Recently amended European (EU) water policies call for an adequate monitoring of the chemical status of sediments and suspended matter (SM) in rivers. In this study, we focus on long-term time series of particle-bound hexachlorobenzene (HCB) and selected polychlorinated biphenyls (PCB-138 and PCB-153) that were monitored biweekly to monthly at eight stations in the River Rhine catchment. Our aims are (1) to detect trends in the concentration series HCB, PCB-138 and PCB-153, (2) to estimate the uncertainty of loads caused by SM collection techniques and load calculation procedures and (3) to detect trends in the subsequently calculated annual load series.
HCB concentration in the SM for the period 1995–2008 significantly (p < 0·01) decreased at six of the eight monitoring stations. Decreasing PCB-138 and PCB-153 concentrations are significant at six of the eight and seven of the eight monitoring stations, respectively.
A two-way analysis of variance (ANOVA) that tested the effect of two collection techniques and four load calculation procedures on annual loads indicates homogeneity of the methods at four of the five monitoring stations. At Weil, only the loads of HCB, PCB-138 and PCB-153 are significantly affected by the collection technique.
The trend analysis of an extended series (1985–2007) of annual HCB loads at Koblenz showed a significant decrease from about 110 kg year−1 to about 15–23 kg year−1; however, in the shorter period (1995–2007) only at two of the eight monitoring stations decreasing trends of annual contaminant load could be detected.
We conclude that any of the tested load calculation procedures can be applied, as loads do no differ systematically. Although a high uncertainty in load estimation exists (e.g. maximum percentage error of E = [18·1, 122·5]% for HCB), the monitoring programme at the Rhine is adequate for analysing the long-term chemical status of SM. Copyright © 2011 John Wiley & Sons, Ltd.