Environmental Problems, Their Causes, and Sustainability 1

Table 22-2 Common Diseases Transmitted to Humans Through Contaminated Drinking WaterType of Organism Disease EffectsBacteria Typhoid fever Diarrhea, severe vomiting, enlarged spleen, inflamed intestine; often fatal if untreatedCholeraDiarrhea, severe vomiting, dehydration; often fatal if untreatedBacterial dysentery Diarrhea; rarely fatal except in infants without proper treatmentEnteritisSevere stomach pain, nausea, vomiting; rarely fatalViruses Infectious hepatitis Fever, severe headache, loss of appetite, abdominal pain, jaundice, enlarged liver;rarely fatal but may cause permanent liver damageParasitic protozoa Amoebic dysentery Severe diarrhea, headache, abdominal pain, chills, fever; if not treated can cause liverabscess, bowel perforation, and deathGiardiasisDiarrhea, abdominal cramps, flatulence, belching, fatigueParasitic worms Schistosomiasis Abdominal pain, skin rash, anemia, chronic fatigue, and chronic general ill healthdie prematurely each year from waterborne diseases.This means that during your lunch hour about 400 peopledied from such diseases. Each year, diarrhea alonekills about 1.9 million people—about 90% of them childrenunder 5 in developing countries. The number ofchildren killed by largely preventable diarrhea in thepast 10 years is greater than the number of peoplekilled in all armed conflicts since World War II.In the United States, an estimated 1.5 millionpeople a year become ill from infectious agents foundin water and food. For example, in 1993 a protozoanparasite called Cryptosporidium contaminated the publicdrinking water supply in Milwaukee, Wisconsin.About 370,000 people developed severe diarrhea andat least 100 people with weakened immune systemsdied.colonies per 100 milliliters. By contrast, raw sewagemay contain several million coliform bacterial coloniesin 100 milliliters of water.When dangerous levels of fecal coliform bacteriaare detected scientists try to determine whether thesource is from humans, various types of livestock, orwild animals such as birds or raccoons. A new field ofscience called bacterial source tracking (BST) uses molecularbiology techniques to determine subtle differencesin strains of E. coli based on their animal host.How Do We Measure Water Quality? Biologyand Chemistry in ActionScientists monitor water quality by using bacterialcounts, chemical analysis, and indicator organisms.Scientists use a number of biological and chemicalmethods to measure water quality. One involves measuringthe number of colonies of fecal coliform bacteria(such as various strains of Escherichia coli) present in awater sample (Figure 22-2). Various strains of thesebacteria live in the colon or intestines of humans andother animals and thus are present in their fecalwastes. Although most strains of coliform bacteria donot cause disease, their presence indicates that waterhas been exposed to human or animal wastes that arelikely to contain disease-causing agents.To be considered safe for drinking, water shouldcontain no colonies of coliform bacteria in a sample of100 milliliters (about 1/2 cup). To be considered safefor swimming, it should have no more than 200Figure 22-2 Fecal coliform bacteria test is used to indicate thelikely presence of disease-causing bacteria in water. It is carriedout by passing a water sample through a filter, placing thefilter disk on a growth medium that supports coliform bacteria(such as E. coli) for 24 hours, and then counting the number ofcolonies of coliform bacteria (shown as clumps in the figure).http://biology.brookscole.com/miller14493