Contamination carrier effects

Contaminants with very low water solubilities (e.g. polycyclic aromatic hydrocarbons) play an important role in risk assessment of dangerous wastes and development of soil remediation. The mobility of such hydrophobic substances can be strongly affected by the existence of carriers (e.g. dissolved organic carbon), which can adsorb the contaminant and thereby enhance or reduce its velocity. The numerical simulation of the spreading of these contaminants, requires the solution of reactive transport equations for all involved components, coupled by the contaminant s sorption to the carrier. Our development is based on a model [2], in which all the carrier s influence on the contaminant transport is contained in an effective adsorption isotherm, depending on the carrier concentration and thereby also on space and time. First we shortly summarize the modelling of reactive transport of a single component (carrier, contaminant, carrier bound contaminant) in a porous medium, then in section 3 we combine the two equations for the contaminant components. The properties of the contaminant s effective isotherm and its influence on the transport equation are discussed in section 4. 

It has been demonstrated that radial dispersion contributes more significantly to the dilution of the sample in the flow than does axial dispersion. This type of fluid movement, termed secondary flow by Tijssen [43], results in a washout effect accounting for the low mutual contamination of samples successively injected into a carrier stream. TTiis advantageous feature is a result of the use of low flow rates and small tubing bores, and results in decreased peak-width and hence to increased sampling rate. 

In several wood-preserving facilities, other wood preservatives such as creosote and chromate-copper—arsenate (CCA) have been used in addition to PCP (e.g., Lamar Glaser, 1994 Mueller et al., 1991a Mahaffey et al., 1991). Environmental contamination by chemical mixtures is likely in these sites. When PCP has been dissolved in an organic carrier such as oil, soil is also contaminated with the solvent (Trudell et al., 1994 Lamar Dietrich, 1990). Chlorinated dimeric impurities in technical CP formulations are also found in contaminated soil. Design of successful bioremediation must address the effects of other chemicals on CP biodegradation. 

Other than its effect on the detector noise, liquid phase bleed may interfere with analytical results and determine the life of the column. Also some supports may have a catalytic effect to decompose the liquid phase, thus reducing its life in the column. Contaminants in the carrier gas (e.g., O2) also may interfere with the stability of a liquid phase. 

There has been considerably less work on steady-state carryover in hens. However, in one detailed study it was shown that the absorption of PCDD/Fs from a contaminated soil was quite high, ranging from 70-80% for the tetrachlorinated congeners to 10% for the octachlorinated ones.68 The authors compared their results to feeding studies with rodents and came to the conclusion that absorption from soil was as effective as absorption from easily digestible carriers such as corn oil. 

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