Air quality assessment by tree bark biomonitoring in urban, industrial and rural environments of the Rhine Valley: PCDD/Fs, PCBs and trace metal evidence

Abstract: Tree barks were used as biomonitors to evaluate past atmospheric pollution within and around the industrial zones of Strasbourg (France) and Kehl (Germany) in the Rhine Valley. The here estimated residence time for trace metals, PCBs and PCDD/Fs in tree bark is >10years. Thus, all pollution observed by tree bark biomonitoring can be older than 10years. The PCB baseline concentration (sum of seven PCB indicators (Σ7PCBind)) determined on tree barks from a remote area in the Vosges mountains is 4ngg−1 and corresponds to 0.36×10−3 ng toxic equivalent (TEQ) g−1 for the dioxin-like PCBs (DL-PCBs). The northern Rhine harbor suffered especially from steel plant, waste incinerator and thermal power plant emissions. The polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) concentrations analyzed in tree barks from this industrial area range between 392 and 1420ngkg−1 dry-weight (dw) corresponding to 3.9ngTEQPCDD/Fs kg−1 to 17.8ngTEQPCDD/Fs kg−1, respectively. Highest PCDD/F values of 7.2ng TEQ kg−1 to 17.8ng TEQ kg−1 have been observed close to and at a distance of <2km southwest of the chemical waste incinerator. However, very close to this incinerator lowest TEQ dioxin-like PCB (TEQDL-PCB) values of 0.006ngTEQg−1 have been found. On the other hand close to and southwest and northeast of the steel plant the values are comparatively higher and range between 0.011ngTEQg−1 and 0.026ngTEQg−1. However, even stronger Σ7PCBind enrichments have been observed at a few places in the city center of Kehl, where ΣDL-PCB values of up to 0.11ngTEQg−1 have been detected. These enrichments, however, are the result of ancient pollutions since recent long-term measurements at the same sites indicate that the atmospheric PCB concentrations are close to baseline. Emissions from an old landfill of waste and/or great fires might have been the reasons of these PCB enrichments. Other urban environments of the cities of Kehl and Strasbourg show significantly lower Σ7PCBind concentrations. They suffer especially from road and river traffic and have typically Σ7PCBind concentrations ranging from 11ngg−1 to 29ngg−1. The PCB concentration of 29ngg−1 has been found in tree bark close to the railway station of Strasbourg. Nevertheless, the corresponding TEQDL-PCB are low and range between 0.2×10−3 ngTEQg−1 and 7×10−3 ngTEQg−1. Samples collected near road traffic are enriched in Fe, Sb, Sn and Pb. Cd enrichments were found close to almost all types of industries. Rural environments not far from industrial sites suffered from organic and inorganic pollution. In this case, TEQDL-PCB values may reach up to 58×10−3 ngTEQg−1 and the corresponding V, Cr, Co, Ni, and Cd concentrations are comparatively high. [Copyright &y& Elsevier]