Become a Creator today!Start creating today - Share your story with the world!
Start for free
00:00:00
00:00:01
Rain Splash on Feces in Produce Fields
73 Plays6 months ago
The FSMA Produce Safety Rule does not give specifics on establishing no-harvest buffer zones, and it can be difficult for growers to determine the size of a no-harvest buffer zone when they find poop in the field. Laurel Dunn, assistant professor and food safety extension specialist at the University of Georgia, and Shirley Micallef, professor in the Department of Plant Science and Landscape Architecture & Center for Food Safety and Security Systems at the University of Maryland, have conducted research on the dispersal of contamination due to rain splash on feces in produce fields. In this episode, Phil Tocco, extension educator for on-farm produce safety at Michigan State University Extension, talks with Laurel and Shirley to find out what they learned from their research, and what growers can take away from their findings.
Additional Resources
Full research article: https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2024.1370495/full
Recommended
Transcript
Introduction to the Podcast
00:00:00
Speaker
Hello and welcome to the Agri-Food Safety Produce Bites podcast, where we discuss all things produce safety and dive into the rules and regulations surrounding the Food Safety Modernization Act Produce Safety Rule. Hi, I'm Laurel Dunn. I'm an assistant professor and food safety extension specialist at the University of Georgia.
00:00:22
Speaker
Hi, my name is Shirley McAuliffe. I'm a professor in the Department of Plant Science and Landscape Architecture at the University of Maryland. And I also have a joint appointment in the Center for Food Safety and Security Systems. And I'm Phil Toko. I'm with Michigan State University Extension. I am an extension educator in on-farm produce safety housed in Jackson, but covering the entire state.
FISMA Produce Safety Rule Ambiguities
00:00:43
Speaker
So I'm curious, guys. My favorite bedtime reading is the FISMA Produce Safety Rule.
00:00:50
Speaker
And I noticed that in a couple of sections, they talk about looking specifically at feces and creating no-harvest buffer zones. They don't ever say you need a no-harvest buffer zone, but they talk about, and this is in 112.112,
00:01:06
Speaker
they say at a minimum identifying and not harvesting covered produce that is reasonably likely to be contaminated with animal excreta or that it's visibly contaminated with animal excreta requires a visual assessment of the growing area and all covered produce to be harvested regardless of the harvest method used. And that seemed really vague to me. And I'm curious, you guys have done some research to try and make that a little less vague. Do you want to talk a little bit about your research?
Research on Fecal Contamination in Produce
00:01:35
Speaker
Sure. So yeah, the produce safety rule does not really give specifics. But it is expected that a grower will determine whether a crop is likely to be safe for consumption. And because there are no specifics, it's very difficult for a grower to kind of determine what what exactly they need to do other than look for evidence of animal intrusion. But if you do find evidence of evidence of animal intrusion, which could be
00:02:02
Speaker
you know, finding tracks or finding feces or seeing that some crops have been eaten, for example, then they have to take measures. And what those measures are is not specific in the produce safety rule. But the Leafy Green's marketing agreement from California does provide some more specific kind of interventions that would need to be
00:02:22
Speaker
taken, and that includes a no-harvest buffer zone with a radius of five feet around the area where evidence of intrusion is found. So that's kind of what we wanted to test. There was no data for the Mid-Atlantic or the South Atlantic, so we wanted to see whether that applies to our region. I'm curious how you guys
Study Methods and Rain Simulation
00:02:44
Speaker
conducted your research or what methods did you guys use to figure this out?
00:02:49
Speaker
We're using lettuce as our model crop. And we actually got rabbit feces from a local rabbit farm and inoculated that with a surrogate E. coli or an E. coli that we could use out in the production field. So we inoculated our feces after we determined that we didn't have any microorganisms in the background that could make our results difficult to interpret.
00:03:16
Speaker
We placed it pretty much throughout these plots of lettuce that we were growing. We had two locations, so Shirley's group up in Maryland and then my group in Athens, Georgia, and pretty much either waited for rain or simulated a rain event. We had two separate ages of our fecal contamination, so we had one where we placed our rabbit feces in the field,
00:03:43
Speaker
and we either sprayed or had it rained on naturally immediately. And then we had an instance where we would place it in the field, we'd wait several days, and then we would have that simulated rain event occur. And we were really just interested in seeing how far that contamination spread from the fecal deposit to the lettuce. So we started with kind of our
00:04:07
Speaker
our zero distance which were those heads of lettuce that were immediately adjacent to the fecal deposit and then we just sampled out from there and pretty much tried to I guess detect our
Bacteria Spread and Regional Differences
00:04:19
Speaker
E. coli and see how far it spread from that initial point source. So now I'm actually really interested in finding out what you guys learned with respect to how far the poop moved.
