Gschwend%20thesis.pdf

102 R. P. SCHWARZENBACH, R. H. BROMUND. P. M. GSCHWEND and O. C ZAFIRIOU
tadecene ()'oungblood et al.. 1971), C¡ i alkenes (dictyopterenes,
Moore, 1977) and pristane (Blumer et al..
1964) at CD is probably much less than that of n-C i 5
and /J-C 17' Assuming the same turnover time with
respect to air-sea gas exchange (Equation (2)), the
resultant steady-state concentrations can be expected
to be undetectably low. Additional sinks, such as
adsorption and mixing with offshore waters can only
lower the steady-state levels even further.
Aromatic hydrocarhons
Toluene and many of the isomeric C2 to C4 alkyl
benzenes are present; together they form the group
of compounds most abundant and consistently
present at CD. They are found in all samples, despite
our precautions to minimize or eliminate contamination
by these compounds. They are absent in the
blanks and in five liter samples of air from CD.
Therefore we believe that they are not artifacts, but
are actually present in the samples. Toluene (No. 45)
is often a major peak; the other alkylated benzene
concentrations covary. The isomer distributions are
conveniently displayed as (M + 1)+ mass chromatograms
of. the CI (methane) mass spectra data files.
Making the reasonable assumption that these isomers
show similar proton affnities, the normalized
(M + i) + mass chromatograms give the isomer distributions
directly. Figure 5 shows the CI-MS spectra
of representative Ci-, Ci-, and C4-alkyl benzenes.
Figure 6 shows (M + 1)+ mass chromatograms
revealing the relative isomer distribution. Relative
ratios can be seen less definitely in the reconstructed
chromatograms themselves. Similar patterns were
found for aII CD samples, suggesting that similar pro-
cesses determine the concentrations of aII these
related compounds. Ethylbenzene (No. 101) and propylbenzene
(No. 142) show changes in relative concentration,
perhaps due to an enhanced ease of biodegradability.
Many of these compounds have been
reported before in municipal and natural fresh waters
(Grob, 1973; K. Grob and G. Grob, 1974; Grob et
al., 1975; Bertsh et aI., 1975; Saunders et al., 1975;
Giger et al., 1976) and in air (Bertsch et aI., 1975).
K. Grob and G. Grob (1974) have suggested that
atmospheric transport of gasoline-derived compounds
was the source. The estimated (wlv air per wlv water)
partition coeffcients foralkylbenzenes are - 0.1- i, so
atmòspheric transport and subsequent dissolution is
reasonable if wlv air concentrations are greater than
or equal to 0.1-1.0 times the observed wlv water concentrations
(see Table 2). However, since we detected
no VC in a preliminary measurement of air, the
atmosphere would appear to be an insignificant or,
at best, irregular source. The ubiquitous toluene has
obvious potential anthropogenic sources, but may
also be of natural geochemical origin. Moderately
high toluene levels have been found in Recent sediments
(J. Whelan, personal communication).
Naphthalene (No. 258) and the methylnaphthalenes
(No. 308, No. 316) both showed concentration max-
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CHO .Cl-CH4 ,I3CJlV .5ES2
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Fig. 5. Selected chemical ionization (methane) mass spectra
of alkylated benzenes (A) 1,2-dimethylbenzene, (B)
1,3,5-trimethylbenzene, and (C) C4-benzene.
ima during the period of oil contamination (Fig. 2A)
and also again late in April, suggesting multiple in-
puts. The Ci- and Ci-alkylated maphthalenes were
only found in the samples presumed to contain petroleum-derived
hydrocarbons. Figure 7 shows CI (methane)-MS
(M + 1)+ mass chromatograms for these
compounds. The isomer distribution is similar to that
found in a No.2 fuel oil sample analyzed (see Figure 7).
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