News Release

Title
Potential application of a hydrotalcite-like compound for reduction of toxicity to aquatic organisms
via rapid and efficient removal of hydrogen sulfideKey Points•MF-HT is a low-cost and safe material for high-efficient removal of H2S in water•MF-HT reduced toxicities for water microorganisms in groundwater with H2S•MF-HT has excellent reusability for H2S removal in water.
Summary
Hydrogen sulfide (H2S) is a toxic gas with a rotten egg odor and is known to occur naturally andartificially in volcanic zones, hot springs, wastewater treatment plants, landfills, and oil refineries,etc. H2S is usually generated by sulfate-reducing bacteria that exist in anaerobic condition, such as
in the lake sediments. It can be easily dissolved in water and exists as HS-, which is toxic to aquaticorganisms at very low concentrations (0.003-2 mg/L). In this study, Professor Masashi Kato's
research group investigated the H2S removal ability of a patented hydrotalcite-type compound(MF-HT) consisting of magnesium and iron and evaluated its potential application for reducing
toxicity to aquatic organisms. The results showed that the MF-HT has a high adsorption capacity of
146.5 mg/g with a fast adsorption equilibrium time of 45 min for H2S removal, both of which are
top-class compared with those of other adsorbents previously reported. In fact, removal of hydrogensulfide (1.2-152.5 mg/L) at an average rate of > 97.6% was achieved in groundwater samples(n=16) by the MF-HT within 60 min. The toxicities of groundwater, indicated by inhibition rate formicroalgae (primary producers) and immobilization rate for crustaceans (secondary consumers),
were reduced by 96.1% and 82.5% in 2-fold and 4-fold diluted groundwater, respectively, aftertreatment with the MF-HT for 60 min. These results indicate that MF-HT has an excellent safety
record for aquatic organisms. After clarifying the adsorption mechanism, excellent reusability of
MF-HT was also confirmed after regeneration using 1 M Na2CO3 solution. Considering the efficacy,speed, safety and cost of MF-HT, it could be a novel promising material for solving the problem ofhydrogen sulfide pollution in the hydrosphere.

Research BackgroundHydrogen sulfide (H2S), a highly toxic chemical, can cause damage to multiple organs including
respiratory and neural systems. Toxicities of hydrogen sulfide have been shown not only as a gas in
the atmosphere but also as dissolved forms (90% as HS- at pH > 8.0) in the hydrosphere due to its
solubility of 4000 mg/L (20°C) in water. It has been shown that hydrogen sulfide affects the growthand survival of aquatic organisms such as fish, invertebrates, plants and algae at concentrations aslow as 0.003-2.0 mg/L. Since hydrogen sulfide can be naturally generated by reduction of sulfate ordegradation of organic matter in the absence of oxygen by sulfate-reducing microorganisms, it isoften detected in groundwater and sediments in water systems. Hydrogen sulfide is also generated
anthropogenically from various industrial activities, such as in petrochemical industry, paper andpulp mills, and tanneries and in sewer treatment plants. Therefore, it is important to develop an
efficient removal method for hydrogen sulfide in the hydrosphere to maintain the diversity of aquaticorganisms and to reduce the dissipation of hydrogen sulfide to the atmosphere in order to prevent
health risks for humans and animals living on land. Thus, in this study, we have first investigated theremoval capacity of our original adsorbent (MF-HT) for hydrogen sulfide removal in water.
Research Results
Firstly, the removal capacity of hydrogen sulfide by MF-HT along with contact time wasinvestigated. Equilibrium removal was achieved after 45 min. The kinetics of hydrogen sulfide
removal by MF-HT were analyzed using pseudo-first-order and pseudo-second-order models. Thekinetic data fitted well to both pseudo-first-order and pseudo-second-order models, indicating thepossible mechanisms of physical and chemical interaction on MF-HT. Then, the removal capacity of
MF-HT was investigated by varying the initial concentrations of sulfide in water. The adsorption
experimental data was analyzed using Langmuir isotherm model. The maximum adsorption
capacity estimated from the Langmuir isotherm model was 146.49 mg/g in theory.
The hydrogen sulfide removal capacity of MF-HT ina real application was further investigated using
groundwater samples (n=16) obtained in Japan.
Hydrogen sulfide in all of the water samples wasefficientlyremovedbyMF-HT.

