Comment on "Fractionation and Oxidation of Chromium in Tannery Waste- and Sewage Sludge-Amended Soils" SIR: We are writing to draw the attention of your readers to serious errors in the paper by MilaEiE and Stupar (1). This paper incorporates a number of serious flaws in the technology used, and from the cited references, the authors were aware of the flaws. The most important weakness is the presumption that all chromium extracted from the aqueous phase by MIBK is hexavalent. As long ago as 1990 Rutland and co-workers (2)demonstrated that false positive results were obtained using the MIBK extraction technique with tannery wastes. The reason is quite straight forward; organometallic complexes are commonly used in leather processing as purchased chemicals; in addition, they may be formed by the complexation of fatty and amino acids with chromium(II1) sulfate used as a primary tanning agent. Speciality chemicals based on organochromium(II1)complexes include chromium stearatochloride (water repellent), chromium fluorocarboxylic acid complexes (stain repellent), chromium(II1)adipic acid complexes formed in situ during processing, complexes of chromium(II1) with aromatic sulfamates (syntans),and chromium-containing dyestuffs. Unpublished work in these laboratories following Rutland's paper (2) indicates that up to 50% of the chromium(II1)present in commercially available dyestuffs may be extracted by MIBK using the procedure adopted by MilaEiE and Stupar ( 1 ) . Some results are shown in Table 1. It is impossible to claim that all the chromium extracted from soil samples by MilaEiE and Stupar was trivalent, but the suspicion must be raised. The second presumption relates to the extrapolation of laboratory data to oxidation of chromium(II1)in soil to field situations. Bartlett, a peer researcher in this area, has reported on the oxidation of trivalent chromium in soil under laboratory conditions. However, in one overview of his, Bartlett (3)reported that on only one occasion has he actually detected hexavalent chromium in natural soil, and even that was a transient finding. The present paper therefore only adds further bad science in an area where regulations are in many countries already based on erroneous data. Bartlett (3)makes the following points: (a)soils that are good chromium oxidizers are also good chromium reducers;
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TABLE 1
dyestuff Acid Acid Acid Acid Acid Acid
% of total chromium extracted by MIBK from aqueous solution of dyestuff
Orange 74 Orange 141 Orange 148 Red 186 Red 201 Red 279
0.5 2.0 6.1 0.01 0.1 45.5
(b) in most soils, reducing organics prevent oxidation; (c) in real soils, hexavalent chromium is the least stable form; (d) following reduction of hexavalent chromium, trivalent chromium is bound by a variety of ligands that render it insoluble, immobile, and unreactive. We would like to point out that for several decades the leather industry in Europe and North America has used chromium only in the trivalent form in the tanning process. In 1993, the U.K. Government, in the form of the Ministry of Agriculture, Fisheries and Food, published the following pronouncement on chromium in soils and sewage sludge's used in agriculture ( 4 ) : "There has been some concern about chromium being added to soil because the chromatem) ion is toxic to plants and animals. However, due to the conditions found in organic waste materials or in soil, it will only exist as the relatively inactive chromic(II1) ion."
literature Cited (1) MilaEiE, R.; Stupar, S. Enuiron. Sci. Technol. 1995,29, 506-514.
(21 Menden, E. E.; Rutland, F. H.; Kallenberger, W. E. J.Am.Leather Ckem. Assoc. 1990, 85, 363-375. (31 Bartlett, R. J. Chromium in the Natural and Human Environmenfs;Wiley: New York, 1988.
of Good Agricultural Practice for the Protection of Soil; Ministry of Agriculture, Fisheries and Food: London, 1993.
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Nicholas J. Cory* and Robert L. Sykes BLC-The Leather Technology Centre Leather Trade House Kings Park Road Moulton Park, Northampton "3 6JD, U.K. ES950215M
0013-936X/95/0929-2470$09 OOiO
C 1995 American Chemical Society
