If a small crustacean does not grow properly, this can affect its reproduction. And if it is no longer able to move normally, it cannot flee from predators or from changing temperatures, which eventually has a fatal outcome. In scientific research, these effects are referred to as "sublethal effects". However, worldwide standard methods of pesticide analysis and the risk assessments associated with them only consider the lethal (deadly) effects. For the first time, three studies published in "Ecotoxicology", "Environmental Science and Pollution Research" and "Environmental Toxicology and Chemistry" demonstrate the sublethal effects on swimming behavior and growth, caused by widely used pesticides on the animals being studied. Moreover, the results indicate that the substances influence the underwater world for weeks, even if they are no longer detectable using standard methods.
Pesticides become more toxic as a combined package
Another factor is the mix of pesticides: "We looked at the insecticides not individually, but as a mixture, in order to investigate their interaction with one another", explains lead author Dr. Simone Hasenbein. "In addition, we observed several species in the contaminated water body, including the less standard species for these tests, such as mini-snails and copepods."
The tests took place over a period of ten days in the laboratory and also for six months in the field. Eventually, significantly negative effects resulting from the combined pesticide pollution in the water were found for twelve of the 15 small invertebrates and ten of the 16 zooplankton species. "Another point that was considered was how long the insecticide remained detectable in water", was Dr. Hasenbein's explanation of the method – "thus, one of the three substances was still detectable after six weeks."
A clear result delivered by a combination of study series
- Firstly, the laboratory tests provided an indication of the concentrations at which the contaminants influence the growth and swimming behavior of the organisms.
- The field studies proved the long-term effects on an entire ecosystem, its food web and its community structures.
Sublethal effects as alarm signals
The changes in the animals which are detectable from their swimming behavior, growth or weight, and which eventually lead to their death (sublethal), are an important indicator of this. To date, however, there is no valid scale showing the point from which, for example, a delay in growth has a fatal outcome for the animal. Therefore, study author Dr. Hasenbein is advocating this approach in particular: "Sublethal endpoints need to be integrated into the methods used in ambient water monitoring, to allow long-term negative effects on aquatic ecosystems to be detectedreliably, even when the pesticide concentrations in the water are low", says the scientist.
"A crustacean population which is exposed to low-level contaminant pollution could be more susceptible to invasive species, changes in water temperature or different salt concentrations, because the permanent, low-level pesticide contamination increases stress on the animals." This is an important aspect, especially in the light of climate change, and should therefore be taken into consideration in future ecotoxicologic assessments.
Hasenbein S, Lawler SP, Geist J, Connon RE.: A long-term assessment of pesticide mixture effects on aquatic invertebrate communities. Environmental Toxicology and Chemistry, 13.11.2015. DOI: 10.1002/etc.3187
Hasenbein S, Connon RE, Lawler SP, Geist J.: A comparison of the sublethal and lethal toxicity of four pesticides in Hyalella azteca and Chironomus dilutus, Environmental Science and Pollution Research International, 2015 Aug;22(15):11327-39. doi: 10.1007/s11356-015-4374-1. http://link.springer.com/article/10.1007%2Fs11356-015-4374-1
Hasenbein S, Lawler SP, Geist J, Connon RE: The use of growth and behavioral endpoints to assess the effects of pesticide mixtures upon aquatic organisms. Ecotoxicology 24:746-759, 29.01.2015. DOI: 10.1007/s10646-015-1420-1
Technical University of Munich (TUM) is one of Europe's leading research universities, with more than 500 professors, around 10,000 academic and non-academic staff, and 38,500 students. Its focus areas are the engineering sciences, natural sciences, life sciences and medicine, reinforced by schools of management and education. TUM acts as an entrepreneurial university that promotes talents and creates value for society. In that it profits from having strong partners in science and industry. It is represented worldwide with a campus in Singapore as well as offices in Beijing, Brussels, Cairo, Mumbai, San Francisco, and São Paulo. Nobel Prize winners and inventors such as Rudolf Diesel, Carl von Linde, and Rudolf Mößbauer have done research at TUM. In 2006 and 2012 it won recognition as a German "Excellence University." In international rankings, TUM regularly places among the best universities in Germany.