Tobias Nilsson

Pressurised liquid extraction of persistent organic pollutants in environmental analysis

Abstract This review updates our knowledge on pressurised liquid extraction, PLE (also known as accelerated solvent extraction and pressurised fluid extraction) of persistent organic pollutants such as polynuclear aromatic hydrocarbons and polychlorinated biphenyls from environmental matrices. The basic experimental set-up is presented, and parameters influencing the extraction process are discussed. PLE can be used for a broad range of applications, and clearly has the potential for replacing tedious classic extraction methods such as Soxhlet extraction.

Pressurized fluid extraction of polychlorinated biphenyls in solid environmental samples

Abstract The effectiveness of extracting native (not spiked) polychlorinated biphenyls (PCBs) from solid environmental samples by means of pressurized fluid extraction (PFE, Dionex trade name Accelerated Solvent Extraction) according to US Environmental Protection Agency (EPA) Method 3545, was determined. Three different certified reference materials, two sediments and one sewage sludge, were utilized. As opposed to most of the previous investigations, a thorough quantitative determination of the extracts obtained by PFE was performed and compared to certified values. Obtained data were in good agreement with certified values for all materials. However, materials with different particle sizes seemed to have influence on the extraction efficiency, with enhanced extraction for smaller particle size samples. PFE is concluded to be at least as effective as previously used methods in terms of quantitative extraction. When compared to data obtained with supercritical fluid extraction (SFE) using EPA Method 3562, the recoveries where slightly higher. This was explained by the less clean extracts obtained in PFE despite clean-up of the extracts. This is contrary to the clean extracts obtained by SFE which are ready for analysis. It can, however, not be excluded that PFE is really more efficient for extraction of very strongly bound analytes.

Introducing selective supercritical fluid extraction as a new tool for determining sorption/desorption behavior and bioavailability of persistent organic pollutants in sediment.

This review article intends to introduce the possibility of utilizing selective supercritical fluid extraction (SFE) as a tool to study sorption/desorption processes and bioavailability of persistent organic pollutants (POP) in sediment. Sorption/desorption behavior and bioavailability studies of POPs is a large research area, but still many unsolved problems exists. Therefore novel approaches to investigate mechanistic behavior of POPs in sediments are needed. Present literature on SFE points to the fact that selective SFE measurements can improve our knowledge, and recent investigations have been performed that demonstrate this. Results obtained with selective SFE can be connected to desorption of POPs in sediments under natural conditions in aquatic ecosytems. The ultimate goal is to use selective SFE as a way to determine the bioavailable fraction present within a matrix. A few preliminary results are presented here which may serve as a starting point for future studies.

Longitudinal displacement and intramural shear strain of the porcine carotid artery undergo profound changes in response to catecholamines

The effects of catecholamines on longitudinal displacements and intramural shear strain of the arterial wall are unexplored. Therefore, the common carotid artery of five anaesthetized pigs was investigated using an in-house developed noninvasive ultrasonic technique. The study protocol included intravenous infusion of low-dose epinephrine (β-adrenoceptor activation), as well as intravenous boluses of norepinephrine (α-adrenoceptor activation). Further, the effects of β-blockade (metoprolol) were studied. There were significant positive correlations between pulse pressure and longitudinal displacement of the intima-media complex (r = 0.72; P < 0.001), as well as between pulse pressure and intramural shear strain (r = 0.48; P < 0.001). Following administration of norepinephrine, the longitudinal displacement of the intima-media complex and intramural shear strain profoundly increased (median 190%, range 102-296%, and median 141%, range 101-182%, respectively, compared with baseline), also when given during β-blockade (median 228%, range 133-266%, and median 158%, range 152-235%, respectively). During infusion of low-dose epinephrine, the longitudinal displacement of the intima-media complex and intramural shear strain decreased (median 88%, range 69-122%, and median 69%, range 47-117%, respectively, compared with baseline). In conclusion, the present study shows, for the first time, that the longitudinal displacement and intramural shear strain of the porcine carotid artery undergo profound changes in response to catecholamines. Increase in longitudinal displacements seems to be strongly related to α-adrenoceptor activation. Thus metoprolol is insufficient to counteract a profound increase in longitudinal displacement and intramural shear strain following a surge of norepinephrine.

Selective supercritical fluid extraction to estimate the fraction of PCB that is bioavailable to a benthic organism in a naturally contaminated sediment

Selective supercritical fluid extraction (SFE) at 40 degrees C, 120 bar and 60 min was utilised as a means to estimate the bioavailable fraction of PCBs to chironomid larvae in a naturally contaminated limnic sediment. This extraction methodology removed about 50% of the PCBs from the sediment. According to the equilibrium partitioning theory, organisms in that sediment should decrease their uptake from the sediment to the same extent, biota-to-sediment accumulation factors (BSAFs) thus remaining constant. Surprisingly, the BSAFs for 11 PCB congeners decreased some 40% for the selectively extracted sediment as compared to BSAFs for organisms dwelling in untreated sediment. The results were statistically significant at the 0.001 level using a paired t-test. This can only be interpreted so that selective SFE removed easily available PCBs preferentially, leaving more tightly bound PCBs behind. Hence, by fine-tuning extraction conditions, this methodology might be used to estimate bioavailable fractions by chemical means.

