Determination of low environmental free cyanide concentrations in freshwaters
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RESEARCH ARTICLE
Determination of low environmental free cyanide concentrations in freshwaters Burkhard Knopf 1
&
Heinz Rüdel 1
&
Dirk Hansknecht 1 & Thorsten Klawonn 1 & Knut Kreuzer 2
Received: 23 July 2020 / Accepted: 10 December 2020 # The Author(s) 2020
Abstract Cyanide compounds are naturally emitted into the environment in low levels by degradation processes or emitted from anthropogenic sources. In surface water, complex cyanide compounds as well as “free cyanide” are present. The latter term covers hydrogen cyanide and cyanide compounds which easily liberate hydrogen cyanide under slightly acidic conditions. Especially free cyanide may cause adverse effects in the environment. To exclude negative impacts on freshwater systems, in the context of the European Water Framework Directive (WFD), preventive regulatory activities for free cyanide are currently under discussion. However, established analytical methods for quantification of free cyanide only obtain limits of quantification (LOQs) in the range of 1 μg L−1. Thus, these methods are not sufficiently sensitive for a potential environmental quality standard (EQS) compliance monitoring at water concentrations below the current predicted no effect concentration (PNEC) level of free cyanide. In the present study, a standardized continuous flow analysis (CFA) method for quantification of low free cyanide concentrations was adapted by applying a special system which allows an ultra-sensitive photometric detection of a colored cyanide derivative. By this means, LOQs in a range of one magnitude below the PNEC are achievable. The method was validated according to ISO/ IEC 17025 requirements. Free cyanide concentrations in tested surface water samples from a small river and a barrier lake with low anthropogenic influences were very low and clearly below the PNEC. The results prove that the adapted CFA method is suitable for the analysis of low concentration free cyanide in freshwaters and appropriate for a possible EQS compliance monitoring. Keywords Free cyanide . Continuousflowanalysis . Environmental quality standard . Surfacewater . Environmental monitoring . Compliance monitoring . Water framework directive
Introduction In environmental waters, cyanide can occur as entity in simple and complex compounds (Jaszczak et al. 2017). Free cyanide, also designated as easily liberatable cyanide, is defined as the sum of cyanide ions and cyanide bound in weak metal cyanide complexes that liberate hydrogen cyanide at a pH of about 4 (ISO 2012). It exists in fresh water systems in low concentrations and originates from naturally occurring degradation Responsible Editor: Xianliang Yi * Burkhard Knopf [email protected] 1
Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Schmallenberg, Germany
2
Röhm GmbH, Deutsche-Telekom-Allee, Darmstadt, Germany
processes of plants and microbes. In contrast to information on total cyanide covering simple and complex compounds, information on background levels of the toxicological relevant free
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