Document Qvw98LL1KoKn84kGqyoe1b55

INSECTICIDE VOLATILITY Codistillation of DDT with Water FRED ACREE, JR. Entomology Research Division, U. S. Department of Agriculture, Orlando, Fla. MORTON BEROZA Entomology Research Division, U. S. Department of Agriculture, Beltsville, Md. MALCOLM C. BOWMAN Entomology Research Division, U. S. Department of Agriculture, Orlando, Fla. 63-1 The codistillation rate of DDT with water from a placid surface in pg. of DDT per gram of water parallels concentration from 1 to at least 100 p.p.b. at 25, 30, and 35 C. At the highest concentrations tested in this study, the codistillation rate was as much as six times greater than that which would be anticipated on the basis of the Rassow-Schultzky equation. This finding is in line with DDT's great affinity for the air-water interface, which facilitates the high codistiflation rate. The significance of these results as related to the practical use of DDT is discussed. n investigation of the factors suspension in 24 hours, was believed to A responsible for the odd results be so great because the concentration of obtained with aqueous DDT suspensionsthe suspension was so extraordinarily in mosquito-larvae bioassays demon dilute and a minute loss was an appreci strated that DDT was heterogeneously able part of the whole; further, that the distributed in 10 p.p.b. (parts per high affinity of DDT for the periphery billion) aqueous suspensions and that of the liquid, specifically for the upper DDT codistilled with water, more than surface, facilitated its loss. (The term 50% of it being volatilized from a 10 `concentration" as here used means p.p.b. suspension in 24 hours 'at room the weight of DDT per unit weight temperature (3). Although these funda of suspension. This use of "concentra mental findings were unexpected, they tion" is unconventional since the DDT are consistent, at least qualitatively, is heterogeneously distributed, but no with the physico-chemical considera better term is available.) However, tions that one would expect to govern no one had determined by actual the volatilization rate of DDT with measurement what the loss of DDT from water. For example, it was possible to a placid surface would be when a determine quantitatively and with close series of its concentrations were exposed. precision the codistillation rate of DDT This paper reports on the results of with water at the boiling point of water. such experiments at 25, 30, and 35 C. However, the volatilization of DDT from a boiling, aqueous DDT suspension, which is being churned to uniformity, Experimental cannot be compared with that which Aqueous Dispersions. Appropriate takes place at ambient temperatures aliquots of acetone containing p,p'-DDT- from a placid surface. 4-C14 (2.1 nc. per mg.), kindly furnished It became of interest to the authors to by P. A. Dahm, of Iowa State College, determine this codistillation rate of DDT and used by authority of the U. S. with water (from water and acetone- Atomic Energy Commission, were added water suspensions) since in actual to pint glass jars. After the acetone practice DDT in the presence of evaporat was removed by evaporation, 250 ml. of ing water would generally be volatilized distilled water was added to each jar from a placid surface. This information giving a range ofconcentrations from 0.36 of the world's most widely used insecti to 81 p.p.b. The jars were sealed and cide may be of practical importance heated at 90 to 1006 C. with frequent and point the way to its more efficient shaking for 1 hour and then equilibrated utilization. It may also provide an in a water bath at 25, 30, or 35, insight into the mechanism of DDT's all 0.5 C. The jars were shaken disappearance from various media. vigorously, opened, weighed, and re On the basis of the authors' original turned to the water bath. After 24 experiments (3), a loss of DDT, amount hours, they were reweighed, and the ing to more than 50% from a 10 p.p.b. water lost by evaporation was calculated. The residual radioactivity