Soil fate and leaching of the natural carcinogen ptaquiloside
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DWRIP 2014 KU-SCIENCE. Soil Fate and leaching of the natural carcinogen ptaquiloside.

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Soil Fate and leaching of the natural carcinogen ptaquiloside

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  • DWRIP 2014 KU-SCIENCE

Soil Fate and leaching of the natural carcinogen ptaquiloside

Hans Christian Bruun Hansena, Lars H. Rasmussenb, Frederik Clauson-Kaasa, Ole Stig Jacobsenc, Rene K. Juhlerc, Søren Hansena, and Bjarne W. Strobela

a Department of Plant and Environmental Sciences, KU-SCIENCE

b Metropolitan University College

c Department of Geochemistry, Geological Survey of Denmark and Greenland (GEUS)


  • Azores, Portugal

  • Bracken form dense ”mats”

  • Præstø Fed, Denmark

  • Bracken is ”invasive” – and outcompetes other vegetation.


  • DWRIP 2014 KU-SCIENCE

Why is this important?

  • Bracken is one of very few plants known to cause cancer in animals

  • Bracken is everywhere in Nature; 5th most abundant plant on Earth

  • The carcinogen in Bracken is produced in high amounts (up to 1 % dw)

  • The carcinogen is very mobile in soil and water

  • Several exposure routes for humans (air, milk, meat, drinking water)

  • Little is known


  • DWRIP 2014 KU-SCIENCE

A well known carcinogen in animals

- Examples for cattle -

  • Bovine enzootic haematuria (BEH): Tumours in the urinary bladder of cows and sheeps. Recognized worldwide. Test animals fed bracken produce similar symptoms.

  • Upper digestive tract carcinomas: Ususally seen in conjunction with papillomavirus that infects the mucosa of the upper digestive tract in cattle. In presence of PTA papillomas transform to carcinomas


  • DWRIP 2014 KU-SCIENCE

Exposure routes for humans

  • Aranho, P (2013)


  • DWRIP 2014 KU-SCIENCE

  • Bracken norsesquiterpene glycosides and hydrolysis products

  • Hydrolysis

  • products


  • DWRIP 2014 KU-SCIENCE

  • Hydrophobic

  • Hydrophilic

  • PTA amphiphilic


  • DWRIP 2014 KU-SCIENCE

  • Methods used for determination of PTA and PTB


  • DWRIP 2014 KU-SCIENCE

PTA production, distribution and hydrolysis in soil and water


  • DWRIP 2014 KU-SCIENCE

Bracken growth, PTA contents and PTA loads

  • PTA contents in fronds during growing season at different sites in DK and UK

  • PTA in fronds (ug g-1)

  • Aug

  • PTA content in fronds per m2 land surface during growing season at different sites in DK

  • 300 mg m-2 = 3 kg ha-1

  • PTA load (mg m-2)

  • May

  • Rasmussen (2003)

  • Julian day number


  • DWRIP 2014 KU-SCIENCE

High variation in PTA content between bracken populations

  • Rasmussen (2003)


  • DWRIP 2014 KU-SCIENCE

  • Hydrolysis of PTA

  • kA = 25.7 h-1 M-1; kN = 9.49 10-4; h-1 M-1; kB = 4.83 104 h-1 M-1

  • - Half-lives at pH 4, 6 and 8 (25 oC): 8 d, 20 d, and 0.6 d

  • - Low temperatures increase half-lives considerably

  • Ayala et al. (2006)


  • DWRIP 2014 KU-SCIENCE

  • Microbial contribution to PTA degradation

  • Degradation of PTA in soils at field moisture and 10 oC with initial PTA concentration of 25 g kg-1

  • Fast reaction: Abiotic

  • Slow reaction: Biotic + Abiotic

  • open symbols: sterilized; closed symbols: untreated soil

  • Ovesen et al. (2008)


  • DWRIP 2014 KU-SCIENCE

Can degradation in soil be attributed to hydrolysis in solution phase?

