The vessels were stoppered and then stirred at 30 °C for one day. Next, one of the standard vials was equilibrated at 25 °C for 24 hours, and then the aqueous solution was collected from the suspension with a syringe equipped with a filter with a hydrophilic membrane. The concentration of test compounds in water was determined spectrophotometrically using a VWR ® UV-5300PC spectrophotometer (VWR International, Belgium) based on calibration curves made previously (at λmax = 235 nm). Second and third vials were tested after being stirred at 30 °C for 2 and 3 days, respectively, using the same procedure. Two additional vials with an increased amount of test substance were tested after 3 days of stirring (alongside the third vial).