Determination of heavy metals and volatile aromatic compounds in used engine oils and sludges


Assessment of contaminant releases during utilization of used oils is essential for the determination of environmental acceptability. These paper reports the results of the study examining a toxic metal leachability from used engine oil and sludge samples employing leaching test (TCLP). The leaching test indicated that lead in oil samples exceeded 5-ppm concentration level what qualified them as a toxic waste. The samples of contaminated sludge were found to contain high concentration of total lead, barium and chromium, but the leaching test showed concentration below regulatory limit. The total content of benzene, ethylbenzene, toluene, and xylenes (BETX), and naphthalene in used oil and sludge samples was also determined and was found not to be a significant factor to contamination.

1. Introduction

The term used oil was employed to describe engine oils, transmission oils, and industrial oils (hydraulic and cutting oils) after use. The 1.7 and 3.5 million tone of used oil is collected in the EU and US each year, respectively [1–3]. Parts of used oils are collected and ultimately aggregated in permitted treatment, storage and disposal facilities. The millions of tones of used oils are disposed of through dumping on the ground or in water, land filling, or non-energy-recovery [4].

Burning as a fuel, re-refining and distillation are the three major methods for recycling of used oils. Used oil, burned for energy recovery, is the subject to regulatory limit which is (in ppm) for arsenic (5), cadmium (2), chromium (10), lead (100), total halogens (4000); and the flash point, according to regulation, cannot be lower than 45 8C [5,6]. Highly contaminated used oil is commonly blended with other fuel oils before combustion. Combus-tion of a blended fuel is assumed not to affect the net release of emissions with time; from an environmental perspective, the net emissions remain the same regardless of dilution [1,7,8].

Evidence of leakage from more than a million of the underground storage tanks have been identified. The leakage-contaminated soil has been found with up to 100 ppm of gasoline and up to 200 ppm of diesel and lubricating oil. No guidelines for fuel leachability test (TCLP) have been established. It was estimated that maximum of 10 ppm should not be exceeded for fuels in soil [9]. Used oil containing more than 1000 ppm of total halogens is presumed to be a hazardous waste because it has been mixed with halogenated hazardous waste compounds [10]. When testing used oils as a part of waste disposal, minimum analysis should address metals, halogenated solvents, aromatics, and polychlorinated bi-phenols (PCBs). Many of analytical methods can be used to analyse organic compounds e.g., solid phase extraction (SPE), gas chromatography with flame ionization detection (GC-FID), gas chromatography with mass spectrometric detection (GC–MS), and UV- and IR-spectrometric analyses [4].

The leaching test evaluation is a possible option for the sludge and used oil samples contaminated by heavy metals. In Europe, the most used leaching procedure since 1984 has been DIN 38414-S4: ‘Sludge and sediments (group 5) determination of leachability by water’. Presently, the European Commission based on DIN norm developed a new procedure Norm prEN 12457: ‘Compliance test for leaching of granular waste materials’. This new standard established procedure uses the water eluant (W) to solid (S) in ratio (W/S) of 2–10. In leaching tests, pH is allowed to vary freely, being dictated solely by the waste matrix dissolution [11,12]. The EPA leaching test (TCLP) was performed at eluent/solid ratio of 20:1 in agitated closed vessel for 18 h [13].

The leaching test (TCLP) is expected to test contami-nated soils and sediments, sludges, metallurgical process residues, combustion residues, waste oils and fuels. Tested materials passing leaching test are deposited in landfills, yet not stable over the long term, can release toxic components into the groundwater. The waste is considered toxic when the leaching test shows that extracted hazardous metals exceeded regulatory limit which is (in ppm) for arsenic (5), barium (100), cadmium (1), chromium (5), lead (5), and silver (5) [13].

Used oil is recognized as a posing carcinogenic risk to a man. The main carcinogenic substances in used oil are polycyclic aromatic hydrocarbons (PAHs) with 3–7 rings, such as benzopyrene, benzantracene, and chrystene [14]. The compound, 3-nitrobenzotrone (nitro-PAH), discovered in the exhaust fumes of diesel engine may be the strongest carcinogen ever analyzed, has highest score in Ames test [15]. 3-Nitrobenzatrone is produced during reactions between ketone by-products of burning diesel fuel and air borne nitrogen oxides. The concentration of 3-nitrobenza-trone in diesel exhaust fumes was found to be 0.6 and 6.6 ppm for engine loads of 6 and 80%, respectively.

