Toxic Tire Wear Compounds (6PPD-Q and 4-ADPA) Detected in Airborne Particulate Matter Along a Highway in Mississippi, USA.

Tire wear particles (TWPs) are a major category of microplastic pollution produced by friction between tires and road surfaces. This non-exhaust particulate matter (PM) containing leachable toxic compounds is transported through the air and with stormwater runoff, leading to environmental pollution and human health concerns. In the present study, we collected airborne PM at varying distances (5, 15 and 30 m) along US Highway 278 in Oxford, Mississippi, USA, for ten consecutive days using Sigma-2 passive samplers. Particles (~ 1-80 µm) were passively collected directly into small (60 mL) wide-mouth separatory funnels placed inside the samplers. Particles were subsequently subjected to solvent extraction, and extracts were analyzed for TWP compounds by high resolution orbitrap mass spectrometry. This pilot study was focused solely on qualitative analyses to determine whether TWP compounds were present in this fraction of airborne PM. The abundance of airborne TWPs increased with proximity to the road with deposition rates (TWPs cm-2 day-1) of 23, 47, and 63 at 30 m, 15 m, and 5 m from the highway, respectively. Two common TWP compounds (6PPD-Q and 4-ADPA) were detected in all samples, except the field blank, at levels above their limits of detection, estimated at 2.90 and 1.14 ng L-1, respectively. Overall, this work suggests airborne TWPs may be a potential inhalation hazard, particularly for individuals and wildlife who spend extended periods outdoors along busy roadways. Research on the bioavailability of TWP compounds from inhaled TWPs is needed to address exposure risk.

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.

Labeling Microplastics with Fluorescent Dyes for Detection, Recovery, and Degradation Experiments.

Staining microplastics (MPs) for fluorescence detection has been widely applied in MP analyses. However, there is a lack of standardized staining procedures and conditions, with different researchers using different dye concentrations, solvents, incubation times, and staining temperatures. Moreover, with the limited types and morphologies of commercially available MPs, a simple and optimized approach to making fluorescent MPs is needed. In this study, 4 different textile dyes, along with Nile red dye for comparison, are used to stain 17 different polymers under various conditions to optimize the staining procedure. The MPs included both virgin and naturally weathered polymers with different sizes and shapes (e.g., fragments, fibers, foams, pellets, beads). We show that the strongest fluorescence intensity occurred with aqueous staining at 70 °C for 3 h with a dye concentration of 5 mg/mL, 55 mg/mL, and 2 µg/mL for iDye dyes, Rit dyes, and Nile red, respectively. Red fluorescent signals are stronger and thus preferred over green ones. The staining procedure did not significantly alter the surface, mass, and chemical characteristics of the particles, based on FTIR and stereomicroscopy. Stained MPs were spiked into freshwater, saltwater, a sediment slurry, and wastewater-activated sludge; even after several days, the recovered particles are still strongly fluoresced. The approach described herein for producing customized fluorescent MPs and quantifying MPs in laboratory-controlled experiments is both straightforward and simple.

Determination of Metals in Tree Rings by ICP-MS Using Ash from a Direct Mercury Analyzer.

