Gas-purge Technique Research Articles

Influence of long contact times on sediment sorption kinetics of spiked chlorinated compounds

The desorption kinetics of hexachlorobenzene (HCB) and 2,4,4'-trichlororbiphenyl (PCB 28) spiked to a field sediment were studied using a gas-purge technique. A contact time of up to 1,461 d was used to assess long-term changes in desorption kinetics. Purge-induced desorption experiments lasted from 300 to more than 4,000 h. Fast-, slow-, and very-slow-desorbing fractions could be distinguished. The desorption patterns changed with contact time from mainly fast- and slow-desorbing fractions toward the domination of slow- and very-slow-desorbing fractions. The desorption pattern for HCB after a contact time of 1,461 d became comparable to previously reported desorption patterns observed for in situ contaminants. An additional spike of HCB, PCB 28, 2,4,6-trichlorobiphenyl, and 2,2',4,5'-tetrachlorobiphenyl applied to the sediment purged for more than 4,000 h showed that very slow sites were accessible for these compounds within a few hours. Only very small fast-desorbing fractions could be detected after a contact time of just 48 h. These results indicate that domination of very slow desorption is caused not only by long contact times but, perhaps, also by the accessibility of specific sites within the sediment matrix.

Laser-induced plasma spectroscopy to as low as 130 nm when a gas-purged spectrograph and ICCD detection are used.

An experimental setup is described for measuring laser-induced plasma emission spectra in the near vacuum UV with a Czerny-Turner spectrograph and intensified charge-coupled device under atmospheric pressure. With a simple gas-purge technique, emission lines down to 130 nm could be recorded. The strongest emission lines of bromine, chlorine, and iodine in the near vacuum UV are easily detected.

Influence of desorption and contact time on sediment‐water distribution of spiked polychlorinated biphenyls and polycyclic aromatic hydrocarbons: Relation with in situ distribution

The long-term sediment-water distribution of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs), spiked to Lake Ketelmeer (The Netherlands) sediment, was studied using a gas-purge technique. Contact times varied from 2 to 1,461 d for the PCBs and from 5 to 100 d for the PAHs. Purge-induced desorption experiments lasted 300 to > 4,000 h. The initial distribution coefficients that were observed during the first part of the experiment were close to literature values for distribution after short contact times. The distribution coefficients increased during the purge-induced desorption experiments. The final distribution coefficients that were observed during the last part of the experiment were one to two orders of magnitude higher than the initial values and were close to distribution coefficients reported earlier for in situ PCBs and PAHs present in a field-contaminated sediment for years to decades. The change in distribution coefficients during a gas-purge experiment may resemble the long-term change in a field sediment. Final distribution coefficients seem to be a more relevant measure for the distribution coefficients of hydrophobic organic chemicals in aged field sediments than values obtained after short contact times.

Resistant sorption of in situ chlorobenzenes and a polychlorinated biphenyl in river Rhine suspended matter.

The desorption kinetics of in situ chlorobenzenes (dichlorobenzenes, pentachlorobenzene and hexachlorobenzene) and 2,4,4'-trichlorobiphenyl (PCB-28) were measured with a gas-purge technique for river Rhine suspended matter sampled in Lobith, The Netherlands. This suspended matter is the main source of sediment accumulation in lake Ketelmeer. In lake Ketelmeer sediment earlier observations showed that slow and very slow fractions dominate the desorption profile. For the river Rhine suspended matter, only for PCB-28 a fast desorbing fraction of around 1.6% could be detected. The observed rate constants were on the average 0.2 h(-1) for fast desorption, 0.004 h(-1) for slow desorption, and 0.00022 h(-1) for very slow desorption. These values are in agreement with previous findings for the sediment from lake Ketelmeer and with available literature data on fast, slow, and very slow desorption kinetics. The results from this study show the similarity of desorption profiles between river Rhine suspended matter, and the top layer sediment from lake Ketelmeer. This indicates that slow and very slow fractions are already present in material forming the top layer of lake Ketelmeer, and were not formed after deposition of this material in the lake. The absence of detectable fast fractions for most compounds could be caused by the absence of recent pollution of the suspended matter. But, the observations may also be explained by a rapid disappearance of compounds from the fast fraction due to a combination of a high affinity of very slow sites for these compounds, and their relatively high volatility.

