Detecting BTEX in Groundwater

Organic BTEX comprising benzene, toluene, ethylbenzene and xylene compounds can be a major pollution problem in groundwater. Their presence in water can create a hazard to public health and the environment. One of the most common sources for BTEX-contamination of soil and groundwater are spills involving the release of petroleum products such as gasoline, diesel fuel and lubricating and heating oil from leaking oil tanks. With their polarity and very soluble characteristics, these organic chemicals of petroleum products can enter groundwater systems and cause serious pollution problems.

How do BTEX compounds enter groundwater?

BTEX groundwater pollutionBTEX can contaminate natural waters through leaks in underground pipes, spills, improper disposal or leaching from landfills. As these chemical compounds are known to cause serious health effects to humans and pose a risk if exposed, a maximum contaminant level of 5 µg/L Benzene was established by the US EPA for drinking water to ensure removal from groundwater and surface water sources.

Measurement is also commonly required for industrial manufacturers discharging petroleum contaminated water to municipal wastewater treatment plants. When gasoline is in contact with water, BTEX compounds account for as much as 90% of the gasoline components that are found in the water-soluble fraction. Consequently, these chemicals are some of the most common contaminants found in drinking water.

What are BTEX compounds?

BTEX is not one chemical, but are a group of the following chemical compounds: Benzene, Toluene, Ethylbenzene and Xylenes. BTEX are made up of naturally-occurring chemicals that are found mainly in petroleum products such as gasoline. Besides gasoline, BTEX can be found in many of the common household products we use every day and are in a class of chemicals known as Volatile Organic Compounds (VOCs).

“Organic BTEX comprising benzene, toluene, ethylbenzene and xylene can be a major pollution problem in groundwater. Their presence in water can create a hazard to public health and the environment”


Benzene (C6H6) is a clear, colourless and flammable liquid with a sweet petrol-like smell. Benzene is found in ambient air as a result of burning fuels, such as coal, petrol and wood. Benzene is also common in unleaded fuel, where it is added as a substitute for lead, allowing smoother running of the engine. Benzene concentrations in fuel were once as high as 20% but have now been reduced to <1% in many countries, due to harmful health impacts. The World Health Organisation (WHO) and International Agency for Research on Cancer (IARC) classify benzene as a group one carcinogen: prolonged exposure to high concentrations of benzene causes leukemia and impacts red and white blood cells.

Outdoor levels of benzene range from 0.06 ppb in remote rural areas to 107 ppb in industrial centres with a high density of motor vehicle traffic. Levels of up to 3,000 ppb of benzene have been measured in air at petrol stations, and driving a car for one hour per day is estimated to add 40 micrograms (µg) of benzene to a person’s daily intake. Spending a little under two minutes a week to refuel a car at the petrol station leads to an additional estimated daily intake of 10 µg. Benzene can also occur in foods and drinks: research in the United Kingdom has found benzene concentrations in soft drinks as high as 28 ppb.


Toluene (C7H6), also known as methylbenzene, is a colourless liquid, with a strong, solvent-like smell. Toluene is inexpensive and simple to produce and is widely used in industrial processes as a solvent. Exposure to toluene can cause eye and nose irritation, tiredness, confusion, euphoria, dizziness, headache, dilated pupils, tears, anxiety, muscle fatigue, insomnia, nerve damage, inflammation of the skin, and liver and kidney damage.

Chronic exposure to toluene, particularly to high levels of this substance, can cause an individual to experience more severe side effects, such as Ataxia, Cerebral atrophy, Drowsiness, impaired speech, hearing, and vision, Neurobehavioral changes, Nystagmus and tremors. In non-industrial uses, toluene can be found in petrol as an octane booster and in glues, solvents and resins. The largest source of toluene release is during the production, transport, and use of petrol, which contains about 5 to 8 per cent toluene, but significant amounts of toluene are used in industrial processes worldwide, with over US$20 billion generated from toluene sales in 2013.

“There is a growing concern over the BTEX contamination of groundwater and the associated environmental and public health consequences from the recent proliferation of fracking in the USA”


Ethylbenzene (C6H5CH2CH3), is a colourless liquid, with a petrol-like aroma. Ethylbenzene is widely used in industrial processes for the manufacture of styrene, which is then used for polystyrene manufacture. Ethylbenzene is also found in products such as pesticides, solvents, paints, varnishes, automotive products, adhesives, and fabric and leather treatments. It may also be present in consumer products such as paints, inks, plastics and pesticides. Ethylbenzene is commonly found in ambient air, primarily resulting from industrial activities and vehicle emissions. Petrol contains about 1 to 2 per cent ethylbenzene, as Ethylbenzene is used as a gasoline and aviation fuel additive.

