Mass Transfer Of Organic Compounds Research Articles

Water flow drives small scale biogeography of pesticides and bacterial pesticide degraders - A microcosm study using 2,4-D as a model compound

Complex interactions between biodegradation and mass transfer of organic compounds drive the fate of pesticides in soil ecosystems. We hypothesized that, at the small-scale, co-location of degraders and pollutants in soils may be a prerequisite for efficient biodegradation of these chemicals. In non-co-localized micro-environments, however, diffusive and advective solute transport as well as active transport of microbial degraders towards their corresponding substrate may improve the accessibility of microbial substrates. The objective of this study was to test whether water flow can accelerate microbial pesticide degradation by facilitating the encounter of spatially separated pesticides and bacterial degraders at the millimeter scale.Combining natural and sterilized soil aggregates, we built soil cores with different spatial localizations of the pesticide 2,4-dichlorophenoxyacetic acid (2,4-D) and microbial degraders: (i) homogeneous distribution of microorganisms and 2,4-D throughout the soil core, (ii) co-localized microorganisms and 2,4-D in a mm3 soil location, and iii) separated microorganisms and 2,4-D in two mm3 soil locations spaced 1 cm apart.Following the fate of 14C labelled 2,4-D (mineralization, extractable and non-extractable residues) as well as the abundance of bacterial 2,4-D degraders harboring the tfdA gene over an incubation period of 24 days, we observed decreased biodegradation of 2,4-D with increasing spatial separation between substrate and bacterial degraders. We found evidence that advection is a key process controlling the accessibility of 2,4-D and pesticide degraders. Advective solute transport induced leaching of about 50% of the initially applied 2,4-D regardless of initial spatial distribution patterns. Simultaneously, advective transport of 2,4-D and bacterial degraders triggered their re-encounter and compensated for the leaching-induced separation of initially co-localized microorganisms and 2,4-D. This resulted in effective biodegradation of 2,4-D, comparable to the homogeneous treatment. Similarly, advective transport processes brought substrate and degraders into contact if both were initially separated. Thus, advection more effectively removed bioaccessibility limitations to pesticide degradation than diffusive transport alone.These results emphasize the importance of considering spatial microbial ecology as well as biogeophysics at the mm scale to better understand the fate of pesticides at larger scales in soil.

Study of complex matrix effect on solid phase microextraction for biological sample analysis

Solid phase microextraction (SPME) has become a useful tool for in vivo monitoring the behavior of environmental organic pollutants in biological species due to its simplicity, relatively non-invasive, and cost-effective manner. However, the complex matrices in biological samples could significantly influence the extraction kinetic, and bias the quantification result. In this study, we investigated the effect of complex matrix on the extraction kinetic of SPME for biological sample analysis. Two sample matrices, phosphate-buffered saline (PBS) with bovine serum albumin (BSA) and agarose gel with BSA were used to simulate the biological fluid and tissue. Results showed that the addition of BSA significantly enhanced the mass transfer of organic compounds onto SPME fiber in both PBS buffer and gel sample. Enhancement factors ranging from 1.3 to 27, and 2.0 to 80 were found for all selected polyaromatic hydrocarbons (PAHs) in PBS buffer and agarose gel with BSA concentration of 0.1–5%, respectively. Then, an improved theoretical model was applied to quantify the observed enhancement effect, and the result showed that the predicted sampling time constant agreed well with the experimental one in complex matrix. Furthermore, a simplified equation was proposed for the real biological sample analysis.

Influence of dissolved humic substances on the mass transfer of organic compounds across the air–water interface

The effect of dissolved humic substances (DHS) on the rate of water–gas exchange of two volatile organic compounds was studied under various conditions of agitation intensity, solution pH and ionic strength. Mass-transfer coefficients were determined from the rate of depletion of model compounds from an apparatus containing a stirred aqueous solution with continuous purging of the headspace above the solution (dynamic system). Under these conditions, the overall transfer rate is controlled by the mass-transfer resistance on the water side of the water–gas interface. The experimental results show that the presence of DHS hinders the transport of the organic molecules from the water into the gas phase under all investigated conditions. Mass-transfer coefficients were significantly reduced even by low, environmentally relevant concentrations of DHS. The retardation effect increased with increasing DHS concentration. The magnitude of the retardation effect on water–gas exchange was compared for Suwannee River fulvic and humic acids, a commercially available leonardite humic acid and two synthetic surfactants. The observed results are in accordance with the concept of hydrodynamic effects. Surface pressure forces due to surface film formation change the hydrodynamic characteristics of water motion at the water–air interface and thus impede surface renewal.

Desorption of Dieldrin from field aged sediments: Simulating flood events

Background, Aim and Scope With the predicted climate change, it is expected that the chances of flooding may increase. During flood events, sediments will resuspend and when the sediments are polluted, contaminants can be transferred to the surrounding water. Mass transfer of organic compounds like Persistent Organic Pollutants (POPs) from soils and sediments to the surrounding aqueous phase are essential regarding fate and transport of these chemicals in the aqueous environment. The distribution of POPs between sorbed and aqueous phases and the time needed to obtain equilibrium are required to calculate the exposure to potential receptors. A reactor was designed in which the water flow is controlled and low POP concentrations could be measured by tenax extraction outside the reactor vessel. This reactor design named SPEED (Solid Phase Extraction with External Desorption) was used to study desorption from aged contaminated sediment in relation to sediment particle size.

Mass Transfer of Organic Compounds in Dilute Aqueous Solutions into High Density Polyethylene Geomembranes

The mass transfer of ten organic compounds into high density polyethylene (HDPE) geomembranes is investigated using batch immersion tests with dilute aqueous organic compound solutions. For the concentration ranges tested, the linear model is suitable to explain the sorption of organic compounds. The HDPE-water (HDPE-W) partition coefficients of the organic compounds (K\DHDPE-W\N) have a good logarithmic linear relationship with their octanol-water partition coefficients and water solubility. The diffusion coefficients (\iD) of all organic compounds tested are on the order of 10\U-9\N cm²/s and decrease with the increase in their molecular diameters. The effects of the presence of other organic compounds, pH, ionic strength, temperature, and five-year aging of HDPE geomembranes on sorption are evaluated. All factors except the temperature are insignificant. As temperature increase, K\DHDPE-W\N values are not affected significantly, but \iD values increase. A mathematical model, together with the experimentally determined mass transfer parameters, is used to predict the mass flux of organic compounds through HDPE geomembranes.

Liquid membrane transport — a highly selective separation process for organic solutes

Mass transfer of organic compounds through aqueous and non-aqueous liquid surfactant membranes was studied in a single-drop extraction colum and in a multi-emulsion. In the case of single-drop membrane permeation of n-hexane/benzene mixtures, the mass transfer rate, membrane thickness, membrane stability, and membrane selectivity, depended on the viscosity, the concentration of the surfactant laurylpyridiniumchloride (LPC), and the ionic strength of the aqueous membrane. Benzene transport selectivities of up to 7.5 were observed. p]Up to 95% removal of phenol from a diluted aqueous phase could be achieved within 20 minutes by means of a silicone membrane in a multi-emulsion. The stripping agent was 0.1 N NaOH. p]The performances of aqueous and non-aqueous liquid membranes are compared from estimates of the corresponding mass-transfer coefficients.