Elemental profiles in cores of tree trunks (bole wood) have been used for environmental monitoring and reconstruction of metal pollution history. Mercury (Hg) is a global pollutant that can be accurately measured in tree rings in a simple and pragmatic fashion using a direct mercury analyzer (DMA) that is based on thermal decomposition, amalgamation, and atomic absorption spectrophotometry. In this feasibility study, we demonstrate that the ash remaining after the DMA analyses can be used to quantify a wide range of other non-volatile elements (Ba, Be, Co, Cr, Cu, Fe, Ga, Mg, Mn, Ni, Pb, Sr, Th, and U) in that same sample of wood by inductively coupled plasma mass spectrometry (ICP-MS) after microwave-assisted acid digestion. Other elements (Ag, Cd, Cs, Rb, Tl, and V) exhibited poor recoveries, possibly due to losses during sample preparation. We assessed the accuracy with reference materials, spikes, and by comparison with EPA Method 3052 (Microwave Assisted Acid Digestion of Siliceous and Organically Based Matrices). For the first group of elements (deemed suitable for the method), recoveries ranged between 80% and 120% and the relative standard deviation was generally < 15%, indicating acceptable precision. We applied the method to five species of trees: eastern red cedar (Juniperus virginiana), loblolly pine (Pinus taeda), shortleaf pine (Pinus echinata), white oak (Quercus alba), and tulip poplar (Liriodendron tulipifera) from Holly Springs National Forest in north Mississippi, USA. Mercury concentrations (ng/g ± SE) were highest in the cedar (1.8 ± 0.3; n = 5), followed by loblolly pine (1.6 ± 0.3, n = 3), shortleaf pine (1.2 ± 0.2; n = 3), oak (1.1 ± 0.2; n = 5), and poplar (0.5 ± 0.1; n = 5). Concentrations of other elements were generally Fe > Mg > Ba ≈ Sr ≈ Mn > Cr ≈ Cu > Ni ≈ Rb > Co > Ga ≈ Ag, with the other elements generally below the method detection limit (MDL). Overall, we showed that the DMA can be used to not only determine total Hg in segments of tree core, but can serve as the ashing step in the preparation of wood for ICP-MS analysis, thus allowing the determination of non-volatile elements along with Hg in the very same sample.

Exposure to mixtures of mercury, cadmium, lead, and arsenic alters the disposition of single metals in tissues of Wistar rats.

Humans throughout the world are exposed regularly to mixtures of environmental toxicants. Four of the most common heavy metal toxicants in the environment are mercury (Hg), cadmium (Cd), lead (Pb), and arsenic (As). Numerous studies have assessed the effects and disposition of individual metals in organ systems; however, humans are usually exposed to mixtures of toxicants or metals rather than to a single toxicant. Therefore, the purpose of the current study was to test the hypothesis that exposure to a mixture of toxic heavy metals alters the disposition of single metals in target organs. Wistar rats (Rattus norvegicus) were exposed to Hg, Cd, Pb, or As as a single metal or as a mixture of metals. Rats were injected intravenously for three days, following which kidneys, liver, brain, and blood were harvested. Samples were analyzed for content of Hg, Cd, Pb, and As via inductively coupled plasma mass spectrometry. In general, exposure to a mixture of metals reduced accumulation of single metals in target organs. Interestingly, exposure to mixtures of metals with Pb and/or As increased the concentration of these metals specifically in the liver. The findings from this study indicate that exposure to mixtures of toxic heavy metals may alter significantly the distribution and accumulation of these metals in target organs and tissues.

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.

Mercury concentrations in fish from three major lakes in north Mississippi: Spatial and temporal differences and human health risk assessment.

The goal of this study was to compare total mercury (Hg) concentrations in fish muscle tissue and assess consumption health risks of fish collected from three north Mississippi lakes (Sardis, Enid, and Grenada) that are extensively used for fishing and recreation. Largemouth bass (LMB; n = 64), channel catfish (CC; n = 72), and white crappie (WC; n = 100), which represent a range of trophic levels, were collected during spring 2013 and 2014. Creel data estimated that anglers harvested approximately 370,000 kg of WC, 27,000 kg of CC, and 15,000 kg of LMB from the lakes annually. Median Hg wet weight concentrations were highest in LMB (443 ng/g), followed by CC (211 ng/g) and WC (192 ng/g). Fish-Hg concentrations were lower than those reported in fish >10 years ago. There were significant differences between lakes consistent across species. Grenada length-normalized fish-Hg concentrations were higher than those from Enid and Sardis. Because existing consumption advisories for CC are length based, the lack of relationship between length and Hg concentration indicated that the recommendations may not be sufficiently protective. Further, five different risk assessment paradigms yielded hazard quotient (HQ) values suggesting that existing fish consumption advisories may be insufficient to protect adults and especially children from exposure to Hg.

