Document JNZ0Rx2Yboj1gbpwMNm0QQnk6

Ecological Magnification Envlronmant/Taehnoiogy Ian C.T. Niabat A commonplace observation in monitor ing persistent chlorinated hydrocarbons is that residue concentrations are much higher in predatory animals than in other organisms or in the general environment. Usually residue levels are higher in her bivorous animals than in plants, higher in carnivorous animals than in herbivores, highest of all in carnivores that feed on carnivores. The spectacularly high con centrations of DDE and pcbs are thus found found in /tab-eating binds (such as ospreys and pelicans), bird-eating birds (such as falcons) and fish-eating mammals (such as seals and porpoises). Scientists commonly account for these frequencies by describing persistent chem icals as "ecologically magnified" or "ac cumulated in food chains." With the pro viso that most animals feed on more than one type of prey -- so that we should speak rather of "food webs" than "food chains" -- this serves as a fairly good em pirical generalisation. However, the sim ple word "accumulation" presents a mis leading impression of the underlying mechanisms' simplicity: Detailed studies show that the phenomenon is quite com plex and biologically inrerearing. Many features of ecological magni fication can be duplicated and studied under controlled conditions in the lab oratory. In one simple aquarium exper iment, algae accumulated dieldrin to levels 1,300 times higher than that in the ambient water, water-fleas to levds II timet those in the Igae; and guppies to levels 3.5 times those in the water-fleas. More sophisticated "model ecosvstems," incorporating both terrestial and aquatic plants and animals, have been designed at the University of Illinois. In these systems the highest concentrations were consist ently observed in fish (predators) and mails (scavengers). A number of different chemicals have now been tested under identical conditions in these systems: The measured degree of ecological magni fication is very closely correlated with and inversely proportional to the watersolubility of the chemical. Thus the prin cipal force behind the phenomenon of ecological magnification appears to be the partitioning of the chemicals between water and fat-containing organisms: The less soluble the chemicals are in water, the more strongly they are taken up into plants and animals. A simple partitioning theory does not work quantitatively, however. Partition coefficients for dot and ode between fat and water are of the order of 10* to 10*; yet in controlled experiments bio-accumu lation factors (ratios of chemical levels in organisms to tevels in ambient water) rarely exceed 10s. Thus the degree of ac cumulation must be limited by biological rather than physico-chemical processes. The Equilibrium Theory When organisms are exposed to constant levels of chlorinated hydrocarbons (cither in their food or, in the case of aquatic or ganisms, in their water environment), the concentrations of the chemicals rise rapidly at first and then level off to reach a quasi-equilibrium. At this point the rate of chemical intake is more or less balanced by the rates of excretion and of metabolic breakdown. The slower the rate of excre tion, the longer the time required to reach equilibrium and the higher the concentra tion in the tissues. As it happens, experi ments show a good general correlation be tween the size of the organism and the time required to reach equilibrium. In ex periments with dot and pcbs, for exam ple, approximate equilibrium is reached in a matter of hours in algae, days in crusta ceans, weeks or months in fish, months in birds and small mammals, and several years in humans. Thus larger animals gen erally have more difficulty excreting these chemicals than do smaller organisms -- a difference that probably has something to do with their lower metabolic rates and surface-to-volume ratios. Since predators are generally larger than their prey, this metabolic difference goes far to explain the phenomenon of ecological magnifica tion. So far, we have expressed in the term "ecological magnification" two rather dif ferent phenomena. Terrestial animals (in cluding man) ingest these chemicals primarily in their food -- or sometimes by inhalation. However, aquatic animals such as fish and crustaceans ingest the Spectacularly high lavaia of cNorinated hydrocarbons hava baan found In fish-eating birds such at tills brown palean. Scavanging animal* art particularly auacaptibia, aa thair t*et la mom HXoty to includa pray which has diad or boon weakened by axposum to tho chamicala. chemicals both in their food and directb from the water in which they live; tho have to process so much water in order tu obtain oxygen that the water is usually th< primary route of exposure to toxic chemi cals. The mechanisms are so different iho are often given different names: For an aquatic animal, the uptake of a chrmit.il from ambient water is termed "binaccumulation"; for an air-breathing am mal, uptake of a chemical from food in called "bio-magnification." "Bo-a. cumulation factors" for persistent chlo rinated hydrocarbons are <ypicai)y in flu range of 10* io 10' in laboratory condi tions, but "bio-magnification factors" .irr much more modest -- typically around ten for dot and pcbs and around one fm more water-soluble chemicals such ,\s dieldrin and lindane. In addition to the quasi-equilibrium ts tablished between an organism and its ex ternal environment, there often appears m be an equilibrium distribution