Retrospective analysis of heavy metal contamination in Rhode Island based on old and new herbarium specimens

Abstract

Premise of the study:Herbarium specimens may provide a record of past environmental conditions, including heavy metal pollution. To explore this potential, we compared concentrations of copper, lead, and zinc in historical and new collections from four sites in Rhode Island, USA.Methods:We compared historical specimens (1846 to 1916) to congener specimens collected in 2015 at three former industrial sites in Providence, Rhode Island, and one nonindustrial site on Block Island. Leaf material was prepared by UltraWAVE SRC Microwave Digestion, and heavy metal concentrations were measured by inductively coupled plasma–atomic emission spectroscopy.Results:Heavy metal concentrations in the historical and new specimens were measurable for all elements tested, and levels of copper and zinc were comparable in the historical and 2015 collections. By contrast, the concentration of lead declined at all sites over time. Significant variability in heavy metal concentration was observed between taxa, reflecting their varied potential for elemental accumulation.Discussion:It seems clear that herbarium specimens can be used to evaluate past levels of pollution and assess local environmental changes. With careful sampling effort, these specimens can be a valuable part of environmental science research. Broadening the possible applications for herbarium collections in this way increases their relevance in an era of reduced funding for collections-based research.

Widespread sampling biases in herbaria revealed from large‐scale digitization

“…Historically, the primary function of herbaria has been to serve as a resource for botanists carrying out taxonomic and systematic research, allowing users to construct classifications of plants, verify identifications, determine the ranges and morphological characteristics of species, and develop local and regional floras (Greve et al ., ). Over time, new uses for specimens have arisen, and now more than ever, they are being used in ways that collectors rarely imagined (Pyke & Ehrlich, ; Lavoie, ; Nualart et al ., ; Rudin et al ., ; Willis et al ., ,b). Accordingly, attempts to assess and categorize biases inherent in these collections have been made (Rich & Woodruff, ; Geri et al ., ; Schmidt‐Lebuhn et al ., ; Meyer et al ., ; Stropp et al ., ).…”

Widespread sampling biases in herbaria revealed from large-scale digitization

“…Historically, the primary function of herbaria has been to serve as an institution of taxonomy, allowing users to construct classifications of plants, verify identifications, determine the ranges and morphological characteristics of species, and develop local and regional floras (Greve et al, 2016). Over time, new uses for specimens have arisen, and now more than ever, they are being used in ways that collectors rarely imagined (Pyke & Ehrlich, 2010; Lavoie, 2013; Willis et al, 2017a,b; Nualart et al ., 2017; Rudin et al, 2017). Accordingly, attempts to assess and categorize biases inherent in these collections have been made (Rich & Woodruff, 1992; Geri et al , 2013; Schmidt-Lebuhn et al, 2013; Meyer et al, 2016; Stropp et al, 2016).…”

Using herbaria to study global environmental change

“…Studying lead pollution levels, for example, the isotopic lead composition in moss or lichen samples collected at roadsides reflects fluctuations in local motor vehicle traffic, efforts to reduce lead emissions and changes in petrol origin or composition over time (Farmer et al ., ). In addition to lead, herbarium samples also track concentrations of other metals such as cadmium, copper and zinc to follow their temporal and spatial trends in relation to anthropogenic activities (Zschau et al ., ; Shotbolt et al ., ; Rudin et al ., ). Combining pollution records and genetic information from historical and contemporary samples from contaminated sites can even enable studies of plants’ adaptation to pollution at the genetic, heritable level, for example by studying the association between pollution levels and specific alleles, and thus give indications about long‐term adaptation to changing conditions.…”

“…Metals from the atmosphere, soils and groundwater are deposited on or taken up by plants, and remain present in herbarium specimens, so the latter can be used as indicators of pollution, and due to their meta-information facilitate the dating of contamination (Lee & Tallis, 1973;Shotbolt et al, 2007;Rudin et al, 2017). Depending on species, their morphology, physiology and proximity to a pollution source, plants are exposed to and take up more or less pollutants (Lawrey & Hale, 1981;Rudin et al, 2017). Studying lead pollution levels, for example, the isotopic lead composition in moss or lichen samples collected at roadsides reflects fluctuations in local motor vehicle traffic, efforts to reduce lead emissions and changes in petrol origin or composition over time (Farmer et al, 2002).…”