Correspondence/Rebuttal pubs.acs.org/est
Cite This: Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Response to “Comment on ‘A Pilot-Scale Field Study: In Situ Treatment of PCB-Impacted Sediments with Bioamended Activated Carbon’”
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For the reasons stated above, we disagree with the statement that it is not possible to draw a conclusion of the “general feasibility” of using bioamended GAC for treatment of PCBimpacted sediments based on the data presented.
t was suggested by Lyu et al. that without data on the background sediments and water chemistry it was not possible to conclude that treatment with bioamended AC is effective. A treatability study was conducted to confirm the suitability of the site for treatment,1 and controls were included that confirm the loss of PCB mass was directly due to the bioamendments. It was also suggested that the decline in halorespiring Dehalobium chlorocoercia DF1 population over time might be due to competition by sulfate-reducing bacteria (SRB) in the presence of high SO4. In prior bioaugmentation studies with estuarine sediments containing >18 mM NaSO4, inhibition of dechlorination by DF1 was not observed.2 Furthermore, in the Supporting Information (Text S1), we state that DF1 was scaled up in coculture with an SRB, which provides an essential growth factor. As discussed in the article, the likely explanation for the decline in titer of DF1 is provided in a report by Lombard et al.,3 which showed that the low aqueous concentration of PCBs typically found in PCBimpacted sediments will not support high numbers of halorespiring bacteria. Based on calculations by Lombard, the aqueous concentration of congeners with four or more chlorines in the current study are at least 2 orders of magnitude lower than that required to support one doubling of halorespiring bacteria at a concentration of 105 cells mL−1. This is a conservative estimate as penta- to nonachlorobiphenyls have lower solubilities (higher kow) and congeners with unflanked chlorines are not substrates for halorespiration at this site. Furthermore, in the current paper and prior treatability study1 using the same sediments and water from the site, we show there is significant reduction in the mass of PCBs only after treatment with bioamendment. No significant decrease in PCB was observed in non-bioamended controls. If co-metabolic degradation by indigenous species occurred as suggested, it would have been observed in the non-bioamended controls, which was not the case. Oxygen is required for several PCB degrading enzymatic reactions by the Bph pathway in Burkholderia xenovorans LB400. Although the level of TOC in the sediments would be expected to maintain a low redox potential due to microbial activities such as SRB respiration, sediments are dynamic and experience changes in redox potential as a result of bioturbation. Anaerobes are generally protected from periodic exposure to oxygen as a result of cellular defense mechanisms and the formation of biofilms. Oxygen diffusion into sediments is a well-documented phenomenon,4−6 and as observed by Payne,1 PCB degradation attributed to LB400 occurred throughout the sediment depth in sediment mesocosms. We agree that bioamendment with an aerobic PCB degrader such as LB400 might not be effective in water bodies with limited DO at the surface water interface; however, PCB degradation by LB400 is co-metabolic and only requires oxygen levels sufficient for enzymatic degradation, not growth. © XXXX American Chemical Society
Rayford B. Payne† Upal Ghosh‡ Harold D. May§ Christopher W. Marshall∥,⊥ Kevin R. Sowers*,†
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† Department of Marine Biotechnology, Institute of Marine and Environmental Technology, University of Maryland Baltimore County, Baltimore, Maryland 21202, United States ‡ Department of Chemical, Biochemical, and Environmental Engineering, University of Maryland Baltimore County, Baltimore, Maryland 21250, United States § Hollings Marine Laboratory, Department of Microbiology and Immunology, Medical University of South Carolina, Charleston, South Carolina 29412, United States ∥ Biosciences Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
AUTHOR INFORMATION
Corresponding Author
*Telephone: (410) 234-8878. Fax: (410) 234-8896. E-mail:
[email protected]. ORCID
Upal Ghosh: 0000-0003-2112-1728 Christopher W. Marshall: 0000-0001-6669-3231 Kevin R. Sowers: 0000-0002-8920-9278 Present Address ⊥
Department of Microbiology and Molecular Genetics, University of Pittsburgh, Pittsburgh, PA 15219. Notes
The authors declare the following competing financial interest(s): Several authors are co-inventors of patents related to the technology described in this paper for which they are entitled to receive royalties. KS and HM are co-inventors of U.S. Patent Nos. 6,946,248 and 7,462,480 B2 issued to the University of Maryland Baltimore County (UMBC) and Medical University of So. Carolina. KS ad UG are co-inventors of U.S. Patent No. 8,945,906 issued to UMBC. UG is a co-inventor of U.S. Patent No. 7,101,115 B2 issued to Stanford University and U.S. Patent No. 7,824,129 issued to UMBC. In addition, UG and KS are partners in a startup company (RemBac Environmental) that has licensed the three former technologies; UG is a partner in a startup company (Sediment Solutions) that has licensed the latter technology.
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DOI: 10.1021/acs.est.9b02107 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
Environmental Science & Technology
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Correspondence/Rebuttal
REFERENCES
(1) Payne, R. B.; Ghosh, U.; May, H. D.; Marshall, C. W.; Sowers, K. R. Mesocosm studies on the efficacy of bioamended activated carbon for treating PCB-impacted sediment. Environ. Sci. Technol. 2017, 51 (18), 10691−10699. (2) Payne, R. B.; May, H. D.; Sowers, K. R. Enhanced reductive dechlorination of polychlorinated biphenyl impacted sediment by bioaugmentation with a dehalorespiring bacterium. Environ. Sci. Technol. 2011, 45, 8772−8779. (3) Lombard, N. J.; Ghosh, U.; Kjellerup, B. V.; Sowers, K. R. Kinetics and threshold level of 2,3,4,5-tetrachlorobiphenyl dechlorination by an organohalide respiring bacterium. Environ. Sci. Technol. 2014, 48 (8), 4353−4360. (4) Pischedda, L.; Poggiale, J. C.; Cuny, P.; Gilbert, F. Imaging oxygen distribution in marine sediments. The importance of bioturbation and sediment heterogeneity. Acta Biotheor. 2008, 56, 123−135. (5) Hölker, F.; Vanni, M. J.; Kuiper, J. J.; Meile, C.; Grossart, H. P.; Stief, P.; Adrian, R.; Lorke, A.; Dellwig, O.; Brand, A.; Hupfer, M.; Mooij, W. M.; Nü tzmann, G.; Lewandowski, J. Tube-dwelling invertebrates: tiny ecosystem engineers have large effects in lake ecosystems. Ecol. Monogr. 2015, 85 (3), 333−351. (6) Baranov, V.; Lewandowski, J.; Krause, S. Bioturbation enhances the aerobic respiration of lake sediments in warming lakes. Biol. Lett. 2016, 12, 20160448.
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DOI: 10.1021/acs.est.9b02107 Environ. Sci. Technol. XXXX, XXX, XXX−XXX
