Different behavior of tetracyclines and sulfonamides in sandy soils after repeated fertilization with liquid manure

Recently we showed that tetracyclines tend to persist and may accumulate in sandy soils after repeated fertilizations with liquid manure. We continued these field investigations from 2001 to 2003 and observed no further accumulation of tetracyclines in soil, but found that the average tetracycline concentration remained higher than 150 μg/kg soil. From 2000 to 2002, approximately 330 g tetracycline, 7 g chlortetracycline, 28 g sulfamethazine, and 57 g sulfadiazine per hectare were transferred via liquid manure to the topsoil (0–30 cm). Nevertheless, no leaching of tetracyclines into deeper soil segments or groundwater was observed. Furthermore, we developed new analytical methods for the detection of various sulfonamides in liquid manure, soil, and groundwater. Investigation of the same fields used in the tetracycline study showed that sulfamethazine occurred in concentrations approximately two orders of magnitude lower than that of tetracycline in the plow layer. Although there apparently were very low concentrations of sulfamethazine in soil, we detected it in groundwater sampled by suction probes at 1.4 m below soil surface in the spring of 2002. Further investigations confirmed these findings. To our knowledge, this is the first direct evidence of continuous leaching of a veterinary drug from soil into groundwater under field conditions. We conclude that tetracyclines and sulfonamides show distinctly different environmental behaviors. One explanation may be their different sorption coefficients in soil, indicating (in part) their different mobilities in this ecosystem.