Detection rate and concentration of tetracycline antibiotics in organic fertilizers raw materials and commercial products in China

Objectives Livestock manures from intensive farming often contain a certain amount of antibiotics, which could get into farmland when applied as fertilizers. To provide a basis for their safe recycling, we investigated the concentration of tetracycline antibiotics (TCs) in the raw materials and commercial products of organic fertilizers in China.

Methods 180 samples of organic fertilizer raw materials (including auxiliary materials) and 244 samples of commercial organic fertilizer products were collected nationwide for the analysis of oxytetracycline (OTC), tetracycline (TTC), chlortetracycline (CTC), and doxycycline (DXC). The commercial organic fertilizer products only included those made from livestock manure.

Results The total detection rate of the four TCs in all the samples was 24.29%, and 35.00% in raw materials and 16.39% in the commercial products, with the rate being lower in the latter than in raw materials. Detection rate of one or two types of antibiotics in total samples was 80.58%, 92.50% in the commercial products and 73.02% in raw materials. The detected concentration of the 4 TCs was in the order of CTC (22.11 mg/kg) > OTC (2.49 mg/kg) > TTC (1.74 mg/kg) > DXC (0.71 mg/kg), and the detection rate was in the order of OTC (14.39%) > DXC (11.08%) > CTC (8.96%) > TTC (6.13%). The detection rate of the four TCs in raw materials was pig manure (83.33%) > chicken dung (66.67%) > cow dung (30.77%) > sheep dung (24.42%). Residues, including oil residues (dry cakes), yeast residues and bone meal were also detected, indicating that TCs were not only widely used in animal husbandry but also had been extended to mushroom cultivation and leftovers from the animal-derived food industry. The contents of CTC, TTC and OTC in sheep dung were higher, and those of CTC and OTC in pig manure were higher. The removal rates of TCs in commercial products were in the order OTC (77.81%) > CTC (75.02%) > TTC (72.84%) > DXC (62.80%). Inner Mongolia and Gansu were the regions with the highest detection rate and concentration of the 4 TCs investigated.

Conclusions The composting process of organic fertilizer generally removes 62.80%−77.81% of the four kinds of TCs in organic fertilizer raw materials, and the order of removal rate is OTC>CTC>TTC>DXC. At present, the detection rate of the four TCs in all the raw-materials and commercial organic fertilizer products is 24.29%, and that in commercial organic fertilizer products (16.39%) is lower than in raw materials (35.00%).