Document mBK9KGN34ozLGaLQ6qvq3BMJ0

UNIVERSITY OF CALIFORNIA, RIVERSIDE B E R K E L E Y * D a VIS IR V IN E LOS A NGELES * RIV ERSIDE SAN DIF.CO SAN FR A N C ISC O | SANTA BARBARA S aNTa CBUZ COLLEGE OF NATURAL AND AGRICULTURAL SCIENCES CITRUS RESEARCH CF.NTFK AND AGRICULTURAL EXPERIMENT STATION DEPARTMENT OF SOIL AND ENVIRONMENTAL SCIENCES RIVERSIDE. CALIFORNIA 92521-042-1 September 25, 1984 Mr. Raymond A. Freeman Mr. Jerry M. Schroy MONSANTO COMPANY 800 N. Lindbergh Boulevard St. Louis, Missouri 63166 Dear Sirs: When Dr. Farmer returned from his meeting with you la s t week, he gave me a copy of several draft publications which you have w ritten concerning the mathematical simulation of dioxin v o la t iliz a t io n . I must confess that a ll of us (Spencer, Farmer and myself) were asto nished to find that a compound with the physical-chemical charac t e r is t ic s of dioxin would v o la t iliz e to the extent predicted in your model. We therefore undertook to check the model assumptions, equations, and also reran isothermal simulations on our screening models. I am afraid that I at least have become convinced that you have made a huge, error in the formulation of your equations, which has the e ffe c t of allowing the chemical to d iffu se in the vapor phase without a reduction in m obility due to adsorption. By sorting through your p u b lication s, I believe 1 have found the place in the derivation where th is error occurred. My lin e of reasoning is as follows: In the paper "Environmental m ob ility of dioxin" the Theory section begins on page 10 with a co n tin u ity equation for the gaseous con centration which is equivalent to the following: (1) which is ide n tical to your equation (1) where the expression for R in equation (2 ) is plugged into equation (1) and Ri is deleted as i t was in your paper. (conti nued) Raymo*'.:. n. Freeman Jerry K. Schroy i *- 2 September 25, 1. \.r ^` t i J l* ` " 1984 quantity in brackets represents the to ta l concentration of dioxin in ;s per volume of s o il. The equation states that the time rate of .nge of th is material is e n tire ly due to the gradient of the vapor ;x which is e s se n tia lly co rrect. There is a small error at th is point the formulation of the paper in that h is set equal to/'i/e and t is signed.a value of 2. If t is considered to be a tortuodit^ i t should iuce the available vapor space compared to a ir . In fa c t, we use the ;lington-Quirk model fo r the combined terms eh Dab (2) ere a is a ir content. This has the e ffe c t of reducing the gaseous ffusion c o e ffic ie n ts s ig n ific a n tly compared to it s value in free a ir , r t ic u la r ly when the s o il is moist. Your model, i f formulated with the rameter values that are indicated in the back of the paper, would - tu a lly increase th is over it s value in free space which is not --- _i meet. r If' wever, the p rin cip al error in the model formulation occurs when you c gin with a rate lim ited expression for the concentration of chemical the adsorbed phase 4 is ed n the rbon ch is is aper. y for a a we p i- , has e 4* r- ides d l t c d ' (Ca - K`Cd) (3) ere my parameters a and K' have replaced many of the symbols in your per. Although you do not state i t e x p lic it ly in your other paper, in e paper "Modeling the tranport of 2,3,7,8-TCDD.. you state at the ttom of page 5 that the vapor phase transport is so rapid that i t ways eq u ilib ra te s with the adsorbed phase from which you set equation ) equal to 0. However, th is is equivalent to the assumption that id hence, that (4) 3^d _ 1 9^a 3t r r " 3t (5) vjs, equation (1) should be modified by plugging in equation (5) and >t by dropping the term involving Cd. Thus, instead of the equation at ie bottom of page 5 of the second paper, the equation should read a , hDab 3zCa = n 32Ca 3t 1 + i y r ) 372 E 322 (6 ) and nd rom ic. p ii" .2 . ould ons 24 11. 66% fir s t l/cm2 i phys0-9 (conti nued) Mr. Raymond A. Freeman M r.Jerry Schroy Page A September 25, 1984 I don't- know the status of th is paper or of your work published in other areas. I do b elie v e , however, that the information ava ila b le for 'dioxin is so scarce that papers such as you have presented would have a s ig n i fic a n t influence on the thinking of s c ie n tis ts and n on -scien tists a lik e . I w ill be happy to ta lk with you in further d etail about t h is i f you are e ith e r uncertain about my reasoning or in disagreement with i t . 1 would hope that we could resolve th is before any mistaken information reaches the open lit e r a t u r e . Sincerely W illiam A. Jury Professor of Soil Physics W. F. Spencer W. J. Farmer