Mercury (Hg) is a persistent environmental contaminant and can accumulate and concentrate in food webs as methylmercury (MeHg), presenting a health risk to humans and wildlife. Multiyear monitoring and modeling studies have shown that atmospheric Hg in litterfall is an important form of Hg deposition to forests. Annual litterfall consists primarily of leaves with some amounts of needles, twigs, bark, flowers, seeds, fruits, and nuts. Atmospheric Hg accumulates in leaves and reaches an annual maximum concentration at autumn leaf drop. This data set is derived from autumn litterfall collected at 30 selected National Atmospheric Deposition Program (NADP) Mercury Deposition Network (MDN) sites in deciduous and mixed deciduous-coniferous forests from 16 states in the eastern United States during 2007-2009 and 2012-2015. The NADP administered litterfall collection at the MDN sites. The U.S. Geological Survey (USGS) distributed sets of passive litterfall sample collectors to MDN site operators for systematic retrieval of samples during the 8 to 16 weeks of autumn leaf drop each year at each site. Samples were processed and analyzed at the USGS Mercury Research Laboratory where concentrations of Hg and MeHg and litterfall dry mass and sample moisture were determined. All sites did not have data for all years. Most sites had four Hg concentrations per year and a few sites had less than or more than four Hg concentrations in specific years. MeHg concentrations were determined in one composite sample per site in 2007 and 2012-2015. Litterfall mass was determined from 4 to 8 samples per site per year. Seven annual groups of data were compiled into this dataset. More information is available from the NADP at http://nadp.sws.uiuc.edu/

The movement of mercury (Hg) from the atmosphere to the biosphere occurs by both wet and dry deposition to solid surfaces, water, and vegetation. Most of the annual dry atmospheric Hg deposition in deciduous forests is believed to originate from litterfall which consists mainly of dead leaves that fall to the earth’s surface, primarily during the autumn and winter seasons. Atmospheric Hg reaches an annual maximum concentration in leaves at the time of leaf fall. Analysis of litterfall samples helps to quantify total annual atmospheric Hg deposition to forests when combined with precipitation Hg data. This data set is derived from litterfall samples collected during 2017-18 and 2018-19 at 27 selected National Atmospheric Deposition Program (NADP) sites in 12 states located across the eastern half of the United States. Through the Litterfall Mercury Monitoring Initiative (LMMI), operated by the U.S. Geological Survey (USGS), litterfall sample collectors were distributed to the selected NADP sites where site operators retrieved multiple 4-week-long samples during the leaf fall period. These samples were collected and shipped to the USGS Mercury Research Laboratory where they were analyzed for concentrations of total Hg and methylmercury (MeHg), and litterfall dry mass was also determined. The samples for total Hg and MeHg analysis represent composites from 4 collectors across all sample collections at each site during the litterfall season. Litterfall dry mass was determined from all 8 sample collectors across all sample collections.

Mercury (Hg) is a persistent environmental contaminant and can accumulate and concentrate in food webs as methylmercury (MeHg), presenting a health risk to humans and wildlife. Multiyear monitoring and modeling studies have shown that atmospheric Hg in litterfall is an important form of Hg deposition to forests. Annual litterfall consists primarily of leaves with some amounts of needles, twigs, bark, flowers, seeds, fruits, and nuts. Atmospheric Hg accumulates in leaves and reaches an annual maximum concentration at autumn leaf drop. This data set is derived from ambient autumn litterfall samples collected at 23 selected National Atmospheric Deposition Program (NADP) Litterfall Mercury Monitoring Initiative (LMMI) sites located near NADP Mercury Deposition Network sites in deciduous and mixed deciduous-coniferous forests in 11 states in the eastern United States during 2016. The NADP administered litterfall collection at the LMMI sites. The U.S. Geological Survey (USGS) distributed sets of passive litterfall sample collectors to LMMI site operators for systematic retrieval of samples during the 4 to 24 weeks of autumn leaf drop at each site. Samples were processed and analyzed at the USGS Mercury Research Laboratory where concentrations of Hg and MeHg and litterfall dry mass and sample moisture were determined. Hg concentrations were measured in 4 samples collected from each site and MeHg concentrations were measured in one composite sample per site. Litterfall mass and sample moisture were determined for 8 samples per site. Duplicate sets of these sample data were determined for 3 sites in 2016.

