Wednesday, 09 March 2011 14:19

Air Pollution

Written by
Rate this item
(1 Vote)

The problem of air pollution has grown steadily since the Industrial Revolution began 300 years ago. Four major factors have exacerbated air pollution: growing industrialization; increasing traffic; rapid economic development; and higher levels of energy consumption. The available information shows that the WHO guidelines for the major air pollutants are regularly exceeded in many major urban centres. Although progress has been made in controlling air pollution problems in many industrialized countries over the last two decades, air quality—particularly in the larger cities in the developing world—is worsening. Of major concern are the adverse health effects of ambient air pollutants in many urban areas, where levels are sufficiently high to contribute to increased mortality and morbidity, deficits in pulmonary function and cardiovascular and neurobehavioural effects (Romieu, Weizenfeld and Finkelman 1990; WHO/UNEP 1992). Indoor air pollution due to domestic combustion products is also a major issue in developing countries (WHO 1992b), but it is not part of this review, which considers only the sources, dispersion and health effects of outdoor air pollution, and includes a case study of the situation in Mexico.

Source of Air Pollutants

The most common air pollutants in urban environments include sulphur dioxide (SO2), suspended particulate matter (SPM), the nitrogen oxides (NO and NO2, collectively termed NOX), ozone (O3), carbon monoxide (CO) and lead (Pb). Combustion of fossil fuels in stationary sources leads to the production of SO2, NOX and particulates, including sulphate and nitrate aerosols formed in the atmosphere following gas to particle conversion. Petrol-fuelled motor vehicles are the principal sources of NOX, CO and Pb, whereas diesel-fuelled engines emit significant quantities of particulates, SO2 and NOX. Ozone, a photochemical oxidant and the main constituent of photochemical smog, is not emitted directly from combustion sources but is formed in the lower atmosphere from NOX and volatile organic compounds (VOCs) in the presence of sunlight (UNEP 1991b). Table 1 presents the major sources of outdoor air pollutants.

 


Table 1. Major sources of outdoor air pollutants

 

Pollutants                                    Sources

Sulphur oxides                                 Coal and oil combustion, smelters

Suspended particulate matter          Combustion products (fuel, biomass), tobacco smoke

Nitrogen oxides                                Fuel and gas combustion

Carbon monoxide                             Incomplete petrol and gas combustion

Ozone                                              Photochemical reaction

Lead                                                 Petrol combustion, coal combustion, producing batteries, cables, solder, paint

Organic substances                        Petrochemical solvents, vaporization of unburnt fuels

Source: Adapted from UNEP 1991b.


 

 

Dispersion and Transport of Air Pollutants

The two major influences on the dispersion and transport of air pollutant emissions are the meteorology (including microclimate effects such as “heat islands”) and the topography in relation to the population distribution. Many cities are surrounded by hills which may act as a downwind barrier, trapping pollution. Thermal inversions contribute to a particulate problem in temperate and cold climates. Under normal dispersion conditions, hot pollutant gases rise as they come into contact with colder air masses with increasing altitude. However, under certain circumstances the temperature may increase with altitude, and an inversion layer forms, trapping pollutants close to the emission source and delaying their diffusion. Long-range transport of air pollution from large urban areas may have national and regional impacts. Oxides of nitrogen and sulphur may contribute to acid deposition at great distances from the emission source. Ozone concentrations are often elevated downwind of urban areas due to the time lag involved in photochemical processes (UNEP 1991b).

Health Effects of Air Pollutants

Pollutants and their derivatives can cause adverse effects by interacting with and impairing molecules crucial to the biochemical or physiological processes of the human body. Three factors influence the risk of toxic injury related to these substances: their chemical and physical properties, the dose of the material that reaches the critical tissue sites and the responsiveness of these sites to the substance. The adverse health effects of air pollutants may also vary across population groups; in particular, the young and the elderly may be especially susceptible to deleterious effects. Persons with asthma or other pre-existing respiratory or cardiac diseases may experience aggravated symptoms upon exposure (WHO 1987).

