Reproduced with pennission from Annua~ Reviews Inc.

Ann" Rev. Energy Envirl»l. 1995. 20:301-24Copyright C 1995 by An/IUa/ Reviews loc. AU rights reserved

THE ELIMIN A TI 0 N OF LEADIN GASOLINE

v. M. ThomasCenter for Energy and Environmental Studies, Princeton University, Princeton, NewJersey 08544-5263

KEY WORDS: unleaded gasoline, exp~ure, valve-seat recession, tetra-etby11ead, MrBE,refinery costs, catalytic converters, benrene

CONTENTS

INTRODUCfION 302STATUS OFrnE USE OF UNLEADED GASOUNE 302

RELATIONSHIP OF LEAD USE IN GASOLINE TO LEAD IN BLOOD. 305NHANES 306ExposureCalculation 308Isotopic Analysis 309Claims That Blood Lead Levels Are Uncorrelated With Leaded Gasoline Use 310

DO SOME CARS NEED LEADED GASOLINE? 312COST OF ELIMINATING LEAD FROM GASOUNE 314

Cost of Lead Additive 314CostofMTBE 315Cost of Refinery Options .'."""" 316

OTHER HEALTH AND ENVIRONMENTAL ASPFcrS OF GASOLINE.FORMULATIONS 316

Catalytic Converters 316Benzene , 317Energy "",."".". 318~ CONCLUSIONS 319

ABSTRACT.Due to the health consequences of lead exposure, as well as to the introductionof catalytic converters, many countries have reduced or eliminated use of leadadditives in motor gasolines. But in many other countries, leaded gasolineremains the norm. In these countries there is often confusion about the healthsignificance of2,asoline lead, the ability of cars to use unleaded gasoline, andthe costs of unleaded gasoline. This chapter shows that leaded gasoline is amajor source of human lead exposure. All cars, with or without catalytic

301

1056-3466/95/1022-0301$05.00

302 maMAS

converters, and with or without hardened exhaust valve seats, can use unleadedgasoline exclusively. Unleaded gasoline typically costs on the order of $0.01more per liter than leaded gasoline to produce. Recent concerns about benzeneexposure from unleaded gasoline have been addressed through choice of gaso-line formulation and other measures.

INTRODUCTION

The health effects of lead and the dynamics of exposure to lead from gasolineare better understood than those of almost any other pollutant. A growingnumber of countries have seen a successful transition to unleaded gasoline.Yet in most countries, leaded gasoline is still used, and in many developingcountries unleaded gasoline is unavailable. When governments consider re-ducing lead levels in gasoline, confusion and argument often surround ques-tions about the health significance of lead in gasoline, the ability of the vehiclefleet to use unleaded gasoline, and the costs of alternatives to lead. This reviewexamines and clarifies the points of confusion, focusing on exposure to leadfrom gasoline and the ability of cars to use unleaded gasoline.

STATUS OF THE USE OF UNLEADED GASOLINE

As of 1993, an estimated 70,000 tons of lead were added to gasoline worldwide(I). As shown in Tables la and lb, about half of the worldwide total of leadused in gasoline is used in the former USSR, eastern Europe, and the Far East.The remainder is used, in approximately equal amounts, in western Europe,Africa, the Middle East, and the Americas. In many countries, unleaded gaso-line is unavailable.

Octel, Ltd. (88% owned by Great Lakes Chemical and 12% owned byChevron) is almost the sole producer of lead gasoline additives worldwide.Ethyl Corporation, until recently the other major producer, stopped productionof these additives in 1994. However, Ethyl continues to sell lead additives,buying its supplies from Octel (2). The other producers are facilities in Ger-many (less than 4000 tons lead per year) (3) and in Dzerzhinsk, Russia (about5000 tons lead per year) (V Prozerov, personal communication). Total annualsales of lead additives are on the order of $1 billion.

The antiknock properties of tetra-ethyl lead (TEL) were discovered in theUnited States by Thomas Midgley and colleagues at the General MotorsResearch Laboratory in 1921 (4). (Nine years later, in the same laboratory,Midgley also developed chlorofluorocarbons.) Commercially introduced in theUnited States in the 1920s, leaded gasoline soon became standard (5). Owingto the introduction of catalytic converters and a better understanding of therisks of lead exposure, leaded gasoline was phased out in the United States

LEAD IN GASOLINE 303

Table la Estimated use of leaded motor gasoline in Europe and the Middle East

Motor gasolineconsumption" Lead content of Leaded gasoline

(109 liters leaded gasoline Total added lead percent share

Country per year) (g liter-l)b (tons per year) (year)

Western EuropecFrance 27 O.IS 2,400 S9 (1993)Italy 19 O.IS 2.200 76 (1993)United Kingdom 33 O.IS 2,300 47 (1993)F~r Yugoslavia 3.6 O.S 1,800 98 (1991)Spain II O.IS 1,600 94 (1992)Gennany 42 O.IS 690 II (1993)Tur1cey 4.4 O.IS 6SO 90 (1994)"Portugal 1.9 0.40" 600 79 (1993)Greece 3.3 0.40" 3SO 77 (1993)Switzerland S.O O.IS 260 3S (1992)Belgium 3.7 O.IS 240 43 (1993)Luxembourg S.2 O.IS 240 31 (1993)Netherlands 4.7 O.IS ISO 2S (1993)Norway 2.4 O.IS 140 40 (1993)'Finland 2.7 O.IS 120 30 (1992)Ireland 1.2 O.IS 110 62 (1993)Denmar1c 2.2 O.IS 79 24 (1993)Sweden S.7 O.IS 9 I (1994)'Austria 3.S -0 0 (1993)Other 0.2 O.IS 30--Total 170 14,000

