Environ. Scl. Technol. 1993, 27, 1517-1523
Correlation Between C-6/C-14 Chlorinated Hydrocarbons Levels in the Vegetation and in the Boundary Layer of the Troposphere Marco Moroslnl, Jorn Schreltmuller, Ulrlch Reuter, and Karlheinz Ballschmlter’ Department of Analytical and Environmental Chemistry, University of Ulm, Albert Einstein Allee 11, D-89069 Ulm, Germany
The concentration of 12 semivolatile organochlorine compounds-SOC-[hexachlorobenzene, a-hexachlorocyclohexane, 7-hexachlorocyclohexane, 4,4’-DDT, 4,4’DDE, and 7 polychlorinated biphenyl congeners (PCB 28 (2,4,4’-C&B),PCB 52 (2,2’,5,5’-CldB), PCB 101(2,2’,4,5,5’C15B), PCB 118 (2,3’,4,4’,5-C15B),PCB 138 (2,2’,3,4,4’,5’C@),PCB 153 (2,2’,4,4’,5,5’-C@),PCB 180 (2,2’,3,4,4’,5,5’C17B)l-has been measured in moss, lichen, and foliage samples collected near Ulm (south Germany). These values are compared with air measurements reported for the same region. The bioconcentration factors vegetation/ air (BCF) obtained in this way are compared with those reported from both environmental and laboratory studies. Some of the latter are used to calculate mean concentrations of SOC in air which are in agreement with direct air measurements. 1. Introduction
Many semivolatile, nonpolar, low degradable organochlorine compounds (SOC) are known global contaminants. Hexachlorobenzene (HCB), polychlorinated biphenyls (PCB), hexachlorocyclohexanes (HCH), and DDT/DDE have been detected in air, water, vegetation, and fauna of the most pristine regions (1-12). The basics of the global distribution of organics in the global scale have recently been reviewed (13-17). As for any chemical, the environmental distribution of SOC in the regional and global mass flow is regulated by their physicochemical properties (see Table I). Chemical stability, vapor pressure, lipophility, and water solubility account for the rates of deposition and of remobilization from the earth surface and for their accumulation in water, soils, sediments, and biomass. Air plays a central role in the fast transport of SOC on aregional and global scale. The input into the atmosphere depends on direct (use, leakage, waste) and indirect (revolatilization from soil, water, biomass) sources. The mobility of organics in the atmosphere is regulated by the ratio between particle-bounded and nonparticle-bounded molecules; this ratio increases with the surface to volume ratio of the particles, with decreasing vapor pressure of the substances, and with decreasing temperature, as parametrized by the equations of Junge (18) and of Yamasaki (19). The output from the atmosphere is regulated by wet and dry depositions of gases and particles (physical output) and by degradation processes (chemical output) (16, 20). The aim of this study is to verify if a limited number of vegetation samples of different species enable the calculation of long-term mean tropospheric concentrations of SOC within an acceptable range. Bioconcentration factors (leaf/air BCF) reported for environmental conditions are compared with those measured in greenhouse experiments. The greenhouse BCF and an equation based on physicochemical properties are used to calculate 0013-936X/93/0927-1517$04.00/0
0 1993 American Chemical Society
tropospheric mean concentrations of SOC in Ulm on the basis of their levels in the vegetation. Calculated air concentrations are compared with directly measured ones.
2. Experimental Section Samples of vegetation were collected in February 1990 in two forests near Ulm, a German town 100 km north of the central Alps. Site A is the forest of Oberer Eselsberg, elevation 600 m, 3 km north of Ulm (48.2O N, 10.OoE); site B is in a rural area near the forest of Berghulen, elevation 610 m, 15 km northwest of Ulm. Five samples of the following species were chosen: lichen (Parrnelia sulcata), whole thallus; moss (Hypnumcupressiforme),green parts; beech (Fugussiluatica),dry leaves on the branches; spruce (Picea abies), needles. The collection sites are in the middle of the forest, the place is wind-sheltered, and the soil is covered with forest litter. Beech leaves and pine needles were taken from the branches. The samples were treated and analyzed as shown in Table I1 (21,22). 3. Results Table I11 summarizes the concentrations of hexachlorobenzene (HCB), a-and y-hexachlorocyclohexane(HCH), 4,4’-DDT, 4,4’-DDE, polychlorinated biphenyl congeners PCB 28 (2,4,4’-C13B), PCB 52 (2,2’,5,5’-C14B), PCB 101 (2,2’,4,5,5’-C&B), PCB 118 (2,3’,4,4’,5-C15B), PCB 138
