Cécile Quantin, Université Paris-Saclay, GEOPS (Geosciences Paris Saclay)Environmental Health: the issue of ultramafic ecosystems
Existence of original environments developed on ultramafic rocks
We find on Earth original environments,
developed on ultramafic rocks. Ultramafic rocks are rocks mainly composed of
ferro-magnesian minerals which contain iron and magnesium,
such as olivine or pyroxene, and which are relics of the oceanic lithosphere. Ultramafic outcrops occupy <1% of the Earth’s land
surface, but are locally abundant in ophiolite belts along tectonic plate
margins (see the red dots on the map).
Why are they original?
Why are they original?
Why
did I say these areas were original?
These environments are original because the soils that form on these rocks have a very particular chemical composition, due to the nature of ultramafic rocks: these soils are most of the time very rich in magnesium (Mg), and poor in calcium (Ca) and essential nutrients such as potassium (K), phosphorus (P) and nitrogen (N). In addition, they are very often rich in metals, such as nickel (Ni), chromium (Cr), or cobalt (Co), which can induce toxicity for most plants.
These environments are original because the soils that form on these rocks have a very particular chemical composition, due to the nature of ultramafic rocks: these soils are most of the time very rich in magnesium (Mg), and poor in calcium (Ca) and essential nutrients such as potassium (K), phosphorus (P) and nitrogen (N). In addition, they are very often rich in metals, such as nickel (Ni), chromium (Cr), or cobalt (Co), which can induce toxicity for most plants.
Presence of Ni hyperaccumulating plants
Presence of nickel hyperaccumulating plants
All these characteristics, chemical imbalance,
lack of nutrients, richness in metals, mean that the soils are generally
covered by a particular flora, perfectly adapted to these conditions and
unique: the rate of endemism is very high in these environments. There are even
plants that contain incredible amounts of metals in their sap or leaves.
For example, the New Caledonian tree Pycnandra
acuminata (Sapotaceae) has a latex that can contain up to 25.7% Nickel: it is
green!
Economical interest of those areas for nickel, cobalt, …
Economical interest of those areas for metals like nickel, cobalt, …
These
environments are also often found in tropical conditions, particularly where
the deep weathering profiles called laterite develop, which are rich in metals
of economic interest.
Economical interest of those areas for metals like nickel, cobalt, …
Nickel for instance is an important metal in
modern infrastructure and technology, with major uses in the production of
stainless steel and alloys and other applications such as electroplating or
production of rechargeable batteries. Cobalt is also used in electronic devices and
batteries, in semi-conductors that make computers work as well as in
healthcare (in alloys for implants) and as a component in powerful magnets used for magnetic resonance imaging - and other metals.
Anthropogenic pressure
Anthropogenic pressure
Due to that metal richness, these environments are subject to strong mining and metallurgical activity.
Currently, about 1/3 of the primary Ni is produced by smelting of lateritic
ores, which represent 60 to 70% of the terrestrial reserves, and is used at 90%
for ferronickel (FeNi) and 10% for sulfide matte. To meet future demand for Ni,
laterite ores are increasingly mined. Huge quantities of residues are produced during the metallurgical processes.
Consequences of anthropogenic pressure
Understanding
and quantifying the consequences in these particular environments is, therefore, essential to maintaining their functions as healthy ecosystems preserving biodiversity, ensuring water quality and of
course safeguarding environmental health.
Our research
Our research
Our
work, carried out for over 10 years in Brazil, but also in India and New Caledonia, seeks
to quantify the impact of mining and metallurgical activities on the
biogeochemical cycle of nickel and other metals like chromium.
Our research
A biogeochemical cycle is the process of
transport and cyclic transformation of an element or several, here nickel, between the large reservoirs that are the geosphere, the atmosphere,
the hydrosphere, and of course the biosphere.
Our research
We studied in detail where
nickel (in green in the image) is in the soil constituents (i.e., solid speciation),
using different tools allowing to characterize the minerals, their
crystallography and the atomic environment of nickel.
This is really important because knowing solid
speciation helps to hypothesis its possible evolution, for instance the release
from the solid phase to the aqueous phase where roots can uptake elements,
according to the evolution of natural conditions but mostly according to anthropogenic
pressure.
We also perform chemical extraction to simulate the activity of roots, or the impact of the soil solution. These extractions give us information on the chemical stability of the minerals containing nickel (i.e., metal-bearing minerals).
We also perform chemical extraction to simulate the activity of roots, or the impact of the soil solution. These extractions give us information on the chemical stability of the minerals containing nickel (i.e., metal-bearing minerals).
Our research
Finally, we use the isotopic composition of nickel in the different
reservoirs to understand both its sources and what happened to nickel. Isotopes are atoms that have the same number of electrons (and
protons, to stay neutral) but a different number of neutrons. For instance,
carbon has several isotopes, carbon 12, carbon 13 and carbon 14, and you
probably hear about carbon 14 to date old human artifacts or bones.
Here we use nickel isotopes to understand where nickel comes from in soils or water, and what happens to nickel between its source and actual reservoir.
Altogether, these approaches and tools give un the key to understand the transfer of nickel from the soil or metallurgical wastes to the surficial water (soil solution, lake water, river water) and finally to organisms.
Here we use nickel isotopes to understand where nickel comes from in soils or water, and what happens to nickel between its source and actual reservoir.
Altogether, these approaches and tools give un the key to understand the transfer of nickel from the soil or metallurgical wastes to the surficial water (soil solution, lake water, river water) and finally to organisms.
One health
One planet, one health
With
that research, we want to alert people on the impact of anthropogenic activities
on the dispersion of metals naturally present in soils, such as nickel, but not only, and also to discover little-known ecosystems, at least less known
than certain large biomes, but which are also essential for environmental
health.
Teams and support
Teams and support
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Environmental Health: the issue of ultramafic ecosystems
Existence of original environments developed on ultramafic rocks
Why are they original?
Presence of nickel hyperaccumulating plants
Economical interest of those areas for metals like nickel, cobalt, …
Economical interest of those areas for metals like nickel, cobalt, …
Anthropogenic pressure
Our research
Our research
Our research
Our research
One planet, one health
Teams and support