Environmental Engineering Reference
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showed a signifi cant DDT concentration decline rate in mussels both when all three
locations were considered together (−0.133 per year, equivalent to a half-life of
5.2 years), and for each individual location (San Diego Creek = −0.292 per year;
Upper Newport Bay = −0.095 per year; Lower Newport Bay = −0.156 per year).
Mussel data were also analyzed for the periods 1982-1990 and 1991-1999. The rate
of decline of DDT concentrations in mussel tissue was statistically signifi cant only
for the earlier period (−0.236 per year). The rate of decline was lower for the later
period, but period regressions for the later period have low statistical power due, in
part, to small sample size. When the entire mussel tissue data set is considered,
statistically signifi cant rates of decline in DDT concentration are evident for each of
the three locations, and these trends are consistent with trends observed in the fi sh
tissue data sets.
However, as noted below, measured concentrations of DDT in red shiner and
mussels indicate a half-life for DDT in biota of the watershed of 3.8 years and
5.2 years, respectively. These observed half-lives suggest that the fraction of DDT
removed from the watershed as a whole since 1972 may be signifi cantly higher than
70%, and declining concentrations of DDT in biota are likely from a combination of
factors in addition to loss from soils.
3.1.5
DDT in Birds
Birds are exposed to DDT through their diet. Fish-eating birds typically attain the
highest levels. DDT levels in fresh eggs correlate with the most sensitive toxic
endpoint, eggshell thinning to the point of shell breakage, hatching failure and
lowered productivity.
Limited data are available on DDT levels in bird tissue from Newport Bay and
Watershed. In a 1984 internal memo, Harry Ohlendorf of the National Wildlife Service
reported organochlorine levels in salvaged eggs from the endangered light-footed
clapper rail; the eggs were collected during the period 1979-1981.
3
DDE levels
ranged from 0.34 to 9.6 ppm. More recently, Sutula et al. (
2005
) reported total DDT
levels of 0.45-1.07 ppm in nonviable eggs collected from light-footed clapper rail
nests. The egg with the highest level had the thinnest shell. However, these more
recent levels were less than those reported by Goodbred et al. (
1996
) for light- footed
clapper rail eggs from the nearby Tijuana Slough, where eggshell thinning was not
observed.
In 2004 and 2005, Gary Santolo at CH2M Hill collected eggs from six species
of birds from Newport Bay and Watershed. DDE levels and shell thickness were
measured in the eggs. Although the study has not as yet been published in the open
literature, Santolo communicated the following general conclusions
4
: no correlation
was found between shell thickness and DDE levels in American coot, black skimmer,
Forster's tern, killdeer, or black-necked stilt eggs. However, there was a negative
3
Richard Zembal, personal communication.
4
Gary Santolo, personal communication.
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