PARENT SESSION

1H c (2) - Pharmaceuticals
Hall 6
8:30 AM - 10:15 AM, Thursday, 1 May 2003
Chair: Tolls, J.¹, ¹
Co-chair: Kümmerer, K.², ²

(TH6/5) Effects of different soil treatments on degradation rates of tetracycline in soils.

Hoeper, Heinrich¹, Quack, Balthasar^{1, 3}, Hamscher, Gerd², Fruend, Hans-Christian³, ¹ Geological Survey of Lower Saxony, Bremen, Lower Saxony, Germany³ Department of Agricultural Sciences, University of Applied Sciences, Osnabrück, Lower Saxony, Germany² Department of Food Toxicology, School of Veterinary Medicine, Hannover, Lower Saxony, Germany

ABSTRACT- Tetracycline is one of the most frequently used veterinary drugs worldwide. It reaches soils via animal manure and has been shown in field studies to be only slightly degraded in soils [Hamscher et al., Anal. Chem. 74, 1509-1518, 2002]. A pot experiment was performed to elucidate the effects of different soil treatments, i.e. light vs. darkness, ploughing, liquid manure supply, acidification and plant cultivation (grass), on tetracycline degradation in a sandy and a loamy soil. Pots receiving 10 mg/kg tetracycline were maintained at a constant humidity and exposed to ambient temperatures. After periods of 2, 4 and 6 months pots were sampled and analysed for tetracycline using the agar diffusion technique. The means of daily mean air temperatures were 19, 22 and 18 degree C during the three periods, respectively. Although temperature was varying during the day and within the periods, all treatments showed first order degradation kinetics. The mean half-life over all treatments was 34 and 45 days in the sandy and loamy soil, respectively. The higher sorption potential in the loamy soil compared to the sandy soil was shown to slow down tetracycline degradation rates. Compared to the dark and non-ploughed control only plant cultivation showed a significant effect (p > 0.95) in reducing the degradation rate. This effect was confirmed by chemical analysis using the method of Hamscher et al. (2002). No effect of light, ploughing, liquid manure and acidification on degradation was found. We conclude that degradation of tetracycline is highly depending on soil temperature and only treatments affecting soil temperature tend to have an effect. In the field, at mean soil temperatures of about 15 degree C during the spring, summer and autumn months, tetracycline is degraded in the soil, but at a low rate. If the supply rate exceeds this degradation rate, accumulation of tetracycline will occur.

Key words: degradation, tetracycline, soil