The extractability and mineralisation of cypermethrin aged in four UK soils Katie A. Fenlon ⇑ , Kostas Andreou, Kevin C. Jones, Kirk T. Semple Lancaster Environment Centre, Lancaster University, Lancaster LA1 4YQ, United Kingdom article info Article history: Received 12 August 2010 Received in revised form 7 October 2010 Accepted 7 October 2010 Available online 30 October 2010 Keywords: Cypermethrin Bound residue Mineralisation HPCD abstract Cypermethrin is a widely used insecticide that has caused concern due to its toxicity in the aquatic envi- ronment. As with all land applied pesticides, the most significant source of water pollution is from the soil, either due to leaching or washoff. The behaviour of cypermethrin in the soil controls the likelihood of future pollution incidents, with two of the most significant processes being the formation of bound res- idues and microbial degradation. The formation of bound residues and mineralisation was measured in four organically managed soils from the UK. The formation of bound residues was measured using three different extraction solutions, 0.01 M CaCl 2 , 0.05 M HPCD and acetonitrile. Biodegradation was assessed by measurement of mineralisation of cypermethrin to CO 2 . The formation of bound residues varied according to extraction method, soil type and length of ageing. In two of the four soils studied, acetoni- trile extractability decreased from 100% initially to 12–14% following 100 d ageing. The extent of miner- alisation increased after 10–21 d ageing, reaching 33% of remaining activity in one soil, however following 100 d ageing the extent of mineralisation was significantly reduced in three out of the four soils. As with the formation of bound residues, mineralisation was impacted by soil type and length of ageing. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Cypermethrin is a synthetic pyrethroid used to control biting insects on livestock, crops, domestic animals and in animal houses (Tomlin, 1997), and was the most extensively used insecticide in the UK in 2004 (Garthwaite et al., 2004). Cypermethrin enters the environment as a direct result of use, from washoff from plants and animals and from the disposal of used sheep dips. Whilst cypermethrin has low toxicity to mammals, it is extremely toxic to aquatic invertebrates. Water pollution by pesticides is a result of soil pollution (Merlin et al., 2002) with the extent of water pol- lution controlled by the behaviour of pesticide in soil. The fate and behaviour of pesticides in soil is governed by factors including soil characteristics, compound properties, environmental factors such as temperature and precipitation (Reid et al., 2000) and by the microbial activity of the soil. The most significant processes deter- mining the fate and behaviour of pesticides are the formation of bound residues and microbial degradation, as these control chem- ical persistence and mobility. The bound residue is defined as a ‘chemical species originating from pesticides, used according to good agriculture practice, that are unextractable by methods which do not significantly change the chemical nature of the residue’ (IUPAC). The formation of bound residues occurs when a chemical species becomes bound, adsorbed or entrapped within soil particles (Northcott and Jones, 2000), with the strength of binding determined by the properties of the soil and of the pesticide, and by the length of contact between the soil and the chemical. The most influential soil properties are total organic matter in soils with greater than 5% organic matter content and clay content in soils with less than 5% organic matter (Spark and Swift, 2002). In both cases, the greater the organic matter or clay content of the soil, the greater the extent of bound residue formation and the lower the mobility of the pesticide. For bound residues resulting from sorption to soil particles, the K ow of the pesticide is an indica- tor as to the likelihood of bound residue formation, with a higher K ow resulting in lower mobility through the soil and a greater affinity for soil particles (Esteve-Turrillas et al., 2006). The K ow of cypermethrin is high, 3.98 Â 10 6 , suggesting that bound residue formation will be a dominant in controlling its behaviour in the soil. Additionally, the degree of sorption or sequestration changes over time, with bound residues becoming more strongly associated to the soil over time through a process termed ageing (Alexander, 2000; Barraclough et al., 2005). The measurement of bound resi- dues is operationally defined by the nature of the extractant and by the conditions under which the extraction is carried out (Gevao et al., 2000). The formation of bound residues reduces the ability for leaching, and may limit microbial degradation, leading to persis- tence and potential for prolonged environmental impact. Microbial degradation is an important dissipation mechanism for many synthetic pyrethroids, and is a major route of loss for pesticides from the soil (Jones, 1999; Bending et al., 2001; Grant 0045-6535/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.chemosphere.2010.10.025 ⇑ Corresponding author. Tel.: +44 (0) 7941521584. E-mail address: katefenlon@hotmail.com (K.A. Fenlon). Chemosphere 82 (2011) 187–192 Contents lists available at ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere