SECTION 2 Biological Hazards · 2020-03-15 · Section 2 Biological Hazards 519 Some of the damage to human health in which the environment plays a role is not caused by toxic chemicals

Section 2 Biological Hazards 519

Some of the damage to human health in which the environmentplays a role is not caused by toxic chemicals but by organismsthat carry disease. Today, we have outbreaks of diseases that didnot exist or that few people had heard of 100 years ago, such asAIDS, ebola, West Nile virus, hanta virus, and mad cow disease.In addition, diseases that have killed people for centuries, such asmalaria, tuberculosis, yellow fever, and hookworm, kill manymore people today than they did 50 years ago. All these diseasesare caused by organisms. One of the reasons these diseases arenow widespread is that we have altered our environment in waysthat encourage them to spread.

The Environment’s Role in DiseaseInfectious diseases are caused by organisms that causedisease. Some of these diseases, such as tuberculosis and whoop-ing cough, are spread from person to person through the air.Other diseases are spread by drinking water that contains thepathogen. Still other diseases are transmitted by a secondary host,such as a mosquito. A is an organism in which a pathogenlives all or part of its life. Table 2 lists the most deadly infectiousdiseases worldwide.

host

pathogens,

Objectives� Explain why the environment is an

important factor in the spread ofcholera.

� List two changes to the environ-ment that can lead to the spreadof infectious diseases.

� Explain what scientists mean whenthey say that certain viruses areemerging.

Key Termspathogenhostvector

S E C T I O N 2

Biological Hazards

Deaths from Infectious Diseases in 2000, Estimated by the World Health Organization

Estimated deaths per yearDisease and examples Cause (in millions)

Total infectious and parasitic diseases bacteria, viruses, and parasites 10.5

Respiratory infections (pneumonia, bacteria, viruses 4.0influenza, and whooping cough)

AIDS virus 2.9

Diarrheal diseases (cholera, typhus, bacteria, viruses, parasites 2.1 typhoid, and dysentery)

Tuberculosis bacteria 1.7

Childhood diseases virus 1.5 (measles and diphtheria)

Malaria parasitic protist 1.1

Tetanus bacteria 0.3

Tropical diseases (trypanosomiasis, bacteria, viruses, and parasites 0.1 Chagas’ disease, schistosomiasis, and leishmaniasis)

Table 2 �

Copyright© by Holt, Rinehart and Winston. All rights reserved.

Waterborne DiseaseNearly three-fourths of infectious diseases are transmitted throughwater. In developing countries, where there is not enough waterfor basic needs, the local water supply is often used for drinking,washing, and sewage disposal. So, the water is usually very pol-luted and is a good breeding ground for pathogens. The pathogensbreed in water and transfer diseases directly to humans throughwater, or organisms that carry the pathogens transfer them tohumans through the water. Organisms, such as mosquitoes, thattransmit diseases to people are called of the disease. Thewidespread construction of irrigation canals and dams, particu-larly in the tropics, has increased the habitat for vectors. Forexample, it is dangerous to bathe in tropical ponds. The watermight contain the snail vector for schistosomiasis, an incurabledisease that kills thousands of people each year.

Cholera The deadliest waterborne diseases come from drinkingwater polluted by human feces. Pathogens, such as those thatcause cholera and dysentery, enter the water in human feces.These diseases cause the body to lose water by diarrhea and vom-iting. These diseases cause most of the infant mortality aroundthe world. A baby’s body has less water than an adult’s body andtherefore suffers more from dehydration. Figure 10 shows a childbeing treated for dehydration.

Malaria Another waterborne disease called malaria was once theworld’s leading cause of death. The disease is caused by parasiticprotists and is transmitted by a bite from females of many speciesof mosquitoes. The mosquito vector lays her eggs in stagnantfresh water, which is where the mosquito larva develops. Noeffective vaccine for malaria exists, but preventative measures areused to control mosquitoes.

vectors

520 Chapter 20 The Environment and Human Health

QuickLABSimulatingan EpidemicProcedure1. Obtain one test tube of water

from your teacher. Your teacherhas “contaminated” one of thetest tubes with an invisible sub-stance.

2. Pour half your water into thetest tube of a classmate. Yourclassmate will then pour anequal amount back into yourtest tube. Exchange water withthree classmates in this way.

3. Your teacher will now put asmall amount of a test chemicalinto your test tube. If your waterturns cloudy, you have been“contaminated.”