Sulphur Dioxide and Particulate Matter

During the first half of the twentieth century, episodes of marked air stagnation resulted in excess mortality in areas where fossil-fuel combustion produced very high levels of SO2 and SMP. Studies of long-term health effects have also related the annual mean concentrations of SO2 and SMP to mortality and morbidity. Recent epidemiological studies have suggested an adverse effect of inhalable particulate levels (PM10) at relatively low concentrations (not exceeding the standard guidelines) and have shown a dose-response relationship between exposure to PM10 and respiratory mortality and morbidity (Dockery and Pope 1994; Pope, Bates and Razienne 1995; Bascom et al. 1996) as shown in table 2.

Table 2. Summary of short-term exposure-response relationship of PM10 with different health effects indicators

Health effect

% changes for each 10 μg/m3
increase in PM
10

 

Mean

Range

Mortality

   

Total

1.0

0.5-1.5

Cardiovascular

1.4

0.8-1.8

Respiratory

3.4

1.5-3.7

Morbidity

   

Hospital admission for respiratory condition

1.1

0.8-3.4

Emergency visits for respiratory conditions

1.0

0.5-4

Symptom exacerbations among asthmatics

3.0

1.1-11.5

Changes in peak expiratory flow

0.08

0.04-0.25

 

Nitrogen Oxides

Some epidemiological studies have reported adverse health effects of NO2 including increased incidence and severity of respiratory infections and increase in respiratory symptoms, especially with long-term exposure. Worsening of the clinical status of persons with asthma, chronic obstructive pulmonary disease and other chronic respiratory conditions has also been described. However, in other studies, investigators have not observed adverse effects of NO2 on respiratory functions (WHO/ECOTOX 1992; Bascom et al. 1996).

Photochemical Oxidants and Ozone

The health effects of photochemical oxidants exposure cannot be attributed only to oxidants, because photochemical smog typically consists of O3, NO2, acid and sulphate and other reactive agents. These pollutants may have additive or synergistic effects on human health, but O3 appears to be the most biologically active. Health effects of ozone exposure include decreased pulmonary function (including increased airway resistance, reduced air flow, decreased lung volume) due to airway constriction, respiratory symptoms (cough, wheezing, shortness of breath, chest pains), eye, nose and throat irritation, and disruption of activities (such as athletic performance) due to less oxygen availability (WHO/ECOTOX 1992). Table 3 summarizes the major acute health effects of ozone (WHO 1990a, 1995). Epidemiological studies have suggested a dose-response relationship between exposure to increasing ozone levels and the severity of respiratory symptoms and the decrement in respiratory functions (Bascom et al. 1996).

Table 3. Health outcomes associated with changes in peak daily ambient ozone concentration in epidemiological studies

Health outcome

Changes in
1-h O
3 (μg/m3)

Changes in
8-h O
3 (μg/m3)

Symptom exacerbations among healthy children
and adults or asthmatics-normal activity

   

25% increase

200

100

50% increase

400

200

100% increase

800

300

Hospital admissions for respiratory
conditionsa

   

5%

30

25

10%

60

50

20%

120

100

a Given the high degree of correlation between the 1-h and 8-h O3 concentrations in field studies, an improvement in health risk associated with decreasing 1- or 8-h O3 levels should be almost identical.

Source: WHO 1995.

Carbon Monoxide

The main effect of CO is to decrease oxygen transport to the tissues through the formation of carboxyhaemoglobin (COHb). With increasing levels of COHb in blood, the following health effects can be observed: cardiovascular effects in subjects with previous angina pectoris (3 to 5%); impairment of vigilance tasks (>5%); headache and dizziness (≥10%); fibrinolysis and death (WHO 1987).

Lead

Lead exposure principally affects haem biosynthesis, but also may act on the nervous system and other systems such as the cardiovascular system (blood pressure). Infants and young children less than five years old are particularly sensitive to lead exposure because of its effect on neurological development at blood lead levels close to 10 μg/dl (CDC 1991).

