Environ. Sci. Technol. 2006, 40, 764-770
Chronicling a Century of Lead Pollution in Mexico: Stable Lead Isotopic Composition Analyses of Dated Sediment Cores M A R T I N F . S O T O - J I M E N E Z , * ,†,§ SHARON A. HIBDON,† CHARLEY W. RANKIN,† JUGDEEP AGGARAWL,‡ A. CAROLINA RUIZ-FERNANDEZ,§ FEDERICO PAEZ-OSUNA,§ AND A. RUSSELL FLEGAL† Department of Environmental Toxicology, WIGS, and Department of Earth Sciences, University of California at Santa Cruz, Santa Cruz, California 95064, and Institute of Marine Sciences and Limnology Institute, UNAM, Mazatla´n, Mexico 82000.
Analyses of lead isotopic compositions (204Pb,206Pb, 207Pb, and 208Pb) of dated sediment cores from two coastal estuaries and two inland lakes chronicle the predominance of industrial lead emissions in Mexico over the past century. These isotopic ratios exhibit a shift in composition from the turn of the previous century (1900) that corresponds with measurable increases (from 2- to 10-fold) in lead concentrations in the cores above their baseline values (3-22 µg/g)sboth changes are consistent with the development of Mexican lead production for export and the manufacture of tetraethyl lead additives for Mexican gasolines. While subsequent changes in lead concentrations in the cores correspond with calculated emissions from the combustion of leaded gasoline in Mexico, isotopic compositions of the cores remain relatively constant throughout most of the 1900s (e.g., 206Pb/207Pb ) 1.200 ( 0.003; 208Pb/207Pb ) 2.463 ( 0.004). That isotopic constancy is attributed to the widespread pollution from lead production in Mexico and the dispersion of some of that lead used as an additive in Mexican gasolines.
Introduction As in many other developing countries, Mexico experienced rapid economic and population growth over the past few decadessdepleting natural resources and increasing pollution (1-3). Major factors in the country’s deterioration of environmental quality have been the smelting of lead ores and the use of some of that lead in the production of tetraethyl lead (TEL) additives for Mexican gasoline from the 1930s to the 1990s. That pollution has exposed urban populations in Mexico to atmospheric lead levels that cause measurable, adverse health effects (4-8). To partially quantify the extent of that pollution, we estimate atmospheric emissions from the combustion of * Corresponding author phone: 01152 669 982 6631; fax: 01152 669 982 6631; e-mail:
[email protected]. † Environmental Toxicology, WIGS, University of California at Santa Cruz. ‡ Earth Sciences, University of California at Santa Cruz. § Institute of Marine Sciences and Limnology Institute. 764
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FIGURE 1. Lead content (g L-1) in Mexican gasoline over time and historic consumption of lead in gasoline (metric tons year-1) in Mexico (see the text for references).
FIGURE 2. Historical anthropogenic lead flux (µg cm-2 year-1) estimates on 210Pb-dated sediments from four representative environments in Mexico. leaded gasoline, alone, in Mexico over the past century totaled 541 000 metric tons (Figure 1). This estimate was derived from records (7, 9-15) of the consumption of gasoline in Mexico and the lead content of that gasoline. On the basis of studies of the dispersion of contaminant lead in soils and sediments published elsewhere (e.g., 16-18), it was assumed that most of that lead was deposited on Mexican sediments that now provide a record of those historical emissions. This assumption was corroborated by recent analyses of lead concentrations in dated sediment cores from estuarine and lacustrine sites in Mexico (18-19). Although there were differences in sediment accumulation rates and lead concentrations among sites (due to differences in adjacent population sizes, industries, and weathering), cores exhibited similar systematic increases in lead fluxes above natural levels beginning around 1900 (Figure 2). Associated estimates of anthropogenic lead fluxes showed increments from low and constant lead values prior to 1900 (0.1-0.5 µg cm-2 year-1) to maximum values in the 1970s to 1980s (2-16 µg cm-2 year-1) followed by decreases toward 2000 (1-4 µg cm-2 year-1). Those temporal variations are comparable with our calculations of emissions of leaded gasoline in Mexico during the 1900s, detailed in subsequent sections. 10.1021/es048478g CCC: $33.50
2006 American Chemical Society Published on Web 12/20/2005
Consequently, the following isotopic composition analyses (e.g., 206Pb/207Pb; 208Pb/207Pb) of the 210Pb-dated sediment cores were designed to identify the principal source(s) of lead contamination in Mexican soils over the past century. This technique has proven to be a successful tool for the reconstruction of the history of lead contamination in other depositional environments (16-17, 20-22), although there have not been any previous measurements of lead isotopic compositions in sediment cores from Mexico. But there have been lead isotopic analyses of crustal formations (23, 24) and industrial ores (25) in Mexico, as well as recent analyses of lead isotopic compositions in urban aerosols in Mexico (26) that enabled comparisons between the isotopic composition of the dated sediment cores and those of natural and industrial sources of lead in Mexico.