Analysis1. Who had the test tube that

started the “infection”?2. Name a disease that could be

spread in this way. Explain youranswer.

Figure 10 � This child is undergoingrehydration therapy during a choleraepidemic in South Africa.


Environmental Change and DiseaseMany ways in which we alter the environment make theenvironment more suitable for pathogens to live and repro-duce. For example, soil is often polluted with chemicals andpathogens. When soil erodes, these pollutants blow away andwash away with the soil and may contaminate areas thousandsof miles away. Many parasites are spread through soil that is con-taminated with feces. Hookworm, which causes acute exhaustion,was once common in the United States. People are infected bywalking barefoot on soil that contains human and animal feces orby consuming contaminated food or water. Figure 11 shows soilerosion in Nepal. In 1984, 87 percent of the population wasfound to be infected by parasitic worms, which people wereexposed to due to widespread soil erosion.

Antibiotic Resistance Our actions cause pathogens to evolveresistance to antibiotics that are used to kill them. For example, inthe United States, large quantities of antibiotics are fed to livestockeach year to speed their growth. As a result, Salmonella, Escher-ichia coli (E. coli), and other bacteria that live in livestock evolveresistance to antibiotics. These bacteria now make thousands ofU.S. citizens sick each year when they eat contaminated meat thathas been improperly refrigerated or undercooked.

We also use enormous amounts of antibiotics to treat humanillnesses. In 1979, 6 percent of European strains of pneumoniabacteria were resistant to antibiotics. Ten years later, 44 percentof the strains were resistant. Tuberculosis (TB) is another illnesstreated with antibiotics. The spread of TB in recent years ismostly due to the evolution of antibiotic resistance in the bac-terium that causes TB.


Figure 11 � Soil erosion in Nepal(top) leads to the spread of parasitessuch as the hookworm (bottom).

EcofactSuburbs Spread Lyme DiseaseLyme disease is the most wide-spread vector-borne disease in theUnited States. It is caused by a bac-terium similar to the one thatcauses the sexually transmitted dis-ease syphilis. The vector is a tickfound on white-tailed deer. Thesuburbs are a suitable place fordeer to grow and reproduce, andtheir populations have exploded assuburbs have expanded. Lyme dis-ease was first described in 1976. Itnow infects more than 13,000 peo-ple a year in the United States.


Malaria on the March Insects that breed in water are the second-ary hosts that transmit malaria. The mosquitoes that transmitmalaria are found in the warmer parts of the world. Epidemi-ologists believe that global warming may increase the area wheremalaria occurs. Figure 12 shows that malaria might spread acrosslarge areas of Central America, South America, Africa, and Asia.

Malaria was common in much of the United States andEurope before the days of mosquito control. Now, it is mostcommon in tropical countries. Historically, malaria was con-trolled by draining marshes and rice paddies where the mos-quitoes breed and by spraying with pesticides. Since the 1970s,however, mosquitoes have evolved resistance to most of the pesti-cides. Newer methods for controlling mosquitoes involve spread-ing growth regulators that prevent mosquito larvae frommaturing into adults or that sterilize the female mosquitoes.

Emerging Viruses In recent years, medical scientists have beenfocusing on previously unknown viruses, the so-called emergingviruses that were unknown 100 years ago. One example is AIDS(acquired immune deficiency syndrome), which is caused by HIV(human immune deficiency virus). Other examples of emergingviruses include the hanta virus, the ebola virus, and the West Nilevirus. Most viral diseases spread directly from one person toanother. Often, the virus invades the body through a cut orthrough mucus membranes. We do not have many effective drugsto treat viral diseases, and the drugs that we have are only effec-tive against a certain virus. Our main defense against viral dis-eases is vaccination. The problem with vaccines is that they arevery specific, and viruses evolve rapidly, so when a new strain ofa viral pathogen evolves, a new vaccine must be developed.

522 Chapter 20 The Environment and Human Health

Figure 12 � This computer modelshows how malaria might spreadunder specific global warming conditions.

www.scilinks.orgTopic: Emerging VirusesSciLinks code: HE4030

BiologyConnection to

The Viral Advantage Anti-biotics kill bacteria but notviruses, such as those that causecolds and flu. Antibiotics kill bac-teria by interfering with their cel-lular mechanisms. Viruses do nothave cellular mechanisms. Manyantibiotics destroy the system abacterium uses to make proteins.Viruses do not make their ownproteins. Instead, they take overthe cellular machinery of the cellsthey invade and use the cell tomake proteins.


