Assessment of Polycyclic Aromatic Hydrocarbons in Fruits of Citrus sinensis (Porcher Michel H.) around Port Harcourt Metropolis Nigeria

Polycyclic aromatic hydrocarbons (PAHs) are chemical compounds containing only hydrogen and carbon in multiple aromatic rings. PAHs occurs naturally in coal, crude oil and gasoline, the simplest are the two aromatic rings and the three rings naphthalene, anthracene and phenanthrene (Abdel-shafy and Mansour, 2016). PAHs can originate from natural sources, such as forest fires and volcanic emissions, and also from anthropogenic sources such as coal burning, vehicular emissions, engine lubricating oils, and cigarette smoke (Kim, et al., 2013). Pyrolytic processes are the major sources of PAHs through anthropogenic activities such as combustion of natural gas, incomplete combustion of organic materials, processing of crude oil and coal, combustion of refuse, vehicle emissions, cooking and tobacco smoking (Abdel-shafy, and Mansour, 2016). PAHs generated from various sources accumulate in the environment and enters the food chain through affected water, air, and soil (Karishma, et al, 2018). PAHs from several pyrolytic sources gets into the environment through the air and could be inhaled directly by human (Superfund Research Program-SRP, 2013). PAHs in the air could be transformed, degraded, or deposited. Deposition could be on vegetation, animals, humans, aquatic environment and even soil (Lee and Vu, 2010). PAHs in soil are mostly from atmospheric deposition from pyrolytic sources and from petrogenic sources such as the release of petroleum or crude oil from natural oil seeps and spillage (Obayori and Salaam, 2010).

Polycyclic aromatic hydrocarbons are ubiquitous in nature and are of environmental concern (WHO, 2003). Several PAHs have been identified as potent human carcinogens and persists in the environment (Lee and Vu, 2010). Recent epidemiological studies with humans and animals have indicated that the increasing cancer prevalence can be partly attributed to PAHs exposure. Furthermore, other epidemiological studies have demonstrated that a large proportion of cancer cases may be ascribed to at least in part dietary factors, including dietary exposure to PAHs (Abid, et al, 2014). PAHs concentrations in urban soil are considered to be higher than PAHs in rural soils due to increased vehicular and industrial activities in the urban areas (EFCSG, 2010). However, most oil exploitation and exploration activities usually occur in the rural areas causing accidental or intentional spillage and could also increase PAHs in soil from petrogenic sources in addition to pyrolytic sources in the rural area. Simbi-Wellington and Ideriah, (2022) reported that sixteen individual PAHs were detected in mangrove soil around at oil exploration site in a rural community in Rivers State. Studies have revealed that the concentrations of PAHs in the wet season could be more than that in dry season (EFCSG, 2010). This could be attributed to the absence of sunlight to breakdown the PAHs through photodecomposition and the probable increase in burning to warm homes. However, observations have shown that more fire incidence or outbreak are likely to occur in the dry season than in the wet season and could likely increase the amount of heating emission and probably PAHs in the environment. Simbi-Wellington and Ideriah, (2022) reported, PAHs were significantly higher in leave samples collected in the wet season month of September and lowest in the dry season month of March.

PAH have been detected in various food such as fruits, leaves, vegetable oil, meat smoked fish, tea and coffee (Lee and Vu, 2010). Absorption of PAHs in fruit can occur through air or soil during the process of cultivation, and prior to consumption through the process of storage and transportation (Alice et al., 2017). PAHs in fruit are mainly due to deposition of airborne particulate on exposed surface, the waxy surface of fruit assimilate low molecular mass PAHs through surface absorption and particle bond. According to Alice et al (2017) trace level of PAHs such as fluoranthene, pyrene and phenanthrene have been detected in every raw fruit while high concentration of lighter PAHs such as naphthalene have been detected in some fruits. Low concentrations (0.001 – 0.5 µg kg-1 wet weight) of PAHs can be detected in raw fruits, however, research have revealed that concentrations exceeding 0.5 µg kg-1 and up to 5 µg kg-1 wet weight can be found in several fruits depending on factors such as air quality around the farm site, the crop itself and the specific PAH. Alice et al., (2017) reported that PAHs concentration in fruits is usually higher for crops grown near roadways or in urban regions than in rural areas. Low temperature combustion such as wood burning and tobacco smoking tend to generate low molecular weight PAHs while high temperature industrial processes typically generate PAHs with higher molecular weight (Rose et al., 2015).

Studies have revealed that PAHs can be detected in fruits and leafy vegetables particularly in industrialized cities. According to reports, volatilized PAHs in air is a major contributor of PAH in plants. Ideriah et al. (2012) reported a high correlation between pollutants in air and total hydrocarbons in leaves collected around selected farms in Port Harcourt. Several of the PAH compounds have been identified by WHO as carcinogenic and/or mutagenic and poses threat to human health. Port Harcourt being the capital and major city of Rivers State with rapid urbanization and an associated growth in industries and automobiles has been reported to have high levels of hydrocarbons in leaves (Ideriah, et al., 2011). This study aims at providing information on the levels of PAHs in fruits of Citrus sinensis grown around Port Harcourt metropolis in the dry and wet season months as PAHs in fruits can act as an indicator of human exposure through consumption.