Persistence and Metabolism of Chlorodioxins in Soils Philip C. Kearney,' Edwin A. Woolson, and Charles P. Ellington, Jr. Agricultural Environmental Quality Institute, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Md. 20705
The persistence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)was determined in Hagerstown and Lakeland (Md.) soils receiving 1, 10, or 100 ppm TCDD after 20, 40, 80, 160, and 350 days. After one year, 56 and 63 of the originally applied TCDD was recovered in the Hagerstown and Lakeland soils, respectively. Neither 2,7-dichlorodibenzo-p-dioxin (DCDD)nor TCDD could be detected in soils receiving 10, 100, and 1000 ppm of the 2,4-dichlorophenol or 2,4,5-trichlorophenol after 70 days. A polar metabolite of D C D D - ' ~ ~ was detected by thin-layer chromatography in the ethanol soil extract. TCDD is degraded slowly in soils, and TCDD and DCDD are not biosynthesized by microbial condensation reactions.
R
ecently, the chlorodioxins have been the subject of intensive investigation, owing to the disclosure that the highly toxic 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD)appeared in some samples of the herbicide 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as an impurity. Woolson et al. (1972) examined 129 phenolic-derived pesticides for dioxins by electron-capture gas chromatography. TCDD was found in 23 of the 42 samples of 2,4,5-T, and the concentration ranged from 10 ppm. Several papers have appeared on the environmental behavior of TCDD. Helling (1971) examined the mobili(DCDD) and ties of two dioxins, 2,7-dichlorodibenzo-p-dioxin TCDD, in five soils using the soil thin-layer chromatographic technique. Both dioxins were immobile in all soils and consequently would tend to remain on or near the soil surface. Isensee and Jones (1971) examined the uptake of DCDD and TCDD from Lakeland, Md. sandy loam by soybeans and oats. Plants accumulated very small quantities of dioxins, and no residues were detected in mature oat grain or in soybeans. The photodecomposition of chlorinated dioxins was investigated by Crosby et al. (1971). TCDD was rapidly degraded by irradiation. The reaction proceeded by dechlorination in methanol to form 2,3,7-trichlorodibenzo-p-dioxin, DCDD, and nonchlorinated dioxins. Plimmer and Klingebiel (1971) could find no evidence for dichlorodioxin formation in riboflavinphotosensitized oxidation of 2,4-dichlorophenol. The objectives of the soil persistence experiments were to learn the effect of soil type and concentration on the rate of TCDD degradation, to isolate and characterize the degradation products from TCDD and DCDD, and to determine whether TCDD or DCDD could arise from microbial condensation of chlorophenols in the soil environment.
and, therefore, is low in microbial activity. The Hagerstown soil is finer textured, relatively high in organic matter, and, consequently, supports a higher microbial population. These soils are used routinely in most of our persistence and metabolism studies because of their well-defined properties and diverse nature. Concentration rates of 1, 10, and 100 ppm of unlabeled TCDD were established in both soils and sampled after 20, 40, 80,160, and 350 days. A benzene solution of TCDD was added to 100 grams of soil, allowed to dry, and then thoroughly mixed. Lower application rates of 1.78, 3.56, and 17.8 ppm of the 'Glabeled TCDD (specific activity 2.80 &i/mg) were also established in these same soils. In addition, the metabolism of the 2,7-dichlorodibenzo-p-dioxin(DCDD)-l4c applied at 0.7, 1.4, and 7.0 ppm was examined in these soils. The soils were maintained at or near field capacity by periodic additions of water and incubated at 28-30OC. At each sampling date, a known fraction of the TcDD-treated soils was extracted with a mixture of hexane-acetone (1:l v/v) and examined by electron-capture gas chromatography after an appropriate cleanup procedure. The cleanup and detection procedures and glc conditions were essentially those described by Woolson et al. (1972). The labeled DCDD-treated soil was extracted successively with 1 :1 hexane-acetone, ethanol, and hexane; the latter after adding concd H2S04to the soil. Each fraction was assayed for 14Cby liquid scintillation counting. Initially, 4C02 evolution from the labeled dioxins was monitored on a weekly basis. All labeled soils were extracted after one year. For total 14C recovery from soils, 100-mg samples were combusted in duplicate, and I4CO2was swept with an O2 stream and trapped in 10 ml of 2-methoxyethanol and monoethanolamine (7:l v/v). A 5-ml aliquot of the CO, trapping solution was added to 10 ml of scintillation solution (PPO and POPOP in toluene) for measuring radioactivity. Extreme care was exercised in all manipulations with TCDD, due to its extreme toxicity. All glassware and solutions receiving low concentrations were irradiated with a uv light source and the glassware stored in a chromic acid bath for several days. All other glassware, including beakers, volumetric flasks, and pipettes were disposed of by the radiological decontamination team at the Plant Industry Station.
