ABSTRACr Employees at six sewage treatment plants and three drinking water plants were interviewed for the presence of specific medical symptoms. Serum immunoglobulin concentrations, white blood cell counts and fibrinogen degradation product concentrations (FDP) in urine were determined as were the number and species of airborne Gram negative rods in order to characterise exposure to aerosols of sewage water. The highest number of bacteria was found in areas where the sewage water was agitated.

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... A significantly higher proportion of employees at sewage treatment plants reported skin disorders, diarrhoea, and other gastrointestinal symptoms than the control group. No significant differences were found between the groups for white blood cell count or serum immunoglobulin concentrations, except that IgM concentrations were slightly higher in the sewage workers. Some workers had serum transaminase concentrations in excess of normal; some of these returned to normal after the summer holiday. Among non-smokers a higher proportion of sewage treatment workers had increased amounts of FDP in urine. It is conceivable that the symptoms observed were caused by toxins from Gram negative bacteria. The occupational health risks of sewage workers have been investigated by several authors, and reviews have been presented by Anders' and Clark.2 The emphasis in most investigations has been on the risk of contracting various types of infectious diseases. A previous study on sewage workers reported that when sewage sludge was heat-dried, employees experienced attacks of fever, chills, and eye inflammation after exposure to high concentrations of the dust.3 The concentrations of serum immunoglobulins and fibrogen degradation products (FDP) in urine were increased in exposed workers. The symptoms were interpreted as being caused by the endotoxin in the dust, originating from Gram negative bacteria in the sewage sludge. This present paper reports a study undertaken to determine whether specific symptoms were also present among sewage workers in plants where sludge was treated by conventional methods. Workers in drinking water plants served as a reference population. The presence of medical symptoms was studied in interviews and serum immunoglobulin concentrations, white blood cell counts, and FDP concentrations ip the urine were measured. The exposure to sewage water aerosols was characterised by measur-ing the number of airborne Gram negative rods. A preliminary report of this work has been presented elsewhere.4 Materials and methods PLANTS INVESTIGATED The investigation was performed at six different sewage water treatment plants in Sweden (three indoors and three outdoors) and three drinking water plants. All sewage treatment plants were equipped for high degree (biological) treatment of the sewage water, and usually also for chemical treatment. None received industrial water containing particularly toxic substances. BACTERIA SAMPLING The number of airborne Gram negative rods was determined with a six stage Andersen sampler,5 using Drigalski agar (see appendix) as a selective medium. After incubation at 300 for 40-65 hours, the number of colonies was counted and corrected as recommended by Andersen5 and May.6 The results were reported as the mean nut.iber of colony forming units (cfu) per cubic meter of air. Several samples were taken at breathing level at the different working sites and the measurements were repeated on two or more occasions on different days. 325 on 20 July 2018 by guest. Protected by copyright.