Spatial variability in¹⁴C‐herbicide degradation in surface and subsurface soils

Abstract

The spatial variability in mineralization of atrazine, isoproturon and metamitron in soil and subsoil samples taken from a 135-ha catchment in north France was studied. Fifty-one samples from the top layer were taken to represent exhaustively the 31 agricultural fields and 21 soil types of the catchment. Sixteen additional samples were collected between depths of 0.7 and 10 m to represent the major geological materials encountered in the vadose zone of the catchment. All these samples were incubated with 14C-labelled atrazine under laboratory conditions at 28 degrees C. Fourteen selected surface samples which exhibited distinctly different behaviour for atrazine dissipation (including sorption and mineralization) were incubated with 14C-isoproturon and 14C-metamitron. Overall soil microbial activity and specific herbicide degradation activities were monitored during the incubations through measurements of total carbon dioxide and 14C-carbon dioxide respectively. At the end of the incubations, extractable and non-extractable (bound) residues remaining in soils were measured. Variability of herbicide dissipation half-life in soil surface samples was lower for atrazine and metamitron (CV < 12%) than for isoproturon (CV = 46%). The main contributor to the isoproturon dissipation variability was the variability of the extractable residues. For the other herbicides, spatial variability was mainly related to the variability of their mineralization. In all cases, herbicide mineralization half-lives showed higher variability than those of dissipation. Sorption or physicochemical soil properties could not explain atrazine and isoproturon degradation, whose main factors were probably directly related to the dynamics of the specific microbial degradation activity. In contrast, variability of metamitron degradation was significantly correlated to sorption coefficient (K(d)) through correlation with the sorptive soil components, organic matter and clay. Herbicide degradation decreased with depth as did the overall microbial activity. Atrazine mineralization activity was found down to a depth of 2.5 m; beyond that, it was negligible.

Rhizoremediation of Contaminated Soils by Comparing Six Roots Species in Al-Wafra, State of Kuwait

“…The usage of plants to concentrate toxic mixes from soils (phytoextraction) is being made as a framework for remediation of metal sullied soils [11,34,35]. Phytoremediation is a suitable remediation technique for petroleum contaminated soil based on evidence from greenhouse and field studies.…”

“…Schroll et al [18], Alberty [19], Guillot et al [20], Mastronicolis et al [21], Singh et al [22] are responsible for changes in microbial diversity and for expanded numbers and metabolic activities of microorganisms in the rhizosphere microenvironment, this phenomenon called the rhizosphere effect [10,15,17,23]. Many studies have investigated the effects of soil moisture, temperature, aeration, pH, and organic matter content on the biodegradation of pesticides [11,24]. The age of a plant, the availability of mineral nutrients and the presence of contaminants are responsible of the rate of exudation changes [25].…”

“…Furthermore, it is reducing percolation to the ground water. Plants may also be used to remove contaminants from soil by phytoextraction and then harvested for processing [8][9][10][11]. There are some promising results suggesting that these techniques might become practical alternatives to mechanical and chemical approaches in remediation of metal contaminated soils [5].…”

Biases in the spatial estimation of pesticide loss to groundwater

“…Pesticide data included two parameters: the half-life, DT 50 (days), of the pesticide and its sorption coefficient normalised by the organic carbon content, K oc (mL/g). Data were either taken from available databases on sorption and degradation properties of pesticides (Dabène et al, 1995;Hornsby et al, 1996) or calculated from measured laboratory data (Coquet and Barriuso, 2002;Charnay et al, 2005).…”

“…These "generic" assessments will be compared with others made using local information on K oc and DT 50 and their variability on the catchment scale that has been previously 466 Y. Coquet et al obtained (Coquet and Barriuso, 2002;Charnay et al, 2005). Some general recommendations for local-scale risk assessment will then be drawn.…”