Environmental Engineering Reference
In-Depth Information
Sediment TMDL targets for total DDT, based on threshold effects levels (TELs),
are inappropriate due to outdated, inaccurate and misinterpreted data. The TEL
method ignores important dose-response relationships in the data sets used to calcu-
late TELs. TELs for total DDT greatly overestimate thresholds for sediment toxicity,
when compared to dose-response studies. The problem with using TELs as TMDL
sediment targets is that risks are over-estimated, resulting in the assignment of
resources disproportionate to risk and thereby not minimizing overall risk to humans
and wildlife.
Terns, cormorants and several other avian species found in Newport Bay and
Watershed are less sensitive to the reproductive effects of DDTs than ospreys and
brown pelicans. Residues of DDE in eggs in excess of 10 ppm, resulting in eggshell
thinning of 15% or more, appear to be necessary to produce signifi cant hatching
failure. The lack of a correlation between DDE levels in Forster's tern eggs and
eggshell thickness indicates that reproduction in the closely related and threatened
least tern probably will not be affected by DDT levels that currently exist in Newport
Bay. The IAP has recommended the least tern as an indicator species for potential
toxicity of DDT to wildlife in Newport Bay and Watershed.
The rare appearance of marine mammals in Newport Bay is unlikely to result in
signifi cant exposures to organochlorines. Worldwide, studies of marine mammals
have disclosed a wide range of body burdens of DDT, but few if any impacts have
been clearly delineated. With wildlife tissue levels clearly on the decline, impacts
that might be identifi ed in the future are unlikely.
Fish tissue targets to protect wildlife were adopted from the 1972 National
Academy of Sciences recommendations. The 50 ppb target for DDT in marine fi sh
is protective, but very extensive study since 1972 indicates that 150 ppb is also
protective of sensitive avian species like the osprey. Successful osprey breeding
began in Newport Bay in 2006 and has continued through 2013. The 150 ppb level
in marine fi sh is also the basis for the national marine water criterion, a level that
would be expected to protect the brown pelican. The 1,000 ppb target for DDT in
fresh water fi sh is not protective and should be lowered to 150 ppb.
Two additional fi sh guidance reports were considered, but were not used as
TMDL targets to protect wildlife. The fi sh guidance of 14 ppb by Environment
Canada is highly protective from the assumption that minimal eggshell thinning is
toxic and from having used an insensitive species to assess worst case ingestion
rates. The fi sh guidance of 50 ppb by US EPA Region IX (Biological Technical
Assistance Group, BTAG) relied on the same study in brown pelicans that is the
basis for the national criterion for DDT in water (150 ppb in the fi sh diet). The
BTAG guidance is threefold lower by having assumed a rapid equilibration of DDTs
between dietary fi sh and brown pelican eggs, even though the underlying data indi-
cates that equilibration may take several years.
The triad analysis, although one kind of weight-of-evidence analysis, is incom-
plete and fl awed, when it was used to assess impairment of aquatic biota by chlor-
dane in Newport Bay. Relying on the mere presence of chlordane, along with
hundreds of other chemicals in toxic sediments, constitutes an incomplete weight-
of-evidence analysis. The chlordane ERM is not a reliable measure of toxicity
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