- Top of page
- MATERIALS AND METHODS
- RESULTS AND DISCUSSION
Applying sewage sludge to soil is a common practice in many parts of the world. Thus, pharmaceutical compounds, such as azoles, can be released into the environment after sludge is applied to soil. To understand the fate of clotrimazole and fluconazole (pharmaceuticals used as antifungals in humans) in soil after its amendment with sludge, a reliable and sensitive method has been developed to determine these compounds in the solid and aqueous phases of soil. Desorption of clotrimazole from soil amended with sludge was negligible, whereas a rapid desorption of fluconazole was observed. Dissipation rates of these azoles were determined in amended soil incubated at 25°C with moisture contents ranging from 4.5 to 20%. Clotrimazole was more persistent than fluconazole in dry soil, whereas the contrary occurred in wet soil. Partitioning soil:soil solution of these azoles varied with time and moisture contents. Clotrimazole was found in soil with negligible amounts in soil solution, whereas fluconazole was approximately partitioned 50:50 during the assay time (60 d) at any soil moisture content. Occasional rainfall coupled with a relatively low binding soil capacity can result in the contamination of surface and groundwaters by fluconazole, whereas clotrimazole will remain in the soil. Environ. Toxicol. Chem. 2012;31:501–507. © 2011 SETAC
- Top of page
- MATERIALS AND METHODS
- RESULTS AND DISCUSSION
Clotrimazole and fluconazole (Table 1) are antimycotic agents widely used in the treatment of fungal infections. These compounds block the sterol biosynthesis by inhibiting cytochrome P450-dependent 14α-demethylases. Clotrimazole is commonly administered in topical formulations, whereas fluconazole is administered topically and orally. After application, these azoles can be removed from the body by washing or through urinary excretion, which are the main entry pathways of azoles to municipal wastewater. Furthermore, the incomplete removal of azoles during wastewater treatment may be the origin of their presence in the effluent and sewage sludge of wastewater treatment plants. Thus, they may be introduced into the aquatic environment by waterways, or into the terrestrial environment by land application of sewage sludge, where they may cause toxic effects in nontarget organisms. Azoles are also inhibitors of the P450 aromatase, which catalyses the conversion of androgens to estrogens affecting sex differentiation in vertebrates exposed to these compounds 1, 2. Clotrimazole has been reported to show endocrine disruption activity in rainbow trout, frog, and salmon, as well as to affect photoprotective xanthophyll pigments in microalgal communities 2–5. In addition, exposure to triazoles can cause skeletal defects and malformations in mouse embryos 6, 7.
Table 1. Physico-chemical properties of studied azoles
|Vapor pressure (Pa)||3.31 × 10−7||3.89 × 10−7|
|Molecular weight (g/mol)||344.8||306.3|
|Water solubility (mg/L)||0.49||1.0|
To monitor these azoles in the environment and understand their environmental behavior, reliable and sensitive analytical methods are needed. Determination of clotrimazole and fluconazole by gas chromatography–mass spectrometry (GC-MS) and liquid chromatography–tanden mass spectrometry (LC-MS/MS) in aquatic environmental samples have been reported in the last eight years 8–13, whereas only a few articles have been published on the analysis of these compounds in sludge by using LC-MS/MS, and where the presence of clotrimazole, and in some cases of fluconazole, in this matrix has been reported 12–14. However, validated methods for the analysis of these azoles in soil or soil solution have not been found in the scientific literature.
The use of sludge as fertilizer in agriculture accounts for a high amount of the total municipal sludge disposal in many countries; thus, soil application of sludge is generally considered a sustainable practice. However, concerns exist with respect to the content and fate of organic contaminants present in the sludge, because its land application over the years could lead to an uncontrolled emission of organic pollutants into the environment that can remain for an extended period of time. In Europe, the pathogen and heavy metals content in sludge are regulated 15, but the levels of organic pollutants in sewage sludge have not yet been regulated in the European Union. Some European countries, however, have set limits for certain organic contaminants.
To evaluate the potential risk of an organic pollutant in sludge, it is not only necessary to know its levels in that matrix before soil application, but other factors have to be taken into account—such as soil properties, environment conditions, and sludge characteristics—which may affect the fate of pollutants in sludge-amended soil. The solid phase of soil represents an important component of the agronomic studies concerning the long-term assessment of the soil–plant system equilibrium, and of the evaluation of soil fertility. Another important component of the soil system is the soil solution, which is an efficient indicator of nutrient supply, with a chemical composition that directly reflects the balance between the soil solid phase and plants by constituting the interface where processes such as root absorption, soil chemical reactions, and solutes redistribution occur 16. Moreover, terrestrial organisms are exposed to chemical contaminants mainly through soil solution and, in addition, the soil solution can transport pollutants to surface water or groundwater.
The behavior of organic contaminants in soil depends on different dynamic physical, chemical, and biological processes that include sorption–desorption, volatilization, chemical and biological degradation, uptake by plants, run-off, and leaching. These processes govern the mobility of organic contaminants in soil, their bioavailability, and their transfer to other environmental compartments, such as the atmosphere and water 17, and are dependent on the physicochemical properties of pollutants, the environmental conditions, and the soil properties.
No data have been found in the literature regarding the behavior of the studied azoles in sludge-amended soil, and no analytical methods are available for their quantification in this matrix and in soil solution. The aim of the present work was to develop a reliable analytical method to quantify clotrimazole and fluconazole in these matrices, and to study the fate of these azoles in sludge-amended soil by determining desorption, dissipation rates, and changes with time of their levels in soil and soil solution under different soil moisture contents.