One of the common criticisms of commercially available Genetically Engineered (GE) seeds is the idea that they have led to an increase in pesticide use. In actuality, it turns out that they’ve corresponded to a decrease in total pesticide use, but this is attributable primarily to insect resistant GE crops, and critics argue that herbicide resistant crops have led to an increase in herbicide usage. It is true that the rise in popularity of glyphosate-resistant (GR) crops in particular has coincided with an increase in the use of glyphosate, which had already been in use to some degree for a couple of decades before the implementation of glyphosate-resistant crops. However, what critics invariably fail to mention is that its rise in popularity also coincided with the phasing out of other herbicides, most of which were significantly more toxic than glyphosate (about which I’ve written in detail here).
The purpose of this article is not to claim that glyphosate and GR crops are the be all end all of weed control (they’re not), nor is it to claim that they were causally responsible for any and every desirable change we see in herbicide usages patterns. Rather, the purpose of this is to show that when opponents of GE technology and of glyphosate claim that GR crops are bad on the grounds that they increased glyphosate use, they are leaving out critical information that would be highly inconvenient for their narrative.
It’s important to note that the data upon which these usage timeline graphs are based is very USA-centric. Perhaps a timeline and analysis of herbicide usage patterns in other places would be a good topic for another article, but the US is not a bad place to start because we do cultivate a lot of glyphosate-resistant crops here, as well as a lot of GE crops in general.
What were some of these herbicides?
Alachlor was one of them. The EPA states the following about alachlor:
According to the EPA’s Water division:
“The greatest use of alachlor is as a herbicide for control of annual grasses and broadleaf weeds in crops, primarily on corn, sorghum and soybeans.”
“Some people who drink water containing alachlor well in excess of the maximum contaminant level (MCL) for many years could have problems with their eyes, liver, kidneys, or spleen, or experience anemia, and may have increased risk of getting cancer.”
The EPA and OSHA list alachlor as a Class L1 Carcinogen, which means they consider it likely to be carcinogenic at high doses but not at low doses. With an LD50 of between 930 mg/kg and 1,350 mg/kg in rats, and between 1,910 and 2,310 mg/kg in mice, its acute toxicity is not generally considered to be a big concern (although you may notice that it is still noticeably more acutely toxic than glyphosate which has an LD50 of 5,600 mg/kg). However, its potential for chronic toxicity remains a concern, particularly for the liver, spleen and kidneys (according to its PMEP profile) , and its NOAEL varied depending on the duration of the study in question.
Okay then. What else? How about Cyanazine?
Cyanazine has an LD50 of between 182 and 332 mg/kg in rats and 380 mg/kg in mice (far more acutely toxic than glyphosate or alachlor), but its long term effects and NOAEL varied from anywhere around 0.198 to 3.3 mg/kg depending on which study you look at (as you may read more about in this WHO report). Although cyanazine is not known to be carcinogenic for certain, it has been observed to affect the central nervous system upon over-exposure and to increase liver weight while decreasing body weight gain.
Cyanazine was eventually put under special review due to concerns over its possible cancer-causing potential. DuPont voluntarily discontinued it in 1999, and its sale in the US was officially prohibited by 2002.
So, needless to say, cyanazine use went way down rather abruptly. What else? According to PMEP, Fluazifop “is a selective phenoxy herbicide used for postemergence control of annual and perennial grass weeds. It is used on soybeans and other broad-leaved crops such as carrots, spinach, potatoes, and ornamentals.”
Fluazifop hasn’t gone away completely, but its use did decline quite significantly, possibly thanks in part to the introduction of glyphosate resistant soybeans. How toxic is it though? its LD50 was 3,680 for male rats and 2,451 for female rats, which is only a little bit more acutely toxic than glyphosate, but PMEP notes the following:
“A single dose of the formulated compound (Fusilade 2000) can cause severe stomach and intestine disturbance. Ingestion of large quantities may cause problems in the central nervous system such as drowsiness, dizziness, loss of coordination and fatigue. Breathing small amounts of the product may cause vomiting and severe lung congestion. This may ultimately lead to labored breathing, coma and death.”
So, yeah. There’s that. The good news is that there was no evidence of chronic toxicity in rats under 10 mg/kg per day in 90 day trials.
The next one up is metolachlor.
Technical grade Metolachlor has an LD50 of between 1,200-2780 mg/kg in rats. That’s between twice and 4.67 times the acute toxicity of glyphosate. Additionally, with an NOAEL of roughly 90 mg/kg/day, metolachlor can exhibit chronic toxic effects at doses MUCH smaller than the levels at which it becomes acutely toxic. Symptoms of human intoxication from metolachlor include abdominal cramps, anemia, shortness of breath, dark urine, convulsions, diarrhea, jaundice, weakness, nausea, sweating, and dizziness.
Okay. Great, but what about Atrazine? In 1996 Atrazine was the #1 herbicide for corn. 2 and 3 were cyanazine and alachalor which, as we just saw, have effectively been zeroed out.
