Combined Effects of Seawater Intrusion and Heavy Metal Pollution on the Groundwater Resources of Tarout Island, Saudi Arabia

Groundwater resources in coastal aquifers are commonly subjected to several anthropogenic threats that deteriorate their quality. This study focuses on the key factors influencing groundwater in Tarout Island, Saudi Arabia, including seawater intrusion, heavy metal contamination, and nitrate pollution. A comprehensive sampling and analysis strategy was implemented, incorporating the primary ion chemistry, stable isotopes (Oxygen-18 (δ¹⁸O), Deuterium (δ²H), Sulfur-34 (δ³⁴S_SO4)), and heavy metals/toxic elements concentrations. Both graphical and statistical tools were used to assess the presence and patterns of seawater intrusion, pollutant sources, and health hazards. According to the hydrochemical facies evolution diagram, stable isotopes and conservative ion mixing tendencies confirmed seawater mixing in 90% of tested samples. The study showed that heavy metals/toxic elements including Fe, Cr, Ni, V, As, and Co have exceeded regulation limits with 79% of groundwater samples tested being unfit for drinking purposes. In addition, nitrate was recorded surpassing the permissible limit in 38% of samples. The potential ecological risk index of the heavy metals/toxic elements varied from moderate to extremely high, with Ni, Cu, V, and As being the most hazardous metals. The results also show that 42% and 100% of tested groundwater showed potential non-carcinogenic and carcinogenic health risks, with total HQ and total CR exceeding the threshold values, respectively. The results show that seawater intrusion, heavy metal pollution, and nitrate contamination have detrimental effects on the island's groundwater quality. To mitigate the health and environmental hazards, groundwater use must be urgently managed alongside implementing suitable pollution control techniques. The study provides a robust scientific foundation for formulating policies that promote the sustainable use of Tarout Island's valuable groundwater resources. Similar anthropogenic pressures on coastal aquifers throughout the world necessitate the scientific understanding and integrated management approaches presented in this study to protect groundwater quality. It is recommended to establish a groundwater monitoring system that constantly monitors critical quality parameters to maintain an in-depth understanding of the complex nature of the vulnerable coastal aquifer.