Themeanconcentration of hydrogen sulfide in the watersamples was reduced from 23.9 to 0.56 mg/L after
treatment with MF-HT, indicating > 97.6% removal ofhydrogen sulfide by MF-HT (Fig. 1).

Fig. 1 Removal of hydrogen sulfide fromspring water samples using MF-HT.

To evaluate the effect of alleviated toxicity foraquatic organisms by MF-HT-mediated removal ofhydrogen sulfide, microalgal and daphnia toxicity
tests were performed. The rate of inhibition on
microalgal reproduction was reduced by 96.1% in2-fold diluted groundwater after treatment withMF-HT. The immobilization rate of daphnia neonates
was reduced by 82.5% in 4-fold diluted groundwater
after remediation by MF-HT (Fig. 2).
To clarify the adsorption mechanism using MF-HT,

Fig. 2 Toxicity evaluation of spring water
samples before and after MF-HT remediation.

analyses by XRD, FTIR and SEM-EDX were performed and changes in the structure and functionalgroups of MF-HT after hydrogen sulfide adsorption were determined. The results showed that thehydrotalcite-like structure of MF-HT was not affected by the adsorption process, while peaks ofsulfate appeared in FT-IR spectra of MF-HT after adsorption and sulfur content was increased on
MF-HT after adsorption. These findings indicated that ion exchange of hydrogen sulfide ion andbicarbonate ion may have occurred and that intercalated hydrogen sulfide ion was further oxidized
to form sulfate. The results imply that regeneration of MF-HT is possible by using Na2CO3 solution
to desorb sulfate from MF-HT. After desorption using 1 M Na2CO3 solution for 30 min, the adsorption
capacity of regenerated MF-HT was evaluated. The results showed that the adsorption capacity ofregenerated MF-HT (71.32 mg/g) was similar to that of raw MF-HT (72.73 mg/g), indicating
excellent reusability of MF-HT for removal of hydrogen sulfide in water.

Research Summary and Future Perspective
Hydrogen sulfide can be generated in eutrophic sediments of lakes and oceans, which would
severely threaten the health and survival of aquatic organisms, especially benthic organisms.
Furthermore, hydrogen sulfide in water is continuing to be produced by various industries worldwide.
In this study, we found that there was a high level of naturally produced hydrogen sulfide ingroundwater. We showed that our adsorbent MF-HT could efficiently remove hydrogen sulfide ingroundwater samples and significantly improved the survival ratios of an aquatic animal(crustacean) as well as an aquatic phytoplankton (microalgae). Our results suggest that our MF-HT
may be useful for maintaining the diversity of aquatic organisms as well as remediating waterpollution caused by naturally and anthropogenically produced hydrogen sulfide. Due to the low costof MF-HT in addition to its high performance and safety shown in this study, it could be a novel
candidate for remediation of water pollution caused by hydrogen sulfide.
Publication
Journal: Journal of Environmental Management
Title: Potential application of a hydrotalcite-like compound for reduction of toxicity to aquaticorganisms via rapid and efficient removal of hydrogen sulfide
Author: Tian Yuana,b, Kazunori Hashimotoa,c,d, Akira Tazakia,d, Masahiro Hasegawaa, Fitri
Kurniasaria,d, Chihiro Ohtaa,d, Masayo Aokia,d, Nobutaka Ohgamia,d, Masashi Katoa,d,*Affiliation:a Department of Occupational and Environmental Health, Nagoya University Graduate School ofMedicine, 65 Tsurumai-cho, Showa-ku, Nagoya, Aichi, 466-8550, Japan.
bFaculty of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba,Ibaraki, 305-8572, Japan.
c Department of Molecular Biology, Faculty of Pharmacy, Meijo University, Nagoya, Aichi, Japan.
d Voluntary Body for International Healthcare in Universities, Nagoya, Aichi, Japan.

DOI: 10.1016/j.jenvman.2022.115861

Japanese ver.
https://www.med.nagoya-u.ac.jp/medical_J/research/pdf/Jou_220830.pdf