Several epidemiological studies have investigated the effect of air pollution, especially ozone exposure, on the health of the population of Mexico City. Ecological studies have shown an increase in mortality with respect to exposure to fine particulates (Borja-Arburto et al. 1995) and an increase in emergency visits for asthma among children (Romieu et al. 1994). Studies of the adverse effect of ozone exposure conducted among healthy children have shown an increase in school absenteeism due to respiratory illnesses (Romieu et al. 1992), and a decrease in lung function after both acute and subacute exposure (Castillejos et al. 1992, 1995). Studies conducted among asthmatic children have shown an increase in respiratory symptoms and a decrease in peak expiratory flow rate after exposure to ozone (Romieu et al. 1994) and to fine particulate levels (Romieu et al. in press). Although, it seems clear that acute exposure to ozone and particulates is associated with adverse health effects in the population of Mexico City, there is a need to evaluate the chronic effect of such exposure, in particular given the high levels of photo-oxidants observed in Mexico City and the ineffectiveness of control measures.


Case study: Air pollution in Mexico City

The metropolitan area of Mexico City (MAMC) is situated in the Mexican Basin at a mean altitude of 2,240 metres. The basin covers 2,500 square kilometres and is surrounded by mountains, two of which are over 5,000 metres high. The total population was estimated at 17 million in 1990. Due to the particular geographic characteristics and the light winds, ventilation is poor with a high frequency of thermic inversions, especially during the winter. More than 30,000 industries in the MAMC and the three million motor vehicles circulating daily are responsible for 44% of the total energy consumption. Since 1986, air pollution has been monitored, including SO2, NOx, CO, O3, particulate matter and non-methane hydrocarbon (HCNM). The main air pollutant problems are related to ozone, especially in the southwest part of the city (Romieu et al. 1991). In 1992 the Mexican norm for ozone (110 ppb one-hour maximum) was exceeded in the southwest part more than 1,000 hours and reached a maximum of 400 ppb. Particulate levels are high in the northeast section of the city, close to the industrial park. In 1992, the annual average of inhalable particulate (PM10) was 140 μg/m3. Since 1990, important control measures have been taken by the government to decrease air pollution, including a programme that prohibits use of cars one day a week depending on their terminating licence plate number, the closure of one of the most polluting refineries located in Mexico City, and the introduction of unleaded fuel. These measures have led to a decrease in various air pollutants, mainly SO2, particulate matter, NO2, CO and lead. However the ozone level remains a major problem (see figure 1, figure 2 and figure 3).


Figure 1. Ozone levels in two zones of Mexico City. One-hour daily maximum by month, 1994

EHH040F1

Figure 2. Particulates (PM10) in two zones of Mexico City, 1988-1993

EHH040F2

Figure 3. Air lead levels in two zones of Mexico City, 1988-1994

EHH040F3

 

Back

Read 8326 times Last modified on Thursday, 13 October 2011 18:28

" DISCLAIMER: The ILO does not take responsibility for content presented on this web portal that is presented in any language other than English, which is the language used for the initial production and peer-review of original content. Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia (1998)."

Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Environmental Health Hazards
Environmental Policy
Environmental Pollution Control
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides

Environmental Health Hazards References

Allan, JS. 1992. Viral evolution and AIDS. J Natl Inst Health Res 4:51-54.

Angier, N. 1991. Study finds mysterious rise in childhood cancer rate. New York Times (26 June):D22.

Arceivala, SJ. 1989. Water quality and pollution control: Planning and management. In Criteria for and Approaches for Water Quality Management in Developing Countries. New York: United Nations.

Archer, DL and JE Kvenberg. 1985. Incidence and cost of foodborne diarrhoea disease in the United States. J Food Prod 48(10):887-894.

Balick, MJ. 1990. Ethnobotany and the identification of therapeutic agents from the rainforest. CIBA F Symp 154:22-39.

Bascom, R et al. 1996. Health effects of outdoor air pollution. State of the Art. Am J Resp Crit Care Med 153:3-50.

Blakeslee, S. 1990. Scientists confront an alarming mystery: The vanishing frog. New York Times. 20 February:B7.

