DOI: 10.6078/d1dh6f
title: Amazon forests capture high levels of atmospheric mercury pollution from artisanal gold mining

description: Mercury emissions from artisanal and small-scale gold mining throughout
 the Global South exceed coal combustion as the largest global source of
 mercury. We examined mercury deposition and storage in an area of the
 Peruvian Amazon heavily impacted by artisanal gold mining. Intact forests
 in the Peruvian Amazon near gold mining receive extremely high inputs of
 mercury and experience elevated total mercury and methylmercury in the
 atmosphere, canopy foliage, and soils. Here we show for the first time
 that an intact forest canopy near artisanal gold mining intercepts large
 amounts of particulate and gaseous mercury, at a rate proportional with
 total leaf area. We document substantial mercury accumulation in soils,
 biomass, and resident songbirds in some of the Amazon’s most protected and
 biodiverse areas, raising important questions about how mercury pollution
 may constrain modern and future conservation efforts in these tropical
 ecosystems.
description: All information regarding sampling sites is described in Gerson et al.
 (2020) and Gerson et al. (In review). All data were collected from the
 Madre de Dios region of Peru. Specific site coordinates and descriptions
 are found in individual data files. All methods for sample collection,
 laboratory analyses, and quality control assurance have been outlined
 fully in two publications: Gerson et al. (2020) and Gerson et al. (In
 review). Briefly, we collected surface water, precipitation, throughfall,
 leaves, sediment, soil, and air samples from across the Madre de Dios
 region of Peru, in locations near and remote from ASGM. These data were
 collected to determine the fate and transport of Hg across the landscape.
 Samples were collected in 2018 and 2019. Data predominantly include total
 Hg and methyl Hg concentrations in surface water, precipitation,
 throughfall, leaves, sediment, soil, and air. Additional water and soil
 parameters were also measured to better characterize their chemistry.
 Coordinates for each site can be found in the csv files and maps can be
 found in Figures 1 and 2. Below is the text on laboratory analysis and
 quality control in surface water and sediment samples, as reported in
 Gerson et al. (2020): “All samples for Hg analysis were collected in July
 and August 2019 during the dry season (Figure 1). River samples were
 collected from the Madre de Dios River mainstem, upstream of a river
 confluence, downstream of a confluence, and from each tributary. One water
 sample was taken from near the water surface at each sampling point after
 the boat motor had been off for at least one minute. For oxbow lakes and
 mining ponds, one water sample was taken from the water surface. Water
 samples were collected using the clean hands-dirty hands protocol (EPA
 Method 1669) in new polyethylene terephthalate copolyester glycol (PETG)
 bottles and acidified to 0.4% with trace grade hydrochloric acid (HCl)
 within 24 hours of collection. Water samples were stored on ice in the
 field and then stored at 4°C until analysis. Note that all water samples
 are unfiltered, and all Hg values reported represent the concentration for
 the total water column. River sediment samples were collected underwater
 from the channel margins by compositing surficial sediment from at least
 five sampling points along a 30-meter transect using a shovel. These
 samples were taken during the dry season; during the wet season, the
 sampling locations are closer to the center of the channel since the width
 of the river increases by tens of meters. We therefore assume that the
 river sediment samples we collected are representative of well-mixed
 fluvial sediments. Oxbow lake and mining pond sediments were collected as
 channel margin sediment using a shovel (collected underwater as surficial
 sediment) and from three points in the center of the lake using an Eckman
 grab sampler. Sediment samples were collected using the clean hands-dirty
 hands protocol, double-bagged, frozen on dry ice in the field, and stored
 frozen until sample processing. Note that mining ponds were sampled in the
 La Pampa region, a watershed located adjacent to the Colorado watershed.
