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 86

effect levels for total DDT. Yet, they are included in the effects data set and the
lowest value is within the 15th percentile. Inspection of the underlying study
(Chapman et al. 1987 ) revealed pollutant levels of 9,460 ppb PAHs (polyaromatic
hydrocarbons), 129,000 ppb Pb, 710 ppb Hg, and 990 ppb Cu. Here, the problem is
one of toxicological plausibility. The plausible explanation for benthic toxicity is
the presence of these other pollutants and not the presence of low ppb levels of total
DDT. The TEL method ignores obvious toxicological interpretation of data.
The effects data points of 22.3, 46.1, 54.5, 55.2, and 125 ppb are all LC 50 values
in pore water (Word et al. 1987 ), rather than LC 50 values in sediments. These values
should be multiplied by the partition coeffi cient (a factor of at least tens of thousands)
to obtain estimates of sediment LC 50s .
The fi rst of the two 27 ppb AET (apparent effects thresholds) values in the marine
sediment effects data set is the highest threshold associated with Rhepoxynius abro-
nius toxicity for total DDT in sediments from Northern California (Becker et al.
1989 ). The highest threshold represents the highest concentration found in sediments
without toxicity. The comparable value for Southern California, where sediments
have much higher levels of total DDT, due to contamination from a DDT manufac-
turing site, is greater than 9,300 ppb! The second 27 ppb value is the highest thresh-
old associated with bivalve toxicity for total DDT in sediments from Northern
California (Becker et al. 1989 ). A similar threshold was not determined for Southern
California. The AET values for Northern California appear to be artifacts of the
method (most likely determined by the presence of toxic levels of other contami-
nants), since sediments from Southern California with much higher residues of total
DDT were not toxic in the selected bioassays.
The association between sediment residue and sediment toxicity at 68 ppb makes no
sense when one considers that in the same study 1,018 ppb total DDT in sediment
was not associated with signifi cant sediment toxicity to the same amphipod species
(Anderson et al. 1988 ). The authors stated: “Most notably, DDT concentration did
not correlate with short-term toxicity or macrofaunal patterns.”
The value of 210 ppb (Lyman et al. 1987 ) is derived in the same way as the
1.58 ppb value by JRB Associates ( 1984 ). The only difference is the use of the
National acute marine criterion of 130 pptr instead of the chronic marine criterion of
1 pptr in the water column. The sediment equilibrium concentration is derived from
a log K ow of 5.98. The slow-stir log K ow 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 nearly an order of magnitude higher.
Using a method similar to the one used to estimate the 505 ppb data point, Neff
et al. ( 1986 ) derived a screening level concentration for fresh water of 1.9 ppb. How
can fresh and salt water screening levels differ by 265-fold when the toxicity of
DDT to fresh and marine benthic organisms is similar? One or both of the screening
levels are most likely in error. Based on bioassay results, the freshwater screening
level appears to be too low.
The claim that DDT is toxic to benthic organisms at low ppb levels in marine
sediments is not supported by fi ndings reported in studies cited in the effects data base.
Reburial and survival of amphipods was not signifi cantly affected by sediments