Reaction to Tierney's bad science

Keith Schneider (who used to work with Tierney at the NYT) comments

Now Tierney is after Rachel Carson, using as the basis of his critique a 1962 review of Silent Spring in the journal Science written by I. L. Baldwin, a professor of agricultural bacteriology at the University of Wisconsin. Baldwin's review was the subject of debate as intense at the time as Carson''s ground-breaking journalism. Her assessment of the toxic trail left by pesticides in plants and animals was defended and confirmed then by independent scientists, some of them working at the behest of President John F. Kennedy. And they've been reconfirmed time and again in the real world since. ...

So you can't tell me that Rachel Carson's reporting inspired "chemophobia" as Tierney charges, or is exaggerated or untrue. What he does is focus the knife edge of an eloquent rhetorical attack on the outer membrane of Carson's reporting, such as the predictions she made that haven't come to pass -- a big loss of robins, for instance. He doesn't note that such a prediction might well have come to pass, and fortunately hasn't, because several of the most toxic compounds she critiqued, especially DDT, have been banned for agricultural use.

I appeal again to the major national organizations to get involved in setting the record straight about the value of Carson's journalism and scholarship. Their credibility and the salience of the environmental movement's science is at stake.

Meanwhile, over on his blog, Tierney gets some well deserved criticism in comments. Also in comments Donald Roberts writes some stuff that is just untrue:

Carson claimed that the insecticides evolved from military research.

No, she said (correctly) that organophosphates evolved from military research. She was careful to distinguish them from DDT and other chlorinated hydrocarbons

DDT resistance is not a reason for not using DDT. Resistance is just not as important as Tim Lambert and others want to believe. ... DDT has been used successfully in regions where mosquitoes are resistant. The basic relationship is that people are protected from indoor transmission of malaria if DDT is used. If DDT is withdrawn from control programs, people lose protections from devastating diseases, those diseases spread, and people get sick and die.

Now this was a response to my comment:

To give just one example: in Sri Lanka in the 1970s there were hundreds of thousands of cases of malaria because the mosquitoes had evolved resistance to DDT and DDT spraying no longer worked to control malaria. This is something that Rachel Carson warned about in "Silent Spring". If they had taken her advice sooner and banned the agricultural use of DDT in Sri Lanka in the 60s, many lives might have been saved.

You can read the history of what happened in Sri Lanka here and judge for yourself whether Roberts is correct when he claims that DDT still prevents malaria when the mosquitoes are resistant. The fact is that Sri Lanka was only able to control the malaria epidemic by withdrawing DDT from the control program and replacing it with malathion. According to Roberts, this should have increased malaria rates, but it didn't -- malaria rates went down.

Tierney also has a post where, unlike before, he manages to quote Ames correctly:

About 99.9 percent of the chemicals humans ingest are natural.

But then goes on to draw an unwarranted conclusion:

Even though these natural chemicals are as likely to be carcinogenic as synthetic ones

But what Ames found was that amongst chemicals tested natural and synthetic chemicals were as likely to be carcinogenic. His conclusion would only follow if the chemicals tested were a random sample, but were not. Tomatis et al write in the FASEB Journal:

Using data in the CPDB has led to the opinion that ~50% of all chemicals tested for carcinogenicity in rats and mice are positive in at least one experiment (18 , 23) . Unfortunately, the criteria on which the evidence of carcinogenicity for chemicals in the CPDB is based are not evaluated critically. A chemical is simply classified as a carcinogen "if it has been evaluated as positive by the author of at least one experiment" (20) . This is at variance with criteria adopted by the IARC and by the NTP whereby expert scientific panels carefully and critically assess all available experimental data before drawing conclusions on the strength of evidence of potential carcinogenic risk to humans. A large proportion of chemicals selected for carcinogenicity studies was based on an a priori suspicion of carcinogenic activity (34 , 39) .

and, responding to Ames' claims of misconceptions:

'Misconception' 4: Human exposures to carcinogens and other potential hazards are primarily to synthetic chemicals
Fact: Humans are exposed to both natural and synthetic mutagens and carcinogens and reduction of exposure to these chemicals will reduce cancer risks. The majority of natural chemicals that humans ingest are not carcinogenic.

