Transcript sources of pahs

Atmospheric vs Biological
sources of polycyclic aromatic
hydrocarbons ( PAHs) in a
tropical rain forest
Author: Krauss et. Al
Presentation : Prasesh Sharma
PAH (polyaromatic hydrocarbons)
Larger systems of benzene
ring structure fused together
is called PAH
Benzene
Anthracene
Chemistry of the structures is
the same but usually more
reactive then benzene
Naphthalene
Phenanthrene
Perylene
Sources of PAHs
• PAHs mainly arise from combustion-related or
oil-related man-made sources.
– burning of coal, oil, gas, wood, tobacco, rubbish, and
other organic substances.
– also present in coal tars, crude oil, and petroleum
products such as asphalt.
• ubiquitous environmental contaminants
• natural sources : forest fires and volcanoes,
Effects of PAH
•
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Short-term : irritation, nausea,
Long term : Carcinogenic
Reproductive failures
Kidney, liver damage, jaundice
Bioaccumulates rapidly in aquatic life
Introduction
• PAH burden in temperate env– mostly pyrogenic
• Burning of fossil fuels, coal, oil refining etc
• Essential to understand and predict the global
dynamics and trends of these compounds
• Tropical rain forest : limited knowledge of its distribution
• Recently, biological sources of PAHs have been known.
GENERAL INFORMATION
• Evidence of NAPH derived from its presence in Magnolia
• NAPH produced by a muscodor vitigenus
(endophytic fungus)
• High concentration in termite nests- forms a part of the termite
defensive system.
• Comparision of 13C between termite nests and fossil fuel derived
PERY : bio. production occurs in termite nests
• Look for natural sources or PAHs production
Objective
• To monitor PAH concentration in different
compartments of a tropical rain forest
• Assess sources of PAHs ( atm.Vs bio.)
by examining their distribution and relating PAHs
concentrations in air to those in external plant parts.
Study site
• 30km north or Manaus,
Brazil.
• Lowland, tropical rain
forest region mixed with
fallow land, agricultural
land and secondary
forests.
Sampling and analyses
•
SAMPLING
– Particulate and gaseous PAHs in air by membrane pump
– Plant samples : stem, twigs, bark, leaves
– Termite nests sampled : inner wall, outer wall, nursery and gallery
– Soil samples, Litter layers : oil, dead leaves, dead plants, and other
organisms collected on the ground
– Samples were also taken in urban areas for comparision.
•
Plant samples from 1 primary and 3 secondary forests.
•
Analysis
– PAHs extracted by Gas Chromatography and quantified with Mass
Spectrometry
Gas Chromatography
For separation of volatile organic compounds
Mass Spectrometry
Calculations
• Sum of all concentrations : ∑21 PAHs
• 18 pyrogenic + 3 possibly biogenic
(NAPH, PERY, PHEN)
• Sum of 18 pyrogenic concn: ∑18 PAHs
Results : Plants
• Highest concentration of PAHs in the following order
– Leaves >bark > twigs > stem
• ∑18PAHs follow same trend as ∑21PAHs, except
NAPH
• Biological production of PAHs assessed !
• In case of PHEN : remarkably high concentrations in
bark and twigs - > via biogenesis.
Results: Plant-air distribution
Log KOA : octanol-air coefficient
Log KLA : avge. concentration in
air
Octanol-air coef. = [K]octanol/[K]air
The octanol-air partition coefficient is
a measure of chemical partitioning
between the atmosphere and the
organic matter in the environment.
Results: Plant-air distribution
• All PAHs plotted show plant-air distribution that fits well into the
perception of PAH uptake by plants from air
• Proof that source of most PAHs is the atmosphere.
• However, NAPH behaves differently
• NAPH – very high concentrations in plant tissue to that in air !!!
• To reach those concentration levels by equilibrium partitioning =>
concentration of NAPH in air must be 50 times higher.
Results : Mineral Topsoil
• Fate of PAHs during organic
matter transformation from
litter to mineral soil acsessed
• Enrichment factor of >1 in the
topsoil compared to the litter
layer.
• PERY about 4 times than
other compounds: microbial
synthesis of PERY in soil !
Results : Termite nests
Log KOWA ( outer wall-air ) vs Log KOA
Similarity to earlier log plots
Regression line only for log KA < 7.5
Results : Termite nests
• Nest is made up of : digested dead or living wood.
• Concentration of 18PAHs higher in the outer wall and the
gallery => pyrogenic deposition
• Higher concentrations of NAPH than expected in outer
wall and gallery … same case as in plant air distribution
• Higher concentration of NAPH and PERY in central part
of the termite nests.
Conclusions
• Naphthalene by far the most abundant PAH in the
whole ecosystem
• Most PAHs derived from biomass or fossil fuel
combustion and is distributed in the atmosphere.
• Numerous local biological sources of PAHs are
present, more research is needed in the area !!!
• Similarity in patterns to temperate regions
References
• Wilcke et.al 2003 , PAHs patterns in climatically
different ecological zones of Brazil
• http://www.atl.ec.gc.ca/epb/envfacts/pah.html
• http://www.separationsnow.com/basehtml/SepH/1,,1-57-0-51405-ezine-0-2,00.html
• http://oz.plymouth.edu/~chrisc/FishResBAFFM.htm
• http://emsi.osu.edu/emsi_kids/PAH.htm