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 58

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1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004

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Fig. 4 DDT concentrations in red shiners from San Diego Creek and tributaries. Data from
California Toxic Substances Monitoring Program (TSMP 1983 -2002). Red shiner data are not
available after 2002

the data are plotted in Fig. 4 . Concentrations of DDT in red shiner are strongly
indicative of concentrations within the Watershed, as this species has a short life
span of approximately of 2 years (Baird and Girard 1853 ) and residents do not range
outside of the fresh water streams fl owing into Newport Bay.
Exponential regression was used to evaluate the strength of the declining trend in
DDT concentration in red shiner tissue over time. A regression through the entire
dataset indicated a highly signifi cant exponential decline in DDT concentrations in
red shiner tissue. The calculated rate of decline (without outliers) is −0.183 per year
(equivalent to a DDT half-life in the watershed, as calculated from the surrogate
endpoint of red shiner tissue, of 3.8 years), signifi cantly shorter than the 20-year
half-life typical for DDT decay in terrestrial soil. To confi rm these trends, a regres-
sion analysis was performed for two 10-year sub-periods within the data set, 1983-1992
and 1993-2002, to evaluate whether rates of DDT loss in this species have changed
over time. The rate of decline of DDT concentration in red shiners was lower for the
later period (−0.135 per year) than for the earlier period (−0.245 per year), but both
rates are highly signifi cant.
Trends in DDT concentrations were also evaluated for seven additional fi sh
species (California killifi sh, spotted sand bass, California halibut, diamond turbot,
black perch, striped mullet, and yellow fi n croaker) for which three or more DDT
concentration data points were available during a time range of fi ve or more years
up until 2004. Although the data sets for any one of the additional fi sh species, taken
alone, contained too few data points to infer long-term trends in Newport Bay, and
in spite of possible sources of DDT for these fi sh outside of the Bay, the combined