RemScan: A tool for monitoring the bioremediation of Total Petroleum Hydrocarbons in contaminated soil

Graphical abstract


Method background
This study aimed to validate the RemScan to be used as an accurate, cost-effective and prompt tool for monitoring the bioremediation of TPH-contaminated soil. To the best of the authors' knowledge, the performance of RemScan in determining TPH concentration during a bioremediation process compared with traditional laboratory analysis has never been reported. The significance of this study is therefore that it represents the first to validate the use of the RemScan to evaluate the efficacy of the bioremediation of a TPH contaminated soil. In this study, a variety of bioremediation treatments were set up and soil samples were collected at different times over 150 days for quantitative analysis of TPH concentrations by an accredited laboratory using conventional GC/MS. In addition, we used the RemScan device to determine the concentration of TPH over a broad concentration range (100 -100,000 mg kg À1 ).

Method details
1 Sample preparation 2 Test soil samples were prepared as shown below: 3 Soil samples (n = 84) were collected from different bioremediation treatments. 4 Contaminated soil samples (n = 16) were collected from hydrocarbon-contaminated sites in Australia. 5 Soil samples (n = 5) were spiked in the lab with a relatively high concentration of diesel (%100,000 mg kg À1 ) 6 Soil samples were collected from all treatments using a Simple Random Sampling technique [7], so the sample represents the entire treatment. 7 About 60 g of each soil sample was air-dried for 24 h at room temperature. 8 Large clumps of the dried soil were ground using a pestle and mortar, sieved using a 2 mm sieve and then mixed thoroughly until fully homogenized. 9 RemScan set up 10 The RemScan was installed on the Lab station and locked with the strap provided ( Fig. 1.A). The Lab station is a steel scaffold structure that can hold the RemScan device on the top and has a sample lift located in the middle. The scaffold is connected to an air pump in order to move the sample left up and down using the Raise-Lower lever. The use of the Lab station helps to minimise human errors associated with instability of the operators' hands. 11 The device was connected to the Personal Digital Assistant (PDA) (Fig. 1.B) by pressing the "START" button on the PDA device. 12 After waiting around 15 min for the RemScan to warm up, the time and date were corrected on the PDA device using the digital pen provided. 13 The "Background cap" was placed on the nose-corn and scanned for about 1 min as instructed on the PDA. Similarly, the "Reference cap" was scanned and then the device was ready to scan the soil samples. 14 Scanning the soil samples 15 30 -50 g of the already prepared soil sample was placed in the "Sample Cup" provided, mixed thoroughly using a spatula and then tamped using the "Sample tamper" provided until a completely flat surface was obtained. 16 The sample-containing cup was placed on the sample lift of the Lab station and raised into position using the Raise-Lower lever. 17 The trigger on the RemScan device was pressed and the TPH concentration displayed on the PDA after 15-20 s. 18 Each soil sample was scanned five times with thorough mixing between the scans and the TPH concentration was recorded after each scan. The average of the five scans was recorded as the final TPH concentration in (mg kg À1 ) of dry soil.

Method validation
The scanned soil samples were sent to Australian Laboratory Services Pty Ltd. (ALS), an accredited external laboratory. ALS uses the UPEPA 5030 and 8260 methods for measuring TPH in soils. TPH concentration was quantified against alkane standards C 10 -C 40 .
To determine the accuracy, the RemScan TPH values were scatter-plotted against the concentrations obtained from ALS, using Prism -Graphpad 7 software. The correlation coefficient (R 2 ) showed that these two methods were 0.998 correlated in measuring the TPH concentration for the test soil samples (Fig. 2). Furthermore, a similar correlation was acquired using the Pearson correlation coefficient between the two groups of data. A comparison of the TPH concentration values measured using both methods for a subset of the test samples (n = 20) is shown in Table 1. Statistical analysis confirmed that no significant differences between the variances (Ftest, α 0.05) were observed.
The total cost of TPH analysis for the test samples by the external laboratory was around AU$ 40 per sample. In contrast, the cost associated with measuring TPH concentration using RemScan was AU$ 5 per sample. Furthermore, the time required by the external laboratory for the TPH analysis results to be reported was about 5 working days for a dozen samples. The same number of samples needed only 2 h for the TPH concentrations to be measured (10 min/sample).

Additional information
Petroleum hydrocarbons have become one of the most worldwide-spread contaminants as a result of global use, transportation and storage of oil [1]. Total Petroleum Hydrocarbons (TPH) are the major component of crude oil. TPH comprise a mixture of chemicals composed largely of carbon and hydrogen and consist of a major group of short and long-chain aliphatic hydrocarbons and a minor group of aromatic compounds. Exposure to TPH may cause permanent damage to the central nervous system; in addition, many compounds associated with petrogenic contamination are carcinogenic [2].
Bioremediation represents a simple, environmentally safe and cost-effective technique to remediate hydrocarbon-contaminated soil [3]. The bioremediation treatment, however, can represent a relatively long process (months to years) and requires regular monitoring of the TPH concentration to evaluate the efficacy of the treatment. Traditional laboratory techniques, such as Gas Chromatography/Mass Spectrometry (GC/MS) and Gas Chromatography/Flame Ionization Detector (GC/FID) are commonly used methods for measuring TPH concentration. However, these techniques are labour-intensive, expensive and time-consuming [4]. In addition, many of the solvents used for hydrocarbon extraction may pose both environmental and human risks [5]. Recently, a quantitative analysis of TPH in contaminated soils was performed using RemScan TM , a new portable device marketed by Ziltek Pty Ltd. [6]. RemScan uses a diffuse reflectance (mid)-infrared Fourier transform (DRIFT) spectrometer and has the advantages of speed and low cost and yet represents an accurate way of estimating TPH concentration.