Lubricants based on renewable resources--an environmentally compatible alternative to mineral oil products

The development of lubricants like, e.g. engine and hydraulic oils was traditionally based on mineral oil as a base fluid. This fact is related to the good technical properties and the reasonable price of mineral oils. The Report to the Club of Rome (W.W. Behrens III, D.H. Meadows, D.I. Meadows, J. Randers, The limits of growth, A Report to the Club of Rome, 1972) and the two oil crises of 1979 and 1983, however, elucidated that mineral oil is on principle a limited resource. In addition, environmental problems associated with the production and use of chemicals and the limited capacity of nature to tolerate pollution became obvious (G.H. Brundtland, et al., in: Hauff, Volker (Ed.), World Commission on Environment and Development (WCED), Report of the Brundtland-Commission, Oxford, UK, 1987), and the critical discussion included besides acid rain, smog, heavy metals, and pesticides also mineral oil (especially oil spills like the case Exxon Valdes). A disadvantage of mineral oil is its poor biodegradability and thus its potential for long-term pollution of the environment. From the early development of lubricants for special applications (e.g. turbojet engine oils) it was known, that fatty acid polyol esters have comparable or even better technical properties than mineral oil. Subsequently, innumerable synthetic esters have been synthesized by systematic variation of the fatty acid and the alcohol components. Whereas the alcohol moiety of the synthetic esters are usually of petrochemical origin, the fatty acids are almost exclusively based on renewable resources. The physico-chemical properties of oleochemical esters can cover the complete spectrum of technical requirements for the development of high-performance industrial oils and lubricants (e.g. excellent lubricating properties, good heat stability, high viscosity index, low volatility and superior shear stability). For a comprehensive review of their technical properties see F. Bongardt, in: Jahrbuchfür Praktiker, H. Ziolkowsky (Ed.), Verlag für chemische Industrie GmbH, 1996, pp. 348-361. This article will focus on the ecological properties of oleochemical (synthetic) esters. The environmental relevance of oleochemicals in comparison to petrochemicals is discussed, and then the principles of an ecological assessment are described. The ecotoxicological properties and the biodegradability of oleochemical esters are presented. Finally, the ecological properties of the oleochemical esters are discussed with regard to existing environmental classification and labeling systems.     

Primary biodegradability of mineral base oils in relation to their chemical and physical characteristics.

The primary biodegradability of 32 mineral base (i.e., unformulated) oils of paraffinic nature was evaluated using the CEC L-33-A-93 test. These oils were refinery products obtained by varying manufacturing processes. Biodegradation percentages ranged between 15% and 75%, i.e., below the commonly accepted standards for environmentally-compatible lubricants. Biodegradability values were compared to the overall chemical composition and main physical properties of base oils. Biodegradability decreased with increasing levels of aromatic and/or polar compounds in the tested oils. For most oils, the biodegradation percentage increased with the viscosity index, but was a decreasing function of the kinematic viscosity (KV), the pour point, the flash point (FP) and the refractive index (RI). Linear relationships between biodegradability and FP or RI values were observed. These results show that, beside chemical features such as the contents in polar and aromatic compounds, simple physical magnitudes such as KV and RI, commonly used to characterize lubricant properties, may be useful parameters for predicting the biodegradability of mineral base oils.     

脂肪酰基氨基酸对矿物润滑油生物降解性的影响研究

通过生物降解试验研究了N-月桂酰基谷氨酸、N-月桂酰基甘氨酸、N-月桂酰基丙氨酸和N-油酰基甘氨酸4种脂肪酰基氨基酸对HVI 350矿物润滑油生物降解性的影响,采用高倍电子显微镜分析了生物降解过程中微生物数量和形态变化。结果表明,在矿物润滑油中添加少量脂肪酰基氨基酸后,矿物润滑油的生物降解性能明显改善,且生物降解过程中微生物数量增多、形态发生变化,这可能是脂肪酰基氨基酸增加了微生物的营养,且具有表面活性,有利于细胞的吸收,从而促进了矿物润滑油生物降解。     