Eastern Europe andFormer USSRFormer USSR 100 0.2h 10,000' 60 (I994YRomania 2.8 0.6 1,700Poland 3.7 O.IS 490 88 (1993)"Former Czechoslo- 2.3 O.IS 330 97 (1991)1vakiaHungary ~ O.IS" ~ 7S (1993)m

Total 120 13,000Middle East

Saudi Arabia 9.3 0.4 3,700 100Iraq 4.4 0.4 1,700 100

-Iran 8.1 0.19 I,SOO 100Kuwait" 1.2 0.S3 620 100UAR 1.3 0.4 S30 100Syria I.S 0.24 360 100Israelo 2.1 O.IS 310 <100Quatar 0.4 0.4 7S 47 (1992)Other ~ 0.4 ~

Total 31 11,000World Total 9SO 70,000

"Aviation gasoline, used by aircraft with piston engines, is not included. In the United States, the lead in aviation gasoline istypically O.S -0.8 g liter-I and about 109 liters per year of aviation gasoline is used, for total lead emission of about 840 tons peryear. Data are taken from Reference 98. "Data from Reference 8, unless otherwise noted. cUnless otherwise noted, fromEurostat, Brussels (1994 data). "Reference 99. .Reference 100. 'Reference 101. .Reference 12. "Reference 102. i V Prozerov,personal communication. j Y Minaev, personal communication. "Reference II. I Reference 81. m B Levy. personal communica-

tion. "Reference 103. °Reference 104.

,

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Table Ib Estimated use of leaded motor gasoline in Europe and the Middle East

Motor gasoline Lead content of Leaded gasoline

consumption" (109 leaded gasoline Total added lead percent shareCountry liters per year) (g liter-')b (tons per year) (year)

North AmericaMexico' 26 0.07 1,300 70 (1993)United Statesd 430 0.026 100 I (1993)Canada -E- -~ 0 (1993)

Total 467 -1,400Central and South Amer-

ica and CaribbeanVenezuela" 7.7 0.37 2,600 ~ (1993)&:uador 1.5 0.84 1,200 >95 (1993)'Argentina' 4.5 0.2 900 70 (1994)"Peru 1.2 0.84 920 91 (1992)Chile 1.6 0.42 660 99 (1992)Puerto Rico 2.9 0.13 380?Virgin Islands 0.23 1.12 260?Trinidad and 0.36 0.4; 140 100

TobagoColombia' 6.4 -0 0Brazil 17 -0 0Suriname 0.06 -0 0Antigua 0.02 -0 0Other 8 0.4 2,700--Total 53 9,700

AfricaNigeria 6.4 0.66 4,200 100South Africa 6.4 0.4 2,600 100Algeria 2.6 0.6 1,700 100Libya 2.0 0.8 1,600 100Egypti 2.0 0.35 700 100 (1994)Other 6.4 0.4 2,600 100--Total 26 13,000

Far East and OceaniaAustralia 17 0.3 2,700 53 (1993)-China' 30 0.03 900 100 (1994)Indiam 4.8 0.15 700 100 (1994)New Zealand 2.5 0.45 640 57 (1994)"Thailand 3.7 0.15 440 79 (1993)"Malaysia 3.8 0.15 300 SO (1994)"Taiwan" 4.9 0.026 70 55 (1993)qSri Lanka' 0.23 0.2 SO 100(1993)Singapore 0.58 0.15 35 40 (1993)"Hong Kong 0.35 0.15 32 62 (1991)'Japan 44 -0 0South Korea 3.8 -0 0Other 15 0.4 6,000--Total 130 12,000

World Total 9SO 70,000

"See Footnote a, Table la. b Data from Reference 8, unless otherwise nnted. 'M Barbiux, personal communication. d JCaldwell, personal communication. "Reference II. 'Reference 105. "Reference 106. hReference 107. ; Ramlel, personalcommunication. jReference 108. -Reference 67. 'Reference 109. mReference 110. "Reference III. °Reference 112.PReference 113. qT-N Wu, personal communication. 'Reference 114. 'Reference 81.

LEAD IN GASOLINE 305

beginning in the 1970s and now accounts for less than 1 % of gasoline sales.The use of leaded gasoline for highway vehicles will be banned in the UnitedStates as of January 1, 1996.

In Japan, reduction of lead in gasoline began in the 1970s, after reports ofhigh blood lead concentrations in Tokyo (6, 7). More recently, leaded gasolinewas eliminated in Canada, Brazil, Colombia, Austria, South Korea, and Swe-den (8-12). In addition, Suriname and Antigua have reportedly eliminatedleaded gasoline (8). In the European Union, the lead content of gasoline islimited to 0.15 g literl, and all new cars are required to have catalytic con-verters, which require the use of unleaded gasoline (13).

The Soviet Union was the first country to restrict use of lead in gasoline:By 1967, its sale was banned in Moscow, Leningrad, Kiev, Baku, Odessa, andtourist areas in Caucasia and the Crimea (14). This action was apparentlyprompted by Soviet research on the effects of low-level lead exposure (15).Use of leaded gasoline continued elsewhere in the country, and the formerUSSR is now apparently the largest user of leaded gasoline additives.

The following countries-all developing nations-allow the highest con-centrations of lead (?; 0.8g liter-I): Aruba, Bahamas, Barbados, Belize, Benin,Burkina, Burundi, Cape Verde Islands, Central African Republic, Chad, Cuba,Curacao, Dominican Republic, Ecuador, Equatorial Guinea, Fiji, Guinea,

Guinea-Bissau, Haiti, Honduras, Indonesia, Ivory Coast, Jamaica, Lebanon,Libya, Macao, Madagascar, Mali, Maritius, Marshall Islands, Myanmar(Burma), Nauru, New Caledonia, Norfolk Islands, Panama, Papua, Paraguay,Peru, Rwanda, Sahara West, Saint Martin, Seychelles, Sierra Leone, SolomonIslands, Somalia, Uganda, Virgin Islands, West Samoa, and Zimbabwe.