At urban sites, ethylbenzene concentrations range from 0.1 to 83 ppb, whereas levels found at rural sites are usually less than 0.46 ppb. Acute (short-term) exposure to ethylbenzene in people results in respiratory effects, such as throat irritation and chest constriction, irritation of the eyes, and neurological effects such as dizziness. Chronic (long-term) exposure to ethylbenzene by inhalation in humans has shown conflicting results regarding its effects on the blood. Animal studies have reported effects on the blood, liver, and kidneys from chronic inhalation exposure to ethylbenzene. Limited information is available on the carcinogenic effects of ethylbenzene in people but this is an area of ongoing investigation.


Xylene (C8H10) is the term used to describe the three isomers of dimethyl benzene; m-xylene, p-xylene and o-xylene. Usually concentrations of each are added together as total xylenes. Xylene is refined from crude oil, and is a clear, greasy liquid. The compound primarily released from industrial sources and motor vehicle exhausts. Xylene is widely used in production of plastic bottles and polyester clothing and as a solvent with a range of applications from circuit board cleaning to thinning paints and varnishes, but also used as a solvent in the printing, rubber and leather industries.

In urban and industrialised areas, xylene levels have been measured at up to 178 ppb. Petrol contains 7 to 10 per cent of xylenes. Typically, background levels of xylene in ambient air are around 0.23 ppb. In suburban areas it can be around three times higher. Ortho-xylene is the only naturally-occurring form of xylene; the other two forms are man-made. Ingestion of xylene will cause a depression of the central nervous system resulting in dizziness, nausea and vomiting. Aspiration of xylene into the lungs during ingestion or vomiting can result in very serious health consequences.

Fracking & BTEX

Fracking is the process of creating cracks in underground rock formations to increase the flow and recovery of gas or oil out of a well. Fracking is also known as fracture stimulation, hydraulic fracturing, fracking, fracking, hydrofracking or fracturing. Due to the varying geology of coal seams, fracking is not carried out in all coal seam gas (CSG) operations. For deep gas and oil activities (such as production of shale gas and oil, tight gas and basin-centred gas) fracking is undertaken in almost every well.

fracking BTEXIn December 2010, the EPA released a report of a study conducted in Pavillion, WY. The study examined water in test wells near fracking sites and found it to contain BTEX compounds, all of which are harmful to public health. There is a growing concern over the BTEX contamination of groundwater and the associated environmental and public health consequences from the recent proliferation of fracking in the USA.

Petroleum hydrocarbon-derived contaminants of concern and various dissolved cations and anions were spatially determined in surface waters around 15 coalbed methane fracking wells in Sullivan County, IN, USA. At least one BTEX compound was detected in 69% of sampling sites (n = 13) and 23% of sampling sites were found to be contaminated with all of the BTEX compounds.

Toluene was the most common BTEX compound detected across all sampling sites, both upstream and downstream from coalbed methane fracking wells. The average concentration of toluene at a reservoir and its outlet nearby the fracking wells was ~2× higher than other downstream sites.

BTEX chemicals occur naturally in underground water sources. So to ensure these levels don’t rise above environmental and human health standards, the use of BTEX in the fracking process has already been strictly regulated in Australia, including a ban on adding these chemicals to fracking fluid. The following Australian environmental and health standards for BTEX in fracking fluids ensure that BTEX chemicals are not at a level that will contaminate drinking water or impact on groundwater dependant plants and animals:

  • Benzene – 1 ppb
  • Toluene – 180 ppb
  • Ethylbenzene – 80 ppb
  • m-Xylene – 75 ppb
  • o-Xylene – 350 ppb
  • p-Xylene – 200 ppb

BTEX groundwater detection from Chelsea Technologies

Uvilux fuel BTEXChelsea’s highly sensitive UviLux FUEL – BTEX fluorometer for the detection of the highly refined groundwater contaminants (benzene, ethylbenzene, toluene and xylene).

The UviLux FUEL – BTEX is depth rated to 1000m, is easy to integrate with monitoring platforms and systems, or combine with our Hawk Hand-held Display and Data Logger for on the spot readings and logging and offers highly sensitive readings to 3 ppb.

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