A Study of Suspended and Colloidal Matter in the Leachate from Lysimeters and its Role in Pesticide Transport

Abstract

The relative importance of suspended (>0.45 µm) and organic colloidal (<0.45 µm) matter in the transport of pesticide through and across a soil was studied by monitoring suspended and colloidal matter from lysimeters over a winter (1994–1995) and relating it to the leaching of pesticides. The major results were: (i) The organic colloidal matter and suspended sediment appeared at different times in the leachate. (ii) The suspended sediment was enriched in total organic carbon (TOC). (iii) The leaching of pesticide occurred largely in first few samples following rainfall, coinciding with the occurrence of the colloidal matter. (iv) Modelling the distribution of pesticide between the colloids, suspended matter, and pure solution suggests that negligible amounts of isoproturon are carried on suspended sediment and the organic colloids are more important. The importance of organic colloids may be even more significant for compounds more hydrophobic than those studied here: this has implications for the management of soils and pesticides in relation to the release of organic colloids into solution.

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

“…One possibility is that pesticides are also transported sorbed onto organic colloidal particles, which the solid extractions would detect and ELISA would not. This possibility was suggested by Foster et al (1991) and its role in pesticide transport in clay soils was investigated by Worrall et al (1999) using shallow lysimeters. If this were occurring the methanol extractions would be measuring pesticides sorbed onto colloidal particles of material with much greater adsorption potential than the chalk matrix itself, and whose downward progress has been restricted by the narrow apertures or constrictions of microfractures.…”

Simulated rainfall study for transport of veterinary antibiotics – mass balance analysis

“…However, this result could be explained by colloids acting as a transport carrier. In fact, a previous study showed that a strongly sorbed pesticide could be transported into subsoil via a colloid-facilitated transport mechanism [34][35][36][37]. In contrast, the sorption capability of STZ and SMT is much less than that of TC and CTC [29,38,39], leading to the expectation that the highest mass of STZ was calculated to be at the very bottom of the soil profile.…”

Lessivage as a major process of soil formation: A revisitation of existing data

“…Mechanical stresses such as wetting/drying cycles (Kaplan et al, 1993), freezing/thawing cycles (Worrall et al, 1999) and moving water impose shear stress; all these processes act on soil particle mobilisation (Ryan et al, 1998;Shang et al, 2008). Experiments conducted by Kjaergaard et al (2004b) and Majdalani et al (2008) showed that the rate of mobilisation is related to the drying intensity i.e.…”