Adsorption behavior of α -cypermethrin on cork and activated carbon VALENTINA F. DOMINGUES, GIUSEPPE PRIOLO, ARMINDA C. ALVES, MIGUEL F. CABRAL and CRISTINA DELERUE-MATOS Studies were undertaken to determine the adsorption behavior of α-cypermethrin [R)-α-cyano-3-phenoxybenzyl(1S)-cis- 3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate, and (S)-α-cyano-3-phenoxybenzyl (1R)-cis-3-(2,2-dichlorovinyl)-2,2- dimethylcyclopropanecarboxylate] in solutions on granules of cork and activated carbon (GAC). The adsorption studies were carried out using a batch equilibrium technique. A gas chromatograph with an electron capture detector (GC-ECD) was used to analyze α-cypermethrin after solid phase extraction with C18 disks. Physical properties including real density, pore volume, surface area and pore diameter of cork were evaluated by mercury porosimetry. Characterization of cork particles showed variations thereby indicating the highly heterogeneous structure of the material. The average surface area of cork particles was lower than that of GAC. Kinetics adsorption studies allowed the determination of the equilibrium time—24 hours for both cork (1–2 mm and 3–4 mm) and GAC. For the studied α-cypermethrin concentration range, GAC revealed to be a better sorbent. However, adsorption parameters for equilibrium concentrations, obtained through the Langmuir and Freundlich models, showed that granulated cork 1–2 mm have the maximum amount of adsorbed α-cypermethrin (q m ) (303 μg/g); followed by GAC (186 μg/g) and cork 3-4 mm (136 μg/g). The standard deviation (SD) values, demonstrate that Freundlich model better describes the α-cypermethrin adsorption phenomena on GAC, while α-cypermethrin adsorption on cork (1-2 mm and 3-4 mm) is better described by the Langmuir. In view of the adsorp- tion results obtained in this study it appears that granulated cork may be a better and a cheaper alternative to GAC for removing α-cypermethrin from water. Keywords: Adsorption; activated carbon; cypermethrin; cork; pesticide; pyrethroid. Introduction Pyrethroids are effective pesticides against a wide range of pests and are commonly used in agriculture, public health and industry. Pyrethroids are synthetic analogs of pyrethrins, which have been developed to circumvent the rapid photodegradation of pyrethrins. [1] Pyrethroids are commonly used around the world, as success- ful alternatives to traditional organophosphorus insecti- cides, given their cost-effectiveness and lower toxicity to mammals. [2] Among the group of pyrethroids, cypermethrin [R) − α- cyano-3-phenoxybenzyl (1S)-cis-3-(2,2-dichlorovinyl)-2,2- dimethylcyclopropanecarboxylate and (S)-α-cyano-3- phenoxybenzyl (1R)-cis-3-(2,2-dichlorovinyl)-2,2-dimethy- lcyclopropanecarboxylate] was introduced in the late 1970s and has since then been used on a wide range of crops, due to its high pesticide activity. [3] In recent years cypermethrin has been commonly used to control wohlfahrtiosis in sheep [4] and several insect pests of cotton. [5−8] The textile industry is one of the largest industrial producers of contaminated wastewaters. Besides the presence of unfixed dyes, pyrethroids used to preserve cotton and wool, are also present in wastewaters. The removal of pesticides such as cypermethrin from waters assumes a critical role in environmental management. Among the methods used to remove micro pollutants from wastewater, activated carbon adsorption despite its high costs has been the most widespread because of its efficiency, capacity and applica- tion on a large scale. Activated carbon has been known as