Effects of Physical-ChemicalCharacteristics on the Sorption ofSelected Endocrine Disruptors byDissolved Organic MatterSurrogatesHIROSHI YAMAMOTO,*,†HOWARD M. LILJESTRAND,†YOSHIHISA SHIMIZU,‡ANDMASATOSHI MORITA§Department of Civil Engineering, The University of Texas atAustin, 1 University Station C1786, Austin, Texas, 78712-0273,Research Center for Environmental Quality Control,Kyoto University, Otsu, Shiga, Japan, and National Institutefor Environmental Studies, Tsukuba, Ibaraki, JapanSorption coefficients (Kocvalues) of selected endocrinedisruptors for a wide variety of dissolved organic matter(DOM) were measured using fluorescence quenching andsolubility enhancement. 17β-Estradiol, estriol, 17R-ethynylestradiol,p-nonylphenol,p-tert-octylphenol, anddibutylphthalate were selected as endocrine disruptors.Aldrich humic acid, Suwannee River humic and fulvic acids,Nordic fulvic acid, alginic acid, dextran, and tannic acidwere selected as DOM surrogates. The resulting sorptioncoefficients (logKoc) were independent of octanol-water partitioning coefficients (logKow) of the selectedendocrine disruptors, indicating the hydrophobic interactionis not the predominant sorption mechanism. Moreover,theKocvaluesfortheselectedendocrinedisruptors,especiallythe steroid estrogens, correlated much better with UVabsorptivityat272nm(A272)andphenolicgroupconcentrationof the DOM than with either the H/O or the (O+N)/Catomic ratio of the DOM. This suggests that the sorptionmechanism is closely related to the interaction betweenπ-electronsandthehydrogenbonds,i.e.,theaffinitybetweenphenolic groups of the steroid estrogens and DOM issuggested to provide a relatively large contribution to theoverall sorption and yield theKocvalues of the steroidestrogens as high as those of the alkylphenols anddibutylphthalate, which are suggested to be dominated bynonspecific hydrophobic interaction.IntroductionIt is widely recognized that the sorption of hydrophobicorganic compounds onto dissolved natural organic mattermaysignificantlyincreasetheiraqueoussolubility(1-6).Thissolubility enhancement affects the fate of these chemicalspecies in an aqueous environment (7-9) and water treat-mentprocesses(10,11).Furthermore,increasesindissolvedorganic matter (DOM) concentration results in decreases inthe bioavailability and the bioaccumulation of these chemi-cals (12-14) while attenuating their toxicity (15-17). Con-sequently, trends in sorption of hydrophobic chemicalcompounds by DOM are of critical importance for theunderstanding of the solubility, fate, and impact of thesecompounds in the environment.Steroid estrogens and endocrine-disrupting phenoliccompounds(e.g.,alkylphenolsandbisphenolA)areoneclassof hydrophobic organics ubiquitous in the environmentwhose fates are important. They have been linked to recentreproductive health problems reported in humans and wildanimals(e.g.,ref18).Inwastewatertreatmentplanteffluentsandsurface waters,concentrationsof steroidestrogenshavebeen found as high as 200 ng/L (19-26), while those foralkylphenols and phthalates have been reported as high as40 µg/L (20, 23, 25-27). Given the difficulties in quantifyingthese trace chemicals and DOM, little is known about howtheir interactionsinfluence thefate of endocrine-disruptingcompounds.Consequently, the sorption of endocrine disruptorsincludingsteroidestrogensbyDOMisofcriticalimportancefor the understanding of the fate of these compounds intheenvironment. Although the sorption of highly hydrophobiccompounds such as PAHs, PCBs, and pesticides by DOMhave been extensively studied over the last three decades(1-6,28-53),littleisknownaboutthesorptionofmoderatelyhydrophobic compounds such as steroid estrogens andalkylphenolsbyorganicmatterexceptforsomerecentstudieson the sorption of steroid estrogens by sediments (54, 55)andthesorptionofnonylphenolbyterrestrialsoil(56).Hencethesorption ofthreesteroid estrogens,17β-estradiol,estriol,and 17R-ethynylestradiol, and three endocrine-disruptingchemicals, p-nonylphenol, p-tert-octylphenol, and dibutyl-phthalate, by a wide variety of DOM surrogates are inves-tigated using fluorescence quenching and solubility en-hancement.Thecorrelationbetweenthemeasuredsorptioncoefficients(logKocvalue)andtheoctanol-waterpartitioningcoefficients (log Kow) for these species are evaluated andcompared with other reported results. Moreover, the rela-tionships between log Kocand physical-chemical charac-teristics (e.g., absorptivity, H/O atomic ratio, and theconcentrationof phenolicgroup) ofthe DOMsurrogates arealso investigated to better understand the sorption mech-anisms.Experimental Section17β-Estradiolwasselectedasoneofthemostcommonsteroidestrogens, one often used as a positive control for thescreeningtestsforestrogeniccompounds.Additionalsteroidestrogensselectedwereestriol(E3),an importantpregnancyestrogen as well as a metabolite of 17β-estradiol (E2), and17R-ethynylestradiol (EE2), the main component of con-traceptivepills.p-Nonylphenol(NP),p-tert-octylphenol(OP),and dibutylphthalate (DBP) were selected as syntheticestrogeniccompoundsbecauseoftheirhighproductionandreleasetotheenvironmentaswellastheirabilitytofluoresce.The chemical structure and physical-chemical propertiesof the selected compounds are shown in Table 1. 17R-Ethynylestradiol (98%, HPLC grade) and dibutylphthalate(98%) were purchased from Sigma Chemical Co. (St. Louis,MO), while 17β-estradiol (Minimum 97%), estriol (98%),p-nonylphenol (tech grade), and p-tert-octylphenol (97%)werepurchasedfromAldrichChemicalCo.(Milwaukee,WI).* Corresponding author phone: +81-29-850-2855; fax: +81-29-850-2880; e-mail: [email protected]. Present address:National Institute for Environmental Studies, Endocrine Disruptorsand Dioxin Research Project, 16-2 Onogawa, Tsukuba, Ibaraki 305-8506, Japan.†The University of Texas at Austin.‡Kyoto University.§National Institute for Environmental Studies.Environ. Sci. Technol.2003,37,2646-265726469ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 37, NO. 12, 2003 10.1021/es026405w CCC: $25.00  2003 American Chemical SocietyPublished on Web 05/21/2003TheselectedDOMsurrogatesincludedAldrichhumicacid,SuwanneeRiverhumicacid,SuwanneeRiverfulvicacid,andNordic fulvic acid. Humic acid and fulvic acid account for6-8% and 54-72%,respectively, of the total organiccarbon(TOC)inDOMextractedfromtypicalriversandstreams(57).Suwannee River humic and fulvic acids and Nordic fulvicacidwerepurchasedfromtheinternationalhumicsubstancesociety