DDT, Chlordane, Toxaphene and PCB Residues in Newport Bay and Watershed: Assessment of Hazard to Wildlife and Human Health - Reviews of Environmental Contamination and Toxicology - page 56

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Jan-80 Jan-85 Jan-90 Jan-95 Jan-00 Jan-05 Jan-10 Jan-15

Date

Lower Newport Bay Upper Newport Bay

Fig. 3 DDT concentrations in sediment from Newport Bay. Values above detection limits are
shown. Sources : Orange County PFRD (1980-1986) (Personal communication from Bruce Moore
of the Orange County Public Facilities and Resources Department (OCPFRD). Unpublished sedi-
ment data for 1980 -1986); SCCWRP ( 1998 ); Bay et al. ( 2004 ); unpublished reports provided by
The Irvine Company (2000-2004); US EPA Region IX ( 2002 ); Masters and Inman ( 2000 ); Orange
County Watersheds (2008-2011)

location at two different times may not represent the change in DDT concentration
for a specifi c quantity of sediment. Sediment movement results both from tidal fl ows
and storm fl ows, as well as from periodic major dredging projects in the Upper Bay,
which have occurred in years previously noted. Third, sediment concentrations in
Newport Bay may be more indicative of DDT loads from years or decades past, since
Bay sediments are transported from the upper watershed in a highly variable, episodic
manner, correlated with storm events and wetter-than-average rainfall years.
Thus, DDT concentrations in Bay sediments refl ect DDT that was applied many
years ago in the upper watershed, and then sorbed to sediments in that location, which
were subsequently eroded into a creek channel and transported to the Bay. Finally,
Bay sediment DDT concentrations found are not necessarily bioavailable. This is
especially true of samples collected from deeper sediment cores. While sample depths
were not available for all data plotted in Fig. 3 , the Orange County PFRD data from
1980 through 1986 refl ect sample depths between 2 and 25 ft, with an average of 11 ft,
well below the biologically active layer, which extends only to a depth of approxi-
mately 6 in. Thus, these early sediment samples are not indicative of concentrations
available to biota in the Bay. For all these reasons, the available sediment data for
Newport Bay are not reliable indicators of bioavailable DDT concentration trends in
the watershed and should not be used independent of other available data.