Monitoring dioxins

Dioxin is the name given to a family of halogenated organic compounds, the most common consisting of polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzodioxins (PCDDs). These chemicals have been shown to bioaccumulate in humans and wildlife due to their lipophilic properties (they are persistent in fatty tissue), and are known teratogens (causing congenital malformations), mutagens (causing genetic mutation), and suspected human carcinogens.

The terms carcinogenic and mutagenic are highly emotive and consequently public concern is at its greatest when there is a risk of dioxins or furans (similar chemical compounds) being introduced into the environment.

Dioxins are produced in small concentrations when organic material is burned in the presence of chlorine. This happens whether the chlorine is present as chloride ions or as organochlorine compounds, so they are widely produced in many contexts including incineration and coal-fired power generation. However, in recent years emissions regulation for modern incinerators has substantially reduced dioxins emissions.

Dioxins are also generated in reactions that do not involve burning — such as bleaching in the paper and textiles industries, and in the manufacture of chlorinated phenols, particularly when reaction temperature is not well controlled. Affected compounds include the wood preservative pentachlorophenol, and also herbicides such as 2,4-dichlorophenoxyacetic acid (or 2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).

Higher levels of chlorination require higher reaction temperatures and generate greater levels of dioxins.

Cigarette smoke can also contain dioxins as a result of chlorine-containing tobacco pesticides and chlorine-bleached cigarette papers.

Occupational exposure is an issue for some in the chemical industry, or in the application of chemicals, notably herbicides and inhalation has been a problem for people living near substantial point sources where emissions are not adequately controlled.

Underestimated emissions

In many developed nations emissions regulations have alleviated some concerns, although the lack of constant sampling of dioxin emissions raises concerns in some quarters about understatement of emissions.

Dioxin and furan concentrations in process emissions are generally extremely small and, as a consequence, it is not currently possible to measure such emissions continuously, in real-time. Rather, it is necessary to sample over a period of hours and subsequently to analyse the collected sample with a high-resolution gas chromatography mass spectrometer (GC-MS).

The tolerable daily intake for dioxins has been set at 2 pico grams (two millionths of a millionth of a gram: 10-12g) per Kg of body mass.

Emissions monitoring for dioxins is required by the Environment Agency for processes that have the potential to release these compounds and the monitoring requirement is generally to sample for around 8 hours twice yearly, or more often if the process presents a higher level of risk.

At a recent emissions monitoring conference, MCERTS 2007, Paulo de Angelis from specialist dioxins sampling equipment manufacturer TCR Tecora, said: “Existing portable dioxins sampling equipment merely provides a ‘snapshot’ of a process, from which it is not possible to quantify mass emissions and for this reason TCR Tecora decided to develop a system that would be permanently installed on a stack and would be able to sample for much longer periods of time.”

This was a bold move for the company because legislation in most countries does not specifically require sampling for periods longer than a few hours. However, Quantitech is introducing this technology to the UK market partly because it believes that process operators will be reluctant to stand up at a public meeting and claim that infrequent sampling provides a clear picture of dioxins emissions.

The new system, known as ‘DECS’ (Dioxins emissions continuous sampling) provides regulators all over the world with the facility to require the creation of samples that represent total process dioxins emissions over much longer periods; up to one month. Furthermore, DECS provides environmentally conscious businesses with the opportunity to generate emissions data that is far more informative and therefore of much greater value to regulators and the public.

The DECS sampling unit is permanently installed on a stack and operates automatically, which means that less labour is involved in the sampling process and the procedure is fully automatic so there is less opportunity for error and operators do not need to be highly trained experts. TCR Tecora claims that, as a permanently installed fixture, DECS is less costly than occasional sampling. Furthermore, a control unit is installed on-site which can operate up to four samplers and thereby reduce the costs per stack even further. Remote access is available via the Internet or Intranet.

Quantitech, which specialises in the provision of environmental monitoring and occupational hygiene testing equipment, has received a high level of interest in the new continuous dioxins sampler which is a pleasant surprise, because Quantitech’s business is mostly driven by a regulatory requirement to monitor emissions rather than a voluntary need to gain a better understanding of the environmental picture surrounding a process. However, we are aware of process operators in France that have recently been required by their regulator to install long-term dioxins sampling equipment, so we suspect that similar circumstances may arise here in the UK.