THE GEOCHEMICAL LEGACY OF ARSENICAL PESTICIDE USE IN NEW ENGLAND

Widespread use of arsenical pesticides and herbicides, principally lead arsenate, calcium arsenate, and sodium arsenate, on apple, blueberry, and potato crops in New England during the early 1900’s may be a significant anthropogenic source of As, Pb, and other metals to sediment and ground water. An Ag-index, based on cultivation data for these crops during this time, indicates where arsenical pesticides and herbicides were used extensively in New England. Geochemical and Pb isotopic variations in stream sediments, considered in relation to the Ag-index, population density, and geologic features, distinguish anthropogenic from natural sources. Pb, Cu, and Zn in stream sediments show significant positive correlations with population density (contamination from urban centers and roadways); As, Pb, and Cu concentrations and a Pb-As principal component factor correlate with the Ag-index. As in public-supply ground water wells, however, does not correlate significantly with the Ag-index. Stream sediments from coastal New England were leached in warm weak acids to examine the concentrations of labile metals and Pb isotopic compositions sorbed on secondary minerals, to distinguish between natural and anthropogenic sources. Pb isotope compositions of stream sediment leaches show a moderate range (206Pb/207Pb=1.1645-1.2233, 208Pb/207Pb=2.4317-2.4569) that overlaps the variation in nearby rock sulfides and their weathering products (206Pb/207Pb=1.1605-1.1965, 208Pb/207Pb=2.4260-2.4790). Pb isotope results for sediment leaches and residues from a range of Ag-index settings are analytically similar and are not uniquely characterized by rock type or land-use contributions. Pesticide contamination of stream sediments is not demonstrated on the basis of Pb isotopic compositions and leach chemistry. Stream sediments integrate contributions of arsenic and trace metals from rocks, surficial deposits, urban areas, and arsenical pesticide sources, although the relative contribution of natural versus anthropogenic sources is difficult to determine. Conversion of agricultural land contaminated with lead arsenate to residential development enhances the likelihood that humans will be exposed to lead and arsenic via dust and soil, but not necessarily by exposure to self-supply drinking water.