of ilu chemical within the organism. If the ex *i htu*liK' It-M.ifi h/Aprii, 19^* MONS 0a2074 posed snimsli are killed and dissected, the chemical is often found distributed among organs in a more or less constant and pre dictable fashion. According to the most plausible model, the chemical is absorbed into the animal and circulated through the body in the blood, reaching an indepen dent equilibrium across the membranes which separate the blood from each organ in the body. Studies of the distribution of dieidrin in man, for example, show that it is partitioned between the blood, brain, liver, and fat In the ratios 1:4:23:136 re spectively. DD8 and rcas are still more strongly partitioned into fat. The more fat an animal contains, therefore, the higher will be its average body concentration and the higher the ecological magnification ratio calculated on a whole-body basis. As a general rule, predatory animals tend to be fatter than their prey, so this fact alone contributes to the phenomenon of ecolog ical magnification. Non-Equilibrium in the Real World Like most simple theories based on a few highly-controlled experiments, the equilibrium theory does not work too well in the real world. In the first place, no wild animal is ever exposed to constant levels of a chemical: Environmental residues are highly variable in space and time, so that it is unlikely that the ideal equilibrium is ever reached -- except in an abstract statistical sense. For large animals, the time required to reach quasi-equilibrium is longer than annual cycles of physiologi cal condition. Under recurrent stresses of food shortage, reproduction, etc, many wild animals deplete their fat stores peri odically, releasing fat-soluble chemicals to circulate through the body at high con centrations. Worse still, there is mounting evidence that the equilibrium theory may rest on an unsound empirical base. Several experi mental studies on various animal species exposed to dieidrin have shown that tissue concentrations reach a quasi-equilibrium after about one year of exposure but then start to rise sharply again after two years. Since most research projects are funded for only about two years, we know little : Continued on p. 68 PROFESSIONAL ENGINEERING FOR CAPITAL EXPENDITURE PROGRAMS provides COMPREHENSIVE SERVICES: CONCEPTUAL PLANNING to establish FINANCIAL FEASIBILITY PROJECT PLANNING for CAPITAL APPROPRIATION IMPLEMENTATION SERVICES for AUTHORIZED PROGRAMS TO ACHIEVE THE CLIENT'S INVESTMENT OBJECTIVE. MAIN Sngmttrs POWER INDUSTRY ENVIRONMENT CHAS.T. MAIN, INC. OSTON CHARLOTTE ' OCNVER PORTLAND I SENIOR RESEARCH ENGINEERS We are the world's leading manufacturer of instruments and systems used in Process Management and Control. Our products are used by over 7000 customers, in every major market of industrial importance. Two key assignments now exist at our modem headquarters in suburban Boston for advanced degreed EE's and ME's with at least seven years research engineering experience, including two years or more of technical leadership in Research, Design or Development work. Qualified candidates will have demonstrated high qualities o< design conception, innovation and leadership tn carrying out applied science research investigations. These investigations will pertain to industrial measurement techniques involving both theoretical procedures and practical design considerations, from basic concept through practical hardware demonstration and the inter action with systems. You may apply by resume or datallad /effer to Mr. Henry Sypfter, Professions/ Staffing, The foxboro Company, Dapt. TP-23, 30 Naponsat Avenue, Foxboro, Mess. 02035. Foxboro la an aqual opportunity amployar. MXBORO HONS 081075 Technology Review, March/April, tv7S 7 - . <*-. . - -->4~ 1'^ consideration In winft ft buck* nlvtl iVm tit mmmo( food: pratwon, kanesamg. ami prcpar* **; m ttcf mifu^rmout coHkihmi. *r*J fund* alum; tf waste man- >Hiww<: Jt>tt av*g * J"r- rrnimmu it to t4* *!, *ivd u*>ng it i>t nuip i of tram- j*satv>; of \t>irnMtniatu*i>: of cdma- of t h'vf h,>}m-n l HV Ivi- I, .innii a lot aS.mi cmrp ,m\M.nby preparing S. bool ,wd m tin- iHmte will consider hutUlmgs m (he hrn.tdrM context of en- tuoimH'tn.tl pl.ummp, taking into account mu only energy savings but all other forms of life-support systems as well. Ar chitecture, a dying profession, must ex pand its horizons from a wholly arsihenc/fi>rmfgoal*oricnted endeavor to mtr dedicated to providing people with meaningful environments that fully en hance the experience of living and that allow us to discover who we are in the context of the total world and the natural environment. Butchering Medicine As a Doctor nl Medicine and Surgery, I deeply resent th. headline "Science Comes to Medicine Slowly" by Mr. Victor ( ohn {/)rvir/vf. I974, [>p. R-9). There is much more to the "science of medicine" than the randomized double-blind con trolled study that Mr Cohn holds as his paragon of knowledge and truth. Dis missing all who came before Mayo as bumbling butchers crazed by the thrill of the knife does a disservice to a profession that since ancient rimes has led the at tempt at finding scientific explanations for natural happenings and whose literature is probably the most voluminous ever re corded. Journalism's "scientific accomplishments" should onfy hope to be as great. Joseph F. Adolph, M.D. Washington, D.C. The headline is the editors' -- not Mr, Cohn's -- responsibility. -- Ed. of chlorinated hydrocarbons. ScJccmc exposure is a particular hazard to scavenging animals -- those which e.it dead or moribund prey -- who arc thus m danger of selecting poisoned individualWe urgently need more critical study <t these processes. However, it is becoming clear that ecological magnification ,*i toxic chemicals is a phenomenon ulti mately controlled by ecologies! variable and not by the physiological or physivo chemical factors usually studied in the laboratory. Ian C. T. Nisbet, who writes regularly /or Technology Review, is Associate Director of the Scientific Staff of Massachusetts Audubon Society; he is a graduate of Cambridge University, England, m physics (Ph.D. I9S8). Purcell Continued from p. 12 The author, who holds three degrees from M.l.T. (B.Mch. and S.B. in Aero, and Astro. 