Fingerprinting of High Boiling Hydrocarbon Fuels,Asphalts and Lubricants

Fingerprinting of hydrocarbon products requires high resolution differentiation of individual hydrocarbon compounds in any mixture. This requires the applications of various measuring techniques. In this paper, we have chosen the heavy hydrocarbons in fuels, lubricants and paving material as examples to discuss the methods for chemical characterization and differentiation. In the category most frequently termed "semi-volatile hydrocarbons" with boiling points from about 500°F to 1200°F or higher, there are several families of hydrocarbons, both natural and refined that are not easily distinguished by conventional EPA tests. Among the groups which we will use as examples are asphalts, hydraulic fluid, transmission oil, motor lubricating oils, heating oils, crude oil and coal. These hydrocarbon families are best studied using combined gas chromatography-mass spectrometry in full scan mode and characterizing various homologous series of hydrocarbons at known fragment ions. The hydrocarbon series providing the best information are: (1) N -alkanes; (2) iso-alkanes; (3) steranes; (4) terpanes; (5) polynuclear aromatic hydrocarbons; (6) aromatic steranes; and (7) specific polycyclic compounds.     

Using Multiple Criteria for Fingerprinting Unknown Oil Samples Having Very Similar Chemical Composition

This paper describes a case study in which a multi-criterion approach was used to fingerprinting and identifying mystery oil samples. Three unknown oil samples were received from Quebec on March 28, 2001 for chemical analysis. The main purpose of this analysis was to detemine the nature and the type of the products, detailed hydrocarbon composition of the samples, and whether these samples came from the same source. The samples were analyzed by gas chromatography with a flame ionization detector (GC-FID) and by gas chromatography coupled with mass spectrometry (GC-MS). Hydrocarbon distribution patterns of unknown oils were recognized. Multiple suites of analytes were quantified and compared. A variety of diagnostic ratios of "source-specific marker" compounds for interpreting chemical data were further determined and analyzed. The chemical fingerprinting results reveal the following: (1) These three oils are most likely a hydraulic-fluid type oil. (2) These three oils are very "pure", largely composed of saturated hydrocarbons with the total aromatics being only 4-10% of the TPH. (3) The oils are a mixture of two different hydraulic fluids. There is no clear sign indicating they had been weathered. (4) The PAH concentrations are extremely low (<10 µg/g oil) in the oil samples, while the biomarker concentration are unusually high (4700-5500 µ/g oil). (5) Three major unknown compounds in the oil samples were positively identified. They are antioxidant compounds added to oils. (6) Samples 2996 and 2997 are identical and come from the same source. (7) The sample 2998 has group hydrocarbon compositions (including the GC traces, TPH, and total saturates) very similar to samples 2996 and 2997. But, it is not identical in chemical composition to samples 2996 and 2997, and they do not come from the same source.     

The effect of oils on PAH, PCDD, PCDF, and PCB emissions from a spark engine fueled with leaded gasoline

The effect of synthetic and mineral oils on the formation of polyaromatic hydrocarbons (PAHs), polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) in emissions from a spark ignition engine was studied on a Skoda Favorit engine fueled with leaded gasoline. The test cycle simulated urban traffic conditions on a chassis dynamometer, in accordance with the ECC 83.00 test. The data for selected PAHs as well as PCDDs, PCDFs, and PCBs congener profiles are presented. PCDD/Fs emissions for an unused oil and the oil after 10000-km operation varied from 300 to 2000 fmol/m3, PCBs emissions from 75 to 178 pmol/m3, and PAHs emissions from 150 to 420 microg/m3. The content of PCBs in oils varied from 2 to 920 mg/kg.     

Testing the ecotoxicology of vegetable versus mineral based lubricating oils: 1. Degradation rates using tropical marine microbes

Vegetable-derived lubricants (VDL) might be more biodegradable than mineral-derived lubricants (MDL) due to the absence of high molecular weight aromatics, but this remains largely untested in tropical conditions. In this laboratory study, the degradation rates of 2-stroke, 4-stroke and hydraulic VDLs were compared with their MDL counterparts in the presence of mangrove and coral reef microbial communities. While MDLs were comprised largely of unresolved saturated and some aromatic hydrocarbons, their VDL counterparts contained, potentially more degradable, fatty acid methyl esters. Degradation of some VDL was observed by day 7, with the 2-stroke VDL markedly consumed by mangrove microorganisms and the hydraulic VDL degraded by both microorganism communities after this short period. All of the VDL groups were significantly more degraded than the comparable MDLs mineral oil lubricants over 14 days in the presence of either mangrove or coral reef microbial communities. In general the mangrove-sourced microorganisms more efficiently degraded the lubricants than reef-sourced microorganisms.     

