Anne Kahru talks with
ScienceWatch.com and answers a few questions about
this month's Fast Breaking Paper in the field of
Article Title: Toxicity of nanosized and bulk ZnO,
CuO and TiO2 to bacteria Vibrio fischeri and
crustaceans Daphnia magna and Thamnocephalus
Authors: Heinlaan, M;Ivask, A;Blinova, I;Dubourguier,
Year: APR 2008
* Natl Inst Chem Phys & Biophys, Akadeemia Tee 23,
EE-12618 Tallinn, Estonia.
* Natl Inst Chem Phys & Biophys, EE-12618 Tallinn,
(addresses have been truncated)
Why do you think your paper is highly
This research paper is novel and very timely considering that there are
widespread urgent concerns regarding the environmental implications of
nanotechnologies/nanoparticles (NP). First, we provided valuable and
reliable quantitative information on the ecotoxicity of three metal oxide
nanoparticles (TiO2, ZnO and CuO) that could be used for
environmental risk assessment purposes. Secondly, this paper presents the
first evaluation of the toxicity of TiO2, ZnO, and CuO to
bacteria Vibrio fischeri and crustaceans Thamnocephalus
platyurus. Also, this was the first study of nano ZnO and nano CuO
toxicity for crustaceans Daphnia magna—one of the "gold
standard" organisms in aquatic toxicology.
Does it describe a new discovery, methodology, or synthesis of
It is also one of the first papers that showed that the solubilisation of
metal-containing nanoparticles is the key factor in their (aquatic)
toxicity. Metal oxide particles do not necessarily have to enter the cells
to induce the toxic effects but the solubilised ions will "do the job."
That, of course, does not necessarily mean that the particles themselves
are harmless—the toxic effects can be combined.
"Being the Chair-person of Estonian
Society of Toxicology, I have learned that
companies or industries are interested in the
expertise of the specialists in toxicological
issues when there is a law to apply and thus
To demonstrate that, we used a novel approach based on a combination of
traditional ecotoxicological methods (comparing the ecotoxic effects of
nanosize metal oxides with their bulk analogues and soluble zinc and copper
salts) and metal-specific recombinant biosensors. This combined approach
allowed us to differentiate the toxic effects of metal oxide NPs per
se and solubilised metal ions.
Would you summarize the significance of your paper in layman's
Synthetic NPs are defined as particles with one dimension less than 100 nm
and they can be organic (C60 fullerenes, carbon nanotubes, dendrimers) or
inorganic (metal oxides, nano-silver, quantum dots). Metal oxide NPs,
especially TiO2 and ZnO, are increasingly used in various
consumer products such as cosmetics and sunscreens, dental fillings,
self-cleaning coatings, and textiles. CuO NPs have potential in gas
sensors, catalysis, and as antimicrobials.
As the use of NPs is constantly increasing in broad applications, sooner or
later the NPs will end up in the environment, either due to accidental
spills or via various waste streams analogously to other
industrial chemicals. Therefore, information on the ecotoxicological
effects of NPs is urgently needed. Usually the first level evaluation of
hazardous environmental effects of chemical compounds is performed on
simplified food-chain model organisms (crustaceans, algae, fish).
In our paper, we showed that differently from TiO2 NPs that were
not toxic, ZnO and CuO NPs were remarkably toxic to bacteria and
crustaceans, showing acute toxic effects to Daphnia magna at level
of ~3 mg per liter. For another crustacean, Thamnocephalus
platyurus, the toxicity of ZnO was even about 19 times higher
(LC50=0.18 mg/l). Thus, the environmental impact of manufactured NPs should
be carefully assessed in order to ensure the sustainable development of
How did you become involved in this research, and were there any
problems along the way?
My first experience with NPs was when I was participating with my group in
the evaluation of the potential toxic effects of polyamidoamine (PAMAM)
dendrimers and polyethylenimine dendrimers (PEI)—organic NPs studied
mainly for the gene delivery applications—on various non-vertebrate
ecotoxicological test organisms concurrently with mammalian cell cultures
in vitro and for mice in vivo.
We showed that a battery of simple tests can be used, not only to assess
ecotoxicological properties, but also for high-throughput screening for
biological effects NPs. My interest in the environmental hazard issues of
NPs was confirmed by a reading in the New Scientist (2004) the
discovery of Dr. Eva Oberdörster concerning the toxicity of C60
fullerenes for fish and daphnids already at sub milligram per liter level.
