Transportation fraction

Another approach is to consider petroleum constituents in terms of transportable materials, the character of which is determined by several chemical and physical properties (i.e., solubility, vapor pressure, and propensity to bind with soil and organic particles). These properties are the basis of measures of teachability and volatility of individual hydrocarbons. Thus, petroleum transport fractions can be considered by equivalent carbon number to be grouped into 13 different fractions. The analytical fractions are then set to match these transport... 

Another method (EPA 3611) that focuses on the to separation of groups or fractions with similar mobility in soils is based on the use of alumina and silica gel (EPA 3630) that are used to fractionate the hydrocarbon into ahphatic and aromatic fractions. A gas chromatograph equipped with a boiling-point column (nonpolar capillary column) is used to analyze whole soil samples as weU as the aliphatic and aromatic fractions to resolve and quantify the fate-and-transport fractions. The method is versatile and performance based and therefore can be modified to accommodate data quality objectives. 

This profile builds on the efforts by the TPHCWG and MADEP to group chemicals into fractions with similar environmental transport characteristics (i.e., transport fractions). An important difference is ATSDR s concern with all possible exposure periods, from acute through chronic, whereas other agencies or groups have focused on longer-term exposures. The common characteristic of all of these approaches is the attempt to gather the available information about the toxicity and the risks associated with transport fractions. 

Although chemicals grouped by transport fraction generally have similar toxicological properties, this is not always the case. For example, benzene is a carcinogen, but toluene, ethylbenzene, and xylenes are not. However, it is more appropriate to group benzene with compounds that have similar... 

The approach to evaluating the potential health effects for these transport fractions taken by ATSDR and the TPHCWG, however, uses a reduced number of fractions, namely three aliphatic fractions and three aromatic fractions. Health effects screening values based on representative chemicals or mixtures for each of the fractions were developed using ATSDR minimal risk levels (MRLs). 

The mixtures of concern for TPH are not the heterogeneous petroleum products, but rather the transport fractions to which populations are more likely to be exposed. Thus, use of health effects data for these fractions would be preferable. When health effects data for petroleum products (mixtures) similar in composition to these fractions are not available, data for individual constituents could be used as surrogates, taking into account the potential for toxicologic interactions. Given the complexity of the interactions data for the individual constituents (Section 6.9), however, the assumption that the toxicity of the constituents is additive may be the most reasonable approach. This implicit assumption underlies the adoption of an MRL as a surrogate value to represent the toxicity of an entire fraction. 

The ATSDR approach, as reflected in this profile, focuses on an assessment of the health effects of petroleum hydrocarbon transport fractions, as suggested by the TPHCWG (1997a, 1997b, 1997c). 

A number of health effects studies in animals of petroleum streams that correspond with the transport fractions have been reviewed by the TPHCWG (1997c) however, most of these are unpublished industry studies. 

Overview. Because TPH is a broadly defined entity consisting of complex mixtures of hydrocarbons of varying chemical composition (due to differences in original petroleum products and differential, time-dependent, fate and transport of components within any particular TPH mixture), this section discusses available information for absorption, distribution, metabolism and excretion of components and petroleum products corresponding to the transport fractions of TPH. Limited... 

The focus of this section is the selection, when possible, of appropriate MRLs for the assessment of health effects of the aromatic and aliphatic fractions of TPH. Approaches to cancer assessment are also discussed. The TPH fractions are environmental transport fractions, as suggested by the TPHCWG (1997c), with a slight modification to include all the BTEXs in a redefined aromatic EC5-EC9 fraction. 

The issue of exposure to complex mixtures was introduced and briefly discussed in Section 6.1.1. In Sections 6.1.2 and 6.1.3 other related TPH approaches are discussed. The ATSDR fraction approach preferentially adopts MRLs for petroleum products that are similar in composition to the transport fraction. When no such data are available, a surrogate MRL from a representative constituent of the fraction is adopted for the entire mass of the fraction, a practice which implicitly assumes that the... 

Figure 1 Operations included within the system boundary for the shale gas life cycle. GHG emissions and freshwater consumption associated with operations up to and including gas treatment and processing are allocated to pipeline quality gas (which goes on to the transmission pipeUne) and the natural gas liquid (NGL) coproduct in accordance with their heat content (HHV) transportation, fractionation and disposition of NGL are not included within the scope of this study. GHG emissions and freshwater consumption associated with power distribution are also excluded from the scope of this study.

The transport fraction and the transport rate of Br" ion are calculated from Equations 34.2 and 34.3, respectively. 

One point to keep in mind when extrapolating data from an animal model to man concerns differences in the distribution of cholesterol over the various plasma lipoprotein fractions. In healthy humans, most of the serum cholesterol is transported in the LDL fraction, whereas in normo-cholesterolemic rabbits and rats, the HDL fraction is the primary cholesterol transport fraction (Terpstra et al, 1981 Van Raaij et al, 1981). 

A further complication is evident in that there exist different transport channels with different properties. The auxin stream seems to contain a fast fraction of low density which is separate from a main and slower fraction (e.g., Vardar 1964, Newman 1965, Rayle etal. 1969, de la Fuente and Leopold 1972, Kaldewey and Kraus 1972, Patrick and Woodley 1973, Krul 1977, Sheldrake 1979, see also Goldsmith 1977, p452ff.). The fast and slow transport fractions may be associated with different compartments of the cells, possibly the cytoplasm and the vacuole, respectively. This possibility is based on the multiphasic efflux and elution profiles of plant sections supplied with labeled auxin (de la Fuente and Leopold 1970 b, 1972, Davies 1974 see also Goldsmith 1977, p 453 f.). 

Concentration by Electro transport. An aqueous BA or BSA solution at 2 mmoVdm was put in both anode and cathode sides of the cell, and then the direct current of 10 mA was continuously applied. The concentrations of BA or BSA in the feed and permeate sides were spectroscopically measured. The transport fraction was calculated from the maximum concentration in the anode side, and the initial concentration, using equation 4 ... 

Tiy (=relative linear velocity) Fraction of resistance due to extmial transport Fractional conversion of A in outlet, xa... 

It is sometimes convenient to measure EMF data for a wide range of concentrations vs. single reference electrode in glass. If, as a result, the activities of the (solvent) cations permeable to the glass in the working solution vary significantly, the contribution of the resultant junction potential is superimposed on the EMF of interest. For a reasonably ideal solution Ej may be calculated directly as the sum of (tiRT/F) In [A,(2 )/ Afi(2)(] for ions permeable to the glass with transport fractions ti therein. 

Transport data have now been secured for a variety of simple halides and nitrates. It is interesting to note that the relationship of Mulcahy and Heymann given earlier regarding the size effect on total conductivity has some support within a series of 1 1 salts with a common anion. In the case that mobility im = tiA/F) is inversely proportional to radius, it follows that the transport fraction of the cation, /jt+f ()u+ -t- m-) is equal to r (r+ -h r ). This appears to be true for the alkali metal chlorides (except for CsCl) and for TlCl (Duke and Bowman, 1959) and the nitrates of lithium, sodium, potassium, and, borderline, silver (Duke and Owens, 1958). This ft — r relationship is again in contrast to aqueous systems where the intermediatesized ions have the maximum mobility (except for H+ and OH ). 

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