Temperature-dependent uptake rates of nonpolar organic compounds by semipermeable membrane devices and low-density polyethylene membranes

The effect of temperature on sampling rates and sampler-water partition coefficients of semipermeable membrane devices (SPMDs) and low-density polyethylene (LDPE) strips was studied in an experimental setup under controlled flow conditions. Aqueous concentrations of chlorobenzenes, polychlorinated biphenyls (PCBs), and polyaromatic hydrocarbons (PAHs) were maintained by continuous circulation of the water over a generator column. Sampling rates for standard design SPMDs (460 cm2) were in the range of 20-200 L d(-1). No significant differences were observed between sampling rates of SPMDs and LDPE strips, but the latter samplers reached equilibrium faster because of their smaller sorption capacity. Sampling rates at 30 degrees C were higher than at 2 degrees C by a factor of about 3. Sampling rate modeling indicated boundary layer-controlled uptake for compounds with log octanol-water partition coefficients smaller than 4.4 and aqueous boundary-layer controlled uptake for more hydrophobic compounds. SPMD-water partition coefficients did not significantly change with temperature, but LDPE-water partition coefficients were larger at 2 degrees C than at 30 degrees C by a factor of 2. For field application of SPMDs, the results imply that temperature is not a key factor that controls uptake rates unless large geographical and temporal scales are involved. The results confirm that water flow velocity has a profound effect on sampling rates.     

Estimation of the uptake rate constants for polycyclic aromatic hydrocarbons accumulated by semipermeable membrane devices and triolein-embedded cellulose acetate membranes

In this paper we report an extension of our previous work on the triolein-embedded cellulose acetate membrane (TECAM) as a passive sampling device (PSD) and describe the results from simultaneous exposure of TECAMs and triolein-containing semipermeable membrane devices (SPMDs) to PAHs in lake water for 16 days. The data obtained provided a comparison of the uptake rates of specific PAHs by the two PSDs. Using 16-day accumulation tests, similar PAH distribution patterns in TECAMs and in SPMDs (R2 = 0.89, p < 0.0001) were observed. However, it was noted that TECAMs could take up greater amounts of PAHs than SPMDs (735 ng/g of TECAM vs 630 ng/g of SPMD). Uptake rate constants of TECAMs and SPMDs for 16 priority pollutant (PP) PAHs, corrected for dissolved organic carbon, ranged from 0.28 to 2.94 L d(-1) and from 0.16 to 0.91 L d(-1), respectively. The elimination rate constants of TECAMs were 1.4-6.7 times greater than those observed for SPMDs, thereby indicating that PAHs required shorter times to achieve equilibrium in TECAMs than in SPMDs. Thus, the results of the present study suggest that TECAMs have significant potential as a good monitor to assess the pollution of hydrophobic pollutants in aquatic environments.     

Environmental monitoring of hydrophobic organic contaminants: the case of mussels versus semipermeable membrane devices

Concentrations of hydrophobic chemicals in mussels and semipermeable membrane devices (SPMDs) from nine studies published over the past decade, amended with new data obtained in the Scheldt-North Sea area, were assessed to understand the similarities and differences between these sampling matrixes. A model was developed to describe the concentration ratios, using literature values of elimination rate constants and steady-state accumulation factors of both samplers as key parameters. The model could successfully describe the results of seven studies. Differences in concentration ratios among these studies were related to the variability of mussel bioaccumulation factors (BAFs) and water sampling rates of SPMDs. For two studies, the model could only describe the data by adopting unrealistically high water sampling rates, and for one study there were not enough data to test the model. We argue that SPMDs will generally yield more reliable estimates of exposure concentrations than mussels, because in situ BAF values are difficult to estimate, whereas the in situ exchange kinetics of SPMDs can be quantified by measuring the dissipation rates of performance reference compounds. The implications of the results for future and existing monitoring programs are discussed.     

