Health effects of work at waste water treatment plants: a review of the literature with guidelines for medical surveillance

Efficacy of laundering and tumble-drying in reducing microbial contamination of wastewater treatment plant worker coveralls

BACKGROUND

Evidence implicates textiles in health care as potential reservoirs of pathogens. No similar data exist for the wastewater treatment plant (WWTP) industry. We investigated if coveralls worn by WWTP workers could present occupational infection risk.

METHODS

We enumerated heterotrophic plate counts (HPCs), total coliforms, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Clostridium difficile, and Acinetobacter spp on coverall swatches experimentally contaminated with raw, primary, secondary, and final effluent. Contaminated swatches were examined by culture-based methods after laundering, tumble-drying, and storing.

RESULTS

Concentrations of microorganisms and efficacy of decontamination differed depending on the contaminating wastewater matrix and the organism. Laundering was an effective decontamination method for coveralls contaminated with all microorganisms, except HPCs. Tumble-drying resulted in statistically significant decreases for HPCs, P aeruginosa, and Acinetobacter. Increases in contamination after laundering were seen in Acinetobacter spp, in P aeruginosa when coverall swatches were contaminated with raw and final effluent, and in HPCs when contaminated with secondary effluent.

DISCUSSION

Results suggest that solely laundering at 60°C for 25 minutes as per ASTM Standard F1449 may not always be an efficient means of controlling microorganisms on coveralls.

CONCLUSIONS

Clearer guidelines are needed to better protect WWTP workers.

Monitoring risks in association with exposure levels among wastewater treatment plant workers

OBJECTIVE

To investigate the relationship between exposure to hydrogen sulfide and endotoxin during specific job tasks and health symptoms among wastewater treatment plant (WWTP) workers.

METHODS

The exposure levels for specific tasks were measured by personal monitoring. The health symptoms of WWTP workers were compared with those of water treatment plant workers through a questionnaire survey.

RESULTS

Exposure levels for all monitored tasks were less than 1 ppm for hydrogen sulfide and 91 EU/m (endotoxin units/m) for endotoxin. Statistically higher odds ratios of respiratory, ocular and skin irritation, neurology, and gastrointestine symptoms were shown among WWTP workers compared with water treatment plant workers. Tasks related to sludge handling and plant inspection showed statistically significant associations with memory/concentration difficulties, throat irritation, and stomach pain.

CONCLUSIONS

These results suggest that exposure control programs for specific job tasks and work locations are needed.

Health survey of residents living near farm fields permitted to receive biosolids

The authors studied the health status of residents living in Wood County, OH, near farm fields that were permitted to receive biosolids. They mailed a health survey to 607 households and received completed surveys from 437 people exposed to biosolids (living on or within 1 mile of the fields where application was permitted) and from 176 people not exposed to biosolids (living more than 1 mile from the fields where application was permitted). The authors allowed for up to 6 surveys per household. Results revealed that some reported health-related symptoms were statistically significantly elevated among the exposed residents, including excessive secretion of tears, abdominal bloating, jaundice, skin ulcer, dehydration, weight loss, and general weakness. The frequency of reported occurrence of bronchitis, upper respiratory infection, and giardiasis were also statistically significantly elevated. The findings suggest an increased risk for certain respiratory, gastrointestinal, and other diseases among residents living near farm fields on which the use of biosolids was permitted. However, further studies are needed to address the limitations cited in this study.

Risk of respiratory cancer around a sewage plant in Prato, Italy

In this study, the authors evaluated the risk of respiratory cancer related to environmental pollutants among a population that resided near a sewage plant in Prato, Italy. Subjects included lung cancer deaths (1987-1996) and incident cases of lung and laryngeal cancers (1987-1994) among residents of Prato. The authors used the mortality or incidence rates for the entire population of Prato (by gender and by 5-yr age group) to calculate the expected cases in each census unit. Data were analyzed and adjusted for an index of social deprivation (Stone test). Among males, the excess risk of lung cancer mortality decreased as distance from the plant increased for 2 time periods (1987-1996 [p = .008] and 1990-1996 [p = .030]) and for lung cancer incidence during 1987-1994 (p = .011). Similar results were obtained when sewage plant workers were excluded from the analysis. A similar, but not statistically significant, trend was observed among female incident lung cancer cases, as well as among male incident laryngeal cancer cases. Despite methodological limitations common to geographic studies, the results were consistent with those previously published on mortality excesses for lung cancer among plant workers under study. The role of environmental pollutants as a risk for respiratory cancer must be further clarified with additional epidemiological studies and an environmental monitoring program.

