Vol. 15—1961 - NorthEastern Weed Science Society
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Vol. 15—1961 - NorthEastern Weed Science Society

Vol. 15—1961 - NorthEastern Weed Science Society Vol. 15—1961 - NorthEastern Weed Science Society

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396. WHATHAPPENS TO PHENOXYHERBICIDES .WHENAPPLIED TO A WATERSHEDAREA by A. W. Winston, Jr. and P. M. Rittyl '. Water supply people responsible for maintaining reservoirs of wholesome water frequently ask about. the effects on water , quality when brush in the surrounding watershed areas is chemically sprayed. What are the breakdown products and how" might they affect water supplies are two of the questions sanitary engineers ask concerning phenoxy herbicides. No discussion will be made here regarding the direct toxicity of 2,4-D and related materials. The wide use of 2,4-D, 2,4,5-T and similar compounds over many years now provides excellent practical assurance of the lack of toxicity. Discussed here will be the products of decomposition by soil microflora and their effects on water supplies. A. MICROBIAL DEGRADATION Bacterial decomposition of 2,4-D, 2,4,5-T, silvex and related chemicals is well reported in the literature. At least eight species of bacteria are known to feed actively on chlorinated phenoxy herbicides. Corynebacterium sp. (8) decomposed 80%of a 1,000 parts per million (ppm) concentration of 2,4-D in four hours, releasing chlorine as the free chloride ion. Bacterium globiforme (1), which is readily found in garden and woods soils, Flavobacterium aguatile (5) and F. peregrenum (12), two species of Achromobacter (2, 12), and a Mycoplana sp. (14) all have been identified as capable of destroying phenoxy compounds. Work conducted by the senior author of this paper shows still another species of bacterium that feeds actively on phenoxy compounds. This bacterium has been identified as PseUdomonas cruciviae, and is one whose source of isolation and habitat 1s soil (3). P. cruciviae fed equally as well on 2,4­ dichlorophenol, pentachlorophenol, and unsubstituted phenol. The hypothesis has been made that soil and water bacteria would convert 2,4-D, 2,4,5-T and related chemicals back to diand trichlorophenols (2,4). Both of these free phenols can cause taste and odor problems in extremely low concentrations. A study was undertaken to evaluate this hypothesis and to positively determine the end decomposition products formed after exposure to bacterial action. 1 The Dow Chemical Company, Midland, Michigan.

- 397. B. PROCEDURE Laboratory apparatus used in these mainly of a source of supply of phenoxy (since biological oxidation by previously bacteria occurs generally under aerobic experiments solutions, mentioned conditions) consisted an aerator, species of a settling chamber and a proportioning pump to provide continuous feed at a set rate. The effluent solutions were collected and chemically analyzed to determine components or degradation products. Seeding of the aerator to obtain phenol digesting bacteria was done in two ways. Activated sludge from an industrial waste treatment plant which treats both sanitary and industrial wastes" provided bacterial "seed" for half of the test equipment. However, since bacteria which decompose these compounds are reported to be found generally in nature (3, 6, 9, 13), a collection of soil samples was gathered from a typical watershed area and used for comparison in the other half of the laboratory setup. These watershed soil samples were taken from areas on which no prior application of any herbicides has been made. C. RESULTS Known amounts (i.e., 55 ppm) of phenoxy herbicides were fed to the influent of the systems. After 3D-hour exposures to the bacterial CUltures, effluent samples were removed and exhaustively analyzed. Beside odor and taste threshold tests, the Gibbs test to determine free phenols with a sensitivity of 10 parts per billion (ppb) was used. Furthermore, to increase this sensitiVity, after color formation with the Gibbs method, a further solvent extraction was made so as to concentrate color and thus increase sensitivity of the test. With the analytical tests then having a sensitivity of 0.5 ppb, no free phenols were detectable. Microflora from either the general waste seeding or from watershed soil samples had decomposed the phenoxy compounds to carbon dioxide, inorganic chlorides and water. A quantitative release of the chloride ion had occurred during the bacterial decomposition (II). In the effluents there was no detectable dichlorophenol nor trichlorophenol residue. The oxygen consumption was that which theoretically would be required to affect complete oxidation. Free phenols as such were also introduced into the system for further tests on biological oxidation. The phenols were reduced in a similar manner. Confirmation of this work with regard to 2,4-D has been reported by TIogoff and Reid (8). Their summary states, "An organism • • • • • • Corynebacterium sp. • • • • decomposes 2,4-D acid in relatively large amounts in synthetic medium. Indications are that complete destruction of the molecule follows ring rupture."

396.<br />

WHATHAPPENS TO PHENOXYHERBICIDES .WHENAPPLIED<br />

TO A WATERSHEDAREA<br />

by<br />

A. W. Winston, Jr. and P. M. Rittyl<br />

'. Water supply people responsible for maintaining reservoirs<br />

of wholesome water frequently ask about. the effects on water ,<br />

quality when brush in the surrounding watershed areas is<br />

chemically sprayed. What are the breakdown products and how"<br />

might they affect water supplies are two of the questions<br />

sanitary engineers ask concerning phenoxy herbicides.<br />

No discussion will be made here regarding the direct<br />

toxicity of 2,4-D and related materials. The wide use of 2,4-D,<br />

2,4,5-T and similar compounds over many years now provides<br />

excellent practical assurance of the lack of toxicity. Discussed<br />

here will be the products of decomposition by soil microflora<br />

and their effects on water supplies.<br />

A. MICROBIAL DEGRADATION<br />

Bacterial decomposition of 2,4-D, 2,4,5-T, silvex and related<br />

chemicals is well reported in the literature. At least<br />

eight species of bacteria are known to feed actively on<br />

chlorinated phenoxy herbicides. Corynebacterium sp. (8)<br />

decomposed 80%of a 1,000 parts per million (ppm) concentration<br />

of 2,4-D in four hours, releasing chlorine as the free chloride<br />

ion. Bacterium globiforme (1), which is readily found in garden<br />

and woods soils, Flavobacterium aguatile (5) and F. peregrenum<br />

(12), two species of Achromobacter (2, 12), and a Mycoplana sp.<br />

(14) all have been identified as capable of destroying phenoxy<br />

compounds. Work conducted by the senior author of this paper<br />

shows still another species of bacterium that feeds actively<br />

on phenoxy compounds. This bacterium has been identified as<br />

PseUdomonas cruciviae, and is one whose source of isolation and<br />

habitat 1s soil (3). P. cruciviae fed equally as well on 2,4­<br />

dichlorophenol, pentachlorophenol, and unsubstituted phenol.<br />

The hypothesis has been made that soil and water bacteria<br />

would convert 2,4-D, 2,4,5-T and related chemicals back to diand<br />

trichlorophenols (2,4). Both of these free phenols can<br />

cause taste and odor problems in extremely low concentrations.<br />

A study was undertaken to evaluate this hypothesis and to<br />

positively determine the end decomposition products formed<br />

after exposure to bacterial action.<br />

1 The Dow Chemical Company, Midland, Michigan.

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