SARF013/SAMS Report No. 256 RISK FACTORS IN SHELLFISH HARVESTING AREAS Final Project Report Prepared for Scottish Aquaculture Research Forum Shona Magill1, Kenny Black1, David Kay2, Carl Stapleton2, Simon Kershaw3, David Lees3, James Lowther3, Carol Francis4 John Watkins4 and Cheryl Davies4 . 1 Scottish Association 2 Centre for Research 3 CEFAS 4CREH Analytical Ltd for Marine Science into Environment The Nothe Hoyland House Dunstaffnage Marine and Health Barrack Road 50 Back Lane Laboratory University of Wales Weymouth Horsforth Dunbeg Lampeter DT4 8UB Leeds Oban, Argyll Ceredigion U.K. LS18 4RS PA37 1PA SA48 7ED U.K. U.K. U.K. ii Recommendations Context This study assessed the risk factors associated with cultured shellfish. The study was carried out on Loch Etive and offers a number of lessons for other sea lochs on the west coast of Scotland. Results from the three elements of this study indicate that E. coli non-compliance issues within the Loch Etive shellfish production areas appear primarily to be summer high flow event driven. Therefore, determining the human (sewage)/ animal (diffuse) mix of pollution impacting on shellfish harvesting areas under high flow events is crucial to the design of remediation measures to prevent impairment of ‘protected areas’. Although there is significant human settlement around the sealoch, the ‘sewage’ contribution to the bacterial compliance parameter loadings during periods of peak input to Loch Etive were tiny when compared to the diffuse catchment flux derived from livestock grazing areas. Some small agricultural catchments were found to generate disproportionately high loadings to the loch which offers scope for clearly targeted remediation effort. 1. A programme of sanitary surveys is currently being carried out across Scottish shellfish growing areas. Such surveys provide an essential detailed assessment of potential pollution sources impacting harvesting areas. However, in rural environments such as Loch Etive, sanitary surveys of shellfish harvesting areas which quantify only anthropogenic microbial hazards will provide little useful information on the reasons for non-compliance with faecal indicator compliance parameters. Thus, for waters at risk of non-compliance a quantitative microbial source apportionment exercise is an essential foundation for any sanitary survey exercise. 2. Attention solely focused on reduction of point source discharges to any rural loch system would be unlikely to produce significant reductions in total bacterial loading. Thus, design of any remediation strategy to reduce sewage fluxes to impaired waters should be undertaken only after a source apportionment study as suggested above is undertaken. 3. Quantification of the diffuse faecal indicator loading requires measured or, if this is not feasible, modelled high flow flux information from all catchment stream inputs and any sewage infrastructure point source discharges. Source apportionment requires targeted high flow sampling (i.e. responsive aseptic sampling capacity on a 24 hour basis) and this should be built in to any sampling programme to inform management decisions designed to effect improvement. 4. Where reduction of pathogen presence (e.g. norovirus) in shellfish flesh is the principal management objective: i.e. when the harvesting is compliant with the coliform parameter but still exhibits virus–positive periods, then additional evaluation of specific anthropogenic point source discharges of sewage would be prudent. 5. Historical routine stream monitoring data (if available) will be biased to ‘low flow’ conditions and use of such data to estimate flux from catchment systems will produce erroneous and dangerously optimistic conclusions concerning the total pollutant flux to adjacent harvesting waters. Thus, historical monitoring data should not be used in isolation to estimate pollutant loadings unless it iii contains information on high flow water quality or is augmented by additional targeted sampling. 6. The sanitary survey results determine the selection of the routine monitoring points. The process requires full cooperation from all relevant stakeholders and relies on the availability of accurate and comprehensive data on both anthropogenic point sources and diffuse catchment sources. Information on all domestic sources (including raw sources, private and public sewage systems) should be centralised and readily available. In addition, access to more detailed livestock census data and management information at the catchment, or even individual farm, level would facilitate a greater evaluation of diffuse sources. 