United States Environmental Protection Agency Robert S. Kerr Environmental Research Laboratory Ada OK 74820 Research and Development EPA/600/S6-89/002 Sept. 1989 AEPA Project Summary Assessment of the Potential for Transport of Dioxins and Codisposed Materials to Groundwater Richard W. Walters, Zohreh Yousefi, Amy L. Tarleton, Stanley A. Ostazeski, and David C. Barry Parameters relevant to the sorptive transport of polychlorodibenzo-p- dioxins (PCDDs) through soils were evaluated In laboratory experiments involving batch snake testing and sat- urated-flow soil column techniques. The experiments were conducted using water/methanol mixtures and four uncontaminated sorbents (two surface soils from Times Beach, MO and aquifer materials from Traverse City, Ml and Lula, OK). Five "re- labeled PCOO cogeners, including 2,3,7,8-tetra (T4COO), 1,2,3,4,7-penta, 1,2,3,4,7,8-hexa, 1,2,3,4,6,7,8-hepta, and octa (O8CDD), and three codls- posed materials pentachlorophenol (POP), and chloroberusene (CB) were used. The partition coefficient (KD) for sorptien of T«CDD from water was found to be in good agreement with the water-phase K0 predicted by log- linear extrapolation according to the cosolvent theory by using KD data generated) for water/methanol mix- tures. This observation validates the use of'log-linear extrapolation to esti- mate water-phase KD values for PCDDs using cosolvent data. KD values for sorption of PCDDs by sur- face soils at volume fraction solvent (fs) of 0.5-0.9 were reduced by a factor of up to 2.5 when PCP or CB were present Reductions in KD for PCDDs in the presence of PCP and CB increased with decreasing fs to enable a better understanding of the influence of codisposed materials such as PCP and CB on the mobility of PCDDs under environmental con- ditions typified by low f, (i.e., f, < < 0.5). Sorption KD values for the aquifer materials were normalized on organic carbon content (f^) to yield values of KQC which were in general agreement with Koc values deter- mined for the surface soils. This ob- servation suggests that sorption by the organic matter content or the aquifer materials was sufficient to mask sorption to mineral surfaces. Desorption of PCOOs from the sur- face soils appeared to be reversible but was limited by kinetics, with roughly 50-90% of reversible-desorp- tion equilibrium being attained within a contact period of 30-50 days. This Project Summary was de- veloped lay EPA's Robert S. Kerr En- vironmental Research Laboratory, Ada, OK, to announce key findings of the research prefect that is fully docu- mented in a separate report of the same title (see Protect Report ord- ering information at back). Introduction Polychlorodibenzo-p-dioxins as en- vironmental contaminants have perhaps received most widespread national at- tention because they were present in waste oils that were used for dust control in Missouri. PCDD-contamination of soils and sediments in various locations throughout the United States and in other countries have been documented. ------- Concentrations of PCDDs in soil and sediment samples as high as 1600 ppb to 100 ppm have been observed. Until recently it was believed that PCDDs were relatively immobile in soils because of their low water solubilities, and that there was little potential for PCDDs to be leached from contaminated soils. Field observations have shown that PCDDs move faster through soils than would be expected based on their water solubilities. Numerous theories have been proposed to explain the "facilitated transport" of PCDDs and other highly hydrophobic organic contaminants, in- cluding a cosolvent which accounts for enhanced mobility in terms of the reduction in soil sorption in the presence of cosolvents. The research presented in the full re- port involved three basic objectives; 1) determine the relative effect of the presence of codisposed materials on the sorptive transport of PCDDs through surface soils, 2) evaluate the equilibrium sorption of PCDDs by aquifer materials, and 3) evaluate the kinetics of desorption of PCDDs from surface soils. Procedure Solutes All PCDDs used in the experiments were radiolabeled with C-14. Individual stock solutions of the radiolabeled PCDDs were prepared by dissolving them in methanol. Other radiolabeled