386 Research Article Received: 14 September 2011 Revised: 26 January 2012 Accepted article published: 15 March 2012 Published online in Wiley Online Library: 15 May 2012 (wileyonlinelibrary.com) DOI 10.1002/ps.3311 Soil contamination and persistence of pollutants following organophosphate sprays and explosions to control red-billed quelea (Quelea quelea) Robert A Cheke, a* Enoch Adranyi, a John R Cox, a Dudley I Farman, a Richard N Magoma, b Collen Mbereki, c Andrew N McWilliam, a,d Boaz N Mtobesya b and Etienne van der Walt e Abstract BACKGROUND: Red-billed quelea (Quelea quelea) are controlled at breeding colonies and roosts by organophosphate sprays or explosions. Contamination with organophosphates after sprays and with petroleum products and phthalates after explosions was assessed. RESULTS: Concentrations in soil of the organophosphate fenthion the day after sprays were uneven (0 – 29.5 μgg -1 ), which was attributable to excess depositions at vehicle turning points, incorrect positioning of nozzles and poor equipment maintenance. A laboratory study using field-collected samples provided an estimate of 47 days for the half-life of fenthion. After sprays, fenthion persisted in soil for up to 188 days. High concentrations were detected 5 months after negative results at the same sites, providing indirect evidence of leaching. Concentrations of total petroleum hydrocarbons (TPHs) and phthalates ranged from 0.05 to 130.81 (mean 18.69) μgg -1 and from 0 to 1.62 (mean 0.55) μgg -1 respectively in the craters formed by the explosions, but declined to means of 0.753 and 0.027 μgg -1 at 10 m away. One year after an explosion, mean TPHs of 0.865 and mean phthalates of 0.609 were detected. CONCLUSION: Localisation of high concentrations of fenthion likely to have effects on soil biota could be mitigated by improved spray management. Given a half-life in the soil of 47 days for fenthion and the possibility of its leaching months after applications raises concerns about its acceptability. The pollutants left behind after explosions have been quantified for the first time, and, given their long-term persistence, their continued use poses a threat to environmental health. c  2012 Society of Chemical Industry Keywords: red-billed quelea; Quelea quelea; soil; organophosphate; fenthion; cyanophos; explosions; diesel; petrol; plastics; phthalates; persistence 1 INTRODUCTION Control of the red-billed quelea (Quelea quelea) is conducted be- cause it is a major pest of small-grain cereal crops in semi-arid areas of sub-Saharan Africa. 1,2 Three subspecies of the bird are recog- nised: the nominate form occurs in West Africa, Q. q. aethiopica in eastern Africa and Q. q. lathamii in southern Africa. All three sub- species are intra-African migrants moving with rain fronts to breed colonially during rainy seasons. 3 In the dry seasons they congre- gate at night to roost communally. Both the colonies and roosts are targets for lethal control measures using either organophosphate sprays or explosions. Such actions have deleterious environmental consequences by killing or debilitating non-target organisms by direct and indirect poisoning. 4 Non-lethal effects on non-target birds and mammals can be monitored by measuring cholinesterase levels, 5 but effects on invertebrates, vegetation and the wider environment, including soil, are poorly documented. Early reports suggested that the most commonly used organo- phosphate, fenthion, broke down quickly, with a half-life on soil exposed to sunlight of only 11 h, 6 but other studies have suggested long-term persistence of 14–40 days in soil, 7 a half-life in soil of ∗ Correspondence to: Robert A Cheke, European Centre for Integrated Pest Management, Natural Resources Institute, University of Greenwich at Medway, Central Avenue, Chatham Maritime, Kent ME4 4TB, UK. E-mail: r.a.cheke@greenwich.ac.uk a Natural Resources Institute, University of Greenwich at Medway, Chatham Maritime, Kent, UK b Plant Health Services, Ministry of Agriculture, Food, Security and Cooperatives, Dar es Salaam, Tanzania c Plant Protection Division, Ministry of Agriculture, Gaborone, Botswana d The James Hutton Institute, Craigiebuckler, Aberdeen, Scotland, UK e ARC Plant Protection Research Institute, Queenswood, Pretoria, Republic of South Africa Pest Manag Sci 2013; 69: 386–396 www.soci.org c  2012 Society of Chemical Industry