Is DDT "nasty stuff"?

[js_dukelow@ccmail.pnl.gov]

On  Mon, 29 Apr 1996 09:24:25 -0400 (EDT) 
Bernard L Cohen <blc+@pitt.edu> wrote

> I object to characterizing DDT as "nasty stuff". There is no evidence 
> that DDT has harmed the health of any human, and it has saved millions 
> of lives. 
> 
> Bernard L. Cohen
> Physics Dept.
> University of Pittsburgh
> Pittsburgh, PA 15260
> Tel: (412)624-9245
> Fax: (412)624-9163
> e-mail: blc+@pitt.edu

Dr. Cohen and I are both out of our areas of expertise here, but I have 
the advantage of having recently researched the toxicity of DDT, in 
order to respond to an accusation made on the RISKANAL risk analysis 
mailing list that Rachel Carson was responsible for the deaths of 
millions of people because her book _Silent Spring_ led to the banning 
of DDT.

DDT and its metabolites are not highly toxic, but that isn't the same as 
being non-toxic or as there being "no evidence that DDT has harmed the 
health of any human," as Cohen would have it.

The following information on the toxicity of DDT is available from the 
WWW page of the National Toxiclolgy Program of the National Institutes 
of Health and the National Cancer Institute. 

   Human poison by ingestion and possibly other routes.  Experimental 
   poison by ingestion, skin contact, subcutaneous, intravenous and 
   intraperitoneal routes.  A suspected human carcinogen.  An 
   experimental carcinogen, neoplastigen, tumorigen and teratogen.  
   Experimental reproductive effects.  Human systemic effects by 
   ingestion.  ...  Human mutagenic data.  A dose of 20 grams has 
   proved highly dangerous though not fatal to man.  This dose was 
   taken by 5 persons who vomited an unknown portion of the material 
   and, even so, recovered only incompletely after 5 weeks.  Smaller 
   doses produced less important symptoms with relatively rapid 
   recovery.  Experimental ingestion of 1.5 g resulted in great 
   discomfort and moderate neurological changes.  Recovery was complete 
   on the following day.  The fatal dose for humans is not known.  
   Judging from the literature, no one has ever been killed in the 
   absence of other insecticides and/or a variety of toxic solvents.  
   However, these common solvent formulations are highly fatal when 
   taken in small doses, partly because of the toxicity of the solvent, 
   and perhaps because of the increased absorbability of the compound; 
   several fatal cases in humans have been reported.  

   Little is known of the hazard of chronic poisoning.  Human 
   volunteers have ingested up to 35 mg/day for 21 months with no ill 
   effects. This compound and some of its degradation products, 
   particularly DDE, are stored in fat.  This storage effect leads to 
   a concentration of this compound at higher levels of the food 
   chain.  DDT stored in the fat is at least largely inactive since a 
   greater total dose may be stored in an experimental animal than is 
   sufficient as a lethal dose for that same animal if given at one 
   time.  A study based on 75 human cases reported an average of 5.3 
   ppm of DDT stored in the fat.  A higher content of DDT and its 
   derivatives (up to 434 ppm of DDE and 648 ppm of DDT) was found in 
   workers who had very extensive exposure.  Without exception, the 
   samples were taken from persons who were either asymptomatic or 
   suffering from some disease completely unrelated to DDT.  Careful 
   hospital examination of workers, who had been very extensively 
   exposed and who had volunteered for examination revealed no 
   abnormality which could be attributed to DDT. Much higher levels 
   have been found in humans than have been observed in the fat of 
   experimental animals which were apparently asymptomatic.  DDT 
   stored in the fat is eliminated only very gradually when further 
   dosage is discontinued.  However, weight loss can speed the 
   release of this stored DDT (and DDE) into the blood.  After a 
   single dose, the secretion of DDT in the milk and its excretion in 
   the urine reach their height with in a day or two and continue at 
   a lower level thereafter. 

Dr. George Waldbott, in _Health Effects of Environmental Pollutants_, 
Mosby, 1973, and Carson, in _Silent Spring_, 1962, report several 
incidents of DDT poisoning.  These resulted from consumer misuse of 
household bug sprays or agricultural worker exposures.  DDT causes 
liver cancers in mice and is considered a "probable human carcinogen" by 
the EPA.

Cohen's other assertion about "millions of lives being saved" may be 
true, but needs to be carefully qualified.  DDT was very effective at 
controlling the insect vectors of several important human diseases, for 
a short period of time -- typically, a few years -- until the insects in 
question developed resistant strains.  Even before DDT was "banned" in 
the U.S. in 1972, its "victory" over malaria in several countries in the 
tropics had been reversed by resistant strains of mosquitos.  DDT's 
short-lived victories came at a high price:  it disperses widely in the 
environment; it is highly persistent in the environment and in humans 
and animals; and it tends to bioconcentrate, both in individual 
organisms (where it concentrates in fatty tissue) and in the food chain 
(where it concentrates in the predators at the top of the food chain, 
such as raptors, and humans, for that matter).  Several avian raptor 
populations approached extinction, at least partly because of egg shell 
thinning caused by DDT.  DDT's "banning" was only partial; it is still 
being manufactured and used in a number of countries around the world. 

Best regards.

Jim Dukelow
Pacific Northwest National Laboratory 
Richland, WA

js_dukelow@pnl.gov

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