Report No FR/W0002



June 1994


As a requirement of the Control of Substances Hazardous to Health regulations (COSHH), employers have to assess all exposures to hazardous substances in the workplace, including microorganisms, and implement appropriate control measures. Recent amendments have been proposed for COSHH in order to implement the EC Directive 'The Protection of Workers from Risks Related to Biological Agents at Work'. Although working at wastewater treatment works does not involve a deliberate intention to work with biological agents, there may be work related incidental exposure.

This report, for the Foundation for Water Research, assesses the hazards to health from working at wastewater treatment works. Firstly, the literature was reviewed to determine the current level of knowledge concerning health hazards at treatment works. Secondly, measurements of microorganisms were made at selected treatment works to determine what workers are potentially exposed to in the workplace. This information was used to make recommendations about the application of the COSHH Regulations.

There is a perceived risk to health from working at wastewater treatment works. Many studies have shown that wastewater treatment processes generate aerosols containing microorganisms, including pathogens. A number of different species of organism have been recovered from the air at wastewater treatment works, the large majority of which can be classed as ACDP (Advisory Committee on Dangerous Pathogens) hazard group 2; they may cause human disease. A number of investigators have attempted to assess the health risks posed by wastewater treatment works through the collection of epidemiological data. The main conclusion of this type of study has been that, working at or living near a wastewater treatment works does not present a hazard to health via exposure to microbial aerosols, However, many researchers stress the fact that wastewater does contain pathogenic organisms and the potential for illness is, therefore, present.

Aerobiological sampling carried out during this study has shown that microbial aerosols are emitted by processes at treatment works. None of the organisms identified within the samples taken were classed as higher than hazard group 2. Generally, the results obtained did not differ significantly from those seen in the literature. A recent report concerned with hazards at enclosed wastewater treatment works has suggested that there is potential for enhanced operator exposure, to microbial aerosols, within the confined conditions of such works. It may be prudent, therefore, to minimise or even prevent release of aerosols into the workplace environment in accordance with guidelines for other biotechnological processes. The requirement for hazard group 2 organisms, is that their release to the environment is minimised. At a minimum, in enclosed wastewater treatment works, measures should be taken to reduce levels of microorganisms, such that they are no greater than at a similar open works. At an open wastewater treatment works, the concentration of microorganisms released into the open air will be reduced by dispersion and this will effectively minimise operator exposure.

On examination of the existing COSHH regulations and the proposed amendments, it seems likely that little additional work will be required by the wastewater industry in order to comply fully with the forthcoming changes. Factors, relating specifically to biological agents, which will require careful consideration are as follows: the biological agents that may be present, which hazard group they belong to, what form they are in, what diseases they may cause, how and where they are present and how they may be transmitted, the likelihood of exposure and consequent disease, practicability of using a less hazardous agent, control measures that may be required, the need for monitoring and the need for health surveillance.

Copies of the report are available from FWR, price 30.00, less 20% to FWR Members.