Gschwend%20thesis.pdf

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These data suggest the source of these alkylated benzenes may be related
to the activities of tourists and summer residents on Cape Cod. A plot
of the o-xylene data according to the day of the week in which the
samples were taken clearly shows higher levels earlier in the week
(figure 3-11). Separating the summer data from those of the "off season"
further emphasizes this trend in the summer. Thus one may reasonably
hypothesize that gasoline use by automobiles or motorboats has introduced
these pollutant hydrocarbons into coastal seawater, especially during
periods of intense tourism. Levels climb to about 3 times those seen
during the rest of the year. Based on the plot of o-xylene concentration
versus day of the week, it appears that this anthropogenic input is
removed from the coastal seawater with a halflife of about l-2 days.
This is consistent with the observed decline of the o-xylene levels after
the Memorial Day weekend, 1978. A combination of air-sea exchange and
tidal flushing may be sufficient to lower the o-xylene levels this quickly.
It is also apparent from this information that the time scale of interest
for these volatiles is on the order of days and not weeks.
Ethyl benzene concentrations do not always appear to covary with
the other alkylated benzene isomers because ethyl benzene was unresolved from
another compound in the chromatograms. CI-CH4 mass spectral examination
of this mixed peak in a sample acquired in February, 1978 revealed the
simultaneous presence of a compound of molecular weight I08 (figure 3-12).
This molecular weight assignment is assured due to presence of M + l, M
+ 29, and M + 41 peaks in the CI-CH4 spectrum. The m/ e 95 fragment
suggests that the compound contains a terminal ethenyl group (Field, 1968),
while the m/ e 93 fragment indicates the presence of a terminal. methyl
substituent. It is known that the brown alga~ Fucus spp.~ utilizes
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trans, cis-l,3,5-octatriene (mw 108) as its sexual chemotactic agent