Dynamic distribution of tetracycline and its degradation products in different organs of the geophagous earthworm Metaphire guillelmi

Tetracycline (TC) residues in the environment are harmful to plants and animals; earthworms play an important role in detoxicating tetracycline in the soil. However, the response of different systems of the geophagous earthworm to TC and its degradation products is still not understood well. To understand this problem, Metaphire guillelmi were exposed to the soil contaminated by 100 mg kg^-1 tetracycline for 21 days. Liquid chromatography was used to detect the tetracycline concentration and its degradation products in different organs of earthworms on the 1st, 7th, and 21st day. Structural equation model (SEM) was used to determine the cumulative interaction of TC among different systems of earthworm. The results showed that the degradation ability of TC of digestive organs (98.29-99.77 %) was stronger than that of reproductive organs (87.46-98.64 %). The main metabolic pathway of TC in earthworms might be direct dehydration. Anhydrotetracycline was the main degradation product in earthworm organs and could last long in production organs. For lipid soluble pollutants, such as TC, the digestive system of earthworms might be the main pathway for absorbing pollutants from the soil. Furthermore, earthworms can expedite the degradation of organic pollutants. Meanwhile, they also need to absorb more nutrients like nitrogen and phosphorus, to counteract the impact of pollutants on their antioxidant system and reproductive organs. Our study improves our understanding of the degradation and detoxification mechanism of earthworms to TC, and provides useful information for further assessment of the soil eco-risk.