Three new species in Russula subsection Xerampelinae supported by genealogical and phenotypic coherence.

Xerampelinae is a subsection composed of species of ectomycorrhizal fungi belonging to the hyperdiverse and cosmopolitan genus Russula (Russulales). Species of Xerampelinae are recognized by their fishy or shrimp odor, browning context, and a green reaction to iron sulfate. However, species delimitation has traditionally relied on morphology and analysis of limited molecular data. Prior taxonomic work in Xerampelinae has led to the description of as many as 59 taxa in Europe and 19 in North America. Here we provide the first multilocus phylogeny of European and North American members based on two nrDNA loci and two protein-coding genes. The resulting phylogeny supports the recognition of 17 species-rank Xerampelinae clades; however, higher species richness (~23) is suggested by a more inclusive nuclear rDNA internal transcribed spacer region ITS1-5.8S-ITS2 (ITS barcode) analysis. Phylogenetic and morphological analyses support three new species with restricted geographic distributions: R. lapponica, R. neopascua, and R. olympiana. We confirm that the European species R. subrubens is present in North America and the North American species R. serissima (previously known as R. favrei) is present in Europe. Most other Xerampelinae appear restricted to either North America or Eurasia, which indicates a high degree of regional endemism; this includes R. xerampelina, a name widely applied to North American taxa, but a species restricted to Eurasia.

PacBio high-throughput multi-locus sequencing reveals high genetic diversity in mushroom-forming fungi.

Multi-locus sequence data are widely used in fungal systematic and taxonomic studies to delimit species and infer evolutionary relationships. We developed and assessed the efficacy of a multi-locus pooled sequencing method using PacBio long-read high-throughput sequencing. Samples included fresh and dried voucher specimens, cultures and archival DNA extracts of Agaricomycetes with an emphasis on the order Cantharellales. Of the 283 specimens sequenced, 93.6% successfully amplified at one or more loci with a mean of 3.3 loci amplified. Our method recovered multiple sequence variants representing alleles of rDNA loci and single copy protein-coding genes rpb1, rpb2 and tef1. Within-sample genetic variation differed by locus and taxonomic group, with the greatest genetic divergence observed among sequence variants of rpb2 and tef1 from corticioid Cantharellales. Our method is a cost-effective approach for generating accurate multi-locus sequence data coupled with recovery of alleles from polymorphic samples and multi-organism specimens. These results have important implications for understanding intra-individual genomic variation among genetic loci commonly used in species delimitation of fungi.

Proton nuclear magnetic resonance (1H NMR) of flammable organic chemicals in radioactive high-level supernatant waste at the Savannah River Site (SRS).

The Savannah River Site stores approximately 36 million gallons of radioactive and hazardous waste that contains approximately 245 million curies. The waste is sent through various chemical processes to reduce its volume and to separate various components. The facility plans to replace formic acid (a chemical used to reduce soluble mercury) with glycolic acid. Recycle solution with glycolate may flow back to the tank farm, where the glycolate can generate hydrogen gas by thermal and radiolytic mechanisms. The current analytical method for detecting glycolate (ion chromatography) in supernatant requires a large dilution to reduce interference from the nitrate anions. Hydrogen nuclear magnetic resonance is an analytical method that requires less sample dilution. It takes advantage of the CH2 group in glycolate. Liquid samples were spiked with four different levels of glycolate to build a calibration line, as it is recommended in the standard addition method. The detection and quantitation limits determined were 1 and 5 ppm, respectively, for 32 scans, which is well below the process limit of 10 ppm. In one test, 800 scans of a supernatant spiked with 1 ppm glycolate resulted in a -CH2 peak with a signal-to-noise ratio of 36.

A global phylogenomic analysis of the shiitake genus Lentinula.

