In summary, our results lend positive support to the use of biological
indices in combination with D. magna in situ bioassays to
assess effects and identify environmentally detrimental factors in
a better way within a complex multi-stressed river systems in the
field, thus contributing to a more realistic assessment of ecological
risks. Furthermore, the observed effects of OP in D. magna in
situ bioassays across the studied rivers were also reported in the
Ebro river (Barata et al., 2007), thus indicating that these highly
active substances should be controlledand if possible their use minimized
in the near future. Contaminant residues of PAHs should also
be considered since they affected negatively three out of the four
D. magna in situ bioassay responses measured. Nevertheless, it is
important to consider that, while the approach used in this study
drives us closer towards the “in situ environmental hazard identification
evaluation”, issues arising from other confounding factors
influencing the responses of macroinvertebrate and D.magnain situ
bioassays still should be considered with caution in the interpretation
of such findings as conclusive diagnostic proofs of individual
factors causing effects