**1. Introduction**

Soil is a great reservoir for contaminants as well as a natural buffer for transportation of chemical materials and elements in the environment. There has been an increasing concern in many countries of the world about the levels of potentially toxic elements (PTEs) in the soil environment [1–3]. There are over 40 chemical elements in the soil [4]; out of which, 21 elements are commonly considered as PTEs, which are zinc, Zn; vanadium, V; uranium, U; tungsten, W; tin, Sn; thallium, TI; silver, Ag; selenium, Se;

molybdenum, Mo; mercury, Hg; manganese, Mn; lead, Pb; gold, Au; copper, Cu; cobalt, Co; chromium, Cr; cadmium, Cd; barium, Ba; arsenic, As, and antimony, Sb [5]. Among these, Pb, Cr, As, Zn, Cd, Cu, Hg, and Ni are most commonly found at contaminated sites [6].

Petroleum hydrocarbons contain PTEs such as cobalt (Co), copper (Cu), lead (Pb), iron (Fe), magnesium (Mg), manganese (Mn), zinc (Zn), cadmium (Cd), chromium (Cr), nickel (Ni), arsenic (As), titanium (Ti), silver (Ag) among others. PTEs contamination in soil has attracted significant ecological concerns because of their toxic, bioaccumulative, and persistence nature in the existing environment. Unlike most pollutants (e.g. petroleum hydrocarbons), PTEs cannot be degraded and have long-lasting effects in soil as a result of strong adsorption of many metal ions on humic and clay colloids in soils [7]. PTEs have been reported to have physiological effects on living organisms as they are not degradable [8]. Vehicle emissions, metal plating/finishing operations, disposal of industrial waste, fertilizer applications, and fly ash from incineration/combustion processes, among others are also sources of PTEs in soils [9]. It is pertinent to also mention that mining, smelting, chemical production, and factory emissions release large quantities of Cd and Pb into soils, causing significant soil pollution [10, 11].

In Nigeria, the Niger Delta region is the heart of the oil and gas Industry (OGI) and has contributed enormously to the growth and development of the country. However, since the beginning of the establishment of the OGI in the region, several oil spill incidents have been reported; and, to date, it has been estimated that 13 million tons of hydrocarbons have been spilled in the region due to pipeline fatigue, well blowout, pipeline vandalism, and sabotage [12, 13]. Additionally, Ite et al. [14] reported that the number of contaminated sites in the Niger Delta region is in excess of 2000. Furthermore, the United Nation Environment Programme (UNEP) reported in 2011 that in Ogoniland alone (a small part of the Niger Delta), over 69 sites were heavily contaminated with crude oil (concentration exceeding 139,000 mg/kg) affecting soil, air, and water quality criteria and posing a serious human health threat. This, in turn, impacts the quality of water resources, directly affecting the health of local communities, which are drinking contaminated water [15–17]. Therefore, there is urgent research need to assess and quantify PTEs in polluted soils using simple, rapid, inexpensive, and accurate analytical methods to help appraise the environmental risk of PTEs to ensure food security, environment safety, and public health safety in the Niger Delta region of Nigeria, and anywhere in the globe faced with such challenges.

Numerous analytical techniques are in use for PTEs detection and quantitative measurement in soils, including atomic absorption spectrophotometry (AAS), inductively coupled plasma-mass spectroscopy (ICP-MS), inductively coupled plasma atomic emission spectroscopy (ICP-AES), atomic fluorescence spectrophotometry (AFS), X-ray fluorescence (XRF) spectroscopy, and laser-induced breakdown (LIB) spectroscopy. Also included are optical techniques [18], electrochemical [19, 20], and voltammetry [21].