Review of Leaded Gasoline Production and Consumption in Mexico There was relatively little consumption of gasoline in Mexico before the 1930s, when the marketing of U.S.-manufactured vehicles began in Mexico and the use of gasoline for the growing motor industry began increasing at an annual rate of 9-10% (10). By then the addition of the gasoline antiknock agent TEL had become standard in the United States (27), and TEL concentrations in Mexican gasoline were 1.3 g L-1 (12). While the initial source of lead in that TEL is unknown, it is known that Mexican lead was used (in varying amounts) in U.S. and Mexican gasoline additives after 1938 (9-12, 27). At that time the oil industry was nationalized, and stateowned Petro´leos Mexicanos (Pemex) took control over the exploration, processing, and marketing of petroleum hydrocarbons (11, 12). Subsequently, the United States and Great Britain led a worldwide boycott to deprive Mexico of the equipment, expertise, and chemicals necessary for oil processing (28), and TEL sales were suspended in Mexico by the Ethyl Gasoline Corporation (12, 28). In response to those constraints Pemex built a plant in 1939 to produce its own TEL additive in secret because TEL production had become an important military commodity during World War II (11, 12, 28). The plant initially encountered numerous interruptions due to serious cases of TEL intoxication, fires, economic problems, technology problems, and lack of materials (11, 12), but production became more stable after international restrictions on Mexican oil and other resources were lifted during World War II (28). After the war, DuPont established two TEL plants in Mexico City and Coatzacoalcos, which were operated by the joint venture of DuPont/Pemex for TEL manufacture used in the domestic market and for exportation (12). As a result, it is believed that most of the TEL consumed in Mexico between 1940 and 1997 was composed of lead from Mexican ores. As the automobile industry was growing and higher performance engines were being produced, the demand for gasoline with higher octane levels increased (11). That escalating demand was reflected in temporal changes in the octane index of Mexican gasoline, which rose from 70 in 1940, to 80 in 1950, to 90 in 1956, and to 100 in 1966 (12, 13). As previously indicated, increases in octane, due to increases in the amount of TEL additives in Mexican gasoline, along with the increases in gasoline consumption in Mexico raised the consumption of TEL in the country from less than 1000 metric tons in 1940, to 7000 metric tons in 1960, and to 12 000 metric tons in 1970 (Figure 1). While many developed countries were then phasing out leaded gasoline because of its recognized public health hazard (29), Mexican sales for leaded gasoline reached an historic maximum during the late 1970s and early 1980s when about 26 000 metric tons of lead was added per year (Figure 1). Although the consumption was more widely distributed
FIGURE 3. Scatter plots showing the relationships between lead fluxes (µg cm-2 year-1) and historic consumption of lead (metric tons year-1) in gasoline in Mexico. throughout Mexico then than it was during the 1940s, the Mexico City metropolitan area (MCMA) was still consuming more than one-quarter of the total gasoline sold in the country at that time. By our estimates, cars emitted ∼20 tons of lead each day into the MCMA atmosphere during the late 1970s to early 1980s, with measurable adverse health effects (4, 5, 8). As a consequence, governmental programs