The parameter total suspended solids (TSS) is often used to evaluate the need for stormwater treatment or to assess the effectiveness of treatment measures. The purpose of this study is to analyze the value and the limitations of this approach using metals as an example. They are of major concern due to their accumulating effects in the environment. Data of a monitoring campaign at a stormwater treatment facility is evaluated. TSS, organic matter and the associated metals (Cr, Cu, Zn, Cd, and Pb) were analyzed in four different particle size fractions (<63 µm, 63–125 µm, 125–250 µm, and 250–2000 µm). While the highest event meant concentrations for all metals were found in the smallest fraction, a rather uniform particulate bound metal concentration (mass of metal per mass of particulate matter) over the first three particle size fractions was detected. Total metal loads correlated well with TSS even better with TSS < 63 µm. However, the removal efficiency in terms of the reduction of the total metal load was not reflected sufficiently by the TSS or TSS < 63 µm removal efficiency.
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