Moulting test on the springtail Folsomia candida exposed via artificial test soils in a laboratory experiment

In a laboratory experiment, the soil invertebrate Folsomia candida (Collembola) was exposed to CuCl2 or copper oxide nanoparticles (CuO-NP) for 6 days. The animals were exposed via artificial test soil which varied in the size (19 or 30% of total mass) or the clay type of their clay fraction (kaolin or montmorillonite). The test substances were dissolved (CuCl2) or dispersed (CuO-NP) in pure miliQ water and stirred into the dry test soils to end up with test concentrations of 1, 3, 10 and 32 mg Cu/kg and a water content of 50% of the maximum water holding capacity of the respective soils. As a control, soil with miliQ water only was tested. For all soils, two tests with 5 replicates per treatment were conducted. At the beginning of the experiment, 30 animals at the age of 10-12 days were inserted into the test vessels containing the spiked test soil. After 6 days, all animals were extracted by floatation of the test soils with tap water and transferred to a Paris-plaster culture plate. After 2, 5 and 7 days, the exuviae shed by the animals were collected under a binocular and analysed for their total Cu content (not per biomass as mass of exuviae is too little to be measured) via atomic absorption spectroscopy (AAS). The number of shed exuviae per animal was calculated for each time point and statistically compared to the control by a linear mixed-effect model considering the two test runs as random factor. The Cu contents of the samples were analysed by an ordinal regression with respect to their ability to exceed the limit of detection or quantification in the AAS.