Spilled mineral oils in the marine environment pose a number of challenges to sampling and analysis. Mineral oils are complex assemblages of hydrocarbons and additives, the composition of which can vary considerably depending on the source oil and product specifications. Further, the marine microbial and chemical environment can be harsh and variable over short times and distances, producing a rigorous source of hydrocarbon degradation of a mineral oil assemblage. Researchers must ensure that any measurements used to determine the nature and extent of the oil release, the fate and transport of the mineral oil constituents, and any resultant toxicological effects are derived using representative data that adhere to the study’s data quality objectives (DQOs).
Mineral oils are complex assemblages of hydrocarbons manufactured from crude petroleum . Mineral oil production involves first distilling crude oils at atmospheric pressure and then, under high vacuum, generating distillates and residuals that can be further refined into mineral oils . Mineral oils refined from crude oils consist of a mixture of straight and branched-chained paraffinic, naphthenic, and aromatic hydrocarbons within a boiling point range of 300–600 °C , with resulting carbon ranges from C15 to C50 . Mineral oil composition and physical characteristics can vary widely depending on the source of the oil and product specifications. Further, base stock mineral oils can be chemically modified into “synthetic” mineral oils . The expansive composition of mineral oils allows for a wide variety of uses , which include non-lubricating products (e.g., agricultural spray oils, insulating oils, coatings, and printing inks), lubricating products (e.g., crank case oils and transmission fluids), and highly refined medicinal white oils and “paraffinum perliquidum” . Further enhancing the complex composition of mineral oils is the liberal use of additives (“additive packages”), often organo-metallic compounds, including corrosion inhibitors, antioxidants, antifoaming agents, detergents, dispersants, and emulsifiers, which are blended into the mineral oils .
Petroleum releases into the ocean are significant, resulting from natural seeps as well as spills during oil extraction, processing, transportation, and use . Oil spills can either be accidental or intentional. Accidental spills are most often from tankers transporting crude oil or petroleum products such as mineral oils or, to a lesser extent, are the result of pipeline leaks, coastal facility spills, and offshore oil production facilities . The largest sources of intentional operational discharges include discharges from vessels (e.g., bilge releases, which may include mineral oils) and water discharges from offshore platforms . The presence of petroleum lubricants, i.e., mineral oils, in today’s ships have varied purposes, including engine lubrication, hydraulics control, and the “oiling” of motors and cranes that may find their way accidentally, or intentionally, into the waterways . Over the past two decades, oil spill occurrences have lessened due, in part, to improved prevention programs, technological advances such as the use of double-hulled tankers , and the enactment of legislation such as the Oil Pollution Act of 1990 (33 U.S.C.&2701 et seq. (1990)) . In addition, there have been recent efforts to promote more environmentally friendly mineral oils for marine applications . Nonetheless, significant mineral oil spill risks still exist and cannot be ignored.
The objective of any sampling and analysis program is to determine the representative physical and chemical characteristics of a sample and, in the case of a mineral oil spill, to reliably understand the nature, extent, and impact of the spill . The need for measurements that are reliable, and of known quality is key to any relevant oil spill study and can be an especially challenging undertaking considering the complex and sometimes unknown composition of mineral oils and the rigorous degradative forces encountered in the marine environment .
|Objectives||Project Details||Sampling||Analytical||Validation and Assessment|
|Need for program||History||Representativeness||Subsampling||Data quality objectives|
|Regulations||Waste generation||Health and safety||Analytes||Documentation of quality|
|Thresholds or standards|
|Logistics||Preparatory method||Documentation of activities|
|Protection of human health||Contaminants||Sampling approach||Analytical method||Completeness/representativeness|
|Environment protection||Fate and transport||Sampling locations and depths||Aquatic toxicity testing||Bias and precision|
|Liability||Sources of contamination||Number of samples||Matrix/interferences||Audits|
|Data quality objectives||Areas to study||QA samples||Detection limits||Performance evaluation samples|
|Company/agency directives||Exposure pathways||Sample volume||Holding/turnaround times||Chain of custody|
|Public relations||Use of dispersants||Compositing||Contamination||Usability assessment|
|End-of-use data||Containers/equipment||QC samples|
To ensure that the analytical samples are representative of site conditions, QA measures must be associated with each sampling and analysis event. The sampling plan must specify these QA measures, which include, but not limited to, sample collection, laboratory standard operating procedures (SOPs), sample container preparation, equipment decontamination, field blanks, replicate samples, performance evaluation samples, sample preservation and handling, and chain of custody requirements .As such, the study design will define the specific number and types of QC samples needed to meet the DQOs, which should be detailed in the QAPP . QC samples typically collected as part of a well-conceived sampling program include :
Unlike standard sampling methods that are often available for chemical analysis, standard methods for collecting samples in marine matrices do not exist. When using non-standard sampling methods for marine mineral oil spill research, understanding and applying methodologies used and accepted by other researchers can be key to implementing a reliable sampling program . Accepted practices for sampling mineral oils , sediments , water column , and ecological samples  have been discussed elsewhere.
- Field, trip, equipment, and decontamination blanks
- Field replicates and duplicates
- Matrix spikes and matrix spike duplicates
- Background samples
- Source materials (mineral oils) potentially spilled, if available
4. Mineral Oil Analytical ChemistryThe characterization of mineral oils is hindered by its complex assemblage of hydrocarbons and unique additives, of which composition can vary widely depending on the source oil and product specifications. Additives may comprise 10–20% of the mineral oil product , which is typically not a consideration when devising a sampling and analysis program for crude oil and refined petroleum spills. As such, additives may prove to be useful as a forensic tool in differentiating mineral oil sources. The testing approach and target analytes will be driven by the DQOs. Broadly, mineral oil spill investigations fall into three categories: (i) the initial spill incident investigation, to better understand the direction of the spill and the amount of material spilled; (ii) the fate and transport of the mineral oil constituents, with forensic implications as to the who, what, how, when, and where of the mineral oil spill; (iii) a toxicological assessment focused on possible human and ecological damages. Fate, source, and transport forensic investigations require rigorous QA/QC programs based on well-crafted DQOs. For example, many forensic studies focus on unique ratios of specific analytes. Known precision and accuracy with tight tolerances are key to producing reliable diagnostic ratios . The minimum laboratory QC measures needed include:
The collection of background samples and source oil samples are key to any successful marine mineral oil spill investigation, particularly for a forensic sampling and analysis program, and should be integral to the development of DQOs for the investigation. Obtaining and analyzing mineral source oils can be fruitful for providing useful fingerprint information for forensic identification .
- Instrument blanks
- Calibration blanks
- Method blanks
- Laboratory control samples (LCSs) (spikes into blank water)
- Matrix spikes (spikes into site samples)
- Laboratory replicates
5. ConclusionsUnderstanding the ramifications of a marine mineral oil spill can be complex. Representative data of known quality and integrity is key to making scientifically sound decisions that can be defended when scrutinized by others. Marine mineral oil investigators should proactively design sampling and analysis studies with clearly defined DQOs and ensure that the study is performed according to the plan and that its implementation is properly recorded.