Combining Passive Sampling and Dosing to Unravel the Contribution of Hydrophobic Organic Contaminants to Sediment Ecotoxicity.

Contaminated sediments are ubiquitous repositories of pollutants and cause substantial environmental risks. Results of sediment bioassays remain difficult to interpret, however, as observed effects may be caused by a variety of (un)known stressors. This study aimed therefore to isolate the effects of hydrophobic organic contaminants from other (non)chemical stressors present in contaminated sediments, by employing a newly developed passive sampling-passive dosing (PSPD) test. The results showed that equilibrium partitioning between pesticides or polyaromatic hydrocarbons (PAHs) in contaminated sediments and a silicone rubber (SR) passive sampler was achieved after 1-3 days. Chlorpyrifos concentrations in pore water of spiked sediment matched very well with concentrations released from the SR into an aqueous test medium, showing that SR can serve as a passive dosing device. Subjecting the 96 h PSPD laboratory bioassay with nonbiting midge (Chironomus riparius) larvae to field-collected sediments showed that at two locations, concentrations of the hydrophobic organic contaminant mixtures were high enough to affect the test organisms. In conclusion, the developed PSPD test was able to isolate the effects of hydrophobic organic contaminants and provides a promising simplified building block for a suite of PSPD tests that after further validation could be used to unravel the contribution of hydrophobic organic chemicals to sediment ecotoxicity.

In Vivo Bioconcentration of 10 Anionic Surfactants in Rainbow Trout Explained by In Vitro Data on Partitioning and S9 Clearance.

Bioconcentration factors (BCFs) in rainbow trout were measured for 10 anionic surfactants with a range of alkyl chain lengths and different polar head groups. The BCFs ranged from 0.04 L kg-1 ww (for C10SO3) to 1370 L kg-1 ww (C16SO3). There was a strong correlation between the log BCF and log membrane lipid-water distribution ratio (DMLW, r2 = 0.96), and biotransformation was identified as the dominant elimination mechanism. The strong positive influence of DMLW on BCF was attributed to two phenomena: (i) increased partitioning from water into the epithelial membrane of the gill, leading to more rapid diffusion across this barrier and more rapid uptake, and (ii) increased sequestration of the surfactant body burden into membranes and other body tissues, resulting in lower freely dissolved concentrations available for biotransformation. Estimated whole-body in vivo biotransformation rate constants kB-BCF are within a factor three of rate constants estimated from S9 in vitro assays for six of the eight test chemicals for which kB-BCF could be determined. A model-based assessment indicated that the hepatic clearance rate of freely dissolved chemicals was similar for the studied surfactants. The dataset will be useful for evaluation of in silico and in vitro methods to assess bioaccumulation.

Sorption and Mobility of Charged Organic Compounds: How to Confront and Overcome Limitations in Their Assessment.

Permanently charged and ionizable organic compounds (IOC) are a large and diverse group of compounds belonging to many contaminant classes, including pharmaceuticals, pesticides, industrial chemicals, and natural toxins. Sorption and mobility of IOCs are distinctively different from those of neutral compounds. Due to electrostatic interactions with natural sorbents, existing concepts for describing neutral organic contaminant sorption, and by extension mobility, are inadequate for IOC. Predictive models developed for neutral compounds are based on octanol-water partitioning of compounds (Kow) and organic-carbon content of soil/sediment, which is used to normalize sorption measurements (KOC). We revisit those concepts and their translation to IOC (Dow and DOC) and discuss compound and soil properties determining sorption of IOC under water saturated conditions. Highlighting possible complementary and/or alternative approaches to better assess IOC mobility, we discuss implications on their regulation and risk assessment. The development of better models for IOC mobility needs consistent and reliable sorption measurements at well-defined chemical conditions in natural porewater, better IOC-, as well as sorbent characterization. Such models should be complemented by monitoring data from the natural environment. The state of knowledge presented here may guide urgently needed future investigations in this field for researchers, engineers, and regulators.

Bioconcentration of Several Series of Cationic Surfactants in Rainbow Trout.