RELATIONSHIP OF LEAD USE IN GASOLINE TO LEADIN BLOOD

The US Public Health Service has said that lead exposure is the greatestenvironmental health threat to children (16). Figure 1 shows the effects of leadexposure at various levels. Prenatal, postnatal, and perinatal blood lead con-centrations of 5-15 ~g dl-1 have been associated with detrimental effects oninfant growth and development (17). Most studies report a 2- to 4-point averageIQ deficit for each increase of 10--15 ~g dl-1 in blood lead within the rangeof 5-35 ~g dl-l, and no threshold has become apparent for this effect.

One of the main points of controversy has been the relationship of lead ingasoline to blood lead levels. Gasoline lead, emitted to the air, falls back tothe earth and contaminates soil, urban dusts, and crops. Thus, this lead is notonly inhaled, but is also ingested as lead deposited on soil and dust, food cropsand pasture land. Exposure to gasoline lead depends not only on the amountof lead used locally in gasoline, but also on traffic patterns, diets, food sources,

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I1g/dLDeath

EncephalopathyNephropathy

Frank Anemia

Colic

Hemoglobin Synthesis ~

Vitamin D Metabolism~

Nerve Conduction Velocity ~

Erythrocyte Protoporphyrint

Vitamin D Metabolism (?)

Developmental ToxicityIQ~Hearing ~Growth~

Transplacental Transfer -

t Increased function ~ Decreased function

Figure J Lowest observed effect levels of inorganic lead in children (l1g dI-1 (18).

and personal habits. Exposure to lead found in paint, plumbing, cosmetics,eating or drinking utensils, soldered food cans, some industries, and drinkingwater complicates measurements of leaded gasoline's contribution to bloodlead levels.

Overall, human exposure to lead is currently two to three orders of magni-tude greater than it was in the preindustrial period (19). How much does leadedgasoline contribute to blood lead levels? Below I review data on changes inpopulation blood lead levels as use of lead in gasoline has decreased, calcu-lations of the expected contribution of lead in gasoline to lead in blood, isotopicstudies of the contribution of gasoline lead to blood lead, and studies claimingthat gasoline lead is only a minor contributor to blood lead levels.

NHANESThe most extensive studies of blood lead concentrations are NHANES (Na-tional Health and Nutrition Examination Study) II and NHANES III. NHANESII surveyed 27,801 people aged 6 months to 74 years living in 64 areas of the

LEAD IN GASOLINE 307

110 -lead used in gasoline

---average blood ~ad levels 16

100

15"& ~.- ,\ ....

90 -

.\ ~""0. \ 14 "'ii 2'5 \ >"tJC \.! '-o~ \"O~~ 0 80 \ 13 : '"ID- \-E..-g \"0 ~.~ \ Obi0." \ 00" -'-

"0 0 70 \ 12 .a \e

~£ \!.E~ \ W'~11-"0 \..-0II \" '-..> ..= 60 \ 11 II Q.~ \ bI0 \ ~..,

1050

oT I I I I ~9

1976 1977 1978 1979 1980 1981

year

Figure 2 Decreases in blooo lead values and amounts of lead used in gasoline during 1976-1980

(18).

United States. The results, in Figure 2, show US use of lead in gasoline andaverage blood lead levels in the United States between 1976 and 1980 (20).The figure shows a 50% drop in use of lead in gasoline, coincident with a 30%drop in blood lead levels (21). Lead from gasoline was the major source of airemissions of lead (22), and the reduction of lead in gasoline is generallyaccepted as the cause of most of the reductions in blood lead levels.

Correlation, of course, does not prove causation. Several factors could havecaused the downward trend. Some authors have suggested that the data couldbe explained by either the reduced use of lead-soldered food cans or by errorsin sampling and statistical analysis (23). A time-dependent sampling or statis-tical error does not plausibly explain the data; the NHANFS II data wereadjusted via regression for the effects of race, sex, region of the country, season,income, and degree of urbanization. Further studies, such as NHAN~ III,confirm that blood lead levels continued to decrease significantly. By 1988-1991, when the use of lead in US gasoline had been almost completely elimi-nated, the average blood lead levels of persons aged 1-74 years in the UnitedStates had dropped to 2.8 ~g dl-l (24).

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Reduced use of lead-soldered food cans might explain some of the decreasein blood lead levels. Although W% of all US-manufactured food cans werestill lead soldered as of 1979 (25), the canning industry had already startedprograms to reduce the lead content of canned foods, especially infant formula,evaporated milk, and baby foods (26, 27).

Exposure CalculationA great deal of effort has gone into developing models for the prediction oflead exposure. Although a review of this body of work is beyond the scope ofthis chapter, the results are used here as a rough estimate of the magnitude ofblood lead levels expected from use of lead in gasoline. In Table 2, the standardparameters for estimating lead transport and exposure are used to estimatetypical adult exposure to gasoline lead through inhalation, dust and soil inges-tion, and food ingestion (17, 28, 29). Total exposure for children would be ofa similar magnitude, with a larger contribution from soil and dust ingestionand smaller contributions from inhalation and food.

In this calculation, exposure through inhalation can be estimated with themost confidence. &tirnating the contribution from food is much more difficult,because this value depends on atmospheric transport and deposition, retentionof lead in the food chain, and what people eat. The US EP A has estimatedthat in the United States, each J!g m-3 in air (for 139 urban sites, based on theaverage of the maximum quarterly average air lead concentration) contributesabout 30 J!g per day of atmospheric lead to adult diets (30).

