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 74

with declining residues of persistent organochlorines, including DDT, suggesting
possible causation.
In recent years, DDT contamination of harbor seals in the U.S. was re-evaluated
because DDT's ban has been in place for well over 30 years. Shaw et al. ( 2005 )
sampled the blubber of 30 stranded harbor seals from the northwestern Atlantic
coast of the U.S. DDT concentrations ranged from 1.4 to 57.5 ppm (lipid weight).
Also of note was substantial variation between adult males (12.40 ± 6.65 ppm),
adult females (4.60 ± 2.56 ppm), yearlings (13.00 ± 14.40 ppm), pups
(21.10 ± 19.70 ppm), and fetuses (2.21 ± 0.62 ppm).
Wang et al. ( 2007 ) reported relatively low levels of DDT in harbor seals from the
Gulf of Alaska. Blubber samples contained 78-325 ppb with a mean level of
159 ppb. The authors point out that levels in nursing females were much lower than
those in male adults, due to lactation transfer of DDT from mother to newborns.
Sakai et al. ( 2006 ) reported on an assay for androstane receptor activity in
Russian seals. The authors concluded that DDT was active in their assay and that the
lowest observable effect level was comparable to a 10 ppm tissue level.
In summary, to date, a number of investigations have confi rmed the presence of
DDT in harbor seals throughout the world, and their ability to accumulate it via
primarily biomagnifi cation. Concentrations vary but have been generally reported
in the parts-per-million range, which would refl ect the varied length of use of the
insecticide (although banned in 1972 in the U.S., it was used much more recently in
other parts of the world), as well as their habit of feeding high on the marine food
web (primarily fi shes). Toxic effects in harbor seals from DDT have yet to be con-
clusively demonstrated via controlled studies.

DDT and Sea Lions . There are several reports of DDT in sea lions ( Z. californianus )
residing along the California coast. In 1971 , Le Boeuf and Bonnell published a
seminal report of blubber concentrations in California sea lions collected in 1970
(n = 12), a full 2 years prior to the banning of the use of DDT in the U.S. In it,
they reported high concentrations for both DDT (geometric mean, 17 ppm; range,
8.8-34 ppm) and DDE (geometric mean, 740 ppm; range, 370-1,500 ppm).
In 1992 , Bacon et al. surveyed milk samples from a number of pinniped species,
including one lactating California sea lion resident to the central coast—geometric
mean values ranged from 3.3 ppb for o , p

-DDE. This was
not considered unusual, as the area is one of intense agricultural activity and has a
history of DDT use.
In 1995, Lieberg-Clark et al. followed up on the above 1971 report of Le Boeuf and
Bonnell by measuring

′ -DDT to 1.4 ppm for p , p ′

DDE concentrations in blubber from seven
California sea lions sampled between 1988 and 1992. Their numbers clearly indicated
a signifi cant decline (greater than 99%) in residues over the 20-year time span for
both DDT (geometric mean, 0.16 ppm; range, 0.07-0.35 ppm) and DDE (geometric
mean, 5.0 ppm; range, 2.5-10 ppm). Therefore, they concluded the following:

ʣ DDT and ʣ

1. The decline in the residue levels in California sea lions over this period was
accompanied by a signifi cant increase in their population during the same time
period.