Cationic surfactants have a strong affinity to sorb to phospholipid membranes and thus possess an inherent potential to bioaccumulate, but there are few measurements of bioconcentration in fish. We measured the bioconcentration of 10 alkylamines plus two quaternary ammonium compounds in juvenile rainbow trout at pH 7.6, and repeated the measurements at pH 6.2 for 6 of these surfactants. The BCF of the amines with chain lengths ≤ C14 was positively correlated with chain length, increasing ∼0.5 log units per carbon. Their BCF was also pH dependent and approximately proportional to the neutral fraction of the amine in the water. The BCFs of the quaternary ammonium compounds showed no pH dependence and were >2 orders of magnitude less than for amines of the same chain length at pH 7.6. This indicates that systemic uptake of permanently charged cationic surfactants is limited. The behavior of the quaternary ammonium compounds and the two C16 amines studied was consistent with previous observations that these surfactants accumulate primarily to the gills and external surfaces of the fish. At pH 7.6 the BCF exceeded 2000 L kg-1 for 4 amines with chains ≥ C13, showing that bioconcentration can be considerable for some longer chained cationic surfactants.

Influence of in Vitro Assay Setup on the Apparent Cytotoxic Potency of Benzalkonium Chlorides.

The nominal concentration is generally used to express concentration-effect relationships in in vitro toxicity assays. However, the nominal concentration does not necessarily represent the exposure concentration responsible for the observed effect. Surfactants accumulate at interphases and likely sorb to in vitro system components such as serum protein and well plate plastic. The extent of sorption and the consequences of this sorption on in vitro readouts is largely unknown for these chemicals. The aim of this study was to demonstrate the effect of sorption to in vitro components on the observed cytotoxic potency of benzalkonium chlorides (BAC) varying in alkyl chain length (6-18 carbon atoms, C6-18) in a basal cytotoxicity assay with the rainbow trout gill cell line (RTgill-W1). Cells were exposed for 48 h in 96-well plates to increasing concentration of BACs in exposure medium containing 0, 60 µM bovine serum albumin (BSA) or 10% fetal bovine serum (FBS). Before and after exposure, BAC concentrations in exposure medium were analytically determined. Based on freely dissolved concentrations at the end of the exposure, median effect concentrations (EC50) decreased with increasing alkyl chain length up to 14 carbons. For BAC with alkyl chains of 12 or more carbons, EC50's based on measured concentrations after exposure in supplement-free medium were up to 25-times lower than EC50's calculated using nominal concentrations. When BSA or FBS was added to the medium, a decrease in cytotoxic potency of up to 22 times was observed for BAC with alkyl chains of eight or more carbons. The results of this study emphasize the importance of expressing the in vitro readouts as a function of a dose metric that is least influenced by assay setup to compare assay sensitivities and chemical potencies.

Membrane-Water Partition Coefficients to Aid Risk Assessment of Perfluoroalkyl Anions and Alkyl Sulfates.

This study determined the sorption affinity to artificial phospholipid membranes ( KMW) for series of perfluorinated carboxylates (PFCAs), perfluorinated sulfonates (PFSAs), alkyl sulfates (C xSO4), and 1-alkanesulfonates (C xSO3). A sorbent dilution assay with solid supported lipid membranes (SSLM) showed consistent CF2 unit increments of 0.59, and CH2 unit increments of 0.53, for the log KMW of perfluorinated and hydrogenated anions, respectively. PFSAs sorbed 0.90 log units stronger than analogue PFCAs; C xSO4 sorbed 0.75 log units stronger than analogue C xSO3 anions. The log KMW values for the octyl analogues increase in the order H(CH2)8SO3- (1.74) < H(CH2)8SO4- (2.58) < F(CF2)8CO2- (PFNA, 4.04) < F(CF2)8SO3- (PFOS, 4.88). Intrinsic partition ratios determined on a phospholipid coated HPLC column (IAM-HPLC) closely aligned with SSLM KMW values. COSMO-RS based molecular calculations of KMW aligned with SSLM KMW values for hydrogenated anions with C8-C14 alkyl chains but strongly underestimated CF2 and CH2 unit increments for C4-C8 based anions. Dividing the critical narcotic membrane burden of 100 mmol/kg by the experimental KMW predicts lethal baseline toxicity concentrations (LC50,narc). The LC50,narc coincides with the lowest reported acute LC50 values for several anionic surfactants but were on average about an order of magnitude lower.

Smarter Sediment Screening: Effect-Based Quality Assessment, Chemical Profiling, and Risk Identification.

