What is TPH?
The term TPH (Total Petroleum Hydrocarbons) is a confusing one, and often misunderstood by the non conversant as being a fixed definition of a petroleum product that can be measured absolutely , and hence be directly compared with other TPH values. Unfortunately this is not the case.
In short analysis of the total petroleum hydrocarbon (TPH) content of soil and water samples is complex and confusing. This web page will attempt to explain some of this subject, help clarify the use of ‘TPH’ as an analytical quantity and direct you to sources of further information.
Definition of TPH
A quick Internet search will yield numerous definitions of TPH some of which can be seen below.
Total petroleum hydrocarbon is the measure of the concentration or mass of petroleum hydrocarbon constituents present in a given amount of soil or water. The word "total" is a misnomer--few, if any, of the procedures for quantifying hydrocarbons can measure all of them in a given sample. Volatile ones are usually lost in the process and not quantified and non-petroleum hydrocarbons sometimes appear in the analysis. (http://www.caslab.com/Total_Petroleum_Hydrocarbons_TPH_Meaning/ )
Total Petroleum Hydrocarbons (TPH) is a term used to describe a broad family of several hundred chemical compounds that originally come from crude oil. (Toxicological Profile for Total Petroleum Hydrocarbons (TPH) (http://www.atsdr.cdc.gov/toxprofiles/tp123.pdf)
TPH is defined as the measurable amount of petroleum-based hydrocarbon in an environmental media. It is, thus, dependent on analysis of the medium in which it is found (Gustafson 1997).
With such a loose definition (and with good reason) is it not surprising that TPH data presents all sorts of problems for the unacquainted who are tasked with making decisions or understand recommendations based upon TPH values.
The crux of the problem stems from the complicated nature of petroleum products as which can be complex mixtures of hundreds of hydrocarbon compounds, with the exact composition varying due to a number of factors including the crude oil source and the subsequent refining process. To complicate this even further are the changes to the refined product/spilled material caused by weathering once exposed to environmental conditions.
It is also worth noting that here are a number of other terms that are often used in conjunction with TPH:
EPH = Extractable Petroleum Compound,
DRO=Diesel Range Organics,
GRO=Gasoline Range Organics
EDRO=Extended Diesel Range Organics,
SVOCs=Semi Volatile Organic Compounds
With TPH being the sum of the aliphatic and aromatic compounds in the GRO and DRO and mineral ranges.
These ranges are essentially determined by the hydrocarbon chain length of the predominant component of the contaminant and have implications on the acceptable limits for disposal and other criteria. For example limits for diesel may be at 10,000 parts per million whilst non diesel hydrocarbon contamination could be 1,000. To the right is a idealised image of a Gas chromatography (GC) trace showing the component ranges in terms of their retention times which in turn tends to be consistent with the hydrocarbon chain length which is how the classification of hydrocarbon characterisation is determined.
Further information can be found above in a power point presentation on TPH or for further reading material on TPH the following publications comes highly recommended. (Total Petroleum Hydrocarbon Criteria Working Group
Dried oak leaves
No.6 Fuel oil
Household petroleum jelly
TPH (mg kg-1)
TPH correlation between Laboratories
Given the above discussion it comes as no surprise, but a very under acknowledged fact that the values reported in TPH analysis are highly affected by the extraction technique and method utilised by the laboratory as well as the TPH standards by which the laboratory quantify the sample. Despite the methods used being MCerts accredited, the different methods will yield significantly different results. In some instances the TPH values reported will exceed threshold limits yet a different but still legally defendable data set will report values below site specific criteria. This renders the decision to remediate/dispose or leave in situ a rather fraught one.
The problematic nature of TPH determination is also implicitly recognised in the way that MCerts allows for a 30% +/- variation in its determination between laboratories for the certified reference material (CRM). Given that the CRM is a well characterised and thoroughly homogenised dried sample the variance between laboratories for ‘real’ fresh field samples can be far greater, and has been shown to be so on many occasions. This margin for error could be further interpreted to allow for a certain amount of leeway when making decisions influenced by TPH values - is your result really 1,000ppm or could it 700ppm?
