Abstract
Rapid urbanization, anthropogenic pollution and frequent flooding events are affecting the soil and water quality along the streams and bayous of Houston. Soil acts as sink and reservoir of heavy metals and nutrients affecting human and animal health. The objectives of the study are 1) to analyze the effects of the metal and nutrient concentration of bayou flood plain surface soil samples on the gut cell cytotoxicity and 2) to evaluate the spatial and temporal difference in soil contamination on cell viability of colon cancer (HT-29) and normal colon epithelial (CCD 841 CoN) cell lines. To evaluate soil contamination between pre- and post-hurricane (Summer and Fall) conditions in six Bayous (Brays, Buffalo, Halls, Hunting, Greens and White Oak Bayous) of Harris County, Texas, in vitro bioassay analysis was applied to soil extracts. The MTT assay determined that, with increase in concentration of Bayou soil from 12.5% to 100%, the viability of CCD 841 CoN and HT-29 cells decreased significantly, across all sampling locations during both summer and fall seasons. Among all the bayous, the viability of CCD 841 CoN cells in summer and fall followed the pattern of White Oak > Greens > Halls > Brays Bayou, where the viability of cells exposed to White Oak soils was 3–4 times higher than cells exposed to Brays Bayou soil at 100% soil concentration. The viability of HT-29 cells in both seasons followed the pattern of Greens > White Oak > Halls > Brays Bayou, where the viability of cells exposed to Greens Bayou soil was more than 3–4 times higher than the cells exposed to Brays Bayou soil at 100% concentration. The higher concentration of metals and nutrients such as P, Zn, Cd, and Cu might have contributed to the significant cell lethality in Brays Bayou samples compared to other locations.
Highlights
Anthropogenic land use impacts, catastrophic tropical flooding, extensive point and non-point source pollution, frequent inundation of neighborhoods are the principal drivers of surface water degradation in Houston, a coastal Metropolitan city
The P, Zn, Pb and Cu concentrations in Brays Bayou soil samples were significantly higher than the Greens, Halls and White Oak Bayou loca tions in both the summer and fall seasons
The concentration of Zn remained significantly higher in the up stream (G58.4) while the concentration of Cd remained significantly higher in the downstream (G6.1) soils of Greens Bayou during summer
Summary
Anthropogenic land use impacts, catastrophic tropical flooding, extensive point and non-point source pollution, frequent inundation of neighborhoods are the principal drivers of surface water degradation in Houston, a coastal Metropolitan city. The City of Houston is the 4th largest city in the United States and is the largest city in Harris County covering 665 square miles with an estimated population of 2.3 million (U.S Census Bureau, 2020). Harris County, Texas, covers 1777 square miles and is home to over 4.7 million people, making it the 3rd largest county by population in the United States (U.S Census Bureau, 2020). The surge of urbanization in Harris County resulted in loss of vegetation and increased amount of impervious surface areas due to residential development and industrialization (Juan et al, 2020). Problems associated with increase in impervious areas include flooding, which can cause alterations to estuarine systems (Chen et al, 2015; Zhang et al, 2018). Flooding cause poor water quality from runoffs and alter tidal prisms resulting in changes in sediment dynamics and increased sedi ment toxicity (Al Mukaimi et al, 2018; Schüttrumpf et al, 2011)
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