Blaustein, AR.1994. UL repair and resistance to solar UV-B in amphibian eggs: A link to population declines. Proc Natl Acad Sci USA 91:1791-1795.

Borja-Arburto, VH, DP Loomis, C Shy, and S Bangdiwala. 1995. Air pollution and daily mortality in Mexico City. Epidemiology S64:231.

Bridigare, RR. 1989. Potential effects of UVB on marine organisms of the Southern Ocean: Distribution of phytoplankton and krill during Austral Spring. Photochem Photobiol 50:469-478.

Brody, JE. 1990. Using the toxin from tiny frogs, researchers seek clues to disease. New York Times. 23 January.

Brody, JE. 1991. Far from fearsome, bats lose ground to ignorance and greed. New York Times. 29 October:Cl,C10.

Carlsen, E and A Gimmercman. 1992. Evidence for decreasing quality of semen during the past 50 years. Br Med J 305:609-613.

Castillejos, M, D Gold, D Dockery, T Tosteson, T Baum, and FE Speizer. 1992. Effects of ambient ozone on respiratory functions and symptoms in school children in Mexico City. Am Rev Respir Dis 145:276-282.

Castillejos, M, D Gold, A Damokosh, P Serrano, G Allen, WF McDonnell, D Dockery, S Ruiz-Velasco, M Hernandez, and C Hayes. 1995. Acute effects of ozone on the pulmonary function of exercising schoolchildren from Mexico City. Am J Resp Crit Care Med 152:1501-1507.

Centers for Disease Control (CDC). 1991. Preventing Lead Poisoning in Young Children. Washington, DC: US Department of Health and Human Services.

Cohen, ML. 1987. Prepared statement in “Hearing before the Committee of Agriculture, Nutrition and Forestry”. US Senate, 100th Congress, First Session. (US Government Printing Office, Washington, DC).

Coleman, MP, J Esteve, P Damiecki, A Arslan, and H Renard. 1993. Trends in Cancer Incidence and Mortality. IARC Scientific Publications, No.121. Lyon: IARC.

Davis, DL, GE Dinse, and DG Hoel. 1994. Decreasing cardiovascular disease and increasing cancer among whites in the United States from 1973-1987. JAMA 271(6):431-437.

Davis, DL and D Hoel. 1990a. International trends in cancer mortality in France, West Germany, Italy, Japan, England and Wales and the USA. Lancet 336 (25 August):474-481.

—. 1990b. Trends in Cancer Mortality in Industrial Countries. Annals of the New York Academy of Sciences, No. 609.

Dockery, DW and CA Pope. 1994. Acute respiratory effects of particulate air pollution. Ann Rev Publ Health 15:107-132.

Dold, C. 1992. Toxic agents found to be killing off whales. New York Times. 16 June:C4.

Domingo, M and L Ferrer. 1990. Morbillivirus in dolphins. Nature 348:21.

Ehrlich, PR and EO Wilson. 1991. Biodiversity studies: Science and policy. Science 253(5021):758-762.

Epstein, PR. 1995. Emerging diseases and ecosystem instability. Am J Public Health 85:168-172.

Farman, JC, H Gardiner, and JD Shanklin. 1985. Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction. Nature 315:207-211.

Farnsworth, NR. 1990. The role of ethnopharmacology in drug development. CIBA F Symp 154:2-21.

Farnsworth, NR, O Akerele, et al. 1985. Medicinal plants in therapy. Bull WHO 63(6):965-981.

Federal Health Office (Switzerland). 1990. Bulletin of Federal Health Office. 29 October.

Floyd, T, RA Nelson, and GF Wynne. 1990. Calcium and bone metabolic homeostasis in active and denning black bears. Clin Orthop Relat R 255 (June):301-309.

Focks, DA, E Daniels, DG Haile, and JE Keesling. 1995. A simulation model of the epidemiology of urban dengue fever: literature analysis, model development, preliminary validation, and samples of simulation results. Am J Trop Med Hyg 53:489-506.

