Dissolved levels of Cu and Zn found across the studied stations
were relatively low and constant between upstream and downstream
reaches, thus indicating that urban and industrial STPs
contributed little to these trace metal levels (Puig et al., 1999;
Fernandez-Turiel et al., 2003). Conversely, most organic residue
levels increased dramatically towards downstream locations, in
particular in those sites located near effluent discharges fromSTPs,