A COSTLY MYTH
IMPORTANT NOTE: This chapter is based on an article published by Prof. Zbigniew Jaworoski, former head of the UNSCEAR (United Nations Scientific Commitee on Atomic Radiation) in "21st Century Science and Technology", ("Posthumous Papers of Leaded Gasoline", Spring 1994, p. 34-41). Professor Jaworowski is a brillant multidisciplinary scientist working at the Central Laboratory for Radiological Protection in Varsaw, Poland. Eduardo Ferreyra only allowed himself to make some observations and comments in order to emphasize the idea that the fraud that has been comitted in the lead issue -no only related to leaded gasolines- is more serious than previously thought.
Also a scientific fraud, with the complacency of the press, whether the common yellow or the pseudoscientific. The ban on leaded gasolines costs France and Great Britain about $500 millions a year, and to the rest of the world probably more than $5 billions. Most of this money goes into special refining, associated with an increase in crude oil consumption of about 25%, a waste made at the expenses of future generations. It has been estimated that the cost of retrofitting for the oil and automotive industries is about $4 .24 billion -- for the USA alone.Short History of Lead Tetraethyl
It is time to ask if the ban on leaded gasolines was something necessary to diminish the levels of lead in the atmosphere, or if it has been an unnecessary waste of resources and money; a sacrifice made for pleasing those that blame mankind and industrial development for ruining the environ-ment.
This expensive ban of a "God´s curse", as gasoline additives have been labeled, was heralded as a victory by those involved with public risks, in a fierce battle against multinational oil and automo-tive corporations.(1) But, do leaded gasolines really contaminate the general public?
The answer is simple: they do not. The lead burden in the human body has decreased since the advent of modern industry and leaded gasolines --in spite of years of anti-lead propaganda that has erroneously led the public to believe the opposite. This decrease is largely due to improvements in technologies that made possible eliminating lead in tableware, kitchen elements, plumbing and other items related to food.
Between 1870 and 1972, lead production increased by a factor of 100. The use of alkydic leaded gasolines increased in the US in a constant manner, from zero in 1923 up to 25,000 tons in 1930, and 270,000 annual tons by 1970. During 1971, the maximum peak was attained worldwide with 640,000 tons. Nevertheless, and in spite of the ill intentioned propaganda against leaded gasolines, the scientific truth is that during the same period lead levels in the human bodies decreased in a sustained way!
It must not be surprising that this huge increase in leaded gasolines does not show up in the lead levels found in the organism, because we must look first into the physiology of lead intake by the organism, and lead concentrations in the atmosphere. First, and fundamentally, only 10% of lead found in the body comes from the air, while the remaining 90% comes from food and beverages ingested.
In general, it did not exist an increase in lead concentrations in air measurements taken in US cities between 1941 and 1965, precisely the moment when the use of leaded gasoline was increasing rapidly. Two give just two proved examples, levels of lead in Cincinnati and Salt Lake City air decreased during that period to a quarter of 1940 levels. (2) At the same time, a parallel reduction of lead content in agricultural produce. In Denmark, for example, lead traces in food decreased since 1962 and 1976 by a factor ranging from 3 to 5, while lead emissions by gasoline multiplied by 2,5! (3)
Properties of lead tetraethyl (LTE) as an additive for gasolines, were discovered in 1921 by Thomas Midgley, chief chemistry researcher at General Motors. Curiously, Midgley also led the team of researchers that discovered and synthesized the famous chlorofluorocarbons, or CFCs, chemicals around which there is an enormous hype going on, because their presumed (and never proved) blame on the destruction of the ozone layer. In my opinion, Thomas Midgley ought to be in the Mankind Benefactors Hall of Fame, in spite of environmentalists dissenting views.Catalytic Converters
Tetraethyl, when added in few thousands of a gram to a liter, makes internal combustion smoother and more uniform, giving increased power (HP), increasing fuel efficiency, and notoriously reducing consumption. Besides, lead deposits lubricate very efficiently valves and keeps valve seats clean. It makes unnecessary the use of chrome-tungsten seats or the use of expen-sive sodium valves. For those reasons, leaded gasolines became popular by 1923, while Public Health authorities in the USA determined that lead addition to gasoline imposed very little risk to the general public --although it was highly toxic during the manufacturing process.
