Are GMOs safe? Define 'safe'

GMO: thumbs up or thumbs down?
People tend to feel strongly about genetically modified organisms, all good or all bad, but of course the story is too complex for a simple up or down. Organisms are genetically modifed for many reasons including to protect against disease, or to protect against pesticides or herbicides, but also to alter some characteristic such as ability to withstand freezing temperatures (tomatoes) or to speed their growth (salmon).  Each case needs to be evaluated on its own merits.

This undated 2010 handout photo provided by AquaBounty Technologies shows two 18 month old salmon, a genetically modified salmon, rear, and a non-genetically modified salmon, foreground.  (AP Photo/AquaBounty Technologies, Huffington Post)

GMO oranges
Amy Harmon had a piece in the New York Times a few weeks ago reporting on sour orange disease affecting oranges in Florida and around the world, and efforts to genetically modify trees to be resistant to the bacterium that's killing them.  No citrus that is naturally resistant has been found, so no 'natural' solution to the problem was possible.  Instead, after a number of transgenic trials, a gene from the spinach plant that attacks the bacterium has been introduced into orange trees for testing.  It's too early to know whether or not it will save oranges, but it seems more likely than any other transgene tried to date.

Harmon notes in her piece that, "Leading scientific organizations have concluded that shuttling DNA between species carries no intrinsic risk to human health or the environment, and that such alterations can be reliably tested."  The link there is to a 2012 statement by the American Association for the Advancement of Science on GMOs, which begins:

There are several current efforts to require labeling of foods containing products derived from genetically modified crop plants, commonly known as GM crops or GMOs. These efforts are not driven by evidence that GM foods are actually dangerous. Indeed, the science is quite clear: crop improvement by the modern molecular techniques of biotechnology is safe. Rather, these initiatives are driven by a variety of factors, ranging from the persistent perception that such foods are somehow “unnatural” and potentially dangerous to the desire to gain competitive advantage by legislating attachment of a label meant to alarm. Another misconception used as a rationale for labeling is that GM crops are untested.

So, broadly speaking, science says GMOs are safe, it's lay people who say it's not.  But not so fast.  Leading food reporter Michael Pollan took issue with Harmon's treatment of the GMO question.  He said on Twitter in a now famous 140 characters, that the piece included too many industry talking points, and he then went on vacation without following up.  He has now explained himself to a reporter for the Columbia Journalism Review, and Harmon responds. Their differences seem primarily to be differences in worldview, rather than arguments over facts -- Pollan critiques Harmon for not challenging the monoculture approach to orange growing, among other things, for example and Harmon responds that she was talking about a single problem, not the general issue.  And so on. 

Harmon's piece does pick up on the widespread misconceptions about GMOs.  She quotes someone wondering if their orange juice will now be green, with the spinach gene introduced into the trees.  It's certainly true that much of the mistrust of transgenics is based on faulty knowledge about genetics and the technology itself, but there is also some well-grounded mistrust, fueled by science.

In the US most of our corn, soy, canola oil and others is transgenic.  We've been eating it for years, to apparently no ill effect, or at least none that has been clearly documented. But it's not only human health that is of concern.  There are also environmental issues.  Glyphosate resistant weeds, for example.  Monsanto's Roundup Ready transgenic crops, bred to be resistant to glyphosate-containing herbicides, have led to "superweeds", weeds that are also resistant to glyphosate, and thus require more toxic herbicides to kill. We've written about this subject before (here, e.g.), but it's also all over the web.

Similarly, transgenic crops, bred to be resistant to pesticides, have naturally lead to resistant pests, and the increased use of more toxic pesticides, and other sequelae (we wrote about that here, but this issue, too, is all over the web). Transgenic orange trees bred to kill bacteria could potentially lead to a similar kind of problem, with intense selection for bacteria that are able to resist.  That's evolution.  Only time will tell if this becomes a problem. 

GMO rice 
So, even if Monsanto's Roundup Ready crops are benign for human consumption, there are environmental consequences.  And the mistrust of GM is likely to spread, given new evidence.  A paper published in New Phytologist (Wang et al.) and described in Nature last week, addresses the concern of gene flow from transgenic crops to their wild relatives.  The paper describes the results of introduction of the Monsanto RoundUp Ready transgene into weedy rice.  Wang et al. introduced the gene experimentally, but it also does happen in the field naturally.

Weedy rice can pick up transgenes from genetically modified crop rice through cross-pollination.

XIAO YANG; Nature Aug 16 2013

They. found that the transgenic weedy rice, a noxious weed that infests rice fields everywhere, "produced 48-125% more seeds per plant than nontransgenic controls in monoculture- and mixed-planting designs without glyphosate application."  That is, the weedy rice with the transgene seems to have substantial fitness advantages, even when not exposed to the herbicide.  (This still needs to be replicated -- see Andrew Kniss's blog post for discussion.  But if it's not true in this particular case, everything we know about evolution suggests it could be, and it's only a matter of time.)  And, hybridization, "pollen-mediated gene flow from rice to weedy rice has been reported."  If this is so, Wang et al. can't say whether it's also true of other plants or whether weedy rice is unique, but if increasing herbicide resistance in a crop increases the hardiness of an already noxious weed, this is potentially a huge problem.

And this is aside from the problem of the spontaneous evolution of resistance to glyphosate that has been documented in at least 24 weed species.  The superweeds.  Wang et al. write, "Our findings have broad implications for plant biology, crop breeding, weed management, biotech risk assessment, and the ongoing evolution of herbicideresistant weeds."

So, are genetically modified organisms safe?  It depends on what you mean by 'safe'.