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Chemical contaminant monitoring

How to detect and monitor chemical contaminants and guidance on the relevant limits.

Last updated: 10 June 2021
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Monitoring process

Live Bivalve Molluscs feed on plankton from the surrounding water that washes through their habitat. This feeding process can lead to the build-up of environmental pollutants in the shellfish.

Legislation requires the monitoring of classified shellfish production areas for chemical contaminants.

Classified shellfish production areas are monitored by our official control monitoring programmes. This ensures that the levels of chemical contamination in live bivalve molluscs do not exceed regulatory limits.

Shellfish samples are collected by sampling officers and delivered to official control laboratories. At the laboratory, chemical testing is carried out to detect in accordance with criteria set out in legislation to detect levels of:

  • heavy metals
  • polycyclic aromatic hydrocarbons (PAHs)
  • dioxins if required poly-chlorinated biphenyls (PCBs) if required

Limits for chemical contaminants

Heavy metals:

  • Lead – 1.5mg/kg
  • Cadmium – 1.0mg/kg
  • Mercury – 0.5mg/kg

Polycyclic aromatic hydrocarbons (PAHs):

  • Benzo(a)pyrene – 5.0µg/kg
  • Sum of benzo(a)pyrene, benz(a)anthracene, benzo(b)fluoranthene and chrysene – 30.0µg/kg

Dioxin and dioxin-like PCBs:

  • Sum of dioxins – 3.5pg/g wet weight
  • Sum of dioxin and dioxin-like PCBs – 6.5pg/g wet weight
  • Sum of PCB28, PCB52, PCB101, PCB138, PCB153 and PCB180 – 75ng/g wet weight

Monitoring programme

Each year we review the current classified harvesting areas and select sites for sampling as needed. The reports are published and mapped to show compliance, dates sampled and analysis type.

Northern Ireland

Chemical contaminant results

Chemical contaminant results for England and Wales