First regulations to restrict the use of lead in gasoline are found in the Clean Air Act of 1970, allowing the EPA to regulate any gasoline additive deemed to be harmful for the health. The EPA ruled that unleaded gasolines must be in the market no later than July 1974. In December 1973, the EPA ordered the progressive and definite eradication of leaded gasolines, because it was discovered that lead acted on the platinum of catalytic converters and made them inoperable. The big Global Warming hype had started.
Finally, the Clean Air Act of 1990 forbids for ever the use of leaded gasolines after December 31st, 1995. And why all this prohibitions? We´ll see that very soon, but first let´s stop and see why the catalytic converters are useless --with or without platinum.
(A short essay by Eduardo Ferreyra)
Originally, it was assumed that these devices would eliminate from the air two of the most "dangerous" polluters known to man: sulphur dioxide and nitrogen dioxide which are, as everybody knows, gases commonly found in car exhausts. Let´s see a list of these components:
- Carbon monoxide (CO), from incomplete fuel combustion.
- Carbon dioxide (CO2), from complete fuel combustion
- Water vapor (H2O)
- Nitrogen oxides (NO, N2, N2O, NO2, etc, commonly known as NOx)
- Sulfur oxides: (SO, SO2, etc.)
- Various hydrocarbons: (Hx - Cx, etc.), cyclics and all types of chains.
Basically, these gases pass from the engine through the catalytic converter in almost all cars presently in use. Everything that goes into the converter exits by the other end, atom by atom.
Nothing "disappears", nothing remains in the converter. All that the converter does is "convert" one substance into another, and does it by ionization of different gases passing through it.
In few words, when carbon dioxide pass through the converter, it makes contact with platinum inside and decomposes in carbon and oxigen ions. Water is decomposed into hydrogen and oxigen ions. The same holds true for any gas that enters the catalytic converter.
But none of ions formed likewise exits the converter under the form of an ion. They can stay in ionized form only in the presence of the platinum inside the converter. As they emerge from the converter, and travel down the exhaust pipe looking for the exterior, all negative ions combine with positive ions at random combinations, following no fixed rules. That way, a free sulfur ion can combine with a hydrogen ion, instead of an oxigen ion. By the same token, a nitrogen ion can combine with hydrogen and carbon ions.
The same chemical reaction eliminates some of the sulfur dioxide in the exhaust, when forming hydrogen sulfide, which is a lethal gas used to execute criminals in the gas chambers.
Another problem is that much of what goes into the converter exits without being converted into anything. It remains in its original chemical condition. This happens because nothing man has designed is 100% efficient. It´s also due to the fact that no chemical reaction can never get to be totally completed. (The sensor inspectors put at the end of the tailpipes is a proof of this, because it´s not being measured if the air is being polluted or not, but how high is the pollution produced).
So, car drivers are only exchanging the relatively inoffensive nitrogen and sulfur dioxides for two of the most poisonous gases known to man. Everybody is familiar with the smell of "rotten eggs" emitted sometimes by their cars: is the odor of hydrogen sulfite. We have also smelled a "perfume aroma" coming out the exhausts. It´s not only the odor of cyanide but also of anilines, nitriles, and other compounds produced by the combination of hydrocarbons and nitrogen.
A final component of car pollution can include hydrocarbons, or big unburned fuel molecules. A good engine tune up can reduce this to tolerable levels, even for the most recalcitrant ecologists.
At the same time, if sulfur and nitrogen were eliminated from gasoline during production at the refineries, the use of catalytic converters would be totally unnecessary. Considering the huge cost imposed by unleaded gasolines, it would be a much cheaper and safer solution. Why has not been regulated and imposed, if regulations is what they love?
Human Physiology and Lead
In order to understand anything about lead in human beings, we must look first in it´s physiology. About 90% of lead in the organism is deposited in the bones, where it is firmly bond to minerals in the bones. Lead is also strongly bond to the keratin in hair. Thus, human bones and hair well preserved, are a good source of information about historical changes in lead concentrations in the human body.
