E. Lichtfouse et al., ANCIENT POLYCYCLIC AROMATIC-HYDROCARBONS IN MODERN SOILS - C-13, C-14AND BIOMARKER EVIDENCE, Organic geochemistry, 26(5-6), 1997, pp. 353-359
Polycyclic aromatic hydrocarbons (PAHs) of soils from two maize growin
g fields were analyzed for molecular structure by gas chromatography-m
ass spectrometry, for C-13/C-12 ratios by isotope ratio mass spectrome
try and for C-14 age by accelerator mass spectrometry. These investiga
tions indicate that the aromatic fractions are dominated by pyrolytic
inputs. Calculation of molecular maturity parameters based on hopanes
and PAHs gives values typical of high thermal stress such as exhibited
by high rank coals and petroleums with equivalent vitrinite reflectan
ces of similar to 0.6-1.5%. The interpretations based on molecular com
positions are corroborated by isotopic data. Specifically, both the ab
sence of C-13/C-12 variations in the aromatic fractions during 23 year
s of maize cropping, and a C-14 age greater than 9820 years demonstrat
e that these substances are not derived by the aromatization of modem
plant material or soil biomass. Together, these results show that soil
PAHs are mainly of pyrolytic origin, e.g. exogenous (airborne) contri
butions of fossil fuel combustion products and (old) vegetation fires,
with a small contribution of uncombusted fossil fuels. This approach
using molecular and isotope information represents a promising way to
study the fate of ancient, reworked, fossil organic matter in modern m
edia such as soils, sediments, plants, air and food. (C) 1997 Elsevier
Science Ltd.