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MEASUREMENT OF PCB EMISSIONS IN INDUSTRIAL SOURCES FOR EU STANDARDS
Francesco Ricucci® Politecnico di Torino
Introduction. The emissions from the anthropogenic combustion processes cause human and dramatic environmental effects from global warming to photochemical smog . The development of emission reduction strategies and the increase of the efficiency of combustion processes represent a very real field for applied combustion research. Recent studies proved a rise in the concentration of PCB in different group of food compared to the past, the cause is not known, although PCB production was banned by the United States Congress in 1979 and by the Stockholm Convention on Persistent Organic Pollutants in 2001, infact According to the U.S. Environmental Protection Agency (EPA), PCBs cause cancer in animals and are probable human carcinogens. However, for different social and economic reasons such substances are still in use and/or released to the environment. PCBs are toxic chemicals that can be transported by wind and water, they are very stable compounds infact they persist for long periods of the time in the enviroment, PCBs have been detected in arctic air. They can be accumulated in one specie and pass to another specie through food chain, included human food chain.
Many countries have taken strong initiatives to reduce and control POPs releasing. Significant source of PCB is the industrial combustion processes due to poorly controlled incineration. For this reason technical developments in combustion processes have been studied, focusing the attention on improved combustion, better operation, modern design, addition of gas clean-up equipment. In this project it is explained the standard way to measure the concentration of PCB in the chimney. This pollutant is presented in a very low concentration in the incinerator's flue gas but this concentration is not negligible for the local populations which live close to these kind of plant. For this reason is necessary to treat this pollutant and a remediation strategy is given in order to reduce the impact either on humans and on environment.
What does PCB mean?
® Francesco Ricucci
Polychlorinated biphenyls (PCBs) are synthetic organic chemical, consisted of two benzene rings joined by a carbon-carbon bond, with chlorine atoms substituted on any or all of the remaining 10 carbon atoms
»H Hoi '"H <"'
a ci ci a
a a a a«n
oiH OLH orH
The chemical formula for PCBs is Ci2H(i0-n)Cln, where n is the number of chlorine atoms within the range of 1-10. The variety of possible positions for the chlorine atoms give rise to 209 different structures (containing at least one chlorine atom), conseguently 209 individual congeners exist. Some PCBs are identified as "dioxin-like" (PCBdl) with relative toxicities 100-1000 times higher than those associated with others PCB congeners. There are 12 dioxin-like PCBs, they consist of four non-orto PCBs and eight mono-ortho PCBs having mostly planar structure. There are no known natural sources of PCBs, they are sintetic organic compounds.
Toxic Equivalence Factors (Teq).
Toxic dioxin congeners and dioxin like compounds have the same mode of action and their toxic effects are additive and to enable comparisons between samples, a comparative scale of toxicity is used. This toxic equivalence (TEQ) value is calculated relatevely to the most toxic congener (2,3,7,8-TeCDD), which the toxic equivalence factor (TEF) is one (TEF2,3,7,8-TeCDD = 1).
The TEF of 2,3,7,8-TeCDD is used to evaluate the toxicity of the other congeners.
The concentration of each congener should be expressed as Toxicity Equivalency Quantity (TEQ)
To determine the TEQ value of a sample, the TEF values are multiplied by the congener concentration .The resulting values are then summarized into a sample specific TEQ value.
TEQ = £„i[PCDDi X TEF;] + 2n2[PCDF; X TEFt] + ^[PCB* + TEF,]
Non-continuous sampling in stationary source emission. PCBs are highly toxic compounds that need to be controlled in order to prevent adverse effects on human health, it is necessary to identify current concentrations of PCBS in the emission source to promote the environmental protection measures against PCBs contamination. The document FrEN 1948-4 describes the sampling, extraction and analyses of dioxin-like PCBs and requires references to EN 1948-1, -2, -3. PCBs and PCDDs/PCDFs are emitted from thermal processes, it will be dealed the determination of dioxin-like PCBs in emission from stationary source. This European Standard it is applicable to PCDDs/PCDFs and due to their similar chemical behaviour, the 12 dioxin-like PCBs designed by the WHO can be sampled together furthermore it is applicable to measure also PCB-cogeners like the "marker PCB" 28, 52, 101, 138, 153, 180.
This European Standard has been developed to measure PCB concentrations at about 0,1 ng I-TEQ/m3. Before sampling, it's required the cleaning of all inner surfaces which partecipate to the sampling-line. We should clean all surface of sampling train:
1) Cleaning of the sampling equipment in the laboratory. Normally rinsing with water and detergent, followed by rinsing with solvent .
2) Rinsing,previous to sampling, with solvent.
3) Rinsing, after the sampling, the equipment being in contact with the flue gas with solvents. Rinsing with solvents normally include different solvents: acetone and/or methanol followed by toluene (not simultaneously. There are three different sampling systems:
a) Filter/condenser method
b) Dilution method
c) Cooled probe method
Gas is sampled isokinetically in the duct, it means that the velocity and direction of the gas entering the sampling nozzle are the same as the velocity and direction of the gas in the duct at the sampling point.
1. Sampling and cleaning
Before collecting of the sample we must add note amount of some sampling standards (13C12-labelled PCBs) to determine the sampling recovery rate of the congeners (efficiency of the collection), the only purpose of the isotope labelled standards added before sampling is to identify anomalies during sampling they are not used for quantification. The
sample gas is brought to a temperature specific to the sampling system and the gaseous and particulate PCBs are trapped. Filter and condenser method:
The sample gas is sucked through the nozzle, probe and filter below 125 °C (to avoid chemical reaction on the activated surface) but above the flue gas dew point. Downstream, a condenser is attached to cool the sample gas below 20 °C. The gaseous and aerosol parts of the PCBs are captured by impingers and/or solid adsorbents.