Although has not been thoroughly investigated, it is possible that minimal quantities of lead could be essential for life (4)
. Lead absorption in the human tract is practically eliminated by a slight increase in the calcium and phosphorous in the diet. Because of this, "hard waters" (rich in these elements) protects who drink them from lead absorption. The highest levels of lead in blood are found in regions of "soft waters".
These are scientifically proved facts (5)
Mineral additives in food supplements for cows are highly efficient for eliminating lead absorption. In the bones of cows exposed to heavy traffic near Paris, scientists couldn´t fin not even a trace of lead, even they employed very sophisticated methods of detection. It turned out that calcium and phosphorous in the food additives completely block lead absorption in French cows. On the other hand, cows in other parts of Europe not having been fed with the mentioned additives --and wild animals too-- had lead concentrations in their bones that were two or three times higher than those found in humans. (6)
This is in part, the reason why between 1940 and 1960 --that is, during the maximum increase in leaded gasoline consumption-- there was not any increase of lead concentrations in residents of many big American cities. (7)
A researcher named Stopps tabulated all available data on "normal" human blood and the levels of lead in human urine, without finding any significant change between 1925 and 1965.(8)
There are not unusually high levels of lead in people living in regions of high traffic, as neither are there an association between owning a car and lead levels in blood.(9)
The big decrease in lead levels in the human body during the last decades is, nevertheless, the continuation of a much ancient tendency. What do statistics show in that respect? During the last hundred years, lead levels of human bones in Germany have been diminishing continuously. Also in Denmark, values have decreased from 19 micrograms for gram of bone (or m
g/g) in the 40s, down to 1.4 m
g/g in 1972.(10)
In the USA, between 1871-1923, lead content in adult hair was 93 m
g/g, but in 1971 it had dropped to 6 m
g/g! Thus, in the period of time when gases with lead from cars increased from zero to 270,000 tons
a year, the level of lead in human hair was reduced by a factor of 15!
These are scientific and undisputed facts accepted by all scientists worldwide.(11)
In a longer time scale, lead content in man has changed even more dramatically in many industrialized countries. Dr. Zbigniew Jaworosky recently reviewed 23 studies on lead content in 1000 bones of humans that lived during the last 6000 years in 13 countries. Data in 7 of those countries allows to make a comparison of the geographical distribution of lead levels, both contemporary and prehstoric. (12)
Present residents of 7 industrialized countries have an average lead level in bone that increments consistently from 1,5 m
g/g in Denmark, up to 25 m
g/g in Great Britain.
Until 200 years ago, there existed a similar trend. (Fig. 1) In places where lead levels were low in prehistoric times (ie.: Denmark, Japan and Poland), they still are low today. And where prehistoric lead levels were high, they continue to be, as in Great Britain. This shows that the control over the human lead burden in bone is exerted more by geology, and local foods and water, and not the industrial activity o exhausts fumes from cars. Figure 1 also show that the present lead level in bones in Denmark, Japan, Poland, Germany and France is just slightly higher than the levels found when came the advent of lead technology, and in the USA and Great Britain are lower than prehistoric levels. In fact, in 186 ancient US bones from the year 900, the lead content is 40 m
g/g, while the content in today´s USA residents go down to 17 m
Between prehistoric period and the 20th
century, both Americans and Europeans had a high lead concentration. In medieval times and until late 19th
century, lead levels in Europeans rose from the low prehistoric levels up to 40 m
g/g in Sweden and Denmark; from 58 m
g/g in Germany up to 100-280 m
g/g in France; and from 100 to 370 m
g/g in Poland. In Perú, lead level in bone went up from 0,1 - 2,7 mg/g in the precolumbian period, up to 100 m
g/g in early 1800s. Virginian settlers in the 17th
century had an average lead content of 93 m
g/g. In the remote Faroe Islands in the Arctic, levels were 33 to 240 m
G/g at the beginning of the Middle Ages.(13)
More Junk Science
As other frauds and scientific hoaxes in ecology, the story of leaded gasoline is based on junk science. In 1979, C.C. Patterson and his colleagues made a curious intent to establish a unique natural value for human bones --valid for all regions of the world and for all eras-- based in only two samples
(!) of ancient bones. (15)
They made essays with five samples of Peruvian bones 1300 years old, washing them in nitric acid and acetone. His drastic procedure took away most of lead deposited in vivo
thus, ulterior analysis gave results utterly invalid.
