WHERE IS THE PRE-INDUSTRIAL GOLD-SILVER MINING MERCURY?

Recent updates on Hg emissions from Ag-Au mining during the colonial and gold-rush era suggest Hg emission rates rivaling that of modern industrial times (Amos et al. 2013). Environmental sedimentary archives (marshes, lakes) should show evidence for such a large Hg emission pulse. Few lake records provide support for these past high Hg emission rates (Engstrom et al., 2014). Lakes in New England may show a Hg deposition record that is slanted towards local emission sources: e.g., marshes around Long Island Sound have Hg from the hat making industry in Connecticut that started in the late 1700s. We present here Hg deposition records from Block Island (RI), a small island 13 miles south of the RI coast line, with sparse population and no industrial history. Fresh Pond is a small lake with a very limited catchment basin and a marsh along the N-side of the island provided a second site. The Fresh Pond sediment cores have minor mixing of the core tops, whereas the marsh core yielded an undisturbed record. Dating was done with ambrosia pollen (Fresh Pond), radiocarbon (marsh core) and 210Pb-137Cs analyses (both cores), and the cores were analyzed for Hg by DMA-80. Both records show natural Hg background concentrations from 1400CE to the mid 1800s, then a slight increase, followed by a strong increase in Hg concentrations and accumulation rates from the mid 1930-1940s on, representing the modern industrial era. The marsh core shows a decrease in Hg at the very top (last 40 years). These two core records have modest excess Hg inventories with ²¹⁰Pb inventories only slightly larger than expected from in situ accumulation. Both records show no evidence for enhanced Hg accumulation rates during the Ag-Au mining era of 1500 to late-1800sCE. We assume, following Engstrom et al, that the amalgamation Hg used in the early noble metal extraction was not fully released into the atmosphere, but probably retained in mineral precipitates or locally recycled.