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 J 
 
 Mareh 1945 E-643 
 
 United States Department of Agriculture 
 
 Agricultural Research Administration 
 
 Bureau of Entonclegy ' nd Plant tyrrantine 
 
 FORMULATION OF DDT SPRAYS AND DUSTSii/ 
 R. D. Chisholm, Division of Insecticide Investigations 
 
 In connection with the intensive studies of the insecticidal proper- 
 ties of DDT (l-trichloro-£,2-bis(p-chlorophenyl)ethane) , which have been 
 made by many workers, methods of formulation of sprays and dusts have 
 received much attention. Such experiments have been conducted largely 
 under laboratory and small field-plot conditions. 
 
 Chemically pure DDT melts at 108.5°-109 C. Two grades of commercial 
 product ere available, one known as "technical DDT" specified to have a 
 setting point not lower than 88°, and "DDT, purified," specified to have 
 a melting point of at least 103°. Tne former has found use in louse 
 po"/der, mosquito larvicide, and in general agricultural experimentation; 
 the latter is intended for use in aerosol bombs. 
 
 DDT has been used in water suspensions, solutions, emulsions, dusts, 
 and aerosols. The last-named have been discussed elsewhere, but the 
 formulation of the other types of mixtures is presented in this paper. 
 
 WATER SUSPENSIONS 
 
 Water suspensions are divided into three classes - those resulting 
 from the nixing of finely ground DDT (ground either dry or wet) with rater, 
 those resulting from the dilution with weter of a solution of DDT in a 
 water-miscible organic solvent, and those obtained by mixing diluents 
 impregnated or coated with DDT with water. 
 
 —'This paper rns rei.d at the joint meetings of the American Associ- 
 ation of Economic Entomologists and the Entomological Society of America 
 at New York, N. Y. , Dec. 13-14, 1944. Much of the information presented 
 •.'as obtained through correspondence with Stete experiment station inves- 
 tigators and from several Divisions of this Bureau. 
 
 APR 2 6 1945 
 
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 Since technical DDT softens considerably below 88°C, and is not 
 free flowing, it is necessary, wh^n dry-grinding this compound, to raix 
 it with a diluent such as calcite, talc, or pyrophyllite. Care must be 
 exercised during grinding to avoid overheating the mill. Mixtures con- 
 taining up to 50 percent of DDT nay be prepared in this way. Mixtures 
 of higher DDT content do not have desirable physical properties and are 
 extremely difficult to grind. 
 
 Several commercial products Containing various proportions of DDT, 
 wetting agent, and diluent have been tested. One containing 10 percent 
 of DDT has a surface mean particle diameter (determined by the air-perme- 
 ation method, which does not necessarily reflect the particle size of the 
 DDT) of 5 microns, as compared with 44 microns, the diameter of the 
 openings in a U. S. No. 3£5 sieve. Another mixture containing 50 percent 
 of DDT, which was micronized, had a surface mean particle diameter of 
 2.8 microns. Since DDT is known to be an effective contact insecticide, 
 the use of snail particles might be expected to rive a more uniform 
 distribution with a consequent improvement of insecticidal properties 
 with cert tin insects. This is borne out by the increase in efficiency 
 against larvae of the codling moth ( Oarpocapsa p ononelLa ±j.) when the 
 p^wticle size is 4 to 5 microns as compared with 8 to 9 microns. On the 
 o -her hand, DDT deposits on glass plates have been observed to decrease 
 in weight by an average of 5 to 10 percent during five successive 16-hour 
 ewncsures to direct sunlight. Since rate of loss is directly related tc 
 the area of the exposed surface, extremely fine particles with their 
 large specific areas may not be desirable if effectiveness over long 
 periods of time in direct sunlight is re -aired. 
 
 Mixtures containing as much as 10 percent of DDT with pyrophyllite 
 can be wetted with water and under some conditions used as sprays. For 
 general purposes, best results are obtained through the use of a surface- 
 active agent to provide uniform wetting and dispersion of the DDT and 
 adequate wetting of the sprayed surfaces without excessive run-off. 
 Mixtures have been prepared by incorporating the surface-active agent 
 before grinding. Y;hil© this method has certain advantages with reference 
 to ease of preparation, it has th«: disadvantage of making it impossible 
 to very the concentration of DDT without also changing the physical 
 properties of the spray mixture and thus affecting the quantity of DDT 
 deposited and the resistance of the residue to weathering. Since DDT 
 studies are largely in the preliminary stage, both variables should be 
 controlled by the investigator in order to insure a maximum of spray 
 deposit and of distribution on specific types of foliage. This can be 
 accomplished by the use of various amounts of surface-active agents. 
 