But, worse yet, data was manipulated in an unacceptable way for present standards of scientific methodology. Lead content in the five Peruvian samples gave values of: 0,11 - 0,16 - 0,71 - 1,4 and 2,7 mg/g, averaging 1,02 mg/g. The authors rejected arbitrarily the three higher values, nevertheless, because they didn´t fit in the levels they wanted to "find" in the bone samples, so they declared those values to be "wrong" because Peruvian didn´t produce lead.
From the remaining values --the lowest ones-- they got an average of 0,13 mg/g, showing an absolute contempt for statistics, scientific methodology and ethics. This grossly manipulated value was then presented and blessed as the "natural value" for all bones in all regions of the world, and for all epochs. Based on this methodological aberration, authors claimed that there was an increase of more than 100 times in lead levels in the bones of present day man, exactly as had been speculated in the famous paper by Patterson in 1965. (17)
Figure 1: Geographic distribution of average lead concentration in contemporary and prehistoric bones
Geographical differences are similar for both types of bones. Prehistoric levels in Denmark, Japan, Poland, Germany and France were slightly lower than present levels, while in the United States and Great Britain prehistoric levels were higher than today´s.
The leaders of the anti-lead movement, like Russel-Jones (18)
, then rejected any other evidence against and accepted this "natural" value as the Ultimate and Absolute Scientific Truth
. Using the same words Patterson, Russel-Jones said the results by Patterson "comprehend all available data of the essential and trustable data . . . the rest of the data about the issue lacked any scientific value"
, and all other researchers "should consider if their work is nothing but futile exercises wasting money and resources"
. Patterson rejected any criticism to his claims without further explanations.
As an example, when professor M. Rutter questioned Patterson saying: "I am sure that you will agree that replication constitutes the essence of Science"
, Patterson replied dryly: "No, I don´t agree"
For those ignoring it, replication is the system used by scientists to evaluate the validity of theories presented by any researcher. This is precisely what was never done with theories like the ozone layer, and many other, as the ban of DDT, PCBs, methyl bromide, CFCs, radon, asbestos, etc. "Replication" consists in repeating the experiments performed by the researcher being evaluated, and see if they give the same results. If the original work respected all steps and methodology required in a scientific work, the "replicants" will arrive indefectibly to the same results shown in the original work. This validate works and suggest that the theory or hypothesis presented by the researcher could be presumed right.
Of course Patterson could ever agree with Prof. Rutter sand, because the working method and his theory never passed any intent of replication. This should be shedding some light on the way the anti-lead lobby managed to obtain the banning regulation.
The Prophets of Lead
Figure 2: Historical trends in global lead production and lead concentrations in bones and hair
In medieval times and until late 19th century, lead subacute intoxication had reached pandemic dimensions. This was due to the extended use of utensils and tableware made of pewter, and lead compounds normally employed in medicines. The subsequent decline of lead intake by the human body happened during the same period that the global production of metallic lead increased 100 times, and production of lead for gasolines grew from zero to 640,000 tons a year.
In 1965 there were two papers (or pseudoscientific works) published that set the foundations for the mythology as lead as a threat. Those fantasies were titled: Lead Poisoning and the Fall of Rome , by S.C. Gilfillan, (who spread world wide the fear for mental deficiency caused by lead) (20), and "Man´s Natural Lead Contaminated Environments", by C.C. Patterson, who dispatched the absurd theory that global environment was presently contaminated wit lead levels 1000 times higher than natural levels. (21) These two works, cornering stones of the anti lead movement, deserve a quick examination in order to see how far the anti-science, anti-progress, anti-mankind dishonesty of the environmental movement can go.