Cross-Species Transfers In recent years, scientists havediscovered an increasing number of pathogens that havemade a cross-species transfer, or have moved from onespecies to another. For example, HIV and West Nilevirus fall into this category. The pathogens that causethese diseases have lived for centuries in some species ofwild animals and have done little damage. When thepathogens invade humans, the pathogens cause seriousdiseases. Some ecologists think that the ways in whichwe are altering the environment and destroying habitatsensure that diseases like these will become more com-mon in the future.

Examples of Cross-Species Transfers One example ofpathogens that made a cross-species transfer occurredin Argentina. Herbicides were sprayed on crops inArgentina. The herbicide killed the native grasses andallowed other plants to invade the farmland. Thesenew plants attracted a species of rodent that feeds onthem. The rodents were carrying viruses for a hemor-rhagic fever, which infected many of the agriculturalworkers. Hemorrhagic fevers cause hemorrhages, orinternal bleeding, by breaking blood vessels. Hantavirus is an example of a virus that causes hemor-rhagic fever.

Influenza, or flu, is highly contagious. The fluvirus passes from humans to animals (particularlybirds) and back to humans again. Hong Kong flu getsits name from the fact that the virus was transmittedto humans from ducks bred in Hong Kong for food. Figure 13shows a poultry market, where the Hong Kong flu virus proba-bly transferred from birds to people. Because flu is so easilyspread from one person to another, epidemiologists predict thatthe greatest threat to human health may be the outbreak of anew, very virulent strain of influenza virus, which would spreadrapidly through crowded urban populations.


1. List two changes to the environment that can lead tothe spread of infectious diseases.

2. Explain why some diseases are likely to spread as aresult of global warming.

3. Explain why the environment is an important factorin the spread of cholera.

4. Explain the term emerging virus.

CRITICAL THINKING5. Understanding Concepts Read the information

under the heading “Antibiotic Resistance.” How is theuse of antibiotics by humans increasing antibioticresistance in pathogens?

6. Analyzing Relationships How do human activi-ties cause pathogens to move from one species toanother? Give examples of cross-species transfer tohelp explain your answer.

READING SKILLS

S E C T I O N 2 Review

Figure 13 � Poultry markets, such asthis one in Hong Kong, can con-tribute to the cross-species transfer ofviruses from birds to humans.


HighlightsC H A P T E R 20

1 Pollution andHuman Health

2 Biological Hazards

524 Chapter 20 Highlights

Key Termstoxicology, 512dose, 512dose-response curve,

512epidemiology, 513risk assessment, 513particulates, 514

Main Ideas� Toxic chemicals from both natural sourcesand human activities that pollute air, soil,water, and food may damage human health.

� Toxicology is used to determine how poison-ous a substance is.

� After an outbreak of illness occurs, epidemi-ologists attempt to find its origin and try tofind ways to prevent future epidemics.

� Most pollutants come from human activities,but some pollutants occur naturally.

� Improperly disposed of wastes may leak haz-ardous pollutants into the environment.

pathogen, 519host, 519vector, 520

� Most human diseases that have an environ-mental component are caused by pathogens.

� The environment provides breeding groundsfor pathogens and for their secondary hostsand vectors.

� The transmission of many infectious diseasesincludes water. We increase the areas whereorganisms that carry these diseases can repro-duce when we create irrigation canals and inad-equate sewage systems.

� Environmental changes that help spreadinfectious diseases include global warming andthe spread of suburbs and farmland.

� Many emerging diseases are caused bypathogens that have made cross-species transfers from animals to humans.


Review

Chapter 20 Review 525

Using Key TermsUse each of the following terms in a separatesentence.

1. dose2. vector3. risk assessment4. particulates5. epidemiology

For each pair of terms, explain how the meaningsof the terms differ.

6. pathogen and host7. response and dose8. toxicology and epidemiology

Understanding Key Ideas9. Which of the following is not a true state-

ment about the effects of pollution onhealth?a. It is difficult to determine how pollution

affects health because many factors oftencontribute to a disease.

b. The toxic effects of a pollutant dependupon the dose to which you are exposed.

c. Many pollutants cause chronic diseasesthat result from exposure to the pollutantover the course of many years.

d. Persistent chemicals are less toxic thanchemicals that break down rapidly.

