AGRICULTURAL CONTROL CHEMICALS

Selenium Residue on and in the Peel of Washington Apples KENNETH C. WALKER

Downloaded by UNIV OF SYDNEY on January 10, 2018 | http://pubs.acs.org Publication Date: January 1, 1950 | doi: 10.1021/ba-1950-0001.ch022

Washington Agricultural Experiment Stations, Wenatchee, Wash.

The average selenium residue on and in the peel of 30 samples of Jonathan, Delicious, and Winesap apples with no history of selenium sprays was found to be 0.001 p.p.m. The selenium residue on and in the peel of Jonathan and Delicious apples that had received one or more sprays of selenium ranged from 0.020 to 0.155 p.p.m. The addition of 1 quart of light grade petroleum oil increased the selenium residue. When single-tree plots were sprayed twice with selenium sprays significantly more selenium on and in the peel was found than in the unsprayed fruit, but there was significant difference due to variety or to position of sample on tree.

T h e literature on the distribution of " n a t u r a l " selenium i n the soils, the absorption b y vegetation, the toxicity of compounds of either natural or applied selenium to man and animals, and the use of selenium as a spray for insect control is voluminous and no a t tempt is made to cover i t here. The literature has been well reviewed fairly recently (#). Very little has been published on the increase i n selenium content of apple peelings, due to the application of selenium-bearing sprays. A proprietary selenium compound, known as Selocide, has been proposed for the control of Pacific mite, Tetranychus pacificus M c G . , and European red mite, Paratetranychus pilosus C a n . and Fanz., i n the apple-producing areas of the state of Washington. Selocide has been used on an experimental basis and to a limited extent on a commercial basis. Selocide is reported (4) to be a 3 0 % solution of a mixture of potassium hydroxide, ammonium hydroxide, sulfur, and selenium i n the proportions corresponding to the e m pirical formula ( K N H S ) S e . The commercial material contains 48 grams of selenium per liter, or approximately 6.4 ounces per gallon. The reactions that occur when a concentrated solution of Selocide is diluted with water to prepare a spray mixture, i n the presence of carbon dioxide and oxygen of the air, may be represented as follows : 4

6

4 ( K N H S ) S e + 10CO (from air) + 1 5 0 (from air) + H 0 — > 4

5

2

2

2

1 0 K C O (soluble) + 2 0 N H + 10H S + 10SO + 4Se (metallic) + H 0 2

3

3

2

2

2

The Selocide spray residue remaining on the fruit is red metallic selenium (3). Selocide is not compatible with acid lead arsenate ( P b H A s 0 ) under normal spray program conditions, but is compatible with cryolite (Na3AIF ) (a). Selocide is compatible with D D T [2,2-bis(p-chlorophenyl)-l,l,l-trichloroethane] and has been used with D D T for the control of mites and Codling moth, Carpocapsa pomonella L . , during the 1947 and 1948 growing seasons. 4

6

108

AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.

WALKER—SELENIUM

109

RESIDUE ON AND IN THE PEEL OF WASHINGTON APPLES

Methods and Procedure Selenium on and i n the peel of apples was determined b y the procedure of the Association of Official Agricultural Chemists (1). Samples of approximately 1 k g . of whole fruit were hand-peeled with a Devault peeler and the parings were digested as directed (1 29.60). Samples, with no selenium on or i n the fruit, were prepared for analysis and known quantities of selenium were added. These were analyzed b y the above noted methods. The quantity of selenium recovered and the percentage recovery are presented i n Table I . 7


Table I.

Recovery of Selenium Added to Apple Parings

Added, 7

Recovered, 7

60 60 80 80 120 120 200 200

59.8 58.8 78.4 82.2 119.0 121.2 198.0 194.2

Recovery, % 99.6 98.0 98.0 102.8 99.7 101.0 99.0 99.4 Average recovery (8) 99.4 Range 98.0 to 102.8

Selenium in Unsprayed Fruit T o establish the level of selenium on and i n the peel of fruit not sprayed with selenium, samples were collected from thirty different commercial growers whose insect-control program contained no selenium sprays. Samples of approximately one-half box (0.5 bushel) were taken at random from incoming trucks at the fruit packing warehouses. Only fruit from growers whose spray programs were definitely known b y the field representatives of the warehouses were selected for sampling. T e n samples per variety, of Jonathan, Delicious, and Winesap from ten different growers, were taken for analysis. The half-box samples were taken to the laboratory and subsampled for analysis. A l l subsamples were properly labeled and stored at 32° F . for 3 to 4 months before being analyzed. The selenium residue on and i n the peel of the non-selenium-sprayed fruit is presented i n Table I I . Table II. Variety

0

Jonathan Delicious Winesap

Selenium Residue on and in Peel of Non-Selenium-Sprayed Fruit No. of Fruit per Sample

Total Weight of Fruit per Sample, Grams

Average Selenium b, P.P.M.

Selenium Range, P.P.M.

7 to 11 5 to 8 6 to 11

1000 to 1102 1020 to 1160 982 to 1112

0.001 0.0006 0.001

0.000 to 0.005 0.000 to 0.004 0.000 to 0.004

° 10 samples per variety analyzed in duplicate. b Whole fruit basis.

