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Biomedical subjects

Joop L M Hermens

Publications and source records attributed to Joop L M Hermens.

At least 19 recordsLinked to original sources
PubMed2006

Distribution of PAHs and PCBs to dissolved organic matter: high distribution coefficients with consequences for environmental fate modeling.

Dissolved organic carbon/water distribution coefficients (K(DOC)) were measured for a selection of PCBs with octanol/water partition coefficients (K(OW)) ranging from 10(5.6) to 10(7.5). A solid phase dosing and sampling technique was applied to determine K(DOC) to Aldrich humic acid. This technique is in particular suitable for determining the distribution of very hydrophobic chemicals to complex matrices like humic acids. The K(DOC) values were calculated from the experimental data using a linear model. Determined K(DOC)'s were evaluated in relation to octanol/water partition coefficients of the test compounds, and compared to literature data. Measured K(DOC) values were somewhat higher than literature data, which can probably be attributed to the overestimation of freely dissolved aqueous concentration as a result of incomplete phase separation in other studies, and to the unique character of Aldrich humic acid as a "sorbent" or co-solute or to the fact that Aldrich humic acid is not a typical DOC, and other (adsorption) processes can occur. This study reports DOC distribution coefficients that belong to the highest ones ever measured. In addition, the DOC distribution was discussed in relation to current risk assessment modeling.

1-Octanol↗
PubMed2006

Freely dissolved pore water concentrations and sorption coefficients of PAHs in spiked, aged, and field-contaminated soils.

Freely dissolved aqueous concentrations in the soil pore water represent an important aspect of bioavailability and risk assessment of contaminated soils. In this study, a negligible depletive partitioning based sampling technique was validated and applied to measure free concentrations of polycyclic aromatic hydrocarbons (PAHs) in spiked, aged and field-contaminated soils. Detailed kinetic studies were performed to select appropriate equilibration times. Freely dissolved aqueous concentrations in the pore water were compared to total concentrations, and sorption coefficients were calculated. Results show that equilibrium partition models can predict sorption coefficients of freshly spiked and lab-aged soils rather accurately. However, freely dissolved pore water concentrations of field-contaminated soils are orders of magnitude lower than model predictions. Consequently, environmental risks can be highly overestimated with these models. The simple and sensitive partitioning-based sampling technique used in this study, could, therefore, be applicable to improve site-specific risk assessment of field-contaminated soils.

Adsorption↗
PubMed2006

Measurement of the free concentration of octylphenol in biological samples with negligible depletion-solid phase microextraction (nd-SPME): analysis of matrix effects.

A negligible depletion-solid phase microextraction (nd-SPME) method is presented to measure free concentrations of octylphenol in biological samples. Potential confounding factors, such as matrix effects, are studied as well. Fouling of the fibre appears to occur, but it does not seem to reduce or enhance the measured uptake of octylphenol. In the setup applied here, without any agitation, it has also been found that there is a large effect of protein presence on the kinetics of octylphenol uptake. In addition, an apparent affinity constant of octylphenol for bovine serum albumin was determined.

Culture Media↗
PubMed2006

Freely dissolved concentrations of PAHs in soil pore water: measurements via solid-phase extraction and consequences for soil tests.

Freely dissolved pore water concentrations are difficult to assess in complex matrixes such as soils or sediments. In this study, a negligible-depletion partitioning-based sampling technique was applied to measure freely dissolved pore water concentrations. A poly(dimethylsiloxane) (PDMS)-coated glass fiber was exposed to a slurry of a soil spiked with several PAHs at concentrations ranging from 2 to 2000 mg/kg. PAH-concentrations in the PDMS coating increased linearly with the total soil concentration until a certain maximum was reached. Freely dissolved pore water concentrations were calculated using PDMS-water partition coefficients, and the calculated maximum pore water concentrations corresponded with the aqueous solubility of the tested compounds. Furthermore, the sampling technique is very sensitive because it can detect freely dissolved pore water concentrations in the ng/L range for the tested PAHs. Freely dissolved pore water concentrations are an important parameter for the exposure of organisms in soil. Saturation of the pore water with increasing soil concentrations should therefore be considered in soil toxicity testing. Sorption coefficients that were calculated from freely dissolved concentrations were slightly higher than estimates based on octanol-water partition coefficients. These differences are discussed in relation to the effects of dissolved organic matter in soil pore water on the determination of sorption coefficients.

Adsorption↗
PubMed2005

Sediment dilution method to determine sorption coefficients of hydrophobic organic chemicals.