Bioavailability of sediment-associated PCDD/Fs and PCDEs: relative importance of contaminant and sediment characteristics and biological factors

Factors that determine accumulation of sediment-associated polychlorinated dibenzo-p-dioxins and furans and polychlorinated diphenyl ethers into semipermeable membrane devices (SPMDs) and benthic oligochaete worms (Lumbriculus variegatus) were examined. These factors included both physical-chemical and structural characteristics of the contaminants (water solubility, lipophilicity, dipole moment, molecular size, and conformation) and sediment characteristics (organic carbon content, particle size, aromaticity, and polarity of organic carbon). The results of partial least squares regression analysis indicated that lipophilicity alone is not a sufficient predictor for contaminant bioaccumulation potential, even though it is a significant contributor. It was shown that contaminant molecular size and conformation (specifically planarity/nonplanarity) as well as sediment characteristics also have a significant role. The studied factors contributed up to 63-88% of the variation in accumulation data for SPMDs and 50-65% for oligochaetes. Comparison of (bio)accumulation factors (BAF28d for oligochaetes and AF28d for SPMDs) revealed that accumulation of contaminants in oligochaetes is largely influenced by biological factors (e.g., feeding habits), while the physical-chemical nature of the process is emphasized for SPMDs.     

Estimation of water sampling rates and concentrations of PAHs in a municipal sewage treatment plant using SPMDs with performance reference compounds

Semipermeable membrane devices (SPMDs) were exposed at ten sampling points, each representing a different stage in the treatment process, in a municipal sewage treatment plant. Differences in SPMD uptake kinetics of polycyclic aromatic hydrocarbons (PAHs) due to variations in conditions at the sampling sites were evaluated by using five performance reference compounds (PRCs) with log K(ow) values of 4.20 to 6.34. PRC release rate constants (k(e,PRC) values) were calculated for PRCs for which 50-98% of the initial amounts were lost during the sampling period. The k(e,PRC) values were high, ranging from 0.08 to 0.11 day(-1) for the studied PRCs, at sampling site W1 (raw sewage), the only sampling site where significant amounts of the PRCs with log K(ow) values > 5 were released from the SPMDs. At the other sampling sites, only PRCs with log K(ow) values between 4.20 and 4.50 were released in significant amounts. The release rates at these sites were lowest (0.04 day(-1)) at sampling site W9 (the secondary clarifier) and highest (0.18 day(-1)) at W8 (the active sludge aeration basin). Differences between sampling rates (R(s)) obtained using published laboratory-calibrated data and PRC-corrected R(s) values were visualized by principal component analysis (PCA). The water concentrations of 24 studied PAHs fell substantially during the course of the sewage treatment process. However, low molecular weight PAHs were more effectively removed than high molecular weight PAHs. Significant deviations between actual and estimated water concentrations may arise unless PRC-corrected R(s) values are applied.     

Calibration and field verification of semipermeable membrane devices for measuring polycyclic aromatic hydrocarbons in water

The use of semipermeable membrane devices (SPMDs) has become common in environmental sampling of nonpolar organic contaminants, yet few data exist for the uptake or sampling rates of polycyclic aromatic hydrocarbons (PAH). Two separate laboratory calibration experiments were conducted to determine the sampling rates of 28 individual PAH and 19 homologues. PAH with a log Kow > 4.5 remained in the linear uptake phase for 30 days, but PAH with a log Kow < 4.5 began to approach steady state within 15 days. Sampling rates, corrected for dissolved organic carbon, ranged from 2.11 to 6.06 L d(-1). Shear flow across the membrane had no statistically significant effect on rates over the range of 0.01-0.50 cm s(-1). Field verification of these sampling rates yielded agreement within about a factor of 2 for most PAH and a factor of 4 for all PAH. The worst agreement was for the most hydrophobic PAH, where partitioning into dissolved and particulate organic carbon pools are more important and less certain. These SPMD sampling rate data will allow quantitative estimations of freely dissolved concentrations of 47 compounds that are commonly used for PAH and petroleum product source identification and allocation.     

Enhancement and inhibition of denitrification by fluid-flow and dissolved oxygen flux to stream sediments

Microscale measurements of nitrate (NO3-) and dissolved oxygen (DO) concentrations in sediments were made in a laboratory channel under turbulent fluid-flow conditions to examine the effects of DO flux on denitrification rates. DO concentrations and flux within sediments increased with increasing velocity in the surface water. Under low fluid-flow conditions (shear stress velocity, u* < 0.23 cm s(-1)), increasing velocity increased NO3- loss from the bulk flow. For high fluid-flow conditions (u* > 0.39 cm s(-1)), increasing velocity inhibited NO3-loss. Sediment cores were collected and sliced to measure the depth distribution of denitrifying biomass in sediments. Quantities of nirK and nirS genes were higher within the surface layer and decreased with depth in the sediments. Microscale concentration profiles of DO and NO3- revealed that denitrification occurs within a thin region just below the oxic-anoxic interface in sediments. The interplay of mass transfer and DO flux generated threshold conditions for NO3- loss by denitrification. These results suggest that for a given sediment and environmental conditions (chemical, physical, microbiological), there exists an optimal range in velocities for enhancing denitrification in aquatic systems.     