&timating exposure to atmospheric lead via ingestion of soil and dust isalso complex. The average amount of soil or dust ingested has been measuredrelatively well, particularly for children, through studies of fecal concentrationsof various indigestible soil minerals. But the concentration of lead in soil ordust depends on atmospheric transport and deposition, the time scale of soil

Table 2 Estimated typical adult lead exposure per microgram per meter cubed of lead in air"

Lead AbsorbedLead in medium Percent (fJ.g per day per

Medium Gross intake per fJ.g m-3 in ail' absorbed fJ.g m-3 in air)

Soil and Dust 0.05gperday" >100 fJ.g g-J 10-15%d >0.5-0.75Food -30 fJ.g per day 10-15% 3-4.5Inhalation 20 m3 per day. 1 30-50%d 6-10Total >9:5"-15

.Air lead in lenns of maximum quarterly average concentrations.bData from References 29, 30.CData from Reference 29..Data from Reference 17.Data from Reference 115.

.

LEAD IN GASOLINE 309

mixing and erosion, dust retention on surfaces, and the personal habits of thepopulation. Based on studies of air, dust, and soil lead levels in severalloca-tions (28), the US EP A has estimated that each J!g m-3 of lead in air conbibutesroughly 100 J!g g-1 or more to lead found in dust or soil (29).

The sum of these conbibutions is an absorption of roughly 10-15 J!g per dayfor each microgram per meter cubed of lead in air. At this level of exposure, eachmicrogmm per day corresponds to about 0.5 J!g dl-1 in blood (28), and thus eachmicrogmm per meter cubed of lead in air corresponds to roughly 5-8 J!g dl-1 inadult blood lead The exposure values for individuals and population subgroupscan vary significantly from this estimated typical exposure.

This estimated exposure can be compared with the measured reductions inblood lead levels as the use of lead in gasoline declined. National data onurban air lead concentrations are only available since 1979. Maximum quar-terly average urban air lead concentrations fell from 0.8 J!g m-3 in 1979 toabout 0.6 J!g m-3 in 1980 (31). Because gasoline lead is the major source ofair lead emissions, most of the air lead can be atbibuted to lead from gasoline.According to the model above, gasoline would have contributed 4-6 J!g dl-1of blood lead in 1979, and 3-5 J!g dl-1 in 1980. In fact, Figure 2 shows thataverage blood lead levels were about 12 J!g dl-1 in 1979 and 10 J!g dl-1 in1980. Because of other significant sources of lead exposure, such as lead-basedpaint and lead-soldered food cans, it is not surprising that the estimated con-tribution of gasoline lead is less than the total lead exposure.

The exposure estimate in Table 2 also predicts a fall in blood lead levels of1-1.6 J!g dl-1 between 1979 and 1980. In fact, they fell by approximately 2J!g dl-1 over this time period. Given the rough nature of the exposure estimate,this is fairly good agreement. Thus, exposure analysis indicates that reductionsin gasoline lead account for at least a large fraction of the drop in blood leadlevels shown in Figure 2.

Isotopic AnalysisThe contribution of lead in gasoline to lead in blood can be directly measuredwith isotopic techniques. The stable isotopes of lead, especially 204, 206, 207,and 208, are present in different ratios in different lead ores. If the lead usedin gasoline has sufficiently different isotopic ratios than the other sources oflead exposure, then by measuring the isotopic ratios of lead in the blood,gasoline, and other sources, we can determine the fraction resulting from leadin gasoline. In Turin, Italy, the lead used in gasoline was switched to a leadwith isotopic ratios significantly different from the other local sources. Before,during, and after the switch, lead isotope ratios were measured in blood andair. The results showed that blood lead atbibutable to gasoline lead wasapproximately 5 J!g dl-l for persons living in Turin and about 3 J!g dl-l forpersons living in the surrounding area. Inhaled lead accounted for approxi-

310 THOMAS

mately half of the exposure to lead from gasoline for residents of the city;outside of Turin, the inhaled contribution fell to less than 10% of the totalexposure to gasoline lead (32, 33).

Claims That Blood Lead Levels Are Uncorrelated WithLeaded Gasoline UseDespite these studies, some have claimed that the declines in blood lead levelsare "for the most part, unrelated in a significant way to lead in gasoline usage"{34, p. 19; see also (23)}. Authors have cited instances of falling blood leadlevels while gasoline lead remained constant as evidence that leaded gasolinedoes not contribute significantly to blood lead levels. For example, in Christ-church, New Zealand, when the manufacture of many types of lead-solderedcans (including beer cans), and the sale of lead-based paints, stopped, averageblood lead levels decreased significantly (36). However, this fmding does notshow that the contribution of leaded gasoline is insignificant. but rather thatother sources of lead exposure are also significant.

Octel, Ltd., the lead additive manufacturer, claims that "recent UK Govern-ment studies demonstrated conclusively that the reduction of leoo levels ingasoline.. .had no direct relationship to the decline in population blood leadlevels" (37, see Executive Summary). In fact, in the UK a 50% drop in use oflead in gasoline (38) resulted in a 20% drop in blood leoo levels (39).

