ter Laak Thomas L, Wouter A Gebbink, Tolls Johannes
IRAS-Institute for Risk Assessment Sciences, Utrecht University, Yalelaan 2, P.O. Box 80176, 3508 TD Utrecht, The Netherlands.
Environ Toxicol Chem. 2006 Apr;25(4):904-11. doi: 10.1897/05-232r.1.
Antimicrobial agents are the most heavily used pharmaceuticals in intensive husbandry. Their usual discharge pathway is application to agricultural land as constituents of animal manure, which is used as fertilizer. Many of these compounds undergo pH-dependent speciation and, therefore, might occur as charged species in the soil environment. Hence, pH and ionic strength of the soil suspension can affect the sorption behavior of these compounds to soil. Consequently, the soil sorption of three antimicrobial agents--sulfachloropyridazine (SCP), tylosin (TYL), and oxytetracycline (OTC)--was investigated. Their respective sorption coefficients in two agricultural soils ranged from 1.5 to 1,800 L/kg. Sorption coefficients were greater under acidic conditions. Addition of an electrolyte to the solution led to decreased sorption of TYL and OTC by a factor of 3 to 20, but it did not influence the sorption of SCP. This behavior was analyzed by accounting for the pH-dependent speciation of TYL and OTC and considering the presence of OTC-calcium complexes. It appears that the decreased sorption of TYL and OTC with increasing ionic strength results from competition of the electrolyte cations with the positively charged TYL species and the positively charged OTC complexes. A model linking sorbate speciation with species-specific sorption coefficients can describe the pH dependence of the apparent sorption coefficients. This modeling approach is proposed for implementation in the assessment of sorption of ionizable compounds.
抗菌剂是集约化养殖中使用最为频繁的药物。它们通常的排放途径是作为动物粪便的成分施用于农田，而动物粪便用作肥料。这些化合物中有许多会发生pH值依赖性的形态变化，因此在土壤环境中可能以带电物种的形式存在。因此，土壤悬浮液的pH值和离子强度会影响这些化合物对土壤的吸附行为。为此，研究了三种抗菌剂——磺胺氯哒嗪（SCP）、泰乐菌素（TYL）和土霉素（OTC）——在土壤中的吸附情况。它们在两种农业土壤中的各自吸附系数在1.5至1800 L/kg之间。在酸性条件下吸附系数更大。向溶液中添加电解质会导致TYL和OTC的吸附减少3至20倍，但不会影响SCP的吸附。通过考虑TYL和OTC的pH值依赖性形态变化以及OTC-钙络合物的存在来分析这种行为。看来，随着离子强度增加，TYL和OTC吸附减少是由于电解质阳离子与带正电荷的TYL物种以及带正电荷的OTC络合物之间的竞争所致。一个将吸附质形态与物种特异性吸附系数联系起来的模型可以描述表观吸附系数的pH值依赖性。建议在评估可电离化合物的吸附时采用这种建模方法。
