposure scenario. The six most frequently mentioned tasks associated with high soil contact included bed preparation, planting, pest management, irrigation, harvesting, and produce handling. Soil contact was categorized as intentional or unintentional, with behavioral and environmental factors identified as contributors to soil contact events. (3) Growers' concerns regarding soil contact: Growers expressed concerns about potential health effects from soil contact, including exposure to contaminants. (4) Growers' practices to modify soil contact: Growers described various practices to reduce soil contact, including using personal protective equipment (PPE) and practicing hand hygiene. The study developed a framework to classify soil contact events based on worker intention and the cause of the event, mapping the descriptions to different exposure routes (ingestion, inhalation, dermal). The findings highlight the need for a comprehensive approach to soil ingestion assessment that considers multiple routes of exposure and the nuances of growers' language and perceptions.

This qualitative study significantly contributes to occupational exposure science by identifying key considerations for improving soil ingestion assessment tools in agricultural settings. The findings demonstrate the limitations of relying solely on traditional methods and highlight the importance of incorporating growers' perspectives and experiences. The variability in growers' descriptions of soil, dirt, and dust underscores the need for clear communication and consistent terminology in exposure assessments. The framework developed for classifying soil contact events provides a valuable tool for future research. The study's findings emphasize the complex interplay of behavioral, environmental, and occupational factors that influence soil ingestion, reinforcing the need for a multi-faceted approach to assessment and intervention. Future research should focus on developing quantitative methods to measure soil ingestion based on the insights gained from this study, potentially incorporating task-based frameworks.

This study provides crucial insights into the complexities of assessing soil ingestion exposure among agricultural workers. The four key considerations identified—variability in terminology, multiple exposure routes, grower concerns, and practices to modify contact—are critical for improving exposure science tools. Future quantitative research should build on this qualitative foundation to develop more accurate and comprehensive assessment methods. A task-based framework could effectively structure future investigations, potentially applicable to other populations beyond agricultural workers.

The study's limitations include the relatively small sample size and the geographical focus on Maryland growers. The findings may not be generalizable to all agricultural settings or populations. The reliance on self-reported data could introduce recall bias. Further research with larger, more diverse samples is needed to validate the findings and refine assessment methods.