Report No FR0158

S C Nixon

Mar 1991



To demonstrate the use of bioassays to locate the source of toxic components in sewage.


Utility discharges are likely to be monitored for Red List substances and control may require tracing the sources and eliminating them. In addition, toxic substances discharged to sewerage systems may have inhibitory effects on the sewage treatment process.


The proposed fieldwork programme was not undertaken due to the contract being postponed by the Foundation for Water Research who required funds for higher priority research. Up until this time effort was concentrated on identifying suitable case-study sites in the North West and Severn Trent Water areas. This work has shown that:

  1. Outfalls discharging into the Mersey estuary offer potential case study sites since the effluent discharged from these outfalls contains different proportions of metal and organic contaminants.

  2. A sewerage system receiving effluent from the carpet manufacturing industry has also been identified as a potential second case-study located near Kidderminster.


Two locations have been identified as potential case study sites. Each has a higher industrial component than that in the Weymouth sewerage system used in the pilot studies of 1989/90 (FR 0084).

The sampling strategy and the bioassays to be used in the work are outlined, and the need for samplers which are safe for use in sewers and confined spaces has been identified. Finally the use of toxicity-based consents in the UK and by the EPA in the United States is discussed.


  1. The proposed work programme at one or both of the case-study sites should be undertaken during the coming year but no provision for funding the work has been made by FWR in their 91/92 Research Programme.

  2. Further work should initially continue to compare the Microtox and oyster larval bioassay, until it is established whether the former is sensitive enough for this particular application.

  3. Composite rather than single point discrete samples should be taken.

  4. Further work is required to establish the temporal as well as the spatial variability of toxic components within sewerage systems.

  5. Standard operating procedures covering aspects such as the storage of samples before testing and the use of particular bioassays will be required once the technique of locating the source of toxic components within sewage is established and fully tested.

Copies of the Report are available from FWR, price 15.00 less 20% to FWR Members