Gilfillan claimed that lead in the luxurious tableware and food was poisoning the rich Romans, but no the poors- Apparently, this "aristonacy" killed the wise and brilliant thinkers that, in each generation, were promoted from the lower classes to richness and then to extinction. The poisoned rich had their fertility decreased, their death advanced, and their surviving children mentally diminished. Because of this --according to Gilfillan-- good genetic components were eliminated from the Roman population and the result was dysgenia and the cultural disaster of Dark Ages and the Byzantine stagnation.
The paper by Gilfillan was simply a fairy tale. Historian gets frantic when they confront this simplistic explanation based on barely anecdotal evidences. (22) Then Gilfillan devoted himself to analyze a collection of ancient Greek and Roman bones in the quest to find high lead levels that would support his crazy theory. Saying "... clinical necromancy will add the final seal of approval to a sufficiently logic evidence that doesn´t need it." He really believed in finding high levels of lead and promised he would publish them in an ulterior paper. He never did.
When, few years later the results were not published, the famous scientist Zbigniew Jaworosky (Professor Emeritus at the Radiological Protection Laboratory in Warsaw, and former president of the UNSCEAR, United Nations Scientific Committee on Effects of Atomic Radiations) asked Gilfillan for the complete results, he never answered a single line, even to the insistent calims by other distinguished scientists. To date, results form the famous theory about lead in ancient Romans are still hidden in the utmost secret. It was a total flop!
Nevertheless, as we´ve seen before, since Medieval times until late 19th Century, Europeans were highly contaminated with sub acute levels of lead. Historically, it is the same period when experimented a cultural, social, artistic, economic and scientific dynamism as never before --a phenomenon contradicting Gilfillan´s theory about mental hindrance due to lead.
In spite of such absurd theory, Gilfillan´s first paper received an immense publicity world wide. and had an immediate popular attractive. Since then, the current opinion is that the fall of the Roman Empire was caused by the lead poisoning of the ancient aristocrats. The message in the paper was quite clear: modern society was doomed to extinction because it uses more lead than ancient Romans did.
This unbelievable theory --mere speculations without any scientific base--was accepted without major intellectual efforts by the American researcher H.L. Needleman, who claimed that the normal levels of lead in school children (24) (sufficiently low in that epoch) diminished their mental capabilities. Although Needleman´s studies were constantly criticized for their scientific and methodological flaws, (25) they were nevertheless accepted for its face value by regulatory agencies. The controversial claims by Needleman were easily accepted by the EPA (nothing better that hearing what you desire to hear...) and other similar agencies in other countries, because the field had been perfectly prepared by C.C. Patterson paper of 1965, which caused a sensation.
Patterson False Hypothesis
Claims by Paterson about the atmosphere being extremely contaminated with man made lead, and that the present lead content in man was 100 times higher than normal environmental levels, were pure speculations not based on measurements of historical changes in levels in air or in the human body. Patterson did not measure lead levels in any object in the past or the present, instead he established what it labeled as "global normal level"
by means of extrapolations, absurd calculations and wild assumptions. The basis for levels corresponding the human body, was the assumption that there is a close correlation (related to atomic weight) between the abundance of metals in the Earth´s crust and man: the "crust/body"
ratio. Fundamental differences between these elements were totally ignored.
Instead, the theoretical normal level of lead in man was found by the simple division of the abundance of lead in Earth´s crust by the "crust/body" ratio for barium! What has to do barium with lead? In spite of this, Patterson claimed he managed to calculate the total natural content
of lead in man and, according to him, it was about 2 mg --that is, 100 times below the levels normally measured by the scientific community. As it has been demonstrated thousand times, Patterson was wrong - and he still is.
In the next table, we can see that crust/body ratio varies widely, without relation to atomic weight, whether for the essential elements as iron and zinc, or for not essential as tin. Using the ratio for radium, for example, natural content of lead in man can computed as being 0.65 mg; using strontium ratio gives 11 mg, and using that of the essential calcium the natural lead burden will be 290 mg!
Such calculations are, nevertheless, simple academic exercises that have nothing to do with the real world. Pre-industrial levels of lead in man can only be correctly estimated by the analysis of ancient human bones, where 90% of the lead absorbed by the organism is deposited. As it is known, in order to obtain these figures, more than 1,000 bone samples were analyzed in the entire world, and results completely refute Patterson´s hypothesis.