Electroosmotic flow stimulates the release of alginate-bound phenanthrene

There is growing interest in employing electro-bioremediation, a hybrid technology of bioremediation and electrokinetics for the treatment of contaminated soil. Most present applications of electrokinetics aim at pollutant extraction, which requires transport over large distances facilitated by electroosmotic flow (EOF). They do not explicitly account for the possibility that EOF passing along soil particles stimulates the release of hydrophobic organic compounds (HOC) and locally improves pollutant bioavailability. Here, we report on the stimulated release of polycyclic aromatic hydrocarbon (phenanthrene) from model organic matter in the presence of direct current (DC)-electric fields (0.5-2 V cm(-1)) typically used in electrobioremediation measures. Alginate beads were employed as a model polymer release system (MPRS) exhibiting similar release behavior as natural organic matter (NOM). In the presence of EOF the phenanthrene release flux from alginate beads was between 1.4- and 1.8-fold higher than under hydraulic flow conditions with equal bulk water velocity and 30-120-fold higherthan under stagnantwater conditions. Our data suggest that DC-electric fields (0.5-2 V cm(-1)) can stimulate the release of PAH bound to particles exposed to stagnant water zones often found at hydraulic flow regimes restricted by low permeability.     

Influence of flow conditions and system geometry on nitrate use by benthic biofilms: implications for nutrient mitigation

The effects of substratum geometry and overlying velocity on nitrate use by periphyton were assessed. Periphyton was cultivated at an average current velocity of 0.5 cm s(-1) in laboratory mesocosms (120 cm long, 60 cm wide) on polyethylene nets of three different geometries, "1-lay er", "3-layer", and "bedform" structures, overlaying a thin bed of sand. Bulk nitrate use was then measured as the reduction of nitrate concentration in the overlying water under average velocities of 0.005, 0.05, and 0.5 cm s(-1). Periphyton structural characteristics were quantified as algal/bacterial biomass, algal species composition, and bacterial densities. Accrual of microbial biomass increased monotonically with increasing benthic net surface area, with upper sections of structures supporting the highest biomass. Maximum rates of nitrate removal were measured in the bedform geometry at intermediate velocity (173 mg NO3-N m(-2) d(-1)), and the lowest was measured with 1-layer geometry at the fastest velocity (11 mg NO3-N m(-2) d(-1)). Oxygen microprofiles within biofilms demonstrated that hydrodynamic conditions and benthic structure both play a key role in the regulation of microbial processing of nitrate delivered from the water column by promotion of denitrification in downstream sections of bedform substrata. Interactions between hydrodynamic conditions and substratum geometry are expected to regulate microbial activity in all surficial natural and engineered environments and must be parameterized to forecast long-term average biochemical transformation rates in rivers and other dynamic aquatic systems.     

Method for testing the aquatic toxicity of sediment extracts for use in identifying organic toxicants in sediments

Biologically directed fractionation techniques are a fundamental tool for identifying the cause of toxicity in environmental samples, but few are available for studying mixtures of organic chemicals in aquatic sediments. This paper describes a method for extracting organic chemicals from sediments and then re-introducing them into water column toxicity tests in a way that mimics, at least in part, the partitioning processes that govern bioavailability in sediment. This involves transferring solvent extracts of sediment into triolein and then placing the mixture inside low-density polyethylene dialysis tubing in a configuration similar to semipermeable membrane devices (SPMDs) used for environmental monitoring. For four model compounds, SPMDs were shown to effectively maintain water column exposure in static systems for 10-14 d, with partition coefficients similar to K(OW). Toxicity tests indicated that the SPMDs were compatible with four of five freshwater organisms tested and could be used to measure both lethal and sublethal end points. An example application showed good correspondence between organism responses in intactsediment and extracts in SPMDsfor both field-collected and spiked sediments. The SPMD-based method offers a simple, flexible test design, amenable to several different test organisms, and the ability to work with complex mixtures of contaminants while maintaining partitioning behavior similar to that within intact sediments.     

