Article pubs.acs.org/est
Experimentally Determined Soil Organic Matter−Water Sorption Coefficients for Different Classes of Natural Toxins and Comparison with Estimated Numbers Judith Schenzel,†,‡ Kai-Uwe Goss,§ René P. Schwarzenbach,‡ Thomas D. Bucheli,† and Steven T. J. Droge*,§ †
Agroscope Reckenholz-Taenikon, Research Station ART, CH-8046 Zurich, Switzerland Institute of Biogeochemistry and Pollutant Dynamics (IBP), Swiss Federal Institute of Technology, CH-8092 Zurich, Switzerland § Department Analytical Environmental Chemistry, Helmholtz Centre for Environmental Research, UFZ, D-04318 Leipzig, Germany ‡
S Supporting Information *
ABSTRACT: Although natural toxins, such as mycotoxins or phytoestrogens are widely studied and were recently identified as micropollutants in the environment, many of their environmentally relevant physicochemical properties have not yet been determined. Here, the sorption affinity to Pahokee peat, a model sorbent for soil organic matter, was investigated for 29 mycotoxins and two phytoestrogens. Sorption coefficients (Koc) were determined with a dynamic HPLC-based column method using a fully aqueous mobile phase with 5 mM CaCl2 at pH 4.5. Sorption coefficients varied from less than 100.7 L/kgoc (e.g., all type B trichothecenes) to 104.0 L/kgoc (positively charged ergot alkaloids). For the neutral compounds the experimental sorption data set was compared with predicted sorption coefficients using various models, based on molecular fragment approaches (EPISuite’s KOCWIN or SPARC), poly parameter linear free energy relationship (pp-LFER) in combination with predicted descriptors, and quantum-chemical based software (COSMOtherm)). None of the available models was able to adequately predict absolute Koc numbers and relative differences in sorption affinity for the whole set of neutral toxins, largely because mycotoxins exhibit highly complex structures. Hence, at present, for such compounds fast and consistent experimental techniques for determining sorption coefficients, as the one used in this study, are required.
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INTRODUCTION Fungi of the genera Alternaria, Aspergillus, Claviceps, Fusarium, and Penicillium infect agricultural commodities and food worldwide, and produce a plethora of toxic metabolites. Prominent examples of these so-called mycotoxins include aflatoxins, alternaria toxins, trichothecenes, resorcyclic acid lactones, and ergot alkaloids. They contaminate food, beverages, and feed and have been ranked as the most important chronic dietary risk factor, higher than synthetic contaminants, plant toxins, food additives, or pesticide residues.1 Estimated crop losses and human and animal health costs were up to billions of dollars per year worldwide.2,3 Consequently, much research has been carried out on the analysis, exposure assessment, and health effects of mycotoxins.2,4,5 Only recently, the environmental exposure to mycotoxins has been investigated in more detail. We demonstrated emission of zearalenone (occasional) and deoxynivalenol (frequent) into the aquatic environment via drainage and runoff from infested agricultural sites.6−8 In addition, besides field runoff, human excretions may be another relevant source of mycotoxins in the aquatic environment,9,10 depending upon the removal rate in wastewater treatment plants (WWTPs). Deoxynivalenol, for example, is only partially eliminated by Swiss WWTPs.11 Trace levels of nivalenol, 3© 2012 American Chemical Society
acetyl-deoxynivalenol, and beauvericin were recently detected repeatedly in various aquatic environments.12 Next to production and degradation of mycotoxins, sorption is a key parameter for a comprehensive assessment of their environmental fate. Sorption controls transport processes, such as runoff or leaching to groundwater, as well as bioavailability to exposed biota, including microbial degraders of such compounds. Generally, sorption of neutral organic compounds in soils is dominated by their distribution between natural organic matter (NOM) and the surrounding pore water phase.13 To date, measured NOM-water sorption coefficients (Koc) are not determined for mycotoxins from an environmental fate point of view, except for the estrogenic compound zearalenone.14 Most sorption studies involving mycotoxins have focused on feed additive sorbents to reduce mycotoxin exposure in farm animals. Humic material has also been considered as mycotoxin binding additive, but so far only for aflatoxin B 1 , 15 deoxynivalenol,16 ochratoxin A,17 and zearalenone.16,17 The main goal of this work was to establish a consistent set of Received: Revised: Accepted: Published: 6118
January 28, 2012 March 29, 2012 April 27, 2012 April 27, 2012 dx.doi.org/10.1021/es300361g | Environ. Sci. Technol. 2012, 46, 6118−6126
Environmental Science & Technology
Article
Table 1. Chemical−Physical Parameters and Experimental Compound-Dependent Conditions, Including pKa, the Speciation at pH 4.5, and the Used Detection Wavelength λmax, Tested Aqueous Concentration [mg/L], and Experimental Log Koc Data Normalized to 100 mg/kgoc CAS no.