 La Pampa is an area that, until recently, contained widespread ASGM
 (Espejo et al. 2018). It has been under military control since February
 2019 (Operacion Mercurio) making it a safe area for field sampling. Due to
 logistical and safety concerns stemming from a lack of police or military
 presence, it was not possible to sample mining ponds from the other
 actively mined watersheds examined in this study; however, mining
 practices in La Pampa are representative of those in the region. Water
 samples for total suspended solids (TSS) were collected immediately after
 collecting water samples for Hg analysis. Water from just below the
 surface was pumped through a drill-operated pump with in-line glass fiber
 filter (pre-weighed), and the amount of water filtered was recorded. The
 filter was stored frozen until sample processing. A filter field blank was
 also taken and frozen for analysis. Unfiltered water samples were analyzed
 for total Hg via oxidation with bromine chloride for a minimum of 24
 hours, purge and trap, cold vapor atomic fluorescence spectroscopy
 (CVAFS), and gas chromatographic (GC) separation (EPA Method 1631,
 revision E) on a Tekran 2600 Automated Total Mercury Analyzer. Calibration
 and continuous calibration verification (CCV) were performed using Brooks
 Rand Instruments Total Mercury Standard (1.0 ng/L) and initial calibration
 verification (ICV) was performed using SPEX Centriprep Inductively Coupled
 Plasma Mass Spectrometry (ICP-MS) Multi-Element in Solution Standard 2A.
 Instrument detection limit was 0.5 ng/L. All standards had average
 recoveries within 10% of the accepted values. The field blank, digestion
 blanks, and analysis blanks were below detection limit (BDL). After
 lyophilization for at least five days, sediment samples were analyzed for
 total Hg on a Milestone Direct Mercury Analyzer (DMA-80) via thermal
 decomposition, catalytic reduction, amalgamation, desorption, and atomic
 absorption spectroscopy (EPA Method 7473). Calibration of the DMA-80 was
 performed using Brooks Rand Instruments Total Mercury Standard (1.0 ng/L).
 CCV and matrix spike (MS) were performed using NIST standard reference
 material 1633c (coal fly ash, 1005 ng/g), and QCS was performed using NIST
 certified reference material 2709a (San Joaquin Soil, 1100 ng/g).
 Instrument detection limit was 0.5 ng Hg. All samples were run in
 duplicate, with values accepted when the relative percent difference
 between the two samples was within 10%. All standards and MS had average
 recoveries within 10% of the accepted values, and all blanks were BDL. For
 MeHg, unfiltered water samples were extracted with trace grade sulfuric
 acid for a minimum of 24 hours (Munson et al. 2014). Samples were analyzed
 by aqueous ethylation with sodium tetraethylborate, purge and trap, CVAFS,
 GC, and ICP-MS on an Agilent 770 (EPA Method 1630) (Imura et al. 1971;
 Hintelmann and Evans 1997). Calibration and CCV were performed using
 Brooks Rand Instruments Methylmercury Standard (1 ng/L). Method detection
 limit was 1 pg. All standards had average recoveries within 13% of the
 accepted values, and all blanks were BDL. For TSS, filters were placed in
 the oven at 105°C for 48 hours. Filters were then reweighed. TSS was
 defined as the difference in filter mass before and after filtration
 divided by the volume of water that passed through the filter. The filter
 field blank had a negligible difference in mass.” In addition to the
 methods employed in Gerson et al. (2020), the following methods were also
 applied. In the field, we measured conductivity, temperature, and specific
 conductivity using a conductivity probe submerged near the surface of the
 water. We also measured pH of the water in the field. We collected
 additional filtered water samples for other chemical analyses with a 0.45
 mm membrane filter. Samples for total organic carbon, total dissolved
 nitrogen, and trace elements were acidified in the field to 0.4% with
 hydrochloric. We stored all samples on ice or in the fridge when possible
 until return to the United States, and then stored samples at 4°C until
 analysis immediately upon return to the United States, within one month of
 sampling. We analyzed unacidified water samples for anions (chloride,
 nitrate, sulfate) and cations (calcium, magnesium, potassium, sodium) via
 ion chromatography (EPA Method 4110B) with a Dionex ICS 2000 ion
 chromatograph. All standards had recoveries within 10% of the accepted
 values, and all blanks were BDL. We analyzed acidified water samples for
 trace elements via inductively coupled plasma mass spectrometry with a
 Thermofisher X-Series II. We analyzed acidified samples for dissolved
 organic carbon and total dissolved nitrogen (USEPA Method 5310C) with a
 Shimadzu total organic carbon analyzer. Instrument calibration standards
 were prepared via serial dilution of certified water standard NIST1643f.