A more egregious approach has been to use old data on blood lead levelsto try to argue that blood lead levels in the United States were decreasingduring the time that gasoline lead use was increasing. Figure 3 shows thepublished reports of blood lead levels in the United States since the 1930s (34,40-46), plotted with data on the use of lead in gasoline (5). These data havebeen used to argue that blood lead levels were uncorrelated with use of leadin gasoline: "The rise in gasoline lead usage was particularly dramatic fromabout 1940 to 1970, as blood lead levels were decreasing" (34, p. 10). A versionof this figure was later published with the statement that (39, p. 22):

it is clear that blood lead levels have been declining steadily in the USA for thepast 60 years, even during the period up to the mid-1970s when consumption ofleaded gasoline underwent rapid increase. It is now generally accepted that: leadfrom gasoline is a very minor contributor to lead in the body

This interpretation of Figure 3 is deeply misleading. In fact. many of themeasurements of lead concentrations in biological and environmental sampleswere incorrect until the rnid-1960s (47-50). Reported blood lead levels mayhave been off by an order of magnitude; reports of the lead concentration ofseawater, now recognized to be in the parts per trillion range, were wrong byseveral orders of magnitude. According to a recent study by the US NationalResearch Council on the measurement of lead exposure (17, p. 191):

LEAD IN GASOLINE 311

60 300

11ft

i 50 250 a-' ..'U ~~ ..~ u...40 200 E

-'UU C> IVU

-.1ft'U .=IV 30 .150 ~.! ...'U ..~8 ,§

-0

~ 20 100 ~U 01~ C0 ..-Do 'UU .U..10 50 1ft=

'UIV.!

0 01930 1940 1950 1960 1970 1980 1990

year

Figure 3 Amount of lead used in gasoline (solid line) and published reports of blood levels for tileUnited States (34).

Ultroclean techniques have repeatedly shown that previously reported concentra-tions of lead can be erroneously high by a factor of several hundred (Pattersonand Settle, 1976 [51)). The flawed nawre of some reported data was initiallyreported in oceanographic research: reported concentrations of lead in seawaterhave decreased by a foctor of 1000 ~ause of improvements in the reduction andcontrol of lead contamination during sampling, storage, and analysis (Bruland,1983) [5Ia] Similar decreases in concentrations of lead in biologic materialshave been reported by laboratories that have adopted trace metal clean tech-niq~s One swdy revealed that lead concentrations in some canned wna were10,000 times those in fresh fish, and that the difference had been overlooked fordecades ~ause all previous analyses of lead concentrations in fish were errone-ously high (Settle and Patterson, 1980 [52)). Another swdy demonstrated thatlead concentrations in human blood plasma were much lower than reported(Everson and Patterson, 1980 [53]) Previous blood lead measurements cannotbe corroborated now, ~ause no aliquots of samples have been properly archived.

Patterson & Settle, leaders in the development of ultraclean trace analysisof lead, reported in 1974 that (51):

Most present analytical practices for lead cannot reliably determine lead concen-trations in...blood. The unreliability of lead analyses is caused by a universal lockof familiarity with the extent, sources, and control of industrial lead contaminationduring sample collection, handling, and analysis. As a consequence, the great

312 maMAS

mass of published lead data.. .is associated with gross positive errors and the errornoise in lead concentration data below a few ppm obscures the meaning of mostwork dealing with lead at these concentration levels.

By the mid-1970s, procedures for contamination avoidance and quality assur-ance had been widely adopted, and the trend in the more recent data in Figure3 can be interpreted as a true reduction in blood lead levels in the UnitedStates. However, the trend in the data up to the 1960s reflects improvedmeasurements and cannot be interpreted as a reflection of the true values.

DO SOME CARS NEED LEADED GASOLINE?

The main purpose of lead additives is to increase the octane level of thegasoline. A secondary role of lead additives is lubrication of the exhaust valves.Cars said to require leaded fuel have exhaust valve seats made of cast iron orsoft steel, and without leaded gasoline, the valve seats can become worn withheavy and long use. In principle, if wear is severe enough, engine failure couldresult (54-57). Concern about valve-seat recession has posed a significantbarrier to the elimination of leaded gasoline in Europe, Australia, and else-where.

Cars with catalytic converters cannot use leaded gasoline because leadpoisons the catalyst Consequently, all new cars sold in countries requiringcatalytic converters have hardened valve seats made of hardened steel oranother hard material. Finding information on which companies are currentlymanufacturing cars without hardened valve seats and where these cars are soldis difficult However, as of 1989, the following companies were manufacturingautomobiles without hardened valve seats for sale in Europe: Austin Rover,Citroen, Dacia, Fiat, Ford, FSO, Honda, Mercedes Benz, Reliant, Renault,Saab, and Skoda (58).

Laboratory studies confirm that under prolonged, severe driving conditions,valve-seat recession will occur if unleaded gasoline is used in engines withouthardened valve seats. However, such tests also show that only very lowconcentrations of lead are needed to prevent valve wear. Even under severeengine conditions, all studies agree that 0.05 g literl is sufficient to preventvalve-seat recession (55, 59, 60). In contrast, current concentrations of lead ingasoline in Europe are 0.15 g literI, three times the amount needed to protectagainst valve-seat recession, even under severe conditions.

But more importantly, all studies have shown that, under normal drivingconditions (real cars, real roads, and nonprofessional drivers), valve-seat re-cession is not a problem in practice. These results, discussed in more detailbelow, can be explained by two factors. First, lead additives have harmful aswell as beneficial effects on the automobile. Lead additives include halogen-ated compounds added as lead scavengers to prevent excess build-up of lead

LEAD IN GASOLINE 313

compounds within the engine. These halogens also form corrosive compounds,which degrade exhaust valves, spark plugs, mufflers, and exhaust pipes (61).Thus, the use of leaded gasoline, while decreasing the risk of valve-seatrecession, increases the risk of other maintenance problems.

Second, valve wear depends on engine operating conditions and increaseswhen engines run for extended periods at high speeds (55). In laboratory testsof valve wear, valves are often subjected to many hours of constant operationat moderate or high speeds; consequently, valve recession in laboratory studiesor specialized road tests is more pronounced than would be expected undernormal driving conditions.