The claim that more than 99.99% of ingested pesticides are natural in origin and less than 0.01% are synthetic pesticides residues (20) is both exaggerated and misleading with respect to human cancer risks. For example, these numbers refer to pesticides in general and do not distinguish carcinogenic pesticides (synthetic or natural) from noncarcinogenic pesticides. Second, even if these estimated values were limited to natural and synthetic pesticides that are carcinogenic, the comparison is flawed because it ignores differences in cancer potency, which may be very great among these chemicals. It should be noted that there is no evidence demonstrating that all chemicals produced by plants for protection against environmental insults can be labeled as natural carcinogenic pesticides. Third, as discussed above, the borderline between natural and human-made (synthetic) chemicals is also rather blurred. Fourth, there is no interdependence among natural and synthetic pesticides, consequently the risk of each chemical must be evaluated independently. Carcinogenic pesticides constitute a risk no matter what the prevalence is of natural chemicals.

'Misconception' 6: Synthetic chemicals pose greater carcinogenic hazards than natural chemicals
Fact: Natural and synthetic chemicals vary in their carcinogenic potency
Most occupational and environmental exposures to chemical pollutants come from synthetic chemical processes and discharges. Occupationally, synthetic chemicals do pose a greater cancer risk to workers. The notion that consumption of 'natural plant pesticides' in our diets poses a greater health risk than synthetic pesticide residues in our foods must be viewed as an unproved hypothesis lacking scientific credibility. See section on natural and synthetic chemicals above and response to misconception 4 for more on this issue.

(Thanks to Dano for pointing out Tomatis et al to us.)


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"But what Ames found was that amongst chemicals tested natural and synthetic chemicals were as likely to be carcinogenic."

Also, the Ames test is for *mutagenesis*, which is not the same as carcinogenic. The Ames test throws up a lot of false positives.

By Sock Puppet of… (not verified) on 11 Jun 2007 #permalink

"For example, these numbers refer to pesticides in general and do not distinguish carcinogenic pesticides (synthetic or natural) from noncarcinogenic pesticides."

That quote from Tomatis is interesting. They refer in the complete article several times to 'carcinogenic pesticides'. Isn't it the case that, in most OECD countries at least, a synthetic pesticide that has been shown to be a potent carcinogen would not be approved for use as a pesticide? If that's the case (?) then there would not be many current pesticides in use with known carcinogenic activity, correct? Are there really any good epidemiological data showing that consumption of foods with pesticide residues is correlated with cancer incidence? Given the lag time, effects of the older generations of pesticides (a number of which were suspected as being carcinogenic) should be showing up in those numbers.

Tomatis et al's main beef with Ames et al seems to be that Ames et al think that pesticide regulation is a waste of time and money. I think that de-regulating pesticides would be crazy, given what we know about the corporate world. But that doesn't mean that naturally-occuring chemicals in foods are harmless. If even a fraction of them were cancer-causing or mutagenic, then would not that be as good an explanation of high cancer rates as pesticide use?

Sock Puppet,

The Ames test has nothing to do with it. When Ames says a chemical is carcinogenic, he means it has been tested in an LD50 rat test.

So Tim is no longer just claiming that Tierney engages in bad science, he's claiming that Bruce Ames -- professor of biochemistry and molecular biology at the University of California, Berkeley, and senior scientist at Children's Hospital Oakland Research Institute, author of over 450 papers, one of the few hundred most-cited scientists -- Bruce Ames is a bad scientist.

Ames and coauthors say "that synthetic residues on food can be ignored because 99.99% of pesticides humans eat are natural, chemicals in plants are pesticides, and their potential to cause cancer equals that of synthetic pesticides." This summary of Ames' views comes from Tim/Dano's link to Tomatis et al, and completely supports Tierney's "bad science."

Go ahead, take on Ames, if you can. But to accuse Tierney of bad science just for quoting an incredibly respected scientist is ridiculous.