Interactive effect of struvite produced from human urine and emerging contaminants on biological indicators of soil quality

Struvite produced from human urine is rich in macronutrients. It can be used as a slow-release fertilizer, which helps to promote growth and increase the productivity of agricultural crops. However, struvite may contain pharmaceuticals that can alter the quality of agricultural soils. Here, a greenhouse study was conducted to investigate the effects of struvite and pharmaceutical-contaminated struvite on biological indicators of soil quality (microbial growth, microbial biomass, basal respiration, metabolic quotient, and enzyme activity). The struvite was separately contaminated with a mixture of four antibiotics and four neuroactive at three different concentrations, 1, 10, and 100 mg kg −1 . The results showed that more than 90% of the pharmaceuticals were not present in the soil after the first 7 days of the study. The effects varied depending on the type of indicator, the pharmaceutical, the concentration, and the day analyzed. Soils that received contaminated struvite generally had lower growth of total heterotrophic bacteria (BHtot) and nitrogen-fixing bacteria (FixN), microbial biomass (MBC), and activity of fluorescein diacetate hydrolases (FDA-H) and dehydrogenases (DHA), but higher basal respiration (SBR) and metabolic quotient (qCO 2 ) in the first 7 days. These results indicate that soil microorganisms exposed to contaminated struvite were under stress during the initial phase struvite application. However, these microorganisms showed the ability to recover by increasing microbial growth by 0.1–1.8 log 10 CFU, microbial biomass by 5.3%–102%, and enzymatic activity by 76%–774%. Both positive and negative effects were observed mainly for struvite contaminated with antibiotics. The results obtained help to clarify concerns about the safety of struvite produced from human urine. The ability of soil microorganisms to recover after stress is important to support the responsible use of this fertilizer and encourage more sustainable agricultural practices. However, the effects of pharmaceutical-contaminated struvite resulting from continuous application during successive crops should be considered in future studies.