Article Cite This: Environ. Sci. Technol. 2018, 52, 1234−1243 pubs.acs.org/est Kinetics of Decomposition of Thiocyanate in Natural Aquatic Systems Irina Kurashova,† Itay Halevy,‡ and Alexey Kamyshny, Jr.*,† † Department of Geological and Environmental Sciences, Ben-Gurion University of the Negev, Beer Sheva, Israel 84105 ‡ Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot, Israel 76100 ABSTRACT: Rates of thiocyanate degradation were measured in waters and sediments of marine and limnic systems under various redox conditions, oxic, anoxic (nonsulfidic, nonferruginous, nonmanganous), ferruginous, sulfidic, and manganous, for up to 200-day period at micromolar concentrations of thiocyanate. The decomposition rates in natural aquatic systems were found to be controlled by microbial processes under both oxic and anoxic conditions. The Michaelis−Menten model was applied for description of the decomposition kinetics. The decomposition rate in the sediments was found to be higher than in the water samples. Under oxic conditions, thiocyanate degradation was faster than under anaerobic conditions. In the presence of hydrogen sulfide, the decomposition rate increased compared to anoxic nonsulfidic conditions, whereas in the presence of iron(II) or manganese(II), the rate decreased. Depending on environmental conditions, half-lives of thiocyanate in sediments and water columns were in the ranges of hours to few dozens of days, and from days to years, respectively. Application of kinetic parameters presented in this research allows estimation of rates of thiocyanate cycling and its concentrations in the Archean ocean. ■ INTRODUCTION aquatic systems, as well as to chemical transformations, 24−26 Thiocyanate (NCS−) is formed in various natural and industrial volatilization and adsorption. processes. It was found in waste waters from coal and oil The presence of thiocyanate was recorded in various natural nonpolluted aquatic systems, for example in stratified lakes processing, steel manufacturing, and the petrochemical −1 1−5 · Rogoznica in Croatia (up to 288 nmol·L ) and Green Lake industry. Thiocyanate concentrations of up to 17 mmol −1 19 −1 4,6 (NY, USA) (up to 274 nmol·L ). In these lakes thiocyanate L were detected in coal plant wastewaters and in gold fi ff extraction wastewaters.7,8 In electroplating, dyeing, photo- is produced in the anoxic, sul de-rich sediments and di uses to finishing, thiourea, and pesticide production the concentration the chemocline, where it is consumed by oxidative processes, of NCS− in wastewater effluents is in the range of 0.09−2 which are likely biologically enhanced. In the oxic North Sea · −1 9 water thiocyanate was detected at concentrations up to 13 mmol L . Thiocyanate is toxic to aquatic species with LC50 −1 16 −1 10 nmol·L . In saltmarsh sediment of the Delaware Great Downloaded via WEIZMANN INST OF SCIENCE on September 20, 2018 at 06:31:37 (UTC). values of 0.01 to 0.5 mmol·L reported for Daphnia magna. μ · −1 See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. Natural sources of thiocyanate include plants, biological and Marsh, thiocyanate concentrations are up to 2.28 mol L in μ · −1 26 abiotic decomposition of organic matter, and in vivo pore-water and up to 15.6 mol kg in wet sediment. In − detoxification of cyanide.11 14 Several species of bacteria, these sediments, concentrations of thiocyanate precursors, algae, fungi, plants, and animals are physiologically capable of cyanide-reactive zerovalent sulfur and free hydrogen cyanide are μ · −1 μ · −1 detoxifying cyanide, and in most cases one of the end products as high as 78 mol L and 1.9 mol L , respectively. fi of detoxification is thiocyanate.10,15 Another important Coexistence of hydrogen cyanide, polysul des and thiocyanate mechanism of thiocyanate formation in natural aquatic systems allows attribution of thiocyanate formation to the abiotic is the reaction between hydrogen cyanide and sulfide oxidation reactions between hydrogen cyanide and reduced sulfur species. − μ · −1 intermediates, which contain sulfur−sulfur bonds, such as Thiocyanate was also found in concentrations 23 40 mol L 27 colloidal sulfur,16 polysulfides,17 thiosulfate, and tetrathio- in the Red Sea Atlantis II Deep brine. Reactions between nate.18,19 Reaction with thiosulfate is ∼1000 times slower abiotically formed hydrogen cyanide and reduced sulfur species than reaction with polysulfides,17,20,21 and is catalyzed by were proposed as the source of thiocyanate in the brine. The Cu(II) and sulfur transferases from the rhodanese family.15,22 Concentrations of hydrogen cyanide in polluted aquatic Received: September 17, 2017 systems may reach levels toxic to aquatic life.23 In nonpolluted Revised: December 25, 2017 aqueous systems, hydrogen cyanide concentrations are usually Accepted: December 28, 2017 very low due to fast degradation by plants, fungi and bacteria in Published: December 28, 2017 © 2017 American Chemical Society 1234 DOI: 10.1021/acs.est.7b04723 Environ. Sci. Technol. 