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Abstract Title: Historical Analysis of Mercury Contamination Trends in German Rivers at Decadal Time Scales
Presenter Name: Jan G. Wiederhold
Company/Institution: German Federal Institute of Hydrology (BfG)
Session: Mercury in Freshwater Ecosystems
Co-Authors: Jan G. Wiederhold,Lorenz Gfeller,Lars Duester

Abstract Information :

The historical contamination of rivers with mercury (Hg) represents a serious long-term threat for human and ecosystem health. The dangers of Hg toxicity have been known for millennia, but a regulation and control of Hg releases into freshwater environments did often not start before the last few decades of the 20th century. The water quality of many German rivers was very poor in the 1970/80s, but has steadily improved since then by the implementation of various environmental measures (e.g., discharge bans, waste water treatment/management) combined with extensive monitoring programs. Due to its high affinity to suspended particles, Hg transport in riverine systems is dominated by the particulate load, while the dissolved load carries only a minor proportion. Bottom sediments represent important Hg sinks, but remobilization can occur, for example linked to erosion during flood event or dredging activities in managed waterways. Here, we present a meta-analysis of Hg concentrations trends in German rivers based on historical data from different monitoring programs (e.g., databases of federal states, national/international river commissions, German environmental specimen bank). The Hg concentrations of unfiltered river water decreased from values above 1 æg/L in the river Elbe and above 0.1 æg/L in the river Rhine in the 1980s to values below 0.05 æg/L and below 0.01 æg/L in recent years, respectively. Similar trends were observed in suspended particulate matter samples, which decreased for example at Elbe sampling sites close to the former Inner German border from Hg contents of above 50 mg/kg in the 1980s to about 1 mg/kg (and below 0.5 mg/kg in most other German rivers) today. Nonetheless, Hg levels in biota still exceed the environmental quality standard of the EU water framework directive in all large German rivers and further decreases appear to be hindered by the legacy contamination in bottom sediments.

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