B. S. Ismail

Adsorption, desorption, and mobility of permethrin in Malaysian soils.

Abstract The adsorption, desorption, and mobility of permethrin in six tropical soils was determined under laboratory and greenhouse conditions. The six soils were selected from vegetable growing areas in Malaysia. Soil organic matter (OM) was positively correlated (r 2 = 0.97) with the adsorption of permethrin. The two soils, namely, Teringkap 1 and Lating series with the highest OM (3.2 and 2.9%) released 32.5 and 30.8% of the adsorbed permethrin after four consecutive repetitions of the desorption process, respectively, compared to approximately 75.4% of the Gunung Berinchang soil with the lowest OM (1.0%) under the same conditions. The mobility of permethrin down the soil column was inversely correlated to the organic matter content of the soil. Permethrin residue penetrated only to the 10–15 cm zone in the Teringkap 1 soil with 3.2% OM but penetrated to a depth of more than 20 cm in the other soils. The Berinchang series soil with the lowest OM (1.0%) yielded leachate with 14.8% permethrin, the highest level in leachates from all the soils tested. Therefore, the possibility for permethrin to contaminate underground water may be greater in the presence of low organic matter content, which subsequently allows a higher percentage of permethrin to move downwards through the soil column.

Method Development for Determination of Fluroxypyr in Soil

Improved methods for extraction and clean up of fluroxypyr residue in water have been established. Two methods of fluroxypyr extraction were used, namely, Direct Measurement of fluroxypyr and Concentration of fluroxypyr onto A Solid Phase Extraction (SPE) Adsorbent, followed by elution with solvent before determination of fluroxypyr. The recovery for Direct Measurement of fluroxypyr in water containing 8–100 µg L− 1, ranged from 86 to 110% with relative standard deviation of 0.7 to 2.15%. For the second method, three types of SPE were used, viz. C18, C18 end‐capped and polyvinyl dibenzene (ISOLUTE ENV +). The procedure involved concentrating the analyte from fluroxypyr‐spiked water at pH 3, followed by elution of the analyte with 4 mL of acentonitrile. The recovery of fluroxypyr from the spiked sample at 1 to 50 µg L− 1 after eluting through either C18 or C18 end‐capped ranged from 40–64% (with relative standard deviation of 0.7 to 2.15) and 41–65% (with standard deviation of 1.52 to 11.9). The use of ISOLUTE ENV +, gave better results than the C18, C18 end‐capped or the Direct Measurement Methods. The recovery and standard deviation of fluroxypyr from spiked water using ISOLUTE ENV + ranged from 91–102% and 2.5 to 5.3, respectively.