Lentinula is a broadly distributed group of fungi that contains the cultivated shiitake mushroom, L. edodes. We sequenced 24 genomes representing eight described species and several unnamed lineages of Lentinula from 15 countries on four continents. Lentinula comprises four major clades that arose in the Oligocene, three in the Americas and one in Asia-Australasia. To expand sampling of shiitake mushrooms, we assembled 60 genomes of L. edodes from China that were previously published as raw Illumina reads and added them to our dataset. Lentinula edodes sensu lato (s. lat.) contains three lineages that may warrant recognition as species, one including a single isolate from Nepal that is the sister group to the rest of L. edodes s. lat., a second with 20 cultivars and 12 wild isolates from China, Japan, Korea, and the Russian Far East, and a third with 28 wild isolates from China, Thailand, and Vietnam. Two additional lineages in China have arisen by hybridization among the second and third groups. Genes encoding cysteine sulfoxide lyase (lecsl) and γ-glutamyl transpeptidase (leggt), which are implicated in biosynthesis of the organosulfur flavor compound lenthionine, have diversified in Lentinula. Paralogs of both genes that are unique to Lentinula (lecsl 3 and leggt 5b) are coordinately up-regulated in fruiting bodies of L. edodes. The pangenome of L. edodes s. lat. contains 20,308 groups of orthologous genes, but only 6,438 orthogroups (32%) are shared among all strains, whereas 3,444 orthogroups (17%) are found only in wild populations, which should be targeted for conservation.

Comparing and contrasting In-Vial and full-scale systems for sparging volatile analytes.

In-vial sparging was demonstrated as an effective, practical alternative to a full-scale sparging system for supporting the analysis of volatile constituents. Using elemental mercury (Hg0) and toluene as representative purgeable analytes, the mass removal for various sparge configurations was measured and a reduced order model was developed and validated. In the primary experiments, Hg0 in the sparge gas was trapped on activated carbon or gold, thermally desorbed, and quantified using atomic absorption or atomic fluorescence spectroscopy. Toluene experiments using the same in-vial sparge apparatus and sparge parameters were performed to demonstrate the applicability of the reduced order model to a broad range of compounds. Toluene removal was tracked by measuring the remaining toluene in sparged aliquots using Ultraviolet-visible (UV-Vis) spectroscopy. For the sparging, flow rates varied from 25 to 75 mL/min for periods from 0 to 30 min. Sparge performance, mass removal as a function of time, and sparge gas volume were measured for both in-vial and full-scale systems. A model based on dimensionless Henry's Law coefficient, normalized sparge gas volume, and fractional extent of equilibrium matched the experimental data for both compounds and provides a practical tool for future applications. For the conditions tested in this study, the calibrated model indicated that the sparge gas in the in-vial system reached approximately 33% of its equilibrium value before exiting the water surface, while a full-scale system reached approximately 100%. The tests validated the quality, reproducibility, and predictability of sparging performance for both full scale and in-vial sparge systems. Related factors such as waste generation, worker risk, and labor were also assessed. Full scale sparge systems provide the advantage of lower detection levels due to larger sample volume, while the in-vial sparge systems provide advantages for most other factors; including automatability, reducing secondary wastes, lessening the need to clean and check the sparge apparatus, and lowering labor and costs. The data and associated reduced order model support continued development and deployment of in-vial sparge platforms as a practical option for analysis of purgeable analytes such as volatile organic compounds and volatile metals/organometallics.

Systematic revision of the Roseinae clade of Russula, with a focus on eastern North American taxa.

The Roseinae clade is a lineage of the genus Russula primarily composed of species of Russula subsect. Roseinae. Species in this morphologically distinct clade possess a white to pale cream spore print, mild taste, positive reaction to sulfovanillin, and primordial hyphae with acid-resistant crystals in the pileipellis. Here, we present a morphological and phylogenetic assessment that distinguishes seven eastern North American species of the core Roseinae lineage and a new subsection, Russula subsection Albidinae, to accommodate members of the Albida clade. We assign the previously described species R. peckii, R. rubellipes, and R. pseudopeckii to three species-level clades, and three other species, R. cardinalis, R. cordata, and R. rheubarbarina, are described as new. Comparative morphological analyses reveal differences in the conformation of terminal elements in the pileipellis, spore size, hymenial cystidia contents, and pigmentation on the stipe surface as key features to recognize species in the group. Based on the analysis of publicly available data, we recognize a potential total of nine temperate North American species within R. subsect. Roseinae, in addition to four from Central America, two from Europe, and 14 from Asia.