Hepatitis A in workers exposed to sewage: a systematic review

OBJECTIVES

To assess whether the scientific literature supports the hypothesis that workers exposed to sewage are at higher risk of hepatitis A (HA).

METHODS

All original papers reporting epidemiological studies published in English, French, or German which reported on the risk of HA infection in workers exposed to sewage were eligible. They were identified by several methods and each original paper was assessed independently with a checklist by two people. Studies were classified according to the strength of their design. Non-eligible studies were also examined to assess the impact of publication bias. If the risk estimates diverged widely, causes for heterogeneity were assessed. A distinction was made between seroprevalence studies based on subclinical HA (defined only by the presence of anti-HA antibodies) and clinical HA.

RESULTS

17 eligible studies were identified. No indication of an increased risk of clinical HA could be found. For seroprevalence the studies with the strongest design suggested a slightly increased risk of subclinical HA with an odds ratio (OR) <2.5. Heterogeneity was considerable and precluded a meta-analysis. Considering non-eligible studies would still decrease the OR.

CONCLUSIONS

The systematic review does not confirm an increased risk of clinical HA in workers exposed to sewage. An increased risk of subclinical HA cannot be excluded but the association between seropositivity and exposure to sewage was not strong and became still weaker if publication bias was taken into account.

Evaluation of occupational transmission of hepatitis A virus among wastewater workers

To provide information concerning potential occupational transmission of hepatitis A virus (HAV) among wastewater workers in a large city in the United States, a cross-sectional survey was performed using a saliva test to detect antibodies to HAV (anti-HAV). Fifty-nine (20%) of 302 participants tested positive for anti-HAV. After controlling for the confounding effects of age and race, wastewater work was not significantly associated with an increase in the prevalence of anti-HAV (prevalence ratio = 1.3; 95% confidence interval 0.7 to 2.4). Additionally, when examining only the wastewater workers, no statistically significant occupational risk factors for anti-HAV were identified. The results of this survey are consistent with the position of the Centers for Disease Control and Prevention regarding groups at risk for HAV infection.

Airway function and respiratory symptoms in sanitation workers

The prevalence of acute and chronic respiratory symptoms and lung-function changes was studied in a group of 81 municipal sanitation workers. In addition, the prevalence of chronic respiratory symptoms and lung function was studied in 65 control workers. There were significantly higher prevalences of all chronic respiratory symptoms among the sanitation workers than among the control workers. Sanitation workers (smokers and nonsmokers) 40 years of age or older had higher prevalences of all chronic respiratory symptoms than younger workers. In addition, sanitation workers (both smokers and nonsmokers) employed for 10 years or longer had significantly higher prevalences of chronic respiratory symptoms than control workers. There was also a high prevalence of acute symptoms, which developed among the sanitation workers during work shifts. Of these symptoms, prevalences were highest for dryness of the nose and throat, followed by throat and eye irritation. Lung-function testing demonstrated significantly diminished forced vital capacity (FVC) and 1-second forced expiratory volume (FEV1) for the 81 sanitation workers compared with control values. These differences only become significant after 10 or more years of employment in the sanitation industry and were not entirely explained by smoking. These differences were smaller and not statistically significant for maximum flow rates at 50% and the last 25% of the vital capacity. Our data suggest that sanitation worker--particularly those with long periods of work exposure--may develop acute and/or chronic respiratory symptoms accompanied by decreases in lung function (primarily FVC and FEV1).

Mortality and incidence of cancer among sewage workers: a retrospective cohort study

To study the incidence of and mortality from cancer among sewage workers a retrospective analysis was performed on a cohort of 656 men employed for at least one year at any one of 17 Swedish sewage plants during the years 1965-86. Assessment of exposure was done by classification of work tasks. Lower than expected total mortality (standardised mortality ratio (SMR) = 0.75, 95% confidence interval (95% CI) 0.58-0.97) and cardiovascular mortality (SMR = 0.61, 95% CI 0.39-0.91) was found. This was interpreted as a result of the healthy worker effect. For all cancers combined the mortality (SMR = 1.08, 95% CI 0.68-1.67) and morbidity (SMR = 1.02, 95% CI 0.72-1.38) were comparable with those of the general population. There were increased incidences for brain tumours (SMR = 2.19, 95% CI 0.45-6.39), gastric cancers (SMR = 2.73, 95% CI, 1.00-5.94), and renal cancers (SMR = 1.68, 95% CI = 0.35-4.90). For lung cancer the risk was reduced (SMR = 0.70, 95% CI 0.15-2.05). Allowance for a latency period of 10 years from the start of exposure did not change the pattern. Logistic modelling was used to search for exposure-response relations. In a logistic model with the confounder age forced in, renal cancer had a significant positive relation with a weighted sum of employment times, where the weights describe the classification of exposure. No exposure-response relations were found for brain tumors or gastric cancers. The increased risks are based on small numbers of cases. A future follow up will add more conclusive power to the study. Specific exposures need to be identified to allow for a better dose-response analysis.

