SELENIUM CONTENT O F W H E A T F R O M VARIOUS PARTS OF THE WORLD
A SELENIFEROUS AREA AND
AN
EXAMPLE OF
THE
EFFECTOF SELENIZED FEED
Note comparative absence of hair on mane and tail.
W. 0. ROBINSON Bureau of Chemistry and Soils, U. S. Department of Agriculture, Washington, D. C.
@ I
main and perhaps accumulate in the soil. In general, then, wheat can be used as a sort of an indicator of the presence or absence of selenium in soils from various parts of the world. Strock (6) showed that selenium occurs widely in the earth’s crust, and Byers ( 2 ) reports that selenium can be detected in practically all soils. Then there must be soils other than those of South Dakota which would produce selenium-bearing wheat. Samples of wheat from various parts of the world were secured through L. A. Wheeler of the Bureau of Agricultural Economics and B. Y. Morrison of the Bureau of Plant Industry of the Department of Agriculture, and some were obtained directly. The location of the soils on which these wheats were grown is not known except in a few cases; presumably they were obtained from the market centers and
N 1931 it was found by the Department of Agriculture that selenium was responsible for the toxicity of certain wheat grown in South Dakota. The selenium is taken up from the soil. The soils containing the selenium are derived from seleniferous shales. In the humid regions selenium is leached, in a great measure, from the soils, and it is only in the drier regions where climatic conditions are such that calcium carbonate and gypsum are present in the soil that selenium will be found in the soil in sufficient quantities to produce toxic wheat. The general facts concerning the agricultural significance of the occurrence of selenium are summarized by Byers (1) in a recent bulletin. The largest part of the world’s supply of wheat is grown on semi-arid soils where selenium, if present, would tend to re-
seleniferous soil were highly toxic to white rats and other animals, and are probably toxic t o man. Some soils in the great wheat-producing countries must contain considerable selenium, and imported wheats should be examined for their selenium content. Since the selenium in wheat gluten is concentrated about five times, the determination of selenium in gluten intended for food becomes of considerable importance.
Probably selenium is a normal constituent of wheat grown in the great producing countries. The quantities of selenium present in random selections from the wheat markets varied from 0.1 t o 1.9 p. p. m. The maximum quantity of selenium present in samples of market wheat examined is probably too low to have any bad effect on human health, though this phase needs further investigation. Certain samples of wheat, however, grown on restricted areas of highly 736
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represent mixtures grown on comparatively large areas. It is regretted that samples of Russian wheat were not obtained up to the time of publication of this work.
Method of Analysis At the begipning of the work on the selenium problem, the presence of selenium in wheat grown in the eastern United States was not detected, but as the work progressed it became possible to discover smaller quantities of selenium in wheat. Further, it was found that nearly all the selenium could be concentrated in a gluten fraction with the elimination of about nine-tenths of the weight of the wheat. By means of this concentration it has been possible to determine the presence of selenium in all samples of wheat examined. The gluten was roughly separated from the wheat in the following manner: One kilogram of the finely ground wheat was treated with enough water to make a dough. This dough was tied in a bag of double-thickness cheesecloth and viporously kneaded under water until practically free from starch. The gluten and adhering bran were removed from the bag, and most of the bran was freed from the mass by flotation in a basin of water. The impure gluten separated in this manner was dried, weighed, and ground. The method of analysis used was that of Robinson, Dudley, Williams, and Byers (5). For the purpose of preventing loss in ashing the wheat or gluten, it was necessary to modify the original procedure; the details of the ignition are as follows: Twenty-five grams of the finely ground whest or gluten in a 400-cc. silica dish were rapidly and thoroughly stirred with 25 cc. of water. Twenty cubic centimeters of a nearly saturated solution of magnesium nitrate were then rapidly and thoroughly stirred into the mixture. Seven to ten grams of otassium hydroxide dissolved in about 40 cc. of water were adfed to the contents of the dish, and the mixture was etirred thoroughly. The contents of the dish were partially dried on the steam bath until the upper surface was dry but the bulk was still moist. The dish was then introduced into an electric furnace, held a t 500" t o 525" C., and covered. At intervals the cover was lifted to aid combustion, but this combustion was not too rapid and the rate was somewhat controlled by frequently raising the cover of the dish. When the violent part of the combustion was over, the cover was removed and the carbonized mass turned with a spatula t o hasten combustion. The dish and contents were then held in the furnace in an oxidizing atmosphere for 15 to 20 minutes. From this point on, the method followed that described by Robinson, Dudley, Williams, and Byers. The estimation of such small quantities of selenium as were found in most of the wheat is difficult, and the results are open to question. The results obtained are the mean of duplicates and frequently triplicates. Where the selenium content was very low, two or more of the 25-gram lots were used in the analysis. Two of the highest results were checked satisfactorily by K. T. Williams of this laboratory using another method of oxidation described by Williams and Lakin (7). Fortunately the reagents employed are practically free from selenium. Blank tests run on twice as much magnesium nitrate and potassium hydroxide as employed in the analysis showed no selenium. Four times as much of those reagents gave a doubtful test.