compound
pKaa
564-36-3 511-09-1
ergocornine ergocryptine
7.8 7.8
518-75-2 149-29-1
citrinin patulin
6795-23-9 1162-65-8 7220-81-7 1165-39-5 7241-98-7
aflatoxin aflatoxin aflatoxin aflatoxin aflatoxin
23452-05-3 641-38-3 29752-43-0 28540-82-1
alternariol MMEc alternariol altenuene tentoxin
7.0 7.2 7.4 8.8
17924-92-4 36455-72-8 71030-11-0
zearalenone α-zearalenol β-zearalenol
7.6 7.6 7.6
21259-20-1 26934-87-2 36519-25-2 2270-40-8 2198-92-7 3148-09-2
T-2 toxin HT-2 toxin neosolaniol diacetoxyscirpenol verrucarol verrucarin A
13.2 13.3 13.1 13.4 15.0 14.6
50722-38-8 88337-96-6 51481-10-8 23255-69-8 23282-20-4
3-acetyl-DONd 15-acetyl-DONd DONd fusarenone-X nivalenol
11.8 11.8 11.9 11.7 11.8
519-57-3 10048-13-2
sulochrin sterigmatocystin
7.3 6.9
486-66-8 531-95-3
daidzein equol
3.1 12.1 M1 B1 B2 G1 G2
7.2 10.0
λmax [nm]
speciation at pH 4.5
ergot alkaloids 100% cationic 220 100% cationic 205 penicillium 96% anionic 214 neutral 276 aflatoxins neutral 226 neutral 223 neutral 216 neutral 217 neutral 215 Alternaria toxins 99.7% neutral 205 99.8% neutral 205 99.9% neutral 241 neutral 217 resorcylic acid lactones 99.9% neutral 235 99.9% neutral 211 99.9% neutral 217 Trichothecenes A neutral 205 neutral 205 neutral 205 neutral 205 neutral 205 neutral 261 Trichothecenes B neutral 218 neutral 223 neutral 218 neutral 218 neutral 211 other mycotoxins 99.8% neutral 207 99.6% neutral 205 phytoestrogens 99.8% neutral 248 neutral 260
tested range CAQ‑est [mg/L]
exp. log KOC [L/kgoc] (N)b
0.01−1.2 0.02−0.3
3.88(5) 4.02(4)
0.2−4.4 0.1−1.5
3.10(3) 1.08(3)
0.7−6.2 0.8−10.7 0.4−3.3 0.7−4.3 0.2−3.6
3.18(3) 3.46(12) 3.05(3) 3.31(3) 2.80(3)
0.01−0.1 0.1−0.6 0.1−1.3 0.1−2.9
1.00(3) 2.10(6) 2.58(12) 1.39(3)
0.2−3.2 0.1−1.2 0.4−2.1
3.42(8) 2.87(10) 2.81(13)
8.7−35.5 3.9−93.3 3.0−8.7 1.3−22.4 0.6−4.9 0.1−5.0
1.03(6) 1.01(5)
