Gschwend%20thesis.pdf

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time of collection. Five samples in the year-round group were taken within
i hour of low tide, and these showed an o-xylene concentration of 8 + 3 ng/kg.
Six other samples, acquired within i hour of high tide, had 16 + 5 ng
o-xylene/kg. All of the remaining samples (21) contained 9 + 5 ng o-xylene/
kg. Thus, there is some indication of a source related to high tide (i.e.
located to the west of Chemotaxis Dock). However, all of the high-tide
samples were obtained in the months of May, June and July. Consequently,
the relatively high o-xylene average found in this group might also be
caused by a seasonal factor.
Another possibility is that rain delivers C2- and C3-benzenes to
coas tal seawater. This may occur by two mechanisms. Firs t, if the a tmos-
phere contains high levels in excess of equilibrium with seawater of these
aromatic compounds, rain may acquire this hydrocarbon burden and deposit it
on the sea. Grob and Grob (1974) favored this explanation for the increase
of the alkylated, benzene concentrations in Lake Zurich after rain. The
other mechanism entails increased runoff from streets and sewers due to
rain.
6
Urban runoff has been cited for delivery of 0.3 x 10 . metric tons
petroleum hydrocarbons per year to the sea (NAS, 1975b) .,
To test for the effects of rain, samples from the Chemotaxis Dock
year-round study were grouped into those (7 samples) taken within I day
of greater than O.L" rain and those (16 samples) acquired at least 4 days
after the last rain. The
samples taken shortly after rain
contained 12 :! 6 ng o-xylene/kg, while those obtained more than 4 days
since the last rain showed 9 :! 4 ng o-xylene/kg. Thus, there is no signifi-
cant difference.
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