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Salient. Victoria University Student Newspaper. Vol 35 no. 4. 22 March 1972

2,4,5-T — Just a Weed Killer ?

page 6

2,4,5-T — Just a Weed Killer ?

The weedkiller 2,4,5-T as presently sold in New Zealand contains significant levels of an impurity called dioxin which could cause birth defects in human babies. Present government warnings and restrictions on 2,4,5-T are seriously inadequate. Farmers should welcome sensible restrictions on 2,4,5-T because it is their babies who are most threatened and in any case 2,4,5-T may well be harmful to stock and pasture. The government should immediately ban domestic and aerial spraying of 2,4,5-T.

Dr Robert Mann was a student at Victoria from 1959-63 where he completed his MSc. He then worked at Berkeley University, California, five years with the Nobel prizewinner (and Dow director), Melvin Calvin.

This article was rejected by the NZ Farmer because their editor thought he would be "irresponsible" to print it while the special government subcommittee is investigating the matter and because the Dow Company might withdraw its advertising.

The Dow company's magazine Service has vigorously supported the use of 2,4,5-T.'

Scientific Facts:

Since the thalidomide disaster it has been common knowledge that chemicals which do not harm a pregnant woman may, during the first few months of pregnancy, cause malformations of the foetus. Commercial 2,4,5-T contains an impurity which is one of the most powerful poisons known and is especially potent in causing malformations to pregnant mammals. This impurity is called 2,3,7,8-tetrachlorodibenzo-para-doxin, commonly abbreviated "dioxin". To summarise briefly a lot of scientific research, it appears that, in the rat, the maximun safe daily dose of dioxin is in the region of 1/8 of one millionth of a gram per kilogram of body weight. Since drug dosages are usually quoted in terms of weight of drug per unit of animal body weight, let us use the abbreviation microg./kg. for "millionth of a gram per kilogram body weight." The hamster is even more sensitive than the rat to the foetus-deforming effects of dioxin: daily doses of 0.02 microg./kg. in early pregnancy cause foetal damage in the hamster.

Of course we do not know how potent dioxin is in pregnant women. It might be less potent than in animals. On the other hand, it might be more potent. Thalidomide is 700 times more potent [unclear: a] at causing malformations in humans than in hamsters. Since we cannot deliberately dose women with such dangerous drugs, we must (as our minister of agriculture pointed out last year) calculate the maximum safe human dose from experiments on animals. In such calculations, the World Health Organisation recommends a safety factor of 2,000; this is reasonable, in view of the possibility that humans are far more sensitive to a particular drug than are the animals which have been tested. Applying this safety factor, and using the results from rats, we would conclude that the most dioxin a pregnant women should take is down around 0.000063 microg./kg. daily. On the other hand, if we calculate from the hamster results, we would conclude that even a daily dose as low as 0.00001./kg. would be dangerous in a pregnant woman.

Danger to Humans:

How serious in fact is the risk to people from the dioxin in 2,4,5-T? The bulk of NZ 2,4,5-T is made in New Plymouth by Ivon Watkins - Dow, who state that their product contains only about 0.5 -0.8 part per million dioxin. This may seem an impressively low impurity, but in fact even this level is significant. The most obvious way a woman could take a dangerous dose of dioxin from 2,4,5-T is through drift of aerial spray. Farmers end advisory officers are familiar with the fact that sprays laid from the air can and do drift for miles even on fairly calm days. If such a spray drifted on to a farm roof from which drinking water is collected, even the 0.5 ppm of dioxin in the 2,4,5-T could administer a daily dose of about 0.015 microg./kg. to a woman in the house. This figure was calculated by the Chairman of the Agricultural Chemicals Board, Mr P.J. Clark; he points out that such a dose is very unlikely, but that it is possible. If we now compare this possible dose from aerial spraying with the maximum safe dose indicated by experiments on animals, given above, we notice that the dose to the woman would be thousands of times the safe level. In fact, even if we were to ignore the safety factor (which no responsible scientist would do), we notice that the possible dose to a woman calculated by Mr Clark (0.015 microg./kg. daily) is very close to a dose (0.02 microg./kg. daily) which is positively known to cause foetal damage in the hamster.

