Degradation of herbicides in shallow Danish aquifers: an integrated laboratory and field study

Abstract

Degradation of pesticides in aquifers has been evaluated based on a number of co-ordinated field and laboratory studies carried out in Danish aquifers. These studies included investigations of vertical and horizontal variability in degradation rates from the vadose zone to an aquifer, the effects of aerobic versus anaerobic conditions, and the importance of concentration on degradation kinetics for a selected range of herbicides. The studies were based on different experimental approaches ranging from simple batch experiments to column studies to field injection experiments and, where appropriate, results were compared. Some herbicides were degraded under aerobic conditions (some phenoxy acids, DNOC and glyphosate) and others under aerobic conditions (other phenoxy acids, DNOC; there was some indication of atrazine transformation). Certain pesticides were not degraded in any investigations (dichlobenil, the dichlobenil metabolite 2,6-dichlorobenzamide (BAM), bentazone, isoproturon, metamitron and metsulfuron-methyl). The spatial variability was substantial, since hardly any of the investigated pesticides were degraded in all comparable samples. This means that it is very difficult to claim that a given pesticide is readily degradable in aquifers. However, the experimental approaches used (with incubations lasting more than a year) may not be sensitive enough to verify the low degradation rates that may be significant as a result of the long retention time of groundwaters.

Impact of Basic Soil Parameters on Pesticide Disappearance Investigated by Multivariate Partial Least Square Regression and Statistics

“…Thus, sampling from deeper soil horizons and incubating in batch may cause a bias in the results, and the representativeness of the results generated by techniques such as batch experiments, column experiments, and in‐field experiment is an important issue for debate. Some comparison studies have been made (Di et al, 1998; Beulke et al, 2000; Mills et al, 2001; Albrechtsen et al, 2001; Gaus and Casteele, 2004; McDonald et al, 2006) and it is clear that further studies are required to identify and characterize the sources of uncertainty in the output generated by the models (Soulas and Lagacherie, 2001; Dubus et al, 2003; Massey and Lenoir, 2003; Bending et al, 2006). However, a review of the present state of the methodology has identified laboratory dissipation studies as the preferred approach (Soulas and Lagacherie, 2001).…”

Pesticide fate and behaviour in the UK Chalk aquifer, and implications for groundwater quality

“…Walker et al (2001) found a five-fold variation in degradation rate over a single field with nominally uniform soil characteristics, together with differences in degradation kinetics. In Denmark, Kristensen et al (2001) also observed large variations in rate and extent of mineralization of mecoprop and isoproturon in a chalk aquifer, and Albrechtsen et al (2001) reported substantial spatial variability in herbicide degradation in a range of shallow aquifers. Earlier work by Heron & Christensen (1992) had noted different patterns and rates of mecoprop degradation for groundwater collected from boreholes only 2-10 m apart.…”

In Situ Exposure to Low Herbicide Concentrations Affects Microbial Population Composition and Catabolic Gene Frequency in an Aerobic Shallow Aquifer

“…It is only in the past few years that microbial acclimation to herbicides in subsurface aquifer environments has been investigated (1,24,37). Most of these studies involved laboratory incubation and primarily focused on the activity and rate of herbicide degradation.…”