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11.1 Toxic algae

The goal of a monitoring programme is to protect public health by providing information on toxic algae sufficiently early to take management action. The basic elements of monitoring and management programmes are the following (Anderson et al,. 2001):

The complete monitoring and management programme can be the responsibility of one agency, or it can be split between a government agency, industry/fishermen and private consultancy as shown in Figure 11.1.

Figure 11.1
Monitoring and management of toxic algae in Denmark.

The structure of a monitoring programme can be complex and vary according to the local situation, but it should preferably be kept as simple as possible to facilitate fast and uncomplicated flow of information. The operational structure should be well documented and it should be clear to everyone involved who is responsible for different parts of the programme.

Environmental observations, including plankton observations, fish kills and anomalous animal behaviour are most often done by local residents or field officers on patrol. Aircraft Visual Operation, underway ferry monitoring and moored sensors can be applied in remote sensing for bloom detection and tracking.

Sampling of water, plankton and shellfish are most easily done by fishermen and industry or by inspection officers. The frequency of sampling and the number of sampling stations depends on the local situation and historical data. Routine sampling every week may be increased to daily sampling when low levels of toxic phytoplankton are observed.

Analysis of samples must be done at a certified laboratory and only approved and official methods of analysis should be applied. In the EU, a national reference laboratory must be designated to coordinate the analysis of biotoxins (EC, 1993). The national reference laboratories shall collaborate with the Community reference laboratory in Vigo, Spain (Laboratorio de biotoxinos marinos del Area de Sanidad).

Results of analysis should immediately be forwarded to the competent authority for evaluation and possible action. An effective communication system is important for rapid action and possible closure of fisheries. Results can be distributed instantly to the users of the monitoring system by telephone, automatic telephone answering machine, fax, e-mail and Internet. The use of Internet is quite common in many countries, although in some cases restricted access websites or list servers available only to governmental officials are used to control sensitive information.

Information and education of the public should be an integral part of the communication programme. It is recommended that booklets and pamphlets about health problems associated with algal blooms and toxic algae, the diagnosis and treatment of poisonings be prepared and published. Using the Internet is also an obvious way of distributing general information. Local web-pages can be linked to other general web-pages such as http:/

The action or regulatory limits for toxins are shown in section 5.1.5. For cell concentration in the water the action level varies from presence (some Alexandrium spp. and Prorocentrum spp.) to several thousands cells/L of other algae (see Anderson et al., 2001). In the USA a closed status shall be established when the cell count of Gymnodium breve exceeds 5 000/L (NSSP, 1999).

When toxin levels in bivalve or cell numbers of toxic algae exceeds the accepted limit, harvesting areas are closed or some sort of restriction of harvesting is imposed. A toxic bloom may vary, being extensive or sporadic only, thus affecting large areas or only spotty locations. The intensity of a bloom may also vary resulting in significant differences in toxicity levels among bivalves of the same species. The decision to close an area should therefore be affected by the dynamics of the bloom, but it is always advisable to include a safety zone in the closure of an affected area.

Procedures to re-open closed areas include increased sampling from the area and adjacent open areas. Samples should be free of toxin for at least two weeks before re-opening is considered. Species with long retention time should, however, remain on the closure list. An example of an action plan for a shellfish-monitoring program is shown in Figure 11.2.

Figure 11.2 Action plan for shellfish monitoring program in the State of Maine, Atlantic, USA. RL = regulatory level (modified from Anderson et al., 2001).

In the USA as well as in the EU, all containers and all consignments of shellfish must be accompanied by a tag and a health certificate that identifies the production area of origin, the harvester and the date of harvesting. This information must follow the shellfish during transport, processing, distribution until retail sales allowing tracing of the product should a health problem arise.

11.2 Pathogenic bacteria and viruses

Pathogenic bacteria and virus may be present in water from which shellfish are harvested. Of particular concern is the situation, when the environment where shellfish grow is contaminated from sewage. Molluscan shellfish filter and concentrate these pathogens from the surrounding water, and high numbers sufficient to cause disease may be reached. As shellfish are often consumed raw or only partially cooked, these pathogens (bacteria or viruses) will not be eliminated, and the risk of causing disease will be high.

To minimize this risk, Government authorities must have a monitoring programme for classifying the waters where shellfish are harvested. This monitoring programme can be based on examination of samples of shellfish or in part on an assessment of water quality. The programme must then be managed so that harvesting only takes place when the area is free of contamination. This programme also requires that all consignments and containers of shellfish are tagged as described above and that shell-fish harvesters and processes are licensed.

The EU requirements and conditions for productions areas are shown in Table 11.1.

