Prospects of emerging PAH sources and remediation technologies: insights from Africa

Remediation of polluted environmental media is critical to realization of the goals of the United Nations Decade on Ecosystem Restoration (UNDER) project. Many natural-resource dependent economies in Africa are characterized by numerous contaminated sites resulting from conventional and artisanal natural-resource mining. Alongside these extractive activities, there are refining, processing, and power plant operations, agriculture, urban, and infrastructure developments that contribute to increased discharges of toxins into the environment, particularly polycyclic aromatic hydrocarbons (PAHs), which are carcinogenic in nature. As a result, human and environmental receptors (i.e., air, water, soil, and biota) face increasing risk of exposure to higher concentrations of PAH. Evidence exists of widespread PAH contamination and in some instances where corrective action has been taken, residual contaminant levels exceeding regulatory thresholds remain in the environment due to the use of inappropriate and unsustainable remedial methods. Considering the long-term harmful effects of PAH on human and ecosystem health, land use, and the complexity of Africa's environmental deterioration, it is essential to explore remediation strategies that benefit both the environment and the economy. This review examined the status, opportunities, and challenges related to the application of emerging green technologies to remediate PAH-contaminated sites in five African countries (South Africa, Nigeria, Angola, Egypt, and Kenya). This paper concludes that bioremediation presents a sustainable option, considering its low net emissions and environmental footprints, and its low economic cost to Africa's poor communities and overburdened economy. However, an integration of biological and physico-chemical approaches could address various compounds and concentrations of PAH contamination.

Environmental impacts of the Chennai oil spill accident - A case study

Chennai, a coastal city in India with a population of over 7 million people, was impacted by a major oil spill on January 28th 2017. The spill occurred when two cargo ships collided about two miles away from the Chennai shoreline. The accident released about 75 metric tons of heavy fuel oil into the Bay of Bengal. This case study provides field observations and laboratory characterization data for this oil spill accident. Our field observations show that the seawalls and groins, which were installed along the Chennai shoreline to manage coastal erosion problems, played a significant role in controlling the oil deposition patterns. A large amount of oil was trapped within the relatively stagnant zone near the seawall-groin intersection region. The initial cleanup efforts used manual methods to skim the trapped oil and these efforts indeed helped recover large amount of oil. Our laboratory data show that the Chennai oil spill residues have unique fingerprints of hopanes and steranes which can be used to track the spill. Our weathering experiments show that volatilization processes should have played a significant role in degrading the oil during initial hours. The characterization data show that the source oil contained about 503,000 mg/kg of total petroleum hydrocarbons (TPH) and 17,586 mg/kg of total polycyclic aromatic hydrocarbons (PAHs). The field samples collected 6 and 62 days after the spill contained about 71,000 and 28,000 mg/kg of TPH and 4854 and 4016 mg/kg of total PAHs, respectively. The field samples had a relatively large percentage of heavy PAHs, and most of these PAHs are highly toxic compounds that are difficult to weather and their long-term effects on coastal ecosystems are largely unknown. Therefore, more detailed studies are needed to monitor and track the long term environmental impacts of the Chennai oil spill residues on the Bay of Bengal coastal ecosystem.

Distribution of PAHs in different compartment of creek ecosystem: Ecotoxicological concern and human health risk

We report levels of polycyclic aromatic hydrocarbons in sediment, seawater, fish and crab samples from Thane creek, India. Concentrations of sixteen USEPA PAH in sediments varies from 874 to 1925ngg^-1, dry weight (dw) in winter, between 219-495ngg^-1 in summer. In seawater Σ₁₆ PAHs concentration during winter was recorded 706±193ngL^-1, and during summer 337±79ngL^-1. Total concentrations of PAHs in consumable portion of lizard fish, bombay duck and crab were found 156.8±18 and 122±24.5ngg^-1, 117.4±17.65ngg^-1 and 95.8±16.2ngg^-1, 348±94.5 and 95.62±31.9ngg^-1 wet weight (ww) in summer and winter respectively. PAHs concentration were compared with sediments quality guidelines viz. ERL-ERM, TEL-PEL indexes for finding ecotoxicological risk on marine organism. The ILCR values were above public screening criteria for carcinogens.