The role of UV-B on the degradation of PCDD/Fs and PAHs sorbed on surfaces of spruce (Picea abies (L.) Karst.) needles

Photodegradation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polycyclic aromatic hydrocarbons (PAHs) sorbed on surfaces of spruce (Picea abies (L.) Karst.) needles was investigated. The role of sunlight and, in particular, the role of short wavelength UV-B radiation were studied in a sun simulator under controlled environmental conditions. The photodegradation of PCDD/Fs and PAHs follows first-order kinetics. Simulated sunlight containing UV-B induced two phases of photodegradation kinetics for PCDD/Fs, whereas no distinct phases of the kinetics were observed for PAHs. UV-B radiation plays a much more important role on the photodegradation for PCDD/Fs than that for PAHs. Direct photolysis dominates the photodegradation of PCDD/Fs and PAHs.     

Biochemistry examinations and health disorder evaluation of Taiwanese living near incinerators and with low serum PCDD/Fs levels

The main objective of this study was to establish background levels of serum PCDD/Fs and biochemistry of residents living near municipal waste incinerators (MWIs) which had been operating between 1 and 8 years, and also to examine the association between the serum PCDD/Fs levels and health outcomes of interest. Information on medical history, life-style, and dietary habits was obtained by questionnaire interview. Significantly elevated levels of glucose and blood urea nitrogen (BUN) were found in those with low to high serum PCDD/Fs levels (p<0.05), and PCDD/Fs levels were found to be positively associated with glucose levels, and marginally with GGT levels even after adjusting for age, sex, BMI and smoking status. Although no conclusive findings on health disorder were associated with the accumulation of serum PCDD/Fs in our study participants, we suggest that the current biochemistry examinations only reflect partially the physiological change in glucose modulation and liver function. However, the low serum PCDD/Fs level does not seem to be sufficient in eliciting pathological process for diabetes or liver-related diseases. The findings suggest that the human body's biochemistry functions such as liver and glucose modulation were affected by PCDD/Fs exposure at even these low serum PCDD/Fs levels found in the general population. Other biochemical functions therefore should be further analyzed, especially for hormone-related and immune functions.     

Characterization of dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the atmosphere of different workplaces of a sinter plant

This study investigated concentrations, contents and congener profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in the workplaces of a sintering plant. Air samples were collected from the charging zone, the sintering zones of the sintering grate and the rough roll shredder, and the control room. The charging zone was found to have a higher total suspended particulate (TSP) but lower PCDD/F concentrations (=4969 microg nm(-3) and 7.61 pg nm(-3), respectively) than the sintering zone (=1422-1448 microg nm(-3) and 19.16-23.17 pg nm(-3), respectively). The TSP and PCDD/F concentrations were lowest in the control room (=98 microg nm(-3) and 1.75 pg nm(-3), respectively). However, the above concentrations were within the range of a typical urban-industrial area. Quite similar PCDD/F contents were found in particles in the sintering zones and control room (=11.72-14.30 and 15.85 ng g(-1), respectively) suggesting that the sintering zone and the control room are very similar. In both charging and sintering zones, 2,3,4,7,8-PeCDF contributed 40-60% to the total I-TEQ in both the gas phase and particle phase. However, in control room, both congeners 2,3,4,7,8-PeCDF and 2,3,7,8-TCDD were the main contributors; the later contributed 30% of the total I-TEQ in gas phase. In control room, the contribution of 2,3,7,8-TCDD to the total PCDD/F concentration in the gas phase greatly exceeded that in particle phase (=5.5% and 0.8%, respectively). Therefore, solutions must be sought to avoid the transfer of not only the particle-phase but also the gas-phase PCDD/Fs from the sintering zone to the control room in the future.     

