Chapter 3: Risk assessment

Transcription

1 Chapter 3: Risk assessment 3.1. Participatory field visits 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 ANNEXES 3.1. Participatory field visits Prepared by Merri Weinger Time: Preparation: 1-1½ hours Field visit: variable Objective: At the end of the exercise, students will be able to: Describe the rationale and procedures for conducting onsite evaluation of potentially hazardous environmental and workplace settings. Procedures: 1. Ask students what they think is the purpose of a field visit. Responses should include: to observe and quantify potential sources of contamination, to collect and analyse data (through biological and atmospheric monitoring, interviews, etc.) and to recommend environmental controls and preventive measures. 2. Describe the site that the group will be visiting. Brainstorm a list of potential hazards that one might expect to find. 3. Instruct students that they will be conducting the field investigation as a team of environmental consultants. Define the objective of the visit, which usually includes the identification of potential hazards on the site and the recommendation of necessary control measures (See sample field visits, Chapter ). Divide into small groups to prepare for the visit. Each group should respond 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 the visit? (e.g. in a factory, students may want to interview supervisors, workers, representatives from the medical service, etc.) 4. Invite brief reports from each group. Students should avoid repeating items that have already been mentioned by other groups. The notes from this discussion will serve as a checklist for the team during the visit. 5. Conduct field visit. 6. Debrief visit in the classroom. Invite oral reports from the small groups on potential hazards observed and intervention strategies proposed. Summarize and conclude the exercise. 3

4 TEACHERS GUIDE ON BASIC ENVIRONMENTAL HEALTH Alternatives Field visits can also be an opportunity to practice developing written reports on observations and conclusions. In this case, each team would be required to submit a report according to a format provided by the instructor. Materials: Written task for field visit, flip chart, coloured markers, tape. 4

5 ANNEXES Sample field visits A. Water purification and recirculation plant (Visby, Sweden) (Note to instructor: For general guidelines on conducting a 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 derived from using the water processed by the Roma water purification and recirculation plant. 2. Determine whether there are any health risks to workers in 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 preparing for 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 what amount of water is being lost? 6. What difficulties are faced in the treatment process due to the recirculation (e.g. frequent clogging of filters, the need to use more chemicals, etc.) 5

6 TEACHERS GUIDE ON BASIC ENVIRONMENTAL HEALTH Water quality 1. What is the quality of the raw water? 2. Which laboratory tests are conducted? Are they conducted at the treatment plant or elsewhere? 3. What are the results of laboratory tests on the treated water? If there has been any contamination, what was the cause? What measures were taken to address the problem? 4. What is the quality control system in the plant? Is it located at different points in the treatment process? 5. How vulnerable is the distribution system? 6. Is there any 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. 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 prevent accidents or injuries? B. Informal food traders (Cape Town, South Africa) (Note to instructor: For general guidelines on conducting a participatory field visit, see Chapter 3.1. There are informal food traders or vendors in most countries. They represent a tremendous challenge to enforcers of food hygiene since they are generally unlicensed and often transient.) Objectives of the visit You are an environmental health specialist whose task is to inspect the food installations in an informal settlement in Cape Town. 1. What are the potential health hazards on the site? 2. What specific recommendations would you make to prevent an outbreak of foodborne disease? 3. What are potential obstacles to implementing these recommendations? 4. How would you propose to overcome these obstacles? 6

7 ANNEXES C. Sewage treatment plant (Budapest, Hungary) (Note to instructor: For general guidelines on conducting a participatory field visit, see Chapter 3.1.) Objectives of the visit You are an environmental health specialist whose task is to: 1. Determine the aim of the treatment process with special regard to the Danube branch where the effluent is discharged. 2. Determine which special health aspects need to be considered where (and when) the discharged effluent enters the area used for recreational activity. 3. Determine whether there are any health risks to workers in the plant, to those employed in nearby facilities or to passers-by (e.g. cyclists). 4. During the visit, what would you need to ask or observe to accomplish this task? Field visit checklist (The following list was compiled by the instructor to complement the list generated by students when preparing for the visit in the classroom.) Process 1. What is the sewerage system? What problems are caused by it? 2. What is the capacity of the plant? What is the actual average loading? 3. What is the influence of the industrial wastewater on the sewage 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? 2. Which laboratory tests are conducted? Are they conducted at the treatment plant or elsewhere? 3. What are the results of laboratory tests on the treated water? 4. How is the chlorination controlled? 5. Is there any odour problem during the process? Is there any measure to control or diminish it? 7