compounds used in the experiments included pentachloro- phenol (PCP), methanol and water. All radiolabeled compounds were used as received from the supplier. So//s and Aquifer Materials The soils obtained from Times Beach, MO were the same as those used in pre- vious investigations of the sorption of PCDDs to soils. These soils were air dried, sieved through 0.3 mm standard sieves, and characterized for pH, cation exchange capacity, organic matter con- tent, organic carbon, organic nitrogen and texture. The soils are referred to here as soil 91 (low-organic carbon soil) and soil 96 (high-organic carbon soil). Lula, OK and Traverse City, Ml aquifer materials were provided by the EPA Project Officer and were used as received. Solvents Methanol and methylene chloride sol- vents used in the experiments described were pesticide grade and were used as received from the supplier. Water was treated by reverse osmosis, activated carbon bed and a pair of mixed bed deionizers. Further, the water was dosed with 0.01% NaN3, as a biocide and its ionic strength was adjusted to 0.01 M using CaCI2. The pH of the water was adjusted to 7.0 using NaOH. Scintillation Cocktail An insta-gel liquid scintillation cocktail obtained from United Technologies was used for all radioisotope analyses. Analyses Liquid Scintillation Counting Analytical determinations were made by liquid scintillation counting (LSC) using a Model 1219 Rackbeta counter. Liquid-phase solute concentrations (C or Ce) were determined by sampling three aliquots of 1-3 ml of liquid phase and adding the sample to 10 ml of Insta- gel cocktail in 20-ml glass counting vials. Soil-phase solute concentrations (S of Se) were determined primarily by the dif- ference of the total solute minus liquid- phase solute. However, to confirm mass balances direct determination of soil- phase solute concentrations was made to determine mass balances. Data Manipulation Isotherm data were evaluated by linear regression to determine best-fit param- eters for sorption constants. Best-fit estimates of KD, the coefficient of de- termination (r2), and the standard error of the estimate (s) were calculated using standard equations. Values of Kobs were determined from the effluent concentration profiles ob- tained from saturated-flow soil column experiments. Kobs is the value of KD calculated from the proper equation under the assumption of local equilibrium and a value of Vr equal to the ratio of sorbing solute to nonsorbing solute re- tention time as determined by the center- of-mass of the respective effluent peaks. Least-squares regression analysis was used to determine the best-fit estimates of the slope (m) and intercept (b) for proposed cosolvent equations. The values of m and b and the regression sta- tistics were determined by using standard techniques. Desorption data were regressed ac- cording to empirical exponential and power-curve models. Solubility Determinations Batch techniques already described to evaluate T4CDD solubility in water/ methanol mixtures were used to evaluate the solubilities of the other PCDDs. E> periments were conducted in 1-ml glas microvials. PCDD crystals were pre coated onto the inner wail near th bottom of vial by delivering a workin solution containing PCDD and the evaporating the solvent with nitrogei One ml of liquid phase was then added t the precoated microvial, the vials wet capped and covered with aluminum fo and then placed on a shaking table. Th vials were shaken daily for 15 minutes ft contact periods up to 28 days. Batch Shake Testing The batch shake testing techniqu which was used to generate data pn sented in this report was based on pul lished procedures to evaluate sorptic and desorption of PCDDs to/from soils. Experiments Involving Water/Methanol Mixtures Batch experiments involving wate methanol mixtures were conducted in 1 ml conical glass centrifuge tubes. Tubes were dosed by direct addition soil or aquifer material (0.2-1.0 gm), liqu phase and solute (delivered by dire dosing of stock solutions). A liquid-pha: volume of 12-ml was added to the tub< except for experiments involving PCP < solute, in which case the tubes were filk completely with liquid phase. Experiments conducted to evaluate tl sorption of PCDDs in the presence