Researchers
contend that manufactured nanomaterials—now popular in consumer
products such as shampoos, gels, hair dyes and sunscreens—may be
detrimental to the quality and yield of food crops, as reported in a
paper in the online edition of Proceedings of the National Academy of
Sciences.

Manufactured
nanomaterials (MNMs) are man-made materials produced by manipulating
matter on an atomic and molecular scale. Their effects on human health
and the environment are the subject of much scientific study.

“As
MNMs are used more and more in consumer products, there is a higher
likelihood that they will end up in wastewater treatment facilities,”
said lead researcher John Priester, an environmental scientist at the
Bren School of Environmental Science and Management at University of
California, Santa Barbara.

Conventionally-treated
wastewater is a primary source of normally nutrient-rich organic
materials applied to agricultural soil, and farmers beneficially use
this treated water and the biosolids from it as fertilizer. As MNMs
become more prevalent, there is concern about MNM buildup in soils and
possible MNM entry into the food supply.

Priester
and his research team reasoned that no single study had before examined
the full implications of environmental buildup of MNMs for a soil-based
food crop. The researchers sought to fill the knowledge gap by fully
growing soybean plants through the seed production stage in soil amended
with high-production nanomaterials.

Soybeans
are a major global commodity. They are the fifth-largest crop in global
agricultural production and second-largest crop in the United States.
Moreover in 2009, the United States exported enough of the crop to
create a $29.6 billion domestic soybean economy, making it a good
candidate for study.

The
research was funded primarily by the National Science Foundation. In
undertaking this study, Priester worked with scientists from NASA’s Jet
Propulsion Laboratory; Iowa State University; Xradia Corporation in
Pleasanton, Calif.; University of California, Riverside; Konkuk
University in Korea; USDA-Agricultural Research Service; and University
of Texas at El Paso.

The
researchers found that the two MNMs in their study—a cerium oxide
powder (nano- CeO₂) and zinc oxide (nano-ZnO)—could profoundly alter
soil-based food crop quality and yield.

Priester
and colleagues monitored plant growth by measuring stem length, leaf
count and leaf cover. Leaf cover estimates total leaf area, which is
affected by water stress and metal exposure and can indicate plant
health.

Most
surprising to Priester was the high level of zinc in the leaves and
beans of plants exposed to ZnO nanoparticles; the component metal was
taken up and distributed throughout edible plant tissues. “Also, the
shutdown of nitrogen fixation in root nodules at high CeO2
concentrations,” he said, noting that nano-CeO₂ diminished plant growth
and yield.

In
the case of the nano-ZnO treatment, the food quality was affected. In
the case of the nano-CeO₂, soil fertility was compromised.

“These
results indicate broader risks to the food supply,” the researchers
write in the paper. They go on to say the environment could be affected
even more since increased synthetic fertilizer would be required to
offset lost nitrogen fixation, a process that soybeans and other legumes
use to convert atmospheric nitrogen into natural fertilizer.

“These
are very significant findings; they highlight the importance of full
life-cycle tracking of manufactured nanomaterials in consideration of
environmental impacts,” said Alan Tessier, a program director in the
National Science Foundation’s Biology Directorate. “If the nanomaterials
tested in this paper were to move into the biosolids or irrigation
system used in agriculture, they could seriously harm agricultural
production.”

“Completely
preventing nanomaterials from entering agricultural soils may be
difficult,” said Priester. “Nanomaterials may be engineered, however, to
minimize impacts once they are released into the environment.”

He
said designing particles to dissolve very slowly, or coating them with
inert compounds, for example, could help prevent detrimental impacts on
crop foods.

In
the meantime, the researchers are examining the effects of ZnO and CeO₂
nanoparticles on other aspects of the soybean, such as the soil system,
looking for indicators of plant damage and changes to the microbial
community in the soil. They also are studying the speciation of the two
nanomaterials within the plant tissue, and how the uptake may have
changed micro- and macro-nutrients in soybeans.

In addition to the National Science Foundation, the U.S. Environmental Protection Agency supported the research.

Source: National Science Foundation