thus supporting previous studies which indicate that effluent discharges
are the major source of organic pollution in these rivers
(Teixido et al., 2001). In particular pesticides with a relatively high
environmental persistence (TRZ, OCL such as lindane, alachlor;
Rivera et al., 1986) or/and broadly used to control pests in agriculture
(OP such as diazinon and chlorpyrifos; Barata et al., 2007)
increased dramatically from upper to downstream sites.