Monitoring chemical contamination of sediments in rivers: relevance of integrative sampling of suspended solids

Abstract

Sediment monitoring for the assessment of water body quality is addressed in the Water Framework Directive (WFD).The daughter directive 2008/105/EC requires long-term trend analysis of concentrations of hydrophobic priority substances. However, surface sediment sampling is a source of variability, especially due to deposits heterogeneity. In comparison, suspended particulate matter (SPM) sampling allows to (i) avoid the heterogeneity of sediment samples as only the fine particles in suspension are sampled, (ii) define the date of the collected samples and (iii) improve the frequency of quantification for trace contaminants (due to their affinity to fine particles). Particle traps is a low cost tool that allows the integrative sampling of SPM at a large scale. However, this tool can induce a bias during sampling, which generally results in an increase of particles size distribution, especially for high flows, but without affecting mercury or polychlorobiphenyls concentrations. The use of the particle trap represents an interesting alternative to surface sediment sampling for the spatial and temporal monitoring of the contamination on the particulate phase in rivers. Nonetheless, the applicability and efficiency of different types of particles traps need to be tested for small streams.