department of a small rural hospital after collapsing at work at an onion farm. She reported no previous episodes of syncope or chest pain and had no significant past medical history other than treatment for mild hypertension. She was doing her ordinary work at the farm’s packing shed, preparing onions for shipment, when she suddenly became dizzy and l o s t c o n s c i o u s n e s s o u t . H e r electrocardiogram (ECG) showed mild ischaemic changes, and she was admitted to the intensive care unit for observation. The emergency department physician contacted the farm owner, who reported that he had called the gas company to check the propane heaters used in the barn. They had tested the barn with a “gas meter” and found no problem with carbon monoxide (CO) or other gases. The two workers went back to work the next morning and again became ill. They returned to the emergency department. This time, their COHb levels were elevated (between 14% and 16%). A nurse from a local occupational health program was notified and visited the farm that afternoon. In discussing the situation with the farmer and other workers, she found a number of potential problems. Temperatures in the barn had been very cold. There was little ventilation. Several small propane heaters provided some heat. A propane- powered forklift was used intermittently in the barn. Because of weather conditions, the doors to the barn had been kept closed for the previous several days. The next afternoon, two other workers from the same farm were brought to the emergency department complaining of headaches, dizziness, and nausea. Blood samples were drawn for determination of carboxyhemoglobin (COHb) concentration, and both workers had slightly increased levels (about 10%). Interpretation was complicated because more than 30 minutes had elapsed before they reached the hospital from the farm, and it was unclear whether they had been treated with oxygen during that time. Lady in the Onion Farm
for a construction fi rm that did bridge repair work complained to his family physician of intermittent stomach pains of several weeks’ duration. The pain was not associated with meals. Onset had been gradual. He had no associated systemic or gastrointestinal symptoms. He had not experienced any unusual stress at home or at work. He reported drinking one or two cans of beer per day. Physical examination was normal. His physician treated him with antacids and his pain gradually resolved. Approximately 2 months later, the patient returned complaining of more severe epigastric pain, associated with abdominal cramping, headaches, and fatigue. He recently started working at a new site, where he had used an oxyacetylene torch to remove paint from an old bridge. After consultation with an occupational medicine physician, the family physician obtained a blood lead level (BLL), which was 75 µg/dL. The patient stopped doing paint removal work, and his symptoms gradually improved. Within 4 weeks, his BLL decreased to 35 µg/dL. The contractor provided a ventilation system for use when paint was being removed from bridges. Subsequent quarterly monitoring of the patient’s BLL showed a gradual further decline.
Hazard identification, exposure assessment, dose-response curve estimation, risk characterisation • Hazard identification - toxicokinetics and toxicodynamics • Exposure Assessment - routes of exposure • Different types of Dose Response curves • Different ways to classify chemical exposure • Case studies of carbon monoxide poisoning and lead to illustrate
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