It is obvious that in the pristine atmosphere lead concentrations must vary in different areas according to local o regional variations of lead sources, as dust from rocks and soils blown by wind and so forth. Thus, and in accordance with geochemical conditions, we can expect to find very little lead in the Antarctic and, on the other hand, high concentrations will be found in swamp plains in the interior of continents, that emits lead tetraethyl in a natural manner (26)
, o places in countries with many mineral diggings as the Peruvian Andes, Equatorial Africa, or Eastern Spitzberg in Norway.
The majority of continental lands are in the Northern Hemisphere, so it follows that the atmosphere there must have more lead than the South. Also, after volcanic eruptions it can be seen a lead increase in the atmosphere. Because of this --and it is fundamental-- it is not possible to have a unique and uniform lead level in the atmosphere, valid for the whole world and for all times.
ABUNDANCE OF METALS IN
EART´S CRUST AND HUMAN BODY
|ATOMIC ELEMENT||CRUST WEIGHT|| HUMAN BODY|
mg/kg - mg/kg
Ca ||40.08 ||41.500||14.000||3 |
87.62||375|| 4.6|| 82|
.Source: Adapted from Weast et al., 1987, and ICRP, 1975
In fact, lead concentrations in remotely dispersed areas vary by a factor of 1,000, from 0.0001 mg/m3 in the South Pole, to 0,01 mg/m3 in Greenland, and 0,1 mf/m3 in the Andes. (27)
All these facts, data and real and proven factors were not taken into account by the Apocalyptic Prophets of Lead like Patterson, when computed just a unique and uniform value for natural lead in the atmosphere of 0,0005 mg/m3, claiming this value was valid for the whole world and for all Ages. This value was estimated from the content of dust in rural areas in some places in the United States, and from the assumed mass of volcanic particles, from forest fires, salt water and parti-cles in meteorites in the global atmosphere, multiplied by lead concentrations assumed for various types of dust abundant in Earth´s crust, silica content, and so forth.
But, the basis for estimates in lead concentration in air, or for similar estimates of lead fluxes in the global atmosphere are not correct because aerial aerosols are very enriched with lead --up to various order in magnitude above levels in Earth´s crust, salt in oceans or organic ashes.
The enrichment with lead by the aerial aerosols, discovered in the early 1970s, was considered at first as a proff of an anthropogenic contribution, and Lead Prophets rapidly interpreted this as a proof of a global scale contamination by the lead coming from the gasoline. But very soon afterwards it was discovered that this was not the case, given the aerial aerosol samples taken in remotes parts of the world and oceans, were enriched with lead levels up to 2,000 times more. (29)
It was also found an enrichment of similar factors or bigger, for other type of metals (cadmium, silver, mercury, zinc, copper and antimony), that were not dispersed in the air by man in quantities comparable with lead.
Even more, it was the discovery that factors for enrichment with lead and other metals in the pre-industrial aerial dust, preserved in many glaciers, were similar to those found in present rains, averaging 300 for lead. (30)
This enrichment is caused by various natural processes, the most important is probably the methylation of metals by bacterias and algae, and volcanic activity.
Consequently, all estimates of the natural content of lead in the atmosphere or fluxes where the metal enrichment of aerial dust is not considered, are wrong by up to two orders of magnitude. The annual flux of dust in the global atmosphere is about 4,500 Ktons -estimated by means of classical methods of tracers, using Pb-210 (natural) and Cesium-137 (from nuclear blasts) . This flux of natural origins dwarfs ridiculously lead emissions form car exhausts, that barely amount to 340 Ktons.
In spite of all this, Patterson´s study is the corner stone of the building of irrational banning of leaded gasolines. Various other works --always related with the powerful environmental lobby-- haver tried to demonstrate, unsuccessfully, that lead in the atmosphere has increased 500 times since ancient times, that man is poisoning with lead and other horrifying stories by the like. It will be an interesting task for historians in the future discover why a great chunk of the scientific community accepted gullibly the conclusions of an increase of x500 in lead, due to human intervention, taken solely from a single ad flawed study, full of anti-scientific methdology while, at the same time, rejecting innumerable studies proving that virtually there is not an increase in environmental lead and, at the same time, an very important decrease of lead in the organism of animals and human beings, beginning in the 19th Century.
