Soil Science Group

Arsenic, Antimony and Mercury in soils

With rhizon sampler and flow pumps equipped flasks in a growth chamber

Arsenic (As), antimony (Sb) and mercury (Hg) have been heavily used throughout the last century and a half as pesticide, chemical weapons, flame retardants, in plastics and in ammunition, as amalgam for gold mining or as chemical catalysts. It was only recently that their negative impacts on the environment and humans have been evaluated. Such investigations almost always originated from reported environmental and human catastrophes. In the case of Hg, it was the Minamata Bay catastrophe in Japan. For As, it was the discovery of very high levels of naturally present As in the groundwater in SE Asia, impacting up to 100 million people. Sb has been much less studied than As or Hg and there is only very little legislation on this element although initial findings show that its behavior and toxicity are similar to As. However, these issues also exist locally. In Switzerland, 15-20t of Sb enters the soil each year through shooting activities while an important Hg pollution exists in Valais between Visp and Raron. Finally, hot-spots of naturally occurring As exist in the Jura, the Valais and in Tessin.

Our main goal is to study the behavior of As, Sb and Hg in soils in Switzerland in order to contribute to the remediation efforts in locally polluted areas. Our research also takes place in polluted areas of Bangladesh and of China so that we can understand the global behavior of these pollutants. Our focus is on assessing the microbial transformation of As, Sb and Hg in soils (e.g. biomethylation and biovolatilisation) by developing new analytical techniques (speciation analysis using chromatography and mass spectrometry). With these techniques we are able to precisely measure the different chemical species of these pollutants. Furthermore, our goal is to evaluate the influence of agricultural practices and climate change on these chemical species.

Research Projects

Geogenic Arsenic in Swiss Rice Paddies

Arsenic is a carcinogenic element that occurs naturally in Swiss soils. For some years now, attempts have been made to cultivate paddy rice in waterlogged areas north of the Alps. The paddy rice is grown on formerly drained peatland which is degraded and is now partially wet again due to the close groundwater table. Growing rice in these fields could be an adaptation strategy for affected farmers. However, the cultivation of paddy rice and the associated flooding of the fileds mobilises arsenic and bacterial activity produces methylated arsenic species. The various arsenic species are absorbed by the rice plant and thus incorporated into the rice grain. The toxicity of the methylated species is not well known and not included in the food safety legislation.

Our aim is to determine the concentrations of the different arsenic species occuring in Swiss rice and to identify possible drivers in the Swiss context. For this, we use state-of-the-art analytical speciation techniques and cooperate with local and European experts. This research will allow a better understanding of the occurrence of arsenic species in rice and the impact of the cultivation of rice in Switzerland.

MSc student: Dominik Dubach
Project leader: Prof. Dr. Adrien Mestrot

Release, biomethylation and biovolatilisation of antimony (Sb) in soils: Drivers, mechanisms and global environmental implications

Sb release upon flooding

Antimony (Sb) can become highly mobile in flooded soils, posing a threat to surrounding environments. The project aims to investigate the mobility of Sb in flooded soils from Swiss shooting ranges and Australian antimony mine surroundings. Through laboratory simulations, we aim to understand the complex geochemistry driving antimony mobility under these conditions. Our analysis includes soil pore water chemistry, various antimony species, and the characterization of antimony-bearing colloids over time. Additionally, we examine volatile antimony and its binding in the soil. By gaining insights into antimony's behavior in flooded soils, this research enhances our ability to assess environmental risks associated with antimony contamination.

Sb Speciation and Biotransformation

The project is also dedicated to advancing analytical methods for investigating the speciation and biotransformation of antimony in soils. This focus involves developing new analytical methods and conducting direct measurements in both laboratory incubations and field environments. These measurements will provide valuable data on methylated and volatile Sb species formation in soils, allowing us to characterise the environmental relevance of biomethylation and biovolatilisation of Sb.

PhD student: Ursina Morgenthaler
Early Postdoc: Dr. Ikram Bakour
Project leader: Prof. Dr. Adrien Mestrot

Dynamic evolution of mercury (Hg) methylation in a polluted agricultural floodplain

Mercury is a toxic metal and methylated mercury (MeHg) is the most common organomercury compound in the environment. MeHg is bioaccumulative and thus biomagnifies in the food chain. The annual variation of MeHg in situ in soils was investigated in temporarily waterlogged and reductive soils, but not in a former floodplain.

The project thus aims to link methylated mercury over the course of one year with soil parameters that can have an influence on (de)methylation (pH, soil temperature, organic carbon, inorganic carbon, C/N ratio, particle size, moisture) and meteorological parameters (temperature, moisture). In addition, forested soil is compared with soil used as a meadow. For this purpose, six 2x2m test squares were sampled monthly from March to October during the year 2023 in the agricultural floodplain between Visp and Raron (VS).

MSc student: Noël Appenzeller
Project leader: Prof. Dr. Adrien Mestrot

Mercury in terrestrial environment in Switzerland: Bioaccumulation and biomagnification in food chains

Studies on mercury bioaccumulation and biomagnification in terrestrial food chains are scarce compared to aquatic food chains. With reducing global mercury levels in the environment, following the Minamata convention, we aim to monitor mercury in different environmental matrices and update the national database for terrestrial biota in Switzerland. Additionally, we aim to investigate biological factors like age, sex and diet, and environmental factors like proximity to local pollution sources and atmospheric Hg depositions to explain variations in tissue mercury levels.

There are three principal focuses:

  1. Method development for quantification of total, inorganic and organic mercury from different tissue samples.
  2. Study bioaccumulation and biomagnification in barn owl food chain using least-invasive tissue samples. The food chain consists of soil, prey fur collected from pellets, and down feathers of juvenile barn owls.
  3. Study bioaccumulation in wildlife (roe deer, lynx, and wolves) and assess threat to apex predators.

PhD student: Sabnam Mahat
Master student: Ladina Gaudy
Project leader: Prof. Dr. Adrien Mestrot