Automated collectors at Elkmont passively accumulated litterfall for two consecutive 4-week periods each in 2008 and 2009. Samples were collected, and submitted for analysis of mercury by low-level, trace-metals methods. Species of leaf included poplar, maple, birch, pine, dogwood, hemlock. and magnolia. The average concentration of total mercury in the eight samples was 32.6 nanograms per gram. The estimated litterfall deposition for the eight samples was 12.4 nanograms per square meter.

Annual litterfall samples were collected and analyzed for THg (total mercury) and MHg (methyl mercury) at a site (WI95) on Bad River tribal lands during 2012 to 2018. Litterfall was collected at a second site, WI01, during 2012 only. Litterfall was sampled in eight collectors, from which annual mass was determined. Total mercury analyses were performed on only four samples from the collectors with the lowest numbers in the sequence. A mass weighted sample based on the four THg samples was analyzed for MHg. Neither the collection of litterfall samples nor the Hg analyses were performed by the U.S. Geological Survey, New York Water Science Center.

Mercury (Hg) is a persistent environmental contaminant and can accumulate and concentrate in food webs as methylmercury (MeHg), presenting a health risk to humans and wildlife. Multiyear monitoring and modeling studies have shown that atmospheric Hg in litterfall is an important form of Hg deposition to forests. Litterfall consists primarily of leaves with some amounts of twigs, bark, flowers, seeds, fruits, and nuts. Atmospheric Hg accumulates in the forest canopy material and transfers to the forest floor in litterfall. This data set is derived from monthly litterfall collected at the National Atmospheric Deposition Program (NADP) Mercury Deposition Network (MDN) site at El Verde, Puerto Rico, identification number PR20, during 2014-2016. The U.S. Geological Survey (USGS) provided passive litterfall collectors to the PR20 MDN site operator who systematically deployed them in a forest plot near the MDN equipment. Each collector was a 0.25 square meter box made of plastic lattice with a 20-micrometer mesh, polyester, netting liner. The operator retrieved the litterfall in the collectors on a monthly schedule and shipped the subsamples to the USGS Mercury Research Laboratory where concentrations of Hg and MeHg and litterfall dry mass and sample moisture were determined using published methods. More information about the litterfall Hg monitoring field and laboratory methods and quality assurance is available from the NADP at http://nadp.sws.uiuc.edu/newissues/litterfall/

Comma-separated values (.csv) file containing data related to amphibian sampling across the United States between 2016 and 2021. Data files contain mercury concentrations in amphibian and dragonfly tissues, mercury concentrations in sediment, as well as amphibian morphometrics, and habitat and climate characteristics where the samples were collected.

Excel spreadsheet with the following columns of data: Date/Time (6/2016 to 10/2016) Total Gaseous Mercury Concentration (ng/m3) Sulfur dioxide concentration (ppb) Carbon monoxide concentration (ppm) Carbon dioxide concentration (ppm) Wind direction in degrees Wind speed in miles per hour Temperature in degrees celcius Percent relative humidity. This dataset is not publicly accessible because: The data used in this study were not generated or funded by the EPA. It can be accessed through the following means: The total-gaseous mercury (TGM) measurement data were collected by Dr. Lynne Gratz, Assistant Professor of Environmental Science, at Colorado College, 14 E. Cache La Poudre St. Colorado Springs, Colorado 80903 USA. This data is not available to EPA for public dissemination. Information on obtaining this data should be directed to Dr. Gratz at: lgratz@coloradocollege.edu or (719) 389-7465. The CO, SO2, temperature, wind speed, wind direction, and relative humidity were collected at the Colorado Department of Public Health & Environment (CDPHE) air monitoring location at Highway 24 in Colorado Springs. This data is already available in the public domain. Certified hourly data from this and other CDPHE air monitoring stations, including the Manitou Springs and Colorado College stations that were also mentioned in this manuscript, are available through the U.S. EPA Air Quality System (AQS) database (https://aqs.epa.gov/api) downloaded on September 1st 2017. Additional information can be obtained by emailing: cdphe.information@state.co.us303. Format: The data are in an Excel format. Citation information for this dataset can be found in the EDG's Metadata Reference Information section and Data.gov's References section.