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 The follovdng netting and sticking agents have been used with DDT- 
 diluent mixtures: Soap powder, not to exc:ed 1 percent of the DDT; 
 several proprietary compounds^/ in amounts ragging from 0.1 to 0.5 per- 
 cent of the DDT; materials of the nature of fish glue at the rate of 
 1 ounce, disoolvcd in 1 pint of water, per pound of DDT; and soybean flour 
 et the rate of 1/2 pound per pound cf DDT. In order to insure complete 
 vetting of the DDT and to eliminate agglomerates, it is best to prepare 
 a paste from the DDT-diluent mixture, the wetting agent, and enough water 
 (about 1 1/2 pints per pound of mixture) to give a fairly heavy paste. 
 This paste may be further diluted and added to the spray tank. 
 
 Several spray mixtures have been used Y/hich contain oil emulsions 
 and DDT. Since DDT is preferentially wetted by oil, it is important to 
 use the proper ratio of oil to DDT. If a large proportion of a quick - 
 breaking emulsion is used, oil-coated DDT may collect on the surface of 
 the spray mixture in curdy masses. One method of overcoming this diffi- 
 culty consists in diluting the emulsion with a glue solution before adding 
 the DDT. A formula consisting of 2 pounds of a 50:50 mixture of DDT and 
 pyrcphyllite or calcite, 1 ^uart of summer oil emulsion, 1 pint of fish- 
 gOue solution (prepared at the rate of 1 pound of semiliquid glue per 
 gaJJ.on of water), and 100 gallons of rater has been found to be satis- 
 i- jtcry. The concentration of the fish-glue solution may be reduced to 
 3/4 pound per gallon of water. 
 
 '.'jet grinding is conducted in the usual manner in a ball mill. A 
 wetting agent in the proportions previously mentioned in connection with 
 
 dry-ground mixtures may be added previous to grinding. Mixtures prepared 
 in this way have been reported to produce heavy spray deposits. They 
 have the disadvantage common to paste products in that they tend to 
 separate during storage. 
 
 DDT may be dissolved in water-miscible solvents such as methyl, 
 ethyl, and isopropyl alcohols and acetone. When these solutions are 
 poured into water, the DDT is thrown out of solution. The DDT dispersed 
 from 1.5-pcrcent solutions in the alcohols is finely divided and may be 
 kept in suspension with moderate agitation. That dispersed from acetone 
 solutions forms a gummy mass at first but later becomes crystalline. 
 
 2/These compounds include Orvus-v»'A (sodium salt of louryl sulfate), 
 Gardinol-ViiA (sodium salt of lauryl sulfate), Vataol OS (sodium salt of 
 an alicyl napthalenesulfonic acid), Tween 20 (a modified sorbitan mono- 
 laurate), Aresket ( sodium monosulfonate of monobutyldiphenyl) , and 
 Ultrawet (water-soluble sodium sulfonate of pctrc ~-um hydrocarbons). 
 
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 This objectionable feature nay be overcome by adding a surface-active 
 agent to the solution before nixing with water. One of the formulas used 
 consists of 24 grams of DDT, 24 grans of Triton X-100 (polyethylene glycol 
 phenylisooctyl ether), and acetone to make 100 ml., which is equivalent 
 to 2 pounds of DDT per gallon of solution. On addition to v:ater the DDT 
 is dispersed as droplets of the gummy material mentioned above, which 
 becomes crystalline and settles out in this form on standing. The extent 
 to v;hich the DDT is dispersed and the time required for crystallization 
 and settling to take place are influenced by the proportion of surface- 
 active agent in the acetone solution. Since this preparation is unstable, 
 it should be used shortly after mixing and with moderate agitation, 
 
 SOLUTIONS 
 
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 Solutions of DDT in organic solvents have been used for spraying 
 the interiors of barns for the control of flies and for impregnating 
 fabrics for the control of clothes moths. From 1 to 5 grams of DDT per 
 100 ml. of a petroleum fraction has been used for the first purpose, 
 and a 1 percent solution of DDT in a volatile solvent such as xylene or 
 acetone for the second. The solvent and concentration of DDT selected 
 depend upon the insect to be controlled. Since technical DDT often 
 contains sone insoluble material-, it may be necessary to filter the 
 solution before use. 
 