Sorption coefficients of hydrophobic organic chemicals (HOC) to sediments and soils can easily be underestimated in traditional batch experiments, especially because analysis of the aqueous concentration often includes compounds sorbed to colloidal organic matter. In this work, a "sediment dilution approach" has been combined with measurements of freely dissolved concentrations to determine sorption coefficients of five chlorobenzenes and two chloroanilines in spiked sediment and of two unknown chemicals in field-contaminated sediment. A range of sediment suspensions with different sediment-water ratios was made. Freely dissolved concentrations in these suspensions were measured by negligible depletion solid-phase microextraction (nd-SPME). Sediment-water sorption coefficients (KD) were derived from the decrease of the freely dissolved concentrations as a function of the "dilution factor" (DF = volume water/mass sediment). The determined sorption coefficients were very similar to literature values. The experimental setup provides sorption coefficients without the need for total extractions, and the negligible depletion SPME technique does not require phase separation. The proposed method might be an alternative for batch equilibrium experiments to determine sorption coefficients.

Adsorption↗
PubMed2005

Solid phase dosing and sampling technique to determine partition coefficients of hydrophobic chemicals in complex matrixes.

Determination of polymer-water and dissolved organic carbon (DOC)-water distribution coefficients of very hydrophobic chemicals (log K0w > 6) is not straightforward. Poor water solubility of the test compounds complicates the spiking and analysis of actual freely dissolved concentrations. By dosing a system via a PDMS-fiber and monitoring the depletion in the polymer, spiking and analysis of concentrations in the aqueous phase are avoided, and sorption to the polymer and other hydrophobic phases can be determined easily and accurate. In this publication we report the determination of poly(dimethyl-siloxane) (PDMS)-water, and Aldrich humic acid-water distribution coefficients for six PAHs with log K0w values varying from 4.56 to 6.85. The distribution coefficients to a PDMS fiber llog Kf) and the DOC (log KDOC) range from 3.86 to 5.39 and 4.78 to 7.43, respectively. Even for the most hydrophobic compounds, the distribution coefficients show small standard errors (< or = 0.05 log units). Therefore, this method might be applied to determine sorption coefficients of numerous, even more hydrophobic compounds, to humic acids as well as other dissolved hydrophobic matrixes.

Adsorption↗
PubMed2005

Bioaccumulation of organic chemicals in contaminated soils: evaluation of bioassays with earthworms.

Earthworms live in close contact with the soil and can thus be considered representative for the bioavailability of chemicals at contaminated sites. Bioavailability can either be assessed by analyzing earthworms from contaminated locations or by exposing laboratory-reared specimens to soil samples from the field (bioassays). In this study, we investigate the relevance of bioassays by using an extended experimental design (to identify signs of depletion of the bioavailable phase by the earthworms) and by using two species of earthworm (the standard test species Eisenia andrei and the field-relevant Aporrectodea caliginosa). Furthermore, bioassay results are compared to body residues of worms collected from the field site: a heavily polluted polder, amended with dredge spoil. We focused on telodrin, dieldrin, hexachlorobenzene, and eight PCBs. With our bioassay design, it was shown that depletion was unlikely, although more subtle effects could have occurred (e.g., changes in sorption during the experiments). E. andrei is a good choice for bioassays because its body residues correlate well to those in A. caliginosa, as well as to those in the field-collected worms. Nevertheless, E. andrei accumulated slightly more than the other species and appeared to be more sensitive to the conditions in soil from one of our sites.

Animals↗
PubMed2004

Toward more useful in vitro toxicity data with measured free concentrations.

In vitro assays and computer models are promising alternatives for in vivo animal testing, but the power of these alternative methods to predict in vivo risk is still very limited. One step forward is to make the outcome of in vitro assays (such as median effect concentrations (EC50 values)) independent of assay conditions such as protein content. Here we show that measured free concentrations of chemicals in the in vitro assay medium result in system-independent EC50 values. We introduce a very simple method to measure free concentrations in miniature test systems using negligible depletion solid-phase microextraction. The generated data are much more suitable for extrapolation to in vivo, provide unbiased input for computational methods (for example, quantitative structure-activity relationships), and can shed an entirely different light on the activity of environmental contaminants.

Animals↗
PubMed2004

Modelling SPME data from kinetic measurements in complex samples.