Design of Continuous Flow Osmotic Dehydration and its Performance on Mass Transfer Exchange During Osmotic Dehydration of Broccoli Stalk Slices

A continuous flow solution unit was designed and built with a sole purpose of achieving better hydrodynamic control during the osmotic dehydration pre-treatment process. The initial study was set up to calibrate the flow meter at different sucrose solutions at different concentrations and temperatures to obtain a flow velocity range between 1.5 to 3.5 mm/s. In this study, broccoli stalk slices were used to investigate the effect of the flow velocity on mass transfer kinetics and compared with static condition. Further, the optimization of this equipment system was performed to achieve higher water loss with minimal solute gain as pre-drying condition. Comparative studies between static and dynamic conditions show that flow velocity helps in faster rate of water removal with lower solute gain during the osmotic dehydration process of broccoli stalk slices. The optimum condition was found to be at a temperature of 30 °C with concentration of 54 °Brix for 120 min of immersion time at flow velocity of 3.5 mm/s.     

Initial test results for a passive surface water fluxmeter to measure cumulative water and solute mass fluxes

The theoretical concept and initial test results of a Passive Surface Water Fluxmeter (PSFM) to directly and simultaneously measure cumulative water and solute mass fluxes in surface water flow systems are presented. The PSFM consists of a symmetric hydrofoil that is vertically installed in a stream and one or more sorbent columns that are connected to the nonuniform flow field around the hydrofoil. Depending on the ambient flow velocity, a flow occurs through each column, which elutes portions of initially present "resident" tracers in the column, while, at the same time, solutes in the water (e.g., contaminants or nutrients) are retained in the sorbent column. Quantification of the resident tracer mass remaining and the mass of solutes sorbed in the column enables determination of the local cumulative or time-averaged water and solute mass fluxes. Laboratory flume experiments show good agreement with independent measurements (R(2) > or = 0.96) for instantaneous water fluxes (tested range: 0.3-0.7 m/s), cumulative water fluxes (50-600 L/cm(2)), and cumulative nitrate fluxes (0.4-5.1 g/cm(2)). Future work is required to validate the PSFM performance under a larger range of flow velocities, transient flow, and transport conditions and for different hydrofoil shapes.     

Screening criteria for long-range transport potential of organic substances in water

Screening of long-range transport potential (LRTP) of organic chemicals in water requires the development of criteria in analogy to the existing LRTP criteria for airborne chemicals. According to the Stockholm Convention, compounds mainly partitioning into air are assumed to be prone to LRTP if they have a half-life in air of more than two days. Using mean flow velocities of European rivers (0.7-1 m/s) and of ocean currents running into the Arctic Ocean (0.28-0.9 m/s), we derived corresponding half-life criteria for freshwater and seawater (10 days and 90 days, respectively). Next, we calculated the characteristic travel distance (CTD) of several thousand chemicals from the Canadian Domestic Substances List (DSL) and all current POPs using the multimedia model ELPOS. This shows that the CTD in water dominates the CTD in air only for chemicals that are characterized by a large half-life in water and a low air-water partition coefficient (about 38% of the nonionic organic substances selected from the DSL). In particular, there are substances that are not classified as persistent compounds in water but exhibit higher CTDs for transport in water than for transport in air. Finally, we evaluated whether the LRTP boundary derived from POP reference chemicals has to be revised if LRTP in water is included and found that this boundary can be applied to all organic chemicals regardless of their transport in air or water.     

241Am migration in a sandy aquifer studied by long-term column experiments

The migration behavior of 241Am(III) in a sandy aquifer was studied under near-natural conditions by long-term column experiments of more than 1 year duration. Columns with 50 cm length and 5 cm in diameter were packed with aeolian quartz sand and equilibrated with two different groundwaters having an original dissolved organic carbon concentration (DOC) of 1.1 and 7.2 mg x dm(-3), respectively,from the Gorleben site (Lower Saxony, Germany). In each experiment, 1 cm3 of Am-spiked groundwater ([Am] = 0.2 to 2 micromol x dm(-3)) was injected into the column. The flow rate of the groundwater was adjusted to 0.28 m x d(-1). A small colloid-borne Am fraction was found to elute together with tritiated water. After 414 and 559 days, respectively, the experiments were terminated. Whereas the nonsorbing tracer of tritiated water would have covered a distance of about 350 m in that time period, the maximum of the Am activity was detected between 32 and 40 mm column length. Applying selective dissolution analysis to the sand surface, Am was found to be preferentially bound to iron hydroxide/oxide sites. From this Am distribution, a retardation factor R of about 10(4) was determined and compared to static batch experiments. The Am breakthrough was calculated forthe conditions of the column experiment     

