ments were collected from the St. Lawrence (H) and Souris rivers (I). Both the I and G samples were freezedried. Wet sediment samples were kept frozen and thawed prior to use. Ten grams of wet or 4 g of dry sediment, reconstituted with 6 ml of organic free water were weighed into a stainless steel beaker. Organophosphate compounds were spiked into the sample, mixed with a spatula and allowed to equilibrate for 2 h.The beaker was placed in an ice bath and extracted three
times using 3-min sonification intervals and 100 ml portions of hexane:acetone (80:20). Combined extracts were filtered using an Allihn funnel containing 20 g of Celite, transferred to a separatory funnel and backextracted with 100 ml of organic free water. After settling the lower layer (acetone–water) was drained into another separatory funnel and extracted two times with 100 ml portions of DCM. The DCM was added to the reserved hexane and filtered through an Allihn funnel filled with 100 g of fired sodium sulphate. Extracts were concentrated to 2 ml using the same method as for
water.