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.

Analysis of automotive paint layers on plastic substrates using chemical imaging µ-FTIR and O-PTIR microspectroscopy.

Automobile paint chips are a crucial piece of trace evidence for forensic investigators. This is because automotive paints are composed of multiple layers, including the primer, basecoat, and clearcoat, each of which has its own chemical composition that can vary by vehicle make, model, year, and manufacturing plant. Thus, Fourier-transform infrared (FTIR) spectral databases for automobile paint systems have been established to aid law enforcement in, for example, narrowing search parameters for a suspect's vehicle. Recently, car manufacturers have implemented primers on plastic substrates that are much thinner (~5 µm) than those on metal substrates, making it more difficult to manually separate for analyses. Here, we evaluated FTIR microspectroscopy (µ-FTIR) and optical photothermal infrared spectroscopy (O-PTIR) to chemically image cross sections of paint chips without manually separating the layers. For µ-FTIR, transmission and transflection modes provided the highest quality spectra compared to reflection and µ-ATR analyses. Point analysis was preferable to chemical imaging, as peaks were identified in the point (MCT) detector's lower spectral range that was below the imaging (FPA) detector's cutoff, such as those associated with titanium dioxide. Reduced spectral range can lead to a similar issue in O-PTIR analyses depending on instrument configuration. However, its complementary Raman spectra showed strong titanium dioxide peaks, providing an alternate means of identification. Both techniques are likely to become more relevant as they are non-destructive and avoid manual separation of the layers. O-PTIR is particularly well-suited for analysis of the thin primer layer due to its superior spatial resolution.

Preliminary evaluation of the use of homing pigeons as biomonitors of mercury in urban areas of the USA and China.

Mercury was determined in the tissues (feather, lung, liver, and kidney) of homing pigeons (Columbia livia domestica) from both the USA (Glendora, California and Midland, Texas) and China (Beijing and Chengdu). Among these cities, mercury concentrations were greatest in samples from Beijing, which is known to have relatively high levels of airborne mercury. Among the tissues, levels were highest in the feather, followed by kidney, liver, and lung. There was no significant trend for mercury with pigeon age, weight, or sex, except for mercury with bird weight in the lung of the Beijing samples. Overall, the data adds to the growing body of evidence that the homing pigeon can serve as a useful biomonitor in urban areas.

Adsorption/desorption of mercury (II) by artificially weathered microplastics: Kinetics, isotherms, and influencing factors.

While both mercury (Hg) and microplastics (MPs) are well-studied global pollutants, comparatively little is known about the interactions between them and the mobilization of Hg from MPs into organisms. We examined the affinity of Hg(II) to artificially weathered MPs, including polyamide (w-PA), polyethylene (w-PE), polyethylene terephthalate (w-PET), polyester fibers (w-PEST), polyvinyl chloride (w-PVC), and polylactic acid (w-PLA), along with crumb rubber (CR) and PE collected from a wastewater treatment plant (WWTP-PE). WWTP-PE, CR, and w-PEST had particularly high Hg(II) affinities, which can be attributed to electrostatic interaction and pore filling. The adsorption followed a pseudo-second-order kinetic process and fitted the Freundlich model, suggesting multi-step (mass transfer and intraparticle diffusion) and heterogeneous adsorptions. Hydrochemical conditions (pH, dissolved organic matter (DOM), salinity and co-existent metal ions) all impacted Hg-MP behavior. Changes in Hg speciation and MP surface properties contributed to the different Hg(II) adsorption capacities for the MPs. Weathering of MPs generally increased the adsorption of Hg(II) onto MPs, but CR, PET and PEST did not follow this trend. Less than 3% of adsorbed Hg(II) was mobilized from the MPs in freshwater, but that increased up to 73% under simulated avian digestive conditions, suggesting increased bioavailability of Hg(II) from ingested MPs. Overall, weathered MPs adsorb and retain Hg(II) under environmentally relevant conditions but desorb much of it in simulated avian digestion fluid, suggesting that birds that ingest MPs may have increased Hg(II) exposure.

