Pseudo-persistence of organic fertilizer-derived antimicrobials and estrogens in soil profiles and their potential ecological risks

Organic fertilizer-derived emerging contaminants, such as antimicrobials and estrogens, could migrate vertically into subsoil and potentially reach shallow groundwater aquifers. This study investigated the vertical distribution of these antimicrobials and estrogens in soil profiles, as well as their potential ecological risks, in the Yellow River Delta of China, a major agricultural zone. A total of 47 emerging contaminants, including 42 antimicrobials, 2 antimicrobial degradation products, and 3 estrogens, along with reference contaminant atrazine, were detected within 7 soil layers that were down to 1 ​m below the surface at 10 farmland sites. The concentrations of individual contaminants varied greatly in these soil layers, ranging from 0.0095 to 1680 ​ng/g. Antimicrobials were ubiquitous (detection frequency up to 85%), while estrogens were only detected occasionally (detection frequency up to 27%). The concentrations of antimicrobials and estrogens in subsoil were generally lower than those in topsoil, e.g., the total concentrations of antimicrobials and estrogens in Level 1 (0–5 ​cm) and Level 7 (70–100 ​cm) at all sampling sites were up to 99.3 and 29.2 ​ng/g, respectively. Nineteen out of the 26 emerging contaminants with relevant toxicity data could pose medium to high ecological risk to potential aquatic organisms, soil microbes, and/or crop plants. The ecological risks posed by the organic fertilizer-derived emerging contaminants were comparable in different soil layers in the soil profiles. These findings demonstrate the pseudo-persistence of these emerging contaminants in soil profiles and their substantial potential ecological risks. The data also indicate the need of controlling the residues of antimicrobials and estrogens in organic fertilizers to protect the quality and health of farmland soils.