The biodegradability and microbial toxicity testing of lubricants--some recommendations

In recent years there has been a growing demand for information on the biodegradability (fate) and microbial toxicity (effects) of lubricants. This has been driven by the need to comply with environmental legislation and to meet the requirements of ecolabelling schemes, standards and customer specifications for 'environmentally acceptable' lubricants. This paper describes suitable approaches for generating this information under a variety of environmental conditions (e.g. aerobic, anaerobic, freshwater, marine), gives examples of the results obtained and discusses their interpretation. Recommendations on the use of each test are made.     

Fingerprinting of High Boiling Hydrocarbon Fuels,Asphalts and Lubricants

Fingerprinting of hydrocarbon products requires high resolution differentiation of individual hydrocarbon compounds in any mixture. This requires the applications of various measuring techniques. In this paper, we have chosen the heavy hydrocarbons in fuels, lubricants and paving material as examples to discuss the methods for chemical characterization and differentiation.In the category most frequently termed “semi-volatile hydrocarbons” with boiling points from about 500°F to 1200°F or higher, there are several families of hydrocarbons, both natural and refined that are not easily distinguished by conventional EPA tests. Among the groups which we will use as examples are asphalts, hydraulic fluid, transmission oil, motor lubricating oils, heating oils, crude oil and coal.These hydrocarbon families are best studied using combined gas chromatography-mass spectrometry in full scan mode and characterizing various homologous series of hydrocarbons at known fragment ions. The hydrocarbon series providing the best information are: (1)N -alkanes; (2) iso-alkanes; (3) steranes; (4) terpanes; (5) polynuclear aromatic hydrocarbons; (6) aromatic steranes; and (7) specific polycyclic compounds.     

Environmental assessment of ester-based lubricants after application

GOAL, SCOPE AND BACKGROUND: Lubricants based on renewable resources are an environmentally friendly alternative to petrochemical products due to their better ecotoxicological performance and their excellent biodegradability. To improve the technical performance of lubricants, and to reduce friction and wear, the use of additives is nowadays obligatory. The collaborative research center SFB 442 aims at developing environmentally acceptable lubricants that facilitate the avoidance of these additives by transferring their function to suitable coatings. For a complete assessment of the ecological performance of these newly developed lubricants, the whole life cycle including production, application as well as disposal and fate in the environment is studied. In the following study the focus was on the application and its influence on the environmental behavior of the lubricant. The application of lubricants leads, among other things, to the intake of metals due to abrasion from tools, work pieces or mechanical components. Previous examinations indicated a possible influence of metals on the toxicity of eluates prepared from used lubricants (Erlenkaemper et al. 2005). To clarify if the apparent toxicity of used lubricants solely results from the intake of metals, the extractability of these metals from the oil matrix is determined. By combining chemical analyses with bioassays, the bioavailability of metals that are present in the extract is estimated. To further investigate the relevance of metals on toxicity, toxic units (TU) were calculated and related to the results of the bioassays. Interactions between the metals were investigated with aqueous mixtures of metal chlorides and calculations based on the concept of concentration addition and independent action. METHODS: A lubricant mixture was applied to a tribological test bench that simulates real conditions of use and extremely short time load, respectively. Samples were taken at particular times, water soluble fractions (WSF) of these fluids were prepared and dilution series were investigated in several bioassays. Concentration of metals and total organic carbon (TOC) were determined in the eluates. TUs were calculated according to Sprague (1970) and mixture toxicity was calculated according to the concept of concentration addition (Loewe and Muischnek 1926) and independent action (Bliss 1939). RESULTS: Analyses of the metal content of the lubricant and the eluates clearly revealed the availability of the metals in the aqueous extracts. Especially copper, zinc, nickel and chromium were found and their concentrations increased during the time of use. The water extractable fraction, e.g., of copper, rose from 8.8% to 45.3% of the total content in the lubricant after 33.5 hours of use. Tests performed with the algal growth inhibition assay and the luminescence inhibition assay revealed the uptake or absorption by the organisms and, thus, the bioavailability of the metals. The calculation of TUs partly indicated a possible influence of the metals on ecotoxicity of the eluates. Copper reached concentrations equal to or higher than the EC50 value of copper chloride in the growth inhibition assays with algae and Ps. putida as well in the immobilization assay with daphnids. TUs for copper are also larger than 1 for the algal growth inhibition assay. The EL50 values indicated that the luminescence inhibition assay was the most sensitive test system, with values between 4.7% and 9.6%. While the toxicity towards algae and V. fischeri in the growth inhibition assay decreased until both organisms were no longer influenced by the exposure, the EL50 values for the D. magna immobilization assay and the Ps. putida growth inhibition assay decreased with the progressing use of the lubricant. The tested metal salt mixtures showed that Ps. putida, algae and daphnids are the most sensitive organisms with EC50 values below 1 mg/l. DISCUSSION: Although the intake of metals mainly occurred via abrasion of particles, the results revealed the availability of these metals in water. The availability varied for each of the four metals. For both the algal growth inhibition assay and the luminescence inhibition assay, an uptake or absorption of the metals could be demonstrated. The calculated TUs indicated an effect in some bioassays that was not verified in the test itself. The influence of copper on V. fischeri, for example, was not confirmed while the EL50 values for the daphnid bioassay decreased, meaning that the eluates became more toxic with progressing use of the lubricant. The calculations of mixture toxicity based on the concept of concentration addition demonstrated good correlations with the tested metal mixtures, but also a different sensitivity of the organisms. CONCLUSIONS: The results presented here reveal the availability of those metals in water that were taken in during the use of the lubricant in a tribological test bench and, thus, have the possibility of interacting with the organisms. The availability of the metals in the bioassays was proven by chemical analyses. The calculation of TUs and the corresponding EL50 values, however, indicate different availabilities of the metals. The results of the metal salt mixtures show good correlations with calculations of mixture toxicity based on concentration addition. Moreover, the varying sensitivity of the organisms when exposed to eluates or metal mixtures indicates a different bioavailability of the metals and/or the presence of other compounds that exert toxic action. RECOMMENDATIONS AND PERSPECTIVES: For further investigations, the organic oil matrix and its influence on the toxicity have to be taken into account. The toxicity of the eluates may not only be due to metals; additional effects could arise from changes in the lubricant itself.     