Distribution and characteristics of microplastics in beach sand near the outlet of a major reservoir in north Mississippi, USA.

Plastic debris both affects and is affected by the beaches it accumulates on. Most studies of microplastics (MPs) in beach sand are focused on coastal beaches or beaches of large lakes near population centers. Here, we assessed MP pollution at a sandy beach near the outlet of a major flood control reservoir (Sardis Lake) in a relatively unpopulated area in north Mississippi, USA, focusing on two prominent wrack zones and areas in-between. Putative MPs were isolated by density separation and matrix digestion, and then examined using stereomicroscopy, with a subset of samples additionally analyzed by µ-FTIR. MP abundance (particles/kg ± 1 standard error (SE), n = 15) averaged of 590 ± 360, with 950 ± 100 in the lower wrack zone, 540 ± 40 in the upper wrack zone, and 270 ± 30 in areas between; these differences were statistically significant (p < 0.01). The MPs generally had similar size and shape characteristics across sites. The majority were fibers (64%), followed by fragments (23%), beads (7%) and films (6%), with a slightly greater proportion of fibers in the wrack zones compared to areas in-between. The number of MPs rose dramatically with decreasing size. Beads were only found in the < 500 µm size fraction. Clear and blue were the predominant colors for all MPs. A total of 29 different types of polymers were detected, with more than half of the particles being composed of polyethylene and polyamide, followed by poly(methyl methacrylate), polyethylene terephthalate, polycarbonate, polypropylene, and others; although this distribution varied some depending on size fraction and location. Because there are no major wastewater discharges into Sardis Lake, the source of the MPs is likely degradation of carelessly discarded plastic, as well as atmospheric fallout. Overall, we found that MP concentrations were highest in the wrack zones and influenced by rates and duration of discharge from the reservoir. Thus, like coastal beaches, wrack zones on freshwater beaches along or downstream of reservoirs accumulate both macro- and micro-plastics and are prime locations for plastic cleanup. Finally, we show that MPs made from naturally weathered LDPE plastic film are prone to fragmentation during pretreatment procedures, which may result in its overestimation.

Concentrations of gaseous elemental mercury in ambient air within an academic chemistry building.

Gaseous elemental mercury (GEM) concentrations were determined within an academic chemistry building by cold vapor atomic fluorescence spectrometry. Concentrations varied depending on the room activity, with night time and weekend levels the lowest and most stable (typically between 10 and 20 ng/m(3)), and daytime weekday levels the highest (averaging about 3-5 times higher). Laboratory air exhibited daytime concentration spikes as high as 1,600 ng/m(3). Office levels were similar to weekend laboratory concentrations, suggesting a general building-wide mercury background. However, concentration spikes suggest GEM levels may be exacerbated by foot traffic which may cause motion-induced wafting from higher concentration areas. Based on current regulations the GEM levels do not present a health hazard.

Ecotoxicological effects of micronized car tire wear particles and their heavy metals on the earthworm (Eisenia fetida) in soil.

As one of the most common and persistent emerging human-made pollutants, microplastics (MPs) have become a global environmental problem. Although many studies have demonstrated the impact of MPs on aquatic organisms, the potential effects on terrestrial fauna are relatively unknown, even though soil is a major sink for plastic pollution. In this study, earthworms (Eisenia fetida) were exposed to MPs from tires (TMPs) in artificial soil at different TMP concentrations (0, 1, 5, 10, and 20%, w/w), at different TMP size fractions (2 mm-350 µm; 350 µm-50 µm; 50 µm-25 µm; and <25 µm), and time periods (14 and 28 days). The purpose was to evaluate the impact of TMPs on the bioaccumulation of heavy metals (Zn, Cd, and Pb) and levels of oxidative stress in the earthworms. Fluorescence imaging of TMPs stained with Nile red dye clearly showed that the worms had ingested the TMPs, with smaller particles preferentially consumed. The ingested TMPs had altered the surface morphology, degradation that increased surface area and uptake of heavy metals into the organisms. Earthworms exposed to TMPs at the higher concentrations showed clear signs of oxidative stress, with significantly (p < 0.05) increased catalase and peroxidase activity and lipid peroxidation levels, and reduced activity of superoxide dismutase and glutathione S-transferase. SOD, POD, and CAT are important cell protection enzymes that prevent excessive levels of reactive oxygen species in cells. MDA represents the total scavenging ability of free radicals in the tissue. SOD decreases and MDA accumulates rapidly. GST has a detoxification effect. Overall, this study adds to the growing body of evidence that TMPs are harmful to certain terrestrial organisms.

