Growers Can Use Well Water Without Risk to Mushroom Safety

By Blake Jackson

Concerns have arisen regarding nitrate levels in mushrooms and whether irrigation water exceeding EPA drinking water limits poses a food safety risk. This study aimed to determine how nitrate concentration in irrigation water affects post-harvest mushroom nitrate levels and whether high-nitrate water could endanger consumers.

The Mushroom Good Agricultural Practices (MGAP) program, developed with support from Penn State Extension and the American Mushroom Institute, has successfully elevated industry food safety standards.

While occasional disagreements arise between auditors and growers regarding MGAP interpretation, they are typically resolved using current produce safety knowledge or additional research.

One example involves restrictions on nitrate levels in irrigation water. Auditors often require water to meet potable drinking standards, while growers argue this is inconsistent with standards for other crops and imposes significant costs for reverse osmosis treatment.

Nitrates (NO3-) are naturally occurring in soil and highly soluble in water, often entering groundwater. While nitrates themselves are not toxic and may even benefit adult cardiovascular health, they can convert to nitrites (NO2-), which pose health risks, especially to infants, potentially causing methaemoglobinaemia.

The EPA sets a maximum contamination level (MCL) of 10 mg NO3-N/L in drinking water. Most well water samples in Pennsylvania and across the U.S. fall well below this limit. Mushrooms are naturally low in nitrates compared with leafy vegetables.

In this study, mushrooms were grown under six irrigation treatments ranging from 0 to 61.5 mg NO3-N/L. Mushrooms were harvested, dried, and analyzed for nitrate content. Results showed a slight increase in mushroom nitrate levels with higher irrigation nitrate, from 18.7 to 33.3 mg NO3/kg across treatments.

However, levels remained well below EPA reference doses. For instance, a 70 kg adult consuming a cup of mushrooms from the highest-nitrate treatment would ingest only 3.4 mg NO3, far below the 490 mg daily limit.

These findings indicate that mushrooms irrigated with water exceeding the EPA MCL for nitrates do not pose a health risk. Growers can continue using well water without costly reverse osmosis systems, while maintaining routine microbial testing to ensure food safety.

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