Sediments play an essential role in the functioning of aquatic ecosystems but simultaneously retain harmful compounds. However, sediment quality assessment methods that consider the risks caused by the combined action of all sediment-associated contaminants to benthic biota are still underrepresented in water quality assessment strategies. Significant advancements have been made in the application of effect-based methods, but methodological improvements can still advance sediment risk assessment. The present study aimed to explore such improvements by integrating effect-monitoring and chemical profiling of sediment contamination. To this end, 28 day life cycle bioassays with Chironomus riparius using intact whole sediment cores from contaminated sites were performed in tandem with explorative chemical profiling of bioavailable concentrations of groups of legacy and emerging sediment contaminants to investigate ecotoxicological risks to benthic biota. All contaminated sediments caused effects on the resilient midge C. riparius, stressing that sediment contamination is ubiquitous and potentially harmful to aquatic ecosystems. However, bioassay responses were not in line with any of the calculated toxicity indices, suggesting that toxicity was caused by unmeasured compounds. Hence, this study underlines the relevance of effect-based sediment quality assessment and provides smarter ways to do so.

Sorbent-modified biodegradation studies of the biocidal cationic surfactant cetylpyridinium chloride.

Biodegradability studies for the cationic surfactant cetylpyridinium chloride (CPC) are hampered by inhibitory effects on inoculum at prescribed test concentrations (10-20 mg organic carbon/L). In this study, we used 14C labeled CPC in the 28 d Headspace Test (OECD 310) and demonstrated that CPC was readily biodegradable (10->60% mineralization within a 10 day window) at test concentrations 0.006-0.3 mg/L with CPC as single substrate. Biodegradation efficiency was comparable over this concentration range. CPC inhibited degradation at 1 mg/L and completely suppressed inoculum activity at 3 mg/L. In an extensive sorbent modified biodegradation study we evaluated the balance between CPC bioaccessibility and toxicity. A non-inhibitory concentration of 0.1 mg/L CPC was readily biodegradable with 83% sorbed to SiO2, while biodegradation was slower when 96% was sorbed. SiO2 mitigated inhibitory effects of 1 mg/L CPC, reaching >60% biodegradation within 28 d; inhibitory effects were also mitigated by addition of commercial clay powder (illite) but this was primarily reflected by a reduced lag phase. At 10 mg/L CPC SiO2 was still able to mitigate inhibitory effects, but bioaccessibility seemed limited as only 20% biodegradation was reached. Illite limited bioaccessibility more strongly and was not able to sustain biodegradation at 10 mg/L CPC.

Cellular Uptake Kinetics of Neutral and Charged Chemicals in in Vitro Assays Measured by Fluorescence Microscopy.

Cellular uptake kinetics are key for understanding time-dependent chemical exposure in in vitro cell assays. Slow cellular uptake kinetics in relation to the total exposure time can considerably reduce the biologically effective dose. In this study, fluorescence microscopy combined with automated image analysis was applied for time-resolved quantification of cellular uptake of 10 neutral, anionic, cationic, and zwitterionic fluorophores in two reporter gene assays. The chemical fluorescence in the medium remained relatively constant during the 24-h assay duration, emphasizing that the proteins and lipids in the fetal bovine serum (FBS) supplemented to the assay medium represent a large reservoir of reversibly bound chemicals with the potential to compensate for chemical depletion by cell uptake, growth, and sorption to well materials. Hence FBS plays a role in stabilizing the cellular dose in a similar way as polymer-based passive dosing, here we term this process as serum-mediated passive dosing (SMPD). Neutral chemicals accumulated in the cells up to 12 times faster than charged chemicals. Increasing medium FBS concentrations accelerated uptake due to FBS-facilitated transport but led to lower cellular concentrations as a result of increased sorption to medium proteins and lipids. In vitro cell exposure results from the interaction of several extra- and intracellular processes, leading to variable and time-dependent exposure between different chemicals and assay setups. The medium FBS plays a crucial role for the thermodynamic equilibria as well as for the cellular uptake kinetics, hence influencing exposure. However, quantification of cellular exposure by an area under the curve (AUC) analysis illustrated that, for the evaluated bioassay setup, current in vitro exposure models that assume instantaneous equilibrium between medium and cells still reflect a realistic exposure because the AUC was typically reduced less than 20% compared to the cellular dose that would result from instantaneous equilibrium.

Sorption of Cationic Surfactants to Artificial Cell Membranes: Comparing Phospholipid Bilayers with Monolayer Coatings and Molecular Simulations.

