Antimicrobial agents in agricultural fertilizers produced from sewage sludge – A cause for concern?

The production of organic-mineral fertilizers from sewage sludge is one of the ecological options in their management. Though, pharmaceuticals and their derivatives, which accumulate in the sludge, could be a problem due to their impacts on the environment. This manuscript aimed at better understanding of risks posed by antimicrobial agents (AAs) in sludge-based fertilizers. Sewage sludge and sewage-based fertilizers (from two sewage treatment plants in two cities in Poland) were tested for 99 AAs. 26 AAs were detected in the sludge at concentrations reaching 112,000 μg/kg. Several AAs were successfully removed during the sludge treatment process (sulfasalazine, sulfapyridine, isoniazid, isonicotinic acid, erythromycin, clarithromycin, erythromycin N-desmethyl, clarithromycin N-desmethyl, azithromycin N-desmethyl, emtricitabine, ANP) with reduction ranging from 34 % to 96,5 %. It is worth noting that penicillin V and ofloxacin/levofloxacin were recorded at higher concentrations in the fertilizer than in the sludge, which indicates the process of concentration of these AAs as a result of drying the fertilizer. Penicillin V content increased by 153 % and 191 % in WWTP 1 and WWTP 2 samples, respectively. The level of ofloxacin/levofloxacin increased by 70 % in fertilizer from WWTP 1, and decreased by 40 % in fertilizer from WWTP 2. The AAs leaching test revealed that 7 AAs (isoniazid, sulfapyridine, ofloxacin/levofloxacin, clindamycin, azithromycin, isonicotinic acid, pyrazinoic acid 5-hydroxy-) have potential to leach into the receiving soil environment after sludge-based fertilizer application. The risk factor (RQ) for sulfapyridine, ofloxacin/levofloxacin, isonicotinic acid and linezolid was too low to estimate, below 0.1, so the risk has mild environmental impacts. An RQ value of isoniazid and clindamycin ranging from 0.1 to 1.0 indicates a low risk to soil. Azithromycin RQ >36 denoted a high environmental risk. This warrants further study to understand risks from AAs present in sludge-based products.