It is pertinent to mention that generally laboratory methods (in this case, laboratory methods are referred to the "chemical methods") are known for quantitative measurement with good detection limits and have been commonly used for the detection of various PTEs in soils, with high sensitivity, selectivity, and accuracy [18, 21]. However, chemical methods require comparatively costly instrumentation, relatively lengthy measurement protocols, and specialized operators needed to achieve the correct measurements [21]. Given the relative disadvantage and cost of the laboratory methods mentioned above, there is a need to assess and use analytical devices that can offer rapid, inexpensive measurements, and requires little or no sample preparation. It is worth mentioning that to date, there is no published work yet comparing the measurement

*Perspective Chapter: Rapid Measurement of Potentially Toxic Elements (PTEs) in Petroleum... DOI: http://dx.doi.org/10.5772/intechopen.108959*

accuracy between the candidate chemical methods including AAS, ICP-MS, ICP-AES, etc., and analytical techniques that do not involve wet chemistry methods on measurement accuracy of PTEs in soil and in sediment samples. In the absence of such a crucial study that is key for method selection for environmental analyses, and knowing that the first step toward decision making on the selection of the best analytical techniques for the measurement of contaminants in environmental sample(s) is driven by time, cost, and the measurement accuracy [22]; methods that can offer timely and cost-effective analysis of environmental contaminants can be applied. As a result, this study aims at using a portable X-ray fluorescence (PXRF) spectroscopy as a cost-effective and rapid measurement tool (RMT) for PTEs in petroleum hydrocarbon-contaminated soils collected from crude oil spill sites in the Niger Delta region of Nigeria.

### **2. Materials and methods**

### **2.1 Study area and soil sampling**

The study area located in Bayelsa and Rivers State, Niger Delta, Southern Nigeria has a tropical rain forest climate characterized by two seasons: The rainy season lasts for about 7 months between April and October with an overriding dry period in August (known as August break); and the dry season lasts for about 5 months, between November and March. The temperature varies between 25 and 35°C. The regional geology of the Niger Delta is relatively simple, consisting of Benin, Agbada (the kitchen of kerogen), and Akata formations, overlain by various types of quaternary deposits [23, 24]. Soils of the area studied were classified according to the United State Department of Agriculture (USDA) [25] soil taxonomy into two orders, that is, inceptisols and entisols, which include four subgroups of typic dystrudepts, aeric endoaquepts, typic udipsammerts, and typic psammaqnents [26]. A total of 45 representative spot sample points were collected from three oil-contaminated sites (Site 1 = Ikarama: 15 samples; Site 2 = Kalabar: 15 samples; and Site 3 = Joinkrama: 15 samples) in August 2015. The three sites were selected for sampling due to their similar exploration activities and oil spill history. The soil samples (approx. 5 kg) were collected from visible "hot-spots" in the top 15 cm soil layer using a shovel. **Figure 1** shows the sampling location map. Soil samples were kept in airtight centrifuge tubes and stored at 4°C using ice block to avoid hydrocarbon volatilization and preserve field-moist status until transported to Cranfield University in the United Kingdom. The samples were then stored in a freezer at **–**20°C prior to PTEs analysis by XRF spectroscopy.

### **2.2 Sample preparation and XRF analysis of PTEs in soils**

The concentrations of PTEs: Cr, Cu, Fe, Pb, Mn, and Zn in petroleum hydrocarboncontaminated soils were determined using a portable Olympus Delta Premium 6000 Series XRF Analyser (Olympus, USA). In diffuse reflectance mode, the Delta XRF analyzer is three beams configured, where each beam was programmed to scan soil samples for 30 seconds. Prior to soil scanning, the instrument's setting and operational conditions were done in accordance with the manufacturer's specifications, and the analyzer was calibrated with alloy 316 stainless steel coupon. Fresh soil samples were thoroughly mixed and scanned using single open-ended and snap-post venting (30.7 mm O.D x 23.1 mm High) sample cups, sealed by Prolene Thin-Film (Diam. 63.5 mm) (Chemplex, USA). Each soil sample was analyzed for Cr, Cu, Fe, Pb, Mn, and Zn concentrations.

**Figure 1.**

*Soil sampling locations for the three petroleum hydrocarbon-released sites in the Niger Delta region of Nigeria. Source: [27].*