 All blanks were BDL. We also analyzed unacidified water samples for UVA in
 order to calculate SUVA on a spectrophotometer with a 254 nm wavelength
 (EPA Method 415.3 Rev. 1.1). In the field, we also pumped water from just
 below the surface through a drill-operated pump with in-line glass fiber
 filter, and the amount of water filtered was recorded. The filter was
 wrapped in foil and stored frozen until sample processing. A filter field
 blank was also taken and frozen for analysis. In the lab, filters were
 digested with acetone and analyzed for chlorophyll on a TD-700 Fluorometer
 (EPA Method 445.0). The filter field blank was BDL. Dried sediment samples
 were analyzed for carbon, hydrogen, and nitrogen (CHN) using a Perkin
 Elmer 2400 CHNS Analyzer and pH using a probe. Dried sediment samples were
 also digested in concentrated nitric acid for S, Se, and Mn analysis using
 USEPA Method 3050B. Samples were analyzed for Se and Mn with a Perkin
 Elmer Elan DRCII ICP-MS and S using a Perkin Elmer ICP-Optical Emission
 Spectrometer Model 8000. All standards had recoveries within 10% of the
 accepted values, and all blanks were BDL. Below is the text on laboratory
 analysis and quality control for precipitation, throughfall, soil, leaf,
 and air samples, as reported in Gerson et al (In review). “We established
 five sites along a 200-km reach of the Madre de Dios River. We chose
 sampling locations based on their proximity to intense ASGM activities,
 with approximately 50 km between each sampling site and accessible by the
 Madre de Dios River (Figure 2A). We selected two sites without any mining
 (Boca Manu and Chilive, approximately 100 km and 50 km from ASGM,
 respectively), hereafter referred to as “remote sites.” We selected three
 sites within the mining zone, hereafter referred to as “mining sites,”
 with two of the mining sites located in secondary growth forests near the
 towns of Boca Colorado and Laberinto and one mining site located in the
 intact old-growth forests of the Los Amigos Conservation Concession. Note
 that Hg-gold amalgam burning also occurs within this mining zone, at both
 Boca Colorado and Laberinto, and we refer to mining and amalgam burning
 collectively as “ASGM activity.” At each of the five sites, we installed
 deposition samplers both in clearings (deforested areas) and beneath the
 tree canopy (forested areas) in the 2018 dry season (July and August 2018)
 and 2018 wet season (December 2018 and January 2019) to collect wet
 deposition (n=3) and throughfall (n=4), respectively. Precipitation
 samples were collected over the course of four weeks in the dry season and
 two to three weeks in the wet season. In the second year of sampling
 during the dry season (July and August 2019), we installed collectors
 (n=4) at six additional forested plots at Los Amigos based on the high
 rates of deposition measured during the first year, for a total of seven
 forested plots and one deforested plot at Los Amigos. The distance between
 plots ranged from 0.1-2.5 km. We collected a GPS waypoint at each plot
 using a handheld Garmin GPS. We deployed passive air samplers (PAS) at
 each of the five sites during the 2018 dry season for a two-month period
 (July to August 2018) and the 2018 wet season for one month (December 2018
 to January 2019). One PAS sampler was deployed per site during the dry
 season, and PAS samplers were deployed in duplicate during the wet season.
 The PAS (developed by McLagan et al. 59) collects GEM by passive diffusion
 through a Radiello© diffusive barrier and sorption onto a
 sulfur-impregnated carbon sorbent (HGR-AC). The diffusion barrier of the
 PAS acts as a barrier to prevent the passage of gaseous organic Hg
 species; thus, only GEM is sorbed onto the carbon. 60 We attached PAS to
 posts approximately 1m above the ground using plastic cable ties. All
 samplers were sealed with parafilm or stored in double resealable plastic
 bags prior to and post deployment. We collected field blanks and trip
 blank PASs to assess contamination introduced during sampling storage in
 the field, storage in the laboratory, and during sample transport. During
 the deployment periods at all five sampling sites, we placed three
 precipitation collectors for Hg analysis and two collectors for other
 chemical analyses in the deforested sites and four throughfall collectors
 for Hg analysis and two collectors for other chemical analyses in the
 forested sites. Collectors were placed within one meter of each other.
 Note that while we installed a consistent number of collectors at each
 site, during some collection periods we had a smaller sample size due to
 flooding of sites, human interference with collectors, and connection
 malfunction between the tubing and collector bottle. At each forested and
 each deforested site, one of the collectors for Hg analysis contained a
 500 mL bottle, while the others contained a 250 mL bottle; all collectors
 for other chemical analyses contained a 250 mL bottle. These samples were
 stored cold until access to a freezer allowed them to be frozen,
 transported to the United States on ice, and stored frozen until analyzed.
