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 89

quality of the various data points. Outdated partition coeffi cients are included and
should be removed or replaced with more accurate constants based on the slow-stir
methodology (de Bruijn et al. 1989 ). Effects associated with relatively low concen-
trations of DDT are included, even though DDT concentrations that were orders
of magnitude higher in sediments were without effect for the same biological
endpoint. Bioassay data are given the same weight as all other data, even though
bioassay data are the only data type representing true dose-response. Probably the
most relevant data points of all, toxicity thresholds from bioassay data using spiked
sediments, are under-weighted in the determination of TELs. Other troubling obser-
vations are the omission of data (even within the same studies), repeated use of the
same data in different data points, the inconsistent correction for OC, and the use of
data for just the parent compound in the determination of the TEL for total DDT.
The only data points that address the issue of bioaccumulation beyond benthic
organisms are the equilibrium-derived data points, but these appear to all have used
older K oc values that underestimate sediment thresholds.
Differences in freshwater and marine ecosystems can account for differences in
toxic effect, but differences of several orders of magnitude are more likely explained by
the presence of toxic levels of pollutants other than DDT in the sediments, rather than
to inherent differences in the biological communities. How else can an effect level of
DDTs at low parts per billion in one water body, and a no-effect-level of several
thousand parts per billion in another water body be explained? The likely explanation
is that other pollutants are present at toxic levels in the former and not in the latter.
The problem with using TELs as TMDL sediment targets is that risks are not
accurately assessed, resulting in the assignment of resources disproportionate to
risk and thereby not minimizing overall risk to humans and wildlife.
As an alternative to TELs, a sediment target for DDT can be derived that is based
on the equilibrium between sediment and water as well as on bioaccumulation in
fi sh and sensitive avian species. If one assumes a proportion of 80% DDE, 10%
DDD and 10% DDT as an example of the residues typically found in sediments, the
weighted log K oc would be 6.77, using the slow stir K oc values selected by the EPA
in their 2002 DDT TMDL for Newport Bay and Watershed. Using this weighted K oc
value and the National criterion for the water column that is based on bioaccumulative
avian toxicity, the resulting sediment target is 59 ppb.

3.2.2 NAS Fish Guidance to Protect Wildlife

The national debate over the impact of DDT on wildlife culminated in the U.S.
cancellation of DDT in 1972. In the same year, the National Academy of Sciences
(NAS) made recommendations for DDT residue levels in fi sh for the protection of
wildlife (NAS 1972 ). One panel made a recommendation of 1,000 ppb in fresh water
fi sh and another panel made a recommendation of 50 ppb in marine fi sh. The two
panels cited many of the same scientifi c studies, in which eggshell thinning and
reproductive failure were measured in sensitive avian species. Why then are the
recommendations so different and which guidance is appropriate?