The recent decrease of lead in the human body was not achieved by any anti-lead regulation. It is a beneficial effect of modern industry, that brought us an improvement without comparison in life standards, and public health. Modern technologies made possible the elimination of many sources of lead form our near environment, such as pewter tableware and kitchen utensils, vessels and containers, water plumbing, medicines, cosmetics, paints and other things that caused lead poisoning in past centuries.
Lead detoxifying in mankind is a process that began 120 years ago and has nothing to do, whatsoever, with the rise and fall of leaded gasolines, nor with any action taken by environmentalist organizations and their absurd regulations. The anti-lead lobby could continue with its myth about killer lead, but society is paying too high a price for this stupid and faudulent myth, costs that future generations will keep paying.
- J.O Nriagu, 1990. «The Rise and Fall of Leaded Gasoline.» The Sci. Tot. Environ. Vol. 92, pp. 13-28
- NAS, 1972. Lead:Airborne Lead in Prespective. Washington D.C. National Academy of Science, pp. 1-330
- P. Solgaard, A. Aarkrog, J. Fenger, H. Flyger y A. M Graabaek, 1978. Nature, Vol. 272, pp. 346-347
- P.T.S. Wong, B.A. Silverberg, Y.K. Chau y P.B. Hodson, 1978. «Lead and the Aquatic Biota», en «The Biochemistry of Lead in the Environment», Part B, ed. J.O. Nriagu, Amsterdam: Elsevier, pp. 279-342 y Royal Commission, 1983
- J. Gallacher, L. Harns y P.C. Elwood, 1983. "Lead Tocisty from Watered Nature," Vol. 305 p.280 - y S.J. Pocock et al., 1983. «Effects of Tap Water Lead, Water Haness, Alcohol and Cigarettes on Blood Lead Concentrations», Journal of Epidemiology & Community Health, Vol. 27, pp. 1-7
- Z. Jaworoski, 1990. «The History of Trace Element Contamination of Human Bones» En: «Trace Metals and Fluoride in Human Bones and Teeth», ed, N.D. Priest y N. Van de Vyer, Boca Raton, Fla., CCR Press, pp. 175-190 y Jaworoski, F. Barbalat, C. Blain, y E. Peyre, 1985. «Heavy Metals in Human and Animal Bones from Ancient and Contemporary France»,The Sci. Tot. Environ. Vol. 43, pp. 103-126
- R.A. Kehoe, 1964. «Standard with Respect to Atmosferic Lead.» Archives on Environmental Health, Vol. 8, pp, 348-354
- G.J. Stopps, 1965. «Lead Concentration in Blood and Urine of 'Normal' Populations: A Review», Symp. Environmental Lead Contaminations, Washington, D.C. (Dec.13)
- P.C. Elwood, 1986. «The Sources of Lead in Blood:A Critical Review.» The Sci. Tot. Environ. Vol. 52, pp. 1-23. Ver también el Isotopic Lead Experiment Status Report, EUR-8352-EN, publicado por la Comisión de Comunidades Europeas en 1982.
- See Jaworoski (note 6)
- D. Weiss, B. Whitten y D. Leddy, 1972. «Lead Contents in Human Hair (1871- 1971)», Science, Vol. 178, pp. 69-70
- Jaworoski, 1990. (note 6)
- O.V. Nielsen, P. Grandjean y P. Bennike, 1982. «Chemical Analysis of Archeological Bone Samples: Evidence for High Lead Exposure on the Faroe Islands.», Journal of Danish Archeology, Vol. 1, pp. 145-148
- Jaworoski, 1990 (nota 6)
- J.E. Ericson, H. Shirahata y C.C. Patterson, 1979. «Skeleton Concentration of Lead in Ancient Peruvians.» New England Journal of Medicine, Vol. 300, pp. 946-951
- P. Grandjean, 1988. «Ancient Skeletons As Silent Witnesses of Lead in the Past.» CRC Critical Reviews in Toxicology, Vol. 19, pp. 11-21
- C.C. Patterson, 1965. «Contaminated and Natural Lead in Environments of Man.» Arch. of Environmental Health, Vol. 11, pp. 344-360
- R. Russel Jones, 1983. «The Contribution of Petrol Lead to Blood Lead Via Air, Dust and Food.» Atmospheric Environment, Vol. 17, pp. 2367-2370
- M. Rutter y R. Russel Jones, 1983. «Lead Versus Health, Sources and Effects of Low Level Lead Exposure.» New York: John Wiley & Sons.