This study reports the distribution coefficient between phospholipid bilayer membranes and phosphate buffered saline (PBS) medium (DMW,PBS) for 19 cationic surfactants. The method used a sorbent dilution series with solid supported lipid membranes (SSLMs). The existing SSLM protocol, applying a 96 well plate setup, was adapted to use 1.5 mL glass autosampler vials instead, which facilitated sampling and circumvented several confounding loss processes for some of the cationic surfactants. About 1% of the phospholipids were found to be detached from the SSLM beads, resulting in nonlinear sorption isotherms for compounds with log DMW values above 4. Renewal of the medium resulted in linear sorption isotherms. DMW values determined at pH 5.4 demonstrated that cationic surfactant species account for the observed DMW,PBS. Log DMW,PBS values above 5.5 are only experimentally feasible with lower LC-MS/MS detection limits and/or concentrated extracts of the aqueous samples. Based on the number of carbon atoms, dialkylamines showed a considerably lower sorption affinity than linear alkylamine analogues. These SSLM results closely overlapped with measurements on a chromatographic tool based on immobilized artificial membranes (IAM-HPLC) and with quantum-chemistry based calculations with COSMOmic. The SSLM data suggest that IAM-HPLC underestimates the DMW of ionized primary and secondary alkylamines by 0.8 and 0.5 log units, respectively.

Dealing with Confounding pH-Dependent Surface Charges in Immobilized Artificial Membrane HPLC Columns.

The retention capacity factor (k(IAM)) on immobilized artificial membrane chromatography columns (IAM-HPLC) is widely used as experimental descriptor of lipophilicity. For predominantly ionized compounds, however, unexpected and significant effects of pH, buffers, and salinity on k(IAM) have been reported. Besides zwitterionic phospholipids, IAM particles contain acidic silanol moieties and positively charged propylamine groups. The electrostatic model and experimental k(IAM) values presented in this study for organic cations show that the net IAM surface charge is positive below pH 5 and negative above pH 5. The resulting confounding electrostatic repulsion/attraction is strongly influenced by eluent salinity: k(IAM) values for cations differ by more than 2 orders of magnitude over the tested range of aqueous eluents. In phosphate buffered saline medium the actual lipophilicity of cationic drugs (K(PLIPW,cation)) is overestimated by at least a factor of 2. The K(PLIPW,cation) can be readily determined by IAM-HPLC in any 10 mM buffered eluent at pH 5. Accounting for, or avoiding, confounding electrostatic effects in IAM-HPLC considerably advances assessments of (phospho)lipophilicity for drug discovery and for environmental risk assessment of organic cations.

Which Molecular Features Affect the Intrinsic Hepatic Clearance Rate of Ionizable Organic Chemicals in Fish?

Greater knowledge of biotransformation rates for ionizable organic compounds (IOCs) in fish is required to properly assess the bioaccumulation potential of many environmentally relevant contaminants. In this study, we measured in vitro hepatic clearance rates for 50 IOCs using a pooled batch of liver S9 fractions isolated from rainbow trout (Oncorhynchus mykiss). The IOCs included four types of strongly ionized acids (carboxylates, phenolates, sulfonates, and sulfates), three types of strongly ionized bases (primary, secondary, tertiary amines), and a pair of quaternary ammonium compounds (QACs). Included in this test set were several surfactants and a series of beta-blockers. For linear alkyl chain IOC analogues, biotransformation enzymes appeared to act directly on the charged terminal group, with the highest clearance rates for tertiary amines and sulfates and no clearance of QACs. Clearance rates for C12-IOCs were higher than those for C8-IOC analogues. Several analogue series with multiple alkyl chains, branched alkyl chains, aromatic rings, and nonaromatic rings were evaluated. The likelihood of multiple reaction pathways made it difficult to relate all differences in clearance to specific molecular features the tested IOCs. Future analysis of primary metabolites in the S9 assay is recommended to further elucidate biotransformation pathways for IOCs in fish.

Sorption of organic cations to phyllosilicate clay minerals: CEC-normalization, salt dependency, and the role of electrostatic and hydrophobic effects.

Sorption to the phyllosilicate clay minerals Illite, kaolinite, and bentonite has been studied for a wide variety of organic cations using a flow-through method with fully aqueous medium as the eluent. Linear isotherms were observed at concentrations below 10% of the cation-exchange capacity (CEC) for Illite and kaolinite and below 1 mmol/kg (<1% CEC) for bentonite. Sorption to clays was strongly influenced by the electrolyte composition of the eluent but with a consistent trend for a diverse set of compounds on all clays, thus allowing for empirical correction factors. When sorption affinities for a given compound to a given clay are normalized to the CEC of the clay, the differences in sorption affinities between clays are reduced to less than 0.5 log units for most compounds. Although CEC-normalized sorption of quaternary ammonium compounds to clay was up to 10-fold higher than CEC-normalized sorption to soil organic matter, CEC-normalized sorption for most compounds was comparable between clays and soil organic matter. The clay fraction is thus a potentially relevant sorption phase for organic cations in many soils. The sorption data for organic cations to clay showed several regular trends with molecular structure but also showed quite a few systematic effects that we cannot explain. A model on the basis of the molecular size and charge density at the ionized nitrogen is used here as a tool to obtain benchmark values that elucidate the effect of specific polar moieties on the sorption affinity.

