Correlation between the occurrence of Dinophysis sp. blooms and Okadaic acid presence in mussels farmed in marine environment of north-eastern Italy: a preliminary study.
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1
Istituto Zooprofilattico Sperimentale delle Venezie, Italy
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2
Agenzia Regionale per la Protezione dell'Ambiente del Friuli Venezia Giulia, Italy
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3
Regione Friuli Venezia Giulia, Servizio sanità pubblica veterinaria, Italy
Introduction
Italy is the third European producer of marine molluscs and Friuli Venezia Giulia Region (FVG) is one of the main shellfish production area located in north-eastern part of the country. The northern Adriatic Sea seems to be particularly subjected to algal blooms, as the detection of marine toxins in farmed mussels represents a quite frequent event. While hydrophilic toxins as Domoic acid (ASP) and saxitoxins (PSP) have never been detected so far in this area, the phenomenon of lipophilic toxins (DSP) accumulation in shellfish, primarily Okadaic acid (OA), has become more and more frequent in the recent years. The presence of OA and its derivatives in shellfish represents a public health concern, since the consumption of contaminated molluscs can cause a severe gastrointestinal illness known as Diarrhetic shellfish poisoning. To protect the consumers, European Union established the mandatory weekly monitoring of shellfish production areas [1], in order to ensure the compliance with the maximum levels for toxins in bivalve molluscs before being placed on the market [2]. The reference analytical method for the detection of lipophilic toxins is the EU-RL LC-MS/MS [3], which replaced the previously used Mouse Bioassay.
Despite the EU legislation on food hygiene sets the possibility to use the phytoplankton as an indicator for the management of shellfish production areas, to date in North Adriatic Regions the investigation of possible correlation between the occurrence of toxin producing algae in water and toxicity levels in shellfish flesh, which could allow an early warning system, has been difficult mainly due to the absence of a chemical test enabling to dose the toxins in shellfish, adopted only by the mid-2012 for DSP.
After a serious intoxication episode occurred in 2011, involving people having eaten OA contaminated mussels harvested in FVG, the Regional Veterinary Authorities, with the collaboration of shellfish producers, have put in place an effective monitoring program. Since 2012 shellfish and water are systematically collected in each production area on a weekly basis and respectively tested for the presence of phytoplankton and marine toxins. The competent authorities implement the official monitoring programme the first week, while in the following self-control testing is carried out by shellfish farmers.
The aim of this work is to present the results of the official controls performed in the context of the mussels production areas monitoring plan of the FVG Region during the timeframe between the mid-2012 and the end of 2015 and to make a preliminary assessment of the possible correlation between the presence of Dinophysis sp. in water and OA in mussels.
Materials and methods
During the considered period, 573 samples of water and shellfish collected in the mussels production areas located in the Gulf of Trieste by the staff of the Regional Agency for the environment protection of FVG (ARPA FVG), were considered for statistical analysis. In the 2012-2014 timeframe water sampling was performed with the net, while starting from 2015 a hose sampler was used, allowing to obtain precise quantitative information representative of the entire water column, instead of the previously semiquantitative data obtained through the use of the net. ARPA FVG performed the phytoplankton determination using the Utermohl technique according to UNI EN 15204:2006. The determination of lipophilic toxins in mussels was performed by the Chemical department of Istituto Zooprofilattico Sperimentale delle Venezie, through a LC-MS/MS screening/confirmatory accredited method according to ISO 17025:2005. The time-series of Dinophysis sp. cell count and OA concentrations in mussels were plotted in figures. The correlation between Dinophysis cell numbers in water and OA and derivatives levels in shellfish measured at the same time was investigated using the nonparametric Spearman’s correlation test, being the data not normally distributed. Furthermore, since the water sampling methods have changed throughout the considered period, we assessed the possible association between the Dinophysis cells presence in water and the detection of toxins at levels near or above the EU legislation limits in shellfish by means the OR calculation. The analysis were carried out both on the overall data and stratifying them by single year and shellfish production area.
Results and discussion
Values of OA above the EU legislation limits where detected in almost 5% of the shellfish samples and they resulted more frequent during the period of late summer and autumn. After the examination of the available data, 7 mussels production areas were selected for statistical analysis, as the frequency of sampling for 3 areas was considered not sufficient.
