Study first to show processes determining fate of new RNA pesticides in soils

March 1, 2019 by Brandie Jefferson, Washington University in St. Louis
Credit: Washington University in St. Louis

A new generation of pesticides can be used to control pest insects by compromising the bug's ability to create essential proteins. These gene-silencing pesticides can be genetically engineered into agricultural crops such that these crops can literally grow their own defense.

New research from the McKelvey School of Engineering at Washington University in St. Louis shows how these emerging move through and degrade in soils. The research was published last month in Environmental Science & Technology.

Although the pesticide is created inside the plant, the questions about its degradation are similar to conventional pesticides applied externally to the crop: Does it break down? If so, under what conditions? In the soil? In lakes and rivers? What is the ecological risk?

Before these questions can be answered however, there needs to be a way to trace the pesticide and follow it as it moves and degrades in the ecosystem.

Kimberly Parker, assistant professor of energy, environmental & chemical engineering, and a team of collaborators devised a method to track this new pesticide in soils and to begin to understand what processes affect its lifespan.

This new pesticide is a molecule of double stranded Ribonucleic acid, or RNA. When a pest eats this pesticide, it prevents the critter from making essential proteins, leading either to stunted growth or to death.

RNA is a macromolecule—meaning: it's large—and because of its size, it cannot be studied through the typical means used for conventional pesticides.

The research team devised a method to tag a pesticide molecule with a radioactive atom, allowing them to follow it as it cycled through closed soil systems representing different scenarios. They were able to quantify the pesticide and its components at just a few nanograms per gram of soil.

With their method to measure the pesticide, the research team next investigated what happens to the pesticide in several . They found that the enzymes in soil can break down the pesticide. In addition, the microbes in soil "eat" the pesticide as well as the fragments left behind by the enzyme reactions.

However, in some soils, another process occurred: the pesticide attaches to the soil particles, like minerals and organic detritus. "In agricultural soil," Parker said, "there is adsorption"—when molecules adhere to a surface. "The pesticide sticks to the soil particle," she said.

"We have found that the soil particles may actually have a protective effect on the pesticide," Parker said, "slowing down the rate of pesticide degradation." The enzymes and microbes have a more difficult time breaking down pesticides that have attached to the soil, but the degree to which the soil protects the pesticide varied among the soils tested.

"Currently our working hypothesis is that in finer , there are more particles available for adsorption," Parker said. The more , the more surfaces for the pesticide to stick to, enhancing that protective effect.

"Now that we have identified the major processes controlling pesticide degradation in soils, we will next investigate in detail the variables that control these processes to enable accurate ecological risk assessment of double-strand RNA pesticides," Parker said. "This will allow us to understand whether or not these new pesticides pose a risk to ecosystems."

Explore further: Pesticides found in more than 80% of tested European soils

More information: Kimberly M. Parker et al. Environmental Fate of RNA Interference Pesticides: Adsorption and Degradation of Double-Stranded RNA Molecules in Agricultural Soils, Environmental Science & Technology (2019). DOI: 10.1021/acs.est.8b05576

Related Stories

Pesticides found in more than 80% of tested European soils

January 18, 2019

The industrialisation of agriculture has radically transformed the way most of our food is produced. By making large-scale production possible, it has led to more food being available at lower prices throughout the world. ...

The persistence of pesticides threatens European soils

November 27, 2018

The use of phytosanitary projects to combat weeds and other pests that affect the crops has led to an increase in the productivity of European agricultural crops in the last 50 years. Their use has been one of the principal ...

Improved prediction of pesticide residues

February 13, 2018

The use of pesticides can lead to a build-up of toxic and ecologically harmful residues in the soil. Until recently, it was not possible to ascertain in detail to which pesticides this applies and to what extent. Now, researchers ...

Common pesticide inhibits brain development in frogs

September 6, 2018

New research published in Environmental Toxicology & Chemistry reveals that low doses of a commonly used pesticide potentially harm the Northern Leopard frog by inhibiting their brain development.

Recommended for you

EPA adviser is promoting harmful ideas, scientists say

March 22, 2019

The Trump administration's reliance on industry-funded environmental specialists is again coming under fire, this time by researchers who say that Louis Anthony "Tony" Cox Jr., who leads a key Environmental Protection Agency ...

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.