Impact of matrix diffusion on the migration of groundwater plumes for Perfluoroalkyl acids (PFAAs) and other non-degradable compounds.

Groundwater fate and transport modeling results demonstrate that matrix diffusion plays a role in attenuating the expansion of groundwater plumes of "non-degrading" or highly recalcitrant compounds. This is especially significant for systems where preferred destructive attenuation processes, such as biological and abiotic degradation, are weak or ineffective for plume control. Under these conditions, models of nondestructive physical attenuation processes, traditionally dispersion or sorption, do not demonstrate sufficient plume control unless matrix diffusion is considered. Matrix diffusion has been shown to be a notable emergent impact of geological heterogeneity, typically associated with back diffusion and extending remediation timeframes through concentration tailing of the trailing edge of a plume. However, less attention has been placed on evaluating how matrix diffusion can serve as an attenuation mechanism for the leading edge of a plume of non-degrading compounds like perfluoroalkyl acids (PFAAs), including perfluorooctane sulfonate (PFOS). In this study, the REMChlor-MD model was parametrically applied to a generic unconsolidated and heterogeneous geologic site with a constant PFOS source and no degradation of PFOS in the downgradient edge of the plume. Low levels of mechanical dispersion and retardation were used in the model for three different geologic heterogeneity cases ranging from no matrix diffusion (e.g., sand only) to considerable matrix diffusion using low permeability ("low-k") layers/lenses and/or aquitards. Our analysis shows that, in theory, many non-degrading plumes may expand for significant time periods before dispersion alone would eventually stabilize the plume; however, matrix diffusion can significantly slow the rate and degree of this migration. For one 100-year travel time scenario, consideration of matrix diffusion results in a simulated PFOS plume length that is over 80% shorter than the plume length simulated without matrix diffusion. Although many non-degrading plumes may continue to slowly expand over time, matrix diffusion resulted in lower concentrations and smaller plume footprints. Modeling multiple hydrogeologic settings showed that the effect of matrix diffusion is more significant in transmissive zones containing multiple low-k lenses/layers than transmissive zones underlain and overlain by low-k aquitards. This study found that at sites with significant matrix diffusion, groundwater plumes will be shorter, will expand more slowly, and may be amenable to a physical, retention-based, Monitored Natural Attenuation (MNA) paradigm. In this case, a small "Plume Assimilative Capacity Zone" in front of the existing plume could be reserved for slow, de minimus, future expansion of a non-degrading plume. If potential receptors are protected in this scenario, then this approach is similar to allowances for expanding plumes under some existing environmental regulatory programs. Accounting for matrix diffusion may support new strategic approaches and alternative paradigms for remediation even for sites and conditions with "non-degrading" constituents such as PFAAs, metals/metalloids, and radionuclides.

Two new Russula species (fungi) from dry dipterocarp forest in Thailand suggest niche specialization to this habitat type.

