Aqueous chlorination of permethrin

War. Res. Vol. 23, No. 4, pp. 523-524, 1989 Printed in Great Britain. All rights reserved

0043-1354/89 $3.00+0.00 Copyright © 1989 Pergamon Press pie

RESEARCH NOTE

AQUEOUS CHLORINATION OF PERMETHRIN M. FIELDING* and J. HALEY The Water Research Centre, Henley Road, Medmenham, Bucks. SL7 2HD, England (First received November 1987; accepted in revised form October 1988) Abstract--Cis and trans permethrin were shown not to react with chlorine under conditions likely to be found during water treatment disinfection. Consequently, no products are likely to be formed should operators wish to maintain a chlorine residual whilst deinfesting mains water supply. Key words--byproducts, chlorination, disinfection, distribution system, drinking water, infestation, insecticide, pesticide, treatment

INTRODUCTION

Solutions of mixtures o f cis and trans permethrin (see Fig. 1) in alcohol are widely used for the removal of aquatic invertebrates, usually Asellus aquatic'us, from water mains. Permethrin has a very low mammalian toxicity but is of high toxicity to insects, aquatic invertebrates and fish. The concentrations of permethrin used in water mains provide a substantial margin o f safety for consumers. After appropriate dilution the insecticide is dosed into the water supply to between 10 and 20/~gl -~. During treatment of the water supplies with permethrin it is customary practice not to maintain a chlorine residual, since it is believed that chlorine could react with the permethrin. Recently, interest has been expressed in modifying the procedure so that a disinfectant residual can be maintained whilst treating for infestation. However, before changes in procedure are likely to be implemented it is necessary to establish the reactivity o f permethrin towards chlorine under appropriate conditions and to identify the products of reaction if any. EXPERIMENTAL

Instrumentation

Gas chromatographic (GC) analyses were performed on a Varian 3700 gas chromatograph fitted with a silica capillary column (J&W, DB-1; 30m, 0.25 mm; Jones Chromatography, Llandbradach, Mid Glamorgan, U.K.) with an OCI-3 on-column injector [Scientific Glass Engineering Ltd (SGE), Milton Keynes, Bucks., U.K.] for sample introduction and flame ionisation detection (FID). The output from the detector was recorded by a Servoscribe dual pen chart recorder (Labdata Instruments Services Ltd, Croydon, Surrey, U.K.). The output from the FID was also recorded on a Hewlett-Packard 3390A integrator (Hewlett-Packard Ltd, Winnersh, Berks., U.K.). Helium gas flow was set at

*To whom correspondence should be sent. ~ . R 23 4--[

1.7 ml min-J and the oven temperature was regulated in the following manner: 30°C held for 4 min then linearly increased at 8°C min-~ to 300°C. Gas chromatography-mass spectrometry (GC-MS) was performed using a Hewlett-Packard 5710-M gas chromatograph fitted with an OCI-2 on-column injector (SGE) and a fused silica capillary column DB-I (60 m x 0.25 mm, Jones Chromatography) directly coupled to a VG 70-70E double-focusing mass spectrometer (VG Analytical, Manchester, U.K.). Data acquisition and processing were performed by a Super-Incos data system (Finnigan MAT, Hemel Hempstead, Herts., U.K.) with mass calibration using perfluorokerosene. Mass spectra were obtained under electron impact (El) conditions using 70 eV electron energy, 200 g A trap current and 6 kV accelerating voltage. Reagents Permethrin was obtained from Mitchell Cotts (Mirfield, Yorkshire, U.K.). Comparison of this material with reference standards obtained from the National Physical Laboratory showed that it consisted of 40% of the cis isomer and 60% of the trans isomer. Methanol and pentane, both distilled-in-glass grade, were obtained from Rathburn Chemicals Ltd (Walkerburn, Peebleshire, U.K.) and were used without further purification. Sodium hypochlorite, (low bromine grade) potassium dihydrogenphosphate, potassium bromide and potassium hydroxide were of Analar grade and were obtained from BDH Ltd (Dagenham, Essex, U.K.). Chlorine-demand-free water was obtained by passing tap water through ion exchange resins, Elga Cylinder Type CI0 (The Elga Group, Lane End, Bucks., U.K.). The deionised water was passed through a column (90 x 5 cm) of granular activated carbon (Chemviron, Brussels, Belgium) to remove trace organic compounds. The water was either used immediately or stored in all glass vessels, in the dark, prior to use. Chlorination procedure The following chlorination procedure, which reflects conditions occurring during drinking water disinfection, was employed and was performed in triplicate for each study. Buffered 1 M potassium dihydrogen phosphate solution (20 ml) was diluted with water to afford a final concentration of 10 mM at pH 7. Sufficient sodium hypochlorite solution was then added to afford concentration of 8 mg lof total available chlorine (> 95% free chlorine), as analysed by the ferrous ammonium sulphate method (Standing Committee of Analysts, 1980). The solution of permethrin in

