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 138

out of, and within the Bay and its Watershed such that even samples taken in the same
location at two different times may not represent the change in chlordane concentration
for a specifi c quantity of sediment. Sediment movement resulted both from the natural
fl ow of water and sediment in the Bay and its Watershed, as well as from periodic
dredging in the Bay, which occurred in 1983, 1985, 1988, and 1999. Third, sediment
concentrations in Newport Bay may be more indicative of chlordane 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, chlordane concentrations in Bay sediments refl ect chlordane 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. For all these reasons, the available sediment data for Newport Bay are not
the most reliable indicators of bioavailable chlordane concentration trends in the
watershed. However, it is notable that since 2002 Bay and Creek sediment samples
have exhibited chlordane concentrations below 20 ppb.

4.1.3 Water Column

Data from 1998 to 2009 reveal a range of chlordane concentrations in water from
Newport Bay and Watershed (Bay and Greenstein 2003 ; Bay et al. 2004 , Orange
County Watersheds). 7 Ten of 91 samples were above detection limits with a range
from 2.5 to 186.5 pptr (ng/L). Detection limits ranged from 1 to 130 pptr. Detection
limits were not reported for 8/10 of the samples above the detection limit, including
the highest fi ve values (22.5-130 pptr). The accuracy of chlordane analysis in water
at the pptr level is questionable due to chromatographic interference caused by high
background levels of organic matter and the binding of chlordane to microscopic
(fi lterable) macromolecular organic matter.

4.1.4 Fish and Mussels

Red shiner tissue concentrations may be taken as an indicator of chlordane concen-
trations in the Watershed, as red shiners are local, short-lived species. For this spe-
cies, chlordane tissue concentrations dating from 1983 show a substantial decline
over time. First-order decay constants were derived using historical red shiner tissue
data for the entire time period (1983-2000) and for two subsets of the data set
(1983-1991 and 1992-2000). The equations of these decay curves are indicated in
Figs. 26 and 27 . Figure 27 also shows projected chlordane concentrations through
2010. Data are not available to confi rm these concentrations.
When all red shiner data are considered together, a statistically strong (R 2 value
of 0.774) downward trend in chlordane concentration is evident. Exponential decay
curves fi t to the two subsets of data revealed consistent downward trends during

7 Personal communication from Amanda Carr at Orange County Watersheds.