Development and evaluation of a new sorption model for organic cations in soil: contributions from organic matter and clay minerals.

This study evaluates a newly proposed cation-exchange model that defines the sorption of organic cations to soil as a summed contribution of sorption to organic matter (OM) and sorption to phyllosilicate clay minerals. Sorption to OM is normalized to the fraction organic carbon (fOC), and sorption to clay is normalized to the estimated cation-exchange capacity attributed to clay minerals (CECCLAY). Sorption affinity is specified to a fixed medium composition, with correction factors for other electrolyte concentrations. The model applies measured sorption coefficients to one reference OM material and one clay mineral. If measured values are absent, then empirical relationships are available on the basis of molecular volume and amine type in combination with corrective increments for specific polar moieties. The model is tested using new sorption data generated at pH 6 for two Eurosoils, one enriched in clay and the other, OM, using 29 strong bases (pKa > 8). Using experimental data on reference materials for all tested compounds, model predictions for the two soils differed on average by only -0.1 ± 0.4 log units from measured sorption affinities. Within the chemical applicability domain, the model can also be applied successfully to various reported soil sorption data for organic cations. Particularly for clayish soils, the model shows that sorption of organic cations to clay minerals accounts for more than 90% of the overall affinity.

Ion-exchange affinity of organic cations to natural organic matter: influence of amine type and nonionic interactions at two different pHs.

Sorption to standard soil organic matter (SOM) has been studied for a wide variety of organic cations using a flow through method with fully aqueous medium as eluent. SOM sorption for weak bases (pK(a) 4.5-7) was stronger at pH 4.5 than at pH 7, indicating that the ion-exchange affinity of the cationic species to SOM was higher than the bulk partition coefficient of corresponding neutral species to SOM. In the range of pH 4.5-7, the effect of pH on the sorption coefficients for strong bases with pK(a) > 7 was small, within 0.3 log units. For cations with the molecular formula C(x)H(y)N, sorption was accurately predicted by a model accounting for size (increase with alkyl chain length) and type of charged group (1° amine >4° ammonium of equal size). In addition to the C(x)H(y)N-model, several empirical correction factors were derived from the data for organic cations with polar functional groups. Models based on K(OW) or pK(a) fail to explain differences in sorption affinity of the ionic species. Our data on ion-exchange affinities for 80 organic cations show many examples where specific chemical moieties, for example, CH(2)-units, aromatic rings or hydroxyl groups, contribute differently to the sorption coefficient as compared to bulk partitioning data of neutral compounds. Other sorption models that were evaluated to explain variation between compounds suffered from outliers of more than one log unit and did not reduce relative log mean standard errors below 0.5. A wider range of sorption coefficients and more sorption data in general are required to improve modeling efforts further.

A framework for understanding the bioconcentration of surfactants in fish.

Surfactants are a class of chemicals released in large quantities to water, and therefore bioconcentration in fish is an important component of their safety assessment. Their structural diversity, which encompasses nonionic, anionic, cationic and zwitterionic molecules with a broad range of lipophilicity, makes their evaluation challenging. A strong influence of environmental pH adds a further layer of complexity to their bioconcentration assessment. Here we present a framework that penetrates this complexity. Using simple equations derived from current understanding of the relevant underlying processes, we plot the key bioconcentration parameters (uptake rate constant, elimination rate constant and bioconcentration factor) as a function of its membrane lipid/water distribution ratio and the neutral fraction of the chemical in water at pH 8.1 and at pH 6.1. On this chemical space plot, we indicate boundaries at which four resistance terms (perfusion with water, transcellular, paracellular, and perfusion with blood) limit transport of surfactants across the gills. We then show that the bioconcentration parameters predicted by this framework align well with in vivo measurements of anionic, cationic and nonionic surfactants in fish. In doing so, we demonstrate how the framework can be used to explore expected differences in bioconcentration behavior within a given sub-class of surfactants, to assess how pH will influence bioconcentration, to identify the underlying processes governing bioconcentration of a particular surfactant, and to discover knowledge gaps that require further research. This framework for amphiphilic chemicals may function as a template for improved understanding of the accumulation potential of other ionizable chemicals of environmental concern, such as pharmaceuticals or dyes.

