EFFECT OF SOIL APPLICATIONS OF INSECTICIDES 17 



lowed by amperometric titration of the chloride ion formed with 

 silver nitrate. 



Their analyses of samples taken on August 2, 1950, of soils re- 

 ceiving two treatments of toxaphene, showed 7.8 p.p.m. of organic 

 chlorine calculated as toxaphene, which was equivalent to 18 

 pounds of toxaphene per acre remaining in the soil to a depth of 8 

 inches. Similar analyses on September 1, 1951, of soils that had 

 received three applications of toxaphene showed 16.0 p.p.m. of 

 organic chlorine, equivalent to 37 pounds per acre of soil. 



Judging by these results, about 45 percent of the toxaphene 

 remained in the soil 10 months after the second application and 

 62 percent 10 months after the third application. 



Their analyses for toxaphene in vegetables showed that neither 

 the lima beans nor portions of the sweetpotatoes and potatoes 

 grown in 1951 contained significant amounts of toxaphene, the 

 maximum quantity being 0.3 p.p.m. found in a peel of sweet- 

 potatoes. 



Aldrin 



Analyses for insecticide residues in crops and soils from the 

 aldrin plots were made by the Julius Hyman Company, employing 

 the procedure described by Danish and Lidov (2). Analyses of 

 crops were made by the bioassay and colorimetric methods, and of 

 soils by the colorimetric method. 



The amount of aldrin present in dry lima beans of the 1949 crop, 

 as determined by the bioassay method, was below the sensitivity 

 of the method, 0.13 to 0.26 p.p.m. The amount present as deter- 

 mined by the colorimetric method was less than the 0.2 p.p.m. 

 that could be measured accurately. The amount of aldrin present 

 in the soil was found to be below the minimum detectable amount, 

 0.1 p.p.m., based on the 100-gram samples used. 



No surface residues of aldrin were found on either the water- 

 scrubbed or unwashed potatoes of the 1951 crop, nor were any 

 residues detected in the peeled potatoes. 



FLAVOR OF VEGETABLES 



The authors and others at the Ventura laboratory tasted coded 

 samples of the vegetables each year. In 1950 these tests indicated 

 that aldrin and possibly chlordane were causing off-flavor to po- 

 tatoes and tomatoes. Therefore, in 1951 samples of green lima 

 beans, tomatoes, and potatoes were submitted to the Western Re- 

 gional Research Laboratory of the Bureau of Agricultural and In- 

 dustrial Chemistry for tests by a panel of taste experts. For this 

 purpose random samples from the six replicate plots used for a 

 treatment were mixed and a composite taken. The samples were 

 taken when the crops were in the best marketable condition, 

 neither immature nor overripe. 



At the Western Regional Research Laboratory the samples of 

 each vegetable were served on 4 days to a panel of 10 to 13 selected 

 and trained tasters. They were told the nature of the experiment, 



