Keywords: trace analytics stream pyrethroids Insecticides Substances: Chlorpyrifos (SBPBAQFWLVIOKP-UHFFFAOYSA-N) Deltamethrin (OWZREIFADZCYQD-NSHGMRRFSA-N) Empenthrin (YUGWDVYLFSETPE-JLHYYAGUSA-N) Chlorpyrifos-methyl (HRBKVYFZANMGRE-UHFFFAOYSA-N)