Correspondence Comment on “Landfill-Stimulated Iron Reduction and Arsenic Release at the Coakley Superfund Site (NH)” Jamie deLemos et al. conclude in their recent article, “Landfill-stimulated iron reduction and arsenic release at the Coakley superfund site (NH)” (1), that the reducing environment present in the Coakley Superfund Site mobilizes arsenic. Such an environment is produced by microbial activity that essentially reduces insoluble Fe(III) to dissolved Fe(II), causing the desorption of arsenic from ferrihydrites present in glaciomarine clays. The active flushing of arsenic from the soil produces levels greater than naturally occurring concentrations, instigating health and safety concerns (1). The findings of the study raise legitimate concerns about the effectiveness of USEPA’s toxicity characteristic leaching procedure (TCLP) (2), the primary criterion for determining the suitability of a material for landfill disposal. The current TCLP protocol fails to take into consideration the redox environment in the vicinity of the disposed material. Thus, any toxic substance whose stability or sorption affinity significantly diminishes under reducing environments may appear in the landfill leachate at significantly higher concentrations. The authors of the subject paper draw parallels between the observations at Coakley Superfund Site and natural subsurface arsenic contamination in Bangladesh and West Bengal, India (3-5). The presence of dissolved iron or Fe(II) is often accompanied by the presence of dissolved As(V) and As(III) in Bangladesh and West Bengal. The authors should have consistently recorded arsenic speciation data, i.e., As(III) versus As(V) species in the Coakley leachate because the reduction of Fe(III) to Fe(II) may not be the only underlying mechanism for enhanced leaching of arsenic from a waste site. The reduction of As(V) to As(III) is also an important factor responsible for causing enhanced arsenic leaching. Other environmentally benign metal oxides, such as Al(III), Ti(IV), and Zr(IV), also exhibit high sorption affinity for As(V) species. Unlike Fe(III), these metal oxides are chemically stable under the reducing environment of landfills. Nevertheless, reduction of As(V) to As(III) and diminished sorption affinity of As(III) species to these metal oxides lead to enhanced arsenic leaching. Arsenic disposal by traditional means is thus a universal problem even in the absence of Fe(III) reduction. Therefore, the availability of As(III) versus As(V) concentration in the Coakley leachate could be quite meaningful for rigorous data analyses. The subject study was carried out for a superfund site but the drinking water industries requiring arsenic removal following USEPA promulgation of the new arsenic maximum contaminant level rule (6) will soon face the same problem. In Bangladesh and West Bengal, arsenic-contaminated groundwater is often treated using 10.1021/es060247h CCC: $33.50 Published on Web 05/13/2006
2006 American Chemical Society
ferric chloride, iron-based sorbent, or activated alumina. The major environmental challenge lies not just in removing dissolved arsenic from contaminated groundwater but also in attaining safe, long-term disposal of arsenicladen sludges. The volume of sludge is often small but disposal in the reducing environment of a landfill will compound the problem as demonstrated by Delemos et al. in their study (1). To overcome the foregoing problem, a comprehensive arsenic disposal strategy was adopted in West Bengal under aerobic, oxidizing environments. Spent regenerant, containing high As(V) concentrations, is precipitated at near-neutral pH using ferric chloride. The resulting sludge, containing an excess of ferric hydroxide, is disposed of and retained at the top of a well-aerated coarse sand filter (7). Figure 1a presents the composite pe-pH diagram for arsenic and iron and highlights three separate predominance zones: neutralized regenerant sludge, groundwater, and landfill leachate. Note that Fe(III) and As(V) predominate in the aerated regenerant sludge while reduced Fe(II) and As(III) are practically the sole species in the landfill leachate. Figure 1b displays the samples of arsenic-laden sludge collected from the top of a coarse sand filter in West Bengal. Figure 1c shows the laboratory simulated leaching test results of one sludge sample from West Bengal at different pH; under atmospheric conditions, both iron and arsenic leaching are relatively insignificant. It is ironic that while commercial arsenic-selective adsorbent manufacturers claim and validate that their products satisfy USEPA TCLP criteria after usage, they will all cause significant arsenic leaching after disposal into landfills due to biogeochemical activity in a reducing environment. The subject study by Delemos et al. (1) and the underlying chemistry reinforce the scientific premise that any engineered process pertaining to longterm arsenic disposal must take place under relatively oxidizing environments.
Literature Cited (1) Delemos, J. L.; Bostick, B. C.; Renshaw, C. E.; Stu ¨ rup, S.; Feng, X. Landfill-Stimulated Iron Reduction and Arsenic Release at the Coakley Superfund Site (NH). Environ. Sci. Technol. 2006, 40, 67-73. (2) U. S. Environmental Protection Agency. Test Methods for Evaluating Solid Waste, Physical/Chemical Methods, 3rd ed.; SW-846, Method 1311; U. S. Government Printing Office: Washington, DC, 1992. (3) Chowdhury, U.K.; Biswas, B. K.; Chowdhury, T. R.; Samanta, G.; Mandal, B. K.; Basu, G. C.; Chanda, C. R.; Lodh, D.; Saha, K. C.; Mukherjee, S. K.; Roy, S.; Kabir, S.; Quamruzzaman, Q.; Chakraborti, D. Groundwater Arsenic Contamination in Bangladesh and West Bengal, India. Environ. Health Perspect. 2000, 108, 5. (4) Nickson, R. T.; McArthur, J. M.; Ravenscroft, P.; Burgess, W. G.; Ahmed, K. M. Mechanism of arsenic release to groundwater, Bangladesh and West Bengal. Appl. Geochem. 2000, 15, 403413. (5) Harvey, C. F.; Swartz, C. H.; Badruzzaman, A. B. M.; KeonBlute, N.; Yu, W.; Ali, M. A.; Jay, J.; Beckie, R.; Niedan, V.; Brabander, D.; Oates, P. M.; Ashfaque, K. N.; Islam, S.; Hemond, H. F.; Ahmed, M. F. Arsenic mobility and groundwater extraction in Bangladesh. Science 2002, 298, 16021606. VOL. 40, NO. 12, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. (a) Composite arsenic/iron pe-pH diagram with groundwater, sludge, and leachate predominance zones; (b) resultant sludge sample; (c) iron and arsenic leaching test results (Modified from ref 7. Copyright 2005 Elsevier Ltd.). (6) National Primary Drinking Water Regulations; Arsenic and Clarifications to Compliance and New Source Contaminants Monitoring. Fed. Regist. 2001, 66 (14), 6976. (7) Sarkar, S.; Gupta, A.; Biswas, R. K.; Deb, A. K.; Greenleaf, J. E.; SenGupta, A. K. Well-head arsenic removal units in remote villages of Indian subcontinent: Field results and performance evaluation. Water Res. 2005, 39 (10), 2196-2206.
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Lee M. Blaney and Arup K. SenGupta* Department of Civil and Environmental Engineering Lehigh University Fritz Engineering Laboratory 13 East Packer Avenue Bethlehem, Pennsylvania 18015 ES060247H