7. Regular monitoring programmes may improve characterisation of E. coli contamination patterns. However, full characterisation following high flow events may only be achieved through higher resolution sampling. High intensity sampling events should be included in the microbiological assessment phase of the sanitary survey in order to a) aid selection of routine monitoring points and b) assess the impact of high flow events on shellfish production areas (particularly new designations and areas at risk from non compliance). 8. The level of norovirus detected in this study was lower than previously seen in other UK studies. The actual risk presented to humans consuming norovirus contaminated shellfish, is currently unknown. Research aimed at quantifying the relationship between norovirus levels in shellfish and the associated health risk is vital in order to truly evaluate any potential risks. Further, standards and guidelines are required both for regulators and industry to assess the suitability of areas for shellfish production. CEFAS is currently leading a working group aimed at method development for accreditation by the European Committee for Standardisation (CEN) for viruses in food. Development of standards is targeted for 2012. 9. E. coli and FRNA+ bacteriophage were found to be poor indicators of norovirus in Loch Etive shellfish. This is likely to be the case in other large catchments where the influence from human sewage is small. E. coli may act as a better norovirus indicator in shellfish from more urban/human impacted catchments. Thus, neither E. coli nor FRNA+ bacteriophage should be considered as reliable quantitative risk indicators of norovirus contamination in shellfish on the west coast of Scotland. However, research to clarify the potential of these indicators in areas thought to be under greater influence from domestic sewage is required. 10. Further to source apportionment assessment, further studies may be required to establish connectivity between key sources, the receiving waters and harvested shellfish. This may include tracer studies or surface hydrodynamic studies. The present study did not investigate potential ‘connectivity’ between the present treated sewage discharge point in Dunstaffnage Bay (or the CSO in Connel) and the harvesting areas in the outer basin and/or the flux of faecal; indicators travelling westward from the inner basin. We would recommend that both investigations are completed to (i) clearly establish the risk of human virus contamination from the sewage infrastructure and (ii) discount the possibility of a major, but unmeasured, flux of faecal pollution from the upper basin. Potential protocols for both investigations have been discussed by the project Steering Group. iv Executive Summary Sanitary survey 1. Shellfish cultivation has seen a substantial increase in recent decades, and is an important industry for coastal rural communities. Molluscan shellfish are efficient filter feeders and suitably sized particles may become concentrated at 100 times the background levels. Suspended particles in the water column can contain faecal bacteria (such as E. coli) and viral pathogens (such as the enteric norovirus). Consumption shellfish containing harmful microorganisms may pose a significant health risk. The objectives of this study were to identify key pollution sources and conditions contributing to viral and bacterial contamination of cultured shellfish. The project consisted of three key elements – a sanitary survey; 12 month monitoring programme; a source apportionment study of faecal indicator bacteria. 2. The study site, Loch Etive, is a large sealoch on the west coast of Scotland and is divided into two main basins, upper and lower. The loch has a large catchment area (approximately 1350 km2) with a number of freshwater inputs to the system. The immediate catchment area of the study has a low human population density (approximately 2500 dwelling on the immediate shoreline) with a further 1000 (approximately) within 4 km of the mouth of the loch. In common with many sealoch coastlines of the west coast of Scotland, the catchment consists of a number of small villages and many rural dwellings. 3. Approximately 53 % of the immediate population is served by public network sewage facilities. Accurate detailed information could not be gathered on all private domestic sewage systems in the catchment but it is estimated that a large number of dwellings are served by septic tank systems. However, in a number of areas shoreline dwellings discharge raw sewage into the loch, both outside and within the Shellfish Growing Waters. 4. One Waste Water Treatment Works (secondary treatment) facility operates within the village of Taynuilt, serving around 60 % (approximately 700) of the local population in that area. Three public network septic systems operate within the area. The two largest systems discharge to marine outfalls outwith