[The entry of bound residues of tetracyclines into the food chain--a contribution to hazard identification].

Actually, some 67% of therapeutical used antibiotics in livestock in the European Union are tetracyclines. Their use can result in unwanted residues in food of animal origin. Apart the risk of the possible development of resistances in enterobacteriaceae we have to keep in mind secondary circuits. This paper focuses on tetracycline residues in bones. Bones have been widely used as raw material for meat and bone meal and gelatine, and are also a frequent contamination of mechanical recovered meat. Bones contain tetracycline residues in concentrations up to 50 mg/kg. These bound tetracycline residues have ever been thought to be of no significance to health. Nevertheless, recent studies have shown that these tetracyclines could be released in vivo and re-obtain their bioavailability. Further, several toxic degradation products of tetracyclines could be formed during heating. Additionally, in acid solutions from the production of gelatine high tetracycline concentrations have been found. These solutions are processed to dicalciumphosphate, which is used as a feed supplement in animal husbandry and as fertilizer in agriculture.