Investigations on the effect of chlorine in lubricating oil and the presence of a diesel oxidation catalyst on PCDD/F releases from an internal combustion engine

This paper reports on an intensive study into releases of polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated furans (PCDF) and polychlorinated biphenyls (PCB) from a diesel engine and the analysis of PCDD/F and PCB in crankcase lubricating oil. Experimental conditions were set and carefully controlled in order to maximize the possible impact of, and our ability to measure the effect of, changes in the levels of chlorine in the lubricant. Emissions to air were measured using modified EPA methods following the principles of the European EN 1948 standards. A series of 40 experimental runs were completed using three reference lubricants formulated to have three levels of chlorine present as a residual component (at levels of 12, 131 and 259 mg kg(-1) or ppm). The engine was run with and without the diesel oxidation catalyst. All lubricants were realistic oils and the use of unrealistic additives or doping of components - particularly chlorine - in the fuel and lubricant was carefully avoided. Analysis of fuel and lubricant (before and after testing) samples required strenuous attention to achieve acceptable recoveries and showed non-detectable levels of PCB and PCDD/F at a detection limit of around 1.5 ng I-TEQ kg(-1) (ppt), indistinguishable from the laboratory blank. The testing demonstrated the need for extreme care to be taken in developing measurement methods that are sufficiently sensitive for measuring chlorine content of fluids and PCDD/F in oils, the latter being particularly challenging. Mean emissions of PCDD/F with the diesel oxidation catalyst in place were 23 pg I-TEQ l(-1) of fuel and with the diesel oxidation catalyst removed 97 pg I-TEQ l(-1) of fuel. The results of this testing showed that the emissions of PCDD/F were greatly reduced by the presence of a diesel oxidation catalyst in the exhaust, a finding that has not been explicitly tested in previous work. They also show that emissions from the engine were not controlled by the level of chlorine in the lubricant and that emissions did not change in response to a much greater step change in the total chlorine entering the combustion chamber due to a change in the level of chlorine in the fuel. Emissions when the engine was configured with a diesel oxidation catalyst showed a consistent pattern that appears to be unique in the experience of the authors.     

