Zinc, copper, nickel, and arsenic monitoring in natural streams using in-situ iron–manganese oxide coated stream pebbles

• Published in: Journal of geochemical exploration Vol. 158; pp. 168 - 176
• Main Authors: Blake, Johanna M., Peters, Stephen C., Casteel, Amanda
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01-11-2015
• Subjects: Iron–manganese oxide coated stream pebbles; Nonpoint source metals monitoring; Nonpoint source metals monitoring; Iron–manganese oxide coated stream pebbles
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/j.gexplo.2015.07.013

Elements such as zinc, copper, nickel, and arsenic pose a concern for drinking water quality and ecosystem health and tracking these often nonpoint source contaminants in groundwater presents a significant challenge due to the heterogeneous spatial distribution of sources. Developing an approach to help locate the sources of zinc, copper, nickel, and arsenic in ground and surface water sources could potentially provide a rapid, repeatable, and inexpensive technique for environmental assessment. Iron–manganese oxide coated streambed pebbles have a surface affinity for metals and could serve as in-situ monitors. The analysis of pebble coatings and surface water sampled from Pennypack Creek and its tributaries, in southeastern Pennsylvania, USA, tests the ability of pebble coatings to reflect in-stream concentrations of zinc, copper, nickel, and arsenic and track the source of higher concentrations upstream and in tributary branches. Quartz pebbles, 5–7cm in diameter, with brown-red coatings were sampled along the main stem and tributaries of the Pennypack Creek followed by leaching coatings with 4M nitric acid with 0.03M hydrochloric acid for 24h. Quartz pebbles were selected to minimize elemental contamination from metal bearing minerals in the sample. All metals in the leachate are significantly correlated (p<0.15) with iron on the coatings. Zinc, copper, and nickel show elevated concentrations on the pebble coatings near the middle of the watershed compared to concentrations on coatings at other sampling sites. To predict the arsenic source in the main stem, two segments of the Pennypack Creek were chosen for calculations of relative discharge and concentration. Arsenic concentrations (normalized to surface area) on pebbles in the main stems are 5.62ng/cm2 and 12.7ng/cm2 and the predicted values are 13.3ng/cm2 and 28.6ng/cm2 which satisfy mixing within the tributaries. Results suggest that iron–manganese coated stream pebbles are useful indicators of zinc, copper, nickel, and arsenic location within a watershed, but that the source of arsenic differs from that of the other metals of interest. Zinc, copper, and nickel data suggest a geochemical signal from nearby railroads or industrial point source contamination and arsenic data suggests a geogenic source or industrial point source contamination that is traced upstream from a main stem to tributaries using pebble coating concentrations and relative discharge.
•Zn, Ni, Cu, and As have significant relationships with iron on stream pebbles.•Zn, Ni, and Cu have similar spatial patterns within Pennypack Creek's watershed.•Binary mixing in the creek predicts As concentrations on pebbles.