Heavy metals are commonly defined as those elements with a high relative density. These metals have the potential to cause environmental or human toxicity. Heavy metal poisoning can be acute or chronic and may be caused by the following:
- lead
- mercury
- iron
- cadmium
- thallium
- bismuth
- arsenic
The metals may enter the body by:
- ingestion
- inhalation
- absorption through the skin or mucous membranes
Common causes
Incineration of refuse
Incineration of refuse is generally considered a convenient method of reducing waste volume since it normally achieves a reduction of about 90%. However, the process is not without disadvantages. It can be harmful to the environment with its associated gaseous emissions and heavy metal by products.
Landfill
The solid residue left over from the incineration of refuse consists primarily of bottom ash (80% - 90%) and fly ash from the dust collection system. Whilst in some countries incineration residues may be treated as toxic waste (eg Canada), it is not uncommon for them to be disposed of by landfilling. However, in recent years there has been an increased concern for the potential hazards posed by leachate from such sites. Leachate is the liquid that drains or 'leaches' from a landfill and contains heavy metals such as cadmium, mercury and lead. These elements can be toxic even at relatively low concentrations.
Reclamation
The lack of suitable inland disposal sites has meant that Jersey has increasingly turned to reclamation as the sole means of disposing of solid waste, with incineration playing an important role in reducing the volume of waste and prolonging the life of reclamation sites. However, the possibility of leachate entering the marine environment is very real. If this occurred locally it would constitute a breach of the The Dumping at Sea Act 1974 (Overseas Territories) Order 1975. This has led to the ash being dumped above mean high water level at the reclamation sites since 1987.
The Dumping at Sea Act 1974 (Overseas Territories) Order 1975 on the Legislation UK website
Public health risk
When such leaching is excessive / prolonged, the metals can become more concentrated the further up the marine food chain you go. Some bivalves, for example, concentrate certain metals tens of thousands of times above the ambient level (a bivalve is any mollusc, such as an oyster or clam, which has a shell with 2 hinged 'valves' or shell halves). In extreme cases, potential public health risks arise because of the ingestion of contaminated seafood.
Samples
In Jersey, the common limpet and brown fucoid seaweed have been sampled since 1994 at 5 locations:
- west of Albert Pier
- La Collette
- St Aubin
- Corbiere
- Gorey
Samples have also been taken from Havre des Pas and Les Ecrehous.
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