[cdn-nucl-l] A reply to Jerry's questions about DDT

["Dukelow, James S Jr" <jim.dukelow@pnl.gov>]

In response to my posting on the history of the banning of DDT in the US, 
Jerry Cuttler asked the questions:

1) Did reputable scientist establish whether proper use of DDT actually causes 
significant harm to birds eggs, or is this a myth?

2) Does DDT last forever? If it reacts with mosquitos, something must break it 
down.

3) How much DDT accumulates in species at the top of the food chain? At what 
concentrations does it plateau?  Is this concentration significantly harmful?

4) Which chemicals do we currently spray in our towns (and nearby marshes) 
when there is a severe mosquito problem?

These are worthy questions, which I'll try to answer.  I apologize for the 
delay, but it took me awhile to find my DDT files (right next to my office 
chair in a mislabeled box).

Easiest first.  In several recent cases of spraying to control mosquitos and 
med flies, malathion has been used.  It is one of the least toxic of the 
organophosphate pesticides, some of which are closely related to nerve gas and 
exceedingly toxic.  Use of malathion, most recently in NY City to help combat 
West Nile disease has usually been opposed by at least some environmental and 
neighborhood groups.  Milloy's FoxNews piece mentions a couple of other 
pesticides used in NY that I am not familar with.

Regarding the other questions, a bit of background first.  I first got 
interested in this issue a few years ago when a RISKANAL subscriber posted 
what I considered a scurillous attack on Rachel Carson, essentially accusing 
her of being a mega-murderer -- arguing that continued use of DDT would have 
prevented millions of deaths.  I didn't actually know as much about the issues 
as I at first thought I did, so I set out to research the history of the 
banning of DDT.  I mostly searched the news and editorial columns of Science 
and Nature and Chemical & Engineering Weekly (published by the American 
Chemical Society) and research reports in Science and Nature.  I considered 
them to be mostly reliable sources and our poor desert library had runs of 
all three going back into the 60s.  It is fair to say that Nature and C&EW 
were strongly opposed editorially to the decision to ban DDT, both before and 
after the decision.  I read parts of Silent Spring and parts of Since Silent 
Spring (written by Frank Graham, Jr. and strongly supportive of Carson).  I 
read about the global campaign in the 50's and 60's to eradicate malaria, a 
campaign built around DDT, reading the accounts in Laurie Garrett's book on 
emerging diseases, The Coming Plague, and in Robert Desowitz' book, The 
Malaria Capers.  I was able to chase down a couple of the blue ribbon 
commission reports written in the late 60's.  The first was Man's Impact on 
the Global Environment (MIT Press, 1970).  The roughly 140 participants were 
heavily loaded with MIT and Harvard faculty.  Names I recognized include Hans 
Panofsky, George Rathjens, Reid Bryson, Roger Revelle, and Herbert Simon.  The 
workgroup on Ecological Effects looked in some detail at the impact of DDT and 
other pesticides on the marine environment.  The other major commission report 
I looked at was the Mrak commission report, from which I quoted at some length 
in my earlier posting.  An interesting and relatively balanced account of the 
DDT issues, written by a defender of DDT, is the chapter "Is DDT a 
disreputable chemical?" in Aaron Wildavsky's book, But Is It True?" 

The picture I got from all of this was that DDT had a significant impact on 
reproduction of some species of birds, including many raptors and other birds 
at the top of the food chain.  There is a lot of species to species variation.  
Indeed, Graham points out [p. 130] that although bald eagle, osprey, and 
peregrine falcon eggshells are drastically thinned by DDT, golden eagles, red-
tailed hawks, and great horned owls are not affected (although he notes 
elsewhere in the book that golden eagle populations in Western Scotland 
crashed during the years that dieldrin was used as a sheep dip, with sheep 
carrion being a major part of the golden eagle diet in the West).  The golden 
eagle population in Eastern Scotland had a different diet and was not 
affected.  Chickens and a number of other birds that can be described as not 
quite at the top of the food chain were unaffected.  The Mrak Commission notes 
[p. 179] that DDT causes eggshell thinning in ducks and falcons, but not in 
pheasant and quail.  Cats seem to be particularly sensitive.  A nice exercise 
for the reader is to do an Internet search on "Bolivian cats".  Even sources 
essentially opposed to the banning of DDT (Nature, C&EN, and Wildavsky,for 
example) agree that DDT had a significant reproductive impact on many species 
of birds. 

In a Nature news article written during the run-up to Ruckelshaus' decision to
ban DDT, the Nature reporter wrote: "But on the other hand, four government
committees which have studied DDT between 1963 and 1969 all recommended phasing
out it use and the Mark [sic] Commission recommended elimination by December
1971 of all uses of DDT not essential to public health." (Nature, v. 232, p.
598)

