HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Pehl, C. E. Search for Related Content PubMed PubMed Citation Articles by Pehl, C. E. Agricola Articles by Pehl, C. E.

Letters to the Editor

Comments on "Transport of Biosolids in Waste-Amended Soils" (A.D. Karathanasis, D.M.C. Johnson, and C.J. Matocha; J. Environ. Qual. 34:1153-1164)

K-3 Resources, Inc., P.O. Box 2236, Alvin, TX 77512

(cepehl{at}earthlink.net)

Comments

Dear Editor:

The referenced article in the July–August 2005 issue of the Journal of Environmental Quality may have succeeded in demonstrating that colloids play a role in pollutant mass balance losses and as agents in transport modeling. Overloading soil-filled tubes with artificially enhanced volumes should produce some leaching and transport through mass flow alone. However, the authors' conclusion that the studied mechanism is critical where heavy applications of biosolids may increase the risk for soil and ground water contamination can only be true if biosolids are normally applied at the Cu, Zn, and Pb concentrations used in this study.

However, the study concentrations do not reflect current wastewater treatment sludge pollutant levels. According to the article, the participants "spiked" the samples (200-mg colloids) with solutions containing 5 mg/L of Cu, Zn, and Pb to "increase metal loads above inherent levels and enhance metal detectability." No information is given on these "inherent levels," but the need to spike indicates that they are low, possibly nondetectable. The study's artificial concentrations are equivalent to sludge with Cu, Zn, and Pb concentrations of 25 000 mg/kg (5 mg pollutant/0.0002 kg colloids, assuming no "inherent" pollutants on the colloids). Under current USEPA regulations, these levels are nearly 6 times the maximum Cu concentration (4300 mg/kg), 30 times the Pb (840 mg/kg), and 3 times the Zn (7500 mg/kg) allowed for land application. In addition, they are over 900 times the mean Cu (27.4 ± 3.9 mg/kg), 90 times the mean Pd (277.7 ± 45.2 mg/kg), and 40 times the mean Zn (614.1 ± 178.8 mg/kg) concentrations in wastewater treatment plant biosolids in the Houston, Texas, metropolitan area (N = 50, 95% CI, samples collected from 1998 to 2005).

Further, sludges with Cu, Pb, and Zn concentrations of 25 000 ppm are not biosolids by definition. Biosolids must comply with the maximum pollutant concentrations for land application (Table 1, 40 CFR 503) determined by the USEPA through risk assessment. Land application of any sludge equivalent to the study colloids would be a violation of federal law and would likely result in fines or imprisonment.

Because of the USEPA permitted pretreatment program, which requires industrial facilities to remove pollutants before discharge into municipal sewer systems, pollutants are now typically low in wastewater treatment sludges. Application of this material poses little danger to soil and ground water when applied in compliance with regulations. The USEPA solves the problem by monitoring pollutant removal "upstream" at the source.

Received 19 Aug. 2005

CHARLES E. PEHL

K-3 Resources, Inc.

P.O. Box 2236

Alvin, TX 77512

(cepehl{at}earthlink.net)

Reply

Dear Editor:

Charles Pehl accepts that according to the findings of the study, biosolids colloids "play a role in pollutant mass balance losses and as agents in transport modeling." However, he disagrees with the conclusions drawn "that the studied mechanism is critical where heavy applications of biosolids may increase the risk for soil and ground water contamination," stating that this can be only true if biosolids are normally applied at the Cu, Zn, and Pb concentrations used in the study. He considers the applied rates used in the study excessive and "not reflecting current wastewater treatment sludge pollutant levels" according to the currently applied USEPA criteria.

First of all, the intent of the study was to demonstrate the potential of biosolids colloids as vectors of contaminant (metal) transport in areas receiving heavy biosolids applications. The findings clearly demonstrated that this indeed is a valid mechanism and the reader agreed with this conclusion. Since this was a laboratory simulation experiment, the study could not address the scale of contamination, which can be better assessed through field experiments. The conclusion drawn about this mechanism being potentially critical in areas receiving heavy biosolids applications was an extrapolation of the findings. Obviously, direct proof of that could come only from conducting similar experiments in the field. However, discarding the potential risk to ground water contamination through colloid-mediated metal transport based on the application loads used in our experiments is at least superficial. Here are some of the reasons:

(i) Based on the reader's calculations, some of the applied metal loads in the study were 3 to 30 times higher than the allowable nominal rates for biosolids material application. However, this calculation assumes that the metal concentration is uniformly distributed within the bulk biosolids material and not mainly with the colloidal fraction used in the study. A typical biosolids material may contain between 10 and 30% colloids. Considering their high specific surface area and metal sorption capacity, it is expected that the vast majority of the metal load will be associated with the colloid fraction. Therefore, it is neither unreasonable nor unlikely to have 3 to 10 times higher metal loads associated with field-dispersed biosolids colloids even in areas receiving nominal application rates.

(ii) Even if the biosolids material is uniformly applied on the surface of a site (which based on my experience is typically impractical), the surface relief of each site (before and after application) is conducive to generating pockets of higher and lower colloid and metal concentration gradients following a sequence of rainfall events. High colloid-metal concentration pockets may reach levels far in excess of nominal levels and generate plumes of metal transport, particularly in soils with increased macroporosity, posing increased risks for ground water contamination. This may be particularly relevant in soils with high shrink–swell potential, which have a tendency to form large cracks during the dry part of the season. The USEPA's policy of monitoring pollutant removal "upstream" at the source, which was alluded to by the reader, will not be of any use as a preventive measure in such cases.

(iii) Finally, the reader's statement that application of biosolids materials "poses little [emphasis mine] danger to soil and ground water when applied in compliance with regulations" has enough ambiguity in itself to raise some concerns. How much is "little"? Is there any quantitative measure for that?

Received 20 Sept. 2005

A.D. KARATHANASIS

Department of Plant and Soil Sciences

University of Kentucky

Lexington, KY 40546

(akaratha{at}uky.edu)

This Article Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Pehl, C. E. Search for Related Content PubMed PubMed Citation Articles by Pehl, C. E. Agricola Articles by Pehl, C. E.