The most extensive study of the car maintenance consequences of usingunleaded gasoline in cars designed for leaded gasoline was a 5-year study of64 matched pairs of cars (62). One vehicle in each pair used leaded gasoline;the other used unleaded exclusively. The mileage on the cars averaged morethan 24,000 km per year. Maintenance costs for the leaded-gasoline users weregreater in terms of spark-plug replacement and exhaust-system repairs (muf-fler, exhaust pipe, etc), whereas those for the unleaded-gasoline users weregreater in terms of engine repairs (valve reconditioning, cylinder-head replace-ments, etc.) Valve reconditioning-the grinding of exhaust valve seats andreplacement of valves-was performed more often on cars using leaded gaso-line, whereas cylinder heads were replaced more often on the cars usingunleaded gasoline, because of excessive valve-seat wear. Although cylinder-head replacement is a more expensive operation than valve reconditioning, thetotal fuel-related maintenance costs (including spark plugs, exhaust-systemrepairs, and valve repairs) were greater for the leaded-gasoline users ($0.0012km-l) than for cars using unleaded gasoline ($0.0008 km-I), even though allof these cars were designed for leaded gasoline. Total maintenance costs,including tires, lubrication, oil filters, brakes, etc, were an order of magnitudegreater than the fuel-related maintenance costs alone, and averaged about$0.008 km-1 for the cars using unleaded gasoline, and about $0.009 kill-I forthe cars using leaded gasoline. The authors concluded that the maintenancecosts of using leaded vs unleaded gasoline in cars designed to use leadedgasoline differ little, and the use of unleaded gasoline may even be slightlybeneficial. Valve-seat recession in the cars using unleaded gasoline was coun-terbalanced by other maintenance problems in cars using leaded gasoline, andin any case, the cost of nonfuel-related maintenance costs far outweighed thefuel-related costs.

The US Army ran a major three-year study in which unleaded fuel was usedin light-duty cars and trucks; heavy-duty trucks, tractors, jeeps, and tacticaland combat vehicles; and some motorized heavy equipment. No untowardmaintenance problems could be attributed to the use of unleaded gasoline (63).

The US Postal service carried out a similar experiment. In 42 months

314 THOMAS

operating 1562 Ford heavy-duty trucks with unleaded gasoline, 1.2% of themexperienced valve-seat problems, less than the failure rate (engine failure fromall causes, including valve problems, using leaded gasoline) from the truckmanufacturer's warranty data (61). Three other studies, conducted about thesame time, gave similar results (64-66).

Despite all this evidence, car manufacturers have nevertheless recommendedthat car drivers in Europe and Australia use leaded gasoline every third to sixthfill for cars without hardened valve seats (58, 67). These recommendations areincreasingly ignored in western Europe (G Muller, personal communication).

Chevron has reported that "valve seat recession has not been seen as aproblem by Chevron in passenger car or commercial operations" (68). More-over, in an advertising campaign, Caltex, an overseas subsidiary of StandardOil and Texaco, guarantees that no car using their unleaded gasoline willexperience problems such as valve-seat recession; this gasoline contains nospecial additives to prevent valve-seat recession (69; L Burke, personal com-munication).

Lead-additive substitutes designed to protect engines from valve-seat reces-sion (61) are used in Europe and South America. The additional cost of onesuch compound (which is based on phosphorus and cannot be used withcatalytic converters) is approximately $0.001 liter) of gasoline (E Squire,personal communication).

COST OF ELIMINATING LEAD FROM GASOLINE

Another factor in the decision to eliminate lead from gasoline is cost, whichis often cited as a reason against switching to unleaded gasoline. Octel claimsthat "it is possible, but extremely expensive to remove lead from gasoline"(70, p. 4). To replace the octane provided by lead, either the gasoline produc-tion must be changed, through various refinery options, or other additives mustbe used, such as the oxygenate methyl tertiary butyl ether (MTBE). The costdifference between leaded and unleaded gasoline depends on the details of therefinery, the gasoline feedstock, as well as many choices concerning refineryreconfiguration, gasoline properties including octane number, and the use ofadditives.

Cost of Lead Additive

The octane added by a given amount of lead additive (TEL) varies somewhatwith the composition of the gasoline (71). Figure 4, a typical octane responsecurve, shows that the rate of increase of octane value decreases as the amountof lead additive increases. (All octane numbers presented here are the averageof the research and motor methods for determining octane.)

LEAD IN GASOLINE 315

94

N~ 92~+~....! 90E~C

QI.C

oati 880

860 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

lead in gasoline. g/L

Figure 4 Octane response curve (71).

Currently, TEL sells for about $7 kg-I (2). With approximately 0.3 g leadper gram TEL, the cost of lead additive is $0.02 g-1 lead. As shown in Figure4, the first 0.1 g liter-I lead added to a gasoline with 87 octane provides abouttwo octane numbers; this addition would cost about $0.002 lite.1 of gasoline.

Cost of MTBE

Octane can also be increased by adding organic compounds such as methanol,ethanol, MTBE, and ethyl tertiary butyl ether (ETBE). These additives haveoctane values ranging from 110 to 120. The wholesale price of MTBE is about$0.161ite.l, and it has an octane value of 110. MTBE displaces gasoline, sothe net cost of MTBE is the cost of MTBE minus the cost of gasoline. For awholesale cost of gasoline of about $0.11 lite.l, the net cost of MTBE is

.$0.16-0.11 = $0.051ite.1 ofMTBE. The MTBE equivalent of the 0.1 g lite.1leaded gasoline, discussed above, would provide a two-octane number in-crease. To increase the octane of an 87 octane gasoline by two octane numbersrequires about 0.1 liter MTBE per liter gasoline. The net cost of the 0.1 literMTBE would be $0.005 literl of gasoline. This is 2.5 times the cost of theequivalent amount of lead additive, estimated above. The cost differencebetween the gasoline with 0.1 g lite.llead and the gasoline with the equivalentamount of MTBE is $0.003 lite.1 gasoline (2).