A correlation between the biodegradability of oil products in the CEC L-33-T-82 and modified Sturm tests

Using a data set for 39 base oils, formulated oil products and pure compounds it was demonstrated that there was a good positive relationship between biodegradation in CEC L-33-T-82 and mineralisation to CO₂ in the modified Sturm test. A mathematical model was developed which described this correlation for most of the materials tested. One outlier from the model was di-iso tridecyl adipate (DITA), the well-degradable calibration oil for the CEC test. The measured mineralisation of DITA was much lower than that predicted by the model based on the compound's high biodegradability in the CEC test. A possible reason for this is given and the implications of this result discussed.     

Ionic liquids as lubricants or lubrication additives: An ecotoxicity and biodegradability assessment

This paper reports on the (eco)toxicity and biodegradability of ionic liquids considered for application as lubricants or lubrication additives. Ammonium- and pyrrolidinium-based cations combined with methylsulphate, methylsulphonate and/or (CF₃SO₂)₂N⁻ anions were investigated in tests to determine their aquatic toxicity using water fleas Daphnia magna, green algae Selenastrum capricornutum and marine bacteria (Vibrio fischeri). Additional test systems with an isolated enzyme (acetylcholinesterase) and isolated leukaemia cells from rats (IPC-81) were used to assess the biological activity of the ionic liquids. These compounds generally exhibit low acute toxicity and biological activity. Their biodegradability was screened according to OECD test procedures 301 B and 301 F. For choline and methoxy-choline ionic liquids ready biodegradability was observed within 5 or 10 d, respectively. Some of the compounds selected have a considerable potential to contribute to the development of more sustainable products and processes.     

Experimental investigation of tribological characteristics and emissions with nonedible sunflower oil as a biolubricant

Plant (vegetable) oil has been evaluated as a substitute for mineral oil–based lubricants because of its natural and environmentally friendly characteristics. Availability of vegetable oil makes it a renewable source of bio-oils. Additionally, vegetable oil–based lubricants have shown potential for reducing hydrocarbon and carbon dioxide (CO₂) emissions when utilized in internal combustion (IC) engines and industrial operations. In this study, sunflower oil was investigated to study its lubricant characteristics under different loads using the four-ball tribometer and the exhaust emissions were tested using a four-stroke, single-cylinder diesel engine. All experimental works conformed to American Society for Testing and Materials standard (ASTM D4172-B). Under low loads, sunflower oil showed adequate tribological characteristics (antifriction and antiwear) compared with petroleum oil samples. The results also demonstrated that the sunflower oil–based lubricant was more effective in reducing the emission levels of carbon monoxide (CO), CO₂, and hydrocarbons under different test conditions. Therefore, sunflower oil has the potential to be used as lubricant of mating components.

Implications: An experimental investigation of the characteristics of nonedible sunflower oil tribological behaviors and potential as a renewable source for biofluids alternative to the petroleum oils was carried out. The level of emissions of a four–stroke, single-cylinder diesel engine using sunflower oil as a biolubricant was evaluated.     

Using Multiple Criteria for Fingerprinting Unknown Oil Samples Having Very Similar Chemical Composition

This paper describes a case study in which a multi-criterion approach was used to fingerprinting and identifying mystery oil samples. Three unknown oil samples were received from Quebec on March 28, 2001 for chemical analysis. The main purpose of this analysis was to determine the nature and the type of the products, detailed hydrocarbon composition of the samples, and whether these samples came from the same source. The samples were analyzed by gas chromatography with a flame ionization detector (GC-FID) and by gas chromatography coupled with mass spectrometry (GC-MS). Hydrocarbon distribution patterns of unknown oils were recognized. Multiple suites of analytes were quantified and compared. A variety of diagnostic ratios of “source-specific marker” compounds for interpreting chemical data were further determined and analyzed. The chemical fingerprinting results reveal the following: (1) These three oils are most likely a hydraulic-fluid type oil. (2) These three oils are very “pure”, largely composed of saturated hydrocarbons with the total aromatics being only 4–10% of the TPH. (3) The oils are a mixture of two different hydraulic fluids. There is no clear sign indicating they had been weathered. (4) The PAH concentrations are extremely low (<10 μg/g oil) in the oil samples, while the biomarker concentration are unusually high (4700–5500 μg/g oil). (5) Three major unknown compounds in the oil samples were positively identified. They are antioxidant compounds added to oils. (6) Samples 2996 and 2997 are identical and come from the same source. (7) The sample 2998 has group hydrocarbon compositions (including the GC traces, TPH, and total saturates) very similar to samples 2996 and 2997. But, it is not identical in chemical composition to samples 2996 and 2997, and they do not come from the same source.     