 Collectors for Hg analysis consisted of a glass funnel connected to a new
 polyethylene terephthalate copolyester glycol (PETG) bottle via new
 styrene-ethylene-butadiene-styrene block polymer (C-Flex) tubing with a
 loop as a vapor lock. At the time of deployment, all 250 mL PETG bottles
 were acidified with 1 mL of trace metal grade hydrochloric acid (HCl), and
 all 500 mL PETG bottles were acidified with 2 mL of trace metal grade HCl.
 Collectors for other chemical analyses consisted of a plastic funnel
 connected to a polyethylene bottle via new C-Flex tubing with a loop as a
 vapor lock. Prior to deployment, all glass funnels, plastic funnels, and
 polyethylene bottles were acid washed. We collected samples using the
 clean hands-dirty hands protocol (EPA Method 1669), kept the samples as
 cold as possible until return to the United States, and then stored
 samples at 4°C until analysis. A previous study using this methodology has
 shown laboratory blanks below detection limit and standard spikes to have
 recoveries of 90-110%. 32 At each of the five sites, we collected foliage
 as canopy leaves, grab leaf samples, fresh litterfall, and bulk litter
 using clean hands-dirty hands protocol (EPA Method 1669). All samples were
 collected under a collection permit from SERFOR in Peru and imported to
 the United States under a USDA import permit. We collected canopy leaves
 from two tree species found at all sites: an emergent tree species (Ficus
 insipida) and a medium-sized tree (Inga feuilleei). We collected leaves
 from the canopy of the trees (n=3 for each species) using a Notch Big Shot
 slingshot in the 2018 dry season, 2018 wet season, and 2019 dry season. We
 collected grab leaf samples (n=1) by sampling leaves in each plot from
 tree branches less than two meters from the ground in the 2018 dry season,
 2018 wet season, and 2019 dry season. In 2019, we also collected grab leaf
 samples (n=1) from the additional six forested plots at Los Amigos. We
 collected fresh litterfall (“bulk litter”) in plastic mesh-lined baskets
 (n=5) in the 2018 wet season at all five forested sites and the 2019 dry
 season at the Los Amigos plots (n=5). Note that while we installed a
 consistent number of baskets at each site, during some collection periods
 we had a smaller sample size due to flooding of sites and human
 interference with collectors. All litterfall baskets were placed within
 one meter of the precipitation collectors. We collected bulk litter as
 grab samples of litterfall on the ground in the 2018 dry season, 2018 wet
 season, and 2019 dry season. In the 2019 dry season, we also collected
 bulk litter in all Los Amigos plots. We cold stored all leaf samples until
 access to a freezer allowed them to be frozen, transported to the United
 States on ice, then stored frozen until processed. We collected soil
 samples in triplicate (n=3) from all five sites (open and canopy) during
 all three seasonal campaigns and from the Los Amigos plots in the 2019 dry
 season. All soil samples were collected within one meter of the
 precipitation collectors. We collected soil samples as surficial soil (0-5
 cm) using a soil corer. Additionally, in the 2018 dry season, we collected
 soil cores up to 45 cm in depth and divided them into five depth segments.
 At Laberinto, we were only able to collect one soil profile because the
 water table was close to the soil surface. We collected all samples using
 clean hands-dirty hands protocol (EPA Method 1669). We cold stored all
 soil samples until access to a freezer allowed them to be frozen,
 transported to the United States on ice, then stored frozen until
 processed. We quantified total Hg concentrations of GEM collected by PAS
 by thermal desorption, amalgamation, and atomic absorption spectroscopy
 (USEPA Method 7473) using a Hydra C instrument (Teledyne, CV-AAS). We
 performed calibration of the CV-AAS using National Institute of Standards
 and Technology (NIST) standard reference material 3133 (Hg standard
 solution, 10.004 mg g-1), with a detection limit of 0.5 ng Hg. We
 performed continuous calibration verification (CCV) using NIST SRM 3133
 and quality control standard (QCS) using NIST 1632e (bituminous coal,
 135.1 mg g-1). We divided each sample into separate boats, placed it
 between two thin layers of sodium carbonate (Na2CO3) powder, and covered
 it with a thin layer of aluminum hydroxide (Al(OH)3) powder. 62 We
 measured the entire HGR-AC contents from each sample to remove any
 inhomogeneity in the distribution of Hg within the HGR-AC sorbent.
