Effect of Aerobic and Anaerobic Conditions on Chlorophenol Sorption in Wetland Soils

ant between the solid phase and dissolved phase (sorption), which is governed by the physical and chemical Sorption of four chlorophenols (CPs) was studied in ten wetland properties of the solute, the sorbent, and the solvent. soils with organic C contents between 1 and 44%, which were incuMuch research on organic pollutant sorption has dembated under aerobic or anaerobic conditions to simulate wetland conditions. The objectives of the study were to (i) determine the influence onstrated a strong link between the distribution ratio of aerobic and anaerobic processes on sorption, and (ii) develop sorp(Kp) and the lipophilicity of hydrophobic organic polluttion models to predict the distribution coefficient based on chemical ants, as expressed by its Kow, and the fractional amount characteristics of soils and compounds. Aerobic soils consistently had of organic C of the sorbent (foc): lower pH than anaerobic treatments, which was a function of the amount of oxidizable constituents present in the sample. Depending Kp foc a(Kow) [1] on the pKa of the compound relative to the pH shift, a greater fraction where a and b are empirical constants that differ deof the CP was in the neutral form in the aerobic treatments, which pending primarily on the nature of the pollutant. The was sorbed to a much greater extent than the ionic form (by about relationship has been very useful for predicting sorption 25 times). The organic C normalized distribution coefficient (Koc) was of many hydrophobic organic pollutants by a wide varistrongly related to the octanol-water distribution coefficient (Kow) and soil pH. Sorption models accurately predicted distribution coefficients ety of sorbents; on occasion, however, it has been found within a factor of 2 from the Kow and pKa of the compounds and the to be deficient for ionizable organic compounds such pH and organic C content of the sorbent. The role of sorption on CP as CPs. retention was partially negated by the formation of the nonseparable In studies on the sorption of CPs in soils and sediphase, which composed up to 8.6% of the total solid mass (depending ments, Schellenburg et al. (1984) and Lagas (1988) on the soil redox status) and had similar distribution coefficients as found that the model for hydrophobic compounds had the separable phase. This study demonstrated that microbial redox limited application because it did not account for the processes significantly influenced the soil properties and CP retention contribution of both the neutral species and the phecharacteristics, and should be considered when designing a bioremedinolate anion to overall sorption. Shimizu et al. (1992) ation plan for these compounds. derived a model that accounted for the contribution of both species to the distribution coefficient of PCP (pKa 4.74): C are common contaminants in soils, sediments, surface waters, and groundwater, largely Kp Ko p φ K p (1 φ) [2] because of their worldwide utilization in the last 50 yr where Ko p and K p are the distribution coefficients, and as wood preservatives, and general biocides in industry φ and 1 φ are the fractional amounts of the neutral and agriculture (ATSDR, 1998). Chlorophenols are also species and phenolate species, respectively. They found by-products of pulp mill effluent chlorination (Paasithat pentachlorophenolate sorption accounted for varta et al., 1983; Kringstad and Lindstrom, 1984), and 90% of overall sorption when the pH was 6, even chloro-aromatic transformations (Mikesell and Boyd, though the distribution coefficient for the anion (K p ) 1985). Pentachlorophenol (PCP) is toxic to all life forms, was up to 60 times lower than for the neutral species is commonly found at National Priorities List sites (Ko p). They also observed that outside the pH range 6 (about 20%), and is classified as a priority pollutant by to 8, there were considerable changes in the chemical the USEPA. nature of the sorbent and solvent that decreased the Chlorophenols are subject to several abiotic and accuracy of the model. They warned that the model biotic processes, including photodegradation (Wong should be appropriately amended under these condiand Crosby, 1981), volatilization (Pignatello et al., 1983), tions. plant and animal uptake (Weiss et al., 1982; Larsson et In natural ecosystems, microbial breakdown of plant al., 1993), and microbial degradation (Laine and Jorgendetritus, solubilization of humic substances, erosion, resen, 1997; D’Angelo and Reddy, 2000). A major factor suspension, and bioturbation events can contribute sigcontrolling these processes is distribution of the pollutnificant levels of dissolved and suspended organic and E. D’Angelo, Univ. of Kentucky, Soil & Water Biogeochemistry Lab., Abbreviations: CP, chlorophenol; CR, Crowley soil; DCP, 3,5-dichloDep. of Agronomy, N-122 Agricultural Science Building North, Lexrophenol; DOC, dissolve organic C; HLPI, Houghton Lake Peat– ington, KY 40546-0091; K.R. Reddy, Univ. of Florida, Soil and Water impacted by domestic waste; HLPU, Houghton Lake Peat–unimScience Dep., 106 Newell Hall, P.O. Box 110510, Gainesville, FL pacted by domestic waste; KOC, organic C normalized sorption 32611-0510. Florida Agricultural Experiment Station Journal Series coefficient; KOW, octanol water distribution coefficient; Kp, linear sorpNo. R-09194. Received 13 Feb. 2001. *Corresponding author (edangelo@ tion coefficient; LSM, Louisiana salt marsh; PCP, pentachlorophenol; uky.edu). TAL, Talladega soil; TeCP, 2,3,4,5-tetrachlorophenol; TCP, 3,4,5trichlorophenol. Published in Soil Sci. Soc. Am. J. 67:787–794 (2003).