10. Which of the following is an emerging dis-ease that was unknown 50 years ago?a. malariab. dengue feverc. Lyme diseased. schistosomiasis

11. Cholera is usually transmitted from personto person by water becausea. it is caused by a snail that breeds in water.b. it is usually contracted by someone drink-

ing water polluted with human feces thatcontain the cholera pathogen.

c. it is transmitted by mosquitoes.d. it is caused by a virus.

12. Tuberculosis (TB), which was once almosteradicated, is becoming more common, evenin developed countries, becausea. new varieties of the tuberculosis pathogen

have evolved in rodents.b. livestock are given antibiotics.c. the pathogen that causes TB breeds in pol-

luted water.d. some populations of the pathogen that

causes TB are resistant to the antibiotics.13. Which of the following statements about

environmental pollutants is true?a. Our environment contains fewer toxic

chemicals than it did 50 years ago.b. Hormone mimics in our water supply pose

no danger to humansc. There is no health risk from pollutants in

indoor air.d. The bodies of people who live in the

United States contain lower levels of sometoxic chemicals than they did 20 years ago.

14. Which of the following actions is most likelyto prevent yellow fever, which is transmittedby mosquitoes, from becoming epidemic?a. preventing dehydration in patients by treat-

ing them with oral rehydration therapyb. taking antibioticsc. encouraging people to empty water out of

old cans, tires, plant saucers, and otherareas that contain standing water

d. spraying the area repeatedly with pesticides

C H A P T E R 20

Vocabulary Practice To practice vocabulary,write the terms and definitions on a piece of paperand fold the paper lengthwise so that the defini-tions are covered. First, see how many definitionsyou already know. Then, write the definitions youdon’t know on another piece of paper, and prac-tice again until you know all of them.

STUDY TIP


ReviewShort Answer15. How do scientists determine the toxicity of a

chemical?16. How can land use change contribute to the

spread of infectious disease?17. What role does the environment play in the

transmission of infectious diseases?18. Why would lung disease be more common

in a large urban area than in a remote rural area?

Interpreting GraphicsThe graph below shows the dose-response curvesfor two chemicals. Use the graph to answer ques-tions 19–21.19. Which chemical is more toxic at a lower

dose?20. Which chemical is more toxic at a very

large dose?21. Can you tell from the graph which chemical

is more likely to be a problem if it persists inthe environment?

Concept Mapping22. Use the following terms to create a concept

map: habitat destruction, pathogen, animal,vector, and human disease.

Critical Thinking23. Making Comparisons In what ways does a

disease such as lung cancer, which is causedby breathing pollutants over a long period oftime, differ from a disease such as malaria,which is caused by a pathogen?

Cross-Disciplinary Connection24. History In 1775, Percival Pott noted that

chimney sweeps had a high rate of cancer ofthe scrotum. What further investigationsmight be performed to find out what occu-pational hazard might be causing the cancer?How many of these would have been possi-ble at the time, and how many require mod-ern technology?

25. Economics Write a proposal to reduce themosquito population of an area. How mightyou encourage the public to assist in thiseffort?

26. Biology Read about mosquitoes under theheading “Malaria.” How would you designan irrigation system to minimize the chancesthat mosquitoes would breed in it?

Portfolio Project27. Collect half a dozen pesticide containers that

still have their labels. Make a table that hasthree columns. List the names of the pesti-cides in one column. Then read the label oneach container. Use this information to decidewhich pesticide is the most dangerous andwhich pesticide is the least dangerous. In thesecond column, label the pesticides as mostto least dangerous. In the third column, listthe most important safety precautionsrequired of anyone who uses the pesticide.CAUTION: Do not get pesticide on yourface, and wash your hands thoroughly afterhandling the pesticide cans.

READING SKILLS

WRITING SKILLS

C H A P T E R 20Pe

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526 Chapter 20 Review

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Chapter 20 Review 527

Read the passage below, and then answerthe questions that follow.

Dehydration is a serious threat to human sur-vival—as dangerous as a high fever. However,as any athlete knows, drinking water alone isoften not an adequate cure for dehydration.Sports drinks contain sugar and electrolytes(minerals) as well as water. This principle alsounderlies oral rehydration therapy, which isused to treat people suffering from diseasessuch as cholera and dysentery. These diseasescause water loss from diarrhea and vomiting.Severe dehydration often causes death, partic-ularly in small children. Patients being treatedfor dehydration are fed a solution of salt,sugar, and water. The sugar and salt help thebody absorb the water from the stomach.Sugar and salt also add electrolytes to thebody fluids so that these are not diluted.Millions of lives have been saved by rehydra-tion therapy.

