emissions from the bags, as stated earlier, consisted mostly of less reactive compounds that did not produce high levels of ozone. The reactivity of hexafluoropropylene was not tested. However, it should be low since halogenation decreases both the photooxidation and ozonolysis rates of ethylene (8, 9). Another possible contributing factor is that there may not have been sufficient NO, to drive the photochemical production of ozone. The NO, remaining after 300 min of irradiation in the low-concentration propylene-NO, system was 20 ppb. However, the peroxyacetyl nitrate (PAN) at this time was 2 1 ppb. Thus, practically all of the NO, was in fact tied up as PAN. (NO2 was measured as NO by thermal degradation of NOz. This procedure also measured PAN as NOz, as PAN was also thermally degraded.) This would suggest that, even if the emissions from the Teflon were reactive, there was insufficient NO2 to produce a significant amount of ozone. With prolonged irradiation, NO2 would probably build up slightly through PAN decomposition. Ozone would possibly then build up because of the bag emissions. However, experiments were not performed to test this hypothesis. Conclusions Wall-contamination problems raise serious questions as to the utility of Teflon-film smog chambers in determining reactivities of hydrocarbons (IO). These studies performed with a fast-reactivity hydrocarbon such as propylene suggest that bag outgassing is not important. With very low-reactivity hydrocarbons (and organic compounds), the reactivity parameters obtained from these smog chambers are of questionable value. Plastic smog chambers are not reliable for use in multiday irradiations when low levels of pollutants are present. The use of large outdoor Teflon smog chambers may minimize the contamination problem because of their high S/V ratio. However, contamination effects are not easily tested in
such chambers since leaks are almost always present. Thus, contamination from ambient air can also occur. Heat treatment of Teflon FEP film was effective in reducing outgassing contamination. Air samples stored in treated containers appeared to be free of severe contamination, a t least for short periods. The heat-treatment process, however, weakened the sealing properties of the film, resulting in frequent bag failure. Acknowledgment Special gratitude is expressed to Dr. Marcia C. Dodge for performing the modeling exercises included in this investigation. Literature Cited (1) Seila, R. L.; Lonneman, W. A.; Meeks,
S.A. J . Enuiron. Sci.
Health, Part A 1976,11, 121-30. (2) Lonneman, W. A. “Ozone and Hydrocarbon Measurements in Recent, Oxidant Transport Studies”; Proceedings of the International Conference on Photochemical Oxidant Pollution and Its Control; EPA-600/3-77-001a; U S . Environmental Protection Agency: Research Triangle Park, NC, 1977; p p 211-23. (3) Lonneman, W. A.; Kopczynski, S.L.; Darley, P. E.; Sutterfield, F. D. Enuiron. Sci. Technol. 1974,8, 229-36. (4) E. I. Du Pont de Nemours and Co. Inc., Wilmington, DE, Technical Information Bulletin, T-3E. (5) Ribbans, R., Du Pont de Nemours and Co., Inc., Wilmington, DE, personal communication, 1977. (6) Arnts, R. R.; Gay, B. W. Research Triangle Park, NC, 1979, U.S. Environmental Protection Agency Report EPA-600/3-79-081. (7) Whitten, G. Z.; Killus, 3.P.; Hogo, H. Research Triangle Park, NC, 1980, U.S. Environmental Protection Agency Final Report EPA-600/3-80-028a, Vol. 1. (8)Gay, B. W.; Hanst, P. L.; Bufalini, 3.J.; Noonan, R. C. Enuiron. Sci. Technol. 1976,10, 58-67. (9) Williamson, D. C.; Cvetanovic, R. J. J . Am. Chem. SOC.1968,9, 4248-52. (10) Bufalini, J. J.; Walter, T. A.; Bufalini, M. M. Enuiron. Sci. Technol. 1977,fl, 1181-5.
Received for review M a y 19,1980. Accepted October 10,1980.