PCP and CB were performed at co centrations from 1-10% of solubility. After dosing, the tubes were place horizontally on a shaking table and we shaken for 15 minutes every hoi Contact periods ranged from 2 hr to 30 and varied according to the type of e periment (kinetic/equilibrium) and tl soil-solute-liquid phase system und study. Following contact, tubes were r moved from the shaking table ai centrifuged at 2,000 x g for 10 minute to achieve adequate separation of liqi and solid phases. Water-Phase Experiments Two batch procedures were utilized generate isotherm data for the sorption T4CDD from water by soil 91. Both s< of experiments were conducted using 50-ml round bottom glass centrifu tubes fitted with Teflon-lined screw caj Soil and water doses to the tubes we approximately 50 mg and 40 ml. PCP Screening Experiments Preliminary experiments were cc ducted to validate mass balances and I ------- centrifugation procedure used to evaluate sorption of PCP. Using general batch shake test pro- cedures mass balance experiments were conducted with and without soil to assess recovery of PCP. Kinetic Evaluations Time series experiments involving sorption of PCP from water by soils 91 and 96 and sorption of P5CDD and OgCDD by the two aquifer materials were conducted to determine the contact time necessary to attain sorption equilibrium and to qualitatively evaluate sorption kinetics. Experiments involving PCP were con- ducted by using 0.3 g of soil and a PCP dose such that initial concentration in the liquid phase was 0.035 ng/ml. Liquid volume in these experiments was 15-17 ml as necessary to completely fill the centrifuge tube in order to minimize volatile losses of PCP into the head- space. Tubes were contacted for various times and prepared in triplicate for each contact periods. Experiments involving aquifer material utilized contact periods of 2-72 hr. These experiments were performed at a fs of 0.65 for 08CDD. P5CDD and 08CDD were chosen on the basis of known kinetic data for surface soils which indicated that these PCDDs bound the kinetic behavior of all PCDDs studied. Saturated-Flow Soil Column Testing Saturated-flow soil column testing was performed to validate the use of the column techniques for estimating the KD of the PCDDs. These column techniques were then applied to study the sorption of PCDDs in the presence of PCP and CB. These soil column experiments used either a glass column (2.5 cm x 25 cm) fitted with an adjustable plunger, to ac- commodate variable soil masses in the column, or a stainless steel column (0.48 cm x 10 cm). Column Packing The glass column was slurry packed by adding a known mass of soil (15-25 g) to roughly 20 ml of liquid phase and slowly pouring portions of the slurry into the top of the column. Solvent was al- lowed to flow from the column by gravity, and small amounts of slurry or fresh solvent were continuously added to the top of the column to maintain a liquid level above the soil at all times. The steel column was dry packed with a known mass of soil (2-3g) with the aid of a vacuum pump. Pore Volume Determination Carbon 14 labeled methanol and 3H labeled water were used as inert tracers for determination of the hydraulic deten- tion volume (HDV) of the soil column. Solute Retention Experiments Pulsed input of the radiolabeled solute similar to that used to evaluate column HDV was used in column retardation ex- periments. A plot of effluent sample con- centration versus cumulative effluent volume was prepared, and the solute ret- ention volume was determined from the center-of-mass of the effluent solute peak. Results and Discussion Solubility Determinations The results of experiments to deter- mine the solubility of P5CDD, H6CDD, H7CDD and OaCDD in methanol are sum- marized m Table 1. Values of os determined from the solubility data for each of the PCDDs and for PCP are also listed in Table 1. These values represent the slope of the log- linear relationship between the log of the mole fraction solubility and the volume fraction cosolvent. Sorption to Surface Soils The time series experiments suggest that equilibrium for sorption of PCP to soil 91 was achieved in less than one day of contact, while a 30-day contact period was necessary for equilibrium when soil 96 was used. Table 1. Summary of Results for Solubility Determinations for PCDDs and PCP in WatertMethanol Mixtures Measured Solubility, mg/L as f* T4CDD Mean St. Dev. n P5CDD Mean St. Dev. n H6CDD Mean St. Dev. n H7CDD Mean St. Dev. n OgCDD Mean St. Dev. n PCP Mean St. Dev. n 0.50 1.0 10.6 0.5 33 0.10 52 0.2 2 18 6 20 2 15 24 2 12 4.0 0.6 56 3. 