DOI: 10.5061/dryad.tqjq2bw1p
title: Measurements of heavy metals in the moss Orthotrichum lyellii collected using community science in the Duwamish Valley, Seattle, Washington, U.S.A.

description: Heavy metals concentrations often vary at small spatial scales not
 captured by air monitoring networks, with implications for environmental
 justice in industrial-adjacent communities. Pollutants measured in moss
 tissues are commonly used as a screening tool to guide use of more
 expensive resources, like air monitors. We piloted a community science
 approach, engaging over 55 people from nine institutions, to map heavy
 metals using moss in two industrial-adjacent neighborhoods. Local youth
 led sampling of the moss Orthotrichum lyellii from trees across a
 250×250-m sampling grid (n = 79). We compared their data with
 expert-collected samples (n = 19) using Principal Components Analysis and
 Procrustes Analysis. We mapped 21 chemical elements measured in moss,
 focusing on 6 toxic ‘priority’ metals: arsenic, cadmium, chromium, cobalt,
 lead, and nickel. We compared local data, using t-tests and boxplots, with
 two ‘reference datasets’ of O. lyellii collected in Portland, Oregon, and
 in Seattle City Parks. We also use Principal Components Analysis to
 describe major gradients in metals in the study area. Our data submission
 includes two R scripts and four datasets of heavy metals in moss,
 including the two reference datasets, which will enable replication of our
 analyses as well as novel analyses.
description: SAMPLING (For main dataset. Reference datasets are similar.
 Citations provided in metadatafile) Moss sampling
 protocols were adapted from prior studies using the widespread epiphytic
 (i.e. “tree-dwelling”) moss species <em>Orthotrichum
 lyellii</em> (Donovan et al. 2016, Gatziolis et al. 2016). The
 Duwamish Valley Youth Corps (DVYC) and adult study partners collected the
 moss from a 250×250-m grid across two industrial-adjacent neighborhoods in
 Seattle's Duwamish Valley (Georgetown and South Park) with
 longstanding air pollution concerns. Moss was collected at the suitable
 tree nearest the centroid of each grid cell. The DVYC led moss sampling
 excursions on four warm, dry days in 2019 (May
 25<sup>th</sup>, June 1<sup>st</sup>,
 4<sup>th</sup>, and 8<sup>th</sup>). Participants met the following week in a
 local high school science laboratory to harvest the upper
 2/3<sup>rds</sup> of living moss stems for heavy
 metals analysis (Gatziolis et
 al. 2016). To
 assess sampling precision, the youth-led teams immediately collected a
 replicate moss sample at 18 sites where ample moss was available.
 Their final analytical dataset had 79 samples from 61 grid
 cells. To check sampling accuracy, experts re-sampled 19 grid cells
 although this occurred about 2 weeks later on June 13, 2019
 due to scheduling difficulties. LAB METHOD (For main
 dataset. Reference datasets are similar. Citations provided in
 metadatafile) All moss
 samples were sealed and mailed
 to the US Forest Service Grand Rapids, MN laboratory where
 they underwent the same treatment. Samples were prepared for heavy metals
 analysis by oven drying at 40 °C for 24 h and homogenizing by grinding to
 a fine powder (IKA tube-mill, 1 min grinding time for each sample at
 15,000 rpm). A 0.500-g subsample of each moss sample was processed using a
 modified microwave-assisted digestion with 10 mL concentrated
 HNO<sub>3</sub> + 2 mL 30%
 H<sub>2</sub>O<sub>2</sub> + 2 mL concentrated HCl
 (CEM, 2019). An overnight pre-digestion of the samples with added reagents
 was done at room temperature. Following the microwave-assisted digestion
 cycle, digests were transferred by rinsing with deionized water to 50 mL
 volumetric flasks, diluted to volume with deionized water, and filtered
 through 0.45-um membrane filters into plastic storage bottles prior to
 analysis. Concentrations of 25 elements in total were measured by
 inductively coupled plasma optical emission spectrophotometry (Thermo 7000
 series dual-view (axial and radial) ICP-OES). Quality control steps included use of method
 blanks, instrument calibration standards, instrument performance check
 standards, and reference lichen samples. The measurement quality
 objectives (MQOs) are the same as the confidence and tolerance levels that
 accompany each standard reference material or check standard certification
 sheet. Quality control/quality assurance (QC/QA) for air-quality sampling
 in our study followed the EPA Quality Assurance Guidance document (USEPA
 2016). Details of the laboratory QC/QA steps are provided in Appendix A of
 the Ecosphere article. All
 data processing/analysis is documented in the two R-scripts provided and
 summarized briefly in the metadata.
description: We provide 2 main datasets, one used for most statistical
 analyses ('Unaveraged_data_all_metals_June8.csv") and one used
 to create maps ("Final_forMAPSV3").
 "Unaveraged_data_all_metals_June8.csv" contains raw
 values of heavy metals measured in all moss samples along with basic
 information for each sample, including collector (expert vs youth),
 collection date, lat and long of sampled tree. ""Final_forMAPSV3"
 was derived from the prior dataset; it includes only youth-collected data and
 replicate samples were averaged, leaving one value for
 mapping. We also include two
 reference datasets we compared values from the main dataset with
 ("Portland_fulldataset" and
 "seattleparks"). Note that Mn
 and Se values are not reliable and are included for informational purposes
 only. Mn in moss is influenced by canopy leachates and ICP-OES detection
 limits for Se are high. Units for all elements are mg/kg unless specified
 otherwise in the metadata. Additionally, a flash thunderstorm occurred
 before experts collected moss samples on June 13, which we believe led to
 systematically lower heavy metals values in expert-collected samples
 (although results, for the most part, were not statistically significantly
 different from youth-collected samples; See Derrien et al.
 2020).