Graphic showing that increasing exposure to cupric oxide bulk particles (BPs) and nanoparticles (NPs) by radish plants also increases the impact on growth with NPs showing the largest impact. From left to right, the exposure concentrations are 0; 100 parts per million (ppm) BPs; 1,000 ppm BPs; 100 ppm NPs; and 1,000 ppm NPs (showing a severely stunted plant). Credit: H. Wang, U.S. Environmental Protection Agency

Researchers
at the National Institute of Standards and Technology (NIST) and the
University of Massachusetts Amherst (UMass) have provided the first
evidence that engineered nanoparticles are able to accumulate within
plants and damage their DNA. In a recent paper, the team led by NIST
chemist Bryant C. Nelson showed that under laboratory conditions, cupric
oxide nanoparticles have the capacity to enter plant root cells and
generate many mutagenic DNA base lesions.

The
team tested the man-made, ultrafine particles between 1 and 100 nm in
size on a human food crop, the radish, and two species of common
groundcovers used by grazing animals, perennial and annual ryegrass.
This research is part of NIST’s work to help characterize the potential
environmental, health and safety (EHS) risks of nanomaterials, and
develop methods for identifying and measuring them.

Cupric
oxide (also known as copper (II) oxide or CuO) is a compound that has
been used for many years as a pigment for coloring glass and ceramics,
as a polish for optics, and as a catalyst in the manufacture of rayon.
Cupric oxide also is a strong conductor of electric current, a property
enhanced at the nanoscale level, which makes the nanoparticle form
useful to semiconductor manufacturers.

Because
cupric oxide is an oxidizing agent—a reactive chemical that removes
electrons from other compounds—it may pose a risk. Oxidation caused by
metal oxides has been shown to induce DNA damage in certain organisms.
What Nelson and his colleagues wanted to learn was whether nanosizing
cupric oxide made the generation and accumulation of DNA lesions more or
less likely in plants. If the former, the researchers also wanted to
find out if nanosizing had any substantial effects on plant growth and
health.

To
obtain the answers, the NIST/UMass researchers first exposed radishes
and the two ryegrasses to both cupric oxide nanoparticles and larger
sized cupric oxide particles (bigger than 100 nm) as well as to simple
copper ions. They then used a pair of highly sensitive spectrographic
techniques** to evaluate the formation and accumulation of DNA base
lesions and to determine if and how much copper was taken up by the
plants.

For
the radishes, twice as many lesions were induced in plants exposed to
nanoparticles as were in those exposed to the larger particles.
Additionally, the cellular uptake of copper from the nanoparticles was
significantly greater than the uptake of copper from the larger
particles. The DNA damage profiles for the ryegrasses differed from the
radish profiles, indicating that nanoparticle-induced DNA damage is
dependent on the plant species and on the nanoparticle concentration.

Finally,
the researchers showed that cupric oxide nanoparticles had a
significant effect on growth, stunting the development of both roots and
shoots in all three plant species tested. The nanoparticle
concentrations used in this study were higher than those likely to be
encountered by plants under a typical soil exposure scenario.

“To
our knowledge, this is first evidence that there could be a ‘nano-based
effect’ for cupric oxide in the environment where size plays a role in
the increased generation and accumulation of numerous mutagenic DNA
lesions in plants,” Nelson says.

Next
up for Nelson and his colleagues is a similar study looking at the
impact of titanium dioxide nanoparticles—such as those used in many
sunscreens—on rice plants.

Copper Oxide Nanoparticle Mediated DNA Damage in Terrestrial Plant Models

Source: NIST