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 83

rather than on direct causation. In addition, TELs for total DDT are many orders of
magnitude below thresholds for DDT in spiked sediment bioassays. These scientifi c
issues triggered a more detailed analysis of the freshwater and marine TELs for
total DDT.
The TEL sediment targets for total DDT were those summarized by Buchman
( 1999 ) from the original publications by MacDonald et al. ( 1996 ) and by Smith et al.
( 1996 ). As shown in Table 5 , the targets are 6.98 ppb for the fresh water drainage into
Newport Bay and 3.89 ppb for the estuarine and salt water of the Bay.
Several key authors in the TMDL regulation for Newport Bay and Watershed
have expressed reservations about TELs for total DDT. Buchman ( 1999 ), author of
the National Oceanic and Atmospheric Administration (NOAA) table listing the
sediment targets, wrote:
These tables are intended for preliminary screening purposes only: they do not represent
offi cial NOAA policy and do not constitute criteria or clean-up levels.

MacDonald et al. (MacDonald et al. 1996 ; Smith et al. 1996 ) authors of the pri-
mary references cited by Buchman wrote:
Low reliability (TS = 0) was indicated for only one substance (total DDT).

Peter Kozelka and David Smith at US EPA Region IX, authors of the 2002
TMDL report for Newport Bay and Watershed, wrote:
We recognize these NOAA values have been derived by associating nationwide sediment
chemistry data sets with benthic toxicity results and there is no direct cause and effect
relationship.

The Regional Board's organochlorine TMDL technical report (SARWQCB 2006 ),
addressed sediment quality guidelines (SQGs), which include TELs as one kind of SQG:
SQGs should be used with caution since individual SQGs are often unreliable indicators of
toxicity and do not necessarily identify the correct cause of toxicity (Vidal and Bay 2005).
In particular, use of empirically-derived marine SQGs for DDT and PCBs has been found
to be relatively inaccurate in predicting toxicity (Long et al. 1995 ).

A detailed analysis of the TEL method and the data sets used to derive the TELs
for total DDT has revealed much more of concern that should be considered and
resolved before TELs are used as TMDL targets.
To gain a full understanding of the individual data points from which the marine and
fresh water sediment TELs for total DDT were derived, each data point in the TELs
reported by Buchman ( 1999 ) as cited by US EPA Region IX ( 2002 ) was reviewed. The
data points and reference citations were purchased from the author of the TELs. 5
The data sets are slightly different from the ones used to derive the published TELs. 6
The derivation of the TELs is explained by MacDonald et al. ( 1996 ) as follows:

“For each analyte, a TEL was derived by calculating the geometric mean of the 15th percentile
of the effects data set and the 50th percentile of the no effects data set.”

5 MacDonald DD, BEDS data bases for total DDT purchased in 2005.
6 Personal communication from DD MacDonald to J. Byard (2005).