Environmental Advances (Jul 2021)
Lead geochemistry of sediments in Galveston Bay, Texas
Abstract
The geochemical behavior of Pb in terrestrial and coastal water systems significantly influences Pb biogeochemical cycling and pollutant exchange at the land-sea continuum. An ideal case study of Pb environmental geochemistry is Galveston Bay, an anthropogenic estuary exposed to industrial runoff, wastewater and shipping vessel spills but also fed by natural rivers. Here, sediments from Galveston Bay were measured for Pb isotope ratios and abundances to constrain Pb sources and fluxes and understand Pb pollution history in the bay. Lead isotopes have been established as source tracers of environmental pollution and allow Pb sources to be reliably fingerprinted and identified. Sediments were leached to distinguish authigenic sediment coatings from lithogenic residual sediments, in addition to bulk sediment digestions. Total Pb concentrations ranged from 1.76 µg/g–29.19 µg/g in bulk digests, which are below federal toxicity thresholds and aligns well with prior measurements of Pb in Galveston Bay sediments in the 20th century. Lead concentrations are spatially constrained by flocculation in eastern bay areas where the Trinity River enters the bay and positively temporally correlated to freshwater discharge. Sediment 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios range between 18.338–19.777±0.002, 15.557–15.755±0.002 and 37.913–43.340±0.005, respectively, and were used in an advanced Bayesian isotope mixing model to identify Pb sources in the Galveston Bay sediment fractions analyzed. Anthropogenic sources supply approximately 83.8%, 16.6% and 25.5% of Pb to the leachates, residues and bulk sediments, respectively. This study showcases the importance of estuaries in moderating terrestrial and marine Pb distribution and provides insight for future contaminant studies in Galveston Bay and other estuarine systems around the world.MAIN FINDINGS Pb isotope ratio and abundance measurements of Galveston Bay sediments demonstrate significant anthropogenic Pb inputs to the estuary despite low Pb levels.