At the end there is the pump and the volume measurement and regulation device.
The sampling train is validated for volume flow rates of around
2 m3/h.
Dilution method:
The sample gas is sucked through the nozzle and the heated probe The waste gas is cooled very rapidly in a mixing channel below 40 °C with dry dilution air.
The dilution avoids (condensation) the relative humidity of the sampling gas rising to 100 %.
After dilution a filter is used to collect the particulate PCBs contained in the waste gas stream. For the separation of the gaseous PCB a solid adsorbent is linked downstream.
Measuring devices for the characteristics of the waste gas, i.e. pressure, temperature, waste gas velocity and waste gas composition, are additionally required in the waste gas channel for the sampling procedure.
The sampling system is validated for flue gas sample volume flow rates of 1,5 m3/h to 4 m3/h.
Cooled probe method:
A sample is withdrawn from the gas stream and collected through nozzle and cooled probe to water condenser in a condensate flask, in which it is cooled below 20 °C. The condensate and most of the particle are caught in a condensate flask. Downstream, impingers and/or solid adsorbents are linked in order to collect the gaseous PCDDs/PCDFs and PCBs. A filter is placed in front of the last adsorbent to increase the sampling efficiency of small particles.
The sampling system is validated for flue gas sample volume flow rates of 0,5 m3/h to 2,5 m3/h.
2. Extraction and clean-up
To complete the measurement procedure, we have to combine one of the three sampling methonds previously described with the extraction, clean-up and identification and quantification in order to measure the 17 congeners necessary to calculate the total I-TEQ.
We should separate a very small amount of analites from the matrix
Extraction
Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and Polychlorinated Biphenyls (PCBs) are extracted from the sampling media by usually soxhlet extraction. Selected extraction standards are added to the different sampling media before extraction, they are used for quantification, differently by sample standards. Extraction procedures are normally based on soxhlet extraction of filters and adsorbents, instead liquid extraction for the condensate.
Before this operation, the sample needs a pre-treatment: any particles collected during sampling on the particle collecting media (glass fibre filters, thimbles, glass wool, etc.) using any of the three methods shall be treated with hydrochloric acid.
After sampling, we have samples in filter, adsorbent and condensate, the extraction procedure is carried out using the following materials and techniques:
a) All collected particles and all adsorbents shall be extracted with toluene for 20 h in a Soxhlet extractor or comparable validated method
b) For aqueous liquids (condensate and bubbler/impinger solution) a liquid/liquid extraction with toluene or dichloromethane shall be performed.
The water/toluene volume ratio should not be greater than 20:1. Three consecutive extractions shall be carried out.
After extraction, the organic solvents containing water shall be dried before the concentration procedure.
Clean-up
For the determination of PCBs it is useful to separate them from PCDDs/PCDFs.
The purpose of clean-up procedures is to concentrate PCBs in the extracts and to remove interfering matrix components present in the raw extract, which may overload the separation method, disturb the quantification or otherwise severely impact the performance of the identification and quantification method.
Sample clean-up is dependent on the type of sample matrix which shall be removed.
Two or more of the following techniques can be combined in different orders for clean-up procedures.
a) Gel chromatography
b) Multilayer column liquid chromatography using silica with different activity grades and surface modifications.
To achieve sufficient quantification limits, the cleaned sample fraction(s) shall be concentrated to a small volume before quantification, but not less than 10 pi
Solvent volume reduction
To achieve sufficient quantification limits, the cleaned sample extract shall be concentrated before quantification.
The cleaned sample fraction(s) are concentrated to a smaller volume before quantification, this solution is the analitical sample
Though dioxin-like PCBs have high boiling points, vapour phase transfer mechanisms and aerosol formation during solvent evaporation might lead to substantial losses when concentrating volumes below 10 ml. We can use :
• Rotary evaporators : this equipment is used for volume reduction down to 10 ml .
Volumes should not be reduced to less than 1 ml.
• Turbovap 500 : for volume reduction from 200 ml to 0,5 ml
• Nitrogen flow : for solvent volume reduction from 5 ml to 25 pl.
3. Identification and quantification
PCBs are identified and quantified by high resolution gas chromatography-high resolution mass spectrometry (HRGC-HRMS). The combination of gas chromatography and mass spectrometry allows the
identification and quantification of 12 dioxin-like PCB cogeners and marker PCB cogeners in the extracts of emission sample by either retention time and/or mass. The gas chromatography gives information about identification of isomers(position of Cl), instead mass spectrometric is able to identify different cogeners Conclusion
PCBs are chemical substances which are persistent, bioaccumulate and pose a risk of causing
adverse effects to human health and the environment. Production was halted in 1977 due to concerns over environmental persistence and alleged health effects,some experiments now show this class of compounds as carcinogenic, even though the evidence of extreme toxicity is not all that clear.
For this reason, it is important to measure and to limit the releasing of this compoud in the enviroment.
In this project we have discussed how the PCB pollutants can be measured and we have shown briefly how we can treat different PCB-contaminated matrices.
Unfortunately, from a global point of view, there are indications that the production of
PCBs has not completely stopped in all countries, conseguently these technology can reduce only the concentration of PCB in the air.
The best methods to achieve the maximum result comes from our awareness, all contries should avoid the using and releasing of PCB, in this way we could save human and enviromental health.