Table I. Soil Properties of Lakeland Loamy Sand and Hagerstown Silty Clay Loam Used in the TCDD Persistence Studies CEC,*
Experimental
Soils used in our investigations were Hagerstown, Md. silty clay loam and Lakeland loamy sand. Their properties are shown in Table I. The Lakeland sand is low in organic matter
Clay,
PH
z
OM,^
z
mes/ 1mg
6.4
12.0
0.9
3.0
6.8
39.5
2.5
14.7
Soil
Lakeland loamy sand Hagerstown silty clay loam
organic matter content. CEC, cation exchange capacity.
a OM,
To whom correspondence should be addressed. Volume 6, Number 12, November 1972 1017
Table 11. Recovery of TCDD from Two Soils at Three Concentrations Over a Period of 350 Days
Applied concn, Soil Lakeland Hagerstown Lakeland Hagerstown Lakeland Hagerstown
PPrn 1
1 10 10 100
100
of TCDD recovered after 20
days 94 79 80 85 95 107
40
days 81 77 80 88
80
days 81 69 80 82
92
86
116
92
160
days 80 83 79 85 73 75
350 days
54
54 57 63 56 71
W E E.K S
Figure 1. I4CO2evolution from 2,7-DCDD when applied to Lakeland and Hagerstown soil at 0.7 ppm
Table 111. Recovery of I4C from Soils One Year After Receiving 1.78, 3.56, and 17.8 ppm TCDD-14C
Applied
Recovery"
TCDD
Soil Lakeland loamy sand
Hagerstown silty clay loam 4
concn,
9
8
Cornbus- Hexane-
PPm
1.78 3.56 17.8 1.78 3.56 17.8
tion 67 70 73 52 52
89
acetone Ethanol 47 3 54 3 48 5 43 3 35 4 48 2
CI
07 0
LAKELAND
0 6 X
-5
E4
"3 2
% Recovery is based on '4C content at time zero.
1 0 WEEKS
Results and Discussion Persistence of TCDD in Soil. The amount of TCDD in the soil extracts from application rates of 1, 10, and 100 ppm after 20, 40, 80, 160, and 350 days as measured by electron-capture gas chromatography is shown in Table 11. Recovery studies at time zero and on several subsequent dates, as measured by combustion of 4C-~c~D-treatedsoils and compared to extraction with hexane-acetone, revealed that about 85 of the applied TCDD was recovered by solvent extraction. Soil type did not appear to have any effect on TCDD residues. Concentration had no effect on persistence in Lakeland loamy sand. Each increase in TCDD concentration resulted in progressively larger residues in Hagerstown silty clay loam on most sampling dates. After one year, the amount of 14C-TCDD recovered in soils receiving 1.78, 3.56, and 17.8 ppm is shown in Table 111. It is apparent that some fraction of the TCDD and/or its metabolites is not extracted with the hexane-acetone solution. Ethanol failed to remove significant amounts of 14Cafter the initial hexane-acetone extraction. Hexane extraction of H2S04treated soil failed to remove any further 14C.Data contained in Tables I1 and 111 suggest that TCDD appears to be a fairly persistent material in soils when compared to other organic compounds applied at similar concentrations. This observation is not inconsistent with its known physical properties, since it is a lipophilic, insoluble (0.2 ppb in water) substance that has no readily metabolizable groups. Metabolism of DCDD and TCDD in Soils. The evolution of 14C02from DCDD at various concentrations is shown in Figures 1-3. There was a measurable evolution of 14C02from DCDD, although no apparent trend is evident from the concentration series. The amounts of I4CO2evolved during the first 10 weeks of the study were small and amounted to about 5 of the added radioactivity. Since the same amount of I4C was added to all soils, the rate of I4COPevolution appeared
z
z
1018 Environmental Science & Technology
Figure 2. 14C02evolution from 2,7-DCDD when applied to Lakeland and Hagerstown soil at 1.4 ppm
2.5 A
g 2.0
-
0
x 1.5 CI
1.0 0
0.5 n
"
I 2
3 4 5 6 7 8 9 IO WEEKS
Figure 3. W02evolution from 2,7-DCDD when applied to Lakeland and Hagerstown soil at 7.0 ppm
to be rate dependent with maximum evolution at the 1.4-ppm treatment. Less 14C02may have been generated at the 7-ppm rate because of the toxicity of DCDD which could adversely affect the microbial population. In contrast, little measurable 14C02was detected from T C D D - ~at~any C concentration. However, the loss of total 14Cfrom the systems can only be explained by l4CO2evolution or by volatilization of TCDD or a metabolite. Isensee and Jones (1971) showed that TCDD was not volatilized from a glass surface. Since TCDD may be steam distilled, loss from the soils may be due to volatilization by the same mechanism as DDT. Extracts of the DcDD-treated soil were reduced in volume