Biodegradation of acidic pharmaceuticals in bed sediments: insight from a laboratory experiment

Pharmaceutical residues are commonly detected micropollutants in the aquatic environment. Biodegradation in sediments is a potentially significant removal process for these compounds in rivers which is constrained by the transfer of water and solutes into the sediment. The aim of this study was to determine the combined effect of flow velocity and sediment dynamics and thus of water-sediment interactions on the attenuation of 6 acidic pharmaceuticals. We carried out experiments with river water and sediment in a bench-scale annular flume at two different hydraulic boundary conditions (flat sediment surface vs moving sediment). The effective biodegradation half-lives of 4 compounds (diclofenac, bezafibrate, ibuprofen, naproxen) were in the range of 2.5 to 18.6 days and were much shorter when the exchange of surface and pore water was fast. For gemfibrozil, a half-life of 10.5 d was determined in the experiment with moving sediment, whereas no degradation was observed with flat sediment bed. These findings can be attributed to the limited transfer of water and solutes into the sediment at low flow velocity and flat sediment bed which rapidly induced anaerobic conditions in the sediment. The only compound that was efficiently removed in deeper, anoxic sediment layers was naproxen. The calculated half-life distances in rivers ranged from 53 to 278 km. Our results indicate that it could be favorable to increase the rate of exchange between surface and pore water during river restoration to enhance the attenuation of organic micropollutants like acidic pharmaceuticals.     

Optimization of a biosorption column performance

The dynamics of copper and zinc biosorption by Sargassum fluitanswas analyzed under variable column operating conditions including different column lengths (15 and 45 cm), metal-feed solution concentrations (1 and 6 meq L(-1)), metal-sorbent affinities (2.01 and 0.45), and interstitial velocities (12 and 4 cm min(-1)). The experimental breakthrough curves obtained under these varying conditions were also simulated using a mathematical model taking into account the mass transfer as well as the axial dispersion phenomena. The column performance was evaluated using two performance indicators: the service time (t(s)) and the unused portion of the column as reflected in the area under the breakthrough curve (A(c)). Sensitivity analysis results indicated that the feed stream concentration, mass transfer coefficient, column length, and interstitial velocity had the most important effect on the column performance. Applying chromatography theories, the optimization of the biosorption process for productivity and sorption performance, in terms of operating conditions (interstitial velocity) and design parameters (column length), was outlined. The corresponding optimum curve relating the interstitial velocity and the column length resulted with the pressure drop limitations recognized. As an example, a laboratory column 100 cm long will necessitate an interstitial velocity of 19 cm min(-1) to yield the best sorption results.     

Passive air sampling using semipermeable membrane devices at different wind-speeds in situ calibrated by performance reference compounds

Semipermeable membrane devices (SPMDs) are passive samplers used to measure the vapor phase of organic pollutants in air. This study tested whether extremely high wind-speeds during a 21-day sampling increased the sampling rates of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), and whether the release of performance reference compounds (PRCs) was related to the uptakes at different wind-speeds. Five samplers were deployed in an indoor, unheated, and dark wind tunnel with different wind-speeds at each site (6-50 m s(-1)). In addition, one sampler was deployed outside the wind tunnel and one outside the building. To test whether a sampler, designed to reduce the wind-speeds, decreased the uptake and release rates, each sampler in the wind tunnel included two SPMDs positioned inside a protective device and one unprotected SPMD outside the device. The highest amounts of PAHs and PCBs were found in the SPMDs exposed to the assumed highest wind-speeds. Thus, the SPMD sampling rates increased with increasing wind-speeds, indicating that the uptake was largely controlled by the boundary layer at the membrane-air interface. The coefficient of variance (introduced by the 21-day sampling and the chemical analysis) for the air concentrations of three PAHs and three PCBs, calculated using the PRC data, was 28-46%. Thus, the PRCs had a high ability to predict site effects of wind and assess the actual sampling situation. Comparison between protected and unprotected SPMDs showed that the sampler design reduced the wind-speed inside the devices and thereby the uptake and release rates.     

