Pesticides and their effect on the environment
Ecotoxicologists from Tübingen are calling for new interdisciplinary approaches in order to improve investigations into the effect of pesticides on the living environment. They expect that a more effective and more frequent combination of field work and laboratory analyses will provide them with a clearer picture of the overall situation. This knowledge will enable all stakeholders involved in solving environmental issues to draw the right conclusions and take action accordingly.
Being invited by the renowned scientific journal Science to write an article is already a distinction in itself and confirms the international reputation of the researchers who receive the invitation. Prof. Dr. Heinz-R. Köhler and Prof. Dr. Rita Triebskorn, ecotoxicology experts from the University of Tübingen’s Institute of Ecology and Evolution, accepted the invitation and have published a review on how pesticides alter ecosystems. “We were tasked with presenting the current state of research as well as highlighting perspectives for the future. The study also included information about our own research into the effect pesticides have on animals,” Köhler said.
The Science paper has a clear message: only a few connections have been recognised between studies focussing on the effects of pesticides in individuals and studies assessing the ecological changes in biological communities and ecosystems. Köhler expresses his criticism of individual investigations through the following example: “The investigation of individual fish embryos of which as many as 80 percent die under natural conditions before they reach reproductive age should not necessarily lead us to believe that the effects of pesticides in individuals have an effect on the entire population. When we look at the potential effects of chemicals, it is therefore of crucial importance to recognise connections between the effects of pesticides in individuals and changes in ecosystems.”
Plausible and causal links provide the whole picture
The researchers are very well aware that is difficult to establish seamless cause-effect chains in all cases; field conditions are just too complex and unforeseeable, which makes it rather difficult to reliably determine the parameters that might have an effect on the life and coexistence of species. The situation is further aggravated by the relatively long periods of time over which field observations need to be carried out in order to obtain a representative database. “Reliable causalities can only be determined in the laboratory. This is why we are looking for plausibilities of causal relationships. We are working on establishing a plausibility chain that covers everything from the molecular effects of pesticides on individuals to the effects on the ecosystem,” Dr. Triebskorn explains.
She is coordinating a large, BMBF-funded cooperative research project entitled “SchussenAktivplus”, a project that shows that it is possible to establish such plausibility chains. The project brings together 20 partners for a period of three years with the objective of investigating the environmental effect of micropollutants, including pesticides, in the river Schussen in a highly populated catchment area in the Lake Constance area. “The project is particularly focussed on animals, but the investigations also include bacteria,” says Triebskorn. Köhler adds: “Our work predominantly involves invertebrates such as snails and amphipods as, in contrast to vertebrates, these groups of animals are not associated with ethical constraints. We use fish to represent vertebrate animals.”
“SchussenAktivplus” involves samples taken from various points and locations in the catchment area of the river Schussen between Lake Constance and the city of Ravensburg. Chemical and physical parameters such as temperature and oxygen content are determined in samples obtained from five locations. In addition, fish, water and sediment samples are investigated for the presence of micropollutants and pathogens. The researchers compare samples taken before and after application of different sewage and rainwater treatment technologies as well as before and after the implementation of innovative cleaning technologies. Passive and active monitoring experiments are carried out in the field in order to assess fish health. Active biomonitoring takes place under controlled conditions in bypass systems where river water is guided through aquaria. The aquaria contain brook and rainbow trout, their eggs and newly hatched fish. Hatchlings are particularly sensitive to pollutants. “Our investigations related to the effect of toxic substances on the development of fish are specifically focussed on potential delays in development, oedemas and crippled spinal columns,” Triebskorn says.
Laboratory investigations focussing on the molecular level involve the use of biomarkers. “As far as organs are concerned, we examine the animals for potential kidney, gill and liver damage and then use biomarkers for in-depth investigations. Detoxification systems such as the cytochrome P450 system are activated when compounds with effects similar to those of dioxin enter the animals’ metabolism. This is why cytochrome P450 is an important biomarker for us,” says Triebskorn. Köhler adds: “Certain stress proteins are found in all organisms. This has the advantage that we can use one and the same antibody for all species under investigation.” The induction of vitellogenin, an egg yolk precursor protein expressed in the females of nearly all oviparous species, is another interesting biomarker. Vitellogenin is normally expressed in response to an ovarian stimulus in the liver of female fish during oocyte development. The accumulation of yolk is important for proper embryonic development after fertilisation. “Environmental substances with an oestrogenic effect might also trigger vitellogenin expression in juvenile and male fish. This uses up energy and might potentially reduce the fertility of the fish,” Triebskorn explains.
Hand in hand: laboratory analyses complement the researchers’ work in the field
Moreover, the researchers use a vast range of other laboratory investigations, including in vitro tests where cell cultures are exposed to river and sewage waters. These tests enable the researchers to determine the potential toxic and hormonal effects of the water. The SchussenAktivplus project uses the river Argen, another Lake Constance tributary, which is far cleaner than the river Schussen, as a control.
In addition to scientists, the cooperative project also involves engineers, government bodies and fishermen. “Interdisciplinary cooperation is key to elucidating a complex issue. The project involves a total of 150 people,” Triebskorn says. Triebskorn and Köhler have also been involved in interdisciplinary EU-funded projects. In one such project, the researchers from Tübingen investigated the potential toxicity of specific compound mixtures on zebra fish (Danio rerio). Another international project dealt with ecotoxicological investigations in the Danube area where the team from Tübingen put its expertise on the transfer of know-how to good use, thereby enabling research groups in other European countries to avoid having to start from scratch. “Pesticides are only one group of micropollutants that are harmful to the environment; there are many more, including household and industry chemicals such as drugs – in general all substances that occur in the micro- to nanogramme range in the environment,” Köhler says.
The researchers from Tübingen are calling for the application of in silico methods in addition to the in vivo and in vitro examinations used. Modelling approaches with which natural population fluctuations can be simulated already exist and can be used to make predictions on the development of populations. “Such models can in principle also be used for ecotoxicological investigations,” Köhler said. However, the models are only as good as the data used, and this is still rather a big problem. Let’s hope that an increase in interdisciplinary research projects will soon provide a reliable database.
University of Tübingen
Institute of Evolution and Ecology
Animal Physiological Ecology
Prof. Dr. Heinz-R. Köhler
Tel.: +49 (0)7071 7573559
Prof. Dr. Rita Triebskorn
Tel.: +49 (0)7071 7573555