The objective of the research was to determine if contaminated engine oil and sludge samples exceed the regulatory limit of toxicity characteristic concentration. Also, total content of organic volatile contaminants (benzene, ethylbenzene, toluene and xylenes) (BETX) and naphthalene were determined.

2. Experimental

2.1. Chemical analysis

Oil and sludge samples were collected from auto-mechanic workshops, petroleum refinery, and gas stations. Samples were digested with nitric acid and peroxide; the hot block digestion procedure was used to analyze metals [16]. The toxicity characteristics leaching procedure (TCLP) is a leaching test used to determine content of heavy metals in contaminated material [13].

The Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES) was used for analysis of total metals and TCLP extract. The performance of instrument was evaluated by determining the method detection limit (MDL) for each metal and several (QC) parameters. Values of method reported limit (MRL), based on MDL results are shown in Table 1.

The Gas Chromatography–Mass Spectrometry (GC–MS) was used for analysis of benzene, toluene, ethylbenzene, xylene (BETX), and naphthalene in used oil/sludge samples. The method reporting limit (MRL) are 0.025 ppm for benzene, toluene ethylbenzene, m-xylene and 0.050 ppm for o- and p-xylene and naphthalene.

Table 1

Content of total metals (1) and leaching test (TCLP) metals (2) in used oil and sludge samples

Sample numberpHa inAsbCdbPbbAgbBabCrb
and descriptionH2O(ppm)(ppm)(ppm)(ppm)(ppm)ppm3B
G—used oil8.00.5!1!88170.5!
H—used oil8.70.5!10.2160300.5!24234.60.4
I—used oil8.10.5!1.40.3110340.4!
J—used oil8.31.3!1.30.3140400.8!23215.40.7

Quality control parameters: Standard reference material: SRM (95–104% recovery), Continuing check standard, CSTD (94–104%), Lab spike blank, LSB (96– 103%), Lab spike blank duplicate, LSBD (95–104%), Lab spike matrix, LSM (94–107%), Lab spike matrix duplicate, LSMD (95–106%).

a pH (5 g of sample C96.5 ml D.I. water), if pH is !5.0, use extraction fluid no. 1 and go to extraction. If pH is O5.0, than 3.5 ml 1 N HCl was added to determine extraction fluid, if pH is !5.0, use extraction fluid no. 1, if pH is O 5.0 use extraction fluid no. 2. Extraction fluid no.1 (11.4 ml HOAcC128.6 ml 1 M NaOH for 2 L) pHZ4.93G0.05 to each sample pH dropped below 5 pH, and extraction fluid no. 1 was used for extraction.

b Value is less (!) than method reported limit (MRL). The results of MRL values are (ppm): arsenic 0.5, cadmium 0.05, barium 0.04, chromium 0.06, lead 0.30, selenium 0.5, silver 0.04, and mercury 0.2.
c Accuracy and precision of metals analysis: Accuracy was determined as a ratio of LSBfound and LSBtrue (96–104%), or LSMfound and LSMtrue (93% to 106%); the precision was determined by calculating the difference between the results found for the LSB and LSBD, and then dividing the difference by the average of the two results (3–9%).

The standards were prepared as specified in US EPA Method 8020B [17].

2.2. Quality assurance (QA)/quality control (QC)

The ICP-AES calibration standards were prepared from multi-element standard solution. Three standard and one blank samples were used for calibration. The standard samples were prepared in nitric acid/hydrochloric acid matrix, as specified in US EPA method 6010 [18]. To assure the accuracy and precision of a method, a series of QA/QC procedures were performed to validate the data from US EPA methods (see summary Tables 1 and 4). The samples were spiked before digestion (1 ppm for Ag, Ba, and 2 ppm for Cr, Cd, As, and Pb).

During the TCLP extraction, blank and duplicate samples, and standard reference materials (SRM) were processed along with the samples. Blank extraction samples were run in order to detect contamination introduced in the sample processing and analysis procedure. Additionally, sample duplicates were also extracted to assure reproducibility of the method. The reported concentration could not deviate more than 20% between the duplicates and reference materials. An extraction blank was processed and analyzed with each leached sample set of 10. In addition, laboratory spike blank (LSB) and laboratory spike blank duplicate (LSBD) were analyzed with each leached sample set of 10. The performance of instrument was evaluated by determining the method detection limit (MDL) for each analyte using EPA protocol [19]. Method reported limit (MRL) are given in Table 1.