Galal-Gorchev, H. 1986. Drinking-Water Quality and Health. Geneva:WHO, unpublished.

—. 1994. WHO Guidelines for Drinking Water Quality. Geneva:WHO, unpublished.

Gao, F and L Yue. 1992. Human infection by genetically diverse SIVsm-related HIV-2 in West Africa. Nature 358:495.

Gilles, HM and DA Warrell. 1993. Bruce-Chwatt’s Essential Malaniology. London: Edward Arnold Press.

Gleason, JF, PK Bhartia, JR Herman, R McPeters, et al. 1993. Record low global ozone in 1992. Science 260:523-526.

Gottlieb, OR and WB Mors. 1980. Potential utilization of Brazilian wood extractives. J Agricul Food Chem 28(2): 196-215.

Grossklaus, D. 1990. Gesundheitliche Fragen im EG-Binnemarkt. Arch Lebensmittelhyg 41(5):99-102.

Hamza, A. 1991. Impacts of Industrial and Small-Scale Manufacturing Wastes On Urban Environment in Developing Countries. Nairobi: United Nations Centre for Human Settlements.

Hardoy, JE, S Cairncross, and D Satterthwaite. 1990. The Poor Die Young: Housing and Health in Third World Cities. London: Earthscan Publications.

Hardoy, JE and F Satterthwaite. 1989. Squatter Citizen: Life in the Urban Third World. London: Earthscan Publications.

Harpham, T, T Lusty, and P Vaugham. 1988. In the Shadow of the City—Community Health and the Urban Poor. Oxford: OUP.

Hirsch, VM and M Olmsted. 1989. An African primate lentivirus (SIVsm) closely related to HIV-s. Nature 339:389.

Hoel, DG. 1992. Trends in cancer mortality in 15 industrialized countries, 1969-1986. J Natl Cancer Inst 84(5):313-320.

Hoogenboom-Vergedaal, AMM et al. 1990. Epdemiologisch En Microbiologisch Onderzoek Met Betrekking Tot Gastro-Enteritis Bij De Mens in De Regio’s Amsterdam En Helmond in 1987 En 1988. Netherlands: National Institute of Public
Health and Environmental Protection.

Huet, T and A Cheynier. 1990. Genetic organization of a chimpanzee lentivirus related to HIV-1. Nature 345:356.

Huq, A, RR Colwell, R Rahman, A Ali, MA Chowdhury, S Parveen, DA Sack, and E Russek-Cohen. 1990. Detection of Vibrio cholerae 01 in the aquatic environment by fluorescent-monoclonal antibody and culture methods. Appl Environ Microbiol 56:2370-2373.

Institute of Medicine. 1991. Malaria: Obstacles and Opportunities. Washington, DC: National Academy Press.

—. 1992. Emerging Infections: Microbial Threats to Health in the United States. Washington, DC: National Academy Press.

Intergovernmental Panel on Climate Change (IPCC). 1990. Climate Change: The IPCC Impacts Assessment. Canberra: Australian Government Publishing Service.

—. 1992. Climate Change 1992: The Supplementary Report to the IPCC Impacts Assessment. Canberra: Australian Government Publishing Service.

International Agency for Research on Cancer (IARC). 1992. Solar and Ultraviolet Radiation. IARC Monographs On the Evaluation of Carcinogenic Risks to Humans. Lyon: IARC.

International Atomic Energy Agency (IAEA). 1991. International Chernobyl Project Assessment of Radiological Consequences and Evaluation of Protective Measures. Vienna: IAEA.

Kalkstein, LS and KE Smoyer. 1993. The impact of climate change on human health: Some international implications. Experiencia 49:469-479.

Kennedy, S and JA Smyth. 1988. Confirmation of cause of recent seal deaths. Nature 335:404.

Kerr, JB and CT McElroy. 1993. Evidence for large upward trends of ultraviolet-B radiation linked to ozone depletion. Science 262 (November):1032-1034.

Kilbourne EM. 1989. Heat waves. In The public health consequences of disasters. 1989, edited by MB Gregg. Atlanta: Centers for Disease Control.

