Wednesday, April 8, 2015

Not one and not the right one

Ecotoxicology combines the methods of ecology and toxicology in studying the effects of toxic substances and especially pollutants on the environment. It employs standardized test procedures that work with model organisms to assess the potentially harmful impact of anthropogenic substances on ecosystems. In order to guarantee the compatibility of these tests on a global scale, the laboratories use model species specified by international guidelines.

Earthworms have been chosen for soil toxicity tests. They are ubiquitous and abundant in most soils, and members of the common family Lumbricidae can reach very high densities. Earthworms play a significant role in soil formation, aeration, and nutrient cycling. Eisenia fetida has been chosen as the standard species for soil toxicity tests. It is widely available, easily reared in laboratory cultures, reproduces quickly and steadily under optimal conditions, and there was baseline data on the ecotoxicology of these worms available. However, ever since these worms have been used in standard testing there were discussions whether the animals used belonged to one species or two. 

An international consortium of five laboratories, led by my former supervisor Markus Pfenninger and Jörg Römbke, closely examined the earthworm species used in ecotoxicology tests and tried to verify its assumed species identity by means of DNA Barcoding . In a broadly designed comparative test, conducted by 28 ecotoxicological laboratories from 15 countries and four continents, they were able to show that only 17 of the 28 labs actually worked with the earthworm species of the genus Eisenia that they had specified. However, at eleven institutes, the tests were conducted de facto with other members of this genus. Since it is not known to what extent the species in questions differ in their reactions to the tested substances, the results and the compatibility of tests are controversial if they were not uniformly conducted with identical species.

In addition, the study also confirmed the existence of a cryptic species in the laboratories, which, although it does not differ morphologically from one of the described Eisenia species, nonetheless constitutes a distinct genetic species. 

The results of this study are now being presented to standardizing organizations such as the Organization for Economic Cooperation and Development (OECD) and the International Standardization Organization (ISO) in order to include this information in their further standardization work, e.g., by modifying existing individual guidelines or by preparing a Guidance Document which describes the DNA Barcoding procedure independently from the individual guidelines. 

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