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Chapter 3: Risk assessment

3.1. Participatory field visits3.1.1. Sample field visits

A. Water purification and recirculation plant

B. Informal food traders

C. Sewage treatment plant

D. Solid waste facility: bale and rail

3.2. The relationship between dose and health

outcome: dose-response versus dose-effect

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3.1. Participatory field visitsPrepared by Merri Weinger

Time: Preparation: 1-1 hoursField visit: variable

Objective:At the end of the exercise, students will be able to:

Describe the rationale and procedures for conducting onsiteevaluation of potentially hazardous environmental andworkplace settings.

Procedures:1. Ask students what they think is the purpose of a field

visit. Responses should include: to observe and quantifypotential sources of contamination, to collect andanalyse data (through biological and atmospheric

monitoring, interviews, etc.) and to recommendenvironmental controls and preventive measures.

2. Describe the site that the group will be visiting.Brainstorm a list of potential hazards that one mightexpect to find.

3. Instruct students that they will be conducting the fieldinvestigation as a team of environmental consultants.Define the objective of the visit, which usually includesthe identification of potential hazards on the site and therecommendation of necessary control measures (See

sample field visits, Chapter 3.1.1.). Divide into smallgroups to prepare for the visit. Each group shouldrespond to the following questions:

What do you want to observe during the visit?

What questions would you like to ask?

Who do you want to be sure to talk to during thevisit? (e.g. in a factory, students may want tointerview supervisors, workers, representatives fromthe medical service, etc.)

4. Invite brief reports from each group. Students shouldavoid repeating items that have already been mentioned

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TEACHERS GUIDE ON BASIC ENVIRONMENTAL HEALTH

by other groups. The notes from this discussion will serveas a checklist for the team during the visit.

5. Conduct field visit.

6. Debrief visit in the classroom. Invite oral reports from thesmall groups on potential hazards observed andintervention strategies proposed. Summarize andconclude the exercise.

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Alternatives

Field visits can also be an opportunity to practice developingwritten reports on observations and conclusions. In thiscase, each team would be required to submit a reportaccording to a format provided by the instructor.

Materials:Written task for field visit, flip chart, coloured markers, tape.

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3.1.1. Sample field visits

A. Water purification and recirculation plant

(Visby, Sweden)

(Note to instructor: For general guidelines on conductinga participatory field visit, see Chapter 3.1.)

Objectives of the visit

You are an environmental health specialist whose task is to:

1. Determine whether there are any health risks derivedfrom using the water processed by the Roma waterpurification and recirculation plant.

2. Determine whether there are any health risks to workersin the plant.

3. If necessary, recommend remedial action.

Potential areas for investigation

(The following list was compiled by the instructor to

complement the list generated by students when preparingfor the visit in the classroom.)

Plant organisation

1. What is the number of staff in the plant in:

administration?

operation?

maintenance?

2. What is the organizational structure of the plant?

Process

1. What is the volume of water being treated?

2. What is the population served?

3. What is the per capita consumption in the community?

4. What is the method or process used to treat the water?

5. Considering that there is a recirculation process, what

percentage of the water is being recirculated and whatamount of water is being lost?

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6. What difficulties are faced in the treatment process dueto the recirculation (e.g. frequent clogging of filters, theneed to use more chemicals, etc.)

Water quality

1. What is the quality of the raw water?

2. Which laboratory tests are conducted? Are theyconducted at the treatment plant or elsewhere?

3. What are the results of laboratory tests on the treatedwater? If there has been any contamination, what wasthe cause? What measures were taken to address theproblem?

4. What is the quality control system in the plant? Is itlocated at different points in the treatment process?

5. How vulnerable is the distribution system?

6. Is there any quality control by local health authorities? Ifso, what does it consist of?

Worker health and safety

1. What are the key risks to workers in the plant (e.g. falls

into sedimentation tanks, electrical hazards)?2. What is the accident/injury/illness rate among workers

over the past 10 years?

3. What facilities or strategies are used to preventaccidents or injuries?

B. Informal food traders

(Cape Town, South Africa)

(Note to instructor: For general guidelines on conductinga participatory field visit, see Chapter 3.1. There areinformal food traders or vendors in most countries. Theyrepresent a tremendous challenge to enforcers of foodhygiene since they are generally unlicensed and oftentransient.)


You are an environmental health specialist whose task is toinspect the food installations in an informal settlement in

Cape Town.1. What are the potential health hazards on the site?

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2. What specific recommendations would you make toprevent an outbreak of foodborne disease?

3. What are potential obstacles to implementing theserecommendations?

4. How would you propose to overcome these obstacles?

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ANNEXES

C. Sewage treatment plant

(Budapest, Hungary)

(Note to instructor: For general guidelines on conductinga participatory field visit, see Chapter 3.1.)


You are an environmental health specialist whose task is to:

1. Determine the aim of the treatment process with specialregard to the Danube branch where the effluent isdischarged.

2. Determine which special health aspects need to be

considered where (and when) the discharged effluententers the area used for recreational activity.

3. Determine whether there are any health risks to workersin the plant, to those employed in nearby facilities or topassers-by (e.g. cyclists).

4. During the visit, what would you need to ask or observeto accomplish this task?

Field visit checklist

(The following list was compiled by the instructor tocomplement the list generated by students when preparingfor the visit in the classroom.)

Process

1. What is the sewerage system? What problems arecaused by it?

2. What is the capacity of the plant? What is the actualaverage loading?

3. What is the influence of the industrial wastewater on thesewage quality and treatment process?

4. What are the main steps in the treatment technology?

5. What is the technology of the sludge treatment?

6. What is the fate of the treated sludge?

7. When and why is it necessary to chlorinate the effluent?

Water quality

1. What is the quality of the raw sewage?

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2. Which laboratory tests are conducted? Are theyconducted at the treatment plant or elsewhere?

