ES&T LETTERS
Sludge on land Dear Sir: "Land use of wastewater and sludge" (ES&T, May 1984, pp. 140-47A) by Ronald W. Crites presents a wealth of information and an impressive list of references. A reader who is not thoroughly familiar with the topic can learn a great deal from Mr. Crites. However, the reader may be misled because the article is presented only from the traditional perspective of the wastewater treatment professional and does not include recent information regarding the health questions raised about the land application of sludge. Cntes devotes considerable discussion to the use of sludge on cropland as a fertilizer, but he fails to mention the long-standing conflict between the NFPA (National Food Processors A s s o c i a t i o n ) , EPA, F D A , and USDA. The NFPA has expressed concern about possible disease among the field and factory workers who grow and process the food crops and among customers who eat processed foods that may contain sludge contaminants (7). Specifically, NFPA is concerned about live bacteria, viruses, and parasites, persistent organics that do not degrade in the treatment process, and heavy metals that concentrate in the sludge. Crites says, "Uptake of lead by plants is not a problem unless lead levels are very high. The health concern is from surface accumulation and direct ingestion. This concern can be avoided by injection of the sludge into the root zone." This represents the position of the agricultural scientists and wastewater treatment personnel who worked with sludge in the 1960s and 1970s. However, a large body of medical research data has grown since Dr. Herbert Needleman's first report in 1979, which showed that very low levels of lead are quite harmful to children during the early years of rapid growth (2).
The research cited by Crites, on which the land spreading of sludge is based, must be reexamined in light of the new medical evidence on lead. According to Crites, "A great deal of research has been conducted on agronomic aspects of sludge use, including trace element uptake and translocation into the food chain." Both lead and cadmium are absorbed by plant crops. In the Illinois case, low levels of both cadmium and lead were found in the milk of cows included in the study. The conclusion has been that the metals do not pose a problem since their concentration levels are low. Given the cumulative nature of heavy metal poisoning, and the newly discovered hazards of low levels of lead, it is imperative that the data from the earlier agronomic research be reevaluated. It is doubtful that even very low levels of lead in the milk fed regularly to an infant can be considered safe. The EPA Office of Policy Analysis should be encouraged to perform the réévaluation as soon as possible. References (1) "Background Document on the Use of Municipal Sewage Sludge in the Production of Foods for Human Consumption"; National Food Processors Association: Washington, D.C., Nov. 22, 1982. (2) Needleman, H. L.; Gunnoe, C ; Leviton, A. N. Engl. J. Med. 1979, 300, 689-93. Stanford L. Tackett Professor, Department of Chemistry Indiana University of Pennsylvania Indiana, Pa. 15705
Ronald Crites replies: Dr. Tackett is correct in stating that low levels of lead are quite harmful to children. Surface-applied sludge in areas frequented by children may be of concern. Sludge-applied lead, however, has been found not to
increase plant levels of lead. This has been observed in all types of soils and for all types of crops (1). Reference (1 ) Logan, T. J.; Chaney, R. In "Workshop on Utilization of Muncipal Wastewater and Sludge on Land"; Denver, Colo; U.S. EPA: Washington, D.C., in press.
