Oil and gas wastewater that is used for irrigation may suppress plant immune systems, giving pause to the idea of using produced water for irrigation.

A team of researchers from Colorado State University, led by Professor Thomas Borch of the Department of Soil and Crop Sciences, conducted a greenhouse study using produced water from oil and gas extraction to irrigate common wheat crops. Their study, published in Environmental Science and Technology Letters, showed that these crops had weakened immune systems, leading to the question of whether using such wastewater for irrigation would leave crop systems more vulnerable to bacterial and fungal pathogens.

For every barrel of oil, oil and gas extraction also produces about seven barrels of wastewater, consisting mainly of naturally occurring subsurface water extracted along with the fossil fuels. That's about 2 billion gallons of wastewater a day, the Colorado State researchers said.

Keep on truckin'?

Typically, oil and gas wastewater, known as produced water, is trucked away from drilling sites and reinjected into the ground via deep disposal wells. The idea for using that water for irrigation has prompted studies testing things like crop yield, soil health and contaminant uptake by plants, especially since produced water is often high in salts, and its chemistry varies greatly from region to region.

The Colorado State team, which included researchers from the Colorado School of Mines, tried to determine whether irrigation water quality impacts crops' inherent ability to protect themselves from disease.

The experiments included irrigating wheat plants with tap water, two dilutions of produced water and a salt water control. Researchers exposed the plants to common bacterial and fungal pathogens and sampled the leaves after the pathogens were verified to have taken hold.

Using quantitative genetic sequencing techniques, the scientists determined that the plants watered with the highest concentration of produced water had "significant changes in expression of genes" plants normally use to fight infections. Their study didn't determine exactly which substances in the produced water correlated with suppressed immunity. They hypothesized that a combination of materials like boron, petroleum hydrocarbons and salt caused the plants to reallocate metabolic resources to fight stress, making it more challenging for them to produce disease-fighting genes.