U.S. Government Responses:

In April 1970, during the U.S. Senate subcommittee hearings on 2,4,5-T, the U.S. Government cancelled use of 2,4,5-Ton crops, near water, and around the home. Also the aerial spraying of Vietnam with 2,4,5-T was stopped, because of the danger of causing malformed babies.

The bans on home and water use of 2,4,5-T were not appealed against by the manufacturers of 2,4,5-T but the crop-use ban was : two manufacturers (Dow and Hercules) asked for a scientific advisory committee to review the decision. This committee reported to the Environmental Protection Agency in mid-1971, recommending that some of the restrictions on 2,4,5-T be lifted. However, this report was virtually demolished by prominent scientists. They pointed out that the report assumed a low dose of dioxin would have no effect, whereas scientific tests had been unable to discover a "no-effect dosage"; that the report had wrongly dismissed the possibility of dioxin's accumulation in body tissues; and that the benefits had not been weighed against the risks. The report was in fact rejected by the administrator of the EPA, Mr Ruckelshaus.

Another investigation of 2,4,5-T was made by the President's Science Advisory Committee, whose 68-page report (March 1971) did not recommend lifting the restrictions on use of 2,4,5-T It did however, recommend that the dioxin content be strictly limited to O.5ppm and preferably 0.1ppm.

The state of Massachusetts (population over 5,000,000) has a special Pesticide Board, which voted on April 28 1971 to ban all spraying of 2,4,5-T because of the potential hazards to health.

In short, then, considerable progress has been made in the U.S.A. toward protecting people from this danger.

2,4,5-T used as a dessicant to dry out gone before burning and clearing.

2,4,5-T used as a dessicant to dry out gone before burning and clearing.

Nz Government Responses:

The Agricultural Chemicals Board is charged by statute with being vigilant on behalf of the public health in matters such as this. The chairman of the Board, Mr Clark, has calculated that this accidental drift of aerially-sprayed 2,4,5-T could give a pregnant woman a daily dose comparable with those known to cause foetal abnormalities in animals. This means that there is one clearly feasible way in which 2,4,5-T could cause human birth defects. There exists, therefore, a clear case for public warnings and for restricting human exposure. Mr Clark, however, has never publicly rescinded his statement of 5 Dec 1970: "There is no evidence to show that foetal abnormalities in humans could be caused by 2,4,5-T. This statement was affirmed by the Registrar of the Board, Mr B.B. Watts, who on 12 Dec 1970 said that the latest reports received by the Board showed no evidence to suggest that 2,4,5-T is in any way hazardous to human health. These claims have been re-affirmed in subsequent broadcasts by both Mr Clark and Mr Watts. Furthermore, they persistently state that there is no evidence that humans have been harmed by 2,4,5-T. This statement is irrelevant, misleading and just plain incorrect. It is incorrect because in fact a select commission from the American Association for the Advancement of Science did find in Vietnam, where large areas have, been heavily sprayed with 2,4,5-T (though not so heavily as parts of the Waitakeres) some evidence of increased birth defects. "Time" of 10 May 1971 quoted an American doctor in a Saigon hospital as saying that every doctor he knew in South Vietnam believes there's been an increase in birth defects in the sprayed areas. The New York Times Weekly Review (Melbourne edn.) of 10 Oct 1971 stated: "There has been a significant increased incidence of birth defects among Vietnamese infants in the wartime years but a paucity of medical records prevents absolute verification". There is, then, no final scientific proof but there is certainly, contrary to Messrs Clark and Watts' repeated statements, some evidence that humans have been harmed by 2,4,5-T. Fur- page 7 thermore, their statements are misleading in that they imply reliable statistics exist on which pregnant women got exposed to 2,4,5-T and which bore defective babies, whereas in fact even the NZ government (let alone the Saigon one) keeps no good records on either. And thirdly, the most important objection to the statements is that they are irrelevant, because they Imply that, wher there is clear evidence from experiments on animals that a chemical could cause human birth defects at dose levels to which women could be exposed, the public should continue to be involuntarily exposed to this risk, pending proof of actual damage.

