Date of Award

Spring 4-2019

Degree Name

Doctor of Philosophy (PhD)

Advisor(s)

LAWRENCE W WHITEHEAD, PHD

Second Advisor

INKYU HAN, PHD

Third Advisor

DEJIAN LAI, PHD

Abstract

Chronic exposure to heavy metals could lead to adverse health effects such as cancer, neurological development diseases and immunological diseases. The ingestion pathway has been considered the major exposure route for heavy metal contaminated soils. Heavy metals may be proportionally bioaccessible for the human body to absorb. There are no risk assessment studies done in Houston to evaluate health risks from exposure to heavy metals and no spatial analysis done yet. The aims of this dissertation are (1) to characterize 13 heavy metals: magnesium (Mg), vanadium (V), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), arsenic (As), lead (Pb), barium (Ba), and cadmium (Cd) in soils in Houston, Texas (TX), and evaluate spatial distribution maps of these metals; (2) to assess bioaccessibility of 13 metals (Pb, Cd, Cu, As, Cr, Zn, Ni, Mn, Ba, Co, Mg, Fe, and V) in soils; (3) to estimate human health risks of 10 toxic metals (As, Ba, Cd, Cr, Cu, Mn, Ni, Pb, Zn, and V) using metal concentrations in soils and bioaccessibility concentrations, and to simulate cancer and non-cancer risks maps. We sampled top soils at 96 locations in Houston, TX. We used microwaved-acid digestion system to prepare the soil samples and analyzed metal concentrations in soils by inductively coupled plasma mass spectrometry. Besides, we obtained Environmental Justice Screening and Mapping Tool Indexes to identify possible high exposure groups and emission sources of metals. We simulated heavy metal distribution by ordinary kriging in SAS software and ArcGIS software. Moreover, we used an in-vitro bioaccessibility method to obtain percent bioaccessibility fractions (%BAF) in gastric phase and gastro-intestinal phase. We assessed human health risks by using metal concentrations in soils and bioaccessibility results among five age groups, 0 to < 1 year old (infants), 1 to < 6 year old (toddlers), 6 to < 12 years old (children), 12 to < 18 years old (teenagers), and 18 to < 78 years old (adults), and estimated hazard index (HI) and cancer risks with SAS software and ArcGIS software for non-sampled area. Ninety-six percent of samples had either one or more than one metal over Texas Commission on Environmental Quality (TCEQ) background values. Pb and Zn had more than 80% of samples over TCEQ background levels. We found that closer proximity to National Priority sites and Risk Management Plan sites had higher Ni, Cr, Ba, Cu, Pb and Zn in soils than further proximity. We also discovered environmental justice issues in Houston as minority and low income groups live in neighborhoods with high Ni, Cr, Ba, Cu, and Zn concentrations in soils. We found that most of the metals had decreasing %BAF from gastric phase to gastro-intestinal phase, except Cu and V. The %BAF in gastric phase ranged from 1.22 % to 69.71 %. The %BAF in gastro-intestinal phase ranged from 0.22 % to 45.87%. For chronic non-cancer health effects, all hazard indexes among 5 age groups were under one (1). The infants group had the highest HI followed by toddlers group. Pb contributing 90% and As contributing 6% in HI when applying all three experimental results. Adults group’s cancer risks were 1.02 in a million followed by toddlers group. We suggested that future metal pollution studies interested to point sources in Houston should focus in East and South side. Other studies interested to traffic volume should have better study design to differentiate emission since Houston doesn’t have zoning between industrial area and residential area. Furthermore, for exposure of young children, future studies should focus for soils in playgrounds, parks, or schools, especially around old downtown areas.

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