The samples reported i n Table I I carried a very low residue level of selenium on and in the peel. The average value of 0.001 p.p.m. for the thirty samples was less than the variation within varieties and less than the variation between duplicates. The selenium residue of 0.001 p.p.m., the average, can be considered as a possible trace of selenium on and i n the peel.

Selenium in Sprayed Fruit T o establish the level of selenium on and i n the peel of selenium-sprayed apples, samples were collected from five commercial Jonathan apple orchards and eight commercial Delicious apple orchards b y representatives of the packing warehouses and submitted to the laboratory for analysis. The sampling and analytical procedure used for these samples was identical to that used for the samples reported i n Table I I . Sufficient fruit was available for duplicate analysis of most of the samples. AGRICULTURAL CONTROL CHEMICALS Advances in Chemistry; American Chemical Society: Washington, DC, 1950.

110

ADVANCES IN CHEMISTRY SERIES

The results obtained from these samples and the dates of the selenium sprays are presented i n Table I I I . Table III.

Selenium Residue on and in Peel of Selenium-Sprayed Fruit

Sample Weight, Grams

No. of Fruit per Sample

1052 1002 1016 1039 924 1082 1010 1050 1090 1036

8 7 6 7 7 7 8 7 8 7

Selenium, P.P.M.«

Average Selenium, P.P.M.

Dates Selenium Sprays Applied b


Jonathan Apples 0.03 0.02 0.03 0.05 0.03 0.06 0.07 0.08 0.06 0.07

0.03

May 5

0.03

June 1

0.05

M a y 6 and June 18

0.07

M a y 5 and 28

0.06

M a y 6 and June 18

0.03

May 5

Delicious Apples 1004 1178 1102 1048 1070 1064 1058 1028 1072 1011 1062 1128 1090 1118 1022 1020 1072

8 6 6 9 9 7 7 5 5 7 8 6 6 6 6 6 6

0.03 0.03 0.04 0.04 0.02 0.05 0.07 0.09 0.03 0.11 0. 10 0.09 0.12 0.12 0.16 0.14 0.13 Av. (27) 0.07 Range 0 .02 to 0.16

0.04

M a y 28

0.03

M a y 5 and June 1

0.06

M a y 5 and June 28

0.06

M a y 5 and June 1 and 28

0.10

M a y 5 and July 9

0.11

May 13 and June 14

c

0.14

May 13 and June 14

c

° Whole fruit basis. b All spray programs consisted of 1 pint of Selocide plus D D T per 100 gallons. Sprays applied on June 14 had 1 quart of light grade petroleum oil per 100 gallons (California state specification). c

Statistical analysis of the data i n Table I I I shows the increase in selenium on and i n the peel, over the samples i n Table I I , to be highly significant. The amount required for significance at the 0.01 level was found to be 0.003 p.p.m. The selenium residue on and in the peel is roughly proportional to the number of applications and the length of time between spraying and harvesting. The addition of 1 quart of light grade petroleum oil significantly increased the selenium spray residue remaining on and i n the peel.

Effect of Variety and Location of Sample on Tree Single-tree plots of Jonathan, Delicious, and Winesap apples were sprayed on June 2 and 28 with 1 pint of Selocide and 1 pound of actual D D T per 100 gallons. Samples of one full box were selected from the north, south, east, and west sides and from the top of the tree to determine the effect of prevailing winds, amount of sunshine, etc., on the selenium residue. These samples were subsampled i n the laboratory, stored, and analyzed by the same procedure as the samples i n Table I I . The results are presented i n Table I V . Table IV.

Effect of Variety and Location of Sample on Tree

Variety"

No. of Fruit per Sample

Weight of Fruit per Sample, Grams

Jonathan Delicious Winesap

8 to 11 6 to 9 7 to 12

1016 to 1138 1006 to 1126 1000 to 1140

Av. Selenium Residue, P.P.M.6 0.16 0.12 0.11 Av. (30) 0.13 Range 0.06 to 0. 17

Range in Selenium Residue, P.P.M. 0.14 to 0.17 0.10 to 0.16 0.08 to 0.17

5 samples per variety analyzed in duplicate. b Whole fruit basis.

a


WALKER—SELENIUM RESIDUE ON AND IN THE PEEL OF WASHINGTON APPLES

111

Statistical analysis of the data i n Table I V shows the selenium residue on and i n the peel to be highly significant over the residue on and i n the peel of nonsprayed apples. There is no significant difference between varieties. Selenium residue is evenly distributed on the trees.

Acknowledgment Appreciation is expressed to the M c L a u g h l i n - G o r m l e y - K i n g Company for assistance in conducting this work.


Literature Cited (1) Assoc. Offic. Agr. Chemists, "Official and Tentative Methods of Analysis," 29.57, 1945. (2) Chilean Nitrate Educational Bureau, New York, "Bibliography of Literature on Minor Ele ments and Their Relationship to Plant and Animal Nutrition," 4th ed., Vol. 1, pp. 747-63, 1948. (3) Frear, D. Ε. H . , "Chemistry of Insecticides and Fungicides," 2nd ed., p. 49, New York, D . Van Nostrand Co., 1948. (4) Gnadinger, C. B., Ind. Eng. Chem., 25, 633 (1933). (5) Moore, J . , J. Econ. Entomol., 34, 116 (1941).


AGRICULTURAL CONTROL CHEMICALS

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