38 CIRCULAR 862, U. S. DEPARTMENT OF AGRICULTURE 



There is no sound evidence, as yet, that BHC from the soil is 

 taken up by the crop plant and translocated to stems, leaves, or 

 fruits above ground, thereby contaminating those parts and giving 

 them a bad flavor. It is well known, however, that applications to 

 above-ground parts of plants must be discontinued long before 

 harvest if fruit contamination is to be avoided. It is not recom- 

 mended for use on crops the leaves and stems of which are eaten. 



Other Substances Studied 



Too little information has been obtained in these particular 

 studies to warrant generalizations about chlordane and toxa- 

 phene. Fairly extensive new work has been established on these 

 and a number of other substances that should yield some valu- 

 able information within 2 or 3 years, but quick results are hardly 

 possible in studies of persistence. Since toxaphene has been 

 reported to be relatively unstable (40) and parathion is known 

 to be highly unstable, they are not expected to cause trouble by 

 accumulating as residues in the soil. 



The persistence of chlordane is not known definitely, but it 

 should probably be described as relatively persistent. 6 The de- 

 pressive effect of chlordane upon germination and stand appears 

 greater than that of DDT. Its toxicity to later growth appears, 

 in general, about the same as DDT, although some crops may 

 be more sensitive than to DDT, others less so. Until more can 

 be learned about chlordane it should be considered as having 

 potentialities for developing a toxic residue. 



CONCLUSIONS 



Agricultural chemicals that are to be applied to crops or soils 

 year after year should be either nontoxic to plants when mixed 

 in the soil or nonaccumulative in the soil. 



Persistent toxic substances that will accumulate in the soil 

 upon repeated use at short intervals should be replaced by non- 

 persistent or nontoxic substances. 



Pending the development of more definite information on the 

 accumulative effects of various new agricultural chemicals under 

 practical field use, such chemicals should be used only when others 

 are known to be ineffective. Dosages and frequency of applica- 

 tion should be kept strictly to the minimum recommended by 

 competent specialists. Improvising, improper use, and excessive 

 use by growers are to be firmly discouraged because they often 

 cause serious losses. 



Heavy annual use of DDT, technical BHC, and probably other 

 persistent chlorinated hydrocarbons appears to have definite dan- 

 ger of reducing within a comparatively few years the productivity 

 of soils to which they are applied. 



Research workers, in both public and private organizations, 

 should investigate the accumulative effects of the new agricul- 

 tural chemicals as extensively as possible in the immediate future 



6 W. E. Fleming and R. D. Chisholm, Bureau of Entomology and Plant 

 Quarantine, found 4 to 5% pounds of chlordane remaining in soil more than 

 a year after applying about 10 and 20 pounds per acre. Unpublished data. 



