Determination of low environmental free cyanide concentrations in freshwaters

Burkhard Knopf,Heinz Rüdel,Knut Kreuzer,Dirk Hansknecht,Thorsten Klawonn

doi:10.1007/s11356-020-12062-7

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.

Highlights

In environmental waters, cyanide can occur as entity in simple and complex compounds (Jaszczak et al 2017)
Since the most recent proposal for a potential environmental quality standard (EQS) for free cyanide (Loos et al 2018) considered a safety factor of 2 to the predicted no effect concentration (PNEC) value of 1 μg L−1, the targeted limit of quantification (LOQ) level of the method was a magnitude below the PNEC
The results prove that a realistic LOQ in the range of 0.1–0.3 μg L−1 during daily routine analysis of environmental samples from freshwaters can be achieved with the implemented continuous flow analysis (CFA) method

Summary

Introduction

Cyanide can occur as entity in simple and complex compounds (Jaszczak et al 2017). Environ Sci Pollut Res (2021) 28:16244–16252 concern” for the aquatic environment via a watch list mechanism (EU 2013; EU 2015a) Consultations on such a multiannual monitoring for free cyanide are currently ongoing and, below other aspects, refer to the current unavailability of a reliable analytical method of sufficient sensitivity, i.e., one order of magnitude below the PNEC (EU 2015b; Loos et al 2018; Peters et al 2012). This concentration range is considered relevant for a potential future environmental quality standard (EQS) in several evaluations (Sorokin et al 2012) (EU 2015b; Peters et al 2012) which should prevent adverse effects by androgenic released substances towards pelagic communities of freshwater organisms. There is a strong demand for an analytical method allowing free cyanide determinations in this low concentration range

Methods

Results

Conclusion