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 87

from the Palos Verdes site (Anderson et al. 1988 ). The total DDT concentration in
the Palos Verdes sediment sample was 5,966 ppb. Marine worms that live in sedi-
ment appeared to be in excellent condition, and displayed normal burrowing
behavior after 288 h of exposure to sediments containing 16,500 ppb DDT
(McLeese et al. 1982 ).
A similar detailed analysis was done for the no-effects and effects total DDT data
points used to derive the fresh water sediment TEL. The DDT analytical data for the
fi rst fi ve data points at 0.384 ppb (Table 6 ) is not consistent with the major degradate
being DDE. The major degradate of DDT in this study (Marking et al. 1981 ) was
DDD. For example, the Red Wing Commercial Harbor sediments contained
5.28 ppb DDD, 0.56 ppb DDT and only 0.28 ppb DDE. The high proportion of
DDD is contrary to the general fi nding that old residues of DDT are predominantly
DDE. DDD is less stable in the environment than DDE.
The four no-effect data points at 5 ppb were all from nontoxic sediments, and the
DDTs were not detected. The value of 5 ppb was chosen as one-half the detection
limit of 10 ppb. Because the TEL is derived, in part, from the median of the no effects
data set, these four data points with no detectable DDTs have much greater weight
than do the last four data points containing thousands of parts per million DDTs, also
with no effects.
The 200 ppb data point is one-half the detection limit of the unspiked control
sediment used to determine the LC 50 of DDT in the amphipod Hyalella azteca .
The 1,300 and 1,800 ppb values are spiked sediments used to determine the LC 50 of
DDT in Hyalella azteca (Schuytema et al. 1989 ). These levels did not measurably
affect the survival of this amphipod crustacean.
In the effects data set for total DDT in freshwater sediments, the study containing
the 1.5 ppb value (Bolton et al. 1985 ) lists threshold contamination concentrations
in Table 2.1 for sediments based on 4% organic carbon (OC) and an equilibrium
existing between organic carbon and water. The threshold in water is the National
chronic criterion. The OC is corrected to 1%. Only DDT is included. Total DDT
from this study is not determined and is not used in the TEL data set. Notably, the
threshold concentration for DDE (the predominant form of DDT in the environ-
ment) in this study is 28,000 ppb. The problem with these data is the apparent use
of old K oc values that give inaccurate estimates of the partition of DDTs between
sediment organic carbon and water. The likely equilibrium partitioning threshold
for DDT is higher than 1.5 ppb and lower for DDE and DDD at 7,000 ppb and
3,250 ppb at 1% OC, respectively.
The fresh water screening level concentration approach (SLCA) data point is
1.9 ppb. The salt water SLCA is 428 ppb and is based on sediments from the Southern
California Bight. Neff et al. ( 1986 ) suggest that the difference is due to low DDT
levels in the fresh water sediment data base and much higher DDT levels in the salt
water sediment data base. Therefore, the difference appears to be an artifact of the
method by which SLCA values are derived. The salt water SLCA was not used to
derive the marine sediment TEL.
The fi sh tissue-based guidance of 5 ppb is derived from the equilibrium between
water and sediment organic carbon, using a log K oc of 5.92 (Hart et al. 1988 ).