Dr. Paul Henning
A Featured Scientist from
Soil organisms form complex ecosystems that are
crucial to the ecological stability of agricultural
land. They also affect the quality of soils and their
agricultural productivity. Land use and introduction of
new agricultural technologies and practices intricately
interact with the soil biodiversity and functions.
Persistent pesticides, for example, may be detrimental
to the soil ecosystem. Soil ecotoxicology is the
scientific discipline that examines the impact of
contaminants on the soil ecosystem.
A recent analysis of Essential Science Indicators from
highlighted the contributions made by Dr. Paul Henning Krogh. In the
analysis, Dr. Krogh's work attained the highest percent increase in total
citations and he was named a Rising
Star in the field of Environment & Ecology. His current record in
this field includes 48 papers cited a total of 410 times between January 1,
1997 and December 31, 2007.
Dr. Krogh is a Senior Scientist in the Department of Terrestrial Ecology at
the National Environmental Research Institute, part of the University of
Aarhus in Silkeborg, Denmark.
European correspondent, interviewed Dr Krogh
to find out more about his high-ranking papers published in the
last 10 years.
Two-thirds of Denmark is arable land, and
agriculture therefore considerably affects its landscape, wild
animals, and plants. Essential Science Indicators shows that
your high-impact papers are focused on testing and risk analysis
concerning the effects of contaminants on soil fauna. How did you get
I am a biologist by education. I graduated with a master’s degree in
soil ecotoxicology. Twenty-five years ago I initiated my first long-term
field experiment on the effect of pesticides on soil fauna, with the aim of
gaining empirical insight into the importance of complexity for ecological
stability. That was an exercise I started as part of my master’s
degree, but it took two years to complete and I continued monitoring for a
further five years, without funding.
Ever since then I have been involved in this area. My engagement with
agriculture and soil ecology became the main motivation for undertaking a
Ph.D. I didn’t want to go into high school education—research
seemed more exciting. My doctoral research was a continuation of my
master’s; I decided to stay on the same track. That’s how I
became an ecotoxicologist.
How have your interests developed over the
Ecotoxicologists study the effects of chemical pollutants on an ecosystem.
My approach is broader than that, however—much broader, in that I do
not restrict myself to chemical pollutants alone. I am interested in
anything that humans do that can affect the life in the soil, so I spread
more widely than just toxicants. I look at disturbance to soil ecosystems
in the broadest sense: even climate change can be considered as a
disturbance from my point of view.
The key focus of my activities is the assessment of the ecological soil
quality of habitats exposed to stress of various kinds. Functional
properties along with biodiversity of soil fauna are the main indicators
used in assessment studies. This concept for ecological risk assessment is
important in advisory and research tasks for the Danish Environmental
Protection Agency and industry.
Ecotoxicology tends not to focus on understanding the ecological
interactions. I have initiated research that seeks to improve the
scientific underpinning of ecotoxicity studies. And further, at the simple
level of collembolan reproductive biology I participate in improving the
basic understanding of Folsomia candida, the model organism for
collembolan biology and the number-one soil arthropod used for routine
Is your field research confined to the
Yes, my investigations were confined to Denmark initially. Working at the
European level is usually required for European Union (EU) funded research.
A more recent interest of mine is to apply my approaches to soil quality
assessment of polluted sites in China through my affiliations with the
Chinese Academy of Sciences.
I find the contributions you have made towards
collaborative research in the EU quite striking. You seem to be a
major force behind getting European ecologists to be more
Thank you! That’s true: I am the co-coordinator of ECOGEN, which was
a large co-operative project funded by the EU. ECOGEN studied the impact of
genetically modified (GM) crops on soil ecosystems. That required in-depth
investigations of ecological and economical consequences, so an almost
all-encompassing evaluation could be delivered.
Following state-of-the-art ecological risk assessment, we combined simple
lab tests, multi-species model ecosystems, and field studies to acquire
mechanistic and realistic knowledge. Hitherto such a comprehensive research
program had not been done to assess consequences of GM crops for the
agricultural soil ecosystem.
EU projects require extensive management and communication. We worked as
virtual teams, supported by first-generation web tools, such as e-mail and
repositories for electronic documents. Maybe the particle physicists have
run their vast collaborations like that for decades—they invented the
World Wide Web—but for ecologists it’s a new way of
facilitating our internationally based collaboration, and I believe
new-generation web tools will profoundly affect and shape the way future
science will be performed.
What is the purpose of the Danish Natural
Environmental Research Institute at the University of
The institute does environmental research, monitoring, and consulting for
clients, in particular the Ministry for the Environment. Our scientific
community here has about 200 professionals divided into several
departments. This is not so very large compared to the national facilities
in many other countries.
