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Determination of low environmental free cyanide concentrations in freshwaters.

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.

SUBMITTER: Knopf B

PROVIDER: S-EPMC7969539 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:The microbial communities in recreational freshwaters play important roles in both environmental and public health perspectives. In this study, the bacterial community structure and its associations with freshwater environments were investigated by analyzing the summertime microbiomes of three beach waters in Ohio (East Fork, Delaware, and Madison lakes) together with environmental and microbial water quality parameters. From the swimming season of 2009, 21 water samples were collected from the three freshwater beaches. From the samples, 110,000 quality-checked bacterial 16S rRNA gene sequences were obtained and analyzed, resulting in an observation of 4500 bacterial operational taxonomic units (OTUs). The most abundant bacteria were Mycobacterium and Arthrobacter of the Actinobacteria (33.2%), Exiguobacterium and Paenisporosarcina of the Firmicutes (23.4%), Planktothrix and Synechococcus of the Cyanobacteria (20.8%), and Methylocystis and Polynucleobacter of the Proteobacteria (16.3%). Considerable spatial and temporal variations were observed in the bacterial community of Actinobacteria, Cyanobacteria, and Firmicutes, where the bacterial community structure was greatly influenced by hydrological and weather conditions. The most influential factors were (1) water inflow for Bacteroidia and Clostridia, (2) turbidity for Gammaproteobacteria, (3) precipitation for Bacilli, and (4) temperature and pH for Cyanobacteria. One noticeable microbial interaction in the bacterial community was a significant negative relationship between Cyanobacteria and Bacilli (P < 0.05). Concerning beach water quality, the level of the genetic markers for cyanobacterial toxin (mcyA) was linked to the abundance of Cyanobacteria. In addition, unique distributions of the genera Enterococcus, Staphylococcus, Streptococcus, Bacteroides, Clostridium, Finegoldia, Burkholderia, and Klebsiella, together with a high density of fecal indicator Escherichia coli, were markedly observed in the sample from Madison Lake on July 13, suggesting a distinctly different source of bacterial loading into the lake, possibly fecal contamination. In conclusion, deep sequencing-based microbial community analysis can provide detailed profiles of bacterial communities and information on potential public health risks at freshwater beaches.

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Determination of low environmental free cyanide concentrations in freshwaters.

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