 EMULSIONS 
 
 Emulsions of solutions of DDT in various solvents which are either 
 substantially insoluble in water or only slightly soluble have been used 
 by several investigators . In order to avoid precipitation, water-mi scible 
 solvents should not be used for this purpose. For the sane reason, if 
 the solvent is appreciably soluble in water, allowance should be made 
 for this when diluting such emulsions. For example, emulsions of DDT- 
 ethylene dichloride solutions have been used, but in some cases enough 
 precipitate was deposited in the tank to clog the serpen. To overcome 
 this difficulty it would be necessary to adjust the concentrations of 
 both materials in the emulsion to provide for enough ethylene dichloride 
 to saturate the water plus the amount required to keep the DDT in solution, 
 
 Consideration should be given to the proportions and types of 
 emulsifiers used. Since DDT is effective against many insects on contact, 
 large proportions of the emulsifier may result in inferior control due 
 to the coating of the DDT deposit by the emulsifier upon evaporation of 
 the water and solvent. For this reason and also to prevent excessive 
 run-off, it appears desirable to use only enough emulsifier to produce 
 an emulsion which on dilution gives a spray with proper wetting qualities. 
 
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 Some investigators have reported that emulsions are more effective for 
 certain insects than suspensions, others have suggested that costs are 
 excessive, and others have encountered difficulties as mentioned above. 
 
 Two types of emulsions have been used (1) those in which the DDT is 
 dissolved in a volatile solvent, such as xylene, and (2) those in which 
 the DDT is dissolved in a relatively nonvolatile solvent, such as petro- 
 leum oil. With the first type DDT crystals are distributed on the sprayed 
 surface upon evaporation of the solvent, and v:ith the second type the 
 sprayed surface is coated ttith the solution on evaporation of the water. 
 
 Two formulas of the first typt- are as follows: (1) DDT 24 grams, 
 Triton B-1956 {a phthalio glycerol alkyl resin) 3 grams, xylene to make 
 100 ml. (£•) DDT 24 -grams, Nacconal NRSF (sodium alkyl aryl sulfonate) 12 
 grams, Butyl Cellosolve (butyl ether of ethylene glycol) 10 ml., xylene 
 to make 100 ml. These stock mixtures contain DDT at the rate of 2 pounds 
 per gallon. They are best diluted to form emulsions by being added to 1 
 or 2 volumes of water, vigorously agitated, and then diluted with the 
 remainder of the water. 
 
 An example of the second t3T?e is DDT 3 grams, mineral oil 75 ml., 
 Gardinol-WA 1 gram, and water 25 ml, The DET is dissolved in the oil, 
 and this solution is emulsified on addition to a solution of the Gardinol- 
 WA in the water stirring the mixture vigorously meanwhile. The volume of 
 the product varies with the amount of air incorporated during emulsification. 
 If the weight of DDT per gallon of spray mixture is to be controlled 
 exactly, the dosage, should be calculated on the basis of the volume of 
 the product. The original proportions are equivalent to approximately 
 1/4 pound of DDT per gallon of emulsion. The solubility of DDT in 100 ml. 
 of mineral oil at r,7-30°C. (80-86°F.) ranges from 4 grams for Deobasc 
 (refined kerosene) to 10 grams for No. 2 fuel oil. Solubility in specific 
 types or grades of oil at the minimum temperature to be encountered should 
 be determined prior to emulsification. Emulsions of this type should be 
 used soon after preparation. 
 
 Solvents other than those mentioned above, alone or in mixtures, as 
 well as different proportions of the same or other surface-active agents, 
 may be more desirable for the preparation of emulsions to be used for 
 specific purposes. It is suggested that preliminary batches of spray 
 mixtures be prepared and the physical properties observed before tests 
 are made with insects. 
 
 DUSTS 
 
 Dust mixtures have, in general , been prepared by mixing diluents, 
 such as pyrophyllite, talc, and walnut-shell flour, with finely ground 
 DDT mixtures. Dusts containing as much as 10 percent of DDT are 
 
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 sufficiently free- flowing for certain dusting purposes. On the other hand, 
 dusts containing from 1 to 3 percent have better physical properties and 
 have given good results. If the dust is prepared from a 50:50 mixture,. 
 care is required to obtain uniform distribution, as this mixture has a 
 tendency to agglomerate in an ordinary dry mixer. Uniformity might be 
 accomplished by passing it through a hammer mill or brushing through a 
 series cf screens. 
 
 Diluents such as pyrophyllite, talc, or walnut- shell flour may be 
 coated or impregnated with DDT by dissolving it in a volatile solvent 
 such as benzene or acetone, wetting the diluent with .the solution, allow- 
 ing the solvent to evaporate, and grinding the product. Fairly large 
 batches may be prepared by spreading the diluent on a clean, hard surface 
 and applying the DDT solution in successive portions from a sprinkling 
 can. The mass should be remixed with a shovel after each sprinkling and 
 then at intervals until all the solvent has evaporated. Only enough 
 solvent should be used to dampen the diluent uniformly. Trial batches 
 using the solvent without DDT will establish the proper proportions. 
 The product should be ground to eliminate coarse agglomerates. A hammer 
 mill is preferable for this purpose. Products containing more than 10 
 percent of DDT are liable to be difficult to grind. 
 