The kinetics of the partition process to solid phase microextraction fibres is often modelled using a stagnant layer model. Despite its usefulness, in some agitation systems such a model cannot be applied because the stagnant layer cannot be characterized precisely. Therefore, in this present study an alternative approach is introduced. Transport from the bulk medium to the fibre coating is simply modelled by a finite mass transfer coefficient instead of diffusion through a stagnant water layer surrounding the fibre. Intra-fibre transport is described by non-steady diffusion. The model is aimed at the analysis of SPME measurements in the kinetic phase for samples including a binding matrix. It was validated with experimental results of SPME measurements concerning the absorption kinetics of [(3)H]estradiol at different concentrations of bovine serum albumin (BSA) as a chemical binding matrix. The model provides excellent fits of the experimental data, resulting in an association constant (K(a)) of estradiol for BSA of 5.66 x 10(4) M(-1), which is similar to literature values and a fibre coating/bulk medium partition coefficient of 5.0 x 10(3). The kinetics of extraction were studied with the model, showing that the rate-limiting step in the extraction process was the diffusion in the fibre. This finding rules out the possibility that the presence of the matrix itself in the diffusion layer affects the kinetics of estradiol uptake into the SPME fibre.

Absorption↗
PubMed2004

Solid-phase microextraction to predict bioavailability and accumulation of organic micropollutants in terrestrial organisms after exposure to a field-contaminated soil.

The risk posed by soil contaminants strongly depends on their bioavailability. In this study, a partition-based sampling method was applied as a tool to estimate bioavailability in soil. The accumulation of organic micropollutants was measured in two earthworm species (Eisenia andrei and Aporrectodea caliginosa) and in 30-microm poly(dimethylsiloxane) (PDMS)-coated solid-phase micro extraction (SPME) fibers after exposure to two field-contaminated soils. Within 10 days, steady state in earthworms was reached, and within 20 days in the SPME fibers. Steady-state concentrations in both earthworm species were linearly related to concentrations in fibers over a 10,000-fold range of concentrations. Measured concentrations in earthworms were compared to levels calculated via equilibrium partitioning theory and total concentrations of contaminants in soil. In addition, freely dissolved concentrations of contaminants in pore water, derived from SPME measurements, were used to calculate concentrations in earthworms. Measured concentrations in earthworms were close to estimated concentrations from the SPME fiber measurements. Freely dissolved concentrations of contaminants in pore water, derived from SPME measurements, were used to calculate bioconcentration factors (BCF) in earthworms. A plot of log BCFs against the octanol-water partition coefficient (log Kow) was linear up to a log Kow of 8. These results show that measuring concentrations of hydrophobic chemicals in a PDMS-coated fiber represents a simple tool to estimate internal concentrations of chemicals in biota exposed to soil.

Animals↗
PubMed2004

Xenoestrogenicity in in vitro assays is not caused by displacement of endogenous estradiol from serum proteins.

The possibility that compounds tested for estrogenicity can compete for binding places on serum proteins and cause an increase of available and very potent endogenous estrogens is of great interest for both the in vitro assay results and the prediction of risk for humans. In in vitro assays, small amounts of estradiol remaining after the charcoal stripping of serum applied in the culture medium could be displaced by the tested compounds, leading to an estrogenic response that might be falsely attributed to the test compound. We have studied the stripping efficiency of charcoal and measured whether reported xenoestrogens can displace estradiol from serum in an in vitro assay using negligible depletion-solid phase microextraction (nd-SPME). Possible competition was also studied with a mathematical exposure model, from which the predictions were compared to the measurements. We found that the common charcoal stripping procedure removed 99% of initially present estradiol. Additionally, our results with charcoal adsorption indicate that charcoal is not useful for serum protein binding assays, as it adsorbs more than the free fraction of ligand. Although the competition model predicted a displacement of estradiol from the serum proteins at the higher applied doses of xenoestrogen, the measurements showed no displacement. Therefore, we conclude that estrogenic responses in the in vitro assay applied here are not caused by displacement of remaining estradiol in the stripped serum. The possibility remains, however, that our displacement hypothesis does apply for estrogen sulfates, as these are present in much higher concentrations than estradiol in stripped serum.

Adsorption↗
PubMed2004

Chronic toxicity and body residues of the nonpolar narcotic 1,2,3,4-tetrachlorobenzene in Chironomus riparius.