70, and M.Arch. '?}), is Principal in the firm of Total Environmental Ac tion, building design, planning, and con sulting, of Harrisville, N.H. Letters Continued from p. 8 Should This Trip Be Up, Not In? It seems to me that our dries need to go up, not nut, in order to save commuting (see "Is This Trip Really Necessary?" De cember, 1974, p. ft4). A cluster city might have, say, eight skyscrapers possibly ar ranged around a park one-quarter mile in diameter. Each would have a purpose: offices, apartments, schools, recreation, medical, shopping, light fabrication, and car rentals. Surrounding the cluster would he tennis courts, soccer fields, garden plots, etc., for at least five miles. While currently people may prefer to "live away from work," they currently "live away from play" too. As car prices, gasoline prices, parking com, and travel rimes in crease, the idea of riding an elevator to work or to a tennis court gets more and more appealing. For vacation or trips to the next duster city, one could rent a car. This concept has been started in Washington, D.C, where apartments are now being built next to offices. Adding the buildings for other purposes could come soon -- and would require, I might add, a lot more thought on balance than I have given it. And sonic thought on how to use two extra hours a day, too. Alan Pope Albuquerque, N.M. Nisbet ContbuMd from p. 7 about this phenomenon. However, in man -- although tissue levels of dot appear to have reached equilibrium some time ago -- those of pdi! rise constantly with age -- an observation hard to reconcile with the equilibrium theory. Worst of all, laboratory studies now seem to underestimate grossly the poten tial for ecological magnification in the natural environment. In Lake Michigan, for example, the average concentrations of DDT and dieidrin in the lake water are in the range of 1 to 3 pans per trillion. Typical concentrations in fish are in the range of 0.2 and 10 parts per million, representing ecological magnification fac tors of roughly 3 x 10* and 10*, respec tively. Yet under experimental conditions ecological magnification factors for these chemicals in fish rarely, if ever, exceed 10* and S x 10*, respectively. Evidently some phenomenon leads to magnification 20 to 30 rimes greater in the wild than in the laboratory. Many similar examples could be cited involving unexpectedly high con centrations in wild fish, birds, and mam mals. One factor contributing to these anomalies is that the chemicals are distributed patchily in the environment and tend to be concentrated in biologi cally productive areas (e.g., sewage effluents or natural surface slicks). Pred atory animals tend to concentrate their activities in such areas, and they thus selectively expose themselves to high levels of pollurants. Probably a more im portant factor is selective predation-. It is well known that predators selectively take prey whose behavior is abnormal, and several studies have shown that they tend to select prey with above-average residues and N. Richard WertHamer, aoltd-staic physicist from Bel! Laboratories, wensponsored by A.P.S.; and Ronal Larson. Associate Professor of Electncai Engineer ing at Georgia Tech, joined os an l.E.E E. fellow. By the time these fellows arrived rn Washington in September, Dr. Hyman, the A.S.M.E. fellow who hod been with the Senate Commerce Committee staff since early spring, had dearly demon strated that a technical person on a fel lowship basis could make significant con tributions to Congressional staff work and win the respect and admiration of hit, peers. Dr. Hyman had become an energy conservation expert for the staff, the or ganizer of an important energy conserva tion hearing held before the Committee several months before the "energy crisis." The tension that preceded the arrtval of the new Congressional fellows gave way during their rwo-week orientation to a free exchange (hat revealed a lot about the curiosity, misconceptions, and mutual in terests of the new fellows and the "old pols." One Congressman's administrative assistant reminded the fellows that their presence probably meant a tripling or quadrupling of the total technical staff capability of Congress. A veteran staff member warned them, "As outsiders, don't expea to accomplish much. You'll probably spend most of your time ad dressing envelopes and answering con stituent mail." A Senator beamed and said, "We need you. You're welcome with open arms." The fellows, having a snappy rwo-week cram course in the institution they were about to serve, learned that privacy does not exist if you work in Congress and that the quiet office or iaborarory from which they had come would only be something to dream about over the next several months. 68 Technology Review, March/April, 1975 MQNS 082076