 Another method of impregnation used consisted in dissolving 2 pounds 
 of DDT 1 in 3 pounds of Velsicol AR-50 (alkylated naphthalenes) and impreg- 
 nating 45 pounds of Pyrax ABB (pyrophyllite) with this solution in a 
 ball mill. The resulting mixture was then added to another 50 pounds of 
 Pyrax ABB and run through a brush mixer. 
 
 COMPATIBILITY 
 
 The compatibility of DDT with other insecticides, fungicides, and 
 accessory materials has been studied from both the chemical and biological 
 viewpoints. While DDT is a rather stable compound by itself, in alcoholic 
 solution it readily reacts with alkalies with the loss of 1 mole of 
 hydrochloric acid per mole of DDT and the formation of l-dichloro-2,2-bis 
 (p-chloroph~nyl) ethylene. This compound, which is comparatively inert 
 as on insecticide, is also formed at temperatures above the melting point 
 of DDT in the presence of certain catalysts. Of the compounds which may 
 be present in small amounts in accessory materials, iron and iron oxides, 
 chromium, and anhydrous ferric, aluminum, and chromic chlorides are known 
 to be active in this respect. Of this group the anhydrous chlorides arc 
 the most active. Ferric and chromic chlorides may be formed by the action 
 of DDT on the metals themselves. Accessory materials such as kaolin, 
 fuller's earth, bentonite, and some samples of talc and Pyrax ABB have 
 shown definite catalytic activity. Other samples of talc and Pyrax ABB, 
 as well as calcium oxide and hydrated lime, are substantially inactive. 
 
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 Commercial grades of sodium fluoride, sodium fluosilicate , cryolite, 
 paris green, calcium arsenate, and lead arsenate showed no catalytic action. 
 With bordeaux mixture 0.04 mole, and with sulfur 0.07 mole of hydrochlorio 
 acid -.vers obtained per mole of DDT. Pure nicotine, in common with 
 strrr^'iy basi? nix rog^r -bearing compounds, reacts with DDI in the same 
 manner as do alcoholic caustics. 
 
 Most of the solvents u^ed with DDT tend to inhibit catalytic 
 deftoffposition. The notable exceptions are n€.pthalene and "/he nitro- and 
 chioro-b'enzenes. With o-dichlorobenzene the oatttlyJic ";n:.ou of ferric 
 chlor,.ne on DDT was shovm to occur at rocrr. t« speratuies lefcroleum frac- 
 soybvian oil, cyelohexanone, xylene, and Vslsiool AR-60 (alkylated 
 lone) either completely or substantially inh.ibit the catalytic 
 reaction of anhydrous ferric chloride. 
 
 Vihile it has been shewn that many compounds acting as catalysts at 
 high temperatures will decompose DDT, it is possible that under field 
 co .f.itions decomposition may net take place or that tie reaction may be 
 bo slow as tc have little influence on insecticidal value of DDT. 
 Apparently, however, spray mixtures containing only ooiELCunds v.'hich do 
 
 decompose DDT or v.'hich act as inhibitors in the ] a'e^ratory would be 
 i :t efficient under field conditions. Tests to dexcrr.ne the importance 
 cf these reactions under field conditions would be in order. 
 
 Biolc gical tests have been made to determine the effectiveness of 
 ^p-ays containing DDT and other materials such as bordeaux mixture, sulfur, 
 oi". .mulsions, Fermate (ferric dimethyl dithiocarbamate) , and various 
 ec .•■•- ssory materials. These sprays have been used successfully with no 
 try to foli are except in a few cases where repeated applications were 
 a. The addition of lime-sulfur, bordeaux mixture, and sulfur has been 
 ad to reduce the period of effectiveness. Whether this was due to 
 decomposition to insecticidally inert compounds, or to the physical masking 
 of the DDT in the deposits has not been established. Since DDT is a 
 
 %ct poison and its deposits are not permanent in direct sunlight, it 
 is suggested that, in addition to normal mechanical loss, part of the 
 decreased insecticidal value may be due tc the loss of DDT from the surface 
 of mixed deposits and the masking of the remainder within the deposits. 
 Faiural constituents, such as apple wax, may also influence insecticidal 
 value. 
 
 DESIRABILITY OF A CQLI'ON STANDARD OF COMPARISON 
 
 Considerable variation has been found in the results obtained With 
 DDT in different parts of the country even when used to combat the same 
 insect species. It is therefore very desirrbl? to include in each set of 
 tests against a given insect, material from a common source of the same 
 formulation. In this way part of the variation in results v.ould be 
 eliminated or could be more readily interpreted. 
 
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