00:04:31
Speaker
The poop didn't move. The bacteria moved from the poop. The idea was that rain could cause that bacterial dispersal at a farther distance or maybe at a faster rate too. That's why we introduced the rain component. But what we found was that
00:04:53
Speaker
We saw a similar trend that the closer the lettuce was to the feces, then the more bacteria we could see on the lettuce. But the farther the distance and the distance we tested was up to five feet, which was what is in the LGMA. The farther the distance, the less bacteria we would detect. But the trend of this decline with distance, the decline in bacterial numbers with distance, was similar between Georgia and Maryland. But what we saw is that in Maryland, we had
00:05:23
Speaker
more dispersal, higher levels and further distance than in Georgia.
Impact of Ground Covers on Bacteria Dispersal
00:05:29
Speaker
So in the beginning, we were kind of scratching our heads like what, you know, why is it why is it that we're seeing these differences, but then we realized that in Georgia, the lettuce were transplanted into the field directly onto the soil. But in Maryland, we used plastic, which is a common practice black plastic or plastic mulch. And so
00:05:48
Speaker
This kind of raised the question, well, do mulches impact this dispersal from the point source of contamination which was our rabbit feces to the lettuce? And so the second year we conducted an even larger field trial, which was actually quite a lot of work, but we tested different mulches to see how dispersal of bacteria from the fecal point source might differ based on the mulches that are present on the ground.
Effects of Rain on Bacterial Spread
00:06:15
Speaker
So you found you were able to recover the bacteria even at that five-foot limit then? No. So yeah, there was a decline. So there were higher levels closer to the feces. So the 0.1
00:06:32
Speaker
meter distance, so that's 10 centimeters from, you know, literally right next to the feces, the lettuce consistently had E. coli on them. But as you, as you moved further away from that point source, we saw gradually lower levels of E. coli and up to around 0.9 or so is when they kind of started to dissipate to below one log. So you would get more erratic results at that point. But yeah, in general,
00:06:59
Speaker
you saw this decline and the trend was the same between Georgia and Maryland.
Salmonella Presence in Bird Feces
00:07:05
Speaker
What was interesting is that, so as Laurel mentioned, we had stale feces that were placed three days before the rain event and fresh feces that were placed an hour before the rain event. And in Maryland, we didn't get any rain between the placement of the stale feces and the rain event that we kind of used as our marker to test. But in Georgia, there was a rain in those three days.
00:07:30
Speaker
And we saw that the wetting of the feces actually affected dispersal in Georgia. But in Maryland, the stale feces did not actually really yield a lot of E. coli. So yeah, so that was an interesting difference as well. So it has to be fresh, or else it doesn't really disperse. It has to be fresh, or it could be old that gets wet.
00:07:53
Speaker
and then kind of keeps it fresh, if that makes sense. No, that does. Wet your feces, do not wet your feces. Yeah. So the drier it is, the better. Right. Well, and to speak to that, Nikki Sherry, one of our researchers at UGA, did a survey of bird feces looking for salmonella in it on farms throughout Florida, Georgia, and South Carolina. And they also found the same thing kind of just in their survey work of
00:08:21
Speaker
They found a really low prevalence of salmonella, I think only like 2% of their samples. And they had well over 1,000 samples that they collected. But none of it ever came from dry feces. They only ever got pathogens out of fresher or, I guess, wet feces. So kind of disagrees with some survey work, too, that we've also seen done in at least our southern region.
Buffer Zones and Mulch in Contamination Prevention
00:08:44
Speaker
That's amazing to me. It would be neat to see if wetting that feces would bring the salmonella back out of those dry spots. Back to your research, from the standpoint of growers, it sounds like the five-foot buffer is more than enough then to keep the contamination from getting on everything. Would that be
00:09:08
Speaker
So yeah, so I guess the answer to that is always complicated. And it would be it depends, right. So it depends on like we said, are the feces fresh or not? Are the feces if they're not fresh, have they been wet during that time that they were in the field. So those things appear to kind of allow for E. coli to persist longer in the feces and therefore be able to be dispersed.