Separation and identification of microplastics in marine organisms by TGA-FTIR-GC/MS: A case study of mussels from coastal China.

Microplastics are ubiquitous in the marine environment but characterizing them in marine organisms is challenging. Herein we describe a method to detect, identify, and quantify microplastics in marine mussels (Mytilus edulis) using thermal gravimetric analysis - Fourier Transform infrared spectroscopy - gas chromatography mass spectrometry (TGA-FTIR-GC/MS) after extracting and isolating the microplastics using chemical digestion, density separation, and filtration. Combining the three instrumental techniques adds discriminatory power as temperature profiles, chromatograms, and vibrational and mass spectra differ among common plastics. First, we tested several digestion schemes after spiking the mussels with plastics commonly found in the marine environment, including polyethylene (PE), polystyrene (PS), polypropylene (PP) and polyvinyl chloride (PVC). KOH (10%, w/v) was the most suitable reagent, providing good recoveries (>97%) without degrading the microplastics. We show that the technique TGA-FTIR-GC/MS can be optimized to readily determine both the type (polymer) and amount (mass) of microplastics in the sample. Applied to 100 mussels from each of six locations along the coast of China, we found an average of 0.58 mg of plastic per kg of tissue (range 0.16-1.71 mg/kg), with PE being the most abundant type of plastic measured. Among the coastal cities, mussels from Dalian had the highest microplastic content. Overall, we demonstrate that the method is a powerful technique to quantify masses of microplastics in marine mussels, a species commonly used as a bioindicator of pollution, and may be applied to other biota as well.

Single-Pot Method for the Collection and Preparation of Natural Water for Microplastic Analyses: Microplastics in the Mississippi River System during and after Historic Flooding.

We describe a simple single-pot method for collection and preparation of natural water for microplastic analyses. The method prepares samples in the same vessel (mason jars) that they are collected in right up until the microplastics are transferred onto filters or spectroscopic windows for analyses. The method minimized contamination, degradation, and losses, while increasing recoveries and throughput when compared with conventional sieving. We applied it to surface grab samples collected from the Mississippi River and its major tributaries during and after historic flooding in 2019. Microplastics (>~30 µm) were quantified using Nile red fluorescence detection, and a small subset of samples were identified by micro-Fourier transform infrared imaging spectroscopy. Concentrations were lower during the flooding, likely due to dilution. Concentrations ranged from approximately 14 microplastics/L in the Tennessee River during flooding to approximately 83 microplastics/L in the Ohio River during low-flow (summer) conditions. Loads of microplastics tended to increase downriver and ranged from approximately 87 to approximately 129 trillion microplastics/d near New Orleans. Most of the microplastics (>60%) were in the lower size fraction (~30-90 µm) and consisted primarily of fragments (~85%), followed by fibers (~8%) and beads (~7%), with polyester, polyethylene, polypropylene, and polyacrylate as the primary microplastic types. Overall, we demonstrate that the single-pot method is effective and versatile and, because it uses relatively inexpensive and easily assembled materials, can be adapted for microplastic surveys worldwide, especially those involving sample collection by volunteers from the community and schools. Environ Toxicol Chem 2020;39:986-995. © 2020 SETAC.

Effect of prothioconazole on the degradation of microplastics derived from mulching plastic film: Apparent change and interaction with heavy metals in soil.