1x103 180xl03 0.6 9 6.25 6.09 7.01 7.35 7.35 3.8 ------- Table 2. Summary of Isotherm Parameters Determined for Sorption of PCP by Soils 91 and 96 Volume Fraction Methanol, fa 0.0 0.25« 0.25« 0.5 0.75 Soil 91 KD, mUg r* n pH*> Km,oc, mollg log (Km.0c) Soil 96 KD, mUg '2 n pH«> «m.oc, mol/g log (Km,oc) Molar Volume, mUmol 18 0.999 12 7.0 150 2.18 180 0.96 14 6.6 130 2.11 18.0 4.5 0.93 13 6.5 33 1.52 96 0.98 15 6.3 61 1.78 20.5 5.0 0.93 14 6.9 37 1.57 20.5 1.1 0.69 7 6.5 6.9 0.84 12 0.98 15 6.2 6.5 0.87 24.7 2.0 0.60 8 6.0 0.87 -0.06 29.8 aReplicate isotherms for soil 91 at fs of 0.25 were determined for contact periods of 2 days and 4 days, respectively. bpH is the value of the pH in solution at the end of the contract period. Table 3. Summary of Kobs Values Determined for Sorption of P5CDD, H6CDD, H7CDD and O8CDD by Soil 91 from Water/Methanol Mixtures Volume Fraction Methanol, fs 0.75a 0.9" Molar Volume, mUmol P5CDD Kobs, mUg Km.oc. mollg log (Km,oc) H6CDD Kobs, mUg Km oc, mollg log (Km,oc) Kobs, mUg Km,oc, mollg log (Xmoc) OgCDD Kobs, mUg Km oc, mollg log (KmtOC) 29.8 1.7 8.6 0.93 3.6 18 1.3 4.8 24 1.38 37.9 0.20 0.79 -0.10 0.23 0.91 -0.04 0.40 1.6 0.20 0.82 3.2 0.51 40.4 0.072,0.057 0.27, 0.27 -0.57, -0.68 0.70, 0.092 0.38, 0.35 -0.42, -0.46 0.72, 0.77 0.45, 0.47 -0.35, -0.39 0.27, 0.79 0.79, 0.77 -0.70,-G 75 Experiments were conducted at a column flow rate of 8 mL/hr (pore velocity of 73.5 m/day), with ps of 1.4 g/mL and e of 0.79. ^Experiments were conducted at a column flow rate of 8 mUhr (pore velocity of 0.77 m/day), with pB of 1.8 g/mL and £ of 0.51. ^Experiments were conducted at column flow rates of 12 mLlhr and 20 mLJhr (pore velocities of 1.78 and 2.96 m/day), respectively, with pB of 1.75 g/mL and e of 0.33. Equilibrium isotherm data for the sorp- tion of PCP by soils were generated by batch techniques at fs of 0.0, 0.25 and 0.5 and for soil 96 at fs of 0.75. The results of regression analysis of the isotherm data obtained for all fs studied are summarized in Table 2. The Kobs values for sorption of PCP by soil 91 were also estimated from column experiments. The log (Kmoc) values for sorption of PCP by soils 91 and 96 plotted against fs agree with the results obtained from batch and column techniques over the entire range in fs studied. Sorption of T4CDD from Water The value of log (K^.) determined from the experiment involving unwashed soil and a contact period of 48 hours w£ 6.44, while the value of log (K0 determined from the experiment involvin prewashed soils and a contact period ten days was 6.66. The value of log (Koc) of 6.67 dete mined by the second procedure co responds to a value of log (Km oc) of 5.4 The experimental value of the wate phase partition coefficient is in goc ------- agreement with the value predicted by log-linear extrapolation of the water/ methanol data, namely 5.30. Based on this observation, it appears that for T4CDD the cosolvent theory applies over the entire range of fs, 0.0-1.0 for water/ methanol mixtures. This provides strong support for the validity of this theory to PCDDs and other highly hydrophobic or- ganic contaminants, and also provides support for the use of log-linear extrapo- lation to estimate water-phase K^. values for PCDDs by using data generated from water/methanol mixtures. Sorption of PCDDs from Mixtures of Water and Methanol Linear sorption isotherms were ob- served for all PCDDs studied. The KD values for the four PCDDs are generally comparable (ranging from 1.8-3.8 ml/g) and do not show the expected trend of increasing with increasing hydrophobicity of the PCDD. The results of column studies used in sorption experiments are presented in Table 3. The values of KD and Kobs determined for the PCDDs by batch and column techniques, respectively were normalized on foc converted to molar units by dividing by liquid-phase molar volume. The results of the batch experiments de- termined in the present