ESR11 Daniel B. Garcia Jorgensen

Project: Natural toxin fate and leaching from soils

Principal supervisor: Prof. Hans Chr. B. Hansen

Intro to project:

In the history of environmental pollution research most attention has been paid to pollutants of human origin such as PCBs, DDT, dioxins, PAHs, drugs, etc. While these human pollutants have caught much public attention, some recent research has indicated that natural toxins might pose a risk for human health. Natural toxins in America have been suggested to represent 99.99% of all pesticides present in the human diet. The hazard of natural toxins depends on factors such as toxicity, load and fate in the environment. Plants are the source of natural toxins, they may be released continuously and in higher amounts, but the release from plants to soils is poorly or not quantified. One example is bracken fern (Pteridium aquilinum), a widely distributed species throughout the world. It produces different toxins, but ptaquiloside is the most studied, as it is present in high concentrations and it has carcinogenic properties.

The overall objective of this Ph.D. project is to develop a model that is able to predict the fate of natural toxin in the unsaturated zone at pedon-scale. Two different toxins will be assessed, ptaquiloside and lupinine (produced by Lupinus spp). The fate of these toxins will be assessed at different levels, from horizon scale with batch experiments, to pedon-scale with soil column experiments and field data. The soil-plant-atmosphere model program DAISY is used for modelling the behavior of the toxins in the soil. The model is being developed and different functions have been implemented to improve the performance of the model to the particular characteristics of natural toxins. These functions introduce important processes such as: toxin development in the plant based on biomass, hydrolysis as a separate degradation process, toxin release from the plants and recovery of the toxin content after precipitation events.

Monitoring programs for the two different toxins will be carried with the purpose of calibrating and validating the models. After validation, the models will be used for assessing the fate and leaching of natural toxins on different locations throughout Europe. Moreover, future scenarios will be performed to assess the effect of Climate Change on leaching of natural toxins.

So far, results has been obtained for bracken biomass production, release of ptaquiloside from the plant and degradation in different soil materials. The concentrations found in the wash off water were in the range of 0-1.2 mg/l, being highly heterogeneuos. Furthermore, the degradation studies showed that ptaquiloside presents a half-life in the range 3.3-105 hours (at a constant temperature of 10oC). The results are proof of the challenge that pose natural toxin fate modelling due to spatial and temporal variation in the different processes.