2018, 52, 1234−1243 Environmental Science & Technology Article Table 1. Rates of Thiocyanate Degradation in Natural and Controlled Systems − · −1 μ · −1· −1 system conditions [NCS ]o (mmol L ) rate ( mol L d ) ref Lake Kinneret and Mediterranean Sea water oxic 0.003 0.026−0.23 this work anoxic 0.003 0.0048−0.021 this work Lake Kinneret and Red Sea sediment oxic 0.003 2.1−2.4 this work anoxic 0.003 0.0074−0.023 this work gold mine tailing storage facility microbial consortium in synthetic medium oxic 0.003 ∼5.4 43 activated sludge mixed liquor oxic 0.003 110 72 wastewater with cultivated microorganisms oxic 0.003 2800 36 Lake Kinneret and Mediterranean Sea water oxic 1 0.43−0.90 this work anoxic 1 0.034−0.34 this work Lake Kinneret and Red Sea sediment oxic 1 45−49 this work anoxic 1 0.078−0.61 this work gold mine tailing storage facility microbial consortium in synthetic medium oxic 1 ∼1700 43 activated sludge mixed liquor oxic 1 2100 72 wastewater with cultivated microorganisms oxic 1 82500 36 water enrichment with Klebsiella species oxic 0.4−3.9 ∼860 79 enrichment cultures from steel plant wastewater oxic 5.7 ∼1.9 53 enrichment cultures from steel plant wastewater anoxic 4.7−5.6 ∼0.79 53 activated sludge anoxic 1.7 0 3 brine liquor with mixed methanogenic cultures anoxic 2.5 0 80 a simulated wastewater containing phenol, thiocyanate, and ammonia-nitrogen anoxic 1.9−10.3 0 81 same processes were proposed to result in thiocyanate the rates may be as high as 83 mmol·L−1·d−1 at 1 mmol·L−1 formation in the hydrothermal springs and pools in the concentration of thiocyanate (Table 1). Thiobacillus species Yellowstone National Park, where it was detected at isolated from steel plant wastewater, are able to degrade 5.2 − − concentrations 133−791 μmol·L−1.28 mmol·L 1 of NCS over 8 days under anaerobic denitrifying Although concentrations of thiocyanate in modern aquatic conditions.53 Rates of thiocyanate degradation depend not only systems are low,16,19,26,28 this may be not the case for the iron- on oxygen concentrations,3,53,80,81 but also on concentrations of rich water column of the Archean ocean. Existence of large nutrients. It was shown that concentrations of NH >70μmol· − 3 atmospheric fluxes of both hydrogen cyanide and zerovalent L 1 may inhibit76 and phosphate concentrations >500 μmol· − − 8 sulfur to Archean ocean has been suggested.29 34 These works L 1 may stimulate thiocyanate biodegradation. provide constraints on cyanide and zerovalent sulfur fluxes but Currently, metabolic pathways for thiocyanate degradation lack of data regarding rates of thiocyanate degradation under are known and the rates of its degradation in bioreactors are environmental conditions in the presence of dissolved iron(II) published, but no data on kinetics of decomposition of prevents estimation of thiocyanate concentrations and its fate in thiocyanate in natural aquatic systems is available. The main fi the Archean ocean. aim of the present research is to ll this gap and to provide Multiple investigations focused on the isolation and constraints on rates of decomposition of thiocyanate in limnic identification of microorganisms that are responsible for and marine water columns and sediments at various redox − thiocyanate biodegradation under controlled conditions.35 52 conditions, which are relevant for modern and ancient natural Thiocyanate-degrading bacteria have been isolated from aquatic systems. To achieve this goal, we have determined activated sludge,41 steel plant wastewater,53 gold mine tailing kinetic parameters of thiocyanate degradation in natural aquatic sites,43,50,51 and extreme alkaline54 and hypersaline55,56 environ- and sedimentary systems at various salinities and concen- − fi ments. The end products of NCS degradation are ammonium, trations of thiocyanate, oxygen, hydrogen sul de, and iron(II). carbon dioxide, and sulfate, subsequent to the formation of − − cyanate57 62 or carbonyl sulfide63 67 as intermediates. A variety ■ MATERIALS AND METHODS − of autotrophic bacteria are capable of using NCS as their sole Materials. Solutions for measurements of the kinetics energy source via sulfur oxidation. Chemolithotrophic bacteria parameters of thiocyanate degradation were prepared in Milli-Q fi − utilize hydrogen sul de formed on the initial step of NCS water, Mediterranean Sea water, Red Sea water, Lake Kinneret degradation and products of its incomplete oxidation (Lake Tiberias) water. Slurries were prepared from Red Sea and (polysulfide, elemental sulfur, or thiosulfate) as an energy Lake Kinneret sediments. All reagents were purchased from 41,63,68,69 source for growth, oxidizing sulfide to sulfate. Sigma-Aldrich and were at least 98% pure. Potassium Utilization of nitrogen released from thiocyanate as ammonia thiocyanate (KSCN) (99%), sodium sulfide nonahydrate 58 · has also been reported. A number of heterotrophic bacteria (Na2S 9H2O) (98%), and iron(II) sulfate heptahydrate − 46,50,52,70,71 · fi utilize NCS as a source of nitrogen and sulfur as (FeSO4 7H2O) (99%) were used without further puri cation.