A Geochemical, Isotopic, and Petrologic Study of a Watershed with Arsenic-enriched Ground Water in Northport, Maine

High mean arsenic concentrations up 26.6 ¹mol/L (1990 ¹g/L) occur in ground water within a watershed at Kelly\u27s Cove, Northport, Maine, USA. The Kelly\u27s Cove watershed is a fractured-bedrock system composed of sul¯dic schist with granitic to dioritic intrusions. Arsenic is enriched in these rocks up to 1050 mg kg¡1 (average: 68 mg kg¡1). The distribution of arsenic in the bedrock appears to be controlled by the presence of arsenopyrite and arsenian pyrite, that occur primarily in post-metamorphic, tourmaline + quartz § carbonate veins and the Kelly\u27s Cove granite. Based on the metamorphic signature of the tourmaline chemistry and the similarity in ±34S values of the sulfides, these veins probably derived from hydrothermal remobilization of surrounding metamorphic rock. Chemical analyses of water from 35 bedrock wells throughout the watershed reveal spatial clustering of wells with high arsenic concentrations. Stiff diagrams and box plots distinguish three distinct water types; calcium bicarbonate-dominated water with low arsenic concentrations (CaHCO3 type), sodium bicarbonate-dominated water with moderately high arsenic concentrations (NaHCO3 type), and calcium bicarbonate-dominated water with very high arsenic concentrations (High-As type). Di®erences in recharge area, ground-water evolution, and possibly bedrock composition contribute to the chemical distinctions within the watershed\u27s ground water. Lack of correlation of aqueous arsenic concentrations with pH indicates that desorption of arsenic is an insignificant control on arsenic concentration. Correlations of aqueous arsenic concentrations with increasing Fe(II)/Fe(III) and decreasing Eh indicates that reductive dissolution of ferric oxyhydroxides plays a role in the occurrence of high arsenic concentrations in the NaHCO3 and High-As type water. Ground water with high arsenic concentrations contains sulfate with enriched sulfur and oxygen isotopes. The range of ±34S[SO4] and ±18O[SO4] values at the Kelly\u27s Cove watershed (+3.4 to +4.9 ?? and -2.01 to +6.72 ?? , respectively) are strikingly similar to that of another Maine watershed (+3.7 to +4.6 ?? and -2.56 to +7.47 ?? , respectively), that has different oxidizing ground-water conditions. The association of high arsenic concentrations and high ±18O[SO4] is not due to oxidizing conditions or reduction of sulfate, but may be related to paleo-aeration of iron oxyhydroxides that are now reducing and releasing arsenic

A Geochemical, Isotopic, and Petrologic Study of a Watershed with Arsenic-enriched Ground Water in Northport, Maine

High mean arsenic concentrations up 26.6 ¹mol/L (1990 ¹g/L) occur in ground water within a watershed at Kelly\u27s Cove, Northport, Maine, USA. The Kelly\u27s Cove watershed is a fractured-bedrock system composed of sul¯dic schist with granitic to dioritic intrusions. Arsenic is enriched in these rocks up to 1050 mg kg¡1 (average: 68 mg kg¡1). The distribution of arsenic in the bedrock appears to be controlled by the presence of arsenopyrite and arsenian pyrite, that occur primarily in post-metamorphic, tourmaline + quartz § carbonate veins and the Kelly\u27s Cove granite. Based on the metamorphic signature of the tourmaline chemistry and the similarity in ±34S values of the sulfides, these veins probably derived from hydrothermal remobilization of surrounding metamorphic rock. Chemical analyses of water from 35 bedrock wells throughout the watershed reveal spatial clustering of wells with high arsenic concentrations. Stiff diagrams and box plots distinguish three distinct water types; calcium bicarbonate-dominated water with low arsenic concentrations (CaHCO3 type), sodium bicarbonate-dominated water with moderately high arsenic concentrations (NaHCO3 type), and calcium bicarbonate-dominated water with very high arsenic concentrations (High-As type). Di®erences in recharge area, ground-water evolution, and possibly bedrock composition contribute to the chemical distinctions within the watershed\u27s ground water. Lack of correlation of aqueous arsenic concentrations with pH indicates that desorption of arsenic is an insignificant control on arsenic concentration. Correlations of aqueous arsenic concentrations with increasing Fe(II)/Fe(III) and decreasing Eh indicates that reductive dissolution of ferric oxyhydroxides plays a role in the occurrence of high arsenic concentrations in the NaHCO3 and High-As type water. Ground water with high arsenic concentrations contains sulfate with enriched sulfur and oxygen isotopes. The range of ±34S[SO4] and ±18O[SO4] values at the Kelly\u27s Cove watershed (+3.4 to +4.9 ?? and -2.01 to +6.72 ?? , respectively) are strikingly similar to that of another Maine watershed (+3.7 to +4.6 ?? and -2.56 to +7.47 ?? , respectively), that has different oxidizing ground-water conditions. The association of high arsenic concentrations and high ±18O[SO4] is not due to oxidizing conditions or reduction of sulfate, but may be related to paleo-aeration of iron oxyhydroxides that are now reducing and releasing arsenic

