ESR11 Daniel B. Garcia Jorgensen

Project: Natural toxin fate and leaching from soils

Principal supervisor: Prof. Hans Chr. B. Hansen

Project: This project aimed to develop a soil-plant-water system model to describe the dynamics of natural toxins in the environment, with special focus on leaching of these toxic compounds towards the groundwater. We used the case study of bracken fern (Pteridium aquilinum) and its derived toxin with carcinogenic properties, ptaquiloside (PTA).

First, we adapted the existing soil-plant-water system model DAISY for the specific case of natural toxins. For that, we implemented several functions to account for toxin dynamics in the canopy and release by precipitation. Simulation results showed that approximately 99.9% of the total PTA input to the soil is degraded, while only 0.1% is leached to the groundwater. Secondly, a 2-year monitoring program was performed in a forested area 60 km west of Copenhagen (Denmark) with the goal of creating a dataset to be used for calibration of the model. In the monitoring program, biomass, PTA content in the canopy and soil water concentrations at 50 cm depth were monitored, as well as several weather variables.

The results of the monitoring showed that PTA production in the plant was proportional to the production of biomass, while the mass of PTA being released by precipitation was found to be a function of the volume, intensity and timing of precipitation. The total mass of PTA in bracken canopy peaked in the middle of summer, with values up to 1600 mg m-2. PTA is effectively released from bracken by precipitation, with estimated PTA masses transferred to the soil up to 13 mg m-2 during a single precipitation event.

Furthermore, leaching of PTA through the soil takes place in form of pulses linked to specific precipitation events, with observed average soil water concentrations up to 1.05 µg L-1. These concentrations are several orders of magnitude above the maximum tolerable concentrations for PTA, hence posing a risk towards drinking water quality.