Kingman, S. 1989. Malaria runs riot on Brazil’s wild frontier. New Scientist 123:24-25.

Kjellström, T. 1986. Itai-itai disease. In Cadmium and Health, edited by L Friberg et al. Boca Raton: CRC Press.

Koopman, JS, DR Prevots, MA Vaca-Marin, H Gomez-Dantes, ML Zarate-Aquino, IM Longini Jr, and J Sepulveda-Amor. 1991. Determinants and predictors of dengue infection in Mexico. Am J Epidemiol 133:1168-1178.

Kripke, ML and WL Morison. 1986. Studies on the mechanism of systemic suppression of contact hypersensitivity by UVB radiation. II: Differences in the suppression of delayed and contact hypersensitivity in mice. J Invest Dermatol 86:543-549.
Kurihara, M, K Aoki, and S Tominaga. 1984. Cancer Mortality Statistics in the World. Nagoya, Japan: The University of Nagoya Press.

Lee, A and R Langer. 1983. Shark cartilage contains inhibitors of tumor angiogenesis. Science 221:1185-1187.

Loevinsohn, M. 1994. Climatic warming and increased malaria incidence in Rwanda. Lancet 343:714-718.

Longstreth, J and J Wiseman. 1989. The potential impact of climate change on patterns of infectious disease in the United States. In The Potential Effects of Global Climate Change in the United States, edited by JB Smith and DA
Tirpak. Washington, DC: US Environmental Protection Agency.

Martens, WM, LW Niessen, J Rotmans, TH Jetten, and AJ McMichael. 1995. Potential impact of global climate change on malaria risk. Environ Health Persp 103:458-464.

Matlai, P and V Beral. 1985. Trends in congenital malformations of external genitalia. Lancet 1 (12 January):108.

McMichael, AJ. 1993. Planetary Overload: Global Environmental Change and the Health of the Human Species. London: Cambridge University Press.

Meybeck, M, D Chapman, and R Helmer. 1989. Global Freshwater Quality: A First Assessment. Geneva: Global Environmental Monitoring System (GEMS/-WATER).

Meybeck, M and R Helmer. 1989. The quality of rivers: From pristine stage to global pollution. Paleogeogr Paleoclimatol Paleoecol 75:283-309.

Michaels, D, C Barrera, and MG Gacharna. 1985. Economic development and occupational health in Latin America: New directions for public health in less developed countries. Am J Public Health 75(5):536-542.

Molina, MJ and FS Rowland. 1974. Stratospheric sink for chloro-fluoro-methanes: Chlorine atom-catalyzed destruction of ozone. Nature 249:810-814.

Montgomery, S. 1992. Grisly trade imperils world’s bears. The Boston Globe. March 2:23-24.

Nelson, RA. 1973. Winter sleep in the black bear. Mayo Clin Proc 48:733-737.

Nimmannitya, S. 1996. Dengue and dengue haemorrhagic fever. In Manson’s Tropical Diseases, edited by GC Cook. London: WB Saunders.

Nogueira, DP. 1987. Prevention of accidents and injuries in Brazil. Ergonomics 30(2):387-393.

Notermans, S. 1984. Beurteilung des bakteriologischen Status frischen Geflügels in Läden und auf Märkten. Fleischwirtschaft 61(1):131-134.

Noweir, MH. 1986. Occupational health in developing countries, with special reference to Egypt. Am J Ind Med 9:125-141.

Pan American Health Organization (PAHO) and World Health Organization (WHO). 1989. Final Report of the Working Group on Epidemiological Surveillance and Foodborne Diseases. Unpublished document HPV/FOS/89-005.

Patz, JA, PR Epstein, TA Burke, and JM Balbus. 1996. Global climate change and emerging infections diseases. JAMA 275:217-223.

Pope, CA, DV Bates, and ME Razienne. 1995. Health effects of particulate air pollution: Time for reassessment? Environ Health Persp 103:472-480.

Reeves, WC, JL Hardy, WK Reisen, and MM Milky. 1994. The potential effect of global warming on mosquitoborne arboviruses. J Med Entomol 31(3):323-332.