The observation of a relatively high toxicity of something that is just a
different form of carbon was scientifically really exciting. Thus, the same
year I wrote an application titled "Biological effects of modified
fullerenes and nano-size metals" to the Howard Hughes foundation call for
"Grants for Biomedical Research Baltics, Central and Eastern Europe,
Russia, and Ukraine." Unfortunately this application was not granted,
probably due to the fact that this Foundation is oriented on the funding of
fundamental biomedical research.
However, in this project application I had summarized a lot of very
interesting ideas and hypothesis and wrote a sound research plan. Thus, I
managed to convince the Head of the Scientific Council of my Institute
(Prof. Mart Saarma, University of Helsinki) and the Directors (Dr. Ago
Samoson in 2005 and Dr. Raivo Stern since 2006) to support this innovative
research from the general budget of our Institute.
In addition to the ideas and seeding money, I had a group of young and
enthusiastic scientists trained in ecotoxicology, environmental chemistry,
microbial physiology, and molecular microbiology. Currently, the
nanoecotoxicological studies of my group are also supported by other
funding sources of the Estonian Government.
Hereby I would like to recognize the work of my group—Prof.
Henri-Charles Dubourguier, Dr. Angela Ivask, Dr. Irina Blinova, and Dr.
Kaja Kasemets. Currently, my research team also involves six Ph.D. students
who are interested in this novel and highly competitive area of
research—Margit Heinlaan, Villem Aruoja, Monika Mortimer, Imbi
Kurvet, Mariliis Sihtmäe and Olesja Bondarenko—in addition to
several students at M.Sc. and B.Sc. level.
Where do you see your research leading in the future?
"...one of the first papers that
showed that the solubilisation of
metal-containing nanoparticles is the key
factor in their (aquatic)
With my group of researchers and Ph.D. students, we have already published
five papers which are listed in
Web of Science® journals and four more papers which
are currently in press or submitted. One interesting current topic is the
different mechanisms involved in the toxicity of different types of NPs
modulated by the physiology of the target organisms and environmental
Research on the hazard of NPs has to integrate or at least to take into
account both human and environmental impacts. I am currently involved as a
managing Guest Editor in the preparation of a Special Issue of
Toxicology entitled "Potential hazard of nanoparticles: from
properties to biological & environmental effects." The interest of
Elsevier to publish this Special Issue shows the need for integrated
approaches in the hazard evaluation of synthetic nanoparticles.
Do you foresee any social or political implications for your
Absolutely—synthetic NPs have been already included in various
consumer products (cosmetics, sunscreens, socks, and even underwear).
However, relevant toxicological and ecotoxicological information is often
misleading. Thus, human exposure to NPs is a real concern.
Naturally, as is the case of all industrial chemicals, workplace exposures
at manufacturing sites of nanoparticles/materials may pose the greatest
risk to humans, but also the potential effects to ecosystems and
environment have to be studied. For example, NPs included in sunscreens
applied by humans get washed into bodies of water and thus, aquatic
organisms will be also exposed to these NPs.
Thus, till we do have enough—how much is enough?—information on
the potential adverse effects of NPs (on all their life cycle levels),
precautionary principles should be applied. Fortunately, we have lessons to
learn from the past (PCBs, asbestos, GMOs), to avoid other potentially
Being the Chairperson of the Estonian Society of Toxicology, I have learned
that companies or industries are interested in the expertise of the
specialists in toxicological issues when there is a law to apply and thus
assistance is needed. For example, the implementation of the REACH
directive, a new European Community Regulation on chemicals and their safe
use, has remarkably increased the interest of the industry and legislative
bodies on toxicological research. Currently, assessing the safety of
synthetic NPs has become a worldwide issue and I am confident that soon the
synthetic NPs will be regulated analogously to bulk chemicals.
Dr. Anne Kahru
Lead Researcher, National Institute of Chemical Physics and
Head, Laboratory of Molecular Genetics
Chairperson, Estonian Society of Toxicology
National Institute of Chemical Physics and Biophysics
KEYWORDS: ANTIOXIDANT ENZYME-ACTIVITIES; LIPID-PEROXIDATION;
TITANIUM-DIOXIDE; OXIDATIVE STRESS; FULLERENE C-60; ANTIBACTERIAL
ACTIVITY; WATER SUSPENSIONS; RISK-ASSESSMENT; QUANTUM DOTS;