Mercury Methylation Potentials in Sediments of an Ancient Cypress Wetland Using Species-Specific Isotope Dilution GC-ICP-MS.

Wetlands are of a considerable environmental value as they provide food and habitat for plants and animals. Several important chemical transformations take place in wetland media, including the conversion of inorganic mercury (Hg) to monomethylmercury (MeHg), a toxic compound with a strong tendency for bioconcentration. Considering the fact that wetlands are hotspots for Hg methylation, we investigated, for the first time, Hg methylation and demethylation rates in an old growth cypress wetland at Sky Lake in the Mississippi Delta. The Sky Lake ecosystem undergoes large-scale water level fluctuations causing alternating periods of oxic and anoxic conditions in the sediment. These oscillating redox conditions, in turn, can influence the transformation, speciation, and bioavailability of Hg. In the present study, sediment cores from the wetland and Sky Lake itself were spiked with enriched stable isotope tracers of inorganic Hg and MeHg and allowed to incubate (in-situ) before freezing, sectioning, and analysis. Methylation rates (day−1) ranged from 0.012 ± 0.003 to 0.054 ± 0.019, with the lowest rate in the winter and the highest in the summer. Demethylation rates were about two orders of magnitude higher, and also greater in the warmer seasons (e.g., 1.84 ± 0.78 and 4.63 ± 0.51 for wetland sediment in the winter and summer, respectively). Methylation rates were generally higher in the open water sediment compared to wetland sediment, with the latter shaded and cooler. Both methylation (r = 0.76, p = 0.034) and demethylation (0.97, p = 0.016) rates (day−1) were positively correlated with temperature, but not with most other water quality parameters. MeHg concentration in the water was correlated with pH (r = 0.80, p < 0.05), but methylation rates were only marginally correlated (r = 0.71). Environmental factors driving microbial production of MeHg in the system include warm temperatures, high levels of labile natural organic matter, and to a lesser extent the relatively low pH and the residence time of the water. This study also provides baseline data that can be used to quantify the impacts of modifying the natural flow of water to the system on Hg methylation and demethylation rates.

Concentrations of select dissolved trace elements and anthropogenic organic compounds in the Mississippi River and major tributaries during the summer of 2012 and 2013.

The Mississippi River drainage basin includes the Illinois, Missouri, Ohio, Tennessee, and Arkansas rivers. These rivers drain areas with different physiography, population centers, and land use, with each contributing a different suites of metals and wastewater contaminants that can affect water quality. In July 2012, we determined 18 elements (Be, Rb, Sr, Cd, Cs, Ba, Tl, Pb, Mg, Al, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and chlorophyll-a (Chl-a) in the five major tributaries and in the Upper Mississippi River. The following summer, we determined both trace elements and 25 trace organic compounds at 10 sites in a longitudinal study of the main stem of the Mississippi River from Grafton, Illinois to Natchez, Mississippi. We detected wastewater contaminants, including pharmaceuticals and endocrine disrupting compounds, throughout the river system, with the highest concentrations occurring near urban centers (St. Louis and Memphis). Concentrations were highest for atrazine (673 ng L-1), DEET (540 ng L-1), TCPP (231 ng L-1), and caffeine (202 ng L-1). The Illinois, Missouri, and Yazoo rivers, which drain areas with intense agriculture, had relatively high concentrations of Chl-a and atrazine. However, the Ohio River delivered higher loads of contaminants to the Mississippi River, including an estimated 177 kg day-1 of atrazine, due to higher flow volumes. Concentrations of heavy metals (Ni, V, Co, Cu, Cd, and Zn) were relatively high in the Illinois River and low in the Ohio River, although dissolved metal concentrations were below US EPA maximum contaminant levels for surface water. Multivariate analysis demonstrated that the rivers can be distinguished based on elemental and contaminant profiles.

Activated Carbon and Biochar Reduce Mercury Methylation Potentials in Aquatic Sediments.

Much of the toxic methylmercury (MeHg) that biomagnifies in the aquatic food chain and accumulates in fish and seafood is believed to originate from microbial methylation of inorganic Hg(+2) in anoxic sediments. We examined the effect amending wetland sediments with activated carbon and biochar on Hg methylation potentials using microcosms and Hg stable isotope tracers. The inorganic (200)Hg(+2) spike was methylated at ~0.37 %/day in the untreated sediment, but that rate decreased to <0.08 %/day for the amended sediments, with 80 % and 88 % reductions in methylation rates for activated carbon and biochar amendments, respectively. Demethylation rates were relatively unchanged. Our key finding is that amending contaminated sediment with activated carbon and biochar decreases bioavailable Hg, and thus may also decrease Hg transfer into food webs. However, further research is needed to evaluate exactly how the sorbents impact Hg methylation rates and for related field studies.

Commercially available mouthguards: Unearthing trace elements for the first time.

The use of mouthguards is advocated by the American Dental Association for orofacial injury prevention and teeth protection. However, the chemical environment in the mouth may cause harmful substances within the mouthguard's polymer material to leach out and be absorbed by the user. Considering this, the present study for the first time analyzed commercially available mouthguards and disclosed the presence of trace elements. Specifically, an analytical method was developed based on closed-vessel microwave-assisted digestion and plasma-based atomic spectrometry for determining toxic trace elements in mouthguard samples. Initially, 75 elements were assessed and, thereafter, quantified cadmium (Cd), copper (Cu) and lead (Pb) in each sample by inductively coupled plasma mass spectrometry (ICP-MS). Method validation was carried out by analyzing a certified reference material of Low-Density Polyethylene, and by addition and recovery experiments. Results for copper were further validated by ICP optical emission spectrometry (ICP-OES). While most samples exhibited elemental levels beneath the method's limit of quantification, Cd, Cu and Pb were detected in four samples. Remarkably, one sample had Cu levels exceeding safe limits by 109 times, highlighting potential toxicity risks. This initial research underscores the need for stricter contamination control in mouthguard materials to minimize potentially health hazards.

Quantification of trace elements in surgical and KN95 face masks widely used during the SARS-COVID-19 pandemic.

During the current coronavirus disease (COVID-19) pandemic, face masks have been the single most important protective equipment against the threat of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). While masks are worn, both the nose and the mouth of the user come in contact with the mask material, and as the latter mediates the inhaled air and may interfere with the swallowed saliva, it is of paramount importance to assure that the mask is free of toxic substances. As there are currently no studies on the total amount of trace elements in masks, the present study fills the void and investigates 24 surgical and KN95 face masks. Specifically, mask samples were analyzed using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to determine the total concentrations of trace elements as well as to assess the possibility that any detected of the elements present could transfer into the human body, based on saliva leaching and breathing experiments. Accordingly, it is reported herein that although most masks analyzed in this study contain trace elements below their corresponding detection limits, a few masks did contain detectable levels of trace elements. In particular, the maximum values that were determined in certain analyzed samples were: Pb (13.33 µg g-1), Cu (410 µg g-1), Zn (56.80 µg g-1), and Sb (90.18 µg g-1). Finally, in the masks that Pb was present, it easily leached out (58% transfer during a 6-h exposure) during the saliva simulation experiments.