316 maMAS

Costs of Refinery OptionsThe basic refinery options include catalytic refonning, which produces higher

octane aromatics (such as benzene, xylene, and toluene) and isoparaffins;

isomerization, which transfonns nonnal paraffins into higher-octane isoparaf-

fins; and alkylation, by which lower-molecular-weight olefins react with iso-

paraffins to fonn higher-molecular-weight isoparaffins.

A transition from 0.66 g liter1 leaded gasoline, which is typically found in

many developing countries, to unleaded gasoline has been estimated to costapproximately $0.005-0.01 liter 1 (72). Similarly, Octel estimates the cost of

one octane number from refining to be about $0.002 liter1 (39).

For example, Thailand is making the transition from leaded gasoline with

0.45 g liter1 lead to unleaded gasoline using both refmery improvements and

MTBE. With investment costs amortized over 12 years, discounted at 12% per

year, the capital cost is $0.010 liter-I, the operating cost $0.0025 liter1, and

the cost of MTBE (11 %) $0.0030 literl (73). In Malaysia, the production cost

for unleaded gasoline is 4% more than it is for 0.15 g literl leaded gasoline

(74). In the United States, the cost per octane number was about $0.0025 literl

in the 1980s (61). In Gennany, the cost of producing unleaded gasoline, vs

that of 0.15 g literl leaded gasoline, is $0.01 liter1 (3).

In summary, refinery improvements and MTBE are roughly three times as

expensive as 1EL. The additional cost of unleaded gasoline is about $0.01

liter1. However, benefits, as well as costs, must be considered. The US EPA

estimated that the car-maintenance benefits of using unleaded gasoline (leaded

gasoline decreases the lifetime of spark plugs and exhaust systems and requires

more frequent oil changes) alone are greater than the cost of eliminating lead

in gasoline. When the health benefits of unleaded gasoline are included, the

benefits are estimated to exceed the costs by a factor of three (61).

OTHER HEALTH AND ENVIRONMENTAL ASPECTS OFGASOLINE FORMULA nONS

Health and environmental concerns associated with the use of gasoline, include

emissions of carbon monoxide and ozone-forming chemicals, the emission of

toxic substances such as benzene, the potential health effects of the oxygenate

MTBE (76), and issues of energy consumption and global warming. Any

reformulation of gasoline, including the decision to eliminate lead in gasoline,

can affect all of these factors. Here, I discuss two of these issues: catalytic

converters and benzene.

Catalytic ConvertersCatalytic converters reduce emissions of hydrocarbons, carbon monoxide, and

nitrogen oxides. These devices require unleaded gasoline because lead poisons

LEAD IN GASOLINE 317

the catalyst As catalytic converters become increasingly widespread, the useof leaded gasoline will of necessity be phased out.

However, the belief that unleaded gasoline can only be used in cars withcatalytic converters is not uncommon, even among vehicle salesmen andgovernment administrators (77, 78). In India, for example, the EnvironmentMinistry said that "the introduction of un-leaded petrol would have to besynchronized with the development of vehicles with new technology and newengine designs which could entail colossal expenditure. The engines wouldalso have to be fitted with catalytic converters" (79, p. 9). This misperceptionis not surprising, given Octel's claim that "unleaded gasoline should only beused in cars with catalytic converters" (70, p. 8). In fact, unleaded gasolinecan be used in any car, regardless of whether or not the vehicle has a catalytic

.converter. As detailed above, the only potential risk is valve-seat recession incars with unhardened exhaust valve seats, and this problem has not beenreported in practice.

Benzene

As mentioned above, increasing the concentrations of benzene and other aro-matic hydrocarbons in gasoline is one way to increase the gasoline's octanerating. Benzene is a carcinogen (80), and the content of benzene and otheraromatics must be considered when choosing a manufacturing process forunleaded gasoline. In the United States, the benzene content of gasoline islimited to 1 % volume; in the European Community and Australia, it is limitedto 5% (81). Especially when used in a car lacking a catalytic converter,gasolinewith higher aromatics will produce higher emissions of aromatics such asbenzene.

Octel, the manufacturer of TEL, has made the benzene emissions of un-leaded gasoline the focus of its international effort to market leaded gasoline.According to John Little, Managing Director of Octel, "We have launched aworldwide effort to promote the dangers of using unleaded gasoline, particu-larly in cars that are not equipped with catalytic converters.. .For the past five

.years we have been visiting developing countries to promote the use of leadedgasoline and to warn against the use of unleaded in non-catalyzed cars" (82).This corporation has actively campaigned in the United Kingdom, Israel,

.Egypt, Hong Kong, Italy, the Philippines, New Zealand, Australia, and else-where (70, 83-89). Octel claims that use of unleaded gasoline in cars withoutcatalytic converters may increase exposure to benzene. Based on this claim,Octel argues that only cars with catalytic converters should use unleadedgasoline.

But human exposure to benzene has little to do with whether or not the carshave catalytic converters. Typical exposure to benzene results primarily fromevaporation from the gasoline tank and not from tailpipe exhaust (90, 91).

318 THOMAS

Exposures can be especially high when the car is parked in a garage attached

to the house, in which case benzene fumes seep into the house (92). Exposures

in parking garages or at gasoline stations can also be high. Moreover, the most

significant source of benzene exposure is cigarette smoke. So although thearomatic content of gasoline is an important consideration, the resulting expo-

sure to benzene bears little relation to the presence or absence of catalytic

converters.

Moreover, the benzene and aromatic content of unleaded gasoline is not

necessarily higher than the benzene content of leaded gasoline. To counter theconfusion caused by Octel's advertising, Shell Australia has issued press

releases to the effect that the benzene and aromatic contents of its gasolines

have not increased with the reduced use of TEL (93).