were initiated in 1982 to reduce lead emissions from automobiles, especially in Mexico City (13, 14). Low-lead gasolines (0.3-0.6 g L-1) were initially distributed in the Mexico City, then to other large cities, and finally to the rest of country. Those efforts reduced the use of leaded gasoline in Mexico by 80% between 1982 and 1986. A concurrent increase in the use of unleaded gasoline ( 0.05) was found between them, and these values were not measurably different than those of Mexican lead ores. For comparison, Figure 6 includes isotopic compositions of the (i) sedimentary data listed in Tables 1 and 2 (ii) range (1.173 g 206Pb/207Pb e 1.191 and 2.440 g 208Pb/207Pb e 2.459) reported for the upper continental crust from Sierra Madre Occidental (37), used as a reference for parental bedrock, and (iii) range (1.186 g 206Pb/207Pb e 1.211 and 2.465 g 208Pb/207Pb e 2.484) reported for Mexican lead ores (25). The figure also includes lead isotopic ranges reported for modern aerosols from rural (1.180 g 206Pb/207Pb e 1.182 and 2.442 g 208Pb/207Pb e 2.446) and urban areas (1.189 g 206Pb/207Pb e 1.198 and 2.453 g 208Pb/207Pb e 2.466) in Mexico and for surface sediments (1.194 g 206Pb/207Pb e 2.005 and 2.454 g 208Pb/207Pb e 2.463) in Mexico. While most of the values for the sediments collected from the four depositional environ-
FIGURE 6. Lead isotopic compositions (206Pb/207Pb vs 208Pb/207Pb) of 210 Pb-dated sediment layers from (a) Rio Culiaca´ n estuary (RC) near the city of Culiaca´ n in northwestern Mexico and (b) Lake Espejo de los Lirios (EL) located in the northern Mexico City Metropolitan Area (MCMA), along with those of (c) natural lead sources in Mexico (i.e., upper crust from Sierra Madre Occidental, NW Mexico), (d) Mexican lead ores, and (e) rural and urban atmospheric lead signatures from the NW Mexico (see the text for references). ments fall along a line constrained by the isotopic compositions of Mexican lead ores and natural Mexican lead bedrock values, some values appear to be outside of that two endmember mixing model. That apparent deviation suggests a third end-member with a more elevated 206Pb/207Pb ratio. It is suggested that the third end-member is atmospheric inputs from U.S. industrial lead emissions, regarded as a major source of lead contamination in the Northern Hemisphere in the previous century (29) with 206Pb/207Pb ratios typically ranging from 1.17 to 1.22 (38). Consequently, lead accumulated over the past century from four disparate depositional environments in Mexico is primarily attributed to depositions from the combustion of gasoline containing TEL manufactured with Mexican lead ores. This conclusion is supported by the temporal changes in lead anthropogenic fluxes accompanied by a shift in isotopic composition of accumulated lead in the geographically distinct sediments in Mexico, although U.S. industrial lead appears to have also been deposited in some of those sediments.
Acknowledgments Thanks to Daniela Arvizu and Rob Franks for their contributions in the laboratory, Margarita Caballero-Miranda, Ricardo Urdapilleta and Martha Chong-Robles for their help in collecting the samples, and Kate Chabaret and Ce´line Gallon for help in the preparation of the manuscript. Financial support was provided by Fulbright and Garcia Robles Postdoctoral Fellowships and a UCMEXUS-CONACyT Postdoctoral Grant to M. Soto-Jimenez, and Grants from the University of California Toxic Substances Research and Teaching Program, the W.M. Keck Foundation, and the PAPIIT IX242504.