8 TEACHERS GUIDE ON BASIC ENVIRONMENTAL HEALTH 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. falls into sedimentation tanks, electrical hazards, enteric or other infections, etc.) 2. Is there any other hazard for workers? 3. What strategies are used to prevent accidents or injuries? D. Solid waste facility: bale and rail (Cape Town, South Africa) Objectives of the visit Bale and Rail is a project which includes the baling or compacting and packing of solid waste to be railed or sent by train to a conventional waste disposal site. You are an environmental health specialist who has been asked to evaluate the bale and rail system from a public health perspective. Among other factors, you are concerned about the potential for underground contamination, leaching, health risks to workers and unpleasant odours. As you conduct the field visit, please consider the following questions: 1. Do you observe any potential health risks for the environment, the employees in the plant or the surrounding community in: the bailing process? the railing process? the disposal site? 2. What interventions would you recommend to prevent potential health risks? 3. In your opinion, from a public health perspective, how does the bale and rail system compare to the conventional solid waste disposal system using long-haul truck transport? Which approach may pose greater health risk to the environment, the workforce and the community, and why? 8

9 ANNEXES 3.2. The relationship between dose and health outcome: dose-response versus dose-effect Prepared by Annalee Yassi * Time: ½ - 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 relationships from 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 specific questions (e.g. in Figure 5, ask whether there is a relationship between speed and the frequency of injury for seat belt usage and non-usage; then ask them how speed affects this relationship). 2. Place Figure 1, a dose-response curve, on the overhead screen, without the title showing. Ask the students to describe the curve. The students should state that this is a dose-response relationship showing the proportion of individuals in an exposed group that demonstrate a defined effect at a given dose. 3. Place Figure 2, a dose-effect curve, on the overhead screen without the title showing. Ask the students to describe this figure. The students should state that this is a simplified, schematic representation of a dose-effect relationship between the percentage of carboxyhaemoglobin in the blood and the severity of health effects (in this case, a slight headache at about 17% carboxyhaemoglobin, headache and dizziness at approximately 33%, nausea and blackouts at about 48%, unconsciousness at approximately 60% and death at approximately 75% carboxyhaemoglobin). 4. Place Figure 3, a dose-response curve, on the overhead screen without the title showing, but with the legend visible. Ask the students to describe what they see. The students should state that this is a series of doseresponse curves for various health effects of lead in children. They should note that decreased aminolevunic acid dehydrase (ALA-D) activity begins at extremely low concentrations of lead in the blood, reaching approximately 90% dysfunction at a concentration of approximately * Dr Annalee Yassi, Occupational and Environmental Health Unit, University of Manitoba, Winnipeg, Canada 9

10 TEACHERS GUIDE ON BASIC ENVIRONMENTAL HEALTH 300µg pb/l. They should be able to continue 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 1150µg pb/l occurs. They may observe that the shapes of the dose-response curves are different, and may discuss the implications of these differences. It may also become apparent that the concentration of lead in blood at which a certain percentage of dysfunction in the central nervous system occurs spans a very large range of concentrations. In contrast, the steepness of the curve for ALA-D activity suggests that the percentage of dysfunction increases rapidly at very low concentrations. Ask the students which would be the most sensitive indicator of lead exposure based on this information. The students should answer that ALA-D activity would be the most sensitive to early effects of lead exposure. 5. Place Figure 4, on dose-response relationships, on the overhead screen without the title showing and ask the students to describe what they see. The students can be expected to note that this is a series of dose-response relationships between occupational sound levels and percentage of workers with impaired hearing, with each curve representing a different age group. The students should note that for any given level of sound exposure, the percentage impairment is greatest in the oldest age group, indicating that both age and noise create impaired hearing. Additionally, they may observe that for any given sound level at work the general population is likely to have a much lower percentage impairment than factory workers exposed to non-industrial noise. A discussion may take place as to why this is so. 6. Place Figure 5, on dose-response relationships, on the overhead screen. Once again, cover the title and ask the students to describe what they see. The students should mention that the graph shows two dose-response relationships between speed and risk of injury, with one being when seat belts are used and the other when seat belts are not used. One can conclude that for any given speed level, more injuries occur when seat belts are not used than when they are used. The students should also note that as speed increases so does the frequency of injury. 7. Finally, place Figure 6 on the screen. Cover the title and ask the students what they see. The students should note that this is a dose-response relationship between noise level and annoyance as discovered in two studies, one American and one German. The students may note that as the integrated sound level increases, the percentage of the population that is highly annoyed increases. They would also note that the percentage annoyance at any given sound level is higher in the American study than in the German study. A discussion may ensue as to why this is so. 10

11 ANNEXES Materials: Figures 1 to 6 on transparencies (Annex 6); overhead projector. 11