Leaching of Br−, metolachlor, alachlor, atrazine, deethylatrazine and deisopropylatrazine in clayey vadoze zone: A field scale experiment in north-east Greece

• Published in: Water research (Oxford) 2012-04, Vol.46 (6), p.1979-1989
• Main Authors: Vryzas, Zisis, Papadakis, Emmanuel Nikolaos, Papadopoulou-Mourkidou, E.
• Format: Article
• Language: English
• Subjects: Acetamides - analysis; Agriculture; Aluminum Silicates - chemistry; Applied sciences; Atrazine - analogs & derivatives; Atrazine - analysis; Brilliant blue; Bromides; Bromides - analysis; Clay; Environmental Monitoring; Exact sciences and technology; Greece; Herbicides; Ions; Leaching; Pollution; Preferential flow; Soil - chemistry; Spraying spatial variability; Suction cups; Water Pollutants, Chemical - analysis; Water treatment and pollution
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2012.01.021

An extensive four-year research program has been carried out to explore and acquire knowledge about the fundamental agricultural practices and processes affecting the mobility and bioavailability of pesticides in soils under semi-arid Mediterranean conditions. Pesticide leaching was studied under field conditions at five different depths using suction cups. Monitoring of metolachlor, alachlor, atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA), and bromide ions in soil water, as well as dye patterns made apparent the significant role of preferential flow to the mobility of the studied compounds. Irrespective to their adsorption capacities and degradation rates, atrazine, metolachlor and bromide ions were simultaneously detected to 160 cm depth. Following 40 mm irrigation, just after their application, both alachlor and atrazine were leached to 160 cm depth within 18 h, giving maximum concentrations of 211 and 199 μg L−1, respectively. Metolachlor was also detected in all depth when its application was followed by a rainfall event (50 mm) two weeks after its application. The greatest concentrations of atrazine, alachlor and metolachlor in soil water were 1795, 1166 and 845 μg L−1, respectively. The greatest concentrations of atrazine’s degradation products (both DEA and DIA) appeared later in the season compared to the parent compound. Metolachlor exhibited the greatest persistence with concentrations up to 10 μg L−1 appearing in soil water 18 months after its application. Brilliant blue application followed by 40 mm irrigation clearly depict multi-branching network of preferential flow paths allowing the fast flow of the dye down to 150 cm within 24 h. This network was created by soil cracks caused by shrinking of dry soils, earthworms and plant roots. Chromatographic flow of the stained soil solution was evident only in the upper 10–15 cm of soil. [Display omitted] ► Atrazine, alachlor and metolachlor residues up to 1795, 1166 and 845 μg L−1, were respectively detected. ► Metolachlor, atrazine, DEA and DIA were detected in 99, 95, 91 and 67% of samples. ► Alachlor was detected in soil water sample 39 months after its application. ► Chromatographic flow was restricted in the first 10–15 cm depth. ► Irrigation or rainfall after a dry period favor preferential flow in clay-loam soils.