was deter mined by the method described pre viously (3). Aqueous-Acetone Dispersions. Ace tone solutions (1.25 ml.) that con tained various quantities of p,^'-DDT (m.p., 106-107 C.) or of the C,4-DDT were added to separate pint jars con taining 250 ml. of distilled water.' The dispersions were stirred with a glass rod, weighed, and placed in a water bath at 25 C. for 24. hours.. Finally the jars were removed, re weighed, and the DDT remaining in each jar was analyzed either radiometrically or spectrophotometrically by the method already cited. Retuht The results of the experiments arc given in Table I. Figure 1 illustrates graphically how the rate of codistillation Gig. of DDT per gram of H2O, hereafter called the DDT codistillation rate) varies with the initial DDT concentra tion. Because the ranges covered by the two variables in Figure 1 are so great, the data are plotted on a log-w.-log basis. The straight lines obtained at three different temperatures with con centrations below 100 p.p.b. indicate that there is a direct relationship be tween initial DDT concentration and the DDT codistillation rate. The DDT codistillation rate is calcu lated from a 24-hour test period and is therefore an average value. The in stantaneous rate of loss necessarily must be much higher than the average rate being reported, especially since less than half of the DDT remained at the Reprinted from ACRICULTIIRAL AND FOOD CHEMISTRY, Vol. 11, No. 4, Page 278, July/August 1063 DSW 201476 STLCOPCB4059543 end of the test period in all instances. Were instantaneous rates available, they would probably be in line with first- order kinetics. The experiments were performed at different times, e.g., those at 25 C. at three different times, and differences in humidity and air movement un doubtedly account for the large variation in loss of water from these systems. However, as may be seen from Figure 1, the DDT codistiilation rate did not show much deviation from the straight line relationship below 100 p.p.b. in spite of the different water losses and the different times of test. * The accuracy of determining by spec- trophotometric analysis the amount of DDT lost from 300 to 1000 p.p.b. concen trations at 25 C. was subject to consider able error since the percentage of change in concentrations during the 24-hour in terval was small. When the average values for the DDT and water lost from these concentrations were substituted in the Rassow-Schultzky (7) equation to calculate the vapor pressure of DDT at 25 C., a value of 1.9 X 10~* mm. was obtained. This value is almost six times the 3.4 X 10"7 mm. reported by i: f l Table I. Volatilization of DDT from Aqueous Suspensions at 25, 30, and 35 C., and from Aqueous-Acetone Suspensions at 25 C. DDT UHhl Cones. tnmr of DDT, Initially, c r.u. *iG. DDT Recovered Aftnr 24 Hr., pG. DDT lest Oaring 24 Hr., MG., CoM. Wafer Latt Daring 24 Hr., Grams %DDT lost pG. DOT tori par Gram Water %DDT tori par Gram Water 25 1000 700 500 300 100 250 175 125 75 25 Ultraviolet Analyses* 232 18 151 24 104 21 58 17 12 13 12.6 12.2 12.7 12.5 12.6 7.2 13.7 16.8 22.7 52.0 1 .4 2 .0 1 .7 1 .4 1 .0 0.6 1.1 1.3 1.8 4.1 25 81 20.2 70* 17.5 58 14.4 35 8.7 12 3.0 8.0 2.0 6.0 1.5 3.6 0.89 3.2* 0.80 1.2 0.30 0.84 0.21 0.60 0.15 0.36 0.09 30 79 19.7 56 14.0 34 8.5 11.6 2.9 c 5.8 1.4 3.1 0.78 1.16 0.29 35 79 19.7 56 14.0 34 8.5 11.6 2.9 5.8 1.4 3.1 0.78 1.16 0.29 0.59 0.149 \ Aqueous-acetone suspensions. Radiometric Analyses 7.6 8.2 6.6 3.4 0.88 0.49 0.33 0.21 0.32 0.06 0.06 0.03 0.02 8.41 3.50 2.87 1.06 0.366 0.295 0.144 5.33 4.1 2.6 0.62 0.26 0.18 0.04 0.023 12.6 9.3 7.8 5.3 2.1 1.5 1.2 0.68 0.48 0.24 0.15 0.12 0.07 11.3 10.5 5.6 1.8 1.0 0.48 0.15 14.4 9.9 5.9 2.3 1.1 0.60 0.25 0.126 14.1 9.3 13.6 13.4 14.0 14.2 14.0 14.8 9.2 14.4 13.0 12.4 13.5 13.4 17.9 17.6 15.6 18.7 16.4 17.5 32.7 31.4 32.7 32.3 30.8 32.5 31.8 28.4 62.4 53.1 54.2 60.9 70.0 75.0 80.0 76.4 60.0 80.0 71.5 80.0 77.7 57.4 75.0 65.9 62.1 71.4 61.5 51.7 73.2 70.6 69.4 79.3 78.5 77.0 86.1 84.6 0.89 1.0 0.57 0.40 0.15 