Cactus collects toxic selenium

Too much selenium in field soil is not a common concern, but it is for parts of California’s San Joaquin Valley. Having too much selenium end up in run-off water is a problem for fish, migratory birds and other wildlife that drink the water from different waterways including drainage ditches.

Cumulating that excess selenium to keep it out of the water has been the goal of a U.S. Department of Agriculture, Agriculture Research Service scientist’s research. And he has discovered that a specific plant grown near where selenium-laced water is headed to waterways takes up the chemical and volatilizes it.

The helpful plant is the prickly pear cactus (Opuntia ficus-indica), and the soil scientist is Gary Bañuelos working at the San Joaquin Valley Agricultural Sciences Center in Parlier, Calif.    `

Bañuelos has spent three years evaluating five prickly pear varieties from Mexico, Brazil, and Chile for salt and boron tolerance in selenium-laden soils by collecting soils and sediments from the area and growing the varieties in field test plots. He showed that prickly pear grow reasonably well in the poor quality soils with very little water.

The studies also showed that the plants took up selenium, volatizing some of it and keeping some in their fruit and leaf-like stems (cladodes), and that tolerance to salinity and boron depends on the genotype. The cactus variety from Chile showed the highest tolerance, as well as being the best at producing fruit and accumulating and volatizing selenium. The work is continuing with a focus on selecting specific varieties that can be used as bioremediation tools.