DDT doesn't last forever.  A paper by Woodwell, Craig, and Johnson, three 
scientists at Brookhaven (Science, v. 174, pp. 1101-1107, 10 Dec 1971) 
attempts, with a lovely series of back of the envelope calculations and simple 
linear box-and-arrow models, to estimate the flow of DDT through the 
environment to its ultimate resting place, the deep ocean abyss.  They 
establish that the main reservoirs are soil, the atmosphere, the ocean mixing 
layer, and the abyss.  The mean time of residency of DDT in these reservoirs 
is only 3 to 5 years in each reservoir.  The small fraction of DDT that enters 
the biosphere, migrates to fat deposits, where its half life might be on the 
order of 10-20 years.  The corollary of DDT's persistence in the environment 
is relatively low toxicity and chemical reactivity, but again with lots of 
species to species variation.  One of the more interesting parts of Woodwell, 
et al. is Table 2, which provides estimates of biomass (in billions of metric 
tons): land plants = 1850, ocean plants = 3, feral mammals = 0.009, domestic 
mammals = 0.17, humans = 0.3, fish = 0.65, ocean mammals = 0.055, other ocean 
animals = 3.  They assume values of 1 ppm of DDT for continental shelf algae, 
land animals, fish, and ocean mammals.  They assume 0.1 ppm of DDT in 
agricultural products.  With these assumptions the major living reservoirs for 
DDT are agricultural plants, algae, domestic mammals and man, fish, and other 
ocean animals. 

The equilibrium amount of DDT in species at the top of the food chain varies a 
lot and its effect varies a lot, with some species tolerating levels that will 
exterminate other species.  Wildavsky points out that the equilibrium level in 
the top level predators will depend on the extent to which all of the plants 
and animals down through that food chain accumulate or excrete DDT.  One 
species in the food chain that is able to eliminate most of the DDT it 
consumes will result in low levels higher in the chain.

That said, here are some values.  Measurements at Clear Lake in California 
showed 0.02 ppm of DDD (a compound closely related to DDT and its breakdown 
produce DDE) in the water, 5 ppm in microscopic plants and animals, 2000 ppm 
in fish, and 1600 ppm in grebes that fed on the fish.  The DDT mystification 
campaign makes a point of the fact that the concentration in grebes was lower 
than in the fish they preyed on, without pointing out that 1600 ppm was enough 
to kill the grebes.

The Mrak Commission [p. 208-9] notes that oysters will concentrate DDT by a 
factor of 70,000, that 24 hour exposure of blue crabs to 0.5 ppm DDT in water 
killed 50% of the crabs, that 72 hour exposure of crab larvae to 5 ppb (Yes,
that's ppb) 
causes 100% mortality, and that lake trout eggs having 5 ppm DDT had 100% 
mortality.  A Canadian trout hatchery found that all 16 commercial dry fish 
foods it tested for possible use contained DDT and its breakdown products and 
that some of them caused 30% to 90% mortality to fry and fingerlings.  
American sparrow hawks, experimentally fed a mixture of 0.28 ppm dieldrin and 
1.4 ppm DDT, levels consistent with those found in raptor food items in the 
field, suffered reduced reproductive success. 

Nature, in commenting editorially (and negatively) on Ruckelshaus' decision to 
ban DDT in the US, said "To be sure, there are some places -- Lake Michigan is 
a conspicuous example -- where the residues of DDT are already so great that 
commercial fishing has been made unproductive" and "This is why most students 
of the problem have come to the conclusion that the chief victims of DDT so 
far are likely to be birds, both predatory birds such as eagles and falcons 
and fish-eating birds, especially the pelicans off the coast of California.  
Over the years, a great deal of evidence has accumulated to suggest that eggs 
containing large quantities of DDT, and which are presumably laid by birds 
with a similar disability, have thinner shells and are therefore less viable 
that they would normally be. ... it is probably wise on balance to suppose 
that DDT is actually bad for individual birds."

Finally, in the same editorial (Nature, v. 237, pp. 417-418, 23 June 1972), 
the editor of Nature wrote, "After all, much of the present fuss would not 
have arisen, and pesticide residues would not have accumulated to the extent 
they have in human fat, if the agricultural uses of the persistent pesticides 
in the past twenty years had been more prudent."  This bears on the phrase 
"proper use" in Jerry's first question and on the current issue of whether DDT 
and eleven other persistent chemicals should be banned worldwide or whether 
DDT should be exempted, at least temporarily, because of its benefits in 
malaria prevention.

An interesting sidelight:  Rachel Carson and William Ruckelshaus are the 
villains of Milloy's op-ed piece and in similar attacks on the historical 
record.  But Ruckelshaus, the Administrator of the EPA, had a boss, Richard 
Nixon.  It is naive in the extreme to assume that Ruckelshaus banned DDT 
without Nixon's concurrence, particularly since the banning was a slap in the 
face of Jamie Whitten, the chairman of the House Agriculture Committee, a 
stauch defender of the use of DDT on cotton, the author of a book in praise of 
pesticides, and the gatekeeper for the Department of Agriculture budget each 
year.  Not a peep about what a bad guy Richard Nixon was for approving the 
banning. 

Another sidelight:  Carson proposed some alternatives to the use of DDT.  The 
first mentioned was biological control and her primary example of successful 
biological control was the extermination of the screw worm in Curacao and 
Florida in the 50's by means of the release to the environment of millions of 
male screw worm flies that had been sterilized by irradiation.  She was 
probably too optimistic about the general applicability of the technique.

Best regards.

Jim Dukelow
Pacific Northwest National Laboratory
Richland, WA
jim.dukelow@pnl.gov

These comments are mine and have not been reviewed and/or approved by my 
management or by the U.S. Department of Energy.