study are in general agreement with the log-linear re- lationship based on the data of other investigators. The results obtained by column techniques were consistently lower than expected from the log-linear relationship of the batch data only. The relatively low values of Kobs in comparison to KD were believed to be attributed to non-attainment of local equilibrium within the soil column for the flow rates utilized. Sorption of PCDDs in the Presence of PGP and CB The effect of the presence of PCP on the sorption of PCDDs was evaluated by batch and column techniques. Batch experiments were conducted to generate sorption isotherm data for 08CDD with both soils at PCP con- centrations of 25 and 200 ppm. Contact periods of 2 and 36 days were utilized for soils 91 and 96, respectively. For both soils and both PCP concentrations, the sorption of 08CDD in the presence of PCP was roughly 30% of the sorption of 08CDD in the absence of PCP. Column experiments were conducted for P5CDD, H6CDD and H7CDD using soil )1, with three liquid phases; 1) fs of 0.75, 2) fs of 0.75 and a PCP concentration of 1000 ppm, and 3) fs of 0.75 and a CB concentration of 10 ml/L. For each PCDD studied, the lowest Kobs values were observed for the solvent/CB system. The K(,bs for both solvent/CB and solvent/PCP systems were consistently below Kobs for the solvent only. These normalized values show that PCDD sorption generally decreased by 25% in the presence of PCP and 50% in the presence of CB. Column experiments were also con- ducted for all PCDDs at fs of 0.9 with and without PCP present. The results for all PCDDs indicate that there was generally no significant change in Kobs in the presence of PCP relative to values in the absence of PCP at a fs value of 0.9. The reduced sorption of PCDDs in the presence of cosolutes may be explained by a number of factors, including the effect of the cosolute on the solubility of PCDDs and/or the effect of the cosolute on PCDD-soil organic matter interactions. However, it is suspected that the reduced sorption of PCDDs in the presence of the cosolutes may be explained in terms of either the effect of soil-phase cosolute on the soil-phase activity coefficients of the PCDDs or the results due to the competition between the sorbed cosolutes and PCDDs. This speculation would support the observation that the effects become more pronounced at lower fs because greater soil-phase concentrations of the cosolutes would be expected via sorption as fs decreases. Sorption by Aquifer Materials Linear isotherms were observed for all PCDDs for fs values of 0.25 and 0.65 with the exception of T4CDD and O8CDD. Comparison of the experimental data points for the aquifer materials with the data for the surface soils, and their cor- responding regression equations, in- dicates that values of log (Km oc) for both sorbents are well described by a single curve for T4CDD, H6CDD and H7CDD. For P5CDD, the experimental values of lOQ (Km,oc) f°r the aquifer materials at each fs' are significantly greater than those determined from surface soil. For O8CDD, the experimental values of log (Km.oc) foe the aquifer materials are slightly below those predicted for the surface soils. The general agreement between values of log (Km oc) for the aquifer materials and the surface soils for PCDDs suggests that foc alone is the dominant factor determining the extent of sorption for highly hydrophobic organic contaminants such as PCDDs, presumably because the organic sorption is sufficiently strong to dominate the weaker sorption to minerals. Desorption From Surface Soils From limited data, it appears that the sorption of PCDDs from the surface soils into water/methanol mixtures may be reversible, but that desorption is char- acterized by very low rates. Preliminary experiments conducted to assess batch and column techniques for the study of sorptive transport of PCDDs through soils in the presence of diesel fuel, were found to be infeasible, owing to the formation of multiple phases. These experiments suggested that relatively stable water/methanol/diesel fuel emul- sions were readily transported through the soil column. Further, although the soil column had been apparently flushed of diesel fuel at a high relative velocity, it was observed