523

524

Research Note

//Cl CO

CH '

H3C

C

CH 3

Fig. 1. Permethrin. Table 1. Mean recoveries (+ SD) of permethrin isomers from water in the presence or absence of chlorine and bromide Recovery Chlorine Internal cis trans concentration standard Permethrin Permethrin (mgl ~) (%) (%) (%) 0 64.7(6.2) 84.9(0.8) 80.1 (1.3) 8 71.9(6.9) 85.2(2.3) 82.4(7.1) 8* 77.9(7.3) 94.3(13.7) 84.5(13.6) *Presence of bromide. methanol (20/~1:1 mg ml- ~ of a mixture of cis and trans isomers) to be chlorinated was added. The permethrin solution also contained methyl octadecanoate (1 mg ml -~) as internal standard, for the purpose of confirming the reproducibility of the extraction procedure. The mixture of permethrin isomers and the internal standard were thus present at 10#gl ~ in the reaction mixture. Sufficient aqueous potassium bromide solution (5 g 1- ~) was added to provide a concentration of 5 mgl t. Bromide was added since it has been observed that some substances react more extensively in the presence of hypobromous acid, produced by the action of chlorine on the added bromide. A similar solution without hypochlorite or bromide was prepared. Aqueous solutions were maintained at 20°C in the dark for 4 h; at the end of the reaction 1 litre of each solution was extracted with pentane (3 × 20ml). These extracts were dried by freezing out water. The solvent solutions were decanted and then concentrated by evaporation using a Junk vessel. The final volume was accurately adjusted to 500#1; l #1 of this solution was analysed by gas chromatography. RESULTS AND DISCUSSION The recovery efficiencies of p e r m e t h r i n from solutions containing 0 or 8 mg I ~ o f chlorine (the latter in the presence or absence o f 5 m g 1-~ o f potassium bromide) are given in Table 1. Analysis by G C - M S of the chlorinated solutions a n d the control confirmed t h a t no observable c o n s u m p t i o n of either isomer of p e r m e t h r i n h a d occurred. F u r t h e r m o r e , this analysis showed t h a t no products (amenable to G C - M S analyses) h a d been formed. F r o m this data

it is evident that no reaction occurs between either of the p e r m e t h r i n isomers a n d chlorine u n d e r the conditions studied. This is a surprising result since previous work carried out in this laboratory ( G i b s o n et al., 1986; Fielding et al., 1987) suggests t h a t u n s a t u r a t e d comp o u n d s such as alkenes or u n s a t u r a t e d fatty acids react with chlorine to form chlorohydrins. Since neither p e r m e t h r i n isomer reacts with chlorine, even in the presence of bromide, it must be assumed t h a t the substitution of the double b o n d plays a n imp o r t a n t role in preventing reaction. The substituents on the double b o n d m a y cause steric h i n d r a n c e or the chlorine a t o m s may, t h r o u g h inductive effects, m a k e the double b o n d less reactive towards electrophilic attack by the chlorine. F u r t h e r work is required to determine the reasons for this apparently a n o m a l o u s behaviour.

Acknowledgements--The authors thank Dr H. A. James for GC-MS analyses. This work was funded by the Department of the Environment and their permission to publish has been obtained.

REFERENCES Fielding M., Haley J., Watts C. D., Corless C., Graham N. and Perry R. (1987) Investigation into the effects of chlorine and ozone on selected organic substances in water. In The Proceedings o f the Second International Conference. The Role o f Ozone in Water and Wastewater Treatment (Edited by Smith D. W. and Finch G. R.), pp. 15-32. Edmonton, Alberta. Gibson T. M., Haley J., Righton M. and Watts C. D. (1986) Chlorination of fatty acids during water treatment disinfection. Reactivity and product identification. Envir. Tech. Lett. 7, 365-372. Standing Committee of Analysts (1980) Chemical disinfecting agents in waters and effluents and chlorine demand. Methods for the examination of waters and associated materials. Her Majesty's Stationery Office, London.