Analysis of Wheats The results of the analysis are given in Table I. Most of the results were obtained by the analysis of the gluten and are somewhat low, as will be explained later. Table I shows a variation in the selenium of commercially purchased wheat of 0.1 to 1.9 parts per million. All wheats contained some selenium, and it is improbable that any field-grown wheat is entirely free from that element. The Canadian wheat (B9600) and the South African wheat (B12724), with selenium contents between 1 and 2 p. p. m., show that there are soils in other countries which contain considerable selenium. The quantities of selenium that wheat will take up are not proportional to the total quantity in the soil. Hurd-Karrer (3) showed that the pres-
737
ence of sulfur in the soil is an inhibiting factor, and that, as the sulfur in the soil is increased, the selenium absorbed is reduced. Byers (1) showed that plants do not take u p selenium in proportion to the total selenium in the soil even when the effect of sulfur is considered. There appears to be a difference in the forms in which selenium occurs and in their availability. The presence of small quantities of selenium in random selections of commercially obtained wheat does not mean that there are not areas represented by the mixed sample which may produce wheat with a sufficiently large content of selenium to be toxic. Samples of wheat from the same field have been found to vary considerably in selenium content. Wheat from a small plot in Wyoming contained 2.7 p. p. m. selenium and a very toxic wheat from a small plot in a larger field in South Dakota contained 26 p. p. m. The wheat from other plots in this field contained from 8 to 15 p. p. m. Soil from this field contained from 3 to 6 p. p. m. selenium. Wheat raised in the greenhouse near Washington by A. M. HurdKarrer of the Bureau of Plant Industry contained 90 p. p. m. This wheat was raised on soil containing 5 p. p. m. selenium as sodium selenate. Selenium in this form is probably more readily taken up by the plant than the selenium occurring in natural soils. Wheat containing 30 p. p. m. selenium has the maximum content of selenium of any field-grown wheat yet analyzed, and Hurd-Karrer's wheat shows the maximum quantity of any wheat yet reported. It is not improbable that some of the small field or plot samples of wheat of a mixture such as may be purchased in commercial quantities may contain highly toxic quantities of selenium, while the selenium content of the entire mixture may be below 1 or 2 p. p. m. TABLEI. SELENIUMCONTENT OF VARIOUSCOMMERCIAL WHEATS Laboratory No.
Location
B6S42 B9585 B9590 B9600 B10199 B10212 B11072 B12723a B12724 B12725 B12726 B12727 B1272S B14198 B14199 B14201 B14819 B14820 B14821 B14822 B14823 B14824
New S. Wales, Australia Argentina Argentina Saskatchewan, Canada Pampa Territory, Argentina Pampa Territor Argentina New S. wales, dllstralia San Jacinto, Mexico South Africa South Africa Spain SDain Spain North Dakota Flour North Dakota Cantgrbury Area. New Zealand New S. Wales, Alstralja New 9. Wales Australia New S. Wales' Australia New 9. Wales' Australia New S. Wales: Australia New S. Wales, Australia
c112 C113 C1048 C1049 C1050 C1051 C1052 C1053 C1054
Flour Maryland Virginia Maryiand
Virginia Maryland Virginia Hungary Spain Hungary
Selenium P . p . m. 0.6 0.4 0.6 1.9 0.8 0.6 0.7
0.6
1.5
0.2 0.2 0.6 0.8 0.3 0.2
0.4
0.2
0.5 0.4
0.1 0.4 0.6 0.1 0.1
0.1 0.2 0.2 0.2
0.4 0.3 0.4
Munsell (4) reports that a diet of 20 per cent of wheat (based on the gross weights of the nearly anhydrous constituents) containing 15 p, p. m. selenium had no noticeable effect on the growth of white rats. This diet, however, had a slightly depressing effect on their reproduction. When the wheat made up 40 per cent of the diet, thereby increasing the selenium content of the diet from 3 to 6 p. p. m., the growth of the rats was depressed and no third generation was born. A diet of 60 per cent of the wheat (9 p. p. m.) was fatal to
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some of the rats and produced acute physiological symptoms in the balance killed for examination.
