Hydrophobic contaminants

It is well established that important photochemical reactions are mediated by humic material in the aquatic environment (Zepp et al. 1981a,b), and that these are particularly signihcant for hydrophobic contaminants. Partial reductive dechlorination of the persistent insecticide mirex associated with... 

Flotation. In many cases, contaminants adsorbed on the surface of clay particles, or contaminants occurring in soil as discriminate particles, have different surface properties to clean soil particles. By adding special chemical substances, the formation of a hydrophobic surface on the contaminated particles is possible. Pulp aeration results in the attachment of hydrophobic contaminated particles to the surface of the small bubbles that are formed. In this way, selective flotation of these particles is achieved. Contrary to the gravimetric separation methods, flotation offers the possibility to separate contaminated and noncontaminated particles of the same grain size and density but with different surface properties. 

Chemical and physical properties of the contaminant should also be investigated. Solubility in water (or other washing fluids) is one of the most important physical characteristics. Hydrophobic contaminants can be difficult to separate from the soil particles and into the aqueous washing fluid. Reactivity with wash fluids may, in some cases, be another important characteristic to consider. Other contaminant characteristics such as volatility and density may be important for the design of remedy screening studies and related residuals treatment systems. Speciation is important in metal-contaminated sites. 

Yang Y, Hunter W, Tao S, Gan J (2008) Relationships between desorption intervals and availability of sediment-associated hydrophobic contaminants. Environ Sci Technol 42 8446-8451... 

Solid phase organic carbon (i.e., Koc) controls partitioning of hydrophobic contaminants such as PCB isomers [392-402]. Koc is a measure of this partitioning. Koc can be estimated from either solubility or fC0W as derived in this chapter and shown in Fig. 4. 

The use of SPMDs to sequester hydrophobic contaminants for incorporation into bioindicator test-based screening is increasing in both frequency of application and in the array of modes of action. Eor example, as a focused part of a broader... 

The authors have been intimately involved in eondueting research to address many aspects of environmental contaminants for about three decades. Historically, samples of environmental matrices, particularly water and air have been collected at narrow windows of time (i.e., minutes or several hours) which are not representative of the exposure experienced by organisms. Consequently, we initiated the development of what would ultimately be the semipermeable membrane device (SPMD). The SPMD has subsequently proven to be an effective passive sampler for a wide range of hydrophobic contaminants in multiple media. To date, there are more than 180 peer reviewed publications in the open scientific literature, where SPMDs are used for a variety of applications. Some of these publications are critical of the use of passive samplers for certain applications. However, constructive criticism has greatly aided in defining information gaps and limitations of the passive sampling approach. 

Reactor in a combination of a membrane bioreactor and a bubble-column and was designed for simultaneous degradation of both hydrophilic and hydrophobic contaminants from the gas phase. 

Compared to other HPLC techniques, RPC has a higher resolution power and allows protein analysis at low ionic strengths. On the other hand, it can be responsible for protein denaturation, loss of biological activity and interferences of hydrophobic contaminants [107]. 

The parfait-distillation method uses a sequential series of adsorbents to remove contaminants from water and vacuum distillation to recover unadsorbed materials. This method recovers a wide range of neutral, cationic, anionic, and hydrophobic contaminants. The first adsorbent, porous polytetrafluoroethylene (PTFE), removed humic acid and a broad range of hydrophobic compounds. PTFE was followed by Dowex MSC-1 and then Duolite A-162 ion-exchange resins. A synthetic hard water spiked parts-per-billion concentrations with 20 model compounds was used to evaluate the method. Poorly volatile, neutral, water-soluble species (glucose) cationic aromatics and most hydro-phobic compounds were recovered quantitatively. Model ampho-terics were removed from the influent but were not recovered from the adsorption beds. The recovery of model acids and bases ranged from 22% to 70% of the amount applied. 

To increase the usefulness of bioremediation as an effective field remedial tool, significant investments have been made towards the development of means to remove sorbed PAHs, attack sources of NAPL, and subsequently increase the aqueous solubility/bioavailability, and thus the biodegradability, of targeted compounds. To date, one of the most effective ways to accomplish these tasks involves the use of surface active agents (i.e., surfactants). A variety of synthetic surfactants have been shown effective in increasing the bioavailability of PAHs and other hydrophobic contaminants (Kile Chiou, 1989, 1990 Edwards et al., 1991 Liu et al., 1991). Although the solubilization process is not completely understood, these studies showed that a variety of ionic and nonionic surfactants could significantly increase the water solubility of monitored chemicals. 