0.11 0.086 0.046 0.052 0.017 0.012 0.0096 0.0052 0.844 0.586 0.317 0.115 0.054 0.030 0.0086 0.440 0.315 0.180 0.071 0.036 0.018 0.008 0.001 4.4 5.7 4.0 4.5 5.0 5.3 5.7 5.2 6.5 5.6 5.5 6.5 5.8 4.27 4.2 3.7 4.0 3.8 3.75 2.95 2.24 2.25 2.14 2.45 2.55 2.37 2.71 2.96 i \- t h'<? V COM >> twf*\ Q \ i . |? > STLCOPCB4059544 Batson (/) for the vapor pressure ot DDT at 25 C. Data in the t p.p.b. range were col lected dose to the limit of measurement and will therefore l>c less acmrtue than the other radiometric analyses. The fact that some of the <lis|>erKioiis were aqueous-acetone seems to have had no great efTcct on the codistillation rate. Loss of weight from acetone-water suspensions was calculated as water loss, and a small error may be involved here. The authors' interest in the codistilla tion of DDT from aqueous-acetone dis persions stems from the use of this dis persion in bioassays on mosquito larvae. Aqueous-acetone is not normally used to apply DDT, and the data are there fore of academic rather than of prac tical interest Discussion If DDT behaves ideally in solution, the - codistillation rate ofDDTshould increase proportionately with its concentration up to its saturation point (Raoult's Law); above saturation the rate should remain constant because the undis solved DDT would be in the bulk of the liquid rather than on the upper surface, the only surface from which volatiliza tion can occur. But the authors' findings did not support the assumption that DDT behaves ideally since the codistillation rate of DDT with water proved to be roughly proportional to the DDT concentration up to about 100 p.p.b. This figure is far above the solubility value (saturation point) of 1.2 p.p.b., recently determined in this laboratory (2). For a logical explanation of these results, we must fall back on the demon strated heterogeneity cf DDT suspen sions and the particular affinity of DDT for the upper surface of the liquid. Since DDT accumulates on' the upper surface, from whence it can volatilize far more readily than if it were uniformly distributed in the aqueous dispersion, it follows from the colligative nature of vaporization from liquid systems that the codistillation rate should exceed that which may be calculated from the Rassow-Schultzky (6) equation. At the 100 p.p.b. level, the rate was almost three times greater than the calculated value; ` at the 300 to 1000 p.p.b. level, it was on the average almost six times greater. v However, the codistillation rates are still roughly in the same order of mag nitude as the value calculated from the equation and therefore not inconsistent with it. The extreme hydrophobic na ture of DDT, and its consequent hetero geneity in aqueous suspension, accounts for DDTs atypical behavior. The effect of temperature on the DDT codistillation rate is interesting. The amount of DDT codistilling per gram of water according to the RassowSchultzky (d) equation given below f^DOT Afprrr X Pprrr ~ M. X P. W -- wt. of distillate M -- molecular weight P -- vapor premure to -- water depends on the ratio of vapor pressure of DDT to that of water at the different temperatures. Substituting these values [Jddt from Balson (7)] in the equation, we obtain: at 25 C., 0.282 Mg. DDT/(,ram H,0 30 C., 0.465 /ig. DDT/gram H,0 35 a, 0.747/ig. DDT/gram H.O It appears from these figures that the codistillation rate of DDT should in crease almost three times when the temperature increases from 25 to 35 C. But the data show that the rate decreases in this temperature interval. A pos sible explanation for this anomaly is the greater thermal agitation of the water molecules and DDT*s increased solubility with increasing temperature. These effects would tend to diminish the accumulation of DDT at the airwater interface and thereby lessen the codistillation rate. At first, the authors had not considered these effects of in creased temperature. Although the codistillation rate of DDT decreased with increasing tempera ture between 25 and 35 C., the water loss increased (averaged 