Document KG0r3ZYZgzZKqm8mbakxZ4k00

RELATIONSHIP BETWEEN CONCENTRATIONS OF PCDDS, PCDFS AND DIOXINLIKE PCBS IN VEGETATION AND SOIL ON RESIDENTIAL PROPERTIES Demond A1, Towey T2, Knutson K3, Hong B3, Adriaens P1, Chang S-C4, Chen Q5, Franzblau A3, Garabrant D3, Gillespie B5, Lepkowski J6, Luksemburg W7, Maier M7 1Department of Civil and Environmental Engineering, University of Michigan College of Engineering, Ann Arbor, MI 48109; 2LimnoTech, Ann Arbor, MI 48108; 3Department of Environmental Health Sciences, University of Michigan School of Public Health, Ann Arbor, MI 48109; 4Department of Environmental Engineering, National Chung Hsing University, Taichung 402, Taiwan; 5Department of Biostatistics, University of Michigan School of Public Health, Ann Arbor, MI 48109; 6Institute for Social Research, University of Michigan, Ann Arbor, Michigan 48109; 7Vista Analytical Laboratory, El Dorado Hills, California 95762 Introduction The University of Michigan Dioxin Exposure Study (UMDES) was undertaken in response to concerns among the population of Midland and Saginaw Counties in Michigan, USA, that the discharge of dioxin-like compounds from the Dow Chemical Company facilities in Midland, Michigan, USA, had resulted in contamination of soils in the Tittabawassee River flood plain and areas of the City of Midland, leading to an increase in residents' body burdens of dioxin-like compounds. To analyze the relationship between soil contamination and residents' body burden, soil samples were taken from residential properties in Midland, Saginaw and Bay Counties (Michigan, USA), and in Jackson and Calhoun Counties (Michigan, USA), located about 180 km to the southwest, as a comparison. A total of about 2081 soil samples from 766 residential properties were analyzed for the World Health Organization (WHO) 29 PCDD, PCDF and dioxin-like PCB congeners. Even if soil contact had not resulted in exposure for the residents of this area, there may have been exposure through the vegetation. Consequently, 579 vegetation samples obtained from a subset of the 766 properties were also analyzed for the same congeners. The transport of dioxin-like compounds into vegetation from contaminated soil can occur through a variety of mechanisms: adsorption onto the root surface; root uptake and transport into the plant shoot; volatilization from the soil surface and adsorption onto the plant surface; and contamination of the plant's foliage by soil1. It appears that volatilization and adsorption may be a major transport pathway in greenhouses, but in the field, this mechanism is of minor importance2,3. Similarly, root uptake and transport into the plant shoot may be important in some circumstances, notably in the cases of zucchini and pumpkin2, but in the case of most plants, this is not a significant mechanism4. Based on the similarities between the congener pattern in plant material and that in the atmosphere5 and the fact that partitioning between the atmosphere and plants, like corn for example, is a function of the saturated vapor pressure6, the deduction is that adsorption from the gas phase is the key process for the contamination of vegetation by the lower chlorinated (tetra-hexa) PCDD and PCDFs7. As such, the contamination of the plant material shows little correspondence to the contamination in the soil8, with the vegetation showing a higher abundance of lower chlorinated congeners9. Yet, in laboratory experiments, the experimental plants were often watered from below7,10, rather than above, as in natural precipitation. Furthermore, in field surveys, the contaminants often entered the environment via the atmosphere such as from incinerators8, and not via flooding as in the Tittabawassee River floodplain. Thus, contamination of foliage by soil particles cannot be ruled out for grass around people's residences, for example. In fact, models based on atmospheric deposition have been noted to underpredict the concentrations of PCDDs and PCDFs in grass11,12 whereas they work well for fresh fruit and above-ground green vegetables11. Materials and Methods Vegetative samples were collected concurrently with soil samples from properties selected from five areas designated as Floodplain (located in the 100-year FEMA [Federal Emergency Management Agency] floodplain of Organohalogen Compounds, Volume 70 (2008) page 001032 the Tittabawassee River or answering yes to the question, "Has your property ever been flooded by the Tittabawassee River?"), Near Floodplain (located in a census block that contained a portion of the 100-year FEMA floodplain), Plume (located downwind of the Dow Chemical facility in the City of Midland), Other Midland/Saginaw (located in Midland, Saginaw or Bay Counties, but outside the above areas) and