The marsupial crab is a good eco-indicator of the state of the polluted seabed, despite the fact that it can move over a somewhat larger area. Photogr

The researchers trace the contaminated 'fingerprint' in the crab

NORWAY
Thursday, August 15, 2024, 00:10 (GMT + 9)

The crab in Jøssingfjorden contains heavy metals. This heavy metal has its own fingerprint that shows where it comes from.

"This method has been used to some extent on mercury, but never on mining waste", says marine researcher Michael Bank. 

A portion of sophisticated chemistry, a dose of advanced mathematics and a sprinkling of machine learning have enabled marine scientists to trace the pollution's route in the Jøssingfjord. 

For over 20 years, waste from the titanium mine was deposited in the fjord. In the most active period, in the 80s, the quantities were estimated at around two million tonnes every single year. 

The researchers are still seeing the consequences of the waste masses in the fjord ecosystem. 

"We have developed a model that allowed us to trace several heavy metals from land to sea to marine sediment and to the marsupial crab, which is often eaten by humans", explains Bank. 

The findings were recently published in an article in the Journal of Hazardous Materials . 

Back to the source

Back in 2018, HI researchers were on fieldwork in the Jøssingfjorden. They then collected sediment samples and marsupial crabs in the landfill area and from a reference area. 

The aim was to investigate what traces of the marine landfill they still found in the marine environment. What element characterizes the sediment and what did the marsupial crab absorb?

"Different tests give us different information", explains the marine researcher. 

The hepatopancreas ("liver" or brown food as it is also called) of the crab tells what heavy metals the crab has been exposed to in recent times, while the claw muscle shows the pollution it has encountered during its entire life. 

The sediment, in turn, is the long-term memory of the ecosystem. Here, the researchers can track pollution from the past 30–35 years.

"We can usually show that sediment has high levels of a given heavy metal, but we cannot directly link these to a source. We can do that now", explains Bank.

Image: Journal of Hazardous Materials/ScienceDirect. Click the image to enlarge

A contaminated "fingerprint"

The key is the heavy metals' distinctive isotopes. They are like your own fingerprint. 

The isotopes reflect their surroundings and the local influences they have been exposed to. Different circumstances produce different "fingerprints" - pollution from a cement factory will have different results than pollution from a marine landfill. 

"When you measure these isotopes, you get different values. These values ​​correspond to their source", says the marine researcher. 

The researchers have carried out isotope analyzes on a whole range of "new" heavy metals, such as lead, cadmium, iron, zinc and copper, in addition to the more well-established mercury. 

"For the Jøssingfjord's ecosystem, the lead isotopes were the most suitable for tracking where the pollution has come from", says Bank.

The marine researchers have examined samples from the seabed and the pocket crab nest in the Jøssingfjorden. Here is an illustration photo from a trip in 2017: Erlend Astad Lorentzen / Havforskingsinstituttet

30 years later: Still "severely polluted"

The investigations show that the isotopic values ​​and elemental composition in the samples from crabs and sediment in the landfill area differ markedly from those from the reference area. 

The sediment in the Jøssingfjord fell under the categories "severely polluted" for copper and "moderately" polluted for nickel, in the Norwegian Environment Agency's classifications. 

"Our findings show how long the time horizon is for marine ecosystems when it comes to this type of activity. The consequences persist, more than 30 years after the deposition ended", says marine researcher Samuel Rastrick. He leads the HI project which examines the ecosystem effects of mining waste. 

For the pocket crab, the cadmium concentration in the brown food was regularly above the recommended limit value. In addition, the results show that there was an increased level of both nickel in the liver and vanadium in the muscle tissue.

"How the element was distributed in the crab depended on which organ we examined. For example, mercury, zinc and arsenic were more attracted to the muscle. This shows how important it is to analyze several organs", underlines Bank. 

Shall use the model in other ecosystems

The marine researchers now plan to test the model they have developed on new fjord island ecosystems, with new data and new species. First up: haddock in Repparfjorden. 

"The findings in this study give us several important advances in our understanding of the consequences of pollution, the biochemical cycles of various metals and what ecological consequences these have in the fjord ecosystem", concludes Rastrick.

Author/Source: Bente Kjøllesdal / Norwegian Institute of Marine Research

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