Ozonation of naphthalene sulfonic acids in aqueous solutions: part II--relationships of their COD,TOC removal and the frontier orbital energies

This paper evaluated the COD, TOC removal and molecular frontier energies in the ozonation of naphthalene sulfonic acids (NSAs). It was found that both COD and TOC degradation of the 11 compounds followed the pseudo-first-order kinetic and the reaction rate constants with ozone varied widely. A linear relationship between logarithm of global COD degradation rate constant and the energy of the highest occupied molecular orbit, E(homo), was obtained for these NSAs with a regression coefficient of 0.88 and a slope of 0.4672 eV(-1). TOC degradation kinetics also reached similar results with a regression coefficient of 0.90 and a slope of 0.9336 eV(-1). The results of correlation analysis suggested that TOC and COD removal in ozonation of NSAs follow the frontier orbital theory and can be predicted by E(homo), which indicated that electrophilic effect was the main factor in the ozonation of NSAs. Therefore, it is possible to improve the biodegradability of dyestuff wastewater bearing mainly NSAs by ozonation at an accepted cost and evaluate the economy of ozonation process.     

Formation of PCDD/Fs from heating polyethylene with metal chlorides in the presence of air

This paper investigated the effect of inorganic chlorine on the formation of PCDD/Fs from heating polyethylene (PE) in the presence of air. There was an increase in the formation of PCDD/Fs with an increasing amount of metal chlorides except NaCl, which was not observed to have any effects on the formation of PCDD/Fs without the presence of catalysts. Although the levels of PCDD/Fs formation in this study have no relevance to full scale municipal solid waste incineration, the results of the present experiments can aid understanding of the mechanisms of the formation of PCDD/Fs from heating PE in the presence of metal chlorides.     

Dietary intake of dioxins and dioxin-like PCBs, due to the consumption of dairy products, fish/seafood and meat from Ismailia city, Egypt

Although dietary intake studies have been carried out extensively in most developed countries, to evaluate the health risks of PCDD/Fs and DL-PCBs, no data of this kind exists for Egypt. In this study, concentrations of PCDD/Fs and DL-PCBs were measured using HRGC/HRMS in the most contributing foodstuffs (dairy products, fish/seafood, and meat) randomly collected from Ismailia city, Egypt. The dietary intake of PCDD/Fs and DL-PCBs were subsequently determined, and compared with the most recent studies. To provide a primary estimation of the whole TEQ intake in Egypt if all the main food categories included, an estimation of the dietary intake (based on EU data) for some important and non-measured groups (cereals, vegetables/fruits, eggs and milk) was carried out. The calculated dietary intake based on the WHO assumption of 60 kg bw ranged from 3.69 to 4.0 pg WHO-TEQ/kg bw/day for PCDD/Fs and from, 6.04 to 6.68 pg WHO-TEQ/kg bw/day, if DL-PCBs were included. PCBs intake contributed about 40% of the total TEQ intake. Dairy products (mainly cheese) were the main contributor to the intake of PCDD/Fs (89%), while fish/seafood and meat have more or less the same percent share (5.4%). The dairy products contamination was the reason for our elevated dietary intake, as the content of PCDD/Fs and DL-PCBs is several times higher than in all the developed countries. The total intake (PCDD/Fs+DL-PCBs) due to consumption of dairy products, fish/seafood and meat, is close to that reported in EU countries at the beginning of 1980s, but much higher than all those mentioned in all the recent reports, and higher than the maximum WHO TDI of 4 pg TEQ/kg bw/day. A recalculation of the dietary intake to include not only our measured data but also the data for the non-measured groups, yielded a total intake in the range of 4.06-6.38 pg TEQ/kg bw/day for PCDD/Fs and a range of 6.59-9.98 pg TEQ/kg bw/day for total including PCBs. Results show that cereals and vegetables/fruits contribute significantly to PCDD/Fs TEQ intake in Egypt and play a more important role than fish/seafood and meat. This is the case even though the intake for cereals and vegetables/fruits based on EU data.     