Dry dipterocarp forests are among the most common habitat types in Thailand. Russulaceae are known as common ectomycorrhizal symbionts of Dipterocarpaceae trees in this type of habitat. The present study aims to identify collections of Russula subsection Amoeninae Buyck from dry dipterocarp forests in Thailand. A multi-locus phylogenetic analysis placed Thai Amoeninae collections in two novel lineages, and they are described here as R. bellissima sp. nov. and R. luteonana sp. nov. The closest identified relatives of both species were sequestrate species suggesting that they may belong to drought-adapted lineages. An analysis of publicly available ITS sequences in R. subsect. Amoeninae did not confirm evidence of any of the new species occurring in other Asian regions, indicating that dry dipterocarp forests might harbor a novel community of ectomycorrhizal fungi. Macromorphological characters are variable and are not totally reliable for distinguishing the new species from other previously described Asian Amoeninae species. Both new species are defined by a combination of differentiated micromorphological characteristics in spore ornamentation, hymenial cystidia and hyphal terminations in the pileipellis. The new Amoeninae species may correspond to some Russula species collected for consumption in Thailand, and the detailed description of the new species can be used for better identification of edible species and food safety in the region.

Evolutionary transition to the ectomycorrhizal habit in the genomes of a hyperdiverse lineage of mushroom-forming fungi.

The ectomycorrhizal (ECM) symbiosis has independently evolved from diverse types of saprotrophic ancestors. In this study, we seek to identify genomic signatures of the transition to the ECM habit within the hyperdiverse Russulaceae. We present comparative analyses of the genomic architecture and the total and secreted gene repertoires of 18 species across the order Russulales, of which 13 are newly sequenced, including a representative of a saprotrophic member of Russulaceae, Gloeopeniophorella convolvens. The genomes of ECM Russulaceae are characterized by a loss of genes for plant cell wall-degrading enzymes (PCWDEs), an expansion of genome size through increased transposable element (TE) content, a reduction in secondary metabolism clusters, and an association of small secreted proteins (SSPs) with TE 'nests', or dense aggregations of TEs. Some PCWDEs have been retained or even expanded, mostly in a species-specific manner. The genome of G. convolvens possesses some characteristics of ECM genomes (e.g. loss of some PCWDEs, TE expansion, reduction in secondary metabolism clusters). Functional specialization in ECM decomposition may drive diversification. Accelerated gene evolution predates the evolution of the ECM habit, indicating that changes in genome architecture and gene content may be necessary to prime the evolutionary switch.

Four new species of Russula subsection Roseinae from tropical montane forests in western Panama.

Species of the genus Russula are key components of ectomycorrhizal ecosystems worldwide. Nevertheless, their diversity in the tropics is still poorly known. This study aims to contribute to the knowledge of the diversity of Russula species classified in subsection Roseinae based on specimens recently collected in tropical montane rainforests in western Panama. A five gene multilocus phylogeny based on the nuclear markers ITS nrDNA, MCM7, RPB1, RPB2 and TEF-1α was constructed to identify the systematic position of 22 collections from Panama. Four new species, Russula cornicolor, Russula cynorhodon, Russula oreomunneae and Russula zephyrovelutipes are formally described and illustrated. None of the four species are sister species and they are more closely related to North American or Asian species. Two of the newly described species were associated with the ectomycorrhizal tree species Oreomunnea mexicana, while the other two species were associated with Quercus species. All four species are so far only known from mountains in western Panama.

Role of uncertainties in protecting ecological resources during remediation and restoration.

Cleanup of contaminated waste sites is a National priority to protect human health and the environment, while restoring land to productive uses. While there are uncertainties with understanding risk to individuals from exposure, the aim of this study was to focus on uncertainties and complexities for ecological systems, complicated by hundreds of species occupying any remediation site which participate in multiple-interacting food webs. The ability to better predict the effectiveness of remediation in fostering future ecosystems might facilitate remedy selection and improve strategic environmental management. This investigation examined (1) uncertainties in ecosystem processes, (2) uncertainties in exposure from contamination before remediation, and (3) uncertainties during remediation. Two Department of Energy sites Hanford Site and Savannah River Site were used as case studies to illustrate how the uncertainties affect eco-receptors. Several types of ecological, physical, and human dimension uncertainties are defined. Ecological uncertainties include temporal, spatial, individual, developmental, and exogenous types. Physical uncertainties are weather-related, watershed variations, slope/aspect, soil/sediment structure and form, unforeseen events, and temporal patterns. Human dimension uncertainties include current land use, future land use, extractive and non-extractive recreation. The effects of remedial strategies varied between the two sites because Hanford is a primarily arid shrub-steppe ecotype, while Savannah River is a wet forest ecotype. Defining the associated ecological sensitivities and uncertainties and providing examples might help policy-makers, managers, planners, and contractors to be aware of issues to consider throughout planning, remediation, and restoration. Adding ecological uncertainty analysis to risk evaluations and remediation planning is analogous to using safety factors in human health risk assessment.

