False Cyanide Formation during Drinking Water Sample Preservation and Storage

Abstract

Carefully controlled bench-scale and on-site experiments demonstrated that cyanide can form in the treated drinking water sample container during preservation and storage. In the bench-scale experiment, treated tap water samples were collected on 20 days over six months. The tap water samples were split and some of the splits were spiked with formaldehyde, a known ozone disinfection byproduct, held for three hours and tested for cyanide. Then they were preserved and held for 2-10 days. None of the 69 initial samples had cyanide detects, but 22 of 49 formaldehyde-spiked samples and three of the 20 unspiked samples developed detectable cyanide concentrations during storage. In the on-site experiment, six samples were collected at a finished water tap at an ozone/chloramination treatment plant over three days. Each sample was split, and a portion was spiked with formaldehyde. Each portion was analyzed in triplicate after three different procedures: (1) immediately distilled on-site, (2) stabilized on-site in a distillation tube and distilled back at the laboratory several days later, or (3) following the conventional procedure of preserving the sample to pH > 12 in a container and distilling the sample back at the laboratory. Only the samples handled in the conventional way had detectable amounts of cyanide. Both experiments demonstrated that cyanide can form during conventional preservation and storage, and it is likely that the cyanide detected for this treated drinking water was formed in the sample container as a consequence of the preservation and storage conditions.

Free Cyanide Forms During Determination of Free Cyanide in Drinking Water

“…“Follow the method.” For regulatory drinking water testing, laboratories are required to “follow the method,” including procedures for how samples are preserved and treated for potential interferences. This regulatory mantra is problematic for cyanide (Delaney & Blodget 2016a), and similar false positives from the sample preservation and testing have been demonstrated (Delaney et al 2007). Cyanide formation during wastewater preservation and testing has also been demonstrated (Stanley & Antonio 2012, Khoury et al 2008, Carr et al 1997, Delaney et al 1997).…”

“…Cyanide has an additional level of complexity in that it can be formed or destroyed by a variety of chemical reactions (ASTM 2009). Previous studies demonstrated that cyanide can form in the preserved sample container (Delaney et al 2007), or during the sample preservation and analysis (Delaney & Blodget 2016a). This simple but illuminating experiment using deionized water in place of a raw drinking water supply was conducted to verify previous observations regarding FCN formation during drinking water treatment and cyanide testing.…”

Discrepancies and artifacts during preservation and analysis of the disinfection by‐product 2,6‐dichloro‐1,4‐benzoquinone

“…Protocols used for sample collection through analysis can sometimes result in serious errors and misclassification of results. Compounds attributed to reaction of natural organic matter (NOM) with both FAC and ozone have been misidentified as novel DBPs due to analytical artifacts (Campbell et al, 1987; Delaney et al, 2007; Dietrich et al, 1988; Kristiansen et al, 1994; Wang et al, 1988; Xie & Reckhow, 1993; Xie & Reckhow, 1994; Xie & Reckhow, 1997). In some cases, artifacts resulted from interactions between organic solvents used during solvent extraction or derivatization in the presence of FAC, bromine, or ozone.…”

Total Cyanide Field Spikes for Industrial Wastewater Samples Verify Successful Sample Integrity, Preservation, Pre‐Treatment and Testing

“…For the manual and automated pyridine–barbituric acid–chloramine‐T colorimetric cyanide methods, interferences are reported to include aldehydes, carbonates, fatty acids, nitrate, nitrite, oxidants, sugars, sulfide, other sulfur compounds, thiocyanate, and turbidity (ASTM Method 7365‐09a, ASTM, 2009). For example, even in drinking water we demonstrated false cyanide can be formed in the sample container after proscribed sample preservation (Delaney, 2007). This has led us to distill our quarterly drinking water total cyanide samples on‐site at the time of sampling at the drinking water treatment plant to avoid forming false cyanide in the container due to the preservation treatment.…”