Selenium i n Gluten Fraction Most of the analyses given in Table I are based on the analysis of the gluten fraction. Some preliminary work indicated that nearly all the selenium present in wheat could be recovered from the gluten. The gluten of wheat sample B14.l.98showed on analysis slightly more selenium than could be recovered from the quantity of wheat from which it was extracted, presumably because of losses in igniting the larger masses of wheat and errors involved in the determinations of such small quantities. Eighty-five per cent of the total selenium in sample B14824 was recovered from the gluten fraction. The toxic wheat from South Dakota showed 80 per cent recovery of the selenium in the gluten. Most of the figures given in Table I are probably somewhat too low, since it appears that as much as 20 per cent of the selenium may be lost in the process of concentrating it in the gluten fraction. No work has been done on the relation between the selenium in the wheat and the flour milled from it. Some idea of the distribution of selenium in the wheat may be obtained from the following: The toxic wheat from South Dakota containing 26 p. p. m. selenium was separated into bran, starch, gluten, and soluble fractions by working 1 kg. of the ground wheat with about 17 liters of water. Eighty-eight grams of Hurd-Karrer’s wheat were treated in a like manner with 2.5 liters of water. All that settled out overnight was considered starch. This starch probably contained some fine particles of bran. The table which follows shows the selenium content of the various fractions in p. p. m.
VOL. 28, NO. 6
Toxic Field-Grown Wheat Hurd-Karrer’s Wheat mihole wheat 26 90 Gluten 121 340 Bran 22 94 6 Starch 7 Sol. and suspended matter lBa 180b a 8.9% of wheat. b 7 . 2 + % of wheat (some lost).
Since the gluten of the wheat carries most of the selenium, the examination of glutens prepared for special diets for selenium becomes of interest, since presumably the dry-land wheats would be used for gluten extractions. Several prepared glutens were examined for selenium. Of two samples of gluten obtained from M. J. Horn of this bureau, one contained 0.8 p. p. m. selenium and the other 16 p. p. m. A gluten purchased in New York contained 12 p. p. m. selenium. The gluten separated from the wheat raised by Hurd-Karrer on artificially selenized soils contained 340 p. p. m. selenium. A gluten of this selenium content and the gluten separated from the toxic field-grown wheat would be dangerous to use, and one containing 16 p. p. m. could hardly be considered wholesome.
Literature Cited (1) Byers, H. G., U. S. Dept. Agr., Tech. Bull. 482 (1935). (2) Byers, H.G., unpublished data. (3) Hurd-Karrer, A. M., J . Agr. Research, 50, 413-27 (1934). (4) Munsell, H.E.,De Vaney, G . M., and Kennedy, M. H., to be published by U. S. Dept. Agr. (5) Robinson, W.O.,Dudley, H. C., Williams, K. T., and Byers, H. G . ,IND.ENG.CHEV..Anal. Ed., 6, 274-6 (1934). (6) Strock, L. W., Am. J . Phnrm., 107,144-57 (1935). (7) Williams, K. T., and Lakin, H. W., IND.ENQ.CHEM.,Anal. Ed., 7, 409-10 (1935). RRJCEIVED February 4, 1936.
SULFITE WASTE LIQUOR Laboratory Study of Its Anaerobic Decomposition When Discharged into Water Bodies ULFITE waste liquor (8. w. 1.) is the liquid waste resulting from the manufacture of cellulose pulp from wood by the acid sulfite process. It contains in solution about 10 to 12 per cent of organic matter, which consists of lignin in the form of “calcium ligno-sulfonates,” sugars formed by hydrolysis from hemi-celluloses of wood, and small quantities of acetic and formic acids, methyl and ethyl alcohols, furfural, and acetone. Polyhydroxy acids, such as mannonic, xylonic, and d-gluconic formed by oxidation of sugars, are also often present (3). Although s. w. 1. can be disposed of in a number of ways, such as by evaporation and combustion, as a binder for road building, for alcohol production, in the manufacture of yeast, and for preparation of tannic substances from lignin, most of the liquor is still disposed of by discharging it into water courses as an industrial waste. It is generally agreed that the water pollution effect of s. w. 1. is not due to the presence of any poisonous substances in the liquor but arises from the fermentable organic substances it contains. Bacteria and other microorganisms present in water attack these organic
H. K. BENSON A N D A. M. PARTANSKY University of Washington, Seattle,Wash.
substances of the liquor, converting them into carbon dioxide and water a t the expense of the dissolved oxygen. Thus s. w. 1. changes the gaseous balance in the water; oxygen concentration is decreased and carbon dioxide concentration is materially increased (4). It has been found, however, that properly aerated liquor in concentrations as high as 1 to 50 has no injurious effect on fish (6). The question of what happens to the liquor itself after it is discharged into a water course-that is, how rapidly and to what extent it is decomposed-except for the work done in this laboratory ( I , I, 6, 8), has been very little investigated. The present paper summarizes the findings and conclusions of two and a half years of work on fermentation of sulfite waste liquor.
