| Figure
5.20b. |
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Total DDT accumulation or depuration in parts
per billion dry weight (ppb) in three species of
transplanted bivalves for nine sampling periods
from 1993ยจ1997 (mean of all stations). Accumulation
or depuration was calculated by subtracting initial
tissue (T-0) concentrations from concentrations
after deployment. Bars indicate range of values
within a sampling period. * In 1996, the reference
population of "clean" Corbicula fluminea
at Lake Isabella crashed and disappeared. Despite
exploring several other potential reference sites,
field staff was unable to find sufficiently large
populations suitable for transplantation into the
Estuary. Beginning with the 1996 data, C. fluminea
bioaccumulation could no longer be compared with
previous years due to the initial high concentrations
of some contaminants, particularly trace organics,
which biases bioaccumulation estimates toward the
low end. Note different y-axis scales. |
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