Containing Arsenic-Enriched Groundwater Tracing Lead Isotopic Compositions Of Common Arsenical Pesticides In A Coastal Maine Watershed Containing Arsenic-Enriched Ground Water

Arsenical pesticides and herbicides were extensively used on apple, blueberry, and potato crops in New England during the first half of the twentieth century. Lead arsenate was the most heavily used arsenical pesticide until it was officially banned. Lead arsenate, calcium arsenate, and sodium arsenate have similar Pb isotope compositions: 208Pb/207Pb = 2.3839-2.4722, and 206Pb/207Pb = 1.1035-1.2010. Other arsenical pesticides such as copper acetoarsenite (Paris green), methyl arsonic acid and methane arsonic acid, as well as arsanilic acid are widely variable in isotope composition. Although a complete understanding of the effects of historical use of arsenical pesticides is not available, initial studies indicate that arsenic and lead concentrations in stream sediments in New England are higher in agricultural areas that intensely used arsenical pesticides than in other areas. The Pb isotope compositions of pesticides partially overlap values of stream sediments from areas with the most extensive agricultural use. The lingering effects of arsenical pesticide use were tested in a detailed geochemical and isotopic study of soil profiles from a watershed containing arsenic-enriched ground water in coastal Maine. Acid-leach compositions of the soils represent lead adsorbed to mineral surfaces or held in soluble minerals (Fe- and Mn-hydroxides, carbonate, and some micaceous minerals), whereas residue compositions likely reflect bedrock compositions. The soil profiles contain labile Pb (acid-leach) showing a moderate range in 206Pb/207Pb (1.1870-1.2069), and 208Pb/207Pb (2.4519-2.4876). Isotope values vary as a function of depth: the lowest Pb isotope ratios (e.g., 208Pb/206Pb) representing labile lead are in the uppermost soil horizons. Lead contents decrease with depth in the soil profiles. Arsenic contents show no clear trend with depth. A multi-component mixing scheme that included lead from the local parent rock (Penobscot Formation), lead derived from combustion of fossil fuels, and possibly lead from other anthropogenic sources (e.g., pesticides), could account for Pb isotope variations in the soil profiles. In agricultural regions, our preliminary data show that the extensive use of arsenical pesticides and herbicides can be a significant anthropogenic source of arsenic and lead to stream sediments and soils

WATERSHED WITH ARSENIC-ENRICHED GROUND WATER IN

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Characterizing the Dynamics of the Leader–Linker Interaction in the Glycine Riboswitch with Site-Directed Spin Labeling

[Image: see text] Site-directed spin labeling with continuous wave electron paramagnetic resonance (EPR) spectroscopy was utilized to characterize dynamic features of the kink–turn motif formed through a leader–linker interaction in the Vibrio cholerae glycine riboswitch. Efficient incorporation of spin-labels into select sites within the phosphate backbone of the leader–linker region proceeded via splinted ligation of chemically synthesized spin-labeled oligonucleotides to in vitro transcribed larger RNA fragments. The resultant nitroxide EPR line shapes have spectral characteristics consistent with a kink–turn motif and reveal differential backbone dynamics that are modulated by the presence of magnesium, potassium, and glycine