From a practical perspective, conventional remedial methods (e.g., pump-and-treat) for hydrophobic contaminants in groundwater have generally failed to produce a... 

The accumulation of hydrophobic contaminants in phytoplankton plays a significant role in the transport and fate of these potentially toxic compounds. However, the limited amount of available field data indicate that partitioning models fail to adequately predict the distribution of these compounds in the water column. Several hypotheses have been proposed to explain these differences. In this chapter we propose additional explanations for these differences. We hypothesize that assumptions in the partitioning model about the rate of uptake, mechanism of uptake, and effect of phytoplankton growth also contribute to these deviations. 

Although a simple bioconcentration model assumes rapid movement of a hydrophobic contaminant through an organism, distribution may be relatively slow. The predominant limiting factor in this case is the blood flow. Slow transport to lipid tissue sinks can result in lower apparent BCF values than would be the case if true equilibrium were attained. 

Evidence for the validity of the hydrophobicity model of bioconcentration is provided by correlations of it with the octanol-water partition coefficient, Km, using n-octanol as a surrogate for fish lipid tissue. The measurement of Kow consists of determining the concentration of a hydrophobic contaminant in water-immiscible n-oclanol relative to water with which it is in equilibrium. Typical Kow values range from 10 to 107, corresponding to BCF values of 1 to 106. Such Kow/BCF correlations have proven to be reasonably accurate when narrowly defined for a specified class of compounds, most commonly poorly metabolized organohalides. Major inconsistencies appear when attempts are made to extrapolate from one class of contaminants to another. 

Enfield CG, Bengtsson G. 1988. Macromolecular transport of hydrophobic contaminants in aqueous environments. Groundwater 26 64-70. 

Hickie BE, Mackay D, De Koning J. 1999. Lifetime pharmacokinetic model for hydrophobic contaminants in marine mammals. Environ Toxicol Chem 18 2622-2633. 

Transport of a contaminant from water to air is influenced primarily by wind velocity.16 The contaminant s density, vapor pressure, and aqueous solubility also factor into its tendency to be introduced into the air phase, and its Henry s constant (KH) provides a good indication of this tendency. Biota have a strong attraction to hydrophobic contaminants, and, as a result, uptake of contaminants by partitioning into plants and animals, known as bioaccumulation, has been reported to be a dominant mechanism of removal.16,25 The tendency of a chemical to be taken up into biota is quantified by the bioconcentration factor (BCF), as measured by the ratio of its concentrations in biota and water. 

Since SOM is most often the main component responsible for sorption of organic chemicals, e.g., contaminants (Fig. 4.19), researchers use octanol (an eight-carbon alcohol) to simulate organic matter-hydrophobic contaminant sorption phenomena. 

Perhaps the most common application of Ko is for predicting the bioconcentration of low-polarity hydrophobic contaminants from water into aquatic biota. A bioconcentration factor (BCF) can be represented as... 

Figure 6.5-6 Combination of distillation with head space analysis for the continuous control of hydrophobic contaminations in waste water (Schrader, 1993).

Organic contaminants in surface and subsurface systems are typically distributed by sorption between the aqueous phase and natural solid phases. The extent to which such contaminants are sorbed significantly affects their transport and distribution, their impacts on the ecosystem, and the selection of strategies for their removal. In cases of hydrophobic contaminants, sorption is governed by a complex combination of interactions associated with solute repulsion from the aqueous phase and solute attraction to particular solid phases and interfaces. The variety of thermodynamically driven and kinetic or mass-transport-controlled solute-sorbent interactions that may occur in natural systems were summarized by Weber et al. (1). 

For example, if the reaction controlling the sorption of each molecule of a contaminant is identical and the capacity of a sorbent for these molecules is operationally limitless, a linear isotherm relationship is prescribed in which the sorbed-phase concentration is a constant proportion of the solution-phase concentration. When the sorption reactions are identical but sorption capacity is limited, an asymptotic approach to a maximum sorbed-phase concentration might be expected. These two limiting-condition models have been described and compared with others for description of the sorption of hydrophobic contaminants on a variety of natural soils, sediments, and suspended solids... 

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