Ecotoxicology studies were performed in the earthworm Eisenia fetida with four different synthetic amorphous silica (SAS) (SYLOID® AL-1 FP, SYLOID® MX 107, LUDOX® P T-40F, and HDK® N20) mixed into artificial soil to determine a NOEC/LOEC for effects on reproduction (56 days after application), mortality and biomass development (28 days after application) using a standardized artificial soil with 10% peat. The LC50 for test-item effects on adult mortality, and an EC10 and EC50 for reproduction were also determined. Furthermore, earthworms underwent histopathology evaluation, and the amount of silica in different organs from these organisms was evaluated using EDX (Energy Dispersive X-ray Spectroscopy). Histopathology revealed no findings in any organ of the earthworms, except for desiccated dissepiments in evaluated decedents at extremely high SAS doses. To measure SAS uptake into the organs, a fully quantitative method for silica was established and validated using standards containing known concentrations of silica to ensure the accuracy of the analyses undertaken. Results from EDX analysis demonstrated the negligible presence of silicon within the brain ganglia and gonads of adult earthworms comparable to controls. Therefore, any deposition of the test items within these two organs was excluded. In contrast, traces of silicon higher than in controls were found in the intestinal lumina of the earthworms due to ingestion of SAS with soil and feed, but not in other organs.