Nitric Oxide Release from the Liver Surface to the Intraabdominal Cavity during Acute Endotoxemia in Rats

Nitric oxide (NO) is produced by the liver during lipopolysaccharide (LPS)-induced endotoxemia. The aim of this study was to examine whether NO, which is produced in the liver, is released from the liver surface to the intraabdominal cavity during endotoxemia. NO was quantitatively determined by chemiluminescence and a newly developed gas purge technique was used to directly measure NO released from the liver surface and the intraabdominal cavity of rats before and after LPS (0.1 mg/kg, intraperitoneally) or saline administration. The expression of inducible NO synthase (iNOS) mRNA in the liver was detected by Northern blot analysis. NO levels from both the liver surface and in the intraabdominal cavity were elevated at 2 h after LPS injection and peaked at 10 h and both the time course of NO level were well correlated with each other. Both NO levels were below the detectable range before LPS and after saline administration. Inducible NOS mRNA in the liver exhibited a sharp increase to a maximum level at 4 h after LPS injection. The present study indicates that the hepatic NO, which might have been produced by iNOS in the liver, is released from the liver surface to the intraabdominal cavity during endotoxemia.

Polychlorinated biphenyl desorption from low organic carbon soils: Measurement of rates in soil-water suspensions

The desorption of 13 PCB congeners from four soils has been investigated using the gas purge technique. The soils from PCB spill sites had been in contact with Aroclor 1242 1254 mixtures for 3 or more years; thus, sorption equilibrium is presumed to have been obtained. Soils were “engineered” ground cover materials used at utility industry substations and consisted of fine rock chips and sandsilt-clay fractions with organic carbon < 0.2%. The congeners contained from three to five chlorine atoms. Agreement of measured Henry's Law constants for the 14C-labeled congeners 24′, 22′55′ and 22′44′55′ with literature values established the proper function of the gas purge technique for measurement of congener release rates from soil-water suspensions. For all 13 congeners and all soils: 1) the labile fraction was typically 80 to 90% of the total congener concentration, 2) the majority of the labile fraction was desorbed or released within 48 hours of contact with water, and 3) the release of the remaining nonlabile fraction persisted for over 6 months with complete release estimated to be 1 to 2 years. Release rate constants, k d, decreased with increasing chlorine number with typical values for labile and nonlabile fractions ranging from 1.4 to 0.5 d −1 and 0.008 to 0.0006 d −1, respectively.

Polychlorinated biphenyl sorption by soils: Measurement of soil-water partition coefficients at equilibrium

The sorption of PCB congeners 24′ (lUPAC number 8), 22′55′ (52) and 22′44′55′ (153) by eight soils differing in their organic carbon content (2.3 to 0.2% by Wt.) and expandable clay mineral content (17 to 53 % by wt.) has been investigated for 0.1 g/L soil-water suspensions. The time to reach sorption equilibrium, i.e. sorption-diffusion equilibrium, for a highly aggregated montmorillonitic soil containing 0.9% organic carbon for congeners 8, 52, 153 was determined to be 3, 5, and 10 months, respectively, using a gas-purge technique. For these sorbate-sorbent contact times soil-water sorption equilibrium partition coefficients on a soil-organic carbon basis (K oc) were measured and for these congeners ranged varied from 2.4 × 10 4 to 6.8 × 10 6 mL/g. Based on these data a correlation relation was derived, log K oc = 1.07 log K ow − 0.98, for estimating K oc from known values of octanol-water partition coefficient (K ow). From literature K ow values this regression equation was used to estimate K oc for 46 of the major PCB congeners in Aroclor 1242, 1254 and 1260.

Temperature effect on the partitioning of Polycyclic Aromatic Hydrocarbons between natural organic carbon and water

The influence of temperature on K DOC was quantified for fluoranthene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[ghilperylene and indeno[1,2,3-cd]pyrene using the gas-purge technique and natural dissolved organic carbon from lake Ketelmeer, the Netherlands. Sorption of PAHs to DOC decreased with increasing temperature over a temperature range of 16 to 45°C. ΔH° values ranged from −18.3 kJ.mol −1 for fluoranthene to −40.6 kJ.mol −1 for benzo[ghi]perylene. A temperature decrease of 10°C lead to an average increase of K DOC with 60%. The partition coefficients (K POC and K DOC) for sorption to particulate and dissolved organic carbon from the same lake were also determined. Log K POC-values ranged from 5.4 ± 0.3 for fluoranthene to 6.8 ± 0.3 for indeno[1,2,3-cd]pyrene and are in agreement with previously published values. Log K DOC- values ranged from 5.18 ± 0.07 for fluoranthene to 6.86 ± 0.03 for indeno[1,2,3-cd]pyrene, which is higher than previously reported for natural DOC. The data support the linear relationship between log K POCpoc and log K DOC with a slope of nearly one. The effect of the temperature and PAH sorption to DOC influenced fate calculations for these components. For compounds with low volatilization rates and high sorption partition coefficients such as the PAHs used in this study, sorption to DOC has a large influence on mobility in porous systems. The influence of temperature is relatively small.