Literature Cited (1) Wu, K. Energy in Latin America: Production, Consumption and Future Growth; Praeger Pulishers: Westport, CT, 1995; p 310. (2) Organization for Economic Cooperation and Development (OECD). Environmental Performance Reviews: Mexico; OECD Press: Paris, 1998. (3) Energy Information Administration (EIA). Mexico Country Analysis Brief 2004. http://www.eia.doe.gov/cabs/mexico.html. (accessed Sept 2004). VOL. 40, NO. 3, 2006 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
769
(4) Albert, L. A.; Badillo, F. Environmental lead in Mexico. Rev. Environ. Contam. Toxicol. 1991, 117, 1-49. (5) Romieu, I.; Palazuelos, E.; Meneses, F.; Hernandez-Avila, M. Vehicular traffic as a determinant of blood-lead levels in children: A pilot study in Mexico City. Arch. Environ. Health 1993, 47, 246-249. (6) The World Bank. Elimination of Lead in Gasoline in Latin American and the Caribbean; Report No. 194/9; Energy Lecture Management Assistance Program; The World Bank: Washington, DC, 1996. (7) The World Bank. Phasing-Out Lead from Gasoline: Worldwide Experience and Policy Implanting; The World Bank: Washington, DC, 1997. (8) Ezcurra, E.; Mazari-Hiriart, M.; Pisanty, I.; Aguilar, A. G. The Basin of Mexico: Critical Environmental Issues and Sustainability; United Nations University Press: New York, 1999; p 216. (9) U.S. Bureau of Mines (1932-1992) Mineral Yearbook. http:// digital.library.wisc.edu/1711.dl/EcoNatRes (accessed Sept 2004). (10) Powell, R. J. The Mexican Petroleum Industry; University of California Press: Berkeley, CA, 1956; p 269. (11) Meyer, L. Mexico and the United States in the Oil Controversy, 1917-1942; University of Texas Press: Austin, TX, 1972; p 367. (12) Barbosa-Cano, F. Technical and Economics Problems of the Newly Nationalized Industry. The Mexican Petroleum Industry in the Twentieth Century; University of Texas Press: Austin, TX, 1992; p 315. (13) Heredia-Veloz, A. Evolucio´n de las gasolinas automotrices en Pemex a partir de la Expropiacio´n Petrolera. Rev. Octanaje 1996, 3, 1-20. (14) Rosas-Jaramillo, J. A.; Rodrı´guez-Martı´nez, N. Nuestros productos: Gasolinas; Rev. Octanaje 1998, 2, 11-20. (15) Energy Information Administration (EIA). World Petroleum Consumption, 1960-2001; International Energy Database, 2003; http://www.eia.doe.gov/international. (16) Erel, Y.; Veron, A.; Halicz, L. Tracing the transport of anthropogenic lead in the atmosphere and in soils using isotopic ratios. Geochim. Cosmochim. Acta 1997, 61, 4495-4505. (17) Ritson, P. I.; Esser, B. K.; Niemeyer, S.; Flegal A. R. Lead isotopic determination of historical sources of lead to Lake Erie, North America. Geochim. Cosmochim. Acta 1994, 58, 3297-3305. (18) Ruiz-Ferna´ndez, A. C.; Hillaire-Marcel, C.; Pa´ez-Osuna, F.; Ghaleb, B.; Soto-Jime´nez, M. Historical trends of metal pollution recorded in the sediments of the Culiacan River Estuary, Northwestern Mexico. Appl. Geochem. 2003, 18, 577-588. (19) Ruiz-Ferna´ndez, A. C.; Pa´ez-Osuna, F.; Urrutia-Fucugauchi, J.; Preda, M.; Renault, I. Historical trace metal fluxes in the Mexico City Metropolitan Zone as evidenced by a sedimentary record from the Espejo de los Lirios lake. J. Environ. Monit. 2004, 6, 1-9. (20) Bra¨nnvall, M. L.; Bindler, R.; Emteryd, O.; Renberg, I. Four thousand years of atmospheric lead pollution in northern Europe: a summary from Swedish lake sediments. J. Paleolimnol. 2001, 25, 421-435. (21) Renberg, I.; Bra¨nnvall, M. L.; Bindler, R.; Emteryd, O. Stable lead isotopes and lake sedimentssa useful combination for the study of atmospheric lead pollution history. Sci. Total Environ. 2002, 292, 45-54. (22) Doe, B. R. Lead Isotopes; Springer-Verlag: New York, 1970. (23) Cameron, K. L.; Robinson, J. V.; Niemeyer, S.; Nimz, G. J.; Kuentz D. C.; Harmon R. S.; Bohlen, S. R.; Collerson, K. D. Contrasting