1. According to the passage, which of thefollowing statements about oral rehydra-tion therapy is not true?a. A solution containing sugars and salts

is absorbed by the stomach more rap-idly than water alone.

b. The salts replace electrolytes in thebloodstream so that these are notdiluted by the water.

c. Any source of water is adequate tomake up the solution of salts and sugar.

d. Millions of lives have been saved byoral rehydration therapy.

2. According to the passage, which of thefollowing statements about dehydrationis not true?a. It may be fatal.b. It is especially dangerous to small

children.c. It may be caused by diarrhea and vom-

iting from diseases such as cholera.d. It is not often caused by exercising on

a hot day without drinking.

MATH SKILLS

The table below shows four diseases and thenumber of cases of each disease that werereported to the United States Centers forDisease Control in 1990 and 1998. Use thetable below to answer questions 28–29.

28. Analyzing Data Malaria cases increasedbetween 1990 and 1998. What other factswould you want to know before decidingthat the United States has a growing malariaproblem?

29. Making Calculations By what percentage didthe number of typhoid fever cases declinebetween 1990 and 1998?

WRITING SKILLS

30. Communicating Main Ideas Why do sewagesystems that overflow when it rains need tobe replaced with modern systems that do notoverflow?

31. Writing Persuasively Write a letter to anewspaper. In the letter, argue either for oragainst homeowners’ use of pesticides ontheir lawns and gardens.

Disease 1990 1998

Cryptosporidiosis 2 3,793

Lyme disease 2 16,801

Malaria 1,292 1,611

Typhoid fever 552 375

Now that you have read the chapter, take amoment to review your answers to the ReadingWarm-Up questions in your EcoLog. If necessary,revise your answers.

READING FOLLOW-UP


528

Lead Poisoning and Mental AbilityPeople are usually exposed to lead in old buildings that werepainted with lead paint. The lead can enter your body as dustwhen you breathe and can permanently damage the brain andnervous system. Lead poisoning can cause aggressive behavior,hyperactivity, headaches, and hearing loss. At high levels, it cancause seizures, coma, and even death. The Centers for DiseaseControl and Prevention (CDC) state that a lead level of only 10micrograms per deciliter in the blood can be harmful. (A micro-gram is one-millionth of a gram, and a deciliter is one-tenth of aliter.) In this lab, you will explore the effect of lead poisoningon the mental ability of children. The children all grew up neara lead smelter, a factory where raw lead ore is processed.Scientists measured the concentration of lead in the children’sblood over time. Psychologists also performed tests on the chil-dren to determine their IQ. You will analyze the data to see ifyou can find a pattern.

Objectives� Analyze the

relationship between lead poison-ing and children’s IQ.

� Graph experimental data.� Interpret graphical data.

Materialsnotebookpen or pencil

USING SCIENTIFIC METHODS

Skills Practice Lab: MATH /GRAPHINGC H A P T E R 20

� Effects of Lead Lead smelters,such as the one below in Yugoslavia,can cause air pollution and lead poisoning.

Procedure1. Design a hypothesis for the relationship between

the lead concentration in the blood, the IQ, and the age of the children. As the blood-leadconcentration increases, how would you expectthe person’s IQ to change? How do you thinkthis relationship would change as the childrengrow older?

2. The table on the next page lists the blood-leadconcentration and IQ data for a group of 494children. The children were measured five timesas they grew up. The first measurement wasmade when they were six months old, and thelast measurement was made when they wereseven years old. The children were divided intofour groups according to the amount of lead intheir blood. Group 1 had the lowest concentra-tion of lead, and group 4 had the highest concen-tration of lead. Prepare a graph for the data inthe table. Plot lead concentration on the x-axis and IQ on the y-axis. Label each axis withthe correct units. Choose an appropriate scale foreach axis so that the entire range of data in thetable will fit on the graph.

3. Plot the data from the table on your graph.Connect all data points for a single age groupwith a single line. You should have five lines ofdata on your graph and have one line for eachage group.

528 Chapter 20 Skills Practice LabCopyright© by Holt, Rinehart and Winston. All rights reserved.

Chapter 20 Skills Practice Lab 529

Analysis 1. Analyzing Data For a single age group, how does IQ vary

with lead concentration? Is this true for all age groups?2. Analyzing Data How does the relationship between lead

concentration and IQ change as a child grows older?

