Atmospheric vs Biological sources of polycyclic aromatic

hydrocarbons ( PAHs) in a tropical rain forest

Author: Krauss et. Al

Presentation : Prasesh Sharma

PAH (polyaromatic hydrocarbons)

Benzene

Naphthalene

Anthracene

Phenanthrene

Larger systems of benzene ring structure fused together is called PAH

Chemistry of the structures is the same but usually more reactive then benzene

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

• 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.

• 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

GENERAL INFORMATION

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.

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

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 !

Log KOWA ( outer wall-air ) vs Log KOA

Regression line only for log KA < 7.5

Similarity to earlier log plots

Results : Termite nests

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,,1-5-7-0-51405-ezine-0-2,00.html

• http://oz.plymouth.edu/~chrisc/FishResBAFFM.htm

• http://emsi.osu.edu/emsi_kids/PAH.htm