Jackson/Calhoun (located in Jackson or Calhoun Counties). Up to four sampling stations were located around the perimeter of the house. If there were soil contact activities, samples were also taken at those locations (maximum of two), usually a vegetable garden and/or a flower garden. For properties located in the Tittabawassee River floodplain, one additional station near the river was sampled. Thus, there were a maximum of seven sampling stations at each residence: 4 house perimeter, 2 soil contact and 1 near river. Individual soil cores were composited as described elsewhere13. Ultimately, each residence yielded all or some of the following composite samples: house perimeter set 0-1 inch composite (HP 0-1 inch); house perimeter set 1-6 inch composite (HP 1-6 inch); soil contact set 0-6 inch composite (Garden); near river set 0-1 inch composite (NR 0-1 inch); and near river set 1-6 inch composite (NR 1-6 inch). Approximately 500 mL of vegetation, typically grass, was collected from each house perimeter sampling station and placed in Ziploc bag. Approximately 1000 mL of vegetation were collected from the near river and soil contact stations, to ensure sufficient sample mass. Vegetation was rarely procured from the soil contact (Garden) stations. Only a small fraction of the field sampling occurred during the time frame during which garden vegetation was available. Furthermore, a decision was made not to seek permission to sample landscaping. Thus, most of the vegetative samples consisted of weeds and grass. The vegetation was cut just above ground level. Any soil clods attached to the vegetation were removed during compositing, but no washing occurred. The samples were composited by set (HP, Garden, NR) using a balance to ensure approximately equal masses from each station. The proportionate aliquots were then mixed by tossing in stainless steel bowls. Both soil and vegetation samples were shipped to Vista Analytical Laboratory (El Dorado Hills, CA) where they were analyzed by high-resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) using US Environmental Protection Agency (EPA) methods 829014 and 166815 for the 29 PCDF, PCDD, dioxin-like PCB congeners listed by WHO. If the concentration of a particular congener was below the limit of detection, the concentration was recorded as the limit of detection divided by 2 16. To analyze the relationship between the contamination in the soil and in the vegetation, linear regression was carried out using SAS statistical software (version 9.1; SAS Institute, Cary, NC), employing the concentrations in the various soil composites, information drawn from the UMDES questionnaire, such as property use (e.g., use of weed killers, trash or yard waste burning), information drawn from field notes (e.g., sampling season), as well as weather information (e.g., elapsed time since last rain) as predictor variables. These analyses were performed to predict the TEQDFP-2005 (based on the 29 congeners listed by WHO and the 2005 TEFs17) of the vegetation as well as to predict the concentrations of 2,3,7,8-TCDD, the top contributor to the TEQ in the Plume; 2,3,4,7,8-PeCDF, the top contributor to the TEQ in the Floodplain; and PCB 126, the top contributor to the TEQ in Jackson/Calhoun13. Results and Discussion The average, median, 75th percentile, 95th percentile and range of TEQDFP-2005 for the soil HP 0-1 inch composites and the vegetation HP composites are shown in Tables 1 and 2, respectively. The mean TEQ for the HP 0-1 inch soil composites was 56.5 pg/g in the Floodplain and 109.2 pg/g in the Plume, the two areas known to be contaminated, whereas the mean TEQ for the HP vegetation composites was 14.2 pg/g and 37.5 pg/g for the same areas. These data show that the mean TEQ in the vegetative samples is 0.25 and 0.34 of that in the soil for these areas. These ratios roughly correspond to that of 0.27 reported by Meneses et al. (based on I-TEQ) for grass and weeds12. Figure 1 shows the profiles for the Floodplain HP 0-1 inch soil composites and the Floodplain HP vegetation composites. A comparison of these profiles shows that they are similar, with the top contributor to the TEQ in both instances being 2,3,4,7,8-PeCDF. Thus, this figure does not show the discrepancy often cited between soil and vegetation profiles8,9. The similarity of the profiles is supported by the results of the linear regression, in that the greatest amount of the variance of the vegetation congener concentration is explained by that in the soil. Based on these results, it is Organohalogen Compounds, Volume 70 (2008) page 001033 inferred that the primary mechanism for the transport of these compounds into the grass samples was by deposition of soil particles; the same conclusion was reached by