Effects of forest fire on the level and distribution of PCDD/Fs and PAHs in soil

Forest fires are believed to produce polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs); however, there is no firm evidence supporting this conjecture. To address this issue, we investigated whether PCDD/Fs and polycyclic aromatic hydrocarbons (PAHs) are formed by forest fires. The present work takes the indirect approach of measuring the levels of PCDD/Fs and PAHs in soil and ash samples 1, 5 and 9 months after forest fires. To determine if PCDD/Fs or PAHs were formed during forest fires, the levels of PCDD/Fs and PAHs measured in the burnt soil samples were compared with those in the corresponding unburnt soil samples. One month after forest fires, the concentrations of PCDD/Fs and PAHs in burnt soils were higher than in the corresponding unburnt soils. In addition, the homologue profiles differed between the burnt and unburnt soils. Five months after forest fires, however, the concentrations of PCDD/Fs and PAHs in the burnt soils were similar to those in unburnt soils. The data presented here strongly suggest that PCDD/Fs and PAHs form during forest fires and are then introduced into the soil. The results further suggest that the ash resulting from the combustion of wood and other organic matter is the main agent influencing the concentration of PCDD/Fs and PAHs in the soil.     

Characteristics of PCDD/F congener distributions in gas/particulate phases and emissions from two municipal solid waste incinerators in Taiwan

Partitioning of PCDD/F (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofuran) congeners between gaseous and particulate phases and removal efficiencies of the existing air pollution control devices (APCDs) for PCDD/Fs at two large-scale municipal waste incinerators (MWIs) in Taiwan are evaluated via stack sampling and analysis. Two MWIs investigated are equipped with activated carbon injection (ACI) and selective catalytic reduction system (SCR) as major PCDD/F control devices, respectively. The average PCDD/F concentrations of stack gases are 2.35 and 1.49 ng/N m(3), and the international toxic equivalent quantity (TEQ) are 0.17 and 0.043 ng TEQ/N m(3) in MWI-A and MWI-B, respectively. The average removal efficiency of PCDD/Fs achieved with ACI+BF (bag filters) reaches 95% (MWI-A) while that achieved with the WS (wet scrubber)+SCR system reaches 99% (MWI-B). The results obtained on gas/particulate partitioning in flue gases indicate that particulate-phase PCDD/Fs accounted for 27.7% and 24.7% of the total PCDD/F concentrations at the outlets of cyclone (CY) and electrostatic precipitator (EP) for MWI-A and MWI-B, respectively. But the gas/particulate partitioning in flue gas after PCDD/Fs control devices is quite different in two MWIs. This study also indicates that total 2,3,7,8-substituted PCDD/F discharges are 142.3 microg TEQ/ton waste for MWI-A and 98.6 microg TEQ/ton waste for MWI-B, respectively.     

Interpreting the dioxin and furan profiles in the lichen Ramalina canariensis Steiner for monitoring air pollution

The purpose of this study was to compare the dioxin and furan (PCDD/F) profiles in lichens with those of air and soil. Lichen samples of the species Ramalina canariensis Steiner were collected from 44 different sites and analysed. The results were compared to PCDD/F air and soil profiles from bibliographic data concerning several countries and locations. When compared to other biomonitors (pine needles, vegetation, fruits), lichens were observed to accumulate greater concentrations of PCDD/Fs. The results showed that, although the concentrations of PCDD/Fs in lichens were at the same level of magnitude as those found for soils from the same country (197.5-1218.7 ng kg(-1) and 2.3-15.2 ng I-TEQ kg(-1)), the PCDD/Fs profiles do not reflect soil particle contamination. On the contrary, the PCDD/Fs lichen profiles seemed to be very similar to the ones in the air, at least for the diversity of the ones used for comparison in this study. These results indicated that lichens of the species R. canariensis are potential biomonitors of PCDD/F air pollution.     

Mobility and profiles of polychlorinated dibenzo-p-dioxins and dibenzofurans in sediment of Ya-Er