Persistence of the coccidiostat robenidine in soil and its impacts on the soil microbiome and enzyme functions

Robenidine is a synthetic coccidiostat that is excreted from animals in its prototype form, leading to soil contamination. Despite its widespread use, comprehensive environmental risk assessments remain limited. Consequently, we initially constructed a manure-soil microcosm and investigated the degradation pattern of robenidine using a highly efficient HPLC-dSPE method. The degradation half-lives of robenidine in soil were 14.74 days at 0.8 mg/kg and 21.26 days at 8 mg/kg. Exposure to 8 mg/kg of robenidine significantly altered the soil microbial community, leading to a 140.0 % increase in the abundance of Proteobacteria. However, the Shannon index indicated that soil microbial diversity decreased by 32.4 % from 1 d to 60 d. Compared to the control check group, 8 mg/kg of robenidine significantly increased the abundance of harmful bacteria (e.g., unclassified_Intrasporangiaceae increased by 33.5 %) in the soil at 60 d, while simultaneously reducing the populations of beneficial bacteria such as Bacillaceae (decreased by 23.8 %), Pseudograilibacillus (decreased by 39.6 %), and Massilia (decreased by 31.7 %). Network correlation and FAPROTAX analyses indicated that long-term exposure to robenidine inhibited chitinolysis and aromatic compound degradation pathways. Furthermore, low-dose robenidine increased the activities of dehydrogenase, acid phosphatase, and β-glucosidase by 34.0 %, 24.7 %, and 21.6 % at 1 d, respectively, while these enzymes returned to control levels over time. These findings provide critical insights into the biological and metabolic impacts of robenidine exposure on soil microbial communities, which is crucial for clarifying the ecological concerns associated with robenidine.