The dataset presented here represents the concentrations and stable isotopic composition of gaseous mercury (Hg) for 31 sites across the United States. This national-scale monitoring effort was performed by the National Atmospheric Deposition Program (NADP) and the USGS over a two-year period (March 2016 - May 2018). The network includes a highly diverse set of sites ranging from remote (e.g. Denali National Park, AK and Mauna Loa, HI) to highly urbanized (e.g. Bronx, NY and Boston, MA). Air samples were collected using a custom designed bulk air sampler, in which air was pumped at approximately 1 L/min through particulate and soda lime filters prior to passing through two quartz tubes containing gold coated glass beads where gaseous Hg was collected. Each sampling period was two weeks long. The Hg was thermally desorbed from the gold beads and collected in a liquid oxidizing trap. The total Hg concentration and isotopic composition was determined on this solution. The average total gaseous Hg concentration across sites was 1.23 ± 0.28 ng/m3, but higher concentrations were observed at sites closer to known Hg sources, such as Oak Ridge National Lab (6.53 ng/m3). For all sites, the average odd isotope mass independent fractionation (MIF, Δ199Hg), an indicator of photochemistry, was -0.20 ± 0.07‰ and had a range of -0.43 to 0.01 ‰. Mass dependent fractionation (MDF, δ202Hg), the commonly used isotope ratio for source tracking, was generally positive with a mean value of 0.45 ± 0.40‰, although intermittent negative MDF was also observed at some sites. Urban sites were consistently lighter in δ202Hg (0.34‰) compared to remote background sites (0.65‰), potentially indicating differences between emission sources. Though regional differences in odd MIF and MDF were small, we observed a trend showing enrichment of δ202Hg in the northeastern United States, from the Ohio River Valley to remote sites in northern Maine and Nova Scotia, suggesting a shift from localized emission sources to globally transported Hg across this region.

The Region 9 CRMS risk assessor specifically identified the need to obtain data for Tribal lands near Fallon, Nevada. Based on a 1994 study performed on OU1 samples, an estimated 12% of total mercury measurements is mercuric chloride (HgCl2). The Quality Assurance Project Plan (QAPP) summarized the OU1 historical analytical approaches for “speciation” with currently available methods summarized. Based on team scoping meeting with EPA Region 10 and the Region 9 Toxicologist, use of the Brooks Applied Lab (BRL) sequential extraction was selected primarily for reasons of comparability of approaches to simplify data assessment. (EPA Method 3200 was presented for comparative purposes.) There are significant sources of uncertainty in “speciation” using any approach, as each is technically a procedurally defined fractionation that may include other mercury species not specifically identified. As an example of this uncertainty, under the OU1 study of the EPA Las Vegas Lab data, it was unclear which fraction would have captured mercury oxide or whether the residual chlorides caused minor amounts of sulfide to combine with the nitric acid fraction. While the Oak Ridge approach may have reported mercuric chloride in the elemental mercury fraction. The primary factors driving the need for this speciation data were uncertainty about the quality of the historical OU1 data; applicability of the OU1 data at the locations below Lahontan Reservoir, and concerns expressed by the Region 9 CRMS risk assessor to better obtain direct measurement data near the Fallon Paiute-Shoshone Tribe. The data generated by this sampling were reviewed for laboratory quality control but decisions with the data were made by the EPA Region 9 CRMS risk assessor.