 Therefore, we calculated the Hg concentration for each sample based on the
 sum of total Hg measured for each boat and the entire HGR-AC sorbent
 contents in the PAS. Given that only one PAS sample was collected in the
 2018 dry season from each site for concentration measurements, method
 quality control and assurance was carried out by bracketing samples with
 monitoring procedural blanks, internal standards, and matrix-matched
 standards. In the 2018 wet season, we measured PAS samples in duplicate.
 Values were deemed acceptable when the relative percent difference (RPD)
 measured for both CCV and matrix-matched standards were within 5% of the
 accepted values, and all procedural blanks were below detection limit
 (BDL). We blank-corrected measured total Hg in PAS using concentrations
 determined from field and trip blanks (0.81 ± 0.18 ng g-1, n=5). We
 calculated GEM concentrations using the total mass of blank-corrected
 sorbed Hg divided by the deployment time and sampling rate (volume of air
 stripped of gaseous Hg per unit of time; 0.135 m3 day-1) 59,63 adjusted
 for temperature and wind using average temperature and wind measurements
 for the Madre de Dios region as obtained from World Weather Online. 63
 Reported standard error of measured GEM concentrations is based on the
 error of external standards ran before and after the samples. We analyzed
 water samples for total Hg via oxidation with bromine chloride for a
 minimum of 24 hours, followed by stannous chloride reduction and analysis
 with purge and trap, cold vapor atomic fluorescence spectroscopy (CVAFS),
 and gas chromatographic (GC) separation (EPA Method 1631, revision E) on a
 Tekran 2600 Automated Total Mercury Analyzer. We performed CCV for the
 2018 dry season samples using Ultra Scientific certified aqueous Hg
 standard (10 μg L-1) and initial calibration verification (ICV) using NIST
 certified reference material 1641D (mercury in water, 1.557 mg kg-1), with
 a detection limit of 0.02 ng L-1. For the 2018 wet season and 2019 dry
 season samples, we performed calibration and CCV using Brooks Rand
 Instruments Total Mercury Standard (1.0 ng L-1), and ICV using SPEX
 Centriprep Inductively Coupled Plasma Mass Spectrometry (ICP-MS)
 Multi-Element in Solution Standard 2A, with a detection limit of 0.5 ng
 L-1. All standards had recoveries within 15% of the accepted values. The
 field blank, digestion blanks, and analysis blanks were BDL. We
 lyophilized soil and leaf samples for five days. We homogenized the
 samples and then analyzed them for total Hg on a Milestone Direct Mercury
 Analyzer (DMA-80) via thermal decomposition, catalytic reduction,
 amalgamation, desorption, and atomic absorption spectroscopy (EPA Method
 7473). For the 2018 dry season samples, we performed calibration of the
 DMA-80 using NIST 1633c (coal fly ash, 1005 ng g-1) and Canadian National
 Research Council certified reference material MESS-3 (marine sediment, 91
 ng g-1). We performed CCV and MS using NIST 1633c and QCS using MESS-3,
 with a detection limit of 0.2 ng Hg. For the 2018 wet season and 2019 dry
 season samples, we performed calibration of the DMA-80 using Brooks Rand
 Instruments Total Mercury Standard (1.0 ng L-1). We performed CCV and MS
 using NIST standard reference material 2709a (San Joaquin Soil, 1100 ng
 g-1) and QCS using DORM-4 (fish protein, 410 ng g-1), with a detection
 limit of 0.5 ng Hg. For all seasons, we analyzed all samples in duplicate
 and accepted values when the relative percent difference between the two
 samples was within 10%. All standards and matrix spikes had average
 recoveries within 10% of the accepted values, and all blanks were BDL. All
 reported concentrations are for dry mass. We analyzed water samples from
 all three seasonal campaigns, leaf samples from the 2018 dry season, and
 soil samples from all three seasonal campaigns for MeHg. We extracted
 water samples with trace grade sulfuric acid for a minimum of 24 hours, 64
 digested leaves with 2% potassium hydroxide in methanol at 55°C for a
 minimum of 48 hours, 65 and digested soils via microwave digestion with
 trace metal grade HNO3 acid. 66,67 We analyzed the 2018 dry season samples
 via aqueous ethylation with sodium tetraethylborate, purge and trap, and
 CVAFS on a Tekran 2500 spectrometer (EPA Method 1630). We performed
 calibration and CCV using Frontier Geosciences certified laboratory MeHg
 standards and QCS for sediment using ERM CC580, with a method detection
 limit of 0.2 ng L-1. We analyzed the 2019 dry season samples by aqueous
 ethylation with sodium tetraethylborate, purge and trap, CVAFS, GC, and
 ICP-MS on an Agilent 770 (EPA Method 1630). 68 We performed calibration
 and CCV using Brooks Rand Instruments Methylmercury Standard (1 ng L-1),
 with a method detection limit of 1 pg. For all seasons, all standards had
 recoveries within 15% of the accepted values, and all blanks were BDL. We
 filtered water samples for other chemical analyses with a 0.45 mm membrane
 filter. We analyzed water samples for anions (chloride, nitrate, sulfate)
 and cations (calcium, magnesium, potassium, sodium) via ion chromatography
 (EPA Method 4110B) with a Dionex ICS 2000 ion chromatograph. All standards
 had recoveries within 10% of the accepted values, and all blanks were BDL.
