Because both population and industry in Greece are highly concentrated in few centres, the majority of coastal waters are very clean. However, the sources of eutrophication which favour bivalve growth are also likely to carry faecal pollution into the area. In the inner bay of Thessaloniki and in Saronikos Bay around Salamina, most of the eutrophication comes directly from untreated sewage. Installation of a long sea outfall from Piraeus will improve the situation there, but in Thessaloniki, discharge of the new sewage treatment plant into the River Axios is likely to increase the contamination of commercial shellfish grounds.
Guidelines for assessing the microbiological quality of shellfish growing waters and of shellfish for marketing were recommended on the basis of interim criteria (WHO/UNEP 1978) as follows:
For satisfactory water of shellfish-growing areas, in terms of faecal coliforms (FC) per 100 ml of water.
Less than 10 FC/100 ml in 80% of samples.
Less than 100 FC/100 ml in 20% of samples.
For shellfish, in terms of faecal coliforms (FC) per 1 g of shellfish flesh.
| 0 – 2 FC/g | Sale permitted. |
| 3 – 10 FC/g | Temporary prohibition of sale. |
| Above 10 FC/g | Sale prohibited. |
These criteria, together with recommendations on sampling procedures, were confirmed in the Proposed Environmental Quality Criteria for Shellfish and shellfish-growing waters in the Mediterranean (UNEP/WG.118/6, 1988) as follows:
PROPOSED INTERIM CRITERIA FOR SHELLFISH AND SHELLFISH-GROWING AREAS IN THE MEDITERRANEAN SEA
Shellfish-growing Waters
| Parameters | Concentration per 100 ml not to be exceeded | Minimum sampling frequency | Analytical method | Interpretation method | |
| 80% | 100% | ||||
| of the time | |||||
| Faecal coliforms | 10 | 100 | In winter: monthly In summer: fortnightly |
Membrane filtrated m-FC broth or agar incubated at 44.5±0.2°C for 24 hours | Graphical or analytical adjustment to a lognormal probability distribution |
Shellfish Flesh
| Parameters | Concentration per gramme of flesh | Minimum sampling frequency | Analytical method | Interpretation method |
| Faecal coliforms | 2 Sale permitted | In winter: monthly | Multiple tube fermentation and counting according to MPN (Most Probable Number) | By individual histograms or graphical adjustment of a lognormal probability distribution MacConkey broth |
| Between 3 & 10 Temporary prohibition of sale | In summer: fortnightly | |||
| 10 Sale prohibited | incubated at 35±0.5°C for 24 hours | |||
| and then at 44.5±0.2°C for 24 hours |
Source: Assessment of the Present State of Microbial Pollution in the Mediterranean Sea and Proposed Control Measures.
UNEP/WG.118/6, 1985
The current EEC Directive on water quality required of shellfish waters (79/923/EEC) is aimed at the suitability of the waters for shellfish growth and is not a public health directive.
Depuration should reduce the FC count on sampled shellfish flesh to no more than 2 per gramme. The systems available to achieve this can be based on:
Chlorination/dechlorination of incoming water (normally open circuit).
Ozone treatment of incoming water (normally open circuit).
Ultraviolet irradiation of water (normally recirculating or semi-open circuit with recirculation).
The one existing plant and two under construction in Greece use both chlorination and ozone. The need for such duplication of systems is not clear. Knowledge of ultraviolet systems is lacking, and needs to be made available urgently, especially as this is the most appropriate method for small growers, such as those near Salamina, not operating within a cooperative. The advantages of ultraviolet systems are:
The units can be small, and are appropriate to the scale of all existing operations in Greece.
Each unit is self contained. Expansion can be by addition of more units.
Low cost.
Reliability and ease of maintenance.
Inherent safety in case of failure of sterilizing system.
Low water requirement.
Of these, the last two are of particular relevance to Greece. The siting of depuration plants, on land close to electricity supply and with good road access, can mean that the microbiological quality of water entering the plant is inferior to that in the growing waters from which the shellfish are brought. Open circuit systems carry a risk that any failure of the sterilizing system will result in the shellfish actually receiving an increased bacterial loading during supposed depuration. In the consultant's experience, such failures are commonplace with ozone and chlorination systems. During his visit to the existing plant at Epanomi (Thessaloniki) the ozone plant was unservicable. Chlorination, particularly when introduced as an emergency back-up, requires careful management. Any chlorine residue in the water reaching the molluscs causes them to stop filtering and close their shells, in which case they do not cleanse themselves of bacteria.
Closed circuit, ultraviolet sterilization on the other hand, uses a small volume of water drawn from the sea once only at the start of depuration. This is resterilized many times during recirculation. Even if the ultraviolet lamps fail, the numbers of viable bacteria decline rapidly during the 36–48 hour period of confinement of the water in the tanks. This is the basis of the fail-safe nature of the system.
The low water requirement of ultraviolet, recirculating systems has special significance in Greece for other reasons. Individual growers, such as those in the Salamina area, report difficulty in obtaining land and planning permission for depuration tanks close to the shore. Small, stacked tray systems (Fig. 5) appropriate to their scale of operation, can be housed in existing buildings and can even be a short distance away from the coast, batch-filled by water bowser. The small volume of water used can be discharged into land drains, rather than directly into the sea. One of the reasons for the refusal of planning permission is a public misconception that shellfish depuration plants (and also cultivation units) will pollute the marine environment. Discharge into land drains should circumvent this objection.
Design specifications and operating guidelines for ultraviolet depuration systems, as recommended in the UK by the Ministry of Agriculture, Fisheries and Food, are given in Laboratory Leaflet 43 (M.A.F.F. 1978). Schematic layouts of the two most common configurations, tanks and stacked trays, are shown in Figs 4 and 5.
Any expansion in the home market for molluscs, and especially mussels, in Greece will rely on improving public confidence in their purity. This will partly improve as more come from cultivation, with concessions only being granted in areas where water quality is satisfactory. However, the public need to be further assured that shellfish being bought through proper market outlets either come from clean waters or have been fully cleansed. The lack of depuration plants in the Athens (Salamina) area is deterimental to achieving public confidence, especially as roadside shellfish stalls make this one of the most conspicuous markets.
The shellfish industry has to realize that not only is depuration important, but it needs to be known by the public. Small ultraviolet systems also serve as holding units for the sale of shellfish. If on show at the selling establishment, they attract interest and trade. The possession of a small holding system obviates any temptation to ‘re-water’ unsold shellfish in sacks in the sea, a practice which was observed by the consultant close to Athens, and which is a serious source of risk to public health, as well as damaging to the public perception of shellfish.
