Heavy metal contamination in the natural world is complex as many metals can be sourced anthropogenically, naturally, or via both vectors. Many heavy metals are known to be toxic, non-biodegradable, and trophic level bio-magnifiers. Therefore, it is important to monitor and study their concentrations, distributions, and processes for transport and sequestration. Near-shore marine sediments act as a sink for heavy metals in the water column due to their physiochemical properties.
In this dissertation’s second chapter, thirty sediment samples from three latitudinally distinct mangrove areas from the Red Sea of Saudi Arabia (near Yanbu, Jeddah, and the Farasan Islands) were analyzed for lead concentrations and isotopic ratios. Lead is persistent in the environment and can cause health problems for humans when exposed. Lead isotopic ratios are used to determine potential sources. End member mixing models were then used to quantify source contribution. Results showed that legacy leaded gasoline and natural sources dominate the lead loading of the Jeddah and Farasn Islands environments while the industrial city of Yanbu has an additional anthropogenic lead source, likely industrial ore. Jeddah has the highest petrol impact compared to the Farasan Islands and Yanbu sites while the dominant Pb source in the Farasan Islands is natural. This is one of very few studies in the region to report environmental Pb isotopic ratios and the first to do so for mangrove sediments.
The third chapter here assessed current and historical ecosystem risk of total heavy metal loadings on mangrove environments in the near-shore mangrove stands of the Saudi Arabian Red Sea. Concentrations of numerous metals (V, Cr, Cu, Ni, Zn, Cd, and Pb) and associated sediment parameters (sediment organic matter, carbonate, and silicate) were measured. Associated environmental risk indices were calculated for distinct mangrove regions, Yanbu, Jeddah, and the Farasan Islands, at surface and at depth. Heavy metal sources were determined and categorized as anthropogenic, natural, or both. Results showed that the Yanbu site has experienced higher stress compared to the other two sites due to its elevated metals concentrations in its lower sediments. The Yanbu location has mostly anthropogenic metals sourcing in addition to natural sources for Cr, Cu, Zn, Cd, and Pb while V and Ni have solely a natural delivery. The Farasan Islands ecosystem receives Cd from anthropogenic sources while Cu and Zn have been derived from natural and anthropogenic sources to the sediments. The rest of elements (V, Cr, Ni, and Pb) have a natural delivery to the Farasan Islands. For the Jeddah site, all measured heavy metals have been delivered to the Jeddah environment via an anthropogenic source, mostly likely wastewater discharge. The lower, older, sediments of Yanbu were the most polluted by heavy metals compared to the older, or lower, sediments of Jeddah and the Farasan Islands. Surface values suggest an amelioration of Yanbu as they show, in general, similar metal concentrations to Jeddah and the Islands. Jeddah and the Farasan Islands have a similar trend in heavy metals concentrations with respect to depth. Organic matter, carbonate, and silicate were measured, and the results showed that most of the heavy metals across the three locations have been complexed by silicates when sequestered to the sediments. This study provides a bigger picture of the current heavy metal environmental status in mangrove sediments as the number of prior studies on mangrove sediments in the Saudi Arabian Red Sea is limited. The overall heavy metals concentrations are relatively low compared to other local and worldwide studies. However, the elevated metal concentrations in the lower sediments of Yanbu made Yanbu site as the most contaminated region in the study area. The controlling anthropogenic source (wastewater discharge) in the Jeddah environment makes the Jeddah site an environmental concern despite low concentrations compared to Yanbu. Clearly, exacerbation is possible, thus, the outcomes of this chapter could inform environmental management decision makers in the region to regulate heavy metals inputs to the Red Sea environment.
The fourth chapter of this dissertation is a meta-analysis of published work on heavy metal loadings in near-shore surface sediment data from the Arabian Gulf. Numerous studies have been published in the last two decades with little to no cross-work synthesis. As the area continues to grow, a holistic summary of these data is necessary for the research and environmental management community. Heavy metal concentrations in 2086 sediment samples from 106 sites distributed across the Arabian Gulf were collected from literature to assess the degree of contamination for the Gulf marine system as well as sourcing. These sites have been divided into three sub-regions to contrast the heave metal contamination level by region. Results showed that the Gulf has a high environmental stress from Cd, Co, Cr, Cu, Ni, Pb, Zn, Fe, V, and As with different degrees of contamination. Cr, Ni, and Fe have lower contaminations than Cd, Co, Cu, Pb and As. Zn and V have the lowest environmental pressure among all elements. Mn has been delivered to the Gulf marine environment from natural sources. The current environmental status of the Arabian Gulf basin is that of heavy pressure from the human and industrial activities which needs urgent attention from management entities in the surrounding countries to help mitigate contamination.
The Saudi Arabian Red Sea coast and the countries adjacent to the Arabian Gulf basin have undergone major coastal economic and urban development due to population growth. This dissertation gives a current assessment of heavy metal pollution in both basins’ environments. Chapter 2 suggests that the northern end of the Saudi Red Sea (Yanbu) has higher Pb concentration from three sources, natural, gasoline, and industrial ore. Meanwhile, the mid-coast and southern end of the Saudi Red Sea (Jeddah and the Farasan Islands, respectively) have a comparable amount of Pb, and both have received Pb from natural and gasoline sources with no third Pb component. However, Jeddah has the highest petrol Pb impact among the three regions. Chapter 3 illustrates that heavy metal contamination was highest in the Yanbu environment based on its lower sediments as Jeddah and the Farasan Islands have similar, and lower, metal concentrations with respect to depth. Both chapters have different methods yet show similar major observations. Yanbu has notably higher environmental risk across the study area of the Red Sea while Jeddah is the next most contaminated site and the Farasan Islands have the least environmental pressure among the three regions.
Eleven elements were analyzed in the near-shore sediments of the Arabian Gulf and only one element was naturally delivered to the Gulf basin while the rest have been anthropogenically delivered. Specifically, the Gulf basin is at very serious environmental risk from Cd, Co, Cr, Cu, Ni, Pb, Zn, Fe, V, and As which have been delivered to the Gulf marine system from anthropogenic sources. These elements have different degrees of pollution where Cd, Co, Cu, Pb and As are the highest contaminants. Cr, Ni, and Fe are the second highest pollutants while Zn and V have the lowest contamination degree. The only element found as solely natural across the Gulf ecosystem is Mn. This dissertation provides useful records of heavy metal contamination status and sourcing in sediments from the Saudi Arabian Red Sea and the Arabian Gulf basins. Also, this work suggests spatial trends of heavy metals in both basins as well as historical changes in the Saudi Arabian Red Sea. These updated records are not only valuable for the research community, but also for the management and environmental regulation entities in the regions.
Civil and Environmental Engineering
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Alnasser, Abdullah, "Assessment and Sourcing of Heavy Metal Contamination of Middle East Semi-Enclosed Marine Environs Via Near-Shore Sediment Analysis" (2023). Civil and Environmental Engineering Theses and Dissertations. 30.