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No. 182: Sanitary survey report 13: Limfjorden (eastern outlets)

Feld L, Larsen MM, Jakobsen HH, Göke C, Hendriksen NB, Rømer JK, Mohn C & Jensen AN. 2020. Sanitary survey rapport 13: Limfjorden (østlige udløb). Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 98 s. - Teknisk rapport nr. 182. https://dce2.au.dk/pub/TR182.pdf


Regulation (EC) No 854/2004 of the European Parliament and the Council of April 29th, 2004 lays down specific rules for the organisation of official controls on products of animal origin intended for human consumption. Classification of production areas for live bivalve molluscs etc.[1] and the associated sampling plan is required to be based on so-called ‘sanitary surveys’. A sanitary survey is an assessment of the interactions between potential sources of microbial pollution, climate conditions and oceanography in the area. The EU Commission guidance for doing a sanitary survey has formed the basis for this report. However, in certain cases, the Danish practice for microbiological sampling frequency and the previous classification on the basis of this is used. The Danish practice is described in ‘muslingebekendtgørelsen’, which is summarized in Appendix 11.

The report covers three production areas P40-P42 situated in the eastern part of Limfjorden from the bridge of Aggersund by Løgstør to the mouth of Limfjorden in Kattegat at Hals and Egense. In the area Limfjorden (eastern strait), no permissions for mussels farming are registered, and commercial fishing does not take place. However, a local mussel farming project at Lindholm Strandpark has been established for self-sufficiency production. The characteristics of the report area are not supporting good growth of mussels since it generally consists of low-levelled water areas with sandy seabed. In addition, there is a general ban against mussel fishing in P40. Thus, no landings of mussels have been registered in Limfjorden (eastern strait) since 2011, where the Fishery Agency initiated data collection.

The report is supported by publicly available data from monitoring of microbiological contamination in the area Limfjorden (eastern strait), which involves data from the Danish mussel surveillance of the concentrations of E. coli determined in samples of mussels collected within the production area. The report points to the most precautionary fixed sampling points for future monitoring. For the use of this report, data and information have been collected through web pages from, e.g. municipalities and Statistics Denmark (Danmarks Statistik). Since these web pages are continuously updated, it cannot be guaranteed that the accessed data will be persistently available.

From the Danish mussel surveillance, a limited set of historical data is available for analyses of E. coli in mussels etc. collected from Limfjorden (eastern strait). During the last 10 years (2010-2019), samples have only been analysed from one production area (P42), while the other two production areas (P40 and P41) are not represented in the sampling data. From the area Limfjorden (eastern strait), only 6 samples have been analysed for E. coli, and no samples have been analysed for Salmonella during the last 10-year period. All samples were collected from the bottom and consisted of blue mussels (Mytilus edulis).

Data from the investigated samples showed a good microbiological hygiene with a low content of E. coli ≤ 230 MPN E. coli/100 g in all samples. All samples were taken in 2017, i.e. within the last 3-year period, however, no samples have been analysed after 2017.

Altogether, the sanitary survey for Limfjorden (eastern strait) shows that there is a lack of analyses reporting on the microbiological pollution with E. coli in mussels, in order to properly evaluate the general hygiene of the area. Data from analyses of bathing water from classified beaches in the area show that periodical outlets of contamination can occur, which potentially may influence the hygiene in the production areas. However, due to the shortage of data, it is not possible to perform a statistical assessment of the individual production areas, years or seasons, and as such, it is difficult to conclude on the impact of potential sources of contamination.

Summary of the recommended sampling programme

Based on an assessment of sources and transport routes for microbiological contamination (sanitary survey) verified as far as possible against historical microbiological data from Limfjorden (eastern strait), a microbiological monitoring programme is recommended for each of the respective production areas P40-P42. In each of the recommended monitoring programmes, proposals for a sampling location, classification status (preliminary or permanent) and a sampling plan are outlined.

Based on the results from the sanitary survey of the production areas and the general shortage of historical data sets on the number, frequency and E. coli concentration in samples, it is assessed that assignment of a permanent classification is not possible for any of the production areas due to the lack of sampling in the past year (2018) and insufficient numbers of analysed samples (less than 24) within the past three years. If unclassified areas are to be upgraded to permanent classification, the EU guideline requires that the collection of data should include at least 24 samples over the last three years and include data for the latest 12 months.

The report is divided into main chapters that provide a summary of identified microbiological contaminants. Appendices 2-8 serve as the starting point of the main chapters. Appendix 9 is a detailed review of historical microbiological data from mussel monitoring obtained from the Danish Veterinary and Food Administration’s[2] verification projects of the industry’s microbial monitoring. It was decided that a so-called ‘shoreline survey’ is unnecessary because all possible sources of sanitary contamination are described in the sewage plans for the cities in the area, the beach water quality monitoring and in the analyses of the Ministry of Environment and Food under the auspices of the Water Framework Directive.

[1] Include live bivalve molluscs, echinoderms, tunicates and gastropods.


[2] Fødevarestyrelsen.