Hydrocarbon Focus

Total Petroleum Hydrocarbons or TPH is a term used to describe any mixture of several hundred compounds that are byproducts of crude oil - although they are all different, they are all mostly made from hydrogen and carbon (thus hydrocarbons). These products are divided into groups (called fractions) of those that tend to behave similarly in either water or soil and have similar boiling points. This is further complicated by the fact the type of analytical methods used to measure the substances impacts some of the terminology.
 
Hydrocarbons make up the bulk of a considerable range of products that are derived from crude oil. These include sealants, tars, lubricants, greases, asphalt and aircraft and vehicle fuels. Many of these are produced in refineries that distil crude oil into these fractions. These are further processed and blended. The lighter fractions - those that boil at relatively low temperatures - are used as petrol, solvents and jet fuels while the medium fractions are used as diesel. The heavy ones - those that have higher boiling points - are used as greases, tars and lubricants.
 
Petroleum hydrocarbons make up a large portion of other products including paints, solvents and creosote.
 
Here we consider TPH division into fractions according to their physico-chemical and toxicological properties, segregated along their environmental behaviour (aliphatic and aromatic compounds) and the Equivalent Carbon number (EC). This approach lets us determine the associated risk for human health through the Human Risk Index.
 
As mentioned above, hydrocarbons can be divided into two main groups - aliphatic and aromatic compounds. 
 
Aliphatic compounds cover straight- and branched-chain compounds that, in turn, can be sub-divided into alkanes (those without double bonds - in the past referred to as paraffins); alkenes (those with one or more double bonds - also known as olefins) and alkynes (those with at least one triple bond).
 
Aromatic compounds include one or more benzene ring structures.
 
The fractions we look at as part of this screen are as follows (please note that organic matter content is part of this screen because the safe-for-use level thresholds we list differ depending on the OMC content in the soil):
 
Aliphatic TPH >C5-C6
Aliphatic TPH >C6-C8
Aliphatic TPH >C8-C10 
Aliphatic TPH >C10-C12 
Aliphatic TPH >C12-C16 
Aliphatic TPH >C16-C21 
Aliphatic TPH >C21-C35 
Aliphatic TPH >C35-C44 
Total Aliphatic Hydrocarbons 
 
Aromatic TPH >C5-C7
Aromatic TPH >C7-C8 
Aromatic TPH >C8-C10 
Aromatic TPH >C10-C12 
Aromatic TPH >C12-C16 
Aromatic TPH >C16-C21 
Aromatic TPH >C21-C35 
Aromatic TPH >C35-C44 
Total Aromatic Hydrocarbons
 
Organic Matter Content
 
This package is often paired with the State of Your Soil or Advanced Gardening Suite packages that provide analysis of soil pH, texture and organic matter as well as measures of major plant nutrients, including potassium, phosphorus and magnesium to help make your growing space as fertile as it can be in addition to being safe. The basic State of Your Soil package costs £125. More on this can be found by clicking here. The Advanced Gardening Suite costs £200 - more details here.