When you browse the web you can find wast info on the risks of eating bivalves. We will not go into scientific detail here. If you are interested in the science of this subject, please contact us with your detailed info, and will supply you with the right info.
The main hazards associated with the consumption of shellfish arise from the microbiological contamination of waters in which they grow. Since molluscs are filter feeders they concentrate contaminants to a much higher level than that of the surrounding seawater. Many of the pathogens, such as viruses causing gastroenteritis and infectious hepatitis, and the bacteria causing typhoid, are usually associated with contamination by human sewage. Others, such as the bacteria causing gastroenteritis (non-Typhi Salmonellae and Campylobacter), may be associated with either sewage or with animal faeces. The latter may contaminate shellfish-growing areas when washed off the land during periods of rain.
Some other hazards are associated with naturally occurring organisms present in the marine environment. These include infections due to pathogenic marine vibrio bacteria and biotoxins produced by some single-celled algae which can cause various forms of poisoning such as paralytic shellfish poisoning (PSP), neurotoxic shellfish poisoning (NSP), amnesic shellfish poisoning (ASP) and diarrhetic shellfish poisoning (DSP).
Chemical contaminants, such as heavy metals, pesticides, organochlorides, petro- chemical substances are a potential hazard in certain areas.
The table below summarizes the potential hazards.
| Hazards associated with bivalve mollusc consumption | ||
| Class of hazard | Contaminant | |
| Infections | Bacteria | Salmonella spp., Shigella spp., Vibrio parahaemolyticus, Vibrio vulnificus, Vibrio cholerae, Campylobacter spp., Listeria monocytogenes |
| Viruses | Norovirus, Hepatitis A virus | |
| Intoxications | Chemical | Heavy metals: including Mercury (Hg), Cadmium (Cd), Lead (Pb). Organics: Dioxins, Polychlorinated Biphenyls (PCBs), Polycyclic Aromatic Hydrocarbons (PAHs), pesticides |
| Biotoxin | Paralytic shellfish poisoning (PSP), Diarrhetic shellfish poisoning (DSP), Amnesic shellfish poisoning (ASP), Neurotoxic shellfish poisoning (NSP) | |
Infections
| Microbial causes of bivalve shellfish-associated illness | ||||
| microorganism | Incubation period | Duration | Principal signs and symptoms | Principal source of contamination of shellfish |
| salmonella typhi and s. paratyphi | Typhi: 1–3 weeks Other source: | Typhi: up to 4 weeks Paratyphi: 2-3 weeks | Malaise, headache, fever, cough, nausea, vomiting, constipation, abdominal pain, chills, rose spots, bloody stools | Human faeces/ sewage |
| Other salmonella | 6 to 72 hours, mean18 to 36 hours | 4–7 days | Abdominal pain, diarrhoea, chills, fever, nausea, vomiting, malaise | Human faeces/ sewage or animal/ bird faeces/slurry |
| Campylobacter | 2 to 7 days | 3–6 days | Diarrhoea (often bloody), severe abdominal pain, fever anorexia, malaise, headache, vomiting | Animal/bird faeces/slurry |
| shigella | 24 to 72 hours | 5–7 days | Abdominal pain, diarrhoea, bloody & mucoid stools, fever | Human faeces/ sewage |
| vibrio parahaemolyticus | 2 to 48 hours, mean 12 hours | 2–14 days (average 2.5) | Abdominal pain, diarrhoea, nausea, vomiting, fever, chills, headache | Marine environment |
| vibrio vulnificus | 16 hours mean < 24 hours | 2–3 days | Malaise, chills, fever, prostration, cutaneous lesions, fatalities occur | Marine environment |
| vibrio cholerae O1 and O139 serotypes | 1–5 days, usually 2–3 days | 2–5 days | Profuse, watery diarrhoea (rice-water stools), vomiting, abdominal pain, dehydration | Human faeces/ sewage |
| vibrio cholerae non-O1/nonO139 | 2 to 3 days | Up to 1 week | Watery diarrhoea (varies from loose stools to cholera-like diarrhoea) | Marine environment |
| Norovirus | 1–3 days mean 36 hours | 20 to 72 hours | Diarrhoea, nausea, vomiting, abdominal pain, abdominal cramps | Human faeces/ sewage |
| Hepatitis A virus | 10 to 50 days, mean 25 days | 10 to 30 days 10% of infected persons will have prolonged or relapsing symptoms over | Fever, malaise, lassitude, anorexia, nausea, abdominal pain, jaundice | Human faeces/ sewage |
| Astrovirus1 | 1 to 2 days | 48 to 72 hours | Diarrhoea, some times accompanied by one or more enteric signs or symptoms | Human faeces/ sewage |
Intoxications
Of the estimated 2000 living dinoflagellate species, about 30 species produce toxins that can cause human illness from shellfish or fish poisoning. When humans eat seafood contaminated by these microalgae, they may suffer a variety of gastro-intestinal and neurological illnesses. The most common shellfish poisoning is paralytic shellfish poisoning (PSP) which in extreme cases can lead to death through respiratory paralysis, diarrhetic shellfish poisoning (DSP) which causes severe gastro-intestinal problems and can promote stomach tumours, neurotoxic shellfish poisoning (NSP) which causes respiratory distress, and amnesic shellfish poisoning (ASP) which can lead to permanent brain damage (short-term memory loss).
Heavy metals are dangerous because they tend to bioaccumulate. Bioaccumulation means an increase in the concentration of a chemical in a biological organism over time, compared to the chemical's concentration in the environment. Compounds accumulate in living things any time they are taken up and stored faster than they are broken down (metabolized) or excreted.