Sorption and desorption of pyrethroid insecticide permethrin on concrete

Use of pesticides around residential homes is linked to contamination of urban waterways, where impervious surfaces like concrete are considered as sources or facilitators of the contamination. However, the fate of pesticides on urban hard surfaces is poorly understood. We characterized sorption and desorption of permethrin, the most used pyrethroid insecticide, on concrete surfaces, to understand its availability for contaminating runoff water. Sorption of (14)C-permethrin to concrete was rapid, and the sorption isotherm was linear, with surface area-normalized K(d) of 1.91 ± 0.1 mL/cm(2). When small permethrin-treated concrete cubes (14 × 14 × 8 mm) were subjected to 300 h sequential desorption, both the parent compound and total (14)C showed an initial rapid desorption, followed by prolonged slow desorption. Meanwhile, permethrin became more resistant to desorption as the pesticide contact time on the concrete increased. When desorption was performed 1 and 7 d after the treatment, the desorbed permethrin after 300 h was 34.1 ± 3.2% and 23.7 ± 1.1% of the spiked amount, respectively, as compared to 56.2 ± 6.1% for the freshly spiked samples. The decreased desorption was partially attributed to permethrin decomposition on the alkaline concrete. However, even after 300 h, over 20% of the applied (14)C still remained in the concrete. Therefore, when pesticide-treated concrete surfaces come in contact with runoff water, elevated concentrations may be expected initially, while the extended desorption implies a potential for sustained contamination.