Continuous sampling of dioxins - latest research results from the Environment Agency

This article for edie provides a summary of work carried out by the Environment Agency to test two commercially available continuous dioxin sampling systems.

Background

Dioxins and furans are a group of chemicals, often referred to simply as dioxins.

They are formed by a number of naturally occurring and human activities such as burning fuels like wood, coal or oil, waste incineration and from a number of industrial processes.

Forest fires, bonfires and barbecues contain small amounts of dioxins, as does cigarette smoke.

Over two hundred dioxins exist but only 17 are considered to have significant toxicity by the World Health Organisation.

These are the ones that are subject to control by regulation. Studies on workers in chemical plants, or people affected following accidental exposure such as Seveso in Italy or Yusho in Taiwan, show that high levels of dioxins can lead to an increased risk of cancer.

These people had substantially higher levels of exposure to dioxins than the general public.

The main route by which the general population takes in dioxins is through food.

Dioxins in food come from traces present in soils, resulting from processes such as stubble burning, forest fires and industrial emissions.

The amount of dioxins in the UK diet has declined substantially over the past 20 years as tighter controls have been placed on industry and stubble burning.

In 1997 the average person consumed only one quarter of the amount that an average person consumed in 1982.

It is expected that further environmental controls, for example the European Union Waste Incineration Directive (WID), will continue to reduce levels of dioxins in food.

Municipal waste incinerators and cement kilns operate at well below their permitted emission limits and only make a very small contribution to the background level of dioxins in the environment.

We are responsible for regulating a number of industrial processes that generate dioxins.

Over the last 15 years, levels of dioxins emitted from these activities have fallen significantly.

For example, between 1990 and 2003, the quantity of dioxins released from the industrial sites we regulate fell by 95%.

We grant permits to companies to operate industrial processes provided they can show that the impact of any emissions does not cause harm to people or the environment.

Emission limits are set in the permits to protect people and the environment. Operators have to monitor their emissions and report the results to us. We may also carry out our own monitoring to confirm the operators' results.

For many common pollutants we require operators to fit continuous emission monitoring systems.

These systems provide the operator with constant feedback on the levels of pollutants being emitted.

There is currently no technology available to take, analyse and display instantaneous readings of dioxins levels due to the very low levels that are emitted.

These levels are so low that they are at the limits of what can be detected by the most sensitive equipment. Dioxins emitted from waste incinerators must meet the standards of the WID which has set the emission limit at a tenth of a nanogram (ng), written in scientific writing as 0.1ng I-TEQ/m3. A nanogram is one billionth of a gram.

As we cannot measure dioxins on a continuous basis, we use instead European Standard BS EN 1948, as do other member states and as is required in the WID.

This involves collecting a sample of emissions manually over 6 hours, which is then sent away for laboratory analysis.

We also ensure that the formation of dioxins is minimised by controlling other things that can be measured continuously and which we know prevent dioxins formation.

These include the combustion temperature, the amount of oxygen present and whether the abatement equipment is operating properly.

These are specified in the permit that we issue to operators. If conditions are not correct the operator is required to stop burning waste.

What we tested

As part of our continuous improvement programme we decided to investigate the performance of two commercial systems that sample dioxins continuously. The systems, known as AMESA and DMS are designed to sample emissions continuously over a typical period of 14 to 28 days, producing a single sample, which is then analysed. The BS EN 1948 method takes a sample over 6 hours, which is then analysed.

The research was carried out at two sites, Eastcroft municipal waste incinerator in Nottingham and Cauldon Cement Works in Staffordshire.

The manufacturers of the continuous systems provided the equipment on loan free of charge.

We placed a research contract with Netcen, part of AEA Technology plc.

A series of tests were carried out in the laboratory and on the sites to assess the systems' performance.

The purpose of tests was twofold, firstly to see how they worked as automatic sampling systems and secondly to assess their performance against measurements made by manual sampling using BS EN 1948.

Conclusions

The extremely low levels of dioxins emissions at both sites meant that the study was working at the limit of what it is possible to measure with any certainty.

Although this is good news from an environmental perspective, it presented the researchers with a considerable challenge.

Within this constraint some conclusions could be drawn:

  • Both continuous systems were able to track the trends in dioxins concentrations as the processes operated.

    However, differences were observed between the continuous sampling systems and manual sampling and between the two continuous systems.

  • The continuous sampling systems did not meet the requirements of BS EN 1948. The emission limit value in the WID applies to the use of BS EN 1948 and this manual sampling method remains the only acceptable way to monitor dioxins for the purpose of regulation.

  • The majority of results were well within the 0.1ng I-TEQ/m3 emission limit value specified by the WID, irrespective of the measurement system and test site.

    A small number of results at the municipal waste incinerator were higher.

    Three slightly elevated results were found during plant start-up when the plant is stabilising and seven elevated results during normal operation which were thought to be due to contamination of the probe.

    Follow up Actions

    On the basis of this report, we will be undertaking the following:

  • We will be commissioning further work to investigate the slightly higher results found at the municipal waste incinerator during start up conditions.

    These start up periods are specifically excluded from the WID and the research was not designed to investigate start up periods. This new work will look at obtaining samples using BS EN 1948 during start up.

    We will do this at a number of municipal waste incinerators around the country.

  • We will discuss these findings with the Dest Testing Association, the principal UK trade association for carrying out emissions monitoring.

    We want to explore the possibility of sampler contamination, particularly when using titanium probes, and consider options for improved clean up of equipment between sample runs.

  • We will make the report available to CEN, the European standards making body, Defra and the European Commission as a contribution to their consideration of developments in sampling and monitoring of dioxins in the future.

    Further information

    For more information please see our detailed report Use of Continuous Isokinetic Samplers for the Measurement of Dioxins and Furans in Emissions to Atmosphere at this link.

    Ackowledgements

    We would like to acknowledge the contribution made by Westech, Casella Stanger, Becker Messtechnik and Dioxin Monitoring Systems in providing monitoring equipment and support.

    We would also like to thank the operators, WRG Ltd and Lafarge Cement who kindly allowed access to their sites for the equipment evaluations to take place.

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