Environ. Sci. Technol. 2008, 42, 7193–7200
Azole Fungicides: Occurrence and Fate in Wastewater and Surface Waters MAREN KAHLE, IGNAZ J. BUERGE,* ¨ LLER, ANDREA HAUSER, MARKUS D. MU AND THOMAS POIGER Plant Protection Chemistry, Agroscope Changins-Wa¨denswil Research Station ACW, Schloss, P. O. Box 185, 8820 Wa¨denswil, Switzerland
Received April 3, 2008. Revised manuscript received July 24, 2008. Accepted July 29, 2008.
The mode of action of azole compounds implies a potential to affect endocrine systems of different organisms and is reason for environmental concern. The occurrence and fate of nine agricultural azole fungicides, some of them also used as biocides, and four azole pharmaceuticals were studied in wastewater treatment plants (WWTPs) and lakes in Switzerland. Two pharmaceuticals (fluconazole, clotrimazole, 10-110 ng L-1) and two biocides (propiconazole, tebuconazole, 1-30 ng L-1) were consistently observed in WWTP influents. Loads determined in untreated and treated wastewater indicated that fluconazole, propiconazole, and tebuconazole were largely unaffected by wastewater treatment, but clotrimazole was effectively eliminated (>80%). Incubation studies with activated sludge showed no degradation for fluconazole and clotrimazole within 24 h, but strong sorption of clotrimazole to activated sludge. Slow degradation and some sorption were observed for tebuconazole and propiconazole (degradation half-lives, 2-3 d). In lakes, fluconazole, propiconazole, and tebuconazole were detected at low nanogram-per-liter levels. Concentrations of the pharmaceutical fluconazole correlated with the expected contamination by domestic wastewater, but not those of the biocides. Per capita loads of propiconazole and tebuconazole in lakes suggested additional inputs; for example, from agricultural use or urban runoff rainwater.
Introduction Azole compounds, classified into triazoles and imidazoles, are widely used as fungicides in agriculture, biocides in various products, and antifungal agents in human and veterinary pharmaceuticals (1, 2). Some azoles are also prescribed in cancer therapy (1). The biological activity of azoles is based on their inhibition of certain pathways of steroidogenesis. Azole fungicides show activity against a broad spectrum of fungi by inhibition of fungal lanosterol-14R-demethylase (a cytochrome P-450 enzyme, encoded by the CYP51 gene) (1). The mode of action of azoles used in cancer therapy is the reduction of estrogen levels by inhibition of aromatase (CYP19); however, specificity of enzyme inhibition of azole compounds is poor, both with respect to fungal versus nonfungal CYP51 and versus other cytochrome P-450 en* Corresponding author phone: +41-44-7836383; fax: +41-447806341; e-mail:
[email protected]. 10.1021/es8009309 CCC: $40.75
Published on Web 08/27/2008
2008 American Chemical Society
zymes including aromatase (1, 3). Since azole fungicides interact with several cytochrome P-450 enzymes, they may have the potential to affect the endocrine system of aquatic organisms (1, 4). As a consequence of their common use, substantial amounts of azoles may reach the environment. In Switzerland, 17 azole fungicides are currently registered for agricultural use, with a total sale of 33 tons in 2004 (5). A survey among pesticide companies revealed that prochloraz, tebuconazole, cyproconazole, difenconazole, flusilazole, propiconazole, and epoxiconazole were the most frequently sold azole compounds in Switzerland in 2004 (decreasing order, range 1-6 tons). Azole fungicides used in agriculture are moderately lipophilic and fairly persistent with typical halflives of weeks to months (Table 1 of the Supporting Information) (6). They may reach the aquatic environment primarily by surface runoff and spray drift (7, 8). According to the biocide evaluation list of the Commission of the European Communities, propiconazole, tebuconazole, and imazalil are existing active substances registered for several biocidal product types, including wood or coating preservatives (2). Unfortunately, precise data on sale and entry pathways to the environment of azole biocides are not available. For human pharmaceutical use, 14 azole compounds are currently registered in Switzerland. In 2005, ketoconazole, clotrimazole, econazole, itraconazole, fluconazole, and miconazole were prescribed most frequently in Switzerland. Altogether, the sales volume of human azole pharmaceuticals was about 1 metric ton (9). The pharmaceuticals are administered orally or topically, depending on substance. Excretion of orally administered parent compounds and metabolites and removal of topically administered azoles from skin during washing are probably the major entry pathways of azole pharmaceuticals to wastewater. Studies investigating occurrence and fate of azole fungicides in wastewater and surface waters are rare. Propiconazole, prochloraz, triadimenol, epoxiconazole, and tebuconazole were detected in water samples from ditches and headwater streams at concentrations of up to a few micrograms per liter (10, 11). In U.K. estuary water samples, clotrimazole was found at concentrations of up to 34 ng L-1 (12, 13), whereas in the German river Elbe, the compound was not detectable (
