Environ. Sci. Technol. 1995, 29, 2472
Comment on “Fractionation and Oxidation of Chromium in Tannery Waste= and Sewage Slwlge4mended Soils” SIR: We have read with considerable concern the paper by MilaEiE and h p a r (1). The use of analytical methodology known to produce false positive results, the apparent lack of analytical verification, and the failure to establish a chromium mass balance all raise very serious questions about the validity and interpretation of data presented. Menden et al. (2) have reported false positive determinations of Cr(VI) in tannery waste materials using the chelation/extraction method (EPA Solid Waste Method 7197) due to the presence of organochromium(II1) compounds that are directly soluble in MIBK and thus are reported as Cr(VI) by this method. Examples of such compounds likely to be present in tannery waste materials are chrome soaps (reaction product of chrome tanning agents with free fatty acids from decomposition of natural hide grease), chrome-complex dyes, water/stain repellent chemicals, etc. The authors reference this work (ref 11 in MilaEiE and Stupar) but give no indication that any steps were taken to validate their Cr(VI) results. In fact, there is no mention of validation procedures for any of the analytical data, leading to the conclusion that this was not done. MilaEiE and Stupar fail to establish a chromium mass balance as a further means of data verification. There is no indication that the leather waste itself or the wastelsoil mixtures were analyzed for total chromium prior to extraction. Rinse water between extractions was discarded rather than being combined with the previous extract. Rainwater leachate was also discarded without analysis. And finally, sampling from only the top 10 cm without prior mixing totally ignored any translocation of chromium within the soil column. Using what data are provided gives calculated chromium recoveries ranging from 66 to 12276, which is unacceptable. In view of these deficiencies, we are forced to conclude that the reported oxidation of Cr(II1) in the soillwaste mixtures is at best highly questionable if not totally erroneous.
literature Cited (1) Milatit, R.;Stupar, J. Environ. Sci. Technol. 1995,29,506-514. (2) Menden, E. E.; Rutland, F. H.; Kallenberger,W. E. J.Am.Leather Chem. Assoc. 1990, 85, 363-375.
Robert M. Lollar, Waldo E. Kallenberger, and Frank H. Rutland*
SIR: The first point is the same as that dealt with in our reply to Cory and Sykes (previous correspondence in this issue). The state by Lollar et al. that there is no indication that the leather waste itself or the wastelsoil mixtures were analyzed for total Cr prior to extraction is quite wrong: on the contrary, the leather waste, sewage sludge, and soils as well as the corresponding waste/soil mixtures were analyzed f o r total Cr prior to extraction. These data are given in Figures 1-3,5, and 6. Procedures for total Cr determination are described in section “Procedures and Methods”. The sum of Cr present in various forms in these materials is not explicitly given since the difference between these values and the total Cr determinations does not exceed &8% in the worst case of inhomogeneous tannery wastelsoil mixtures. Between the two extractions, each residue was washed with water to remove the previous extractant solution. The rinse water between extractions was discarded because the Cr concentration in this water was negligible in comparison to the total Cr in this particular fraction. Rainwater leachates were actually analyzed (although this was not explicitly stated in the paper) twice in the first months and once 6 months after the start of the experiment for total Cr and Cr(VI) content. The presence of Cr(VI)was evident in tannery waste-amended clay and sand soil leachates (0.5pg~rn-~). In peat/tannerywaste soilleachate as well as in all sewage sludge/soil leachates, the concentration of total Cr and Cr(VI)was negligible (afew ng ~ m - ~ ) . However, the total leached Cr in tannery waste/clay and sand leachate (1pg of Cr ~ m - would ~ ) contribute less than 1%of the total added Cr, which is insignificant for making mass balance calculations. The authors do not understand how the recoveries quoted in the letter of Lollar et al. were calculated. Apparently, a small Cr gradient might be established in soil in 2 years time since the results for total Cr in the upper 10-cm soil layer indicated a small decrease in Cr concentration (8-13%).
Radmila Milatie* and Janez Stupar
Leather Industries Research Laboratory University of Cincinnati P.O. Box 210014 Cincinnati, Ohio 45221-0014
Department of Physical and Environmental Chemistry “Joief Stefan” Institute University of Ljubljana 6100 Ljubljana Jamova 39, Slovenia
ES950180Q
ES95 10018
2472 rn ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 29, NO. 9,1995
0013-936X/95/0929-2472$09.00/0
1995 American Chemical Society
