Feld L, Jakobsen HH, Göke C, Hendriksen NB, Rømer JK & Jensen AN. 2021. Sanitary survey rapport 16. Nissum Bredning. Aarhus Universitet, DCE – Nationalt Center for Miljø og Energi, 72 s. - Teknisk rapport nr. 217. http://dce2.au.dk/pub/TR217.pdf
Regulation (EC) No 854/2004 of the European Parliament and the Council of 29 April 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 and the associated sampling plan must be based on so-called ”sanitary surveys”. A sanitary survey assesses the interactions between potential sources of microbial pollution, climate conditions and oceanography in the area. The EU Commission guidance for conducting a sanitary survey forms the basis for this report. However, in some instances, the Danish practice for microbiological sampling frequency and the previous classification are used. The Danish practice is described in Executive order on mussels etc., called “muslingebekendtgørelsen” (BEK no. 1793 of 02/12/2020), which is summarised in Appendix 7.
The report covers the Danish area Nissum Bredning, which includes seven production areas (P1, P2, P3, P4, P10, P29 and P216) that are located in Nissum Bredning and bordered by Oddesund to the east and Thyborøn channel, which opens up to the North Sea, to the west.
The report is a revision of the previous report for Nissum Bredning (Larsen m.fl., 2017). Experience has shown a difference in the significance of the topics covered in the individual appendices for potential microbiological contamination of the production areas. In addition, for some of the topics, no significant changes were expected to have occurred within the previous 56-year period. Therefore, it was decided that no new data should be collected for the appendices covering these topics. Instead, the main report refers to the corresponding appendix in the previous report (Larsen m.fl., 2017).
In all seven production areas in Nissum Bredning, small populations of blue mussels (Mytilus edulis) were present, and fishing of blue mussels was negligible, with catches of only a few tonnes in 2014 and 2015 from P1. The primary commercial fishery in the area was directed at European oysters, which were available in large amounts from P1-P4 within the latest period from 2012-2020. The catches in the individual production areas varied largely between years. In addition, catches of other mussels, including cockles and small amounts of Pacific oysters, were also registered. Starfish was also caught in considerable amounts. Two permissions for mussels farming were given within Nissum Bredning; however, no regular production has been carried out.
The report was supported by publicly available data from the monitoring of microbiological contamination in Nissum Bredning. The concentrations of E. coli and Salmonella were determined in mussel samples taken at different sampling points within each production area. The report identifies the most precautionary fixed sampling points for future monitoring. Part of the data used in this report was collected from web pages belonging to, for instance, municipalities and Statistics Denmark (Danmarks Statistik). 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 of E. coli in mussels etc., collected from the production areas within Nissum Bredning throughout the last ten years (2011-2020). During this period, 374 samples were analysed for E. coli from the whole area. From the latest 3-year period (2018-2020), 21, 22 and 10 samples were collected from each of the areas P1, P2 and P216, respectively. For the remaining areas, no samples were collected during this period. Accordingly, an inadequate number of samples (< 24) were collected from all areas, and thus no areas qualified to obtain a classification.
The samples analysed were exclusively collected from the bottom and consisted of oysters. Half of the samples were not determined to species level, and the remaining belonged to European oysters (Ostrea edulis) and Pacific oysters (Crassostrea gigas). Additionally, 86 samples were analysed for Salmonella (during 2011-2017), and all of these samples were negative.
The overall data from the area Nissum Bredning revealed good microbiological hygiene in the samples investigated for E. coli with 98% (corresponding to 366 samples) from the latest 10-year period having low levels ≤ 230 MPN E. coli/100 g. Out of these, 278 samples (74%) were below the detection limit with < 18 MPN E. coli/ 100 g. In eight samples (2%), collected from P2 (1 sampled in 2017), P3 (1 sample in 2011) and P10 (6 samples in 2016), respectively, E. coli were detected in concentrations of 230 < MPN ≤ 4600 E. coli /100 g.
In summary, the sanitary survey of Nissum Bredning showed a generally good microbiological hygiene with low historic levels of microbial contamination in the analysed samples from most of the production areas. However, only a limited set of microbiological data exists from the latest 3-year period and for all areas, this was insufficient to obtain a classification. No statistical difference (P<0.05) was observed for the proportion of E. coli positive samples between the production areas; however, data indicate a higher proportion of samples with E. coli in higher concentrations 230 ≤ X ≤ 4600 MPN/100 g in P10 (15%) compared to the other areas (0-2%). Generally, there a limited number of samples was collected during summer. However, there seemed to be a higher number of positive samples in autumn (61%) and winter (39%) than in spring (4%). Statistical analysis could not be made because of the limited number of samples.
Based on an assessment of sources and transport routes for microbiological contamination (sanitary survey), a microbiological monitoring programme was recommended for each of the production areas P1-P4, P10, P29 and P216. In each of the recommended monitoring programmes, proposals for a sampling location, classification status (preliminary or permanent) and a sampling plan were outlined.
Based on the results from the sanitary survey of the production areas, supported by the historical data sets on the number, frequency and E. coli concentration, it was assessed that none of the production areas were considered suitable for permanent classification. This was due to an insufficient number of analysed samples (less than 24) within the past three years. Except for a few samples collected in P1 and P2, sampling was not carried out in the past year (2020). Suppose unclassified areas are to be upgraded to permanent classification; in that case, the EU guideline requires that the collected data should include at least 12 samples for the latest six months or 24 samples over the last three years. This implies a future sampling frequency of at least eight samples per year over three years.
The report is divided into main chapters that provide a summary of identified microbiological contaminants. Appendices 1-4 serve as a starting point of the main chapters. In addition, relevant data representing characteristics of the areas, as described in the previous sanitary survey for Nissum Bredning, have been included. Appendix 5 is a detailed review of all historical microbiological data from mussel monitoring consisting of the fishery’s own-check and the Danish Veterinary and Food Administration’s[1] 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 were 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.