The main point is that the public ought to be protected from a risk which is already known for certain to be significant. Suppose that thalidomide had been shown by pre-sale tests to cause deformities in several species of mammal at doses which women would take. Would anybody then advocate the release of thalidomide for public consumption? of course not. Yet our Messrs Clark and Watts are in the position of advocating a similar exposure risk. To make things even worse, they ignore the distinction that at least thalidomide was of some benefit to and was voluntarily taken by women, whereas aerial spraying of 2,4,5-T can result in involuntary poisoning, with no compensating benefits to the victim.

The only action taken by the Agricultural Chemicals Board to protect people from the risks attendant upon spraying of 2,4,5-T is label amendments which have been and are being made. At present, one can buy from the Food department of a large Auckland store a bottle of 2,4,5-T which is not even labelled "Poison", and bears no warning of the possible hazard to health. Proper labels would be welcome; but they scarcely begin to meet the need. If your wife gets dosed with 2,4,5-T from your neighbour's aerial spraying, she can hardly be helped by any label which may have been on your neighbour's bottle.

What should be Done?

1. In view of the grave risks, aerial application of 2,4,5-T should be banned forthwith where there is any danger of exposure of humans.

The Minister of Agriculture has the power to do this. Farmers should not object, because:
(a)the main real need for aerial spraying of 2,4,5-T is on back blocks hill country where it should be possible to control rigidly the spraying on any but completely still days, and beyond a radius of many miles from any people;
(b)there may well be risks of deformed and/or dead lambs. After all, it's not much use to kill gorse and blackberry it the object of producing live sheep is defeated;
(c)the high doses of 2,4,5-T which are needed to kill gorse ere, according to a Department of Agriculture expert on herbicides, deadly to clover! He sees this in fact as a major economic loss to the country. Furthermore, research on persistence of 2,4,5-T in soil has shown that even in hot moist countries it remains at very significant concentrations after two months; in New Zealand, the figure might be of the order of a year.
(d)It is farmers' babies who are probably being maimed by 2,4,5-T.
Dow routinely conductsanimal feeding studies as part of toxicology research on herbicides. Rabbits (New Zealand White) are used in some experiments

Dow routinely conductsanimal feeding studies as part of toxicology research on herbicides. Rabbits (New Zealand White) are used in some experiments

Chemical Structures:



"dioxin" (2,4,5-T - tetrachiorodibenzo-p-dioxin)

"dioxin" (2,4,5-T - tetrachiorodibenzo-p-dioxin)

2. The Agricultural Chemicals Board at present is mainly made up of users and producers of chemicals. Several scientists should be added.

3. There is a 50% subsidy to the manufacturer (recently introduced). This tends to encourage use of chemicals rather than burning or slashing, and should be replaced by selective financial aid to those farmers who, in the judgement of competant advisers, must use agricultural chemicals.

4. New statutes should be passed to prohibit use of agricultural chemicals in ways which endanger the public health. (At present, farmers and home gardeners are free, under perhaps some pressure from chemicals salesmen, to use dangerous kinds and amounts.)

5. The government should support research into possible poisoning of animals and people by inhaled sprays of 2,4,5-T and other chemicals.

References: The leading British scientific journal "Nature" has summarized facts and opinions on 2,4,5-T:
"Nature" 226 309 (April 26 1970)
"Nature" 231 210 (May 28 1971)
"Nature" 231 438 (June 25 1971)
"Nature" 232 365 (Augusts 1971)
See also "Science" 173 313 & 610 (23 July & 13 August 1971)

"Want to Help?

This article is mostly a summary of the scientific section of the petition which was recently presented to the Ag Chem Board by the Environmental Defence Society, a group of scientists, town planners and lawyers which will be considering court action against the Board if it does not act to protect people from 2,4,5-T. To support the EDS, join it: $5 (students $1) to P.O. Box 8, Auckland.