Taxonomic revision of Russula subsection Amoeninae from South Korea.

Russula subsection Amoeninae is morphologically defined by a dry velvety pileus surface, a complete absence of cystidia with heteromorphous contents in all tissues, and spores without amyloid suprahilar spot. Thirty-four species within subsection Amoeninae have been published worldwide. Although most Russula species in South Korea have been assigned European or North American names, recent molecular studies have shown that Russula species from different continents are not conspecific. Therefore, the present study aims to: 1) define which species of Russula subsection Amoeninae occur on each continent using molecular phylogenetic analyses; 2) revise the taxonomy of Korean Amoeninae. The phylogenetic analyses using the internal transcribed spacer (ITS) and multilocus sequences showed that subsection Amoeninae is monophyletic within subgenus Heterophyllidiae section Heterophyllae. A total of 21 Russula subsection Amoeninae species were confirmed from Asia, Australia, Europe, North America, and Central America, and species from different continents formed separate clades. Three species were recognized from South Korea and were clearly separated from the European and North American species. These species are R. bella, also reported from Japan, a new species described herein, Russula orientipurpurea, and a new species undescribed due to insufficient material.

Legacy Contaminants in Aquatic Biota in a Stream Associated with Nuclear Weapons Material Production on the Savannah River Site.

Former nuclear weapons material production at the U.S. Department of Energy's Savannah River Site (SRS) has resulted in contamination of certain terrestrial and aquatic ecosystems on site with legacy wastes such as radiocesium (137Cs), tritium (3H), and metals. We collected fish and invertebrates from five beaver ponds (sites) above, adjacent, and downgradient of three SRS facilities (H-, F-, and C-Areas) to evaluate whether the accumulation of metals and radionuclides in biota were associated with specific facility operations and if the measured levels could pose risks to aquatic organisms. We compared concentrations of various metals, 137Cs, and 3H in fish, as well as in water (3H only), among sites along the stream gradient. Fish collected from sites adjacent to H-Area had significantly higher 137Cs concentrations compared to fish from other sites. Both biota and water samples indicated significantly greater levels of 3H in sites adjacent to and downstream of C-Area. Concentrations of zinc (Zn), copper (Cu), and mercury (Hg) in some samples exceeded effects levels reported for fish and may pose a risk to fish populations. This study reported fish tissue concentrations of 137Cs and 3H, which have not been documented extensively in ecotoxicological studies. Our results suggested that industrial operations such as nuclear material production at SRS could have long-lasting impact on the aquatic ecosystem via the release of radionuclides and metals, and long-term monitoring of physiological effects and population level impact in biota exposed to these contaminants are recommended.

Coalescent-based delimitation and species-tree estimations reveal Appalachian origin and Neogene diversification in Russula subsection Roseinae.

Numerous lineages of mushroom-forming fungi have been subject to bursts of diversification throughout their evolutionary history, events that can impact our ability to infer well-resolved phylogenies. However, groups that have undergone quick genetic change may have the highest adaptive potential. As the second largest genus of mushroom-forming fungi, Russula provides an excellent model for studying hyper-diversification and processes in evolution that drives it. This study focuses on the morphologically defined group - Russula subsection Roseinae. Species hypotheses based on morphological differentiation and multi-locus phylogenetic analyses are tested in the Roseinae using different applications of the multi-species coalescent model. Based on this combined approach, we recognize fourteen species in Roseinae including the Albida and wholly novel Magnarosea clades. Reconstruction of biogeographic and host association history suggest that parapatric speciation in refugia during glacial cycles of the Pleistocene drove diversification within the Roseinae, which is found to have a Laurasian distribution with an evolutionary origin in the Appalachian Mountains of eastern North America. Finally, we detect jump dispersal at a continental scale that has driven diversification since the most recent glacial cycles.