Roberts, D. 1990. Sources of infection: Food. Lancet 336:859-861.

Roberts, L. 1989. Does the ozone hole threaten antarctic life. Science 244:288-289.

Rodrigue, DG. 1990. International increase in Salmonella enteritidis. A new pandemic? Epidemiol Inf 105:21-21.

Romieu, I, H Weizenfeld, and J Finkelman. 1990. Urban air pollution in Latin America and the Caribbean: Health perspectives. World Health Stat Q 43:153-167.

—. 1991. Urban air pollution in Latin America and the Caribbean. J Air Waste Manage Assoc 41:1166-1170.

Romieu, I, M Cortés, S Ruíz, S Sánchez, F Meneses, and M Hernándes-Avila. 1992. Air pollution and school absenteeism among children in Mexico City. Am J Epidemiol 136:1524-1531.

Romieu, I, F Meneses, J Sienra, J Huerta, S Ruiz, M White, R Etzel, and M Hernandez-Avila. 1994. Effects of ambient air pollution on respiratory health of Mexican children with mild asthma. Am J Resp Crit Care Med 129:A659.

Romieu, I, F Meneses, S Ruíz, JJ Sierra, J Huerta, M White, R Etzel, and M Hernández. 1995. Effects of urban air pollution on emergency visits for childhood asthma in Mexico City. Am J Epidemiol 141(6):546-553.

Romieu, I, F Meneses, S Ruiz, J Sienra, J Huerta, M White, and R Etzel. 1996. Effects of air pollution on respiratory health of children with mild asthma living in Mexico City. Am J Resp Crit Care Med 154:300-307.

Rosenthal, E. 1993. Hibernating bears emerge with hints about human ills. New York Times 21 April:C1,C9.

Ryzan, CA. 1987. Massive outbreak of antimicrobial-resistant salmonellosis traced to pasteurized milk. JAMA 258(22):3269-3274.

Sanford, JP. 1991. Arenavirus infections. In Chap. 149 in Harrison’s Principles of Internal Medicine, edited by JD Wilson, E Braunwald, KJ Isselbacher, RG Petersdorf, JB Martin, AS Fauci, and RK Root.

Schneider, K. 1991. Ozone depletion harming sea life. New York Times 16 November:6.

Schultes, RE 1991. Dwindling forest medicinal plants of the Amazon. Harvard Med Alum Bull (Summer):32-36.

—.1992: Personal communication. 24 January 1992.

Sharp, D. (ed.). 1994. Health and Climate Change. London: The Lancet Ltd.

Shope, RE. 1990. Infectious diseases and atmospheric change. In Global Atmospheric Change and Public Health: Proceedings of the Center for Environmental Information, edited by JC White. New York: Elsevier.

Shulka, J, C Nobre, and P Sellers. 1990. Amazon deforestation and climate change. Science 247:1325.

Statistisches Bundesamt. 1994. Gesundheitswersen: Meldepflichtige Krankheiten. Wiesbaden: Statistisches Bundesamt.

Stevens, WK. 1992. Terror of the deep faces harsher predator. New York Times. 8 December:Cl,C12.

Stolarski, R, R Bojkov, L Bishop, C Zerefos, et al. 1992. Measured trends in stratospheric ozone. Science 256:342-349.

Taylor, HR. 1990. Cataracts and ultraviolet light. In Global Atmospheric Change and Public Health: Proceedings of the Center for Environmental Information, edited by JC White. New York: Elsevier.

Taylor, HR, SK West, FS Rosenthal, B Munoz, HS Newland, H Abbey, EA Emmett. 1988. Effects of ultraviolet radiation on cataract formation. N Engl J Med 319:1429-33.

Terborgh, J. 1980. Where Have All the Birds Gone? Princeton, NJ: Princeton University Press.

Tucker, JB. 1985. Drugs from the sea spark renewed interest. Bioscience 35(9):541-545.

United Nations (UN). 1993. Agenda 21. New York: UN.

