Water samples were refrigerated at 4 C until used. One litre water samples were added to separatory funnels,spiked (in 100 ll of acetone) with organophosphate compounds, mixed and allowed to equilibrate to room temperature for 2 h. Samples were extracted with three 100 ml portions of dichloromethane (DCM) and dried by passage through pre-cleaned sodium sulphate. The extracts were combined in a 500 ml round bottom flask and after addition of 5 ml isooctane concentrated to 3 ml using rotary evaporation. The concentrates were quantitatively transferred to 15 ml centrifuge tubes with two 2 ml rinses of hexane and further concentrated by nitrogen evaporation. Final extract volumes were 1 ml. Suspended sediments were collected from the Schomberg (F) and Detroit rivers (G). Bottom sediT