Relationship between polychlorinated dibenzo- p -dioxin, polychlorinated dibenzofuran, and dioxin-like polychlorinated biphenyl concentrations in vegetation and soil on residential properties

The University of Michigan Dioxin Exposure Study was undertaken to address concerns that the industrial discharge of dioxin-like compounds in the Midland, Michigan, USA area had resulted in the contamination of soil and vegetation in the Tittabawassee River floodplain and downwind of the incinerator in the City of Midland. The study included the analysis of 597 vegetation samples, predominantly grass and weeds, from residential properties selected through a multistage probabilistic sample design in the Midland area, and in Jackson and Calhoun Counties (Michigan), as a background comparison, for 29 polychlorinated dibenzo- p -dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). The mean toxic equivalent (TEQ) of the house perimeter vegetation samples ranged from 4.2 to 377 pg/g. The ratio of TEQs (vegetation to soil) was about 0.3, with a maximum of 3.5. Based on a calculation of the similarity of the congener patterns between the soil and the vegetation, it appeared that the source of the contamination on the vegetation was the surrounding soil. This conclusion was supported by linear regression analysis, which showed that the largest contributor to the R 2 for the outcome variable of log 10 of the vegetation concentration was log 10 of the surrounding soil concentration. Models of vegetation contamination usually focus on atmospheric deposition and partitioning. The results obtained here suggest that the deposition of soil particles onto vegetation is a significant route of contamination for residential herbage. Thus, the inclusion of deposition of soil particles onto vegetation is critical to the accurate modeling of contamination residential herbage in communities impacted by historic industrial discharges of persistent organic compounds. Environ. Toxicol. Chem. 2010;29:2660–2668. © 2010 SETACPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78291/1/344_ftp.pd

Enhanced biodegradation of PAHs in historically contaminated soil by M. gilvum inoculated biochar

The inoculation of rice straw biochar with PAH-degrading Mycobacterium gilvum (1.27 × 1011 ± 1.24 × 1010 cell g−1), and the subsequent amendment of this composite material to PAHs contaminated (677 mg kg−1) coke plant soil, was conducted in order to investigate if would enhance PAHs biodegradation in soils. The microbe-biochar composite showed superior degradation capacity for phenanthrene, fluoranthene and pyrene. Phenanthrene loss in the microbe-biochar composite, free cell alone and biochar alone treatments was, respectively, 62.6 ± 3.2%, 47.3 ± 4.1% and non-significant (P > 0.05); whereas for fluoranthene loss it was 52.1 ± 2.3%; non-significant (P > 0.05) and non-significant (P > 0.05); and for pyrene loss it was 62.1 ± 0.9%; 19.7 ± 6.5% and 13.5 ± 2.8%. It was hypothesized that the improved remediation was underpinned by i) biochar enhanced mass transfer of PAHs from the soil to the carbonaceous biochar “sink”, and ii) the subsequent degradation of the PAHs by the immobilized M. gilvum. To test this mechanism, a surfactant (Brij 30; 20 mg g−1 soil), was added to impede PAHs mass transfer to biochar and sorption. The surfactant increased solution phase PAH concentrations and significantly (P < 0.05) reduced PAH degradation in the biochar immobilized M. gilvum treatments; indicating the enhanced degradation occurred between the immobilized M. gilvum and biochar sorbed PAHs

Quantifying the importance of the atmospheric sink for polychlorinated dioxins and furans relative to other global loss processes.

Previous attempts to establish global mass balances for polychlorinated dioxins and furans (PCDD/Fs) have focused on the terrestrial sink, thereby neglecting deposition to the oceans and atmospheric losses. In this study, the atmospheric sink of polychlorinated dioxins and furans (PCDD/Fs) was calculated on the basis of their presence in soils. OH radical ([OH]) depletion reactions compete with atmospheric deposition fluxes for the fate of atmospheric PCDD/Fs. Three different steady state scenarios were considered: scenario A was a one-box atmosphere with globally averaged [OH], temperature (T), atmospheric lifetime (tlife), and a constant gas-particle partitioning (Φ); in scenario B, [OH], T, and Φ were averaged in a multibox atmosphere, with a constant tlife; and in scenario C, tlife was varied. In scenario A the strength of the atmospheric sink was 2400–2800 kg/yr; in scenario B it was ∼2100 kg/yr; in scenario C, it was ∼1,800 kg/yr (tlife = 5.4 days) to ∼2,800 kg/yr (tlife = 14 days). The majority of the atmospheric sink was due to the depletion of Cl4DFs (1300–1400 kg/yr), followed by Cl4DDs (360–380 kg/yr) and Cl5DFs (230–240 kg/yr). On a global scale, major sinks for PCDD/Fs are the deposition to terrestrial soils and the oceans. For Cl6–8DDs, deposition to soils outweighs depletion reactions in the atmosphere and ocean uptake. The more volatile Cl4–5DD/Fs, however, are true “multimedia” compounds, with their estimated atmospheric sink being roughly as important as the terrestrial sink (in the case of Cl5DD/Fs) or outweighing it (e.g., Cl4DD/Fs)