B05002: Evaluation of methods for the assessment of sewage discharge consent applications with respect to shellfisheries
Tuesday 11 May 2004
This research project intends to improve the technical assessment of applications for sewage discharge.
Study Duration: October 1999 to July 2001
Contractor: Centre for Environment, Fisheries and Aquaculture Sciences (CEFAS)
Background
Filter-feeding bivalve molluscs can concentrate contaminants from the water column and these contaminants may include human pathogens, such as Norovirus (NV) and hepatitis A virus, occurring as a result of contamination with human faeces. Other pathogens, such as salmonella and campylobacter, may arise from human or animal sources. Determination of the extent of faecal contamination is usually undertaken by estimating the concentration of faecal coliforms and/or E. coli. Under the Shellfish Hygiene Directive (91/492/EEC), commercial bivalve mollusc harvesting areas have to be classified according to the extent of contamination with these indicators and this dictates the level of post-harvesting treatment to which the shellfish have to be subjected.
Shellfish-associated infection in temperate developed countries is predominantly due to viruses such as NV and is thought to derive from continuous and intermittent sewage discharges. Due to the failure of some post-harvesting process methods to completely remove viruses, the most effective means of reducing the extent of contamination with these pathogens is to minimise the contamination at source. This will have commercial benefits for the shellfish industry due to lower processing costs and/or, with improvement to class A, improved marketability.
Research Approach
The approaches used in this project comprised:
- A review of current methods of shellfishery and bathing water directed assessments;
- Determination of the impact of environmental factors on the microbiological contamination of shellfisheries;
- An investigation into the use of simple hydrodynamic models in the assessment process;
- Quantitative methods for prediction of the effects of sewage discharge schemes with respect to the microbiological contamination of shellfisheries;
- Recommendation of a revised protocol for the technical assessment of consent applications, incorporating proposals for inclusion of novel elements identified by the project.
Results and findings
The review of the current technical assessment procedure identified a number of areas where the supply of additional information would improve the basis of the assessments. The environmental factors shown to principally affect the concentration of E. coli in shellfish were season, tidal cycle and rainfall. The effect of these factors differed both between geographically separate production areas and between individual monitoring points within single production areas. A simple hydrodynamic model could be used to assist in the assessment of the impact of sewage discharges, and proposed schemes, on the microbiological contamination of shellfisheries in cases where modelling output was not available. Semi-quantitative and quantitative predictions of the concentration of E. coli in shellfish gave reasonable correlation with observed concentrations in a study of a small number of historical sewage improvement schemes. However, the models need further refinement and calibration with locally derived data.
Recommendations have been made to organisations involved and have been incorporated into a revised standard operating procedure for the technical assessment of sewage discharge consent applications.
Dissemination information
Final report is available from the FSA Library and Information centre. To obtain a copy, please contact the Enquiry Desk, Dr Elsie Widdowson Library and Information Services, Food Standards Agency (Tel: +44 (0) 20 7276 8181/8182 or by e-mail to: library&info@foodstandards.gsi.gov.uk).