The Use of Compound-Specific Isotope Analysis to Assess the Degradation Potential of Pesticides in Deep Aquifers - PESTDEGRADE

Coordinating Institution: CRP Henri Tudor
Contracting Partner(s): Administration de la Gestion de l'Eau
Other Partner(s): Helmholtz Zentrum, München (D)
From: 01/04/2010
To: 31/03/2012
Budget: 259,000.00€
Contact(s): Bayerle Michael , Zwank Luc

Summary

In previous projects it has been shown that Luxembourg’s groundwater resources used for drinking water production are contaminated with trace levels of a series of pesticides from different sources. The Luxembourg Sandstone is the aquifer providing the majority of drinking water supplies in Luxembourg. This fractured rock aquifer can be regarded as a double porosity system with fractures as transport channels and sandstone porosity as reservoir.

Depending on the local distribution of fracture and pore volumes mean water residence times in the aquifer can vary substantially. The FNR SPRING project investigates groundwater residence times with conceptual models and groundwater dating methods. The results of the groundwater dating methods indicate ages of up to 20 years.

Typically, the determination of the environmental fate of phytosanitary compounds considers mainly degradation rates that apply for the topsoil. This can be explained by the fact that the few reported degradation rates in deeper aquifers are generally up to 2 orders of magnitude slower than in the upper first centimeters of agricultural soils. Considering the previously mentioned high residence times, a significant attenuation of pesticide concentrations in the saturated zone and consequently in the spring outcrops cannot be excluded. The regulatory framework for the registration of phytosanitary products requires specifications on their environmental fate. Different approaches including laboratory batch experiments and field-scale tests as well as modelling of pesticide leaching and degradation are applied to assess the environmental risks associated with pesticide applications. Since the degradation half-life of any given pesticide is a very essential and sensitive parameter in pesticide fate models, a better understanding of the degradation potential in deep aquifers is of strong interest. Determining the actual existence and if possible the rate of pesticide degradation in the aquifer is therefore of pivotal importance for sound pesticide modelling and water resources management. Compound-specific stable isotope analysis (CSIA) is a new promising tool to allow such insight into naturally occurring degradation processes in deep regions of the aquifer. This approach relies solely on information contained in the investigated molecules and does not depend on tracer tests, transport modelling or even detection of metabolites. By analyzing the isotope values of organic trace compounds, it records the fingerprint of different sources and can pick up the footprint of chemical and/or biological transformation that the compounds have undergone. A major challenge of the project will consist in adapting existing analytical preconcentration methods in order to achieve sufficient sensitivity to measure stable isotope compositions in the target analytes at concentrations in the low to medium ng/L range.