that the column had a residual capacity to retain significant amounts of diesel fuel which was released from the column as a stable emulsion at low liquid-phase flow rates. Conclusions The sorption and desorption of PCDDs by surface soils and the sorption of PCDDs by aquifer materials has been in- vestigated by using batch shake testing and saturated-flow soil column tech- niques. Experiments were conducted using water and water/methanol mixtures and two model codisposed materials (pentachlorophenol (PCP) and chloroben- zene (CB)). Sorption isotherm data were generated by batch techniques to evaluate the sorp- tion of T4CDD from water by soil 91. A contact period of 10 days, and a water prewash procedure which was used to re- move nonseparable suspended particles (NSP) from the water phase, appeared to be adequate for evaluating an equilibrium KD value which was not biased by the inadvertent sampling of NSP during liquid phase analysis. A linear sorption isotherm was obtained which indicated that KD was 30,600 (log (KD) = 4.49). A value of Km oc of 2.58x105 (log (Kmoc) = 5.41) was de- termined by dividing this KD value by f^ and by the molar volume of water. This corresponds to a value of log (Km oc) of 5.30 predicted by log-linear extrapolation of KD data generated by other in- vestigators for T4CDD and soils 91 and 96 and water/ methanol mixtures. This observation provides support for the ap- plicability of the cosolvent theory to the sorption of PCDDs to soils from water/methanol mixtures over the entire ------- range in fs from 0.0-1.0, and provides justification for log-linear extrapolation using data generated for water/methanol mixtures to predict equilibrium water- phase KD values for PCDDs and other highly hydrophobic organic contaminants. The effect of the presence of PCP on the sorptive transport of PCDDs through soils was studied by using batch and column techniques, in which the liquid phase consisted of water/methanol mix- tures ranging in fs from 0.5-0.9 and con- taining PCP at concentrations ranging from 1-10% of solubility. These experi- ments indicated that the sorptive reten- tion of PCDDs by soils was reduced by about a factor of 3 when PCP was present in the liquid phase to that ob- served in the absence of PCP. The effect of the presence of CB on the sorptive transport of PCDDs through soils was studied by using column tech- niques, in which the liquid phase con- sisted of water/methanol mixtures ranging in fs from of 0.75-0.9 and a CB concen- tration of 10 mL/L. These experiments in- dicated that the sorptive retention of PCDDs by soils was reduced by a factor of 2 in the presence of CB at an fs of 0.75 relative to that observed in the absence of CB. Experiments to evaluate the sorption of PCDDs by aquifer materials included an assessment of sorption kinetics and equilibrium KDs. The results of these experiments suggested that a two-day contact period was sufficient to achieve sorption equilibrium for all PCDDs studied for these low carbon soil materials. Sorption isotherm data were generally linear, and equilibrium KDs, when converted to Km (partition coef- ficient), were log-linearly related to fs in accordance with the cosolvent theory. When Km values were normalized on f^ of the aquifer material, the resulting KmiOC values were in general agreement with Km.oc values determined for surface soils from the Times Beach, MO area. It is suspected that the agreement between aquifer material and surface soil sorption for PCDDs indicates that sorption to or- ganic carbon is sufficient to mask sorption to mineral surfaces. Experiments to evaluate the desorption of PCDDs from surface soil were con- ducted by batch techniques, in which PCDDs were previously sorbed by soil for thirty days prior to the initiation of the desorption experiments. The results of these experiments suggested that de- sorption appeared to be generally re- versible but was limited by kinetics, with roughly 50-90% of reversible-desorption equilibrium being attained within a 30-day contact period. Recommendations Additional research in six areas of the transport of PCDDs andrelated con- taminants through soils is recommended: 1. Sorption of PCDFs. No data have been reported on the sorptive partitioning of polychlorodibenzofurans (PCDFs). High-purity standards of these contami- nants are now available in radiolabeled form, and it is suggested that issues relevant to sorptive partitioning be inves- tigated using several PCDF congeners. 