Ecotoxicity of Selected Pharmaceuticals and Their Effects on Soil Microbiota

The UN, through the FAO and UNEP, emphasizes that soil health is vital for food production, with 95% of food deriving from soil. However, one-third of global soils are already degraded, posing a threat to food security and nutrition. Emerging contaminants, such as pharmaceutical products (PPs), are now continuously detected in water, soils, food, animals, and plants. Their increasing presence in agricultural soils is of particular concern. Nevertheless, scientific evidence regarding the ecotoxicity of PPs and their impact on soil ecosystem functions—processes in which soil microbiota play a crucial role—remains scarce. This study aimed to determine and evaluate the toxic effects of four pharmaceuticals—the antiseptic chlorhexidine, the antibiotic sulfadimethoxine, the anticonvulsant sodium valproate, and the steroidal anti-inflammatory prednisolone—on soil microbiological activity using standard ecotoxicity tests. The experiment included the following assays: OECD TG 216 (Soil Microorganisms: Nitrogen Transformation Test); OECD TG 217 (Soil Microorganisms: Carbon Transformation Test); and ISO 18187:2018 (Soil quality – Contact test for solid samples using the dehydrogenase activity of Arthrobacter globiformis). The results indicated that, at the tested doses, these PPs did not significantly reduce the overall microbiological activity of the reference soil, suggesting an EC₅₀ greater than 100 mg kg⁻¹ for these compounds. Soil nitrifying activity was highly variable; however, sulfadimethoxine was the only compound found to inhibit nitrification after 28 days of incubation. In contrast, chlorhexidine exhibited a clear toxic effect on the dehydrogenase activity of A. globiformis. This finding implies that environmental consequences could be significant if chlorhexidine is present at relatively high concentrations in soils. Our results suggest that natural biodegradation by soil microorganisms is key to mitigating the toxic effects of the studied pharmaceuticals. Further research is necessary to investigate potential cumulative, synergistic, and long-term environmental impacts.