Environmental Science: Processes & Impacts blog

In the Arctic, there are high concentrations of mercury in humans and animals and scientists are investigating how the mercury got there. Mercury has a tendency to accumulate in organisms and bio-magnify (increase in concentration) up through the food chain, so monitoring its levels in the environment is important. In previous investigations, polar bear organs, such as the liver, kidney, hair and blood have been analysed for mercury content, but the results can be inaccurate because soft tissues change throughout the lifetime of the animal.

Polar bear teeth from the Natural History Museum at the University of Oslo, Norway, were used as biotracers of temporal changes in mercury pollution exposure. © Aurore Aubail

Now, Aurore Aubail from the National Environmental Research Institute, Denmark, and colleagues from France and Norway, have investigated the temporal trends of mercury using polar bear teeth. Teeth are seen as better materials to use, as contrary to soft tissues, the tooth is not remodelled throughout its life and the mercury is not remobilised.

‘Lots of teeth of various Arctic species are stored in natural history museums of Nordic countries and these institutions are a mine of environmental pollution archives,’ says Aubail. ‘Their collections often go back 100-200 years, which allow researchers to establish time trends of pollutants. Working with these polar bear skulls was really exciting, but extracting the teeth was quite a hard task. It even involved a toolbox!’

The team collected teeth samples from 87 polar bear skulls from the Natural History Museum at the University of Oslo, Norway. They analysed mercury concentrations by solid sample atomic absorption spectrophotometry and the relative abundance of carbon (¹³C/¹²C) and nitrogen (¹⁵N/¹⁴N) stable isotopes by an isotope-ratio mass spectrometer to provide information about potential changes in feeding habits or habitats for polar bears.

The results showed that there has been an overall decrease in mercury concentrations in the Arctic over the last 50 years, which supports earlier results found in polar bear hair from Greenland and human deciduous teeth from Norway. The results from the stable isotope ratios eliminated variations in the feeding or foraging habits as a potential explanation. As the mercury emissions are not sourced from the Arctic, another possible cause is a decrease in the source of the mercury emissions from Europe and North America.

‘Polar bears are an especially useful species for the biomonitoring of contaminants,’ says Sara Moses, an environmental biologist from the Great Lakes Indian Fish and Wildlife Commission, US. ‘Because they are long-lived and sit atop the Arctic food web, they are particularly susceptible to accumulating high levels of mercury in their tissues. As a result, mercury levels in polar bears integrate exposure throughout the food web and provide important information about lower trophic levels as well.’ She adds that teeth are useful monitoring tools because bone is more readily available than soft tissues in many archives and provides a matrix that is relatively stable over time.

Aubail hopes that further investigation into the use of polar bear teeth to study mercury will continue as it is ‘still a valuable material that allows us to study long term trends of pollutants’.

Interested? Read Andrew Shore’s full Chemistry World article here or download the JEM paper:

Temporal trend of mercury in polar bears (Ursus maritimus) from Svalbard using teeth as a biomonitoring tissue
Aurore Aubail, Rune Dietz, Frank Rigét, Christian Sonne, Øystein Wiig and Florence Caurant
J. Environ. Monit., 2012, Advance Article
DOI: 10.1039/C1EM10681C

New field-portable infrared (IR) devices that can measure mine workers’ exposure levels to silica in coal dust have been designed and tested by scientists in the US.

The inhalation of microscopic particles of crystalline silica is a serious health hazard, and causes a debilitating, and often fatal, condition called silicosis. Miners in particular are at risk of developing this condition.

Currently, samples collected at the field site are sent to a laboratory for testing, often taking weeks to get the results. This time delay between collection and analysis reduces the usefulness of the results in modifying workplace practices to decrease exposure. As the mining workplace is often moving into new geological strata, with changing levels of silica, a faster turnaround in silica measurements is a priority.

Arthur Miller at the National Institute for Occupational Safety and Health, Spokane, and colleagues have based their work on the successful personal dust monitor (PDM), which measures workers’ exposure to coal dust. However, the PDM does not measure silica levels specifically.

