467 



O'Kane (W.C), Hadley, Jiinr. (C. H.) & Osgood (W. A.). Arsenical 

 Residues after Spraying. — New Hampshire Agric. Exp. Sta., 

 Durham, N.H., Bull. no. 183, June 1917, 62 pp., 5 figs. [Received 

 24th August 1918.] 



This bulletin records experiments conducted from 1912 to 1916 

 in order to ascertain the amounts of arsenical residues remaining 

 on fruits and vegetables after spraying with lead arsenate, and the 

 toxic properties of the poison both with regard to persons and stock. 



The standard medicinal dose of arsenic is 2 to 5 milligrams. The 

 dangerous dose is quoted as 60 to 120 mg. ; there is, however, lack 

 of data for drawing comparison between the toxic properties of 

 arsenic referred to in Uterature and the possible properties of arsenic 

 in lead arsenate. Experiments detailed in this bulletin show that a 

 single apple might, under extraordinary conditions, retain the equiva- 

 lent of 4 mg.' of white arsenic. The condition of such an apple would 

 be obvious, and ordinary handling of the fruit would be certain to 

 remove an appreciable part of the residue, "o mg. being the maximum 

 amount of poison likely to be left on any one apple, taking 3 lb. lead 

 arsenate paste to 50 U.S. gals, water as the usual strength of the spray 

 used. It is believed therefore that under ordinary conditions no 

 apples will reach the consumer carrying such amounts of lead arsenate 

 that a healthy human adult can eat enough at one time to 

 cause fatal poisoning. The case of strawberries is rather different 

 as, owing to the nature of the fruit, larger amounts of the poison 

 might be retained and escape notice, and would be less likely to be 

 rubbed or washed off. The authors are therefore of opinion that 

 strawberries that are fully formed, or nearly so, should not be directly 

 sprayed with lead arsenate unless they are to be thoroughly cleansed 

 before using. For a similar reason, it is suggested that blackberries 

 should not be directly sprayed with lead arsenate after the berries 

 are formed, while currants, if so sprayed, should be well washed. 

 To cabbage or lettuce, ready for market, lead arsenate should be 

 applied only lightly and sparingly, and the outer leaves should be 

 removed and the heads washed before use. 



With regard to the effect upon live-stock of feeding upon sprayed 

 grass or upon grass growing beneath sprayed trees and receiving the 

 drips from the trees, experiments indicate that healthy calves may be 

 pastured for a time on grass carrying a considerable amount of 

 spray when the strength of solution used is 3 lb. lead arsenate paste 

 to 50 U.S. gals, water. When the concentration of spray material 

 is increased to 6 lb. of the paste to 50 U.S. gals, water, continued 

 feeding on such grass may result in definite and serious symptoms of 

 poisoning. With 10 lb. lead arsenate to 50 U.S. gals, water, serious 

 or fatal poisoning is likely to follow. The same results seem to 

 apply to sheep. To poultry the danger from lead arsenate poisoning 

 seems to be practically neglible, even if the concentration of the 

 spray material is as high as 10 lb. lead arsenate to 50 U.S. gals, 

 water. 



Experiments were carried out to test the possible danger that may 

 lie in feeding hve stock upon hay cut beneath trees that have been 

 sprayed. Sixteen days elapsed between the time when the spray 

 was applied and the time when the grass was cut and made into hay. 

 In this period there were heavy rains. Of samples analysed 3 months 



