Total Petroleum Hydrocarbons (TPHs) are a broad term that includes all the chemical compounds found in crude oil. Total petroleum hydrocarbon refers to a large group of chemical compounds that originated in crude oil [1]. They are referred to as hydrocarbons since they are virtually entirely made up of hydrogen and carbon. They are found in the range of C8 through C40 as mixture containing hundreds to thousands of hydrocarbons comprising of aliphatic which are straight carbon chain and aromatic (carbon ring) compounds and may also contain priority pollutants including volatile organic compounds (VOCs), semi-volatile compounds [2]. Their existence in soil and water has led to serious concerns about their influence on plant and human [3]. The total concentration of all hydrocarbons eluting from n-nonane (C9) to n-hexatriacontane (C36), as well as the sum of aliphatic and aromatic hydrocarbons, particularly those belonging to the following group; C9 to C18 (aliphatic), C19 to C36 (aliphatic), and C11 to C22 (aromatic) can be used to determine Total Petroleum Hydrocarbons. Generally, Total Petroleum Hydrocarbon (TPHs) may not constitute an immediate adverse health implications and concern to human or have adverse climatic implication on the environment [4], however their presence demonstrates the adverse negative ecological state of the water body and can be utilized as a pointer with respect to contamination in sediments and waters [5-7]. TPHs have been linked to the occurrence of psoriasis and dandruff in children and are known to cause uterine, stomach, and oral cancers as well as neurological disorders. Haematological, immunological, neurological, gastrointestinal, and even potentially fatal conditions are brought on by aromatic petroleum hydrocarbons such as benzene, toluene. In human health risk evaluation, the hazard index and overall cancer risk were found to be a source of concern. This implies that children will eventually experience a range of health issues, including cancer [8]. Rapid industrialization [9] and the improper disposal of petroleum hydrocarbon wastes in the environment creates a modification in the chemical and physical properties of the surrounding soils and causes underground pollution when these contaminants leached into the underground water aquifers [10]. At the point when TPH is discharged into the environment deliberately or by accidental spillage, industrial waste and wastewater release and from domestic activities into the soil through spills or leakages [11], it leaches from the soil into underground water and a few organisms in the soil might separate a portion of the pollutants into more modest divisions while some might vanish into the environment, others will remain in the soil for a longer period which might have hazardous health implications [9]. TPH released into the environment will, according to the United State Environmental Protection Agency (USEPA), pose a threat to public health and safety by contaminating drinking water, posing a risk of fire and explosion, reducing the quality of the air and water, harming agriculture, destroying recreational areas, destroying habitats and food, and wasting non-renewable resources. Recovery from a petroleum hydrocarbon (TPH) contamination of the soil can take several years. Oil hydrocarbons polluted soil is a worry for various reasons. As a matter of some importance, once delivered into the dirt, the unpredictability of TPHs can represent a fire or even explosive risks, particularly when fume enter confined spaces. Impurities can disrupt supplement and water transmission resulting in degradation of the environment. Residues of TPHs might remain bound to soil particles and stay in the soil for a really long time. Even though contaminants may benefit from carbon source as a degrader, the majority of soil biota still find them toxic [5]. TPHs have the potential to ruin the aesthetic by creating an unpleasant taste, smell, or appearance in environmental media. Lastly, TPHs will pose a potential threat to the environment. TPH content in a sample can be used as a general indicator of petroleum contamination at a given location [5]. Petroleum hydrocarbons in organisms and exposed individuals often result in numerous health implications such as: disruption in the activities of various body organs, severe damage to the pancreas, kidney, liver, blood circulatory system, and ultimately death [12]. The aim of this research is to determine the concentration of total petroleum hydrocarbons in different groundwater samples in Orji auto repair workshops and also to assess the risk posed by consumption of such polluted water [18-20, 27].

The number of total petroleum hydrocarbons (TPHs) detected in the water samples are presented in Table 1 in the groundwater of Orji auto repair workshops in Owerri, Southeast Nigeria. Over the years, this vicinity has been involved in a number of automobile maintenance activities that are known to release toxic hydrocarbons into the environment which most likely might have contributed immensely to the presence of total petroleum hydrocarbon (TPH) concentration in the groundwater of this area a result of leaching and flooding after rainfall. Apart from these maintenance activities, related emissions from associated petroleum industries including automobiles, diesel generators, and domestic chores like cooking and burning could have caused an increase in the level of TPHs in underground water as well [25, 28].

From the result obtained as shown in Figure 4, it is obvious that groundwater in this current study area is heavily contaminated with Total petroleum hydrocarbons with C15 (Pentadecane) having concentration as high as 48.90ug/mL, C30 (Triacontane) 38.18 ug/mL and C9 (Nonane) 18.18 ug/mL which could be as a result of both anthropogenic and natural chemical processes, such as volatilization, photo-oxidation, and biodegradation, combine with air moisture before atmospheric rainfall deposition, which might have impacted significantly on the quality of groundwater [13, 29].

From the result obtained, groundwater in the current study area is heavily contaminated with Total petroleum hydrocarbons, concentration of TPHs in samples 4 and 5 are 10.118 ug/mL and 4.6236 ug/mL accounting for 6.14 % and 2.81 % respectively and are less compared to those obtained in samples 1, 2, and 3 which are 32.6354 ug/mL, 19.0591 ug/mL and 98.3664 ug/mL respectively, accounting for 19.8 %, 11.57 %, and 59.69 % an implication that sample 3 had the greatest concentration of TPHs as presented in Figure 5.

With respect to the carbon chain C15 and C30 are the most predominant with 29.6 7% and 23.17 % respectively, which indicates the presence of both low molecular weight and high molecular weight hydrocarbons while C8, C34 and C13 are the least with 0.88 %, 0.67 % and 0.08 % respectively as seen in Figure 6 and 7.

In this investigation, the water TPH level (168.33 g/L) was significantly lower than the values reported for the Niger Delta region. Groundwater from Ubeji in Warri, Nigeria [11] had 73,500 g/L of TPH, some groundwater samples from various villages in the Niger Delta were found to have significant levels of TPH (1352-12,110 g/L), Deepwater Horizon in the Gulf of Mexico [14], Malaysia's Dungun River Basin water [15], with reported TPH concentrations of 60,000–260,000 g/L and 12-41 g/L respectively and Israel's Levantine Basin, which was 19-88 g/L [16].

In this research the anthropogenic source determination and risk evaluation of total petroleum hydrocarbons (TPHs) in different groundwater samples as well as their risk assessment within Orji auto mechanic village, Imo State, Nigeria was conducted. The outcome of this research ascertained the presence of total petroleum hydrocarbon pollution indicating an inherent health risk in the consumption of these water without proper treatment. It could be inferred that the anthropogenic activities of artisan within this vicinity and seasonal contribution due to rainfall and leaching are responsible for the occurrence for the presence of Low molecular weight and high molecular weight TPHs contamination in the study area. Hence the likely sources of TPHs in this study are both pyrogenic and petrogenic. TPHs concentration levels determined, contamination factor as well as pollution load index, Average daily intake, degree of contamination and Heath quotient index all revealed that the groundwater sources are contaminated and unsafe for human consumption due to the contamination level and risks associated with their consumption. There is the need to set up inspection protocol for water contamination to help proffer a realistic strategy and remedial approach to avoid potential health issues in the future. This study also serves as an appeal to relevant government agencies and stakeholder on the need for provision of potable water as well as comprehensive remediation process within this vicinity.