Eﬀect of soil amendments on sorption and mobility of metribuzin in soils Kaushik Majumdar, Neera Singh * Division of Agricultural Chemicals, Indian Agricultural Research Institute, New Delhi 110 012, India Received 1 February 2006; received in revised form 29 July 2006; accepted 31 July 2006 Available online 14 September 2006 Abstract Metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one), is weakly sorbed to soil therefore, leaches easily to lower soil proﬁles. Soil amendments play a signiﬁcant role in the management of leaching losses of pesticides. Therefore, present study reports the eﬀect of organic manure and ﬂy ash amendments on metribuzin downward mobility in sandy loam soil columns. Application of animal manure [T-1(OM) and T-2(OM)] and ﬂy ash [T-1(FA) and T-2(FA)] at 2.5% and 5.0% levels increased the metribuzin retention in the soil. Freundlich constant [K f (1/n)] values of metribuzin for treatments T-1(OM) and T-2(OM) were 0.70 and 1.11, respectively, which were signiﬁcantly higher than the value (0.27) in natural soil (T-0). The respective values for treatments T-1(FA) and T-2(FA) were 1.80 and 4.61. Downward mobility of metribuzin was studied in packed soil columns [300 mm (l) · 59 mm (i.d.)]. Both the amend- ments signiﬁcantly reduced the downward mobility of metribuzin and aﬀected breakthrough time and maximum concentration of metribuzin in the leachate. Leaching losses of metribuzin were decreased from 97% in natural soil (T-0) column to 64% [T-1(OM)] and 42% [T-2(OM)] for animal manure-amended columns and 26% [T-1(FA)] to 100% [T-2(FA)] for ﬂy ash-amended columns, as metribuzin did not leach out of 5% ﬂy ash-amended column. Study indicates that both animal manure and ﬂy ash were quite eﬀective in reducing the downward mobility of metribuzin in packed soil columns of a sandy loam soil. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Metribuzin; Sorption; Leaching; Organic manure; Fly ash 1. Introduction Presence of pesticides in ground water resources has grown in the past few years and has become an intensive and burning issue of discussion. Groundwater contamina- tion not only aﬀects the health of human beings as it is being directly used for drinking purpose, but also can act as a source of contamination for food chain, when used for irrigation. Metribuzin (4-amino-6-tert-butyl-4,5-dihy- dro-3-methylthio-1,2,4-triazin-5-one), a triazine herbicide, is used as selective herbicide for pre-emergence and post- emergence control of annual grasses and broadleaf weeds in sugarcane, soybean, wheat, etc. Metribuzin is weakly sorbed in soils and has potential of lateral and downward movement in the soil (Peter and Weber, 1985; Harper, 1988; Kim and Feagley, 1988; Bedmar et al., 2004). Hall- berg (1989) provided a summary of several reports of metribuzin detection in the groundwater. Reports suggest that leaching of metribuzin to lower soil proﬁles is the main factor responsible for loss in its activity (Peek and Appleby, 1989; Mpofu, 1991). Soil amendments can play a crucial role in the manage- ment of run oﬀ and leaching losses of pesticides. Any amendment to soil changes its physico-chemical properties, which in turn, aﬀect the sorption, transport and degrada- tion of the soil-applied pesticides. In soil, the organic mat- ter and clay fractions are the major constituents which aﬀect the sorption–desorption behaviour of pesticides (Chiou et al., 1979; Karickhoﬀ et al., 1987). Application of organic carbon in the form of compost, sludge, eﬄuent and crop residues is a common agronomic 0045-6535/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2006.07.095 * Corresponding author. Tel.: +91 11 25841390; fax: +91 11 25846420. E-mail address: drneerasingh@yahoo.com (N. Singh). www.elsevier.com/locate/chemosphere Chemosphere 66 (2007) 630–637