United Nations Conference on Environment and Development (UNCED). 1992. Protection for the quality and supply of freshwater resources. In Chap. 18 in Application of Integrated Approaches to the Development, Management and Use of Water Resources. Rio de Janeiro: UNCED.

United Nations Environment Programme (UNEP). 1988. Assessment of Chemical Contaminants in Food. Nairobi: UNEP/FAO/WHO.

—. 1991a. Environmental Effects of Ozone Depletion: 1991 Update. Nairobi: UNEP.

—. 1991b. Urban Air Pollution. Environment Library, No. 4. Nairobi: UNEP.
Urban Edge. 1990a. Reducing accidents: Lessons learned. Urban Edge 14(5):4-6.

—. 1990b. Road safety a lethal problem in third world. Urban Edge 14(5):1-3.

Watts, DM, DS Burke, BA Harrison, RE Whitmire, A Nisalak. 1987. Effect of temperature on the vector efficiency of Aedes aegypti for dengue 2 virus. Am J Trop Med Hyg 36:143-152.

Wenzel, RP. 1994. A new hantavirus infection in North America. New Engl J Med 330(14):1004-1005.

Wilson, EO. 1988. The current state of biological diversity. In Biodiversity, edited by EO Wilson. Washington, DC: National Academy Press.

—. 1989. Threats to biodiversity. Sci Am 261:108-116.

—. 1992. The Diversity of Life. Cambridge, Mass.: Harvard University Press.

World Bank. 1992. Development and the Environment. Oxford: OUP.

World Health Organization (WHO). 1984. Toxic Oil Syndrome: Mass Food Poisoning in Spain. Copenhagen: WHO Regional Office for Europe.

—. 1987. Air Quality Guidelines for Europe. European Series, No. 23. Copenhagen: WHO Regional Office for Europe.

—. 1990a. Acute Effects On Health of Smog Episodes. WHO Regional Publications European Series, No. 3. Copenhagen: WHO Regional Office for Europe.

—. 1990b. Diet, Nutrition and Prevention of Chronic Diseases. WHO Technical Report Series, No. 797. Copenhagen: WHO Regional Office for Europe.

—. 1990c. Global Estimates for Health Situation, Assessment and Projections. WHO Technical Report Series, No. 797. Geneva: WHO.

—. 1990d. Potential Health Effects of Climatic Change. Geneva: WHO.

—. 1990e. Public health impact of pesticides used in agriculture. World Health Statistics Quarterly 43:118-187.

—. 1992a. Indoor Air Pollution from Biomass Fuel. Geneva: WHO.

—. 1992b. Our Planet, Our Health. Geneva: WHO.

—. 1993. Weekly Epidemiol Rec 3(69):13-20.

—. 1994. Ultraviolet Radiation. Environmental Health Criteria, No. 160. Geneva: WHO.

—. 1995. Update and Revision of the Air Quality Guidelines for Europe. Copenhagen: WHO Regional Office for Europe.

—. in press. Potential Health Effects of Global Climate Change: Update. Geneva: WHO.
World Health Organization (WHO) and ECOTOX. 1992. Motor Vehicle Air Pollution. Public Health Impact and Control Measures. Geneva: WHO.

World Health Organization (WHO) and FAO. 1984. The Role of Food Safety in Health and Development. WHO Technical Report Series, No. 705. Geneva: WHO.

World Health Organization (WHO) and UNEP. 1991. Progress in the Implementation of the Mar Del Plata Action Plan and a Strategy for the 1990s. Geneva: WHO.

—. 1992. Urban Air Pollution in Megacities of the World. Blackwells, UK: WHO.

World Health Organization (WHO) Commission on Health and Environment. 1992a. Report of the Panel On Urbanization. Geneva: WHO.

—. 1992b. Report of the Panel On Energy. Geneva: WHO.

World Meteorological Organization (WMO). 1992. GCOS: Responding to the Need for Climate Observations. Geneva: WMO.
Young, FE. 1987. Food safety and FDA’s action plan phase II. Food Technol 41:116-123.