2.3. Leaching test (TCLP)

The TCLP tests were performed as specified in the method 1311 [13]. The samples were tested as received and sampled with no preservation being added. A sample of at least 100 g had been tumbled for 18 h with fluid number 1; fluid no.1 is 0.1 N acetic acid, which has been adjusted with NaOH to pH of 4.93. The ratio of extracting fluid to sample was 20: 1. After tumbling, extracts were filtered using a 0.1 mm cellulose nitrate filter, acidified with nitric acid, digested, and analyzed for content of metals. The results are shown in Table 1.

3. Results and Discussion

3.1. Total metals and leaching test (TCLP) analysis

Ten sludge and used oil samples were analyzed for total metal content and metal content after using leaching TCLP test. The results are shown in Table 1.

Six samples of contaminated sludge were found to contain high concentration of total lead (av. 330 ppm), barium (av. 960 ppm) and chromium (av. 270 ppm), however, after leaching concentration of those metals did not exceed regulatory limit. Different results were obtained with used oil samples. Total concentration of heavy metals was much lower than in sludge. Total leached lead concentration was in range of 88–160 ppm and after leaching exceeded regulatory limit of 5 ppm. Leached barium concentration, in some oil samples, was in range of 11–23 ppm but below the regulatory limit of 100 ppm. Our spiked matrix recoveries, continuing check standard (CSTD), laboratory blank spikes (LSB, LSBD), and standard reference material (SRM) deviate only a few percent from the listed true values shown in Table 1.

Prediction of concentration of leached metals, based on total metal contents, is difficult because there are many variables that affect leaching behavior including matrix redox properties, reduction by metal not being hazardous e.g., iron, additives present, sorption processes, and contaminated oil samples could differ [20].

In Table 2 content of metals leached from contaminated oils using TCLP test was compared with the total metal values. Percent of leached lead (19–31%) and leached barium (86–96%) were very high in comparison with sludge or solid samples [21]. This is a very valuable information on contaminated engine oil, which is leaching much higher than any solid material with high concentration of metals.

The other authors reported the following results for total heavy metals in used engine oils for the last two decades, see Table 3 below.

Table 3 shows the distinct decrease in lead content for engine oil. The most significant finding, related to the content of metals, is that lead is present over regulatory interest (5 ppm) when using leaching test (TCLP) and is identified as a hazardous waste, therefore cannot be disposed of in landfill sites [5,6].

Table 2

Total and leached barium and lead content in used engine oil samples and their ratios

Sample number[T-Pb][TCLP-Pb]Ratio[T-Ba][TCLP-Ba]Ratio
and description(ppm)(ppm)[TCLP-Pb]/[T-Pb](ppm)(ppm)[TCLP-Ba]/[T-Ba]
(%) extracted(%) extracted
G—used oil881719.313.111.386.3
H—used oil1603018.8242395.8
I—used oil1103430.918.117.295
J—used oil1404028.6232191.3

Table 3

Concentration of metals in used mineral-based engine oil. Comparison of results with past studies.

LocationAs, ppmBa, ppmCd, ppmCr, ppmPb, ppmZn, ppm
Franklin Assoc. 1984 [22]nrnrnrnr2500Nr
EPA Composite, 1985 [23]102102112570980
Oregon State, 1986 [24]0.2nr1.23662357
ABB-Environm. 1990 [25]54836.6240480
Vermont State, 1996 [26]nra3 (7)b2(6.6)b3 (6.8)b49(146)b1150
California State, 1996 [27]nr18 (26)b1(2)b1.4 (2)b33(38)b822
Spain, 2000 [28]nrnr7341Nr
Portugal, 1996 [29]nrNr!2!101500Nr
Canada, 1995 [30]nrnr!210 (233)b29(265)b,cNr
Poland,1999 [2]nrnrnr1070001100
This work, 20040.7201.25125cNr
Leaching test (TCLP)!5!100!1!5!5Not reg.
requirements [10]

a nr, not reported.

b Max concentration.

c Leaching test (TCLP) is above the TCLP limit of 5 ppm.