Microplastic pollution is a major global environmental problem in both aquatic and terrestrial environments. Pesticides are frequently applied to agricultural soil to reduce the effects of pests on crops, but may also affect the degradation of plastics. In this study, we generated microplastics from polyethylene (PE) film and biodegradable poly(butylene adipate-co-terephthalate) (PBAT) film and determined (1) the effect of prothioconazole on degradation of the microplastics, and (2) the adsorption and release characteristics of heavy metals (Cr, Cu, As, Pb, Ba, and Sn) by the microplastics during degradation process. Changes of surface functional groups and morphologies were measured by FTIR and SEM, while metal concentrations were determined by ICPMS. Prothioconazole was found to promote plastic degradation. PBAT degraded faster and adsorbed more heavy metals from the soil than PE. Whether the microplastics adsorb or release heavy metals depended on the metal and their concentrations. Prothioconazole inhibited the adsorption of Cr, As, Pb and Ba by microplastics, promoted the adsorption of Cu, and had no significant effect for Sn. These results can help to assess the ecological risk of microplastic pollution from plastic mulch when combined with heavy metals.

Occurrence of Microplastic Pollution at Oyster Reefs and Other Coastal Sites in the Mississippi Sound, USA: Impacts of Freshwater Inflows from Flooding.

Much of the seafood that humans consume comes from estuaries and coastal areas where microplastics (MPs) accumulate, due in part to continual input and degradation of plastic litter from rivers and runoff. As filter feeders, oysters (Crassostrea virginica) are especially vulnerable to MP pollution. In this study, we assessed MP pollution in water at oyster reefs along the Mississippi Gulf Coast when: (1) historic flooding of the Mississippi River caused the Bonnet Carré Spillway to remain open for a record period of time causing major freshwater intrusion to the area and deleterious impacts on the species and (2) the spillway was closed, and normal salinity conditions resumed. Microplastics (~25 µm-5 mm) were isolated using a single-pot method, preparing samples in the same vessel (Mason jars) used for their collection right up until the MPs were transferred onto filters for analyses. The MPs were quantified using Nile Red fluorescence detection and identified using laser direct infrared (LDIR) analysis. Concentrations ranged from ~12 to 381 particles/L and tended to decrease at sites impacted by major freshwater intrusion. With the spillway open, average MP concentrations were positively correlated with salinity (r = 0.87, p = 0.05) for sites with three or more samples examined. However, the dilution effect on MP abundances was temporary, and oyster yields suffered from the extended periods of lower salinity. There were no significant changes in the relative distribution of MPs during freshwater intrusions; most of the MPs (>50%) were in the lower size fraction (~25-90 µm) and consisted mostly of fragments (~84%), followed by fibers (~11%) and beads (~5%). The most prevalent plastic was polyester, followed by acrylates/polyurethanes, polyamide, polypropylene, polyethylene, and polyacetal. Overall, this work provides much-needed empirical data on the abundances, morphologies, and types of MPs that oysters are exposed to in the Mississippi Sound, although how much of these MPs are ingested and their impacts on the organisms deserves further scrutiny. This paper is believed to be the first major application of LDIR to the analysis of MPs in natural waters.

Total mercury and methylmercury migration and transformation in an A2/O wastewater treatment plant.

