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Dr. Paul Henning Krogh
A Featured Scientist from Essential Science IndicatorsSM

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 Thomson Reuters 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.

Simon Mitton,'s 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 into ecotoxicology?

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.

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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 years?

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 ecotoxicity testing.

  Is your field research confined to the European area?

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 collaborative.

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 Aarhus?

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 partners.

  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) guideline program.

  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 enchytraeids.

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 research?

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.
Senior scientist
National Environmental Research Institute
University of Aarhus
Department of Terrestrial Ecology
Silkeborg, Denmark

Keywords: toxic contaminants, soil fauna, ecosystem, agricultural land, environmental toxicology.


2008 : May 2008 - Author Commentaries : Paul Henning Krogh
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