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

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)


  • Bracken form dense ”mats”

  • Præstø Fed, Denmark

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


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


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


Exposure routes for humans

  • Aranho, P (2013)


  • Bracken norsesquiterpene glycosides and hydrolysis products

  • Hydrolysis

  • products


  • Hydrophobic

  • Hydrophilic

  • PTA amphiphilic


  • Methods used for determination of PTA and PTB


PTA production, distribution and hydrolysis in soil and water


Bracken growth pta contents and pta loads

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


High variation in PTA content between bracken populations

  • Rasmussen (2003)


  • 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)


  • 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)


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)


Leaching


  • 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)


  • 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)


  • 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)


  • 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)


  • 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).


  • 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


  • 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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