For people who drink untreated well water, sometimes the only thing that stands between them and pathogenic bacteria is soil. New research shows that high concentrations of phosphate, a key ingredient in fertilizer, help a deadly strain of Escherichia coli to slip through the dirt (Environ. Sci. Technol., DOI:10.1021/es201132s). The result is a potentially greater risk of groundwater contamination.
On rural fields, cow manure is a major source of E. coli O157:H7, a strain that can trigger internal bleeding and kidney damage when people ingest it. Each year, this pathogen causes about 73,000 illnesses and 60 deaths in the U.S., says Jin Li, an environmental engineer at the University of Wisconsin, Milwaukee. Contaminated drinking water is the culprit in about 15% of those infections.
Interesting, but to me it raises more questions than answers. I fully admit that I’m not a microbiologist or an expert in organic chemistry or someone who knows as much about farming as he should, but when I think about what this article means for the real world, I have some doubts.
The paper (which I skimmed) connects the dots by saying that applying cow manure to fields increases risk of O157 in the soil, and that applying commercial fertilizers rich in phosphates increases risk of transporting O157 through the soil to groundwater. But I wonder: how many farmers out there are applying untreated manure AND commercial fertilizers?
Put another way: organic farmers seem much more likely to apply manure or manure-based compost to fields than commercial farmers, yet commercial farmers are the only ones adding synthetic phosphate-based fertilizers to their fields. That is, these are two different farmers. Since the whole point of synthetic fertilizers is to do what manure does - add nitrogen, among other things - I don’t think there are many farmers applying both commercial fertilizers and untreated manure. But this is just my gut feeling and maybe I’m way wrong. If anything, it’s just one more reason why using untreated manure is risky, but we knew that already.
Regardless, isn’t cow manure much more likely to contaminate groundwater in a more direct manner, through rain runoff from feedlots or wherever into streams and rivers, rather than through the complicated process involved here, where someone is collecting manure, possibly treating it, adding it to fields, then adding fertilizers, then irrigating so inefficiently that the soil is fully saturated? This just doesn’t seem like a particularly relevant pathway to me.
Another thing this raises to me, though it’s more philosophical, is that if you view this from a food safety standpoint, if phosphates increase risk to groundwater by transporting O157 out of the soil, don’t they correspondingly reduce risk to the vegetables grown in that soil? Again, this probably isn’t relevant in the real world, because I think the issue of uptake of O157 through root systems is largely overblown, but it’s an interesting aside.
To be clear, I’m not saying this isn’t good science or even that it’s not relevant. It might be very good work and indeed, might be very important for understanding non-point pollution issues. But I think the specific example invoked in the press release does a bit of a disservice by pushing it too far. Believe me, I sympathize. Someone might even criticize press releases related to my own work for the same reason, to which I would say, with puppy dog eyes: Yes, I know.
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