Fuel Oil Additives for Controlling Air Contaminant Emissions

An addition of additives to fuel oils prior to combustion is one way of reducing combustible contaminant emissions to the outer air. Reported test results show that some additives improve, moderately, the combustive properties of fuel oils. Combustion is also improved but to a lesser degree, in boiler systems that are deficient in operation and design. Being combustible, polynuclear hydrocarbons emissions would be reduced by use of additives. Other types of additives to reduce slagging and inhibit corrosion from combustion of fuel oils are also available. The cost of using additives is low. Improved additives are required, especially ones to better combustion in the deficient boiler systems. These can be found by research and literature surveys. Their effectiveness and nontoxicity would be confirmed by laboratory and field testing.     

Ex situ remediation of contaminated sediments using mineral additives: assessment of pollutant bioavailability with the Microtox solid phase test

The aim of this work is to assess the potential ecotoxicological effects of contaminated sediments treated with mineral additives. The Microtox solid phase test was used to evaluate the effect of mineral additives on the toxicity of sediment suspensions. Four Mediterranean port sediments were studied after dredging and bioremediation: Sample A from navy harbor, sample B from commercial port and samples C and D from pleasure ports. Sediment samples were stabilized with three mineral additives: hematite, zero-valent iron and zeolite. Results show that all studied mineral additives can act as stabilizer agent in highly contaminated sediments (A and C) by decreasing dissolved metal concentrations and sediment toxicity level. On the contrary, for the less contaminated samples (B and D) hematite and zeolite can provoke toxic effect towards Vibrio fischeri since additive particles can favor bacteria retention and decrease bioluminescence emission.     

An 'inherent' biodegradability test for oil products: description and results of an international ring test. CONCAWE Biodegradation Task Force.

Current test guidelines for assessing 'inherent' (potential) biodegradability were designed for water-soluble, organic compounds of low volatility and are unsuitable for most oil products. It was against this background, that CONCAWE (the oil companies' European organisation for environment, health and safety) formed a task force to develop a standard test protocol for assessing the 'inherent' biodegradability of oil products.     

Metal concentrations in used engine oils: Relevance to site assessments of soils

Used engine oils contain metals, which upon entering soils may pose risks to human health or the environment. In this study, previously published concentrations of 23 metals in 213 used engine oil samples from the early 1970s to the mid-1990s are statistically evaluated. Neat (100%) used engine oils were found to contain relatively high concentrations of lead, calcium, and zinc, attributable to piston blow-by of leaded gasoline, calcium salt detergent additives, and zinc-bearing anti-corrosion/anti-oxidation additives, respectively. Wear metal concentrations were lower. The lead concentration in used engine oils in the U.S. declined between the 1970s and early 1990s, potentially providing a basis to constrain the “age” of used engine oil(s) in soils. The concentrations of 23 metals in used engine oils were compared to soil risk benchmarks in 15 representative jurisdictions in the U.S., Canada, Australia, and Europe. The maximum concentrations in neat (100%) used engine oil of eight metals – Be, Co, Fe, Mn, Ni, Se, Ag, and Ti – were lower than their collective minimum benchmarks in soils for the jurisdictions surveyed, indicating their concentrations in soils could not be reasonably expected to exceed any soil benchmarks. Nine metals (As, Ba, Cd, Cr, Cu, Pb, Sn, V and Zn), but particularly arsenic, cadmium, lead, tin, and zinc, were identified as potential contaminants of concern (PCOC) for soils from locations impacted with used engine oils, owing to their higher median concentrations (i.e., 2.5, 1.4, 1038, 5.0, and 922 mg/kg in oil, respectively) relative to most soil benchmarks. Site-specific benchmarks and metal concentrations at reasonable oil in soil concentrations require consideration when developing the suite of PCOC metal analytes for conducting site assessments of soils impacted by used engine oil.