"Atrazine is selective. It tends to be more active on broad-leaf plants than it is on grass plants
The first, I'll call it residual, pre-emergent herbicide that you would apply to the soil to control a weed before the weed germinated would have been Atrazine. And Atrazine became the most widely used herbicide across the Corn Belt shortly thereafter. It probably isn't the most widely used herbicide right now. But it certainly was through the '60s, '70s, '80s and '90s
Now, in contrast to 2, 4-D the reason that Atrazine doesn't kill a corn plant is not anything to do with the structure of the corn plant, but it's the fact that the corn plant has a biochemical pathway that allows it to detoxify Atrazine extremely rapidly. It can just Corn plants can detoxify 10, 20 times the normal use-rate of Atrazine. They just have, if you will, excess capacity to detoxify. And most broad-leaf plants don't have that same pathway. So, they simply can't get rid of the toxin
"A lot of times an herbicide would first come out. And we would discover they had potential for controlling weeds and not injuring the crop, but without fully understanding how or why it didn't injure the crop. Now, we knew 'what' but not 'why.' In other words, you treat the crop and the weeds. And the 'what' is, it killed the weeds [and] didn't hurt the crop. But 'why?' That's a slower process to figure out why that happened.
"But to accompany that, before any of these products were introduced to the market, a standard set of toxicology experiments had to be conducted to make sure that they didn't result in a risk to the ultimate consumer. Again, we might not know why the Atrazine would not be found in the corn plant. We knew it wasn't there, but we don't know why. Later we found out that the plant was able to degrade it. So you know, it's like everything else. We find out 'what' usually before we find out 'why.'
"Two things have been at issue with Atrazine. Some cases we find it in surface water. And it's not hard to think of how it comes in surface water. If you use Atrazine on sloping land, very sloping land, and you think about when we use it we plant corn in the spring. If you prepare a seedbed, there's no cover on the land. We tend, especially in the central U.S., to get strong thunderstorms, high intensity rains which results in runoff. And so on sloping land if a high percentage of land is cultivated clear cultivated, clean cultivated and a high percentage of the land is treated with Atrazine, we're applying the material during that window in the spring when we have the risk of these high-intensity storms which are the biggest contributor to runoff. So, many other compounds we use would also have runoff under those circumstances. But the reason Atrazine was found more widely and in higher concentration is it was used so widely. It was used on 80 percent of the corn in Nebraska. We don't have any other compound that was used anywhere near that extensively. Now, so, since that issue has been identified as a problem, there are regulations in place regarding Atrazine use on sloping or steeply sloping land because if you don't have a topography that causes runoff obviously you don't have a serious runoff issue.
"It also Atrazine has been found in groundwater. And by groundwater, I mean water that you might extract from a well. And there is a lot of debate but pretty good evidence, at this point, that most of the groundwater contamination comes from using Atrazine and two things happen. Either using it in an environmentally sensitive site. By that I mean where the water table is fairly shallow 10, 12, 15 feet from the surface and you have sandy soil above. Water and Atrazine are going to move through sand more readily than they do through a clay-loam soil
"The other place and it's been a significant contribution to groundwater contamination is so called 'point source.' By point source, I mean somehow it's seeped into a well or some other conduit directly to the water table
"And it has a lifespan in the soil. Our normal figures the half-life would range perhaps 35 or 40 days. And so, it doesn't degrade so rapidly that its gone even on sandy soils it could get to the water table before it degrades. So, it's longevity and it's mobility along with its widespread use contributed to Atrazine being found in the water table." "