13.8 grams at 25, 16.7 at 30, and 31.6 at 35), and the net result was an increasing weight of DDT codistilling per 24-hour period with increasing temperatures. Practical Considerations ' The DDT-water codistillation phenom enon adds another dimension to the picture describing the loss of DDT from various media. For example, DDT ap plied to a wool garment will protect against insects for several years (5), but applied to livestock it will not pro tect more than several weeks (4). Although the insecticide on an animal is known to be absorbed, metabolized, stored, excreted, and otherwise dissi pated, some of the DDT undoubtedly volatilizes with water vapor emitted through the skin of the animal. For example, the water vapor lost from a lactating cow at 25 C. has been reported to be about 35 pounds per day per 1000 pounds of body weight (72), the greatest percentage of these losses occurring from the outer body surfaces (at least 80% at high temperatures). Similarly, soil is known to volatilize considerable quantities of water, and over a period of time the loss of DDT codistilling by this route may be considerable. These examples are indicative of how codistillation may operate, but they do not establish the role of codistillation losses in its proper perspective, and this should be done. Under precise con ditions, it is possible to predict the loss ot ~DT from a laboratory test container and qualitatively, at least, predict the effects of the loss in, let us say, a mosquitolarvae bioassay. The authors' colleagues at the Orlando, Fla., laboratory of this Division have amply demonstrated with biological tests the effects of DDT*s codistillation and heterogeneity in. suspension (7, 8, 10, 77). They have shown that these factors must be con sidered in bioassays with DDT. How ever, estimation of codistillation losses in a less controlled practical situation would undoubtedly be subject to much error. Such a situation is to be expected since dissipation of DDT or any insecti cide from soil, to cite a practical situ ation, is a complex problem and may be influenced by many variables, e.g., de composition, erosion, sorption (9), tem perature, rainfall, sun exposure, humidity, type of soil, as well as accompanying in gredients in the formulation applied. At our present stage of knowledge, each situation has to be studied individually to determine how great a part codistilla tion plays. The fact that we are aware of codistil lation will enable us to seek means to employ or avoid it in planning for the more efficient utilization of an insecti cide. For example, the long-chain alcohols, which act as water-evaporation retardants, may extend the effectiveness of DDT when codistillation of this in secticide occurs. In some applications, water can be excluded to avoid codis tillation. Another point worth con sidering with the persistent insecticides is that codistillation losses may be very small over a period of a day or two, yet over a period of months or years, they may become appreciable. literature Cited (1) Balson, E. W., Trans. Faraday Sac. 43, ' 54 (1947). (2) Bowman, M. C., Acree, F., Jr., Corbett, M. K., J. Aon. Food Chem. 8, 405 (1960). (3) Bowman, M. C., Acree, F., Jr., Schmidt, C. H., Beroza, M., J. Eton. Entomol. 52, 1038 (1959). (4) Eddy, G. W., Yearbook Agr., U. S. Dept. Agr. 1952, p. 657. (5) Laudani, H., U. S. Dept. Agr. Bur. Entomol. Plant Quarantine E-858, May 1953. (6) Rassow, B., Schultzky, H. S., Z. Angew. Chem. 44, 669 (1931). (7) Schmidt, C. H., Weidhaas, D. E., J. Eton. Entomol. 51, 640 (1958). (8) Ibid., 52, 977 (1959). (9) Weidhaas, D. E., Gahan, J. B., Ford, H. R., Florida Entomologist 42, No. 3,105 (1959). (10) Weidhaas, D. E., Schmidt, C. H., J. Eton. Entomol. 53, 106 (1960). (11) Weidhaas, D. E., Schmidt, C. H., Bowman, M. C., Ibid., 53,121 (1960). (12) Yeck, R. G., Stewart, R. E., Trans. ASAE 2, No. 1,71 (1959). Rtctioid for revitw August 2, 1902. Accepted Neoember 2, 1962. DSW 201478 j i1 t < j 280 AGRICULTURAL AND POOD CHEMISTRY i STLCOPCB4059545