(2,2’,3,4,4’,5’-CkB),PCB153 (2,2’,4,4’,5,5’-C@),andPCB 180 (2,2’,3,4,4’,5,5’-Cl~B)in the vegetation of the region of Ulm. Examples of HRGC-ECD chromatograms of air and of vegetation samples are presented in Figures 1-4. Quantification of the 12 compounds was done with HRGCECD by external calibration. 4. Discussion Airborne semivolatile compounds can reach the earth surface in the followingways: (1)adsorbed on dryparticles, (2) adsorbed on particles included in the precipitations, (3) dissolved in precipitation, (4) by gas diffusion, or (5) per biomass deposition. The proportion among these mechanisms depends on the physicochemical properties of the substance, the meteorological conditions, and the properties of the receiving surface. The global land surface, excluding Antarctica, amounts to 130 X 106 km2 of which 71 X lo6 km2 are covered with vegetation (23). A mean leaf area index (LAI) of 5 m2 of leaf/m2of land (one side area) gives a global foliage surface of 710 X lo6km2in interaction with the lower troposphere. In the scavenging of SOC from the atmosphere, the vegetation plays an active role, complementary to that of wet and dry depositions. Taking the reported global mean concentrations of SOC in the troposphere and in the foliage (12, 24) and comparing the load of the troposphere (5.6 X l O l 8 m3) with that of the foliar biomass (47 X 109 tons dry wt), the estimable foliage/troposphere ratio of the global burden of SOC is 0.02-0.08 for HCB, 0.2-0.8 for Environ. Sci. Technoi., Vol. 27, No. 8. 1993
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Table I. Physicochemical Properties of Some Semivolatile Organochlorine Compounds MW
mp ("(2)
sWster(L)
temperature references HCB a-HCH Y-HCH 4,4'-DDT 4,4'-DDE PCB 28 (2,4,4') PCB 52 (2,2',5,5') PCB 101 (2,2',4,5,5') PCB 118 (2,3',4,4',5) PCB 138 (2,2',3,4,4',5') PCB 153 (2,2',4,4',5,5') PCB 180 (2,2',3,4,4',5,5')
(m0i/m3)
20 "C b 1.9 x 10-2 8.4 X 10-2 1.9 x 10-1 6.5 X 106 6.3 X 10-4 7.9 x 10-4 d 8.1 X 10dd 1.2 x l e d 4.7 x 1o-B d 4.8 X 1o-B 2.4 X 1O-a 7.9 x 10-7 d
P(L)(Pa) 25 "C
20 "C
c
c
Kaw'
Kow
25 OC b 284.8 230 1.9 x 10-2 3.2 X le2 1.0 x 106 290.8 158 8.3 X 3.6 X 10-4 6.3 x 103 290.8 113 3.2 X 8.3 X 1od 6.3 X 109 1.7 X 10-4 7.1 X 10-4 1.0 x 106 354.0 109 319.0 88.5 1.7 X 10-9 3.1 X 10-9 5.0 X 106 257.5 57 3.2 X e 7.9 x 10-9 f 3.15 X los 292.0 87 2.0 x 10-2 e 8.0 X 10-9 f 6.3 X lo6 326.4 77 4.0 X 10-3 e 3.7 x 10-9 f 2.5 X 10" 326.4 105 1.1 x lwe 1.6 X 10-9 f 4.0 X lo6 360.9 79 4.9 x 10-4e 8.4 X 10-4 f 5.0 X lo6 360.9 103 7.2 X 10-4 e 9.3 x 10-4 f 6.3 X 10" 395.3 109 1.2 x 10-4 e 4.0 X 1 P f 1.6 x 107 d Knw(aidwater): derivated from refs 24 and 57, through K,, = H/RT, where H is the Henry's law constant (Pa m3/mol);R is the gas constant, 8.314 Pa m3/mol K and T i s the temperature (K).PCB numbers as suggested by Ballschmiter and Zell (53). P(L)(Pa) = subcooled liquid vapor pressure (25 "C). S(L)(mol/ms) = subcooled liquid water solubility (20 "C). Ref 58. Ref 24. Refs 59 and 60. e Ref 61. f Ref 57. Ref 62. f
f
Table 11. Sample Treatment and Analysis Collection and Storage aluminum foil: stored 1 week at -20 "C Drying and Homogenizing 48 h at 40 "C; weight loss 70 % ; residual water 5 % ; grinding 1 min in a Retsch mill; particle diameter 0.5 mm Extraction and Cleanup 5-g sample extracted with Soxhlet in 100 mL of n-hexane (18 h) 15 mL of sulfuric acid, 9 5 9 7 % cleanup evaporation of n-hexane phase to 1 mL elution of extract on a Florisil column (1.5 g, 2% water); elution with 50 mL of n-hexane evaporation to 1 mL
(1) (2) (3) (4) (5)
Fractionation' 50 mL of n-hexane dichloromethane (9:1, v:v) fraction 1 fraction 2 HCB,4,4'-DDE,PCB HCH,4,4'-DDT 30 mL of n-hexane
evaporation to 0.2 mL with isooctane as keeper (1) (2)
Separation high-resolutioncapillary gas chromatography (HRGC), chromatomaDh HP 5890: column A, HP SE54 50 m, 0.20 mm
