When is it safe to eat this when grown on manure or compost? Edible “low-growing” greens expose consumers to soil bacteria & fungi, and organic setback rules seem safe, but compost rules need upgrading.

The FDA Food Safety Modernization Act (FSMA) proposes new food safety rules  that could seriously affect organic growers who use manure and compost to feed plants. The Organic Trade Association (OTA) commissioned Dr. Will Brinton to examine manure and compost studies before responding to FDA.  Brinton felt that the 270-day setback proposed by FDA (before the lettuce at right could theoretically be eaten) was probably “scientifically extreme” and set out to test that hypothesis.

In his final report posted with OTA’s FDA response, Brinton constructed a chart of “best-case/worst-case” time frames for pathogen reduction based on current scientific reports. Using a risk-equation he found that 131 days instead of the FDA’s proposed 270 would be sufficiently safe. “There is no reason for FDA to change the existing NOP rule (of 90-120 days) which protects consumers based on current science”.

Compost hygiene was more challenging. Brinton contrasted the safety of using manure  according to current USDA-NOP rules – to using compost according to EPA 503 rules – again, based on reviewing current science. “Composting is operating under weaker guidelines” found Brinton, and suggested that using manure in organic farming could be considered safer than using compost. Surprisingly, virtually no current science studies support the lenient assumptions of the EPA CFR40 503 sludge standard, dating to 1989, which composters adhere to.  In that early rule, “in-vessel” compost was viewed as safe after only 3-days of composting and “windrowing” after 15 days “but you sure can’t find much science backing this” says Brinton. Woods End’s landmark study on compost pathogens published in 2009 was cited recently in Food Safety News as justification for better review of how compost is monitored for quality. Modernizing compost standards based on science may therefore be very much in order.  This conclusion appears in harmony with FDA’s call to impose a wait period for compost applied to soil,- which many composters oppose.  Brinton agrees that compost science definitely shows superior performance in terms of pathogen reduction compared to using raw manures, but with very wide, concerning margins of error. Brinton urges FDA to create a better definition of “curing” and “maturity” since aging is a key to hygiene.