Coal miners are at risk of developing silicosis by inhaling microscopic particles of crystalline silica in coal dust. © Shutterstock

‘It is our intent to develop a field-portable method for measuring silica that miners can use to get immediate feedback regarding their exposure. Such a device could be used to inform immediate adjustments to the mining process that reduce silica exposures, thereby reducing disease and death due to silicosis,’ says Miller.

The challenge was to design an IR device that could measure quantities of silica at low levels, and get around the interference from other minerals in the air, especially kaolin, using a correction scheme. Two IR devices were tested, one using FTIR spectrometry, the other variable filter array (VFA) IR spectrometry. When compared with the current, laboratory-based method, the FTIR data was found to be comparable.

‘The originality of the approach is to bring an analytical method near to the workplace that enables immediate exposure control in order to prevent occupational lung diseases of miners,’ comments Peter Görner, head of the aerosol metrology laboratory at the National Research Institute on Occupational Safety and Health, Vandoeuvre, France.

The next step is to test the feasibility of the new devices as end-of-shift methods of data collection. Work is still needed to determine the best ways of gathering and handling samples, as well as error analysis, but the hope is that this new technology will one day provide immediate results that can allow miners to adjust the mining process to reduce silica exposure.

Interested? Read Rebecca Brodie’s full Chemistry World article here or download the JEM paper:

Evaluating portable infrared spectrometers for measuring the silica content of coal dust
Arthur L. Miller, Pamela L. Drake, Nathaniel C. Murphy, James D. Noll and John C. Volkwein
J. Environ. Monit., 2012, Advance Article
DOI: 10.1039/C1EM10678C

Scientists from Puerto Rico have discovered plants that are not only resistant to high levels of TNT but can remove it completely from aqueous media in under 48 hours.

The explosive trinitrotoluene (TNT) is a persistent contaminant that is toxic and mutagenic, and thanks to its use in over 80 per cent of the landmines worldwide, it can be found throughout the globe at military sites and war zones alike.

Military sites and war zones contaminated with TNT could be cleared by tough Caribbean plants

Samuel Hernández-Rivera and co-workers at the University of Puerto Rico-Mayagüez investigated the ability of three Caribbean plants – Rubia tinctorum, Lippia dulcis and Spermacoce remota – to remove TNT. Plantlets of each were added to flasks containing solutions of TNT and samples were taken at timed intervals for high performance liquid chromatography analysis, with a flask containing just the TNT solution used for comparison.

R. tinctorum and L. dulcis removed nearly 100 per cent of the TNT from the liquid medium, showing a roughly 10-fold increase in the rate of TNT removal compared to loss by evaporation in the control flask. What is even more significant is that S. remota, under identical conditions, can completely remove TNT from the media in under 48 hours.

Hernández-Rivera and his colleague Fernando Souto-Bachiller say that the main mechanism for TNT removal from the media is via adsorption through the roots, but once adsorbed, S. remota seems to have a different mechanism of action. They say that this result was initially attributed to either ‘a possible enzyme exudate, which would then be responsible for TNT degradation, or a symbiotic relationship between the plant roots and a persistent microorganism, fungus or bacteria.’ Future work within the group will involve isotopically labelling TNT to investigate the enhanced behaviour of S. remota.

Tomás E. Macek from the Institute of Organic Chemistry and Biochemistry, Czech Academy of Sciences, Czech Republic, says that the work deals with an ‘important topic and that detoxification of contaminated sites is a global problem’, but ‘there is much to be done to allow effective exploitation in the field’.

Hernández-Rivera says that ongoing experiments are focused on using the plants in TNT contaminated soil, and although ‘physical and biochemical processes in soils are much more complicated’, initial results look promising.

Interested? Read James Anson’s full Chemistry World article here or download the JEM paper:

TNT removal from culture media by three commonly available wild plants growing in the Caribbean
Sandra N. Correa-Torres, Leonardo C. Pacheco-Londoño, Eduardo A. Espinosa-Fuentes, Lolita Rodríguez, Fernando A. Souto-Bachiller and Samuel P. Hernández-Rivera
J. Environ. Monit., 2012, Advance Article
DOI: 10.1039/C1EM10602C