 We analyzed water samples for trace elements via inductively coupled
 plasma mass spectrometry with a Thermofisher X-Series II. Instrument
 calibration standards were prepared via serial dilution of certified water
 standard NIST1643f. All blanks were BDL.” In addition to the methods
 employed in Gerson et al (In review), the following methods were also
 applied. Dried soil samples were analyzed for CHN using a Perkin Elmer
 2400 CHNS Analyzer and pH using a probe. Dried sediment samples were also
 digested in concentrated nitric acid for S, Se, and Mn analysis using
 USEPA Method 3050B. Samples were analyzed for Se and Mn with a Perkin
 Elmer Elan DRCII ICP-MS and S using a Perkin Elmer ICP-Optical Emission
 Spectrometer Model 8000. All standards had recoveries within 10% of the
 accepted values, and all blanks were BDL.
description: Note that values of &lt;DL imply that the value is below detection
 limit. Table 1: Dataset identities Data file name Description Size (not
 including headers) Aquatic.data.csv Contains data for all surface water
 and sediment samples collected 136 kb 4 columns 4079 rows
 Aquatic.data.coordinates.csv Contains information on site type, latitude,
 and longitude for all surface water and sediment samples collected 2 kb 4
 columns 54 rows Deposition.csv Contains data for all deposition samples
 collected 51 kb 6 columns 979 rows Litter.and.foliage.csv Contains data
 for all leaf samples collected 4 kb 5 columns 88 rows Soil.csv Contains
 data for all soil samples collected 22 kb 8 columns 365 rows GEM. csv
 Contains data for all atmospheric samples collected 0.5 kb 4 columns 15
 rows Terrestrial.coordinates. csv Contains information on site type,
 latitude, and longitude for all terrestrial (deposition, leaf, soil, and
 atmospheric) samples collected 0.6 kb 4 columns 13 rows   Table
 2: Aquatic.data.csv Attribute Definition   Site.ID Identification
 used across aquatic data   Collection.date Date sample was
 collected   Value Measured value of given parameter  
 Parameter Parameter analyzed in surface water or sediment  
   Value     Aluminum    
 Antimony     Arsenic     Barium
     Beryllium     Boron  
   Bromide     Cadmium    
 Calcium     Chloride     Chlorophyll
     Chromium     Cobalt  
   Conductivity     Copper    
 Dissolved.organic.carbon     Gold    
 Iron     Lead     Lithium  
   Magnesium     Manganese    
 Methylmercury     Molybdenum    
 Nickel     Nitrate     pH  
   Phosphate     Potassium    
 Rubidium     Sediment.carbon    
 Sediment.manganese     Sediment.nitrogen  
   Sediment.pH     Sediment.selenium  
   Sediment.sulfur     Sediment.total.mercury
     Selenium     Silver  
   Sodium     Strontium    
 Sulfate     SUVA     Temperature
     Thallium     Thorium  
   Total.dissolved.nitrogen     Total.mercury
     Total.suspended.solids     Uranium
     Vanadium     Zinc   Unit
 Units parameter were measured in     Value Definition
   ug.L Micrograms per liter   mg.L Millgrams per liter
   mgN.L Milligrams nitrogen per liter   mgS.L Milligrams
 sulfur per liter   uS.cm Microsiemens per centimeter  
 NA Unitless   percent Percent   ug.g Micrograms per gram
   L.mg.m Liters per milligram per meter   Degrees.C
 Degrees Celsius   ng.L Nanograms per liter   Table 3:
 Aquatic.data.coordinates.csv Attribute Definition   Site.ID
 Identification used across aquatic data   Site.type
 Classification of water body     Value Definition
   river.downstream Sample taken from a river downstream of
 artisanal and small-scale gold mining activity   river.upstream
 Sample taken from a river upstream of artisanal and small-scale gold
 mining activity   mining.pond Sample taken from a mining pond
 near artisanal and small-scale gold mining  
 oxbow.lake.downstream Sample taken from an oxbow lake downstream of
 artisanal and small-scale gold mining activity  
