An estimated 40 percent of world deaths can now be attributed to various environmental factors, especially organic and chemical pollutants, according to a study led by David Pimentel, professor of ecology and agricultural sciences at Cornell.
"More and more of us are living in crowded urban ecosystems that are ideal for the resurgence of old diseases and the development of new diseases," said Pimentel, lead author of the BioScience report titled "Ecology of Increasing Disease: Population Growth and Environmental Degradation."
"We humans are further stressed -- and disease prevalence is worsened -- by widespread malnutrition and the unprecedented increase in air, water and soil pollutants," he said.
Global climate change will make matters even worse for humans and "better" for disease, the Cornell study predicts. Increased heat favors most human diseases, as well as the diseases and pests of food crops, and the coming century will see masses of weakened "environmental refugees" fleeing their home areas in a desperate search for food, the researchers said.
The disease-ecology analysis was performed by a team of 11 graduate student researchers who gathered data from a variety of sources, such as the World Health Organization (WHO) and the U.S. Centers for Disease Control and Prevention (CDC), as well as previous studies at Cornell and other universities. Their findings span a planet made less habitable by human habitation:
-- Each year, air pollutants adversely affect the health of 4 to 5 billion people worldwide. An expanding world population is burning more fossil fuels, emitting more industrial chemicals and driving more automobiles. The number of automobiles is increasing three times faster than the rate of population growth.
-- The snail-borne disease schistosomiasis,causes an estimated 1 million deaths annually and is expanding its range as human activities provide more suitable habitats in contaminated fresh water. Following construction in 1968 of Egypt's Aswan High Dam and associated irrigation systems, prevalence of the Schistosoma mansoni organism in humans in the region increased from
5 percent to 77 percent.
-- Of the 80,000 pesticides and other chemicals in use today, 10 percent are recognized as carcinogens. Cancer-related deaths in the United States increased from 331,000 in 1970 to 521,000 in 1992, with as estimated 30,000 deaths attributed to chemical exposure.
-- Smoke from indoor cooking fires that burn fuelwood and dung is estimated to cause the death of 4 million children each year worldwide.
-- Lack of sanitary conditions contributes each year to approximately 2 billion diarrhea infections and 4 million deaths, mostly among infants and young children in developing countries. In the United States, inadequate sanitation accounts for 940,000 diarrhea infections and about 900 deaths each year.
-- Dengue fever, spread by mosquitoes that breed in old tires and other water-holding junk in crowded urban environments, infects an additional 30 million to 60 million people each year.
-- Less than 1 percent of 500 Chinese cities have clean air. Respiratory disease is the leading cause of death in China.
-- In China, where tobacco smoking increased from approximately 360 to nearly 1,800 cigarettes per person per year, males smoke 98 percent of the cigarettes. However, mortality due to lung cancer is approximately equal in males and females.
-- Although the use of lead in U.S. gasoline declined since 1985, other sources inject about
2 billion kilograms of lead into the atmosphere in this country each year. An estimated 1.7 million children in the United States have unacceptably high levels of lead in their blood.
-- Production of another gasoline component, the carcinogen benzene that causes leukemia even at low dosages, rose from 0.5 billion kilograms in the United States in 1950 to current levels of about 7.5 kilograms per year.
-- The global use of agricultural pesticides rose from about 50 million kilograms a year in 1945 to current application rates of approximately 2.5 billion kilograms per year. Most modern pesticides are more than 10 times as toxic to living organisms than those used in the 1950s.
The only chance for relief, the researchers wrote in the BioScience report, comes from "comprehensive, fair population-control policies combined with effective environmental management programs. Without international cooperative efforts," they predicted, "disease prevalence will continue its rapid rise throughout the world and will diminish the quality of life for all humans."