THAMES ESTUARY - ENVIRONMENTAL STATUS WITH RESPECT TO SLUDGE DISPOSAL - FINAL REPORT
Report No FR0074
T ap Rheinallt, S C Nixon, I Codling and J Orr
- To assess the dispersion of sludge after discharge and identify
any areas where sludge material accumulates;
- To determine the effect of sludge disposal on the concentration
of contaminants in the sediments;
- To investigate the diversity and nature of benthic communities in
order to resolve the difference in results obtained by TW and MAFF
from earlier studies, and to assess MAFF's statement (Norton et al
1981), that "current rates of dumping have somewhat exceeded the
dispersive capacity of the area... these have placed the natural
fauna under stress and promoted the growth of pollution indicator
species... suggest that further increases in dumping may lead to
more widespread, significant and readily identifiable effects";
- To assess the effects of sludge disposal on sub-lethal stress in
organisms and disease prevalence in fish populations within the
- To define the area of impact resulting from sludge disposal and
develop a monitoring strategy for the future management of the
Concerns among certain EEC member states and environmental pressure
groups over the effects of sewage sludge disposal to sea were
threatening to curtail or prevent this activity. The cost
implications of this for the UK water industry are considerable. A
case study has been undertaken into the effects of sludge disposal
at the UK's largest discharge site - the Barrow Deep region of the
outer Thames estuary. This study will provide data to enable
decisions over the future of marine disposal of sewage sludge to be
made on a scientific basis.
- The Barrow Deep disposal site is highly dispersive: tracer
studies have shown sludge to be widely dispersed over the northern
part of the estuary within days of release.
- Traditional techniques of impact assessment (such as
physicochemical measurements) have shown only limited effects of
sludge disposal. Sensitive new field and laboratory bioassay
techniques have detected effects which may be useful for the future
monitoring of the site.
- Studies of the prevalence of disease in fish populations from the
Thames estuary have not shown a direct link with sludge disposal.
The effects of sewage sludge disposal at dispersive marine sites are
subtle and difficult to detect and interpret by traditional means.
The sensitivity of new bioassay techniques offers promise for future
monitoring of marine disposal operations. Further work should be
undertaken to develop these tests so that observed bioassay
responses can be related to likely ecosystem effects.
The occurrence of disease in fish populations is affected by many
natural factors, which make the detection of pollution effects
difficult. Further research is required to obtain a clearer
understanding of the ways in which natural and anthropogenic factors
influence fish health.
V RESUME OF CONTENTS
This report describes work undertaken on the Thames estuary sludge
disposal project over a four year period (1985-89). The main
elements of the project were:
- A study of all inputs of contaminants to the tidal Thames.
- Dispersion studies to quantify the distribution of sludge solids.
- Studies of sediment quality with respect to the distribution of
metals and organic contaminants.
- Assessment of sublethal stress and contamination levels in mussels
after set periods of exposure at key sites in the estuary.
- Statistical analysis of ecological survey data collected by WRc,
Thames Water and MAFF.
- A study of the prevalence of external and internal abnormalities
- Laboratory-based bioassay tests on sewage sludge and sediments.
- Monitoring of indigenous species.
Copies of the Report are available from FWR, price £35.00 less 20% to FWR Members