A recent study conducted by scientists affiliated with the Woods Hole Oceanographic Institution and other institutions has found that human activities contribute significantly to the presence of toxic thallium in the Baltic Sea. Thallium, considered the most toxic metal for mammals, is currently present in low levels in Baltic seawater. The study suggests that the amount of thallium could increase due to further human-induced activities or natural re-oxygenation of the sea, which could reduce sulfide levels. Most of the thallium in the Baltic Sea accumulates in sediment due to sulfide minerals.
The research revealed that anthropogenic activities have been releasing considerable amounts of toxic thallium into the Baltic Sea since around 1947. Lead author Chadlin Ostrander stated that if human activities continue to release thallium into the sea or if the sea’s chemistry changes, more thallium could accumulate, posing a concern due to its toxicity. The study aimed to understand how thallium and its isotopes cycle in the Baltic Sea. Modern thallium cycling was studied by collecting data from seawater and sediment core samples, while historical thallium cycling was analyzed using a longer sediment core.
The study identified that Baltic seawater had higher levels of 205Tl than predicted, with enrichment observed around 1940 to 1947 according to the longer sediment core. The increase in 205Tl was likely connected to anthropogenic activities, though the exact sources of this thallium are still unknown. The research suggests that regional cement production, increased after World War II, may be a significant source of thallium. Other potential sources include coal combustion and the roasting of pyrite, an iron sulfide.
Co-author Sune Nielsen emphasized that the study revealed extensive contamination of the Baltic Sea with thallium from human activities, making it the most geographically extensive area of thallium contamination documented. The findings add another dimension to the existing poor conditions in the Baltic Sea, highlighting the urgency of restoring the sea’s ecosystem. Additionally, co-author Colleen Hansel warned against oxygenating the Baltic Sea’s bottom waters to combat anoxia, as this could lead to the release of thallium and other metals into seawater, potentially reaching toxic levels in fish.
The study also highlighted the importance of isotopes in identifying pollutant sources in marine ecosystems, which may be challenging to determine using concentration data alone. The research was funded by the U.S. National Science Foundation and the Leibniz Association. Overall, the study underscores the significant impact of human activities on thallium levels in the Baltic Sea and the need for more sustainable practices to protect marine life and ecosystem health in the region.