Using membrane-water partition coefficients in a critical membrane burden approach to aid the identification of neutral and ionizable chemicals that induce acute toxicity below narcosis levels.

The risk assessment of thousands of chemicals used in our society benefits from adequate grouping of chemicals based on the mode and mechanism of toxic action (MoA). We measure the phospholipid membrane-water distribution ratio (DMLW) using a chromatographic assay (IAM-HPLC) for 121 neutral and ionized organic chemicals and screen other methods to derive DMLW. We use IAM-HPLC based DMLW as a chemical property to distinguish between baseline narcosis and specific MoA, for reported acute toxicity endpoints on two separate sets of chemicals. The first set comprised 94 chemicals of US EPA's acute fish toxicity database: 47 categorized as narcosis MoA, 27 with specific MoA, and 20 predominantly ionic chemicals with mostly unknown MoA. The narcosis MoA chemicals clustered around the median narcosis critical membrane burden (CMBnarc) of 140 mmol kg-1 lipid, with a lower limit of 14 mmol kg-1 lipid, including all chemicals labelled Narcosis_I and Narcosis_II. This maximum 'toxic ratio' (TR) between CMBnarc and the lower limit narcosis endpoint is thus 10. For 23/28 specific MoA chemicals a TR >10 was derived, indicative of a specific adverse effect pathway related to acute toxicity. For 10/12 cations categorized as "unsure amines", the TR <10 suggests that these affect fish via narcosis MoA. The second set comprised 29 herbicides, including 17 dissociated acids, and evaluated the TR for acute toxic effect concentrations to likely sensitive aquatic plant species (green algae and macrophytes Lemna and Myriophyllum), and non-target animal species (invertebrates and fish). For 21/29 herbicides, a TR >10 indicated a specific toxic mode of action other than narcosis for at least one of these aquatic primary producers. Fish and invertebrate TRs were mostly <10, particularly for neutral herbicides, but for acidic herbicides a TR >10 indicated specific adverse effects in non-target animals. The established critical membrane approach to derive the TR provides for useful contribution to the weight of evidence to bin a chemical as having a narcosis MoA or less likely to have acute toxicity caused by a more specific adverse effect pathway. After proper calibration, the chromatographic assay provides consistent and efficient experimental input for both neutral and ionizable chemicals to this approach.

Experimentally determined soil organic matter-water sorption coefficients for different classes of natural toxins and comparison with estimated numbers.

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 (K(oc)) were determined with a dynamic HPLC-based column method using a fully aqueous mobile phase with 5 mM CaCl(2) at pH 4.5. Sorption coefficients varied from less than 10(0.7) L/kg(oc) (e.g., all type B trichothecenes) to 10(4.0) L/kg(oc) (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 K(oc) 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.

Polyparameter linear free energy models for polyacrylate fiber-water partition coefficients to evaluate the efficiency of solid-phase microextraction.

The fiber-water partition coefficient, K(fw), is decisive for performance of solid-phase microextraction (SPME) techniques in organic chemical analyses. In this study, polyacrylate (PA)-coated fiber was evaluated for its K(fw) values toward diverse neutral organic compounds. Literature K(fw) data were thoroughly evaluated, and additional K(fw) values for 69 compounds were measured in phosphate-buffered saline (PBS) solution at 37 °C. These K(fw) data, spanning over 6 orders of magnitude, were used to construct polyparameter linear free energy relationship (PP-LFER) models. The PP-LFER models fit well to the data with a standard deviation of 0.15-0.23 log units. Additional experiments indicated that the differences in temperature (25 vs 37 °C), electrolyte concentrations (pure water vs PBS), and conditioning methods (heat vs methanol) had only minor influences (<0.3 log units) on K(fw). Using the established PP-LFERs, the SPME extraction efficiency of PA coating toward compounds of differing polarity was evaluated in comparison to poly(dimethylsiloxane) (PDMS) coating. PA exhibited higher extraction capacities for H-bond donor compounds (e.g., phenols, anilines, amides, and many drugs and pesticides) with the estimated K(fw) values being 1-4 log units higher than those of PDMS. Also, PA was shown to be more efficient than PDMS for hydrophobic aromatic compounds.