Hulster and Marschner1 for hay samples. Thus, on grassy residential properties, the possibility of soil particle deposition as the primary means of contamination of vegetation by dioxin-like compounds should be taken into account. Acknowledgements Financial support for this study comes from the Dow Chemical Company through an unrestricted grant to the University of Michigan. The University of Michigan has complete independence to design, carry out and report the results of the study. The authors are grateful to Drs. Linda Birnbaum, Paolo Boffetta, Ronald A. Hites, David Kleinbaum and Marie Haring Sweeney for their guidance as members of University of Michigan Dioxin Exposure Study (UMDES) Scientific Advisory Board. Opinions contained in this report are those of the authors and do not necessarily reflect those of the Dow Chemical Company or members of the UMDES Scientific Advisory Board. References 1Hulster A., Marschner, H. Chemosphere 27:439. 2Hulster A., Muller J., Marschner H. Environmental Science and Technology 1994; 28:1110. 3Trapp S., Matthies M. Environmental Science and Technology 1997; 31:71. 4Simonich S., Hites R. Environmental Science and Technology 1995; 29:2905. 5Lovett A., Foxall C., Creaser C., Chewe D. Chemosphere 1997; 34:1421. 6Wagrowski D., Hites R. Environmental Science and Technology 1998; 32:2389. 7Welsh-Pausch K., McLachlan M., Umlauf G. Environmental Science and Technology 1995; 29:1090. 8Schuhmacher M., Granero S., Rivera J., Muller L., Llobet J., Domingo, J. Chemosphere 2000; 40:593. 9Schuhmacher M., Nadal, M., Domingo J. Environmental Science and Technology 2004; 38:1960. 10McCrady J., Maggard S. Environmental Science and Technology 1993; 27:343. 11Eduljee G., Gair A. Science of the Total Environment 1996; 187:211. 12Meneses M., Schuhmacher M., Domingo J. Chemosphere 2002; 46:1393. 13Demond A., Adriaens P., Towey T., Chang S.-C., Hong B., Chen Q., et al. Environmental Science and Technology 2008; in press. 14EPA. Washington, DC:U.S. Environmental Protection Agency Office of Solid Waste and Emergency Response, 1994. 15EPA. Washington, DC:U.S. Environmental Protection Agency Office of Water, 1999. 16Hornung R. W. and Reed L. D. Applied Occupational and Environmental Hygiene 1994; 5:46. 17Van den Berg M., Birnbaum L., Denison M., De Vito M., Farland W., Feeley M. et al. Toxicological Sciences 2006; 93:223. Table 1. TEQDFP29-2005 of the Soil Composites (NR = near river; HP = house perimeter) Soil Composites TEQDFP29-2005 ( pg/g) Zone N Mean S.E. Median 75th%ile 95th%ile Min Max Floodplain HP 0-1 inch Near Floodplain HP 0-1 inch 203 56.5 9.7 164 52.0 36.7 11.4 3.9 35.4 223.1 1.1 1881.4 10.4 102.9 0.8 2299.8 Other M/S HP 0-1 inch 168 13.5 2.0 5.3 13.2 59.4 0.8 157.7 Plume HP 0-1 inch 37 109.2 31.0 Jackson/Calhoun HP 0-1 inch 194 6.9 0.8 58.2 3.6 111.9 7.6 257.2 22.6 6.3 745.5 0.4 186.2 Organohalogen Compounds, Volume 70 (2008) page 001034 Contribution to Total TEQ (%) Contribution to TotalTEQ (%) Table 2. TEQDFP29-2005 of the Vegetation Composites (NR = near river; HP = house perimeter) Vegetation Composites TEQDFP29-2005 (pg/g dry wt) Zone N Mean S.E. Median 75th%ile 95th%ile Min Max Floodplain HP Near Floodplain HP 188 14.2 3.4 69 376.6 354.1 3.4 3.3 7.4 50.2 0.4 1427.2 10.1 152.0 0.6 7994.9 Other M/S HP 71 4.2 0.4 3.3 5.1 10.1 1.0 27.5 Plume HP Jackson/Calhoun HP 361 37.5 12.7 18.3 52 4.5 0.6 3.3 31.1 125.4 0.8 268.9 6.7 8.7 0.6 25.9 Figure 1. Congener Contributions to TEQDFP29-2005 for Vegetation and Soil Composites from the Floodplain. The plus sign indicates the arithmetic mean. The horizontal line across the box indicates the 50th percentile (median), the lower and upper margins of the box indicate the 25th percentile and 75th percentile, respectively; the upper ticked line extends to the 99th percentile and the lower ticked line extends to the 1st percentile. The stars show the values above the 99th percentile and below the 1st percentile. s_reg ion 2008_83_F P 100100 HP Vegetation Composites 7575 5050 2525 00 s_region2008_81_FP 100 100 HP 0-1 Inch Soil Composites 7575 5050 2525 00 2378_TCDD 12378_PeCDD 123478_HxCDD 123678_HxCDD 123789_HxCDD 1234678_HpCDD OCDD 2378_TCDF 12378_PeCDF 23478_PeCDF 123478_HxCDF 123678_HxCDF 123789_HxCDF 234678_HxCDF 1234678_HpCDF 1234789_HpCDF OCDF PCB_77 PCB_81 PCB_126 PCB_169 PCB_105 PCB_114 PCB_118 PCB_123 PCB_156 PCB_157 PCB_167 PCB_189 ContriCbonuttriiboutniotnotoTToottaallTETQE(Q%)(%) 2378_TCDD 12378_PeCDD 123478_HxCDD 123678_HxCDD 123789_HxCDD 1234678_HpCDD OCDD 2378_TCDF 12378_PeCDF 23478_PeCDF 123478_HxCDF 123678_HxCDF 123789_HxCDF 234678_HxCDF 1234678_HpCDF 1234789_HpCDF OCDF PCB_77 PCB_81 PCB_126 PCB_169 PCB_105 PCB_114 PCB_118 PCB_123 PCB_156 PCB_157 PCB_167 PCB_189 Organohalogen Compounds, Volume 70 (2008) page 001035