CharacterizingChemical and Microbial Hazards on Farms: a First Step Towards Co-managing Farms for Chemical and Microbial Food Safety

Commodities

• Vegetables: greens (lettuces)
• Animal Products: honey

Practices

• Crop Production: water management
• Farm Business Management: risk management
• Soil Management: soil analysis

Farms often operate on land with complex histories that can lead to elevated soil heavy metal concentrations. At the same time, growers must manage preharvest microbial hazards from pathways common to all farms (e.g., water, soil amendments) and unique to farms (e.g., litter, pests, pets). At the same time, conditions and management practices vary within and across farms, leading to variation in chemical and microbial hazards across production areas. Although research has examined chemical and microbial hazards individually, relatively little is known about how these hazards co-occur on farms or how management practices influence both simultaneously. Limited information on the co-occurrence of chemical and microbial hazards limits growers' ability to make decisions about how to manage both.

This project addresses this need by building on an existing dataset from 43 farms that includes data on land-use history and management practices, along with microbial soil contamination and archived soil samples with partial heavy metal testing. The project has four objectives: (1) complete heavy metal testing on archived soil samples; (2) evaluate raised beds as a management strategy by assessing their effects on chemical and microbial hazards; (3) identify farm practices and factors associated with elevated chemical and microbial hazard levels in soils and food products; and (4) translate these findings into practical, decision-relevant guidance for co-managing these hazards on farms.

To meet these objectives, archived soil samples will be tested for heavy metals, followed by targeted sampling of soil and produce from adjacent raised and in-ground beds. Sampling will focus on contamination hotspots identified using archived data. These data will be analyzed to evaluate whether raised beds are associated with reduced heavy metal contamination in soils and crops. The archived and newly collected data will then be combined into a single dataset and used to identify management factors associated with chemical and microbial hazards.

Results from this work will be translated into practical guidance for growers on strategies for co-managing heavy metal and microbial hazards. Specifically, findings from Objectives 2 and 3 will be used to develop fact sheets and other outreach materials that outline strategies for co-managing hazards in farming systems. These materials will be shared with participating farms, grower networks, and extension professionals who support agriculture.

1. Expand the dataset on heavy metal contamination in farm
   soils. We will test archived soil samples collected as
   part of a previous study of 43 farms that generated extensive data
   on farm management practices, land use history, and microbial
   hazards in soils. So far,160 samples have been tested for heavy
   metals. Testing conducted here will expand the dataset with paired
   microbial and chemical data and complete the data for farmer
   partners' operations.
2. Evaluate raised beds as a management strategy for
   reducing heavy metal contamination in farms. To evaluate
   whether raised beds reduce heavy metal contamination in soils and
   translocation into edible crop tissues, paired soil and food
   samples will be collected from participating farms. Half of sampled
   beds will be raised beds and half adjacent in-ground beds. Where
   present, other food product (e.g., honey) samples will also be
   collected to assess whether heavy metals detected in soils are
   reflected in other food products produced on site and to inform
   co-management strategies.
3. Identify farm practices and other factors associated
   with elevated chemical and microbial hazard levels. Using
   historic and newly collected soil and food data, we will evaluate
   how farm management practices (e.g., soil barriers, raised beds,
   soil amendments) and land history (e.g., past land use, repeated
   flooding) are associated with chemical and microbial hazard levels.
   Structural equation modeling will characterize covariation between
   chemical and microbial hazards and identify pathways through which
   management practices can mitigate both.
4. Develop guidance for co-managing chemical and microbial
   hazards on farms. Findings from Objective 3 will be used
   to evaluate tradeoffs and synergies among management strategies
   associated with higher or lower chemical and microbial hazard
   levels. These findings will be translated into practical guidance
   (e.g., factsheets) on co-managing farms operations to mitigate
   chemical and microbial hazards.