770
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 40, NO. 3, 2006
(24)
(25)
(26) (27) (28) (29)
(30)
(31)
(32)
(33)
(34) (35) (36)
(37) (38)
styles of pre-Cenozoic and mid-Tertiary crustal evolution in northern Mexico: evidence from deep crustal xenoliths from La Olivina. J. Geophy. Res. 1992, 97, 353-376. Cumming, G. L.; Kesler, S. E.; Krstic, D. Isotopic compositions of lead in Mexican mineral deposits. Econ. Geol. 1979, 74, 13951407. Bollho¨fer, A.; Rosman, K. J. R. Isotopic source signatures for atmospheric lead: the Northern Hemisphere. Geochim. Cosmochim. Acta 2001, 65, 1727-1740. Nickerson, S. P. Tetraethyl lead: a product of American research. J. Chem. Educ. 1954, 31, 560-571. Velasco, J. A. Impacts of Mexican Oil Policy on Economic Development; Lexington Books: Lexington, MA, 1983; p 237. Nriagu, J. O. The rise and fall of leaded gasoline. Sci. Total Environ. 1990, 92, 13-28. Bravo-Alvarez, H. La atmo´sfera de la Zona Metropolitana de la Ciudad de Me´xico. Desarrollo y Medio Ambiente. Fund. Mex. Rest. Ambiental 1986, 2, 2-3. Secretaria del Medio Ambiente, Recursos Naturales y Pesca (SEMARNAP). Programa para mejorar la calidad del aire en el Valle de Me´xico 1995-2000; Instituto Nacional de Ecologı´a, SEMARNAP, Departamento del Distrito Federal, Gobierno del Estado de Me´xico; Secretaria de Salud: Me´xico, D.F., 1996. INEGI. Tabulados Ba´sicos Nacionales y por Entidad Federativa; Base de Datos y Tabulados de la Muestra Censal. XII Censo General de Poblacio´n y Vivienda; Imprenta de INEGI: Aguascalientes, Mexico, 2001. Flegal, A. R.; Smith, D. R. Measurements of environmental lead contamination and human exposure. Rev. Environ. Contamin. Toxicol. 1995, 143, 1-45. National Institute of Standards and Technology. Certificate of Analysis. Standard Reference Material 981. Common Lead Isotopic Standard; Gaithersburg, MD, 1991; https://srmors.nist. gov/certificates/view_cert2gif.cfm?certificate)981 (accessed Sept. 2004). Secretarı´a de Economı´a. Produccio´n Nacional Minero-Metalu ´ rgica 2002; Aguascalientes, Mexico, 2002. Martin, J. M.; Meybeck, M. Elemental mass-balance of material carried by major world rivers. Mar. Chem. 1979, 7, 173-206. Smith, R. D.; Cameron, K. L.; McDowell, F. W.; Niemeyer, S.; Sampson, D. E. Generation of voluminous silicic magmas and formation of mid-Cenozoic crust beneath north-central Mexico: evidence from ignimbrites, associated lavas, deep crustal granulites, and mantle pyroxenites. Contrib. Mineral. Petrol. 1996, 123, 375-389. Zar, J. Biostatistical Analysis, 2nd ed.; Prentice-Hall: Upper Saddle River, NJ, 1984; p 718. Chow, T. J.; Snyder, C. B.; Earl, J. L. Isotopic compositions of lead as pollutant source indicators. In Proceedings, United Nations FAO International Atomic Energy Association Symposium, April 1975, Vienna, Austria, Vol. IAEA-SM- 191/4 p 95108.
Received for review September 27, 2004. Revised manuscript received August 5, 2005. Accepted September 14, 2005. ES048478G