As previously outlined numerous methods of TPH determination exist involving different sample preparation regimes, different extraction techniques (different solvents, temperatures, pressures, extraction times, etc), different purge and trap methods for volatiles, different analytical techniques (e.g. IR and GC) and combinations thereof. Even the method of sample collection and storage (as well as sample preparation) can have a profound bearing on the determined TPH as volatiles can be easily lost by unavoidable transfer losses or by careless or lax procedures. It is a recognised reality that there is no ‘gold standard’ method of TPH determination.
There is a reason for the availability of a large number of TPH measurement techniques. Because petroleum and petroleum-derived products are such complex mixtures, there is no single “best” method for measuring all types of petroleum contamination. (Total Petroleum Hydrocarbon Criteria Working Group Series, Volume 1. Analysis of Petroleum Hydrocarbons in Environmental Media)
Essentially the important concept to understand from this is that TPH determination of a soil or water sample is very method specific.
This means that it is difficult to compare data from one TPH technique to another without the full method information being provided. This view is succinctly expressed in the ATSDR report on Toxicological Profile for Total Petroleum Hydrocarbons on its web site.
The term “total petroleum hydrocarbons” (TPH) is generally used to describe the measurable amount of petroleum-based hydrocarbons in the environment; and thus the TPH information obtained depends on the analytical method used. One of the difficulties with TPH analysis is that the scope of the methods varies greatly. Interpretation of analytical results requires an understanding of how the determination was made.
(Toxicological Profile for Total Petroleum Hydrocarbons (TPH)- 3. Identity And Analysis of Total Petroleum Hydrocarbons, September 1999 (http://www.atsdr.cdc.gov/toxprofiles/tp123-c3.pdf)
A preview of a study relating to TPH issues concerning a large coke works project in the UK and a US Navy Jet fuel bioremediation project can be seen in the pdf document to the right. The study also considers at a new solvent developed by QROS and its extraction efficiency on these hydrocarbon contamination sources. For a free full copy of this report, please contact using the contact web page.
In summary the use of TPH as a measurement tends to be as a surrogate for want of a better readily available technique and as we have alluded to previously TPH is as a measurement largely defined by the method used for its determination. Consequently unless the contamination is well defined, reliance on this parameter alone is not an appropriate basis for contaminated soil management. In addition to this, non-petroleum derived compounds (e.g. naturally occurring humic and fulvic acids) are frequently inadvertently (and wrongly) quantified as TPH even by MCerts analytical techniques. The table (left) clearly shows the extent of possible influence from non petroleum sources that could be quite readily found in soil samples.
As a point of interest here it should be noted that TPH quantification by QROS’s hydrocarbon analyser QED, is not unduly influenced by non petroleum hydrocarbon content.
API (2001) Risk-based Methodologies for Evaluating Petroleum Hydrocarbon Impacts at Oil and Natural Gas E&P Sites, API Publication 4709, API Publishing Services, Washington DC. (May 2003) (http://www.api.org/aboutoilgas/sectors/explore/upload/4709.pdf)
TPH determination by QED
QROS offer an on-site hydrocarbon analytical method where many of the above limitations are circumvented. For instance QROS can solvent-extract samples in the field during the sampling procedure with no sample pre-processing, therefore minimising the loss of volatile hydrocarbons. This alleviates the problem of volatile loss in packaging, storing, transporting, sub-sampling and pre-processing of samples for laboratory analysis.
Using this unique hydrocarbon analyser (QED™) a value for the TPH content of the sample can be derived in minutes and hence many (typically 50-60+) samples can be analysed in a day. This enables SIs, remediation monitoring and hotspot delineation to be performed rapidly and consistently. A key feature of QED is the immediate generation of a characteristic fingerprint of the hydrocarbon contamination. This identification of the hydrocarbon type is important when deciding upon the most appropriate standard to use for quantification of the contamination (e.g. BTEX, DRO, TPH, PAH, creosote, crude oils, various grades of jet fuel and kerosene) Whilst with QED QROS can call upon a number of calibration standards or even site-tailored calibration standards to to determine accurate and reliable TPH values (QED routinely uses a multi-calibration of four standards BTEX, DRO, TPH and PAH) a laboratory would typically calibrate using only standard fuel hydrocarbons (BTEX, DRO) and a mineral oil).