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Federal Register / Vol. 86, No. 231 / Monday, December 6, 2021 / Proposed Rules
conducted under proposed 112.43d, or other scientifically valid data or information in accordance with proposed 112.12;
Increasing the time interval between harvest and the end of storage using an appropriate microbial die-off rate, and/or conducting other activities, such as commercial washing, to reduce pathogens using appropriate microbial removal rates, except as supported by scientifically valid data and information;
Changing the method of water application to reduce the likelihood of produce contamination such as by changing from overhead spray to subsurface drip irrigation of certain crops;
Treating the water in accordance with proposed 112.46; and An alternative mitigation measure, in accordance with proposed 112.12.
We are revising our approach to mitigation measures involving microbial die-off and/or removal in proposed 112.45b1 to reflect our proposal to remove the pre-harvest microbial quality criteria and testing requirements from the produce safety rule. These changes also reflect feedback we have received throughout stakeholder engagement activities.
Proposed 112.45b1i would provide for an established time interval between last direct application of agricultural water and harvest of the covered produce to allow for microbial die-off, with a minimum interval of 4
days between application and harvest, except as supported by test results conducted under 112.43d, or other scientifically valid data or information in accordance with 112.12.
Survival of pathogens and other microorganisms on produce commodities prior to harvest is dependent upon several environmental factors, including sunlight UV
intensity, moisture level, temperature, pH, the presence of competitive microbes, and suitable plant substrate Ref. 55. Generally, pathogens and other microbes die-off or are inactivated relatively rapidly under hot, dry, and sunny conditions compared to inactivation rates observed under cloudy, cool and wet conditions. The impact of these variables results in a range of microbial die-off rates of 0.5 to 2.0 log per day, as explained in the 2015
produce safety final rule 80 FR 74534, 7444374446.
In general, high initial rates of die-off during the period immediately following contamination suggests field conditions through the first few days are critical in reducing microbial populations on produce compared to
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weeks after the event. 80 FR 74354 at 74445. In studies reporting decay constants measured over time e.g., 0
hours to 14 days or more, pathogen dieoff rates were found to be highest immediately following contamination inoculation and to slow over time; this phenomenon is known as tailing and suggests that pathogen die-off curves are biphasic 80 FR 74354 at 74445.
A die-off rate of 0.5 log per day provides a reasonable estimate of die-off under a broad range of variables including pathogen characteristics, environmental conditions, crop type, and watering frequency 80 FR 74354 at 74416. We derived this die-off rate based on a review of currently available scientific literature and recognize that microbial die-off rates are dependent on various environmental factors, including sunlight intensity, moisture level, temperature, pH, the presence of competitive microbes, and suitable plant substrate.
We reviewed available literature for a time interval that is appropriate when applying a microbial die-off rate of 0.5
log per day. See 80 FR 74354 at 74444
74445. The studies we reviewed indicate that greater microbial die-off or decay rates occur during the early timeframe post-contamination, and although the die-off rate in these studies was established from survival data or decay rates for bacterial studies ranging from 27 days, the specific timeframe for the biphasic shift in die-off was not identified. Within this range identified in the literature, we determined that a time interval of 4 days is reasonable because it serves as a general mid-point in time representing neither end of the range where microbial die-off was observed in these studies.
Based on this information, in 112.45b1iA of the produce safety final rule, we allowed covered farms to apply a time interval between last irrigation and harvest using a microbial die-off rate of 0.5 log per day, for no greater than 4 days, if their water quality exceeded the pre-harvest microbial water quality criteria 80 FR 74354 at 74443. We consider the scientific data used to support this approach as one example of adequate supporting scientific data and information on which a time interval between last direct application and harvest could be established under proposed 112.45b.
Therefore, we have tentatively concluded that it would be appropriate to allow covered farms to use the following approaches for implementing a pre-harvest time interval as a mitigation measure under proposed 112.45b, without having to develop and maintain additional supporting
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scientific data and information. We seek comment on this tentative conclusion.
1. Time Interval Without Testing Data If a covered farm does not test its preharvest agricultural water as part of an agricultural water assessment under proposed 112.43d but determines that the application of a time interval prior to harvest would be an appropriate mitigation measure, the farm could use a time interval between last direct application of agricultural water and harvest of at least 4 days. This would correspond to the broadly-applicable time frame identified in the 2015
produce safety final rule that corresponds to the amount of time associated with the first phase of die-off, when bacterial reduction rates are greatest on produce surfaces and before tailing of bacterial populations occurs. Lacking quantitative test data, the covered farm could not use less than 4 days as a time interval between last direct application and harvest under proposed 112.45b1ii, unless the farm had scientifically valid data or information to support use of a die-off rate of 0.5 log per day for less than 4
days in accordance with proposed 112.12.
2. Time Interval With Testing Data If a covered farm tests its pre-harvest agricultural water as part of an agricultural water assessment under proposed 112.43d and determines that the application of a time interval prior to harvest is an appropriate mitigation measure, the farm could choose to use a microbial die-off rate of 0.5 log per day, for potentially less than 4 days between last direct water application and harvest, to achieve a calculated log reduction to meet the criteria the farm would establish per proposed 112.43d3. Alternately, the covered farm could choose to use a different time interval and accompanying die-off rate if the farm has scientifically valid data or information in accordance with proposed 112.12.
While we consider the information used to support the use of a die-off rate of 0.5 log per day with a maximum time interval of 4 days as being one example of adequate supporting scientific data and information on which a time interval between last direct application and harvest could be established under proposed 112.45b, we recognize that covered farms may have additional information on in-field die-off that is applicable to their unique circumstances. For example, we acknowledged in both the 2014
supplemental produce safety notice and
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