  • Hydrolysis in soil solution

  • Kinetics of PTA degradation in soil solutions from sandy and clayey top- and subsoils (10 oC).

  • Open symbols represent solutions filtered (0.2 µm) before incubation; closed symbols unfiltered solutions.

  • !! No significant hydrolysis

  • PTA is stabilized in soil solution!

  • pH 4.5 - 7

  • Ovesen et al. (2008)


  • DWRIP 2014 KU-SCIENCE

Leaching


  • DWRIP 2014 KU-SCIENCE

  • PTA and PTB in shallow groundwater at Bracken infested areas

  • Study sites

  • Sampling in small inspection wells.

  • Determination of PTA and PTB by a SPE-LC-MS/MS

  • Clauson-Kaas et al. (2014)


  • DWRIP 2014 KU-SCIENCE

  • PTA and PTB distribution in soil

  • PTAw, PTBw: Extracted with water

  • PTBa: Extracted with methanol

  • -PTA concentrations highest in the litter layer, but much higher total quantities in the mineral soil

  • Higher PTB than PTB concentrations in mineral soil

  • PTB as ”memory” effect of PTA?

  • Clauson-Kaas et al. (2014)


  • DWRIP 2014 KU-SCIENCE

  • Observed groundwater concentrations of

  • PTA and PTB (µg L-1)

  • T = trace

  • -PTA could be detected at all sites

  • -Max. PTA concentration observed 0.09 ug L-1; max PTB observed 0.49 ug L-1.

  • -Big variations over time!

  • Clauson-Kaas et al. (2014)


  • DWRIP 2014 KU-SCIENCE

  • Observed concentrations of PTA in pond

  • water near Bracken stands (µg L-1)

  • T = trace

  • -PTA detected in all surface waters

  • -max. PTA concentration 1.1 g L-1; max. PTB concentration 0.56 g L-1.

  • -Large temporal and spatial variation

  • Clauson-Kaas et al. (2014)


  • DWRIP 2014 KU-SCIENCE

  • Modelling of PTA leaching from a sandy soil using the DAISY Plant-Soil-Water model

  • - First attempt -

  • PTA production: Biomass production data of Rasmussen and Hansen (2002)

  • PTA in biomass: 200 g g-1 DM (low)

  • PTAsoil transfer:Leaching from fronds (Rasmussen et al., 2003), and decaying plants (frost for 3 consecutive days)

  • Soil: Sandy soil (Præstø), 2 - 6 % of clay

  • Hydraulic properties estimated according to Mualen and van Genuchten

  • PTA degradation: Model from Ovesen et al. (2008)

  • Climate data:Data for Zealand (Højbakkegaard) 1962 - 2001 used.

  • Modelling:Leaching modelled for the period 1962 - 2001, and for a selected 1-year period (1967 - 1968).


  • DWRIP 2014 KU-SCIENCE

  • Modelling results for the period 1962 - 2002

  • Separate degradation rate constants have been used for O, A and B soil horizons for fast and slow degrading PTA pools

  • Annual total PTA addition to soil 1.6 kg ha-1.

  • Note the extremely variable soil contents and amounts of PTA leached


  • DWRIP 2014 KU-SCIENCE

  • Conclusions

  • PTA proven animal and suspected human carcinogen.

  • PTA production of kg ha-1 y-1. High spatial and temporal variation.

  • Initial PTA degradation due to hydrolysis; highly sensitive to pH and temperature. Apparent stabilization in soil water

  • Fast abiotic and slower biotic degradation of PTA in soil; stabilization of PTA in soil by clays.

  • Sorption of PTA in soil is insignificant  fast leaching

  • PTA and PTB present in groundwater and surface water; µg L-1 to ng L-1 range

  • Groundwater and surface water monitoring is strongly needed; high time and spatial resolution is critical.


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