Thanks to Bryce Beukers-Stewart for forwarding this information.
The Conversation ‘Shellfish such as scallops, mussels and oysters – bivalve molluscs – readily take up tiny specs of metals into their tissues and shells. In sufficient concentrations this can harm their growth and survival chances, and even threaten the health of any human who eats their contaminated meat. Such shellfish provide one-quarter of the world’s seafood, so the impact of pollution from the “heavy metals” such as lead, zinc and copper, is hugely important. We recently investigated the effects of metal pollution on the great scallop, Pecten maximus, for a new scientific study. This is a common species which supports the most valuable fishery in England and the third most valuable in the UK overall.
We first discovered these effects of pollution by chance. While carrying out routine stock assessment surveys around the Isle of Man, a self-governing island that lies between Britain and Ireland, we noticed that scallops found on the Laxey fishing ground off the east coast were much more likely to have lethally damaged shells than scallops from elsewhere. Laxey is famous for the world’s largest working waterwheel, a spectacular example of Victorian engineering used to pump water from a mine which produced lead, copper, silver and zinc. The mine closed in 1929, but its legacy is that sediments in the rivers, estuary and sea waters around Laxey are unnaturally high in metals.
It looked as though metal pollution may be responsible for the damaged shells we discovered. To test this hypothesis, we analysed the strength of scallop shells that had been collected from Laxey and other fishing grounds around the Isle in both 2004 and 2013. In both groups the shells from Laxey were found to be significantly weaker than those from all other areas.
A detailed analysis revealed the Laxey shells were proportionally thinner than shells found at other areas, and that the internal structure of shells contained a disruption, or fault line. We were not able to detect metals in the shells themselves, but we think that even in low quantities the metals are either affecting the physiology of the scallops or disrupting chemical reactions during the mineralisation (shell-growing) process.’
Lethal damage to scallops was higher during fishing at a metal contaminated site.
Higher damage correlated with lower shell strength and disrupted shell structure.
A wide range of alternative explanations to metal contamination were ruled out.
Bivalve shell characteristics should be used more in ecotoxicology assessments.