Document DMgOK8KYLjEb4e3Z5gVzkK55O

February 1948 Industrial Hypienc Newsletter 9 INDUSTRIAL TOXICOLOGY Lawrence T. Fairhall, LSPHS 2.4-DICHLOROPHEN- weed eradicator. Further, an important OXYACETIC ACID factor in the use of this material is re lated to residual 2,4-D on plants in tended for human or animal consump 2.4- Dichlorophenoxyacetic acid, tion. Hill and Carlisle () found that known as 2,4-D, has come into extensive the 1.050 dose of 2,4-D by mouth was use within the past 3 years as a plant 375 milligrams per kilogram for mice,. hormone which kilts common lawn weeds 666 for rats, 800 for rabbits, and 1,000 such as dandelion, morning glory, this for guinea pigs. Rats were led up to tle, and burdock, without harming one-tenth percent by weight of their ordinary grass. It is reported to hasten diet over a period of 1 month without the ripening of fruit and has been uaed any harmful effects. Guinea pigs tol in orchards to prevent the premature erated 1 gram of the material adminis dropping of apples. This substance is tered in divided doses of 100 milligrams prepared commercially by causing chlo- over a period of 12 days. The experi ronoetic acid and 2,4-dichlorophenol to mental work indicated that the mist or react to aqueous alkali or by the direct clouds of the dry dust of the sodium salt chlorination of phenoxyacetic acid. was relatively nontaxic. Since 2,4-D is a plant hormone, it Mitchell and his associates (5) have acts as a plant growth regulator rather shown that no harmful effects on the than as a contact poison. In its action health or performance of farm animals on ieafv plants it appears to be absorbed resulted from the consumption of pas primarily into the epidermal cells from ture grass liberally sprayed with 2,4-D. which it is translocated to various parts The 2,4-D was not found to be secreted of the plant. 2,4-D induces rapid hy into the milk nor was it found in the drolysis of starch to sugar and increased blood Berum of s calf fed milk from the respiration (I). The killing of plant cow that received it in her ration. Ac tissues is usually a slow process and the cording to experiments conducted by killing time may require two weeks or the U. S. Department of Agriculture, even longer. Young, vigorous plants one cow received a special dose of about are quickly affected and the most effi one-fifth of an ounce of 2,4-D daily. cient herbicidal effect occurs when Blood samples showed its presence in plants are treated in a state of active her circulation but it did not appear in vegetative growth. her milk. Mitchell quotes the experi Since 2,4-D is not very soluble in mental work of Kraus concerning the in water or oil, water-soluble salts or oil- gestion of 500 milligrams of purified soluble esters prepared in the form of 2,4-D per day by a man over a period emulsions or as dry dust mixtures are of 21 days without ill effect. used. Water-soluble salt dusts of 2,4^P The possible presence of poisonous have been used extensively in rice and impurities in commercia! preparations of sugar cane fields with uniform weed 2,4-D should be noted. Methods for control. During 1945, the first year in the determination of 2,4-dichlorophe- which production figures are given for noxyacetic acid consisting essentially of 2.4- D, 917,000 pounds were prepared in the titration of the acid group have the United States. been developed by Rooney (4). Owing to the phenomenal effects of 2.4- dichiorophenoxyacetic acid on weed eradication and the consequent commer cial development of this substance as a weed killer, knowledge of its toxicity is important. Workers are exposed to the dust of the sodium or ammonium salts and to the mist from tributyl phosphateDiesel oil emulsions, in applying this References U) Southwick, L. Chemical weed killers. Chem. Ind., SO, 786 (1947). () Hill, E. V., and Carlisle, H. Toxicity of 2,4-dichiorophenoxyacetic acid for experimental animals. J. Ind. Hyg. & Toxicol. $9, 85 (1947). (3) Mitchell, J. W., Hodgson, R. E., and Gaetjens, C. F. Tolerance of farm animals to feed containing 2,4-diclilorophenoxyacetic acid. J. Animal Science, 5, 226 (1946). (/,) Rooney, H. A. Determination of 2,4-dichiorophenoxyacetic acid and its compounds in commercial herbi cides. Ind. Eng. Chem., Anal. Ed., 19, 475 (1947). MAC VALUES (ConUnited front page I) times, that 1,000 p. p. m. is the most which should be allowed of any un natural atmospheric contaminant. "Five substances, benzene, ethylene chlorhydrin, nitroethane, nitromethane, and tetrachiorethane were changed in the light of recent data which certainly can be classed as experimental evidence. Two others, ethylene dichloride and methyl cetiosolve, were revised in ac cordance with previously reported field evidence which had been ignored when the previous list was compiled. Three other substances,, arsine, stibine, and dioxane, were reduced because a very superficial examination of the data avail able indicated that,the values previously given were much tod high. Three ad ditional substances, styrene, MXK, and methyl butanone, were reduced to make them all more in line with other similar substances. Finally, two other sub stances, tri- and tetra-chlorethylene, were reduced on the basis of extensive experience by one of the divisions involved." Furthermore, the observations of ex perienced members of the conference derived from various plant surveys have added to our knowledge of the effects of many of these substances on humans and should be considered as valuable supplementary information beyond that obtained by an animal experimentation. For the benefit of those who would ascribe a legal interpretation to such values, it may perhaps be advisable to use the older expression "threshold limit" rather than "maximum allow able concentration." Furthermore, it is the writer's opinion that the maximum allowable concentration values referred to should not form part of a code itself but should appear as supplementary information in an appendix and should be used only as originally intended, that is, as a guide and not as fixed values. SPNY 000321