Where is the evidence to suggest that evaporated dicamba is able to condense in sufficient quantity to effect plants at a distance?
I've lived among large production farm, much of my life. The application of spray products (keyword: sprayers that produce mists of liquid products) are easily caught and carried by the lightest winds.
Dicamba does not "evaporate" in any appreciable amount. It is highly soluble in water and has a melting point 237-241 degrees F.... The water would evaporate, leaving the chemical behind.
Bob Scott, a weed scientist at the University of Arkansas, recently showed me some experiments that he and his colleagues conducted. They sprayed trays of soil with dicamba, then placed those trays in a field of soybeans far from any dicamba spraying. The soybean plants next to the dicamba-treated soil showed clear signs of exposure to the chemical.
"We had a lot of volatility in these trials, a lot of movement" in unpredictable directions, Scott says. It wasn't what they were hoping to see, Scott says, but the results "do help explain why we had 966 complaints in our state."
The evidence is the study in which they applied Dicamba as directed to waterproof trays of dirt in one field. They then trucked the trays of dirt to another field, and laid them between rows of non-resistant crops. The crops died, showing that the Dicamba in the trays must have affected the crops.
Water has a melting point of 212F. Nonetheless, it evaporates, and does not all stay behind.
Water boils at 212F, melts at 32F. It is a sufficient model of evcaporation. For dicamaba to have a sufficient concentration to harm (even targeted plants) it must be rather concentrated, compared to what one might find in concentrations produced by condensation (one field over). Having a degree in organic chemistry and thousands of hours of bench chemistry, I can speak with some authority on the matter.
Liquid water has a vapor pressure, dependent mostly on temperature. When this vapor pressure exceeds the partial pressure of the water in the gas phase, water crosses the phase barrier. This is how you can have trace measurements of water vapor in (1 bar) air that is cooler than 100 degC.
Some volatile chemicals--such as the acetone in nail polish remover--are detectable as odors even when their temperature is well below their boiling point. This is the liquid phase establishing an equilibrium with the gas phase at that temperature. The most energetic molecules in the liquid escape into the gas (cooling the liquid in the process).
Imagine a lake in a desert. The maximum daytime temperature in that desert is 40 degC, well below the boiling point of 100 degC. The lake has no outflows. Over the course of a month, the lake disappears. Where did the water go? It evaporated, and the water in the gas phase blew away and was replaced by dry air, thus allowing more of the liquid water to evaporate. If you put an airtight dome over it, the lake would stay put, and the air in the dome would get very humid. You would probably also be able to see condensation on its walls, as the vapor movement continuously transfers heat from the lake to the dome.
The dicamba is likely evaporating from the soil into air with no gaseous dicamba in it, blowing to adjacent fields, and the plants are uptaking it as a gas via their normal respiration. No condensation is required, for the same reason that plants don't eat dry ice to get their CO2. Once inside the plant, the vapor dicamba is free to dissolve into the plant's own water. It is not necessary for it to dissolve in water outside the plant to be taken up by the roots. Those plant cells might not have a lot of water in them, or they might be filled to bursting with it. Plants have to deal with deluge and drought differently than we animals do.
The questions everyone have to ask are what concentration of dicamba is damaging to the plant, and what is the exact relationship between wind, distance, ambient moisture, and concentration? By calculating from the vapor pressure vs temperature of the chemical, and solubility, you should be able to draw a plume-shaped area on a map that shows where dicamba-vulnerable plants will die after an application. If plants outside that area die, something in your model is wrong. And people are claiming that plants outside the area are dying. What part of the model is wrong? Based on the article, it seems like the volatility is off.
Why do you think it needs to condense to harm plants?
Why do you think the melting point matters? Camphor has a melting point of ~350F and still has sufficient vapor pressure to serve as an insect repellent.
IANAS, but my understanding is that plants leaves are porous, they interact with and exchange gas with the environment. It's one of the things they are most known to do.
I've noticed a lot of comments like this showing up on Reddit when Monsanto is mentioned. Are they paying a PR firm to gaslight for them on social media?
IIRC the temperature of the H2O doesn't change until the bonds have changed. There is a state of constant temperature during this phase change, often referred to as a temperature plateau. Therefore it melts @ 32F (assuming 1 atmosphere of pressure) after that the temperature of the liquid water will rise, but not until it has already melted.
I've lived among large production farm, much of my life. The application of spray products (keyword: sprayers that produce mists of liquid products) are easily caught and carried by the lightest winds.
Dicamba does not "evaporate" in any appreciable amount. It is highly soluble in water and has a melting point 237-241 degrees F.... The water would evaporate, leaving the chemical behind.