Author's personal copy Journal of Hazardous Materials 244–245 (2013) 111–120 Contents lists available at SciVerse ScienceDirect Journal of Hazardous Materials jou rn al h om epage: www.elsevier.com/loc ate/jhazmat Biotransformation of chlorpyrifos in riparian wetlands in agricultural watersheds: Implications for wetland management M. Ekrem Karpuzcu a,c,∗ , David L. Sedlak a , William T. Stringfellow b,c a Department of Civil and Environmental Engineering, University of California Berkeley, Berkeley, CA 94720-1710, United States b Ecological Engineering Research Program, School of Engineering & Computer Science, University of the Pacific, 3601 Pacific Avenue, Stockton, CA 95211, United States c Earth Sciences Division, Geochemistry Department, Lawrence Berkeley National Laboratory, MS 70A-3317, Berkeley, CA 94720, United States h i g h l i g h t s ◮ Chlorpyrifos biotransformation rates vary spatially and temporally in sediments. ◮ Phosphotriesterase enzyme activity is correlated with chlorpyrifos biodegradation. ◮ Hydroperiod differences affect the biotransformation rates. ◮ Wet-dry cycling is proposed as a wetland management strategy. a r t i c l e i n f o Article history: Received 24 August 2012 Received in revised form 29 October 2012 Accepted 21 November 2012 Available online 29 November 2012 Keywords: Chlorpyrifos Organophosphate insecticides Wetlands Agricultural drainage Biodegradation a b s t r a c t Biodegradation of the organophosphate insecticide chlorpyrifos (O,O-diethyl O-(3,5,6-trichloropyridin- 2-yl) phosphorothioate) in sediments from wetlands and agricultural drains in San Joaquin Valley, CA was investigated. Sediments were collected monthly, spiked with chlorpyrifos, and rates of chlorpyrifos degradation were measured using a standardized aerobic biodegradation assay. Phosphoesterase enzyme activities were measured and phosphotriesterase activity was related to observed biodegradation kinet- ics. First-order biodegradation rates varied between 0.02 and 0.69 day -1 , after accounting for abiotic losses. The average rate of abiotic chlorpyrifos hydrolysis was 0.02 d -1 at pH 7.2 and 30 ◦ C. Sediments from the site exhibiting the highest chlorpyrifos degradation capacity were incubated under anaero- bic conditions to assess the effect of redox conditions on degradation rates. Half-lives were 5 and 92 days under aerobic and anaerobic conditions, respectively. There was a consistent decrease in observed biodegradation rates at one site due to permanently flooded conditions prevailing during one sampling year. These results suggest that wetland management strategies such as allowing a wet-dry cycle could enhance degradation rates. There was significant correlation between phosphotriesterase (PTE) activity and the chlorpyrifos biotransformation rates, with this relationship varying among sites. PTE activities may be useful as an indicator of biodegradation potential with reference to the previously established site-specific correlations. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Agricultural pesticides are indispensable in modern agricul- ture and are required to maintain high levels of production, but they can have adverse effects on aquatic ecosystems [1]. Due to the extremely long persistence and toxicity of organochlorine insecticides, more biodegradable and environmentally less prob- lematic insecticides have been sought to replace them. The use of ∗ Corresponding author at: Department of Civil and Environmental Engineering, University of California Berkeley, Berkeley, CA 94720-1710, United States. Tel.: +1 510 637 9705. E-mail address: ekarpuzcu@berkeley.edu (M.E. Karpuzcu). organophosphate insecticides has been growing as an alternative, as they were more biodegradable and were regarded biologically more efficient [2]. Organophosphate insecticides rank among the most widely used insecticides in the United States and are used extensively worldwide. Over 500 million kg of pesticides are used each year in the United States, of which approximately 18 million kg consist of organophosphate insecticides [3]. An important pathway for unintentional introduction of these compounds into aquatic ecosystems is surface runoff from treated fields. Runoff from irrigation and precipitation mobilize and transport dissolved and particle-associated pesticides into adja- cent water bodies, where they may impact non-target aquatic invertebrates and fish [4]. Organophosphate insecticides are ubiq- uitous in streams and surface waters draining agricultural and 0304-3894/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jhazmat.2012.11.047