Too Much Technology May Be Killing Beneficial
Bacteria
May 2, 2008
MU engineer concerned about environmental impact of silver nanoparticles in
wastewater treatment
Columbia, MO — Too much of a good thing could be harmful to the environment.
For years, scientists have known about silver's ability to kill harmful
bacteria and, recently, have used this knowledge to create consumer products
containing silver nanoparticles. Now, a University of Missouri researcher
has found that silver nanoparticles also may destroy benign bacteria that
are used to remove ammonia from wastewater treatment systems. The study was
funded by a grant from the National Science Foundation.
Several products containing silver nanoparticles already are on the market,
including socks containing silver nanoparticles designed to inhibit
odor-causing bacteria and high-tech, energy-efficient washing machines that
disinfect clothes by generating the tiny particles. The positive effects of
that technology may be overshadowed by the potential negative environmental
impact.
"Because of the increasing use of silver nanoparticles in consumer products,
the risk that this material will be released into sewage lines, wastewater
treatment facilities, and, eventually, to rivers, streams and lakes is of
concern," said Zhiqiang Hu, assistant professor of civil and environmental
engineering in MU's College of Engineering. "We found that silver
nanoparticles are extremely toxic. The nanoparticles destroy the benign
species of bacteria that are used for wastewater treatment. It basically
halts the reproduction activity of the good bacteria."
Hu said silver nanoparticles generate more unique chemicals, known as highly
reactive oxygen species, than do larger forms of silver. These oxygen
species chemicals likely inhibit bacterial growth. For example, the use of
wastewater treatment "sludge" as land-application fertilizer is a common
practice, according to Hu. If high levels of silver nanoparticles are
present in the sludge, soil used to grow food crops may be harmed.
Hu is launching a second study to determine the levels at which the presence
of silver nanoparticles become toxic. He will determine how silver
nanoparticles affect wastewater treatment processes by introducing
nanomaterial into wastewater and sludge. He will then measure microbial
growth to determine the nanosilver levels that harm wastewater treatment and
sludge digestion.
The Water Environment Research Foundation recently awarded Hu $150,000 to
determine when silver nanoparticles start to impair wastewater treatment. Hu
said nanoparticles in wastewater can be better managed and regulated. Work
on the follow-up research should be completed by 2010.
The silver nanoparticle research conducted by Hu and his graduate student,
Okkyoung Choi, was recently published in Water Research and Environmental
Science & Technology.
SOURCE: University of Missouri
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