The use of internal concentrations as a dose parameter for baseline toxicity requires an understanding of the relationship between accumulation level and toxic effects, not only for acute but also for chronic exposure. In this study of chronic toxicity of the nonpolar narcotic 1,2,3,4-tetrachlorobenzene (TeCB) to Chironomus riparius, the chronic median lethal concentration (LC50) was determined to be 0.99 (0.54-1.82) microM, the median sublethal effect concentration (EC50) for growth was 0.76 (0.73-0.97) microM, and the chronic (sublethal) no-observed-effect concentration (NOEC) was 0.24 +/- 0.01 microM. An acute-to-chronic ratio of 9.8 was calculated from a previously determined acute LC50 value and this NOEC. The chronic critical body residue (CBR), 136 mmol/kg lipid, was the same as the acute CBR, previously determined. The similarity of the chronic and acute CBRs lends support to the exposure time independent aspect of baseline toxicity theory. An implication of this is that internal concentrations estimated by biomimetic sampling devices may be compared to acute CBR data to determine chronic baseline toxicity risk. Such sampling devices, solid-phase microextraction (SPME) fibers, were simultaneously exposed during the toxicity test. The results of this study suggest that body residues estimated with SPME may be used to predict baseline toxicity for various exposure durations.

Animals↗
PubMed2004

Baseline toxicity of a chlorobenzene mixture and total body residues measured and estimated with solid-phase microextraction.

Body residues of compounds with a narcotic mode of action that exceed critical levels result in baseline toxicity in organisms. Previous studies have shown that internal concentrations in organisms also can be estimated by way of passive sampling. In this experiment, solid-phase microextraction (SPME) fibers were used as a tool to estimate the body residues, which were then compared to measured levels. Past application of SPME fibers in the assessment of toxicity risk of samples has focused on separate exposure of fibers and organisms, often necessitated by the amount of agitation needed in order to achieve steady state in the fibers within a convenient time period. Uptake kinetic studies have shown that in SPME fibers with thin coatings, equilibrium concentrations can be reached without agitation within the time frame of a toxicity test. In contrast to toxicity experiments to date, the SPME fibers in the current study were exposed concomitantly to the test water with the organisms, ensuring an exposure under the exact same conditions. Fibers and two aquatic invertebrate species were exposed to a mixture of four chlorobenzenes with a narcotic mode of action. The total body residue of these compounds in the organisms was determined, as was the acute toxicity resulting from the accumulation. The total body residues of both species were correlated to the total concentrations in SPME fibers. It was concluded that toxicity could be predicted based on total body residue (TBR) estimates from fiber concentrations.

Animals↗
PubMed2004

Environmental quality criteria for organic chemicals predicted from internal effect concentrations and a food web model.

Environmental quality criteria (EQC) for hydrophobic organic chemicals were calculated with a model for bioaccumulation in food webs. The model was calibrated and verified using polychlorinated biphenyl concentrations in food webs of shallow lakes. The EQCs in water and sediment were derived based on internal effect concentrations (IECs) for several modes of toxic action. By reverse calculation with the food web model for each organism in the web, a different water or sediment concentration is calculated corresponding to the IEC in each organism. A statistical procedure with an acute-to-chronic value is used to derive chronic EQCs based on bioaccumulation. The model-based chronic EQCs were compared with previously established EQCs. The EQCs calculated with the food web model generally are within an order of magnitude of the previously derived EQCs based on toxicity data on individual chemicals. Some previously derived EQCs are much lower than model predictions and usually based on small samples of toxicity data such as no-observed-effect concentrations (NOECs) with large assessment factors. When faced with data gaps, it is proposed to use model-based chronic EQCs for (polar) narcotic chemicals. Other modes of action require a different model concept to account for receptor-based toxicity.

Animals↗
PubMed2003

Removal of two polycyclic musks in sewage treatment plants: freely dissolved and total concentrations.

In the current study, the removal of slowly degradable hydrophobic chemicals in sewage treatment plants (STPs) has been evaluated with emphasis on the combination of free and total concentration data. Free and total concentrations of two polycyclic musks were determined in each compartment of four STPs. The free concentration of the polycyclic musks remains virtually constant throughout all the compartments of the STPs with values between 0.21 and 0.57 microg/L for AHTN and between 0.79 and 2.0 microg/L for HHCB. Total concentrations of these fragrances are highly dependent on the volatile solids in a given compartment resulting in much more variation with values between 0.42 and 92 microg/L for AHTN and between 1.25 and 258 microg/L for HHCB. It is concluded that free concentrations of these hydrophobic chemicals in the compartments of STPs are mostly biodegradation mediated, while total concentrations are mediated by the concentration of solids. The combination of measurements of free and total concentrations can improve estimations regarding removal efficiency and removal pathways.

Odorants↗