with a gentle N2 stream and examined for products by twodimensional thin-layer chromatography (tlc) using acetonitrile as the first solvent and benzene as the second. The ethanol soil extract was found to contain one or more products in addition to DCDD. The major metabolite was less mobile than DCDD in both solvents and appeared to be more polar than DCDD. The metabolite was eluted from silica gel and methylated with diazomethane. The methylated metabolite was rechromatographed in benzene on tlc and migrated to R, 0.80.9, suggesting a polar group on the metabolitz. Attempts to obtain a mass spectrum of the metabolite have been unsuccessful. No metabolites were found for TCDD in treated soil after one year. Biosynthesis of TCDD and DCDD in Soils. To determine whether TCDD or DCDD could be formed in vivo by microbial condensation reactions. 2,4-dichlorophenol and 2,4,5-trichlorophenol were incubated in the Lakeland and Hagerstown soils at 10, 100, and 1000 ppm for 70 days. Condensation reactions are rare in soils; nevertheless, Bartha and Pramer (1967) showed that at high concentrations of 3,4-dichloroaniline, the 3,3 ',4,4'-tetrachloroazobenzene can be formed in soils. In contrast, no evidence for in vivo formation of TCDD or DCDD was found in either soil at any concentration of the chlorinated phenols. This is an important finding, since biosynthetic production from chlorinated phenols or herbicide metabolites would be impossible to regulate under environmental conditions, while the inherent dioxin content in commercial pesticides can be lowered by changes in the manufacturing process. Results in Tables I1 and I11 suggest that TCDD is relatively persistent, when compared to other organic substances, in soils at the concentrations examined. Isensee and Jones (1971) pointed out, however, that TCDD at 1 ppm in soils is many thousand times greater than the amount that could result from normal application of the herbicide 2,4,5-T. For example, a
2.24 kg/ha application of 2,4,5-T containing 1 ppm TCDD would contain 2.2 mg TcDD/ha (or 0.9 mg/acre). Incorporation of the above 2.24 kg/ha (or 2 lb/acre) of 2,4,5-T into the surface soil layer (15 cm) would result in a TCDD concentration as great as the soil concentration of 1 ppm TCDD used at the lowest rate in the present experiments. Consequently the residue picture under actual field conditions is difficult to determine from the data presented in Tables I1 and 111. The concentrations initially selected for these experiments were based on the following factors: the rate of degradation of chlorodioxins in soils was unknown, consequently a number of concentrations were desirable, should the process be rapid; the highest concentration would produce major metabolites in sufficient quantities to isolate; and early analytical and cleanup work indicated that quantities less than 1 ppm might be difficult to detect. However, subsequent research improved techniques for the detection of low levels of TCDD in soils. Acknowledgment
The author would like to thank Dow Chemical Co. for samples of 1 4 C - and ~ ~ l4C ~ - ~~ c oAlbert ~, L. Pohland and David Firestone for standard samples of reference dioxins, and Peter D. J. Ensor for his help in performing the analysis. Literature Cited
Bartha, R., Pramer, D., Science, 156, 1617 (1967). Crosby, D. C., Wong, A . S., Plimmer, J. R., Woolson, E. A . , ibid., 173, 748 (1971). Helling, C. S.,SoiZSci.'Soc. Amer. Proc., 35, 737 (1971). Isensee, A. R., Jones, G. E., J . Agr. Food Chem., 19, 1210 (1971). Plimmer, J. R., Klingebiel, U. I., Science, 174, 407 (1971). Woolson, E. A., Thomas, R. F., Ensor, P. D . J., J . Agr. Food Chem., 20,351 (1972). Receicedfor review January 12, 1972. Accepted August 17, 1972
National Air Surveillance Cascade Impactor Network. I. Size Distribution Measurements of Suspended Particulate Matter in Air Robert E. Lee, Jr.' and Stephen Goranson U. S. Environmental Protection Agency, National Environmental Research Center, Research Triangle Park, N.C. 2771 1
C
haracterization of suspended particulate pollutants in ambient air is usually limited to estimating the quantity of total suspended particulate matter (pg of particulate/m of air), and determining the gross concentrations of a number of chemical components. The National Air Surveillance Networks (NASN) of the U.S. Environmental Protection Agency (EPA) operate a nationwide network of high volume (Hi-Vol) air samplers; particulate matter is collected on glass fiber filters for a 24-hr period, followed by gravimetric and chemical analyses. Although these measurements can give some indication of the general pollution level in an area, they do not provide information concerning the size distribution of total suspended particulate matter.
Since the degree of respiratory penetration and retention is a direct function of aerodynamic particle size, knowledge of the particle size distribution of suspended particulate matter is essential to assess the inhalation health hazard (Morrow, 1964). The particle size as well as the concentration and composition of aerosol constituents determines the extent of visibility reduction (Middleton, 1952), particle-particle and particle-gas interactions, soiling, deterioration of materials, and a wide range of atmospheric phenomena. Furthermore, the particle size of suspended particulate matter is important
To whom correspondence should be addressed. Volume 6, Number 12, November 1972 1019
