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 88

The log K oc of 5.92 is a geometric mean of values ranging from 5.26 to 6.58.
The slow-stir log K ow for DDT reported by de Bruijn et al. ( 1989 ) is 6.914. The K ow
derived by the superior slow-stir method gives a sediment acute marine threshold
for DDT that is one order of magnitude higher.
The SLCA method that is used to derive the 7 ppb data point is the same as used
by Neff et al. ( 1986 ) to derive the above mentioned value of 1.9 ppb. The method is
described, but the actual data used to determine the 7 ppb value were not presented
(Persaud et al. 1991 ).
The value of 9 ppb for DDT is for the parent compound and not total DDT. Actual
data and calculations are not presented in the reference (Environment Canada 1992 ).
The SLCA is not corrected for organic carbon. This data point, the 1.9 ppb data
point (Neff et al. 1986 ) and the 7 ppb data point (Persaud et al. 1991 ) are all derived
by the SLCA method, and are essentially the same, except for regional differences
in sediment residue levels and biota. All three of these data points rely on mutual
occurrence. None of them identify causality or represent a measure of dose-response
to DDT.
The value of 50 ppb is reported to be the 90% effect level for the parent DDT
according to the SLCA method (Environment Canada 1992 ). That is, 50 ppb of total
DDT in sediments is associated with an effect on biota in 90% of those sediments.
Any one or more of many hundreds of chemicals potentially present in those same
toxic sediments could have accounted for the measured toxicity.
The 120 ppb effect data point is supposed to be the 95% effect level for the parent
DDT according to the SLCA method (Persaud et al. 1991 ). This severe effect level
is defi ned as that level “…that could potentially eliminate most of the benthic organ-
isms.” Any one or more of many hundreds of chemicals potentially present in those
same toxic sediments could have accounted for the measured toxicity. The observa-
tion of apparently healthy benthic communities at sediment residue levels in excess
of 120 ppb certainly puts in question the concept of this severe effect level for DDT
as determined by the SLCA method.
According to the Illinois Environmental Protection Agency (IEPA 1988 ), the
DDT effect level of 222 ppb is the average of three stations that had organisms of
the lowest taxa. These three stations were also polluted by several additional con-
taminants, not just DDT. For example, Station GBL-08 sediments contained
270,000 ppb lead and 3,900 ppb mercury.
The value of 4,200 ppb is the calculated LC 50 from the dose-response data from
spiked sediment determination of the DDT LC 50 for Hyalella azteca (Schuytema
et al. 1989 ).
Discussion and conclusions . The TELs for total DDT are calculated from a variety
of data types. Some sediment residue levels are considered to be background levels
found in relatively unpolluted and nontoxic sediments; some are levels associated
with toxic sediments; some are calculated from water column criteria and partition
coeffi cients; some represent true dose-response from bioassays of spiked sediments.
All of these data types should be considered in the determination of a sediment
threshold for DDT toxicity. However, the TEL does not appropriately weigh the