Q. My community organic garden receives compost that has always seemed really excellent. But I made the mistake of asking what went into it, and learned that some of the raw ingredients were leftovers from a large university food service. I know that they're not serving organic food, so I have to assume that some of the ingredients include GMOs (genetically modified organisms).
It's my understanding that at least some herbicides and chemical pesticides can break down into harmless substances during the composting process. Is the same true for GMOs? Are they rendered inert? My concern is that the modified genetic material could be transferred to bacteria in the soil and then into our edible plants. Am I totally off the mark with my concerns?
One reason I've become so suspicious was a supposedly organic fertilizer I found in the garden center of a 'big box store' whose list of ingredients included chicken litter. I knew that the chickens probably weren't raised organically, and that their feed would likely contain GMO corn—so I decided to err on the side of caution and not purchase the fertilizer. Then I learned about the problems with arsenic in chicken litter and was really glad I passed! Any insight you could shed on the risks of using compost that might contain GMOs would be appreciated.
- ---Margaret in State College, PA
A. Issues surrounding the raw materials that go into compost have been around for decades. Cow manure sourced from factory farms, for instance, would be expected to contain resides of antibiotics and growth hormones. And as you wisely note, arsenic when chickens are involved. It's a really serious problem; the USDA found so much arsenic in some American rice that had been fertilized with chicken litter that it issued an advisory warning people to limit consumption of rice that had been grown in certain states. (Where is the arsenic coming from, you ask? In this Brave New World of ours, so-called 'conventional' farmers add arsenic to chicken feed because it apparently strengthens the shells of the eggs.)
And there's a different concern with horse manure. Horses aren't over-medicated or fed poison like animals raised for consumption, but—as we have been warning recently—if horses graze on fields where a 'persistent herbicide' was used, their manure will contain some of the herbicide. And these herbicides are SO persistent that the composted manure of affected horses has killed plants. So here's a case where we know that the composting process didn't make an herbicide inert.
Now we'll speak directly to your concerns. Most of the non-organic corn and soybeans grown in the US have been genetically modified to tolerate applications of the herbicide known as "Roundup" so massive they would kill normal versions of those crops. Roundup is a systemic herbicide, meaning it is taken up through the root systems of these plants and into the actual corn and soybeans. So I personally worry more about eating 'conventional' corn chips or tofu, as some of the corn and soybeans used to make these products have been found to contain as much as 13 parts per million of the herbicide. (That may not sound like a lot, but it is a significant amount. And it's the maximum amount allowed by Federal law.)
Now, food waste is notoriously difficult to compost, especially "leftovers", which were often fried, salted, ketchuped, you name it. So I wouldn't be surprised if much of the food involved was actually 'raw'—wilted lettuce, apple cores, broccoli stalks and other things that get trashed as salads and such are prepared. So, since you've already been snooping around, I would suggest you snoop a little more; and specifically ask: a) what percentage of the raw ingredients was/is food; b) how much of the food was/is kitchen waste as opposed to tray scrapings; and c) how was it composted—with worms or some sort of advanced fermentation process? (You can't pile up lots of garbage in big open, outdoor systems; the vermin issues would be fast and furious.)
And commercially produced compost is supposed to be tested—so you should be able to get paperwork that shows the pH, nutrient content and any contaminants in the finished product.
But no matter what, your material is likely safer than compost made using factory farm manures or suspicious horse manure. Or grass clippings from a chemically treated lawn, which have also been shown to produce 'killer compost'. Or…
You get the idea. This is a dicey issue in a dicey world, and unfortunately, there is some weed killer in virtually every bite of "conventionally grown" corn and soy. (That unfortunate reality made me give up one of my favorite snack foods, which was otherwise great—high in fiber and low in salt and fat. But Mrs. McGrath's Little Baby Boy ain't be eatin' no Roundup.)
I suspect your compost is safe, perhaps wonderful. But you should always ask to see the paperwork with mass-produced compost. And give every new batch 'the duck test'—if it looks like good compost, smells like good compost and feels like good compost, it should be good compost. And finally: plant some bean and/or tomato seeds in the suspect compost (in a pot; BEFORE you spread or otherwise use the bulk of it); those plants are especially sensitive to these herbicide residues.
And if the paperwork is sketchy, the test plants don't thrive and/or the material doesn't seem quite ducky enough, don't use it. Instead buy one of the many high-quality, premium bagged composts or make your own; the tree leaves that are essential to great personal compost making are about to fall---all you have to do is shred them. You'll find lots more details on how to do so in our many previous composting articles—just mouse on over to the letter C!