MONITORING TOXIC HEAVY METAL CONCENTRATIONS OF MASSACHUSETTS SALT MARSH SEDIMENTS

The onset of the industrial revolution in the mid-19^th century triggered the ascent of anthropogenic emissions of carbon dioxide and of hazardous pollutants such as toxic heavy metals. Although CO₂ emissions have continued to climb into the 21^st century, emissions of heavy metals are generally thought to have decreased, at least in the United States, since the passage of the Clean Air and Water Acts almost five decades ago. However, given the dangers toxic metals pose to human health, continuing to monitor their environmental levels is essential. The sedimentary record in coastal salt marshes provides an opportunity to study contaminant deposition and post-depositional fate. We analyzed the concentrations of heavy metals and other elements in the upper 50cm of four salt marsh peat cores taken from the Plum Island Estuary (Massachusetts) in 2016. The concentrations of Arsenic, Copper, Nickel, Lead and Zinc were measured by Inductively Coupled Plasma Atomic Emission Spectrometry and Mass Spectrometry following partial sample digestion using aqua regia. This digestion approach targets elements on particle surfaces rather than within recalcitrant mineral lattices, and therefore likely yields information on pollutant loadings. Previous ²¹⁰Pb and ¹³⁷Cs analyses at our core sites provide chronological control, allowing us to interpret our results as a snapshot of changing heavy metal pollutant levels in New England over the last 100 years. While concentrations of As, Cu, Ni, Pb and Zn did indeed decrease in the latter part of the 20^th Century from their mid- to late 20^th Century highs, this decline appears to have halted in the past two decades, with concentrations of Arsenic and Copper remaining above EPA thresholds for safety in soils. These data provide insight on how heavy-metal pollutant loading has varied through time and across various pollutants in coastal New England, and can serve as baseline information to monitor whether contamination levels increase in the future.