Millions of tons of casting waste are generated annually worldwide, which should be subjected to recycling, as per the principles of circular economy. Spent foundry sands can be used for producing soil substitutes, but the process should yield products with guaranteed biological safety. The goal of this work was to conduct a safety evaluation of soil substitutes produced based on casting and organic waste. Toxicity tests were performed for this purpose, based on measurements involving the germination efficiency and the effect of the studied compositions on the biomass, sprout and root growth of Sinapis alba. In addition, an analysis of the content of chlorophyll A and B and of carotenoids was carried out, as well as a measurement of the lipid peroxidation level (content of malondialdehyde - MDA) to assess the potential oxidative stress in the tested plants. The compositions for soil formation prepared using casting waste as a mineral fraction and organic waste (compost, green waste, biogas plant digestate) had a stimulating effect on the rhizospheric and epigeal part growth of Sinapis alba. The germination efficiency in the prepared soil substitutes exhibited no significant difference from the germination efficiency in the control sample. However, the presence of oxidative stress (increased carotenoid and MDA contents) was found in the substitute containing green waste, which could be the result of water deficiency in the plants growing in this substrate. The complex testing of the compositions prepared based on casting waste (spent foundry sand) proved the validity of using such products as soil substitutes.