Russulaceae: a new genomic dataset to study ecosystem function and evolutionary diversification of ectomycorrhizal fungi with their tree associates.

The family Russulaceae is considered an iconic lineage of mostly mushroom-forming basidiomycetes due to their importance as edible mushrooms in many parts of the world, and their ubiquity as ectomycorrhizal symbionts in both temperate and tropical forested biomes. Although much research has been focused on this group, a comprehensive or cohesive synthesis by which to understand the functional diversity of the group has yet to develop. Interest in ectomycorrhizal fungi, of which Russulaceae is a key lineage, is prodigious due to the important roles they play as plant root mutualists in ecosystem functioning, global carbon sequestration, and a potential role in technology development toward environmental sustainability. As one of the most species-diverse ectomycorrhizal lineages, the Russulaceae has recently been the focus of a dense sampling and genome sequencing initiative with the Joint Genome Institute aimed at untangling their functional roles and testing whether functional niche specialization exists for independent lineages of ectomycorrhizal fungi. Here we present a review of important studies on this group to contextualize what we know about its members' evolutionary history and ecosystem functions, as well as to generate hypotheses establishing the Russulaceae as a valuable experimental system.

Lactarius subgenus Russularia (Basidiomycota, Russulales): novel Asian species, worldwide phylogeny and evolutionary relationships.

Lactarius subg. Russularia is a large group of milkcaps occurring almost worldwide and dominant in many ecosystems. In this study we focus on new diversity, evolutionary relationships, divergence time, and origin of the subgenus. Six conifer symbionts are described as new to science: Lactarius atrii, L. aurantionitidus, L. dombangensis, L. flavigalactus, L. lachungensis, and L. sikkimensis. Species delimitation is assessed based on the concordance between morphological characteristics and an ITS phylogeny. Infrageneric relationships were studied using a phylogeny constructed from concatenated ITS-rpb2 data using Maximum Likelihood and Bayesian inference. Results show that species in this subgenus do not cluster together according to their geographic origin. Intercontinental sister relationships between Europe/Asia/North America are common but actual conspecificity is rare. This result suggests that allopatric speciation has played an important role within this subgenus. Only few morphological characteristics tend to be phylogenetically informative, with the most important being presence or absence of true cystidia and the pileipellis structure. Two datasets were generated in order to estimate the age of L. subg. Russularia. The results suggest the origin of L. subg. Russularia to be in the Mid Miocene period.

Multilocus phylogenetic reconstruction of the Clavariaceae (Agaricales) reveals polyphyly of agaricoid members.

The genus Camarophyllopsis contains species with lamellate (agaricoid) basidiomes in the family Clavariaceae (Agaricales), a group otherwise dominated by club-like (clavarioid) or branched (coralloid) forms. Previous studies have suggested that species classified in Camarophyllopsis occur in two independent lineages. We reconstructed a multilocus phylogeny of the Clavaria-Camarophyllopsis-Clavicorona clade in the Clavariaceae using RNA polymerase II second largest subunit (rpb2), nuclear ribosomal 28S, and nuclear ribosomal ITS1-5.8S-ITS2 regions data and detected three independent groups of agaricoid fungi, including the genera Camarophyllopsis, Hodophilus, and Lamelloclavaria gen. nov, which distinctly differ in their pileipellis structure. In all, nine major lineages within the Clavaria-Camarophyllopsis-Clavicorona clade were recovered: Clavaria sensu stricto, Camarophyllopsis sensu stricto, Hodophilus, the Clavaria pullei clade, the Clavaria fumosa clade, Lamelloclavaria gen. nov., the Clavaria atrofusca clade, Holocoryne (= Clavaria sect. Holocoryne), and Clavicorona Clavaria is paraphyletic and represented by five clades. Additional gene sampling is necessary to determine and confirm relatedness of these lineages before splitting Clavaria into additional genera.

