Freshwater microcosms showed showed to be suitable for assessing the effect of endocrine disruptive chemicals (Höss et al. 2004), veterinary pharmaceuticals (Brinke et al. 2010), heavy metals (Brinke et al. 2011) and nanoparticles (Höss et al. in prep.) on the structure of meiofaunal and nematode communities. The microcosms are 2L glass jars filled with approx. 800 g of sediment (see Fig. 1).