Well, apparently the rise of GR crops has had little to no effect on atrazine usage in the US. This might come as both a surprise and a disappointment to some because atrazine is known to degrade very slowly in soil (often lasting for months) and has been known to inadvertently end up in drinking water, a fact which contributed to it being banned in the EU. It’s also a suspected endocrine disruptor and is more acutely toxic than glyphosate (with an LD50 of 672 to 3,000 mg/kg in rats). The EPA also classified it as a possible carcinogen, and multiple undesirable biochemical and morphological changes in various organs have been observed in high dose studies of its chronic toxicity. That’s probably not what most of my readers wanted to hear. However, part of being a responsible skeptic is understanding the importance of not cherry picking data. Additionally, we may be able to learn something by asking why this is the case. While at first glance this result is not so exciting, bear in mind that resistant weeds have increased quite a bit without increasing use AND corn production is greatly increased (by about 54%) since 1996, so use per bushel is down (as is use per capita because the population is up in the US by about 50 million people since then). Alright then. That’s not as spectacular as those previous examples, but at least it wasn’t a total bust.
What else? How about Metribuzin?
In 1992, over 2.5 million lbs of metribuzin was used just on soybeans alone. After that, its usage on fruits and vegetables didn’t change too drastically, but we can see that its use on soybeans and its overall use dropped dramatically. It eventually started climbing back up, and there a number of possible reasons for that, but it did initially go down, particularly in soybeans (for which a glyphosate-resistant variety was introduced by Monsanto in 1996). Metribuzin’s LD50 is 1,090 to 2,300 mg/kg in rats, which is about 2.5 to 5 times as toxic as glyphosate. None of the studies looking at chronic toxicity revealed any negative effects at any of the dosages tested.
Another one that was popular in the mid 90s in the US was Nicosulfuron.
The acute toxicity of Nicosulfuron is not much worse than glyphosate, with an estimated LD50 of in excess of 5,000 mg/kg of body mass. As for chronic toxicity, its NOAEL was found to be about 125 mg/kg/day, and its LOAEL (Lowest Observed Adverse Effect Limit) was found to be 500 mg/kg/day according to the EPA.
If you’ve made it this far, you may be wondering how this data was obtained. The website was created by USGS National Water Quality Assessment (NAWQA) Program.
“The pesticide-use maps provided on this web site show the geographic distribution of estimated use on agricultural land in the conterminous United States for numerous pesticides (active ingredients). Maps were created by allocating county-level use estimates to agricultural land within each county. A graph accompanies each map, which shows annual national use by major crop for the mapped pesticide for each year.
Methods for generating county-level pesticide use estimates are described in Estimation of Annual Agricultural Pesticide Use for Counties of the Conterminous United States, 1992–2009 (Thelin and Stone, 2013) and Estimated Annual Agricultural Pesticide Use for Counties of the Conterminous United States, 2008-12 (Baker and Stone, 2015). Two different methods, EPest-low and EPest-high, were used to estimate a range of use, with the exception of estimates for California, which were taken from annual Department of Pesticide Regulation Pesticide Use Reports (Baker and Stone, 2015).”
A PDF copy of the entire Thelin and Stone report can be found here, but their quick summary of the data sources is as follows:
“Data sources used to develop EPest pesticide-by-crop use rates and annual pesticide-use estimates by county included the following: (1) proprietary pesticide-by-crop use estimates reported for CRDs; (2) USDA county harvestedcrop acreage reported in the 1992, 1997, 2002, and 2007 Census of Agriculture (http://www.agcensus.usda.gov/), and NASS annual harvested-crop acreage data collected from crop surveys for non-census years (http://quickstats.nass.usda. gov/); (3) boundaries for CRDs and counties; (4) regional boundaries derived from USDA Farm Resource Regions; and (5) pesticide-use information from California DPR-PUR. Each of these sources is described in following sections.”
The USGS also includes this statement on the strengths and limitations of the data:
“Pesticide use estimates from this study are suitable for making national, regional, and watershed assessments of annual pesticide use, however the reliability of estimates generally decreases with scale. For example, detailed interpretation of use intensity distribution within a county is not an appropriate use. Although county-level estimates were used to create the maps and are provided in the dataset, it is important to understand that surveyed pesticide-by-crop use was not available for all CRDs and, therefore, extrapolation methods were used to estimate pesticide use for some counties. Surveyed pesticide-by-crop use may not reflect all agricultural use on all crops grown. In addition, state-based restrictions on pesticide use were not incorporated into EPest-high or EPest-low estimates. EPest-low estimates are more likely to reflect these restrictions than EPest-high estimates. With these caveats in mind, including other details discussed in Thelin and Stone (2013) and Baker and Stone (2015), the maps, graphs, and associated county-level use data are critical data for water-quality models and provide a comprehensive graphical overview of the geographic distribution and trends in agricultural use in the conterminous United States.”
Many people never even hear about the herbicides that were phased out in favor of glyphosate simply because they aren’t pertinent to the anti-agricultural biotech narrative, and because their popularity had waned by the time it had become trendy to demonize GMOs and everything remotely associated with them.
I said this before, and I’ll say it again:
“Opponents of glyphosate often seem to hold this unfounded notion that, if they can manage to get glyphosate banned or simply willingly abandoned, then it would mean an improvement in both food and environmental safety, but the truth is it would likely be the exact opposite of that. Weeds are a legitimate problem in farming that has to be dealt with one way or another. In its absence, it would have to be replaced with something else, and it would likely be something more caustic: not less.”
– Credible Hulk.
Check out my Facebook page.
I also help run Stop the Anti-Science Movement.