Spatial Distribution of Antimony and Arsenic Levels in Manadas Creek, an Urban Tributary of the Rio Grande in Laredo, Texas

Abstract

The Rio Grande and its tributaries represent a critical water source for both the human population and the ecological resources of the Rio Grande drainage basin. Manadas Creek, an urban tributary of the Rio Grande, is located in an industrialized area of Laredo, Texas, where warehouses, a major railroad, and a decommissioned antimony (Sb) smelter are located. Previous studies have found that the creek water is contaminated with heavy metals such as Sb and arsenic (As). However, data on the metal distribution in this creek are very limited. Herein, water and sediment core samples were collected from six sites along the creek in February, April, and May 2008. Samples were analyzed for dissolved and total metals in water, total metals in sediments, and available (soluble-exchangeable, surface adsorbed, and organically bound) fractions of metals associated with the sediments. Results show that concentrations of Sb in the water and sediment samples were significantly lower at the upstream control site compared to the two sites located near the decommissioned smelter. Decreasing levels of Sb were found at the sites located downstream. The As levels in the sediment remained constant at different depths, whereas Sb varied significantly. A high level, 420 mg/kg, of sediment Sb was found at the maximum sediment depth of 35.0 cm sampled. In addition, 65.7-76.9% Sb and 80.3-85.6% As were in their residual form, 15.0-22.5% Sb and 6.2-11.4% As were bound to organic matter, and the remaining As and Sb were in the soluble and surface adsorbed fractions. Pearson correlation analyses indicated that the distribution of Sb was only moderately correlated to iron and nickel in the sediment and its correlation with the sediment properties measured was insignificant. Cluster analyses only grouped the two Sb isotopes together for the sediments collected in May, indicating that sources other than natural occurrence were associated with Sb. The high level of sediment Sb observed indicates that the sediment bed of Manadas Creek was acting as a holding reservoir for Sb and a potential source for the Sb level in the stream water. Thus, the loss of the sediment Sb and the Sb level in the water column must be closely related to the mobility of the bed sediments and the fate of the sediment-associated Sb.

Antimony, Arsenic and Thallium Bioaccumulation in Asiatic Clam (<i>Corbicula fluminea</i>) Transplanted along the Manadas Creek, Laredo, Texas

“…The second study shows a reduction of metal concentration especially Sb which was recorded at about 50% reduction. A study in Feb-May 2008 recorded As and Sb concentrations in the creek as 20.6 and 219.3 μg/L respectively, and a study in in February 2010 recorded mean As and Sb concentrations 47.99 μg/L and 22.80 μg/L respectively [18] [41]. These results highlight fluctuations over the years of study which can be attributed to seasonal variations in geochemical conditions [42].…”

“…Manadas Creek is an urban tributary of the Rio Grande. It flows along residential, recreational, and business areas, a major highway, heavily traveled roads, warehouses, a ready-mix cement factory, a major railroad, and an antimony smelter [18]. Because water from the Rio Grande is an important natural resource, there is much concern about protecting this river from urban pollution.…”

“…This operation is associated to the heavy metal contamination in Manadas Creek and still poses a threat to the surrounding aquatic environment [19]. A study by Baeza et al, 2010 sampled six different sites in Manadas Creek that were upstream and downstream from the antimony site [18]. Higher than normal antimony and arsenic levels were measured in both water and sediments from the creek.…”

The Asiatic Clam (Corbicula fluminea) as a Bio-monitor for Determining the Distribution of Antimony, Arsenic and Thallium in the Water Column and Sediments of Manadas Creek, Laredo, Texas

“…This operation is associated to the heavy metal contamination in Manadas Creek and still poses a threat to the surrounding aquatic environment [19]. A study by Baeza et al, 2010 sampled six different sites in Manadas Creek that were upstream and downstream from the antimony site [18]. Higher than normal antimony and arsenic levels were measured in both water and sediments from the creek.…”

Antimony Isotope Fractionation during Adsorption on Iron (Oxyhydr)oxides

“…Antimony (Sb) contamination is currently emerging as a significant concern due to the toxicity of Sb and its links to cancer. − Naturally occurring Sb is usually found in water, primarily as oxyanions in two oxidation states: +3 and +5. , In soil systems, Sb behaves similarly to arsenic as it partitions onto mineral phases and is preferentially associated with iron or aluminum (oxyhydr)­oxides. − Adsorption and precipitation processes could be crucial factors of Sb mobilization. − …”