This conference presentation describes the invention of molecular carbon-13 dating, a relative dating method that allows to mesure the relative age of organic substances in complex. This invention is based on the discovery of temporal pools of molecular susbtances in soils. The findings open a new scientific field, named Molecular Chronology, to study the source, transformation, persistence, sequestration, transfer and toxicity of organic substances in complex media, such as living organisms, food, soil, waters and sediments. Similarly to sedimentary stratigraphy that uses layers to date sediments, molecular chronology uses temporal pools to date molecules. As a consequence, any biological or environmental samples becomes a 'fossil record' of substances of different age. Molecular chronology is thus expected to deliver new knowledge in all fields studying complex systems, such as biology, medicine, food science, agronomy, environmental science, soil science and geology. This is an invited conference at SIL2018, the Congress of the International Society of Limnology, in Nanjing, August 2018.

1. Invention of Carbon 13 Dating
and Molecular Chronology
Eric LICHTFOUSE
Aix-Marseille University
Chief Editor, Environmental Chemistry Letters
SIL2018 Nanjing Publications: https://cv.archives-ouvertes.fr/eric-lichtfouse

2. Old materials in modern media
A glass of water contains 2,000 water molecules from the
last glass of water drank by Julius Caesar, 100-44 BC

3. Pollutant societal issues
8.4 million people deaths caused by pollution each year
All natural media and living organisms are contaminated
Pesticides in
suface waters
2017

4. Pollutant scientific issues
Sources? Transfer? Persistence? Health risk?
How much time a pollutant stays in a complex system?

5. Bound residues
Unknown sequestration and release mechanisms
Dating is actually limited to sedimentary studies

6. Compound specific
isotope analysis
Access to 13C composition of
individual substances in
complex media
Invented by Prof. John Hayes
Analusis 23, 364 (1995)
Rapid Commun Mass Spectrom 14, 1337 (2000)

7. 13C Labelling
Natural or artificial
Soils, sediments, water, living organisms...
Reveals sources and dynamics
Few studies at the molecular level
First 13C analysis of soil
Individual compounds
Org Geochem 22, 349 (1994)
Tetrahedron Lett 36, 529 (1995)

8. Discovery of temporal pools
Hypothesis: encapsulated substances are older
We fractionated a soil sample into six pools
13C analysis of the soil C31 n-alkane

9. Carbon 13 dating
Calculation using first order kinetic law
C31 alkane trapped in humin is older
C31 alkane in large particles is younger
Can be applied to any media, any isotope
C31 ALKANE IN: d13C
(‰)
Maize-C
(%)
Relative age
(years)
Bulk soil extraction -28.1 50.33 0
Humin extract -29.7 39.74 - 6.7
Humin pyrolysate -29.7 39.74 - 6.7
0-50 µm fraction -27.3 55.63 + 3.2
50-200 µm fraction -24.3 74.50 + 21.1
200-2000 µm fraction -24.0 77.48 + 25.1
Env Chem Lett 10, 97 (2012)

10. Mecanism of
encapsulation
Isotopic difference: humin-bound
compounds are really bound
Not a lack of exhaustive extraction, as
pointed by reviewers…
Humin-bound alkane are trapped by non-
covalent bonds
Naturwissenschaft 85, 449 (1998)

11. Sources of alkanes
in cultivated soils
C16 : not labelled – fossil
C27 : labelled – plant derived
Absence of labelling in a system
is also significant
Geochim Cosmochim Acta 61, 1891 (1997)
Time (years)
d13C (‰)

12. Sources of PAH in
cultivated soils
PAH: not labelled - fossil
Organic C: labelled – plant
derived
Org Geochem 26, 353 (1997)

13. Sources of fatty
acids in soils
Labelling with 13C-glucose
Short-chain: labelled - microbes
Long-chain: not labelled – plant derived
Org Geochem 23, 849 (1995)

14. Reconstruction of
fossil fuel pollution
- Plant n-alkane d13C -30‰
- Fossil fuel n-alkane d13C -35‰
Calculation of fossil fuel C% in
each compound
Env Chem Lett 10, 97
Org Geochem 23, 969 (1995)

15. Biogenic links of compounds in sediments
Green River sediment, 60 million years old
n-Alkanes and fatty acids have similar biological source
Tetrahedron Lett 33, 8093 (1992)
COOH

16. Conclusion 1: a new science: Molecular Chronology
10 years
20 years
30 years
Stratigraphy
Geochronology
- Use layers
Molecular chronology
- Use temporal pools
KNOWN NEW

17. Conclusion 2: invention of carbon 13 dating
Can be applied to any organic substance in complex media
Can be used in any complex media labelled naturally or articicially
Other isotopes are possible
Biology
Medicine
Food
Science
Environmental
Science
Soil Science Water Science
Geology

18. Conclusion 3
Collaborations to develop 13C dating and molecular
chronology are welcome
Eric.Lichtfouse@inra.fr
Biology
Medicine
Food
Science
Environmental
Science
Soil Science Water Science
Geology