 oxbow.lake.upstream Sample taken from an oxbow lake upstream of artisanal
 and small-scale gold mining activity Latitude Latitude in decimal degrees
   Longitude Longitude in decimal degrees    
 Table 4: Deposition.csv Attribute Definition   Site Location
 where sampling occurred   Type Type of sample collected
     Value Definition   Bulk.precipitation
 Precipitation collected in a clearing   Throughfall Precipitation
 collected under forest canopy Date.collected Date sample was collected
   Concentration Measured concentration of given parameter
   Parameter Parameter analyzed     Value
     Aluminum     Antimony  
   Arsenic     Barium    
 Beryllium     Boron     Bromide
     Cadmium     Calcium  
   Chloride     Chromium    
 Cobalt     Copper     Iron  
   Lead     Lithium    
 Magnesium     Manganese    
 Methylmercury     Molybdenum    
 Nickel     Nitrate     Potassium
     Rubidium     Selenium  
   Silver     Sodium    
 Strontium     Sulfate     Thallium
     Thorium     Total.mercury
     Uranium     Vanadium  
   Zinc   Units Units parameter was measured in
     Value Definition   ug.L Micrograms per
 liter   mg.L Millgrams per liter   mgN.L Milligrams
 nitrogen per liter   mgS.L Milligrams sulfur per liter  
 ng.L Nanograms per liter   Table 5: Litter.and.foliage.csv
 Attribute Definition   Site Location where sampling occurred
   Year Year that the sample was collected in   Season
 Season that the sample was collected in     Value
 Definition   wet.season Sample collected during the wet season
 (December and January)   dry.season Sample collected during the
 dry season (July and August) Type Type of sample collected  
   Value Definition   bulk.litter Sample collected by
 gathering litter from the forest floor in the plot  
 Ficus.insipida Leaves collected from the canopy of ficus insipida using a
 slingshot   Inga.feuillei Leaves collected from the canopy of
 inga feuillei using a slingshot   litter.basket Sample collected
 from litter baskets suspended above the forest floor in the plot
   leafgrab Sample collected by gathering leaves within arms’
 reach from trees within the plot Total.mercury.ug.g Concentration of total
 mercury in the sample in mg/g     Table 6: Soil.csv
 Attribute Definition   Site Location where sampling occurred
   Type Type of sample collected     Value
 Definition   forested Site was located under a tree canopy
   deforested Site was located in a clearing Depth.cm Depth range
 that the soil sample was taken from in cm, with the soil surface
 representing 0 cm   Season Season that the sample was collected
 in     wet.season Sample collected during the wet season
 (December and January)   dry.season Sample collected during the
 dry season (July and August) Year Year that the sample was collected in
   Concentration Measured concentration of given parameter
   Parameter Parameter analyzed     Value
     Carbon     Manganese  
   Methylmercury     Nitrogen  
   pH     Selenium     Sulfur
     Total.mercury   Units Units analyte was
 measured in     Value Definition   percent
 Percent   ug.g Micrograms per gram   ng.g Nanograms per
 gram   NA Unitless   Table 7: GEM.csv Attribute
 Definition   Site Location where sampling occurred  
 GEM.ng.m3 Gaseous elemental mercury concentration in the sample in ng/m3
   Season Season that the sample was collected in  
   wet.season Sample collected during the wet season (December and
 January)   dry.season Sample collected during the dry season
 (July and August) Year Year that the sample was collected in  
   Table 8: Terrestrial.coordinates.csv Attribute Definition
   Site.Number Location where sampling occurred   Type
 Classification of site type     forested Site was
 located under a tree canopy   deforested Site was located in a
 clearing Latitude Latitude in decimal degrees   Longitude
 Longitude in decimal degrees