Waste at sea Dear Sir: Desmond Bond's article, "At-sea incineration of hazardous wastes" (ES&T, May 1984, pp. 1485 2A) questions the analysis of measurements, recorded data, and system performance for U.S. at-sea incineration studies. He states that the ". . . reputed success of ocean incineration of hazardous waste rests on invalid measurements and assumptions. .. ." He then discusses why he feels the measurements are invalid and uses this discussion to conclude that closer review and assessment are necessary before another U.S. at-sea permit for the incineration of hazardous wastes is approved. I recognize that at-sea incineration has certain environmental hazards, but I feel that this article does not discuss them. Instead, it picks apart the source testing and process measurement methods used by the EPA and others involved in the project. From reading his article, I conclude that the tests and measurements are valid and probably as accurate as can be made on a short-stack incinerator mounted on shipboard. He quotes from an article ("At-Sea Incineration of Shell Chemical Organic Waste," Shell Development Co. Technical Progress Report BRC CORP 13-75-F, 1975; referenced in EPA-430/9-75-014), which states that the variables involved need to be measured with 0.1% or better accuracy to determine if 99.9% combustion efficiency is achieved. This, of course, Environ. Sci. Technol., Vol. 18, No. 8, 1984
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is incorrect. If the unburned material is measured at 900 ppm, the combustion efficiency would be 99.91 % and if measured at 1100 ppm, the combustion efficiency would be 99.8%. If the " t r u e " value was 1000 ppm, both values would be in error by 10%, but rounding off the answers to three significant figures would show 99.9% combustion efficiency. Mr. Bond is concerned because "the total flow of flue gas was not and could not be measured according to the EPA Method 2." This is correct. The only satisfactory alternative is to calculate the flue gas flow using the fuel flow and the exhaust gas analysis, which is exactly what was done. This does not result in an "assumed" answer as he states, but a more accurate estimate of flue gas flow than one could determine by a greatly modified EPA Method 2 on a short stack, with nonuniform flow and high-temperature gas. The choice to calculate the flue gas flow by this procedure was proper application of the state of the art in this case because it gave the most accurate answer. Mr. Bond also refers to "scattered readings, frequent calibration and maintenance, very erratic thermocou-
ple readings, and several problems during incinerator o p e r a t i o n s . " I would expect that in a field experiment, under difficult conditions, these problems would be accepted and every attempt made to obtain the best data in spite of them. I would expect similar problems in testing such an incinerator on solid ground. I do not feel that any of the conclusions that Mr. Bond has "flagged" invalidate t h e referenced studies. These studies were trial burning tests for development of permitting procedures for future ocean incineration operations. I do hope that E P A has recognized that there was a possibility for errors in much of the field data and that it has taken such errors into account, along with a generous factor of safety, when it permits ocean incineration of U.S. hazardous wastes to be considered as a viable, low-risk disposal method. Richard W. Boubel Professor of Mechanical Engineering Oregon State University Corvallis, Ore. 97331 Desmond Bond replies: It is pleasing to find that interest in an environmental matter, particular-
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ly one involving the determination of chemical reaction effectiveness and its instrumentation, has widened to include a professor of mechanical engineering; some points made in the article referenced in his letter should, apparently, be explained. As noted, the article does not discuss the environmental hazards of ocean incineration per se. Certainly, "it picks apart the source testing and process measurements used," to illustrate the invalidity of conclusions reached as to the success of ocean incineration to date. Each waste disposal by that means (except for the first, admitted in its report to have been with uncertain effectiveness) can be seen to be looking back to predecessors to substantiate claims of the acceptability of means of measurements attempted, and of the supposed desirability of at-sea destruction of wastes. The letter's suggestion of combustion efficiency, propounded as 99.91 % when b a s e d on m e a s u r e m e n t of 900 ppm unburned material, sounds somewhat unusual, certainly without relevance here. Say, for instance, a vaporized organic (PCB-containing) waste were to be bled into and mixed with a hot stream of nitrogen, so that the combined flow resulted in a stream with 900 ppm organic (PCBcontaining) waste content; would it be reasonable to conclude that the unfired mixture had achieved a 99.91% combustion efficiency? Method 2 is an essential component of M e t h o d 5, according to E P A Codes. Without determination—with complete disregard of measurement, in fact—of the particulates contained (Method 5) in the flue gas from ocean disposal of hazardous wastes (the wide incidence of presence of particulates certainly was acknowledged in Vulcanus reports), how can destruction efficiencies be claimed with any degree of accuracy at all? As in reports of Vulcanus waste burns, the Boubel letter expects concessions to be granted because of atsea conditions. Methods, procedures and tests, even equipment formulation and design, either the best practical or good enough, considering the circumstances, can hardly be considered to be appropriate, despite their inadequacy, just because of the imperfect context. Measurements invalidly made, some without the accuracy or the frequency essential when accompanying attempts to destroy a hazardous waste, do not constitute a "no-risk" situation or support claims of a disposal method's adequacy.