Occurrence and environmental behavior of the bactericide triclosan and its methyl derivative in surface waters and in wastewater

The bactericide triclosan and methyl triclosan, an environmental transformation product thereof, were detected in lakes and in a river in Switzerland at concentrations of up to 74 and 2 ng L(-1), respectively. Both compounds were emitted via wastewater treatment plants (WWTPs), with methyl triclosan probably being formed by biological methylation. A regional mass balance for a lake (Greifensee) indicated significant removal of triclosan by processes other than flushing. Laboratory experiments showed that triclosan in the dissociated form was rapidly decomposed in lake water when exposed to sunlight (half-life less than 1 h in August at 47 degrees latitude). Methyl triclosan and nondissociated triclosan, however, were relatively stable toward photodegradation. Modeling these experimental data for the situation of lake Greifensee indicated that photodegradation can account for the elimination of triclosan from the lake and suggested a seasonal dependence of the concentrations (lower in summer, higher in winter), consistent with observed concentrations. Although emissions of methyl triclosan from WWTPs were only approximately 2% relative to those of triclosan, its predicted concentration relative to triclosan in the epilimnion of the lake increases to 30% in summer. Passive sampling with semipermeable membrane devices (SPMDs) indicated the presence of methyl triclosan in lakes with inputs from anthropogenic sources but not in a remote mountain lake. Surprisingly, no parent triclosan was observed in the SPMDs from these lakes. Methyl triclosan appears to be preferentially accumulated in SPMDs under the conditions in these lakes, leading to concentrations comparable to those of persistent chlorinated organic pollutants.     

Transport of methyl tert-butyl ether through alfalfa plants

Concentrations measured in alfalfa plant stem segments indicated that plants grown in methyl tert-butyl ether (MTBE)-contaminated soil took up the chemical through their roots. Assuming a cylindrical shape for the plant stem, a mathematical model was developed to describe the transport of MTBE through the stems. Simulation results from uniform and nonuniform initial concentration distributions across the stem radius were compared with steady-state experimental data. With known values of plant stem radius, water usage, water content, and the distance over which the concentration decreased by 50%, the diffusion coefficient of MTBE radial transport across the plant stem was estimated with 95% confidence to be in the range of 8.43-16.2 x 10(-8) cm2/s with a mean of 1.23 x 10(-7) cm2/s. When the diffusion coefficient was calculated based on transient experimental data, the values with 95% confidence interval ranged from 4.14 x 10(-7) to 8.00 x 10(-7) cm2/s with a mean value of 6.07 x 10(-7) cm2/s. The difference between these two results can be reduced by more accurate estimation of the water flow velocity through plant stems. The model is applicable to other species including sunflowers and poplars upon substitution of appropriate parameters.     

Capacities of membrane lipids to accumulate neutral organic chemicals

Lipids have been considered as the predominant components for bioaccumulation of organic chemicals. However, differences in accumulation properties between different types of lipid (e.g., storage and membrane lipids) have rarely been considered. Moreover, in view of toxic effects on organisms, chemical accumulation specifically in biological membranes is of particular importance. In this review article, partition coefficients of 240 neutral organic compounds between liposomes (phospholipid membrane vesicles) and water (K(lipw)), reported in the literature or measured additionally for this work, were evaluated. Values of log K(lipw) and log K(ow) (octanol-water partition coefficients) differ by 0.4 on average. Polyparameter linear free energy relationships (PP-LFERs) can describe the log K(lipw) data even better (standard deviations = 0.28-0.31) than the log K(ow) model. Recent experimental data for highly hydrophobic compounds fit well to the PP-LFERs and do not indicate the existence of a previously postulated "hydrophobicity cutoff". Predictive approaches based only on the molecular structure (KOWWIN, SPARC, COSMOthermX, COSMOmic) were also evaluated for K(lipw) prediction. The PP-LFERs revealed that partition coefficients into membrane lipids can be two log units higher than those into storage lipids for H-bond donor compounds, suggesting that distinguishing between the two lipids is necessary to account for the bioaccumulation of these compounds, and that tissues rich in membrane lipids (e.g., kidneys, liver) instead of fat tissue can be the primary phase for accumulation.