Conclusions3. Drawing Conclusions What conclusions can you draw from

your analysis about the effect of lead on IQ?4. Applying Conclusions Based on your conclusions, what long-

term effects might lead poisoning have on a community?

Group of Average blood-lead concentration Average IQchildren (micrograms per deciliter) score

6 mo 1 8.3 109.42 12.6 104.73 16.8 102.94 24.2 100.0

15 mo 1 11.8 109.32 18.6 106.53 24.4 102.94 34.4 101.3

3 yr 1 11.6 110.22 17.4 106.53 22.4 102.24 30.2 100.0

5 yr 1 8.3 109.32 12.6 106.13 17.2 104.14 23.6 98.8

7 yr 1 6.6 109.62 10.1 107.73 13.7 102.74 20.0 98.7

� Lead Paint Dust from lead paintpeelings can cause lead poisoning.

1. Analyzing a Viewpoint Based on the data presented in this lab, do you think the CDC’s limit of 10 microgramsper deciliter is reasonable? Explain your answer.

Extension


530 Chapter 20 Maps in Action

LYME DISEASE RISK

M A P S K I L L S

Use the Lyme disease risk map for the United States toanswer the questions below.

1. Using a Key Using the map above, determine therisk of contracting Lyme disease in your city or town.

2. Using a Key In what general region of the UnitedStates is the risk of contracting Lyme disease greatest?

3. Analyzing Relationships Can you determine therelationship between the risk of contracting Lyme

disease and the concentration of ticks that act asvectors for the disease? Explain your answer.

4. Analyzing Data What is the difference betweenthe risk of contracting Lyme disease in ruralMassachussetts and the risk of contracting Lyme dis-ease in rural Nevada?

5. Forming a Hypothesis What factors mightaccount for the relatively high risk of contractingLyme disease in the Northeast?

� The map above shows the risk of contracting Lyme disease by geographic location inside the United States.


Chapter 20 Society and the Environment 531

TOXIC MOLD

What Do You Think?School districts and home-owners have spent millions ofdollars replacing moldy partsof buildings. But in many casesthe mold had not causedhealth problems. Should thegovernment require schoolsand homeowners to repairmoldy buildings? Who shouldpay for it?

You may have seen stories in thenews with titles such as “MoldCloses Schools” or “Homes Infestedwith Toxic Mold.” In the past 10years, news stories have reported onschool evacuations, strange illnesses,and multimillion dollar lawsuits, alldue to mold. What is toxic mold,and why is it a problem?

“Toxic mold” is a popular termfor molds that grow indoors andthat are suspected of making peo-ple sick who are exposed to them.

Recall that molds are fungi and arefound almost everywhere on Earth.In buildings, molds tend to growon damp surfaces, especially dampwood, where they appear as ablack or dark green fuzzy layer.

Are Molds Toxic?Some species of mold produce tox-ins that they use mainly to competewith other molds. These toxins canalso harm people. The toxinsbecome airborne attached tospores, the mold’s reproductiveparticles, or on tiny mold frag-ments. Once the toxins are air-borne, people can breathe them in.

The most commonly mentionedtoxic mold is Stachybotrys char-tarum. This mold produces severalpotent toxins that affect theimmune system and cause hemor-rhaging in toxicology tests on mice.

People handling material con-taminated with Stachybotrys reportcoughing and burning sensations of

the throat and nose. Some peoplehave also reported memory lossand bleeding in the lungs. But sci-entists have not found a firm linkbetween indoor mold and thesemore serious health problems.

Molds and BuildingsMolds are especially common inareas with high rainfall. If wood orpaper stays damp for any length oftime, odds are that mold sporeswill land on it and begin to grow.

Most of the problems withindoor mold occur in areasbetween walls or in other rarelyseen places. The solution is to fixleaks as soon as possible andimprove air circulation so thatdamp areas dry out.

Scientific UncertaintyThere are only a small number ofwell-studied cases of toxic mold poi-soning, and even in these there existsthe possibility of other causes for theillnesses. Scientists see toxic mold asan example of the difficulty of link-ing environmental exposure withhuman health. “You can’t prove cau-sation from epidemiological studies,”notes one doctor. “All you can do isshow that there is a correlation.”

� The mold pictured below,Stachybotrys, is commonly impli-cated in toxic building episodes.

� This health worker is removing portions of a house infested withmold that may be toxic.


Documents

SECTION 2 Biological Hazards · 2020-03-15 · Section 2 Biological Hazards 519 Some of the damage to human health in which the environment plays a role is not caused by toxic chemicals