Marine bacteria will ingest mercury before it reaches fish and humans
By Marek Grzybowski
Mercury pollution is a serious problem worldwide, with major socio-economic, environmental and health consequences. The toxic effects of mercury are significant at all ages, but children are particularly sensitive to this toxin. Despite the drastic reduction in mercury emissions in recent years, the concentration of this element in marine fish from various European seas has not decreased significantly, warn participants of the MER-CLUB Project, led by AZTI from Spain.
The problem is significant because mercury reaches humans in various forms. This toxic metal is no longer used in thermometers, but it can still enter humans in various forms. Among other things, it reaches us through food. One of the sources is fish.
SGS states in a special publication that “one of the main routes of human exposure to mercury is through the consumption of fish, because mercury tends to bioaccumulate in aquatic organisms”. The European Union is allocating significant funds for research because mercury pollution poses a major threat to the environment and human health, and the increase in its concentration in fish is particularly dangerous.
A team of scientists working within the EU project ITN GMOS-Train developed chemical models and analyses of the fate of mercury on land, in the air and in the seas. The results of the work support public health activities and will enable more informed dietary choices. The project allowed the development of an accurate methodology for testing mercury in fish. Fish contain more than just mercury. As a result of environmental pollution, fish meat may therefore contain heavy metals (e.g. mercury), dioxins and polychlorinated biphenyls (PCBs). The Sea Fisheries Institute calculates that the most characteristic pollutants found in fish are: organochlorine pesticides, polychlorinated biphenyls – PCBs, toxic metals – Cd, Pb, Hg, dioxins and dioxin-like polychlorinated biphenyls – dl-PCBs, Histamine, PAHs in fish products. Dioxins + dl-PCBs, on the other hand, are organic pollutants most characteristic of fish.
Fish on the EU table
According to EUROSTAT data, estimated fish consumption in the EU exceeded 10.4 million tonnes of live weight equivalent (according to data from “THE EU FISH MARKET. Edition 2024”). This corresponds to the consumption of 23.28 kg of fish per person. This is the lowest level of consumption in a decade. In contrast to the negative trend in the entire EU, there were slight increases in several countries. The highest estimated increase in consumption was recorded in Bulgaria and amounted to 6%.
Portugal continues to stand out as the main consumer of fishery and aquaculture products in the EU with consumption exceeding 57 kg per year. Spaniards eat over 44 kg of fish and seafood per year. In Denmark, the consumption of fish and fish and seafood products exceeds 35 kg, in France – 32.5 kg, in Luxembourg it is over 32 kg.
In Poland, fish consumption has exceeded 13 kg per year for several years. – Mercury released into the environment does not stay in one place – it hits different places, like a ping-pong ball bounced off the ground. The last step of this process is bioaccumulation in the bodies of fish, and its concentration is then a million times higher than in the surrounding water, explains Milena Horvat, head of the environmental science department at the Jožef Stefan Institute in Slovenia and coordinator of the GMOS-Train project – reports the EU portal “Research and Innovation”. Horvat emphasizes that “This is a particular problem for countries where fish are an important part of the diet, for example in European coastal countries. Significantly elevated levels of mercury are detected in the bodies of residents.”
The EU-funded MER-CLUB project has contributed to solving the problem of mercury pollution in waters, making great progress towards the creation of a mercury purification system based on marine bacteria, which can be used to purify pollutants in a process called bioremediation.
The project, coordinated by AZTI (the Spanish Centre for Marine Research) and financed by the European Maritime and Fisheries Fund (EMFF, now EMFAF), involved universities and research centres from Spain, France, Sweden and Germany, as well as a Spanish company specialising in waste management and soil decontamination.
Project participants, source: MER-CLUB, 2024
Bacteria fight mercury
– Reducing mercury levels in sediments through bioremediation is essential for restoring polluted environments. Detoxifying marine ecosystems from mercury will undoubtedly have a direct and positive impact on human health, assures Dr Andrea G. Bravo, a young researcher at MER-CLUB.
The project tested thousands of bacterial strains. Marine microorganisms have the genetic potential to detoxify mercury. MER-CLUB partners used advanced isolation methods to obtain more than 1,000 bacterial strains from heavily contaminated European sediment samples in the Baltic, Mediterranean and Atlantic Oceans. They identified marine bacteria with high potential for mercury bioremediation using molecular markers and tested the ability of the most promising candidates to reduce mercury in the laboratory. This provided the basis for the future development of a mercury treatment system that could operate in extracted marine sediments.
The enormous complexity of marine sediments has proven to be a challenge for scientists. Problems have occurred at both the chemical and biological levels. Here, the main obstacles to achieving an effective bioremediation solution were encountered during the project. The partners worked on alternative solutions, such as the use of microbiological consortia and deepening the analysis of chemical species associated with mercury sediments.
It is emphasized that “MER-CLUB has overcome challenges by providing new scientific knowledge on mercury-transforming microorganisms in complex marine sediments, including those with a previously unrecognized role in mercury demethylation and reduction”. The project has also provided technical progress towards the design of a pilot mercury bioremediation plant for ex situ decontamination of sediments. A pilot plant has been built. It must be optimized before assessing the level of technological readiness for its commercialization.
Nevertheless, the pilot plan is a key step forward, establishing the basis for a feasible solution for purification, the researchers emphasize. They assure that “By solving the problem of water pollution with innovations such as bioremediation, we can work to ensure that our freshwater and marine ecosystems are free of toxins.” And it should be emphasized that we are consuming more and more fish and seafood from aquaculture. So I already have a choice whether to consume fish with mercury and other toxins or fed specially prepared feed. It seems that carp, which will soon be on the Christmas table, do not have such an alternative.