2. Sorption from Water/Methanol Mix- tures. The sorption of PCDDs as a func- tion of volume fraction cosolvent (fs) for water-miscible cosolvents is generally well understood. However, further re- search is necessary to better understand solubility and sorption behavior at low fs (e.g., fs below 0.05-0.1). This work should be conducted using PCDDs and PCDFs as well as slightly less hydrophobic contaminants, such as polycyclic aromatic hydrocarbons (PAHs) and poly- chlorinated biphenyls (PCBs). Research should also be initiated to evaluate the cosolvent effects attributed to ethylene glycol, a water-miscible solvent which is relevant to the manufacturing process of PCP and thus relevant to waste sites contaminated by PCDDs. 3. Sorption in the Presence of Codis- posed Materials. Additional research is needed to better understand the sorption of PCDDs and related contaminants in the presence of codisposed materials. Three groups of codisposed materials are important. The first group consists of slightly soluble solvents. Much is known regarding the sorption of hydrophobic contaminants in the presence of miscible cosolvents such as methanol and ace- tone, but little is known regarding the effect of immiscible solvent such as methylene chloride, benzene, and aniline. The second group consists of slightly soluble solids. For example, the effect of the presence of 2,4,5-trichlorophenol and terpenes, as well as PCP, at low fs should be evaluated. The third group consists of oil/carrier liquids. There is a significant requirement to further understand the movement of oil through soils, and the manner in which oil movement affects the sorptive transport of PCDDs and codisposed materials. Thus, research should be conducted to evaluate the sorptive transport of oils, oils and PCP, and oils, PCP and terpenes, as well as the sorptive transport of PCDDs in the presence of these materials. This re- search should focus on evaluating the relative contributions to transport attribu- ted to dissolved oil constituents versus oil droplets and oil/water emulsions, ir eluding water-phase sorption-desorptioi dislodging of entrapped droplets, an potential for emulsion formation. 4. Sorption of PCDDs in the present of colloids. Much is known regarding tti sorptive transport of moderately hydrc phobic organic contaminants in the pre: ence of colloidal organic matter, and th work suggests that colloids can substar tially increase the mobility of organi contaminants through soils. Addition work is necessary to extend this researc to include highly hydrophobic organic such as PCDDs. 5. Sorption of PCDDs by aquifer mi terials. Additional research is needed I evaluate the relative mineral contributior to sorptive transport of PCDDs an similar organics through low f^ aquif< materials. This research should focus c organic contaminants that are very hydrc phobic, such as PAHs and PCBs, as we as PCDDs. The research should include variety of sorbents to enable a bett< fundamental understanding of the relativ effects of KOW, mineral surface area, ar foe on sorption to low-foe sorbents. 6. Desorption of PCDDs. Desorption i PCDDs from soils at low fs in the pre: ence of codisposed materials, such < oil, should be investigated. This researc should include development of a mod which incorporates desorption kinetics enable better prediction of the moveme of PCDDs through soils under real-wor conditions. ------- R. W. Walters, Zohreh Yousefi, Amy L. Tarleton, Stanley A. Ostazeski, and David C. Barry are with University of Maryland, College Park, MD 20742 Carl G. En field is the EPA Project Officer (see below). The complete report, entitled "Assessment of the Potential for Transport of Dioxins and Codisposed Materials to Groundwater," (Order No. PB 89- 166 6071 AS; Cost: $21.95, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Robert S. Kerr Environmental Research Laboratory U.S. Environmental Protection Agency Ada, OK 74820 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 EPA/600/S6-89/002 0000*5833 60604 ------- |