In general weak but significant correlations were detected between Dinophysis cell numbers and the levels of OA (rho=0.2082; p=0.0000 for the overall data). Considering each year, the maximum correlation were detected for 2013 (rho=0.5961; p=0.0000) and 2015 (rho=0.4543; p=0.0000). Analysing the data related to each single shellfish production area, a positive correlation was detected for 4 zones among the 7 considered.
The OR indicates a significant association between the finding of Dinophysis in water and the detection of OA level above the EU legislation limits in mussels; the presence of Dinophysis in water entails an odds of having non-compliant mussel 3 times higher than when dinoflagellates are not detected (OR=3.70; p=0.0011).
The correlation between phytoplankton in water and toxins in shellfish, although probable, is quite controversial and difficult to detect, especially for OA [4]. Even if looking at the produced plots the increase of Dinophysis cells seems to correspond to higher level of OA in mussels, the statistical analysis indicated a moderate correlation. Anyway, in this preliminary evaluation only results of official controls were considered, thus having a fortnightly generated time series that should be cautiously interpreted [5] .
Although this exploratory data analysis demonstrated some limits, it represents a first important step towards further investigation with the aim to better understand the dynamics of dinoflagellates blooms and toxins accumulation in shellfish and to put in place an early warning system based on the phytoplankton monitoring, which could contribute to save resources in terms of time and costs related to the control of shellfish production areas, ensuring at the same time the consumer health.
References
[1] EU Council. (2004). Regulation (EC) No 854/2004 of the European parliament and of the council of 29th April 2004 laying down specific rules for the organisation of official controls on products of animal origin intended for human consumption. Official Journal of the European Union, Series, L 226, 83e127, 25.06.04.
[2] EU Council. (2004). Regulation (EC) No 853/2004 of the European parliament and of the council of 29 April 2004 laying down specific hygiene rules for food of animal origin. Official Journal of the European Communities, Series L, 139, 55e205. http://europa.eu.int/eurlex/pri/de/oj/dat/2004/l_139/l_13920040430de00550205.pdf, 30.4.04.
[3] EU Commission. (2011) Commission Regulation (Eu) No 15/2011 of 10 January 2011 amending Regulation (EC) No 2074/2005 as regards recognised testing methods for detecting marine biotoxins in live bivalve molluscs. Official Journal of the European Union. Series L. 6, 3
[4] Alves-de-Souza, C., Varela, D., Contreras, C., et al. Seasonal variability of Dinophysis spp. and Protoceratium reticulatum associated to lipophilic shellfish toxins in a strongly stratified Chilean fjord. Deep Res Part II Top Stud Oceanogr. 2014;101:152-162. doi:10.1016/j.dsr2.2013.01.014.
[5] Bresnan, E., Fryer, R., Hart, M., & Percy, L. (2005). Correlation between algal presence in water and toxin presence in shellfish. Fisheries Research Services Contract Report, 4, 05-27.
Keywords:
DSP,
Okadaic Acid,
Dinophysis,
Correlation,
Shellfish
Conference:
AquaEpi I - 2016, Oslo, Norway, 20 Sep - 22 Sep, 2016.
Presentation Type:
Oral
Topic:
Aquatic Animal Epidemiology
Citation:
Bille
L,
Toson
M,
Bordin
P,
Venuti
M,
Casarotto
C,
Benetti
C,
Lega
F,
Cocchi
M,
Palei
M,
Arcangeli
G and
Dalla Pozza
M
(2016). Correlation between the occurrence of Dinophysis sp. blooms and Okadaic acid presence in mussels farmed in marine environment of north-eastern Italy: a preliminary study..
Front. Vet. Sci.
Conference Abstract:
AquaEpi I - 2016.
doi: 10.3389/conf.FVETS.2016.02.00061
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Received:
05 Sep 2016;
Published Online:
14 Sep 2016.
*
Correspondence:
DVM. Laura Bille, Istituto Zooprofilattico Sperimentale delle Venezie, Legnaro (PD), Italy, lbille@izsvenezie.it