The risk assessment of chemicals requires information on their hazard to soil invertebrates. For that purpose, toxicity tests are performed with different species representative of the soil ecosystem. Currently, test methods for toxicity testing with earthworms, enchytraeids and springtails have been standardized and published in international test guidelines by OECD and/or ISO. Oribatid mites also are important members of the soil community, with abundances in forest ecosystems as high as 100,000 per m2. For that reason, a draft toxicity test with the species Oppia nitens was described in the literature and recently this test was further developed by Environment Canada. First experiences with the method have been gained in a ring test.
Our lab participated in the ring test, but we already did some additional testing with this species, determining among other their sensitivity to metals (Cu, La, Pb) and neonicotinoid insecticides. These tests typically determine effects on the survival and reproduction of young adult mites after 3-4 weeks exposure in a standardized test soil. So far, the species Oppia nitens seems to be quite insensitive compared to other soil invertebrates, although we also found it to show a high bioaccumulation of metals. For that reason, further testing of the animals is needed to investigate their potential suitability as a test organism to be added to the battery of tests representative of the soil ecosystem. This further testing may involve several questions, like what the influence of soil type is on the mite response to different chemicals, what toxicity is of a range of different chemicals with different modes of action, whether they are able to avoid contaminants, how do environmental conditions like temperature and soil moisture content affect toxicity, etc.
You will perform toxicity tests with Oppia nitens in soil, investigating your own research question. The research question may be developed in close cooperation with your supervisor and of course by checking with available literature data. During the internship you will learn several methods commonly used in soil ecotoxicology, including culturing the test animals, characterizing soil properties, spiking soil with different concentrations of a test chemical, performing exposures of the test animals, chemical analysis to determine available and total metal concentrations in soil and in test animals, analyzing results using dose-response models and other mathematical or statistical methods etc.
Dr. Kees van Gestel, e-mail: firstname.lastname@example.org