Into and out of the tropics: global diversification patterns in a hyperdiverse clade of ectomycorrhizal fungi.

Ectomycorrhizal (ECM) fungi, symbiotic mutualists of many dominant tree and shrub species, exhibit a biogeographic pattern counter to the established latitudinal diversity gradient of most macroflora and fauna. However, an evolutionary basis for this pattern has not been explicitly tested in a diverse lineage. In this study, we reconstructed a mega-phylogeny of a cosmopolitan and hyperdiverse genus of ECM fungi, Russula, sampling from annotated collections and utilizing publically available sequences deposited in GenBank. Metadata from molecular operational taxonomic unit cluster sets were examined to infer the distribution and plant association of the genus. This allowed us to test for differences in patterns of diversification between tropical and extratropical taxa, as well as how their associations with different plant lineages may be a driver of diversification. Results show that Russula is most species-rich at temperate latitudes and ancestral state reconstruction shows that the genus initially diversified in temperate areas. Migration into and out of the tropics characterizes the early evolution of the genus, and these transitions have been frequent since this time. We propose the 'generalized diversification rate' hypothesis to explain the reversed latitudinal diversity gradient pattern in Russula as we detect a higher net diversification rate in extratropical lineages. Patterns of diversification with plant associates support host switching and host expansion as driving diversification, with a higher diversification rate in lineages associated with Pinaceae and frequent transitions to association with angiosperms.

The effects of a stannous chloride-based water treatment system in a mercury contaminated stream.

We assessed the impacts of an innovative Hg water treatment system on a small, industrially-contaminated stream in the southeastern United States. The treatment system, installed in 2007, removes Hg from wastewater using tin (Sn) (II) chloride followed by air stripping. Mercury concentrations in the receiving stream, Tims Branch, decreased from >100 to ∼10 ng/L in the four years following treatment, and Hg body burdens in redfin pickerel (Esox americanus) decreased by 70% at the most contaminated site. Tin concentrations in water and fish increased significantly in the tributary leading to Tims Branch, but concentrations remain below levels of concern for human health or ecological risks. While other studies have shown that Sn may be environmentally methylated and methyltin can transfer its methyl group to Hg, results from our field studies and sediment incubation experiments suggest that the added Sn to the Tims Branch watershed is not contributing to methylmercury (MeHg) production or bioaccumulation in this system. The stannous chloride treatment system installed at Tims Branch was effective at removing Hg inputs and reducing Hg bioaccumulation in the stream, but future studies are needed to assess longer term impacts of Sn on the environment.

Bench-scale evaluation of aerosol delivery for biostimulation and bioaugmentation in the vadose zone.

Aerosol delivery was evaluated for distributing biostimulation and bioaugmentation amendments in vadose zones. This technique involves transporting amendments as micron-scale aerosol droplets in injected gas. Microcosm experiments were designed to characterize reductive dechlorination of trichloroethene (TCE) under unsaturated conditions when delivering components as aerosols. Delivering amendments and/or microbes as aqueous aerosols resulted in complete dechlorination of TCE, similar to controls operated under saturated conditions. Reductive dechlorination was achieved with manual injection of a bioaugmentation culture suspended in soybean oil into microcosms. However, aerosol delivery of the culture in soybean oil induced little reductive dechlorination activity. Overall, the results indicate that delivery as aqueous aerosols may be a viable option for delivery of amendments to enhance vadose zone bioremediation at the field-scale.