Municipal wastewater treatment plants (MWTPs) serve an essential role in reducing mercury (Hg) pollution. However, few studies quantified the transport and transformation of Hg through MWTPs, particularly plants based on the anaerobic-anoxic-aerobic (A2/O) process. Here, we present a mass balance for total mercury (THg) and total methylmercury (TMeHg) at the plant, and investigate the influence of pH, temperature, and dissolved oxygen on the occurrence and fate of methylmercury (MeHg) in the system. The concentrations of the THg and TMeHg in the raw sewage were 40.3 ± 26.6 ng/L (4.3 ± 2.7 g/day) and 1.9 ± 0.6 ng/L (193 ± 58 mg/day), respectively. Their concentrations in the plant's effluent water were 7.4 ± 1.5 ng/L (0.74 ± 0.2 g/day) and 0.04 ± 0.01 ng/L (3.9 ± 1.0 mg/day), corresponding to decreases of ~82% for THg and ~98% for TMeHg. Within the plant, only ~10% of the THg was removed with primary sedimentation, as Hg in the raw sewage was predominately in dissolved form. In contrast, a significant portion of TMeHg (~43%) was associated with incoming particulate matter. Much of the remaining Hg was removed in subsequent A2/O process and secondary clarifiers, with a ~78% of the THg entering the plant transferring to the dewatered sludge (concentration 1.05 ± 0.28 µg/g; 3.2 ± 0.8 g/day). These same steps decreased TMeHg in the water by ~95%, with <10% of that reduction being TMeHg transferred to the sludge (concentration 2.1 ± 1.1 ng/g; 6.2 ± 3.3 mg/day), suggesting >90% TMeHg degradation. In addition, the most important factor that impacted the variation of TMeHg concentrations was pH, then was temperature. Dissolved oxygen showed no relationship with TMeHg and DMeHg. Overall, this study demonstrates that A2/O MWTPs effectively remove MeHg from wastewater, however, sludge remains an important potential source of Hg to the environment.

(239, 240, 241)Pu fingerprinting of plutonium in western US soils using ICPMS: solution and laser ablation measurements.

Sector field inductively coupled plasma mass spectrometry (SF-ICPMS) has been used with analysis of solution samples and laser ablation (LA) of electrodeposited alpha sources to characterize plutonium activities and atom ratios prevalent in the western USA. A large set of surface soils and attic dusts were previously collected from many locations in the states of Nevada, Utah, Arizona, and Colorado; specific samples were analyzed herein to characterize the relative contributions of stratospheric fallout vs. Nevada Test Site (NTS) plutonium. This study illustrates two different ICPMS-based analytical strategies that are successful in fingerprinting Pu in environmental soils and dusts. Two specific datasets have been generated: (1) soils are leached with HNO3-HCl, converted into electrodeposited alpha sources, counted by alpha spectrometry, then re-analyzed using laser ablation SF-ICPMS; (2) samples are completely dissolved by treatment with HNO3-HF-H3BO3, Pu fractions are prepared by extraction chromatography, and analyzed by SF-ICPMS. Optimal laser ablation and ICPMS conditions were determined for the re-analysis of archived alpha spectrometry "planchette" sources. The best ablation results were obtained using a large spot size (200 microm), a defocused beam, full repetition rate (20 Hz) and scan rate (200 microm s(-1)); LA-ICPMS data were collected with a rapid electrostatic sector scanning experiment. Less than 10% of the electroplated surface area is consumed in the LA-ICPMS analysis, which would allow for multiple re-analyses. Excellent agreement was found between (239+240)Pu activities determined by LA-ICPMS vs. activity results obtained by alpha spectrometry for the same samples ten years earlier. LA-ICPMS atom ratios for 240Pu/239Pu and 241Pu/239Pu range from 0.038-0.132 and 0.00034-0.00168, respectively, and plot along a two-component mixing line (241Pu/239Pu = 0.013 [240Pu/239Pu] - 0.0001; r2 = 0.971) with NTS and global fallout end-members. A rapid total dissolution procedure, followed by extraction chromatography and SF-ICPMS solution Pu analysis, generates excellent agreement with certified (239+240)Pu activities for standard reference materials NIST 4350b, NIST 4353, NIST 4357, and IAEA 385. (239+240)Pu activities and atom ratios determined by total dissolution reveal isotopic information in agreement with the LA-ICPMS dataset regarding the ubiquitous mixing of NTS and stratospheric fallout Pu sources in the regional environment. For several specific samples, the total dissolution method reveals that Pu is incompletely recovered by simpler HNO3-HCl leaching procedures, since some of the Pu originating from the NTS is contained in refractory siliceous particles.