EnergyThe energy implications of the transition to unleaded gasoline are determined

by several factors, including the extent to which new components are addedto the gasoline to furnish the octane formerly provided by lead additives; the

energy and extra petroleum that may be required to make these new compo-

nents; the potentially higher energy density of unleaded gasoline; and whether,if octane levels drop below the octane requirement of a car, the ignition timing

must be adjusted to reduce the car's octane requirement.

First consider the case in which not all of the octane provided by lead

additives is replaced in the unleaded gasoline, so that the resulting fuel has a

lower octane level. Because the lead additives have essentially no fuel value,

the reduction in octane number has no direct energy implications. However,

because reduced octane is widely believed to result in reduced fuel efficiency

(39), a more detailed discussion follows.

The main purpose of adding lead to gasoline is to prevent engine knock.

Although the octane required to prevent knock depends on several factors, the

basic parameter is compression ratio: Each unit increase in compression ratio

requires approximately three octane numbers (94), and each unit of increaseraises energy efficiency by approximately 3% for practical fuels and engines

(95). The net result is that each unit of octane number provides the potential

for a I % increase in fuel efficiency. However, reducing the octane number of

the gasoline does not reduce the fuel efficiency of the car. The compression

ratio is a property of the car's engine. For a given car, increasing the octane

will not in itself change energy efficiency (unless, as mentioned below, the

octane is provided by components that increase mileage).

When the gasoline octane is reduced below the octane requirement of the

car, the car's octane requirement can be decreased somewhat by retarding the

ignition timing. Spark retard of approximately 10°, a typical recommendation

LEADINGASOLINE 319

to compensate for an octane requirement reduced by three octane numbers

(58), can result in a decreased fuel efficiency of about 1 % (96).

A different set of considerations pertains to the energy required for increased

octane in unleaded gasoline. Refinery production of unleaded gasoline requires

more crude oil, and more energy to run the refinery components, than would

be needed for leaded gasoline of the same octane rating. The petroleum indus-

try has estimated that a refinery-produced, seven-octane number increase

(equivalent to about 0.3 g liter1 lead additive) requires an approximately

1.0-1.5% increase in crude oil (97). However, the resulting gasoline may have.a higher energy density or, in the case of oxygenates, may provide more

efficient combustion, resulting in increased mileage (97). Exxon estimated that

in the United States, unleaded gasoline would have 1.0-1.5% greater energy

.efficiency than the octane-equivalent gasoline with 2.5 g literl1ead (61). These

estimates indicate that the 1.0-1.5% energy penalty resulting from increased

octane in unleaded gasoline may be counterbalanced by a similar increase in

mileage.In summary, if the octane of leaded gasoline is replaced with high-octane

gasoline components or additives, -1 % more energy may be required to pro-

duce the gasoline, but the resulting fuel may provide a roughly similar amount

of additional energy, for a net change in energy use of considerably less than

1 %. The lead additive itself has no energy value, so the removal of lead, with

a resulting drop in octane, results in no change in energy use or energy

efficiency. If, however, the octane is reduced below the octane requirement ofa given car, and if the car's ignition timing is adjusted to reduce its octane

requirement, that car's energy efficiency may decrease slightly.

CONCLUSIONS

The use of leaded gasoline is gradually being phased out worldwide, because

of increasing recognition of the health risks of lead exposure and the introduc-

.tion of catalytic converters, which require unleaded gasoline. However, as each

country considers the issues of leaded gasoline, the same questions are revis-

ited-those concerning health risks, technical feasibility, and costs.

.As to health effects, many independent studies have produced a scientific

consensus that blood lead levels of 10-15 J1g dl-l are associated with reduced

intelligence and effects on growth and development of children. Because ofthe multiple pathways of exposure to lead from gasoline, a precise quantifi-

cation of the average contribution of gasoline lead to blood lead .is not

available. But between 1976 and 1990, as use of lead in gasoline in the

United States fell from near its peak to almost zero, average blood lead levels

in the United States decreased from 16 J1g dl-l to 3 J1g dl-i. Calculations of

320 maMAS

expected exposure indicate that much of this decrease can be attributed tothe reduced use of leaded gasoline.

The problem of valve-seat recession has often been cited as a barrier to theuse of unleaded gasoline in cars without hardened valve seats. Althoughvalve-seat recession can be induced in laboratory experiments and speciallydesigned road tests, this problem does not arise in practice. Normal drivingdoes not provide the extreme conditions most conducive to valve-seat reces-sion, and any effects seem to be small and outweighed by corrosion causedby the halogenated additives used as scavengers in most leaded gasolines.

In genernl, the transition to unleaded gasoline will require refinery improve-ments and perhaps use of other additives such as MTBE. The components ofunleaded gasoline (and all other gasolines) should be carefully considered inlight of other potential health and environmental risks. The use of catalyticconverters, however, is an entirely separate issue: If a gasoline does have ahigh benzene (or other aromatic) content, evaporntion--from the tank, notthrough the tailpipe-will be the typical primary source of exposure. Hence,catalytic converters are unlikely to make much difference in the prevention ofbenzene exposure.

The cost of the transition to unleaded gasoline must be calculated on acase-by-case basis, but experience in the developing and developed countriesindicates that the net cost increase is about $0.01 literl.

ACKNOWLEDGMENTS

The author thanks Sharmon Anciola for invaluable assistance with researchand an anonymous reviewer for detailed and thoughtful comments.

Any Annual Review "hapter, as well as any artkle "ited in an Annual Review "hapter,may he purehased from the Annual Reviews Preprints and Reprints servic:e.

I~OO-347~OO7; 415-259-5017; email: arpr@"lass.org

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