Temperature dependence of henry's law constants for selected chlorobenzenes, polychlorinated biphenyls and polycyclic aromatic hydrocarbons

AbstractModeling the fate of organic micropollutants in aquatic systems requires information about gas/water partitioning at environmental temperatures. In this paper experimental data are presented on Henry's law constant (H) for seven chlorobenzenes, three polychlorinated biphenyl (PCB) congeners, and six polycyclic aromatic hydrocarbons (PAHs). The studied compounds were 1,2,3–; 1,2,4– and 1,3,5–tri–; 1,2,3,4– and 1,2,3,5–tetra–; penta–; and hexachlorobenzene; 2–5–di–; 2,4,4′–tri‐; and 2,2′5,5′–tetrachlorobiphenyl; and the PAH compounds fluoranthene, benzo[b]flu‐oranthene, benzo[kfluoranthene, benzo[a]pyrene, benzo[ghi]perylene, and indeno[1,2,3–cd]pyrene. H was measured in a buffer solution using a modified gas‐purge technique. Values for this set of PAH compounds have not been determined experimentally before. The temperature dependence of H was measured for the tetra‐, penta‐, and hexachlorobenzenes and for all PCBs and PAHs over a temperature range of 10 to 55°C. The experimental data and temperature dependence are in good agreement with partitioning theory and available literature data. The observed temperature dependence results in a doubling of H for every 10°C temperature increase.

Predicting Henry's law constants for polychlorinated biphenyls

Molecular connectivity indices were tested with regard to their ability to describe the Henry's law constants of PCBs. A model is derived which accounts for 95% of the variation in the Henry's law constants determined in a recent study by the gas purge technique.

Aqueous solubility and Henry's law constant data for PCB congeners for evaluation of quantitative structure-property relationships (QSPRs)

Aqueous solubilities and Henry's Law Constants (HLCs) were measured for selected PCB congeners for evaluation of quantitative structure-property relationships (QSPRs) relating chlorine substitution pattern to the chemical parameter. Experimental results were consistent with previously published values. Aqueous solubilities (as solids at 25°C, column generation technique) determined for 26 congeners ranged from 1.08×10 −5 to 9.69×10 −10 mol/L and generally decreased with molecular weight. Values converted to subcooled liquids are also reported. HLCs (25°C, gas purge technique) determined for 20 congeners ranged from 0.3×10 −4 to 8.97×10 −4 atm·m 3/mol. Measured HLCs were not correlated with molecular weight, but increased with degree of orthochlorine substitution within a molecular weight class. Vapor pressures calculated from the product of solubility (mol/m 3) and HLC (atm·m 3/mol) data, generally decreased with molecular weight and increased with increasing degree of ortho- chlorine substitution. Currently available QSPRs were found to be ineffective for predicting solubilities, HLCs and vapor pressures when compared to experimentally determined results. An empirical data fitting approach based on coefficients related to chlorine substitution patterns appears promising.

Thermal desorption—gas chromatography of plasma isovaleraldehyde in hepatic encephalopathy in man

The validation of a new assay for the leucine degradion product isovaleraldehyde in biological fluids is described. A gas purge technique was used with trapping of volatile constituents in a Tenax cartridge followed by automated thermal desorption and gas chromatographic analysis. The concentration of isovaleraldehyde during the course of hepatic encephalopathy (80 observations in 48 patients; 25 cirrhotic, 23 fulminant hepatic failure) was significantly increased compared to control subjects (0.58 ± 0.08 compared to 0.17 ± 0.02 mol/l; p < 0.001). However, concentrations in grades 3–4 coma (37 observations) and grades 1–2 coma (30 observations) were similar and were not significantly different from values when encephalopathy was absent (grade 0; 13 observations). These results do not support an important role for isovaleraldehyde in the pathogenesis of hepatic encephalopathy.