Used oil is contaminated not only with heavy metals but also with polycyclic aromatic hydrocarbons that are insignificant in the unused oil. In our study total volatile organic compounds in used oil and sludge samples were analyzed by gas chromatography–mass spectrometry [17]. The volatile compounds selected as target analytes were benzene, toluene, ethylbenzene, and o-, m-, and p- (total)-xylenes, and naphthalene. Table 4 presents the results for ten oil/sludge-contaminated samples. The results indicated that analyzed samples were contaminated by volatile aromatics in low concentration, below 1 ppm for most analytes. They correspond to concentration of volatile hydrocarbons found, by the other research group, in diesel fuel [31].

Total aliphatic/aromatic hydrocarbons in used engine oil determined (in ppm) by the other researchers were as follows: dichlorodifluoromethane (20), trichlorotrifluor-oethane (160), (1,1,1)-trichloroethane (200), trichloroethy-lene (100), tetrachloroethylene (106), benzene (20), toluene (380), xylenes (530), benz(a)antracene (12), benzo(a)pyrene (10), naphthalene (330), and polychlorinated biphenyl or PCB (5) [25].

The high solubility in water of the BETX compounds originated from gasoline contaminated soil e.g., benzene (29.5 ppm), toluene (42.6 ppm), ethylbenzene (2.4 ppm), and o-, m-, p-xylenes (14 ppm), can lead to significant contamination of groundwater [4]. In the soil samples studied by the others, correlation between the organic matter and the leachable and volatile hydrocarbons was noted. Their results indicated that volatile hydrocarbon contami-nation seems to be primarily associated with the organic fraction of the soil [11].

Organic contaminants from underground tank fuel leaks, industrial oily hazardous waste release, and pesticide formulations are almost always released to the environment as solute mixture. The competitive sorption of 1,2-dichlorobenzene and other chemicals in soils is associated with voids in natural organic matter (NOM) structure, and (NOM) plays a central role in determining sorption characteristic. Our understanding of factors controlling the competitive interaction among hydrophobic organic com-pounds, in geo-sorbents having natural organic matter, is still limited [32].

4. Conclusions

The efficacy of cleanup methods in reducing oil contamination at spill sites is typically determined by

Table 4

Total volatile organic aromatic hydrocarbons (BETX) in the oil/sludge samples

Sample no.Aromatic compounds (ppm)
1—sludgeToluene (0.27), xylene (0.09)
2—sludgeEthylbenzene (0.03), toluene (0.15), xylene (0.62)
3—sludgeEthylbenzene (0.04), toluene (0.40), xylene (0.20)
4–sludgeEthylbenzene (0.20), toluene (2.00), xylene (0.90)
5—sludgeEthylbenzene (0.08), toluene (0.30), xylene (0.16)
6—sludgeEthylbenzene (0.05), toluene (0.07)
7—used oilEthylbenzene (0.08), toluene (0.40), xylene (0.62)
8—use oilEthylbenzene (0.15), toluene (0.70), xylene (1.20)
9—used oilEthylbenzene (0.15), toluene (0.42), xylene (0.72)
10—used oilEthylbenzene (0.11), toluene (0.51), xylene (0.67)

Quality control (QC) parameters. Reference standard material, SRM (85– 115% recovery), Continuing check standard, CSTD (80–120%), Lab spike blank, LSB (85–115%), Lab spike blank duplicate, LSBD (85–115%), Lab spike matrix, LSM (80–120%), Lab spike matrix duplicate LSMD (80– 120%). Accuracy and precision of BETX analysis: Accuracy was determined as a ratio of LSBfound and LSBtrue (85–115%), or LSMfound and LSMtrue (80–120%); the precision was determined by calculating the difference between the results found for the LSB and LSBD, and then dividing the difference by the average of the two results (85–115%). measuring concentration of benzene, toluene, ethylbenzene, xylenes (BETX), naphthalene and hazardous metals in used oil and sludge samples. Although, these values may provide a direct concentration of contaminants, they may not be indicative of what is transferred to groundwater. When sludge and used oil is released onto the soil or water, BETX compounds cause serious damage to the natural environ-ment. The lead concentrations observed are much lower than earlier studies due to the change of unleaded gasoline, but lead is still a problem.


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