- S.G. Gilfillan, 1965, «Lead Poisoning and the Fall of Rome.» Journal of Occupational Medicine, Vol. 7, pp. 53-60
- C.C. Patterson, 1965 (nota 17)
- A. Cameron, 1983. «Fall of the Roman Empire: More Than Lead.» International Herald Tribune (June 20); y J. Eisinger, 1984, «Lead in History and History of Lead.» Nature, Vol. 307, pp. 573
- H.L. Needleman, C. Gunnoe, A. Leviton, R.R. Reed, H. Peresie, C. Maher, y P. Barret, 1979. «Deficits in Psycologi-cal and Classroom Performance of Children With elevated Dentine Lead Levels.» New Englan Journal of Medicine, Vol. 300, pp. 689-695
- Needleman critics have filed a legal suit in the Federal Court claiming Needleman incurred in scientific fraud. See: J. Palca, Science, Aug. 23, 1991.
- R.M. Harrison y D.O.H. Laxen, 1978. «Natural Source of Tetraalkyllead in Air.» Nature, Vol. 275, pp. 738-739
- J.H. Harley, 1970. «Sources of lead in Perennial Ryegrass annd Radishes», Environmental Sci. Technology, Vol. 4, pp.225; y G.B. Wiersma y C.I. Davidosn, 1986. «Trace Metals in the Atmosphere of Remote Areas.» En: J.O. Nriagu y C.I. Davidson: «Toxic metals in the Atmosphere.» The Sci. Tot. Environ. Vol. 91, pp. 201-266
- L. Kownacka, Z. Jawoeoski y M. Suplinska, 1990. «Vertical Distribution and Flows of Lead and Natural Radionuclides in the Atmosphere.» The Sci. Tot. Environment, Vol. 91, pp. 199-221
- F.C. Boutron, U. Görlach, J.P. Candelone, M.A, Bolshov y R.J. Delmas, 1991. «Decrease in Antropogenic Lead, Cadmium, and Zinc in Greenland Snows since the Late 1960s», Nature, Vol 353, pp. 153-156
- See references in Z. Jaworoski, M. Bysiek y L. Kownaka, 1981, «Flow of Metals into the Global Atmosphere.» Geochim. Cosmochim. Acta. vol. 45. pp. 2185- 2199
- M. Murozumi, T.J. Chow, y C.C. Patterson, 1969. «Chemical Concentrations of Pollutant Lead Aerosols, Terrestrial Dusts and Sea Salts in Greenland and Antartic Snow data.» Geochim. Cosmochim. Acta. vol. 33. pp. 1247-1294
- See review in D.H.M. Alderton y D.O. Coleman, 1985. «Ice Cores and Snow.» En: «Historical Monitoring». Monitoring and Assessment Research Centre, University of London, pp.97-153.
- See the report on 1983 «Lead in the Environment: The Ninth Report of the Royal Commission on Environmental Polution», Her Majesty's Printing Office.
- Alderton y Coleman, 1985, (nota 33)
- R.S. Bradley y J. England, 1978. «Volcanic Dust Influence on Glacier Mass Balance at High Latitudes.», Nature, Vol. 271, pp. 736-738
- 1975, Report of the Task Group on Reference Man. International Commission on Radiological Protection. Oxford, Pergamon Press, pp. 1-480
- C. Weast, M.J. Astle y W.H. Beyer. 1987. CRC Handbook of Chemistry and Physics. Boca Ratón, Fla. : CRC Press, pp. F-137
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