The work I undertake is a mixture of commissioned research and reports for
industry, and investigations driven by my own intellectual curiosity. But
because the Danish government in effect employs us, most of our consultancy
is for other government departments. I was therefore pleasantly surprised
to see from Essential Science Indicators that my science papers
are making an impact more widely than just our Ministry and governmental
What kind of ecological problems in Denmark
are addressed by your institute at University of Aarhus?
All problems, with the exception of the effects of pollutants on humans.
The latter is taken care of by other institutes. We are interested in all
aspects of ecology, particularly checking the quality of the natural
environment, and the need for environmental protection.
In terms of historical development, the infancy of environmental protection
in Denmark began with concern about the pollution of water: run-off from
agricultural land polluted the water with nitrogen.
Through my research I have participated in broadening the field to include
terrestrial ecotoxicology, which really took off during the 1990s. In those
days we started describing procedures for how to do biological testing of
contaminated soil, and we have now submitted a collembolan test procedure
for the Organisation for Economic Co-operation and Development (OECD)
I’d like to turn to your highly cited
papers. Can we start with #1 in our ranking? This has your colleague
Line Sverdrup as the first author and it considers the soil toxicity
of polycyclic aromatic hydrocarbons (Sverdrup L, et al.,
"Soil ecotoxicity of polycyclic aromatic hydrocarbons in relation to
soil sorption, lipophilicity, and water solubility," Environ.
Sci. Technol. 36: 2429-35, 2002).
I’ll start with the background to the paper. Contamination by
polycyclic aromatic hydrocarbons (PAHs) is one of the main problems related
to industrial soils. We had a Danish program on the soil toxicity of PAHs.
This is a quantitative paper that drew on a number of lab studies. It
presents a simple formula for the relationship between the properties of a
PAH molecule and its toxicity.
We published a simple, but powerful, model where other papers have very
complicated models to describe such quantitative structure-activity
relationships (QSAR), but this paper extracts the essential toxic
properties of those chemicals. It is highly cited because the results
provide important input to future model predictions of the ecological risk
posed by PAH contaminated sites.
Your second paper, with Angel Baguer as the
lead author, looks at the effects of two veterinary antibiotics on
soil fauna (Baguer A, et al., "Effects of the antibiotics
oxytetracycline and tyrosin on soil fauna," Chemosphere 40:
751-7, 2000). What did you find?
There is presently a lot of concern about pharmaceuticals contaminating the
natural environment. Antibiotics may enter the terrestrial environment when
improving soils with animal manure. Our study tested the effects of two
widely used antibiotics, tylosin and oxytetracycline, on three species of
soil fauna: earthworms, springtails, and enchytraeids. We concluded that it
is unlikely that antibiotics potentially present in manure pose any direct
risk to the soil fauna. The high citations are because it was a trendy
topic and a ground-breaking paper.
You and your colleagues have published several
papers in Environmental Toxicology and Chemistry looking at
the effect of other compounds on springtails and
Some papers (Jensen J, et al., 20: 1690-7, 2001; Holmstrup M,
et al., 20:1680-9, 2001; and Holmstrup M, et al., 20:
1673-9, 2001 for example) were on one compound we have studied in
considerable depth: namely, linear alkylbenzene sulfonates, which are a
very common contaminant from washing powder, where they are used as anionic
surfactants. This contaminant has attracted a lot of attention because it
is so widespread. It persists in water and enters agricultural soil through
the application of sewage sludge to the land.
Through these papers we supported two kinds of customers through our lab
and field experiments. Partly we worked for the Danish EPA, who wanted
limit values for these compounds. Then strategic environmental research
programs were launched, and finally the industry asked us for further
investigations and they paid us to do that. The industry requests
stimulated further quality-assured toxicity testing. We found that under
normal environmental conditions the compounds do not pose a risk.
What is the direction of your current
Through the ECOGEN initiative I have participated in studies on the effects
of genetically modified (GM) crops on soil organisms. The issue here is
that in GM cropping systems there are shifts in the agricultural practice
towards reduced tillage and modified, perhaps less, pesticide use. Hence
evaluation of GM crops essentially becomes evaluation of a whole new
farming system. This calls for the tools we have employed in ECOGEN that
can integrate the disparate farming system attributes and provide overall
environmental and economic scoring of new agricultural scenarios.
The constant quest for financial support has brought me into various
topics: quantitative studies of earthworm burrows, the effect of which is
to provide a pathway for water into the soil; and a climate change
monitoring program in Greenland. I am also trying to develop research
programs in partnership with China. We will transfer our experience and
knowledge to Chinese soil toxicologists, hopefully to contribute to the
rising environmental concerns here.
Paul Henning Krogh, MSc Ph.D.
National Environmental Research Institute
University of Aarhus
Department of Terrestrial Ecology
Keywords: toxic contaminants, soil fauna,
ecosystem, agricultural land, environmental toxicology.