Scientists Study the Effects of Manufactured Nanoparticles on Agriculture

The team was led by sci­en­tists at UC Santa Barbara’s Bren School for Environmental Science & Management. The team is also affil­i­ated with the UC Center for Environmental Implications of Nanotechnology (CEIN), a $24 mil­lion col­lab­o­ra­tion based at UCLA, with researchers from UCSB, UC Davis, UC Riverside, University of Texas at El Paso, Columbia University, and other national and inter­na­tional part­ners. The results of the study are pub­lished this week in the Proceedings of the National Academy of Sciences.

“Our soci­ety has become more envi­ron­men­tally aware in the last few decades, and that results in our gov­ern­ment and sci­en­tists ask­ing ques­tions about the safety of new types of chem­i­cal ingre­di­ents,” said senior author Patricia Holden, a pro­fes­sor with the Bren School. “That’s reflected by this type of research.”

She explained that the research, which is funded by the National Science Foundation (NSF) and the U.S. Environmental Protection Agency (EPA), is help­ing to dis­cover poten­tial envi­ron­men­tal impli­ca­tions of a new indus­try that includes nano­ma­te­ri­als. The ulti­mate goal is to help find more envi­ron­men­tally com­pat­i­ble sub­sti­tutes, Holden said.

Soybean was cho­sen for the study due to its impor­tance as a food crop—it is the fifth largest crop in global agri­cul­tural pro­duc­tion and sec­ond in the U.S.—and because it is vul­ner­a­ble to MNMs. The find­ings showed that crop yield and qual­ity are affected by the addi­tion of MNMs to the soil.

The sci­en­tists stud­ied the effects of two com­mon nanopar­ti­cles, zinc oxide and cerium oxide, on soy­beans grown in soil in green­houses. Zinc oxide is used in cos­met­ics, lotions, and sun­screens. Cerium oxide is used as an ingre­di­ent in cat­alytic con­vert­ers to min­i­mize car­bon monox­ide pro­duc­tion, and in fuel to increase fuel com­bus­tion. Cerium can enter soil through the atmos­phere when fuel addi­tives are released with diesel fuel combustion.

The zinc oxide nanopar­ti­cles may dis­solve, or they may remain as a par­ti­cle, or re-form as a par­ti­cle, as they are processed through waste­water treat­ment. At the final stage of waste­water treat­ment there is a solid mate­r­ial, called biosolids, which is applied to soils in many parts of the U.S. This solid mate­r­ial fer­til­izes the soil, return­ing nitro­gen and phos­pho­rus that are cap­tured dur­ing waste­water treat­ment. This is also a point at which zinc oxide and cerium oxide can enter the soil.

The sci­en­tists noted that the EPA requires pre­treat­ment pro­grams to limit direct indus­trial metal dis­charge into pub­licly owned waste­water treat­ment plants. However, the research team con­veyed that “MNMs—while mea­sur­able in the waste­water treat­ment plant systems—are nei­ther mon­i­tored nor reg­u­lated, have a high affin­ity for acti­vated sludge bac­te­ria, and thus con­cen­trate in biosolids.”

The authors pointed out that soy­bean crops are farmed with equip­ment pow­ered by fos­sil fuels, and thus MNMs can also be deposited into the soil through exhaust.

The study showed that soy­bean plants grown in soil that con­tained zinc oxide bioac­cu­mu­lated zinc; they absorbed it into the stems, leaves, and beans. Food qual­ity was affected, although it may not be harm­ful to humans to eat the soy­beans if the zinc is in the form of ions or salts, in the plants, accord­ing to Holden.

In the case of cerium oxide, the nanopar­ti­cles did not bioac­cu­mu­late, but plant growth was stunted. Changes occurred in the root nod­ules, where sym­bi­otic bac­te­ria nor­mally accu­mu­late and con­vert atmos­pheric nitro­gen into ammo­nium, which fer­til­izes the plant. The changes in the root nod­ules indi­cate that greater use of syn­thetic fer­til­iz­ers might be nec­es­sary with the buildup of MNMs in the soil.

Holden com­mented on the like­li­hood of high con­cen­tra­tions of these nanopar­ti­cles in agri­cul­ture: “There could be hotspots, places where you have accu­mu­la­tion, includ­ing near man­u­fac­tur­ing sites where the mate­ri­als are being made, or if there are spills. We have very lim­ited infor­ma­tion about the quan­tity or state of these syn­thetic nano­ma­te­ri­als in the envi­ron­ment right now. We know they’re being used in con­sumer goods, and we know they’re going down the drain.”

First author John H. Priester is a staff sci­en­tist in the Holden lab at UCSB. Other co-authors from UC CEIN are Yuan Ge, Randall E. Mielke, Allison M. Horst, Shelly Cole Moritz, Roger M. Nisbet, Joshua P. Schimel, Jose A. Hernandez-Viezcas, Lijuan Zhao, and Jorge L. Gardea-Torresdey. Co-authors Katherine Espinosa and Reid G. Palmer are affil­i­ated with Iowa State University; Jeff Gelb is affil­i­ated with Xradia Corporation; and Sharon L. Walker is with UC Riverside. NASA/JPL-Caltech, the USDA, and The University of Texas at El Paso were sub­stan­tially involved in the research.

Source: University of California – Santa Barbara Release