Table 11.1 Classification of harvesting areas for shellfish in the EU. Microbiological examination of shellfish samples (EC, 1991).


Microbiological criteria
(cfu /100 g shellfish)



No restriction. Shellfish acceptable for immediate consumption

<230 E. coli or
<300 faecal coliforms no Salmonella in 25g

5 tubes 3 dilutions MPN-test


Shellfish must be depurated or relayed until they meet category A standard

<4,600 E. coli or
<6,000 faecal coliforms in 90% of samples

5 tubes 3 dilutions MPN-test


Shellfish must be relayed over a long period (>2 months) until they meet category A standard

<60 000 faecal coliforms

5 tubes 3 dilutions MPN-test

Sampling plans for the purpose of monitoring harvesting and production areas must be established by the competent authorities. Sampling must be done at regular intervals or on a case-by-case basis in the event of irregular periods of harvesting. The sampling plan must take account of likely variation in faecal contamination at each production and relaying area.

In the USA either a total coliform or a faecal coliform standard is applied in classification of a growing area as shown in Table 11.2.

Table 11.2 Classification of shellfish growing areas. Microbiological examination of water samples (NSSP, 1999).


Faecal coliform


Geometric mean

<10% of samples


MPN <14/100 ml

MPN <43/100 ml
MPN <49/100 ml

5 tube dec. dilution
3 tube dec. dilution


MPN <88/100 ml

MPN <260/100 ml
MPN <300/100 ml

5 tube
3 tube

It will be noted that both the EU and the USA classification programmes are relying heavily on conventional bacterial pollution indicators for measuring water quality. Although it has been generally accepted that it is better to monitor for the indicators of faecal pollution than for specific bacterial pathogens this is not the case for pathogenic viruses. There is ample evidence that viral pathogens are more resistant to environmental conditions, sewage and water treatment processes compared to coliform organisms (review by Leclerc et al., 2000). Enteric viruses can survive for months in the marine environment, which is far longer than any bacterial indicator (Lees, 2000). New viral test methods are needed and under development as reliable faecal pollution indicators, but a number of critical issues must be addressed before their use.

11.3 Chemical contaminants

Chemical contaminants (heavy metals, persistent organic pollutants) may pose a potential human health hazard (section 5.2). Concern for these contaminants are mainly related to fish harvested in fresh water, estuaries and coastal waters where shore-side industries are located or intensive agriculture are using large amounts of pesticides or other agro-chemicals. In such areas, a government programme for monitoring all possible chemical contaminants in the harvesting area for fish and shellfish should be implemented and in place. The council directive (EC, 1991) makes reference to the compounds listed in the annex of directive 79/923/EEC (EC, 1979) and specify that these substances must no occur on shellfish in quantities that the calculated dietary intake exceeds the permissible daily intake (PDI). The directive (EC, 1979) states sampling frequency of several chemical contaminants, such as organohalogenated substances and metals which must be measured half-yearly. Tolerances, action levels and guidance levels for the more toxic chemical contaminants are discussed in section 5.2.


Anderson, D.M., P. Andersen, V.M. Bricelig, J.C. Cullen and J.E.J. Rensel 2001. Monitoring and Management Strategies for Harmful Algal Blooms in Coastal Waters, APEC # 201-MR-01.1. Asia Pacific Economic Program, Singapore and Intergovernmental Oceanographic Commission, Technical Series No. 59, Paris.

EC (European Commission) 1979. Council Directive 79/923/EEC of 30 October 1979 on the quality required of shellfish waters. Official Journal of the European Communities No.L 281, 10/11/1979. pp. 0047-0055.

EC (European Commission) 1991. Council Directive 91/492/EEC of 15 July 1991 laying down the health conditions for the production and placing on the market of live bivalve molluscs. Official Journal of the European Communities No.L 268, 24/09/1991. pp. 001-0014.

EC (European Commission) 1993. Council Decision 93/383/EEC of 14 June 1993 on reference laboratories for the monitoring of marine biotoxins. Official Journal of the European Communities L116, 08/07/1993. pp. 0031-0033.

Leclerc, H., S. Edberg, V. Pierzo and J.M. Deláthe 2000. A review. Bacteriophages as indicators of enteric viruses and public health risk in groundwaters Journal of Applied Microbiology 88, 5-21.

Lees, D. 2000. Viruses and bivalve shellfish. International Journal of Food Microbiology 59, 81-116.

NSSP (National Shellfish Sanitation Program) 1999. Guide for the Control of Molluscan Shellfish, Model Ordinance, Chapter IV. U.S. Department of Health and Human Services, Food and Drug Administration, Center for Food Safety and Applied Nutrition, Washington, DC, USA.

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