Ecologist David Pimentel and his graduate students at Cornell pulled together statistics from the World Health Organization in Geneva, the Centers for Disease Control and Prevention in Atlanta, and other sources to analyze the effects of population growth and environmental degradation on human disease. Overall, they report, some 40 percent of all deaths can now be attributed to various environmental factors. A few of their findings:
HUMAN ACTIONSBuilding Egypt's Aswan High Dam. ENVIRONMENTAL EFFECTSExpanded the habitat for snails that host the flatworm Schistosoma mansoni, second only to the parasite that causes malaria in the number of people it kills worldwide. DISEASE INCIDENCEProportion of people in the Nile Valley with schistosomiasis increased from 5 percent in 1968 to 77 percent in 1993.
HUMAN ACTIONSDeforestation and doubling of some African populations every 20 years. ENVIRONMENTAL EFFECTSMore people living near areas favorable for breeding mosquitoes. DISEASE INCIDENCEFrom 1970 to 1990, malaria incidence in Rwanda increased eightfold. Malaria kills about 2.7 million people each year.
HUMAN ACTIONSGlobal use of pesticides increased from 110 million pounds a year in 1945 to 5.5 billion pounds in 1995. Most modern pesticides are ten times more toxic than those used in the 1950s. ENVIRONMENTAL EFFECTSIncreased contact with toxic chemicals. DISEASE INCIDENCEThere were 3 million cases of pesticide poisoning in 1992. In California, 40 percent of children working in agricultural fields show signs of pesticide poisoning.
HUMAN ACTIONSThe number of automobiles is growing three times faster than the human population. Fossil-fuel emissions and industrial pollutants are also increasing. ENVIRONMENTAL EFFECTSAir pollution levels in the world's 20 largest cities exceed WHO guidelines. Fewer than 1 percent of 500 Chinese cities surveyed have clean air. Depletion of ozone in Earth's atmosphere. DISEASE INCIDENCERespiratory diseases are the leading cause of death in China. The incidence of skin cancer in the United States jumped from 10,000 cases in 1975 to 40,000 in 1996.
HUMAN ACTIONSGlobal population expansion. ENVIRONMENTAL EFFECTSLess cropland per person. DISEASE INCIDENCEMore than half the world's population suffers from malnutrition.
HUMAN ACTIONSSuburban expansion. ENVIRONMENTAL EFFECTSClose contact with white-tailed deer populations and thus the deer tick, which carries the bacterium Borrelia burgdorferi. DISEASE INCIDENCELyme disease, discovered in 1976, now affects 12,700 people a year in the United States.