(b) The reader is not told what an “extractable” metal is (Table 11),but is left to guess that perhaps an ammonium acetate solution was used. (c) The comparison with Chaney’s recommendations (2) is very puzzling. Taking Cd first, Chaney recommends (his Table 14) that the Zn/Cd ratio be at least 200. The actual ratio recorded in the sludge is 10 (Table I) and in the soil is 30 (Table 11)-that is, 20 times and 7 times as much Cd as Chaney recommends, not 100 times as stated in the Note. When we consider the content of the sludge in other metals, Table I has values 6, 4,5, and 5 times as high as Chancy's recommendations for Cu, Ni, Pb, and Zn respectivelynot 40-50 times as stated in the Note. 3. Also when we consider crops and contents of heavy metals: (a) The reader is told nothing of the health of the corn crop, only that the corn of the control plot might have been P-deficient. But as evidence for this possibility there is no report of symptoms, only an indirect inference from the high Fe, Al, and (perhaps) Cd content of the leaves. Now if this inference is correct, the sludged plants must have been even more P-deficient because their contents in these three metals are higher. But this is most improbable for plants treated with sludge containing 2% P. This section of the Note might have been prudently omitted. (b) It is reassuring to see that the Cd content of grain is probably not significantly higher in the treated plots (0.9, 1.0 ppm) than in the controls (0.8 ppm), and this similarity fits other unpublished findings that I know of. But it is rash to imply, as in the Note, that this content is normal for corn grain. Literature Cited (1) Kirkham, M. B., Enuiron. Sci. Technol., 9,765-8 (1975). (2) Chaney, R. L., in “Proceedings of the Joint Conference on Recycling Municipal Sludges and Effluents on Land”, p p 12941, Nat. Assoc. State Univ. and Land-Grant Coll., Washington, D.C., 1973.
G. W. Leeper
Flat E6, 89 O’Shanassy St. N. Melbourne Victoria 3051, Australia
SIR: I appreciate Professor Leeper’s comments. I have found his treatise on heavy metals in soils a valuable reference ( I ). In response to his points: 1. I agree that pH and organic content of the treated soil are important to know. Unfortunately, I did not measure them. Because the study was not a thorough one, I wrote a “Note”. I felt that the results I did have were significant to publish. 2. (a) This “back-to-front” method was the only way I could estimate the unknown total weight of sludge added. I regret that the paper “confuses the reader” on this point. In the abstract, I should have said that the amount of sludge added was an estimated amount. (b) In the original manuscript submitted to Enuiron. Sci. Technol., I described the techniques used to analyze sludge, plant, and soil samples. In the review process, it was suggested that I omit the detailed procedures and only give the references. ( c ) In my calculations, I used Equation 1 developed by Chaney ( 2 ) , a cation-exchange capacity of 15 (on the low side), and the maximum values for metals in sludge he sets forth (2, 3 ) which are, in ppm: Zn, 2000; Cu, 1000; Ni, 200; Cd, 10; Pb, 1000. According to that Equation 1, the total quantity of sludge, in tons per acre, equals:
C.E.C. (meq/100 g unamended soil) X 1.63 X lo4 (kgms;u?ge
-50)
f 2
(kgmsludge g C u - 25)
t
- 25)
(kgyu?ge
46 T/A (105 metric tons/ha) Using the maximum concentrations for metals in sludge, I obtained the following: Permissib Ie loading , metric tons/ha 0.207 0.103 0.021 0.001 0.103
Element
Zn
cu Ni Cd Pb
These values are 40-50 times lower for Zn, Cu, Ni, and Pb, and more than 100 times lower for Cd, than those in Table IV. I did not cite Chaney’s work in the Environmental Protection Agency reference (2) because it is not published. I should have been more explicit in describing how I compared the metal loadings on the soil a t the Dayton, Ohio, site to those recommended by Chaney. 3. (a) The plants on the treated plots looked as healthy as those grown on the control plots. Phosphorus availability in sludge-treated soils is important to know, as Professor Leeper ( 1 ) and Chaney ( 3 ) have pointed out. Hence, I included the discussion on phosphorus. Since I published this study, I have analyzed the corn samples for phosphorus content. They are as follows: %
Plant part Roots
Leaves Grain
Control 0.09 0.13 0.42
Supernatant 0.3 1 0.25 0.39
Sludge 0.14 0.16 0.44
Plants grown on the sludge-treated soil had a higher phosphorus content than those grown on the control soil. But the phosphorus contents of both control and sludge-treated plants were low. Chapman ( 4 ) reports the normal concentration ranges for phosphorus in corn leaves and grain are 0.12-0.52% and 0.43-0.80% respectively. A high phosphorus content in the sludge-treated plants, therefore, cannot explain “minimal transport of the elements to the grain”, as I postulated in the note. (b) Because there is little published information on cadmium content of grain, it is hard to know what “normal” contents are. Literature Cited (1) Leeper, G. W., “Reactions of Heavy Metals with Soils with Special Regard t o Their Application in Sewage Wastes”, Prepared for Department of the Army, Corps of Engineers, Contract No. DACW73-73-C-0026,70 pp, 1972. (2) United States Environmental Protection Agency, “Policy Statement on Acceptable Methods for the Utilization or Disposal of Sludges”, Appendix I, 23 pp, Environmental Protection Agency, Office of Air and Water Programs, Washington, D.C., 20460, 1974. (3) Chaney, R. L., in “Proceedings of the Joint Conference on Recycling Municipal Sludges and Effluents on Land”, p p 12941, Nat. Assoc. State Univ. and Land-Grant Coll., Washington, D.C., 1973. (4) Chapman, H. D., Ed., “Diagnostic Criteria for Plants and Soils”, 2d Printing, 1973, 793 pp, Quality Printing Co., Inc., Abilene, Tex., 1966.
M. B. Kirkham
Department of Plant and Soil Sciences University of Massachusetts Amherst, Mass. 01002 Volume 10, Number 3, March 1976
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