3. What are the results of laboratory tests on the treatedwater?

4. How is the chlorination controlled?

5. Is there any odour problem during the process? Is thereany measure to control or diminish it?

6. Is there quality control by local health authorities? If so,what does it consist of?

Worker health and safety

1. What are the key risks to workers in the plant? (e.g. fallsinto sedimentation tanks, electrical hazards, enteric orother infections, etc.)

2. Is there any other hazard for workers?

3. What strategies are used to prevent accidents orinjuries?

D. Solid waste facility: bale and rail

(Cape Town, South Africa)


Bale and Rail is a project which includes the baling orcompacting and packing of solid waste to be railed or sentby train to a conventional waste disposal site.

You are an environmental health specialist who has beenasked to evaluate the bale and rail system from a publichealth perspective. Among other factors, you are concernedabout the potential for underground contamination,leaching, health risks to workers and unpleasant odours.

As you conduct the field visit, please consider the followingquestions:

1. Do you observe any potential health risks for theenvironment, the employees in the plant or thesurrounding community in:

the bailing process?

the railing process?

the disposal site?

2. What interventions would you recommend to preventpotential health risks?

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3. In your opinion, from a public health perspective, howdoes the bale and rail system compare to theconventional solid waste disposal system using long-haul

truck transport? Which approach may pose greaterhealth risk to the environment, the workforce and thecommunity, and why?

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3.2. The relationship between dose and healthoutcome: dose-response versus dose-effect

Prepared by Annalee Yassi*

Time: - 1 hour

Objective:At the end of the exercise, students will be able to:

1. Distinguish between dose-response and dose-effect

relationships.

2. Interpret dose-response and dose-effect relationshipsfrom data displayed graphically.

Procedures:1. This exercise is designed to elicit student observations

and conclusions about the dose-response and dose-effect curves found in Annex 6. If there is limited

response to the request for observations, ask specificquestions (e.g. in Figure 5, ask whether there is arelationship between speed and the frequency of injuryfor seat belt usage and non-usage; then ask them howspeed affects this relationship).

2. Place Figure 1, a dose-response curve, on the overheadscreen, without the title showing. Ask the students todescribe the curve. The students should state that this isa dose-response relationship showing the proportion ofindividuals in an exposed group that demonstrate adefined effect at a given dose.

3. Place Figure 2, a dose-effect curve, on the overheadscreen without the title showing. Ask the students todescribe this figure. The students should state that this isa simplified, schematic representation of a dose-effectrelationship between the percentage of carboxyhaemoglobin in the blood and the severity ofhealth effects (in this case, a slight headache at about17% carboxyhaemoglobin, headache and dizziness atapproximately 33%, nausea and blackouts at about 48%,

* Dr Annalee Yassi, Occupational and Environmental Health Unit, University of Manitoba,

Winnipeg, Canada

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ANNEXES

unconsciousness at approximately 60% and death atapproximately 75% carboxyhaemoglobin).

4. Place Figure 3, a dose-response curve, on the overheadscreen without the title showing, but with the legendvisible. Ask the students to describe what they see. Thestudents should state that this is a series of dose-response curves for various health effects of lead inchildren. They should note that decreased aminolevunicacid dehydrase (ALA-D) activity begins at extremely lowconcentrations of lead in the blood, reachingapproximately 90% dysfunction at a concentration of

approximately 300g pb/l. They should be able tocontinue this commentary for the other effects listed in

the legend, noting that severe effects, such as palsy,colic pain and encephalopathy do not begin until a

concentration of lead in blood of approximately 1150gpb/l occurs.

They may observe that the shapes of the dose-responsecurves are different, and may discuss the implications ofthese differences. It may also become apparent that theconcentration of lead in blood at which a certainpercentage of dysfunction in the central nervous systemoccurs spans a very large range of concentrations. In

contrast, the steepness of the curve for ALA-D activitysuggests that the percentage of dysfunction increasesrapidly at very low concentrations. Ask the studentswhich would be the most sensitive indicator of leadexposure based on this information. The students shouldanswer that ALA-D activity would be the most sensitiveto early effects of lead exposure.

5. Place Figure 4, on dose-response relationships, on theoverhead screen without the title showing and ask thestudents to describe what they see.

The students can be expected to note that this is a seriesof dose-response relationships between occupationalsound levels and percentage of workers with impairedhearing, with each curve representing a different agegroup. The students should note that for any given levelof sound exposure, the percentage impairment isgreatest in the oldest age group, indicating that both ageand noise create impaired hearing. Additionally, theymay observe that for any given sound level at work thegeneral population is likely to have a much lowerpercentage impairment than factory workers exposed tonon-industrial noise. A discussion may take place as towhy this is so.

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6. Place Figure 5, on dose-response relationships, on theoverhead screen. Once again, cover the title and ask thestudents to describe what they see.

The students should mention that the graph shows twodose-response relationships between speed and risk ofinjury, with one being when seat belts are used and theother when seat belts are not used. One can concludethat for any given speed level, more injuries occur whenseat belts are not used than when they are used. Thestudents should also note that as speed increases sodoes the frequency of injury.

7. Finally, place Figure 6 on the screen. Cover the title andask the students what they see.

The students should note that this is a dose-responserelationship between noise level and annoyance asdiscovered in two studies, one American and oneGerman. The students may note that as the integratedsound level increases, the percentage of the populationthat is highly annoyed increases. They would also notethat the percentage annoyance at any given sound levelis higher in the American study than in the Germanstudy. A discussion may ensue as to why this is so.

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Materials:Figures 1 to 6 on transparencies (Annex 6); overhead

projector.

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