m
LETTERS
July editorial Dear Sir: It was with great interest that I read the editorial “The protection quandary” in the July issue of ES&T, for I too wish to be protected from harm. However, if I extend the thoughts expressed by the editor in the opening paragraphs, the best of all possible worlds would be one in which there were no facts and I would know nothing, believe nothing, and have no worries. This state of blissful ignorance is in keeping with the belief that the “federal Goliath” can protect me “from any contaminant that may have an adverse effect on my health.” I know that there are possible adverse effects, not only from contaminants, but also from consumption of many common chemicals. It is wellknown that excessive consumption of any chemical, even sodium chloride or sucrose, will provide undesirable effects. The undesirable effects can be controlled by regulation of dosage, because for all materials there is a dose-response relationship which must be considered in evaluating the potential degree of adverse effect. Suggesting that EPA should offer protection “from any contaminant that may have any adverse effect on my health” is asking for the impossible. It is impossible to prove absolute safety. It is possible to make risk assessments that are based on both exposure and toxicity. The editorial calls for studying the hazards “continuously.” Neither the manpower, financial resources, nor the need exist to study all potential hazards “continuously.” It is, of course, prudent to reevaluate risk judgments whenever circumstances indicate such an action. It would not be prudent, however, to study all hazards on a continuous basis. It would be well to be guided by assessment app’roaches being developed by such bodies as OECD, EEC, and EPA for the evaluation of human and environmental safety of chemicals. I do not want “some specialists” who be1156
Environmental Science & Technology
lieve that some hazard might exist to forestall the introduction of a new chemical until all questions have been answered. I do not want those “specialists” to have the power to decide to remove man-made (and natural) chemicals from the environment completely (Le., zero residual) until all questions have been answered. It would seem more reasonable for these issues to be settled on the basis of scientific facts which are used by open-minded scientists who can deliberate and decide whether the risks involved are acceptable or unacceptable. In this way society would have the benefit of chemicals that are judged to be acceptable, based upon a sufficient amount of scientific data which deal with the particular questions raised by each chemical. The potential for hazard needs to be addressed with the best resources available, but the probability of injury needs to be the factor which controls decision making. As for me, I know that chloroform (and other chemicals) are in my drinking water; I know that the relevant chemistry of chloroform (and other chemicals) is complex; I know that chloroform (and other chemicals) can be hazardous; but I don’t worry about such matters without factoring in the amounts of the chemical which might be ingested and the reasons for having that chemical in the environment. One should worry only when the information is not available to make a risk assessment. Herbert E. Allen
Professor Pritzker Dept. of Environmental Engineering Illinois Institute of Technology Chicago, Ill. 606 16 Bioenergy effects Dear Sir: Your article on the environmental effects of biomass use (“Bioenergy: the lesson of wood burning?” ES&T, July 1980, p. 769)
clearly presents some important concerns about the use of firewood for residential heating. In generalizing from residential wood combustion to other biomass energy options, however, your article presents a very misleading picture. As your article states, the most serious environmental problem with the direct combustion of wood is particulate emissions. The formation of particles is especially high in decentralized applications (in which incomplete combustion conditions are preferred), and also particularly hard to control in such cases. Thus when it comes to burning wood, the decentralized systems are indeed the dirtiest. But is the same true for converting biomass materials to liquid and gaseous fuels, or for producing biomass residues? Biomass can be converted to synfuels via thermochemical or biological pathways. Most thermochemical conversion technologies are economically infeasible at small scale, so scale is not an issue in assessing their environmental impacts. The bioconversion technologies, which use microorganisms to convert biomass into methane or ethanol, are practical for a broad range of system scales. In many cases, small-scale operations may lead to significantly reduced waste (or byproduct) handling problems for these technologies. The waste sludge resulting from the biogasification of biomass is rich in nutrient and soil-building values. In applying the sludge to agricultural fields it is important to disperse it over a wide area, preferably over the entire area that produced the original biomass feedstock. This is recommended in order to avoid a buildup of toxic materials in fields treated with sludge. Small-scale conversion operations clearly help to avoid such problems by facilitating adequate sludge redispersal. Similarly, stillage handling after alcohol fermentation may be simpler (continued on page 1158)
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Volume 14, Number 10, October 1980
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LETTERS
(continued)
and cheaper for small-scale conversion systems where the stillage needs only minimal drying before it can be used. The most serious environmental liabilities associated with the use of most forms of biomass are the environmental costs of producing the biomass residues. Collecting crop residues that are currently returned to the soil will exacerbate some of the environmental problems currently plaguing agriculture, such as erosion and the loss of humus and nutrients from agricultural soils. Intensive production of biomass will have all of the environmental liabilities of intensive agriculture. It is difficult to relate the scale of a biomass farm to its environmental costs, except that more dispersed operations will allow the environment’s natural defenses to function more effectively. It is interesting to note that some of the adverse impacts of collecting field wastes and of producing intensively grown biomass could be substantially mitigated by coupling biomass production operations with decentralized biogasification facilities.
When it comes to utilizing standing-forest biomass for energy, largescale users will exert a tremendous pressure for high-density harvesting of wood, probably by clear cutting. Decentralized users, by contrast, may be able to harvest their wood by selective harvesting operations. Selective cutting is considerably more environmentally benign, and can even be used to upgrade the timber quality on many woodlots. Thus while wood combustion produces substantially greater combustion emissions when used at small-scale decentralized facilities, it cannot be generalized that the environmental liabilities of biomass energy utilization are greater when decentralized systems are used. In many cases, the opposite is true. Biomass energy options span a broad range of technologies and applications, each with its own unique environmental characteristics. The scale of a particular biomass energy enterprise is not indicative of its environmental impact. Gregory Morris Energy and Resources Group University of California Berkeley, Calif. 94720
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November 1979, p. 1353, Figure 2. “Sulfate loading to lake water (g S04-2/ha/y)” should read “Sulfate loading to lake water (kg S04-*/ ha/ y) .” August 1980, p. 885. The name of the first author of the correspondence entitled “Accumulation of polychlorinated biphenyls in surficial Lake Superior sediments” is incorrectly reported. The correct name is Roger R . Greenburg. August 1980, p. 904. A study of nonpoint-source particles in the atmosphere was incorrectly attributed to John Cooper and co-workers a t the Oregon Graduate Center. The work was performed by Douglas W. Cooper and co-workers at the Harvard University School of Public Health.
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Environmental Science & Technology
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Corrections
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