Respiratory function in sewage workers

Respiratory symptoms and ventilatory capacity were studied in a group of 74 sewage workers employed in cleaning the city sewage system of Zagreb, Croatia. Workers were studied by their work stations: closed channels (N = 26), drainage (N = 31), and other sewage workers (N = 17). The prevalence of chronic respiratory symptoms was higher in closed channel and drainage workers than in controls, particularly for chronic cough (range: 41.9-46.2% vs. 14.3%), chronic phlegm (range: 38.7-46.2% vs. 14.3%), chronic bronchitis (range: 32.3-42.3% vs. 8.6%), and chest tightness (range: 29.0-53.8% vs. 0%). In the first two groups of sewage workers there was a high prevalence of acute symptoms which developed during the work shift, being particularly pronounced for eye irritation (range: 16.1-26.9%), dyspnea (16.1-23.1%), dizziness (range: 6.5-23.1%), throat burning (9.7-19.2%), and skin irritation (range: 22.6-26.9%). Baseline ventilatory capacity was significantly decreased compared to predicted values in sewage workers; in particular, values for FEF50 and FEF25 were reduced, suggesting obstructive changes in smaller airways. Our data indicate that sewage workers experience frequent acute and chronic respiratory symptoms and exhibit objective evidence of respiratory dysfunction.

Retrospective cohort mortality study of cancer among sewage plant workers

There is little known about the incidence of cancer among sewage workers. In this paper we examine findings from a retrospective cohort study of 487 white male sewer authority workers employed between January 1950 and October 1979. Vital status was ascertained for 93% of the cohort yielding a total of 6,886 person years. Total mortality from all causes was comparable to that of the general white male U.S. population (Standardized Mortality Ratio [SMR] = 0.91, 95% Confidence Interval [CI] = 0.77-1.07). The cohort was subdivided into those not exposed, and sewer workers who were exposed to sewage effluent, sludge, or wastewater containing chemicals including potential carcinogens. Among the nonexposed group, mortality from all causes was significantly low (SMR = 0.55, 95% CI = 0.33-0.88). Among the exposed sewer workers, mortality from all causes was not significantly different from that of the general white male U.S. population (SMR = 1.00, 95% CI = 0.84-1.19). Mortality from all cancers among exposed sewer workers was slightly higher than that of the general population (SMR = 1.19, 95% CI = 0.79-1.7). Statistically significant elevated mortality ratios were seen for cancer of the larynx (SMR = 7.93, 95% CI = 1.59-23.96), and cancer of the liver (SMR = 5.4, 95% CI = 1.10-16.05). Careful study of the medical and occupational histories of these cases suggested that larynx cancer was possibly work-related, while liver cancer was not. A group estimated to be the highest exposed, composed predominantly of operatives, had a higher directly adjusted death rate from all malignant neoplasms combined compared to all other workers (rate ratio = 1.64). These findings of increased risk of cancer among exposed sewage workers, especially operators, are based on small number of cases and should be interpreted with caution. Studies of larger cohorts are needed to clarify the risk of these cancers among sewage workers.

Neurotoxic effects of solvent exposure on sewage treatment workers

Nineteen Sewage Treatment Workers (STWs) exposed to industrial sewage that contained benzene, toluene, and other organic solvents at a primary sewage treatment plant in New York City (Plant A) were examined for evidence of solvent toxicity. Fourteen (74%) complained of central nervous system (CNS) symptoms consistent with solvent exposure, including lightheadedness, fatigue, increased sleep requirement, and headache. The majority of these symptoms resolved with transfer from the plant. Men working less than 1 yr at Plant A were more likely to complain of two or more CNS symptoms than men who were working there longer than 1 yr (p = .055). Objective abnormalities in neurobehavioral testing were found in all 4 men working longer than 9 yr at this plant, but in only 5 of 15 employed there for a shorter period (p = .03). These results are consistent with the known effects of solvent exposure. Occupational health personnel must be aware that STWs can be exposed to solvents and other industrial wastes.