A method to measure shear strain with high spatial resolution in the arterial wall non-invasively in vivo by tracking zero-crossings of B-mode intensity gradients

We have previously shown that there is a distinct longitudinal movement of the arterial wall during a cardiac cycle. This movement is larger in the intima-media region than in the adventitial region which introduces a substantial shear strain within the arterial wall. Our previously developed echo-tracking algorithm measured this shear strain by tracking two separate echoes, one in the intima-media region and one in the adventitia region and thus only a linear distribution was evaluated. The objective of this study was to suggest and evaluate a new improved method which can measure the intramural shear strain with higher spatial resolution and thereby provide more information on this new and rather unknown phenomenon. The mean maximum shear strain was 0.82 radians with a standard deviation of 0.17 radians and a CV-value of 14.2%. The total mean difference in measured longitudinal movement between the new and previous method was 10µm with a standard deviation of 90µm and a CV-value of 12.8%. The spatial distribution of the intramural shear strain seems to be very non-linear with a large amount of shear strain occurring in a small section around the transition between the media and adventitia layers.

Comparison of two extraction methods independently developed on two conceptually different automated supercritical fluid extraction systems for the determination of polychlorinated biphenyls in sediments.

Two extraction methods that independently have been developed on conceptually different automated supercritical fluid extraction systems, ISCO SFX 3560 (syringe pump and liquid trapping) and Hewlett-Packard 7680T SFE (reciprocating pump and solid-phase trapping), were compared for the extraction of polychlorinated biphenyls from two Swedish sediments. The results demonstrated that the high-temperature ISCO method in some cases yields a more exhaustive extraction, but also less clean extracts due to co-extraction of unwanted matrix components which are all present in the trapping solvent. The medium-temperature Hewlett-Packard method may sometimes cause problems with quantitative recoveries, but on the other hand it yields very clean extracts due to the extra selectivity resulting from collection on a solid-phase trap.

Particle-specific sorption/desorption properties determine test compound fate and bioavailability in toxicity tests with Chironomus riparius - high-resolution studies with lindane

We studied the sorption (batch equilibrium experiments) and desorption (consecutively harsher supercritical fluid extractions) of lindane to different types of sediment and food particles, as well as larval uptake in standardized peat-based artificial sediment toxicity tests with the midge Chironomus riparius. Lindane sorption to organic particles was fast and efficient, reaching 98+/-0.1 and 97+/-0.1% of added compound in 48 h for peat and Tetraphyll(R), respectively, and 77+/-0.2% in whole sediment. Sorption to inorganic particles, that is, sand and kaolin clay, was much lower, 9.6+/-1.3% and 8.3+/-0.8%, respectively. Supercritical fluid extractions showed that most of the lindane sorbed to organic particles and sediment was loosely bound, as only 9 to 14% remained associated with particles after weak and intermediate extractions strengths. Larval uptake of dissolved lindane was 4.9+/-0.71 and 10.8+/-1.2 microg/g wet weight in 22 and 68 microg/L treatments, respectively, and four to five times higher than that of particle-associated lindane, ranging 1.0+/-0.15 to 2.7+/-0.21 microg/g in the above treatments. Surprisingly, larval uptake of lindane was similar from refractory peat and the more labile Tetraphyll particles. Despite an efficient larval uptake of dissolved lindane, sorption/desorption of lindane to/from Tetraphyll particles will facilitate digestive uptake in toxicity tests, particularly in spiked-water scenarios where food particles may act as vectors. Our results show that the exposure scenario is an important determinant for the behavior and bioavailability of test compounds in standardized toxicity tests.

A robust and fast method for arterial lumen diameter and intima-media thickness measurements

Lumen diameter, distension and intima-media thickness (IMT) in human arteries are important parameters in cardiovascular research. The signal reflected from the arterial wall strongly depends on the ultrasound scanner and settings. The signal also varies with age and health of the subject. A general method insensitive with respect to the subject and the scanner would be of great help. We have developed a novel and robust method for ARTerIal Characterization (ARTIC), suitable for real-time in vivo measurements of diameter, distension and IMT using B-Mode images. The aim of this study was to evaluate ARTIC on different subjects and scanners. ARTIC was evaluated in vivo in different groups of subjects using two scanners, HDI5000 (Philips Medical Systems, Bothell, WA, USA) and ULAOP (University of Florence, Italy). First, a comparison was made against a previous method validated on phantoms. Then measurements of young (healthy) and old (healthy and unhealthy) subjects were evaluated for both scanners. Finally, a comparison between scanners was made. The evaluation of different subjects shows a coefficient of variation (CV) ranging from 1.4-2.0% for diameter, 4.3-8.8% for distension and 3.66.6% for IMT.

Methods for measurements of the longitudinal movement and the shear-induced longitudinal elastic modulus of the arterial wall

We have recently shown that a previous unknown longitudinal movement and a corresponding longitudinal strain are present in the arterial wall. The objective of this study was to introduce and evaluate an improved method for measurement of the longitudinal movement as well as to show results from the first in vivo trial of measurement of the shear induced longitudinal elastic modulus of the arterial wall. The total mean difference in estimated displacement between the new and old algorithms was 1 ¿m with a standard deviation of 76 ¿m. The mean shear induced longitudinal elastic modulus was 95 Pa (SD 39), range 49-153. This indicates that the longitudinal elastic modulus of the inner layers of the arterial wall might be 1000 times lower than the values reported for exposed vessel walls in vitro. The unavoidable sources of inaccuracy present in our methods cannot justify such a large discrepancy. Possible explanations are discussed; based on differences between adopted approaches and on the presence of forces other than shear stress.