Possible Clay Concentration Effects on Soluble Phosphate Contents of Runoff Everett M. White Plant Science Department, South Dakota State University, Brookings, South Dakota 57007
Different amounts of clay (montmorillonite, bentonite, kaolinite, illite, or pyrophyllite) were equilibrated with different concentrations of P (PO,-P) to evaluate whether changing clay concentrations could alter the soluble P concentration in runoff. Bentonite and montmorillonite had decreasing P sorption as the clay concentration increased above 1.5 g/50 mL if exchangeable cations were mainly Na but not if they were mainly polyvalent cations. Na-rich highexchange-capacity clays in runoff would sorb P if precipitation dilutes runoff or release it if water evaporates. Thus, P transport processes in runoff could be different with montmorillonitic Na-rich soils and mine spoils than those for runoff from most landscaDes. Introduction The ratio of sediment to solution can change rapidly in runoff water flowing over a soil and subsequently into a stream or lake. Sediment in runoff is sorted during transport so that the average particle size usually decreases with distance. This sediment transports much of the potentially active P(P04) as adsorbed anions on the mineral surfaces. The effect of 0013-936X/81/0915-0103$01.OO/O
@ 1981 American Chemical Society
sediment concentration on the solution P-sorbed P equilibrium apparently has not been studied for different kinds of clay minerals. The equilibrium was studied at several clay concentrations with some of the more common clay minerals to determine whether P transport processes were affected by clay kind or concentrations in runoff. Literature Review Sorption studies have been used to evaluate the solid phase-solution equilibria for many soils and sediments. At high P concentrations, sorption may be limited by the repulsive forces of sorbed phosphate anions on a mineral such as gibbsite unless the negative charges from P anions or those causing cation exchange of the clay are neutralized by a cation. Ca cations neutralize the charges more effectively than Mg, K, or Na ( I ) . In natural soils, a neutral salt may displace exchangeable Ca into the solution to react with sorbed P and increase sorption. In some cases, P sorption may remove surface cations and free negative charges in the mineral surface ( 2 )which may reduce the total P sorption if the unneutralized negative charge of the mineral is very high. Barrow and Shaw ( 3 )suggested that desorption of previously sorbed Volume 15, Number 1, January 1981 103
Table 1. Phosphorus Sorbed by Different Amounts of Bentonite from 50 mL of 5.1- or 52.1-ppm P04-P Solutions P sorbed, pg bentonite Wt
5.1 -ppm soin
52.1-ppm soin
0.25 0.50
51 156
55 150
1.oo 1.50
181 187
665 1090 800
2.00
182
2.50
121
405
3.00
113
485
P was slower from soils when cations which balanced the charge of the adsorbed P were close to the mineral surface. Thus, desorption was fastest with Na, intermediate for Mg, and slowest with Ca in the equilibrating solution. Ryden and Syers ( 4 )reported that P adsorption increased with increasing ionic strength and that Ca and Na influenced sorption during the first 40 h but not at infinity. However, Singh and Tabatabai (5) concluded that 0.01 M CaC12 added to an aqueous equilibrating solution reduced the adsorption of P. An increase in Ca increased adsorption of P in a study by Barrow (6).Na in comparison to Ca is less likely to cause tactoid (quasi-crystal) formation in a clay soil and is more likely to cause a large solution clay interface. Exchangeable Ca in tactoids is concentrated more than Na in the interplanar surfaces where it neutralizes the negative clay charges that repel P anions from the clay surface. Methods
Samples of clay, ranging from 0.25 to 6 g, were equilibrated for 17 h (overnight) on a reciprocating shaker with 50 mL of
ca. 0,5,10,15,20,25,or 52 ppm P as monocalcium phosphate in 0.01 M CaCl2 regardless of the kind of clay or its exchangeable cations. Equilibrated samples were centrifuged and the supernatants filtered (Whatman No. 5). Initial and equilibrated P concentrations were determined by the ascorbic acid method (7), and adsorbed P was calculated from the difference of the two. The pHs of the filtered equilibrated solutions were determined by the routine glass-electrode method. Montmorillonite (Wards No. 26), kaolinite (Wards No. 4), pyrophyllite (Wards No. 49), illite (Wards No. 38), and bentonite (Sargent-Welch 325 mesh) were studied. Bulk clay samples, except for bentonite, were ground a few seconds in a micromill, screened (
