British lab sets the standard

A method to identify and quantify dioxins in water, developed by Analytical & Environmental Services (AES), has been adopted as an ISO standard and will soon be used the world over.

The process involved adapting an existing complex analytical technique and submitting it for stringent validation procedures by international experts. The result was unanimous approval and the method is to be published by International Organisation for Standardisation (ISO) imminently.

Present danger

Dioxins generate major environmental concern because of their ubiquitous nature and potential cancer-causing effects, even at very low levels. They have been described by environmentalists as one of the most dangerous substances known.

The term dioxin is a generic description for dioxins and furans which are a class of 210 individual chlorine containing organic compounds of a similar chemical structure. They are generally produced as unwanted by-products

during thermal processes involving the burning of organic material or following chemical manufacture.

Typically, municipal and chemical incineration, coal combustion, metals manufacture and chlor chemical production can create dioxins and consequently these industries operate highly controlled processes. Large-scale uncontrolled burning of any type can also be a major potential source. Most recently, the risk of dioxin emission resulting from the mass burning of livestock carcasses during the foot and mouth disease outbreak in 2001 increased public awareness of the substance.

Once produced, dioxins may be present in the environment in air and in soil as landfill ash for instance. If found in water they are most likely to be present bound to particulate matter. It is the entry of dioxins into the food chain which causes most risk to humans as once ingested, dioxins bio-accumulate in tissue and have been linked strongly to causing cancer.

Of course, dioxins are not a threat to the drinking water supply as organic compounds are removed through filtration, flocculation and activated carbon treatment. The Drinking Water Inspectorate (DWI) therefore do not require them to be monitored routinely.

In wastewaters however, they are a potential problem. For instance they may be present in industrial effluents or groundwater run-off and from there they may enter a water course, be ingested by an animal or up-taken by crops and so enter the food chain for human consumption. The measurement of dioxins in the environment is therefore extremely important.

AES has established a reputation as a centre of excellence in the field of dioxin analysis and employs a team of scientists who are internationally renowned for their expertise. Indeed, the company has United Kingdom Accreditation Service (UKAS) accreditation for the analysis of dioxins in soils, air and non-biological materials in addition to water.

In order for the company’s existing in-house method for the analysis of dioxins in water to be adopted as an international standard, a team of senior scientists worked for three years. Sue Owen, commercial director at AES led the development team, which included development scientist Dr Ian Barnabas and organics lab team leader Steve Wilson.

The method first had to be accepted by the British Standards Institution (BSI) before being submitted to ISO. A programme of rigorous validation by dioxins experts from standards bodies all over the world was then carried out.

The method itself is a complex analytical technique. It begins with a one-litre sample of water taken in a specially cleaned glass bottle. On return to the lab this sample is then spiked with a series of carbon 13 labelled dioxins. These are used as a control throughout the preparation procedures and to quantify the concentration of dioxin in a technique called isotope dilution.

The next stage is extraction. Here the sample is filtered to remove particulate matter which is then extracted using the classic Soxhlet extraction technique for organic analysis. The filtrate is extracted with an organic solvent and the two extracts are combined prior to extensive clean up procedures to remove any interferences.

The clean-up procedures are carried out over a minimum of two to three different stages using classical chromatography techniques. Further stages may be required if the samples are particularly contaminated and clean-up may take a day to perform. The next stage is to concentrate the cleaned extracts by controlled evaporation resulting in a sample volume of just 10µg/l from the original one litre sample — a 100,000 fold concentration.

Finally, analysis is carried out using a high-resolution gas chromatography, high-resolution mass spectrometry (HRGC/HRMS) instrument. This is highly sophisticated equipment used to achieve very low detection limits required for the measurement of dioxins. It ensures the very greatest level of accuracy is achieved and a single sample takes around an hour to run through the HRGC/HRMS. Typically, batches of samples are run overnight.

Results are then reported in picograms per litre of the 17 individual 2,3,7,8 dioxins that are of particular toxic concern. They are also reported as international toxic equivalency units (I-TEQ) which is a means of reporting dioxins based on their relative toxicity.

Total dioxin concentrations are also given for each level of chlorination. These results are then compiled in an extensive report together with full details of the quality control criteria employed.

The European Union is placing a greater importance on the monitoring of dioxins and it is a real achievement that AES has set the standard for the rest of the world to follow with this method.

It is not legally binding to use the technique but it is internationally recognised best practice and it is likely a range of organisations will now use it including waste companies and industry, as well as environmental regulators.

The legislation governing the monitoring of dioxins in water includes the EC groundwater directive which specifies the monitoring of organohalogen compounds. Routine monitoring is not carried out but may be undertaken on an ad-hoc basis when there is a potential risk.

For instance, the foot and mouth burial sites contained a large mass of burnt livestock carcasses as well as the waste from fuel that was used which included railway sleepers coated in preservatives. Here, the risk of releasing dioxins in leachate was high and monitoring was required.

It is in such cases the AES method is typically used. Following the publication of the ISO standard, this will now occur all over the world.