Estonian 16-year-old Zirk, a pupil at Plymouth College, finished an impressive sixth in the men’s 50m butterfly event with a time of 24.21 seconds.
That was four hundredths of second inside the Estonian previous best set by Ralf Tribuntsov in 2014 and faster than Ben Proud’s British 16-year-old age group record.
Zirk had clocked 24.61 in the morning heats in Stockhlolm.
Passon, meanwhile, broke her own Seychelles 50m butterfly record twice in the same day in Sweden. The 16-year-old Plymouth College student clocked 28.22 seconds in the heats before going under 28 seconds for the first time in the evening session, touching in 27.90 seconds to finish 14th overall.
Leander’s Belgium swimmer Juliette Casini finished 11th in the women’s 200m freestyle in 2:02.20.
Olympic champion Ruta Meilutyte will be in action on the second day.
Meanwhile, there was also aquatic success on Wednesday for Plymouth Diving’s Owen Weymouth and Alex Kostov, who won silver in the boys’ 14-18 years-old three-metre synchro event at the British Junior Elite Championships, which are being held at the Life Centre.