Mulch Types and E. Coli Spread
00:09:33
Speaker
But then it also depended on the mulches. So we did in the second year, as I said, we tested different mulches being the burr ground was kind of our no mulch. You can say it's a control, but not really. It was just another treatment. And then we had the black plastic and also straw as a ground cover. And we found that dispersal was dependent on the ground cover. What effect did the ground cover have on the dispersal?
00:10:03
Speaker
So what we found was that when we used the plastic mulch, we got much greater spread of that E. coli, much more so than our straw. So it almost seemed like our straw treatment was almost capturing and preventing a lot of that dispersal from happening. And our bare ground was kind of in that middle range. A lot seemed to be kind of absorbed by that bare ground soil.
00:10:30
Speaker
And we really think that that plastic mulch just kind of, that water would hit it, it would splash whatever was in that fecal material. That was really the mulch type where we got the greatest dispersal.
00:10:41
Speaker
It makes a lot of sense, and part of the reason why people put mulch down, yeah, it's to prevent weeds, but it's also to reduce the erosion, like for some erosion control. And certainly if you're putting straw mulch down, that reduces that impact of the water on the surface. So then growers definitely should consider not only whether or not the poop is fresh or wet, but also then if they're using a mulch in that buffer zone.
00:11:11
Speaker
It does seem that if you're using plastic, which is a very common practice, practically everybody uses it because it's so helpful for retaining moisture and suppressing weeds and maintaining temperature in the soil. We also used, we had black plastic and then Georgia, I think used white plastic, right, Laurel? And that didn't seem to make a difference, but it did to make a difference between biodegradable plastic and conventional plastic. And that could be because of the material. I think it has to do with how
00:11:41
Speaker
the kind of how permeable the material is. So if it's like straw, the splashes would just fall back into the soil, depending on what type of plastic you might have more ricocheting. So those were the main things I would say. Okay. We did look at time. Okay. Past the first, because we sampled at 24 hours, but we had still lettuce in the field at 72 hours and
00:12:10
Speaker
one of our extension agents actually asked us the question, like, well, what happens after that first day? We're like, that's a great question. We should, we still had some lettuce. So we went back and took more samples three days later.
Need for Further Studies
00:12:23
Speaker
And we did see that E. coli had declined on the lettuce. It didn't go back up. So that was a good sign. So, you know, not that you want to harvest any lettuce that's close to feces, of course, but, um, it's good to know that over time there is the expectation that the E. coli would decline.
00:12:40
Speaker
unless there's rain, which could mean that it comes back. I can certainly see this, particularly out West, where often before they harvest lettuce, they actually overhead irrigate the lettuce to try and plump it up before harvest. I can definitely see there being at least some reason for a grower to pay attention to this a little bit more if they're using black plastic. Yeah, I would think so.
00:13:09
Speaker
Is there anything else that struck you about this research? I think as with anything, we answered a very specific question and I think it only brought out like a thousand more questions and variables that we could add to this. You started to mention the overhead irrigation.
00:13:31
Speaker
That could completely change what we're looking at. Our system was a drip irrigated system. So I think as with anything, we have more questions and more things that we're interested in looking at and variations to the study to answer those what if scenarios. As much as you brought up more questions for me, you were able to define that five foot is a safe harbor, which is kind of nice.
00:13:56
Speaker
And under the conditions, as Laurel says, that we tested, one thing that we did not test was rain intensity. But I think that's a factor. It looks like there's evidence, at least from our data, that depending on how much rain for how long and how intense it is, it would affect dispersal. But maybe if there is a really big rain event, it could even wash away some of the bacteria that are dispersed. But if it's a kind of a moderate rain event, might be the worst case
00:14:26
Speaker
scenario where you have maximal dispersal with less washing off of bacteria from the surface of the lettuce. So that would be an interesting follow up study if we do that.
Closing Remarks and Future Episodes
00:14:38
Speaker
But currently, you know, the data that we have currently cannot answer that question, but there is evidence that this could be a factor.
00:14:45
Speaker
cool cool that's that's again i think there's there's some exciting possibilities for where to go with this next in terms of being able to hone in thank you very much both of you for joining and for for talking to us today
00:15:00
Speaker
Thank you for inviting us. Thank you for having us. Links to anything referenced in this episode are provided in our show notes, which can be accessed on the website at c-a-n-r dot m-s-u dot e-d-u slash agri-food underscore safety. Thank you to everyone for listening. And don't forget to tune in next month for another episode of our Produce Bites podcast.