Apple trees were sprayed with commercial formulations of the organochlorine pesticides aldrin, endrin, dieldrin, endosulfan, gamma‐BHC, DDT and TDE. Samples of leaves were taken at approximately fortnightly intervals up to three months and examined for the presence of both the unchanged pesticides and their conversion products. Deposits resulting from the application of emulsifiable concentrates were more persistent than those from the same pesticides applied as dispersible powders. The dieldrin and DDT emulsifiable concentrates gave the most persistent deposits, residues taking eleven weeks to fall to below 5% of the initial deposits. Only aldrin, dieldrin and endosulfan gave significant amounts of ultraviolet irradiation products. Details are given of the experimental work undertaken on the characterisation of two previously unknown conversion products, both of which are of similar toxicity to, but more persistent than their respective parent compounds.

A simple dimethylformamide partition method is described for the clean-up of animal fat samples and of certain dairy products for the analysis of chlorinated pesticide residues. Supplementary column chromatography is necessary for some samples. The purified extracts can be examined quantitatively by gas chromatography with an electron-capture detector. The extracts are often suitable for qualitative examination by paper chromatography as further evidence of the identity of individual residues. Practical methods are given for the clean-up of mutton, beef and human fats; muscle tissue, liver, kidney and brain; milk, butter, eggs; and fleece and flour.THE acetonehexane partition clean-up method described by Goodwin, Goulden and Reynolds for plant tissue extractsf and extended by Taylor to extracts of certain animal tissues2 is not in general suitable for the examination of animal fats. Goodwin, Goulden and Reynolds,3 have also described the application of a similar technique to pig fat and blood. However, acetone is a poor solvent for animal fats, and its use sets a limit to the range of animal tissue samples that can be handled successfully. The original partition technique of Jones and Riddick4 used acetonitrile (methyl cyanide) as the polar organic solvent. In their method, fat containing the residue of a chlorinated pesticide is dissolved in hexane (or a suitable light-petroleum fraction), the solution is shaken with acetonitrile, and the acetonitrile phase is separated and shaken with water; the resultant one-phase system is then extracted with hexane, and the aqueous acetonitrile phase is discarded. Most of the original fat has been removed in the initial hexane phase, and the pesticide residue is contained in the second hexane phase. If this method is used, it is important to ascertain that the partition coefficients are favourable for each of the pesticides and to adjust the volumes of the various solvents accordingly ; departure from the appropriate conditions must be avoided. The disadvantages of the process are the toxic nature of the solvent, its relatively high cost, the interference that it causes in the operation of the electron-capture detector in gas chromatography and, for certain residues, a relatively poor efficiency of the separation process. Burchfield and Storrs6 showed, for yBHC and pp'-DDT, that dimethylformamide (DMF) can be used as an alternative to acetonitrile in the partition clean-up process. Other workers have used dimethyl-sulphoxide6; both this and sulpholane (tetrahydrothiophen-1 ,l-dioxide'), which has been briefly investigated in the present work, are regarded as too expensive for routine use and are, in any event, unpleasant to use. Sulpholane (m.p. 27" to 28" C) gives considerable emulsion trouble in the extraction process, and, when used without purification, gives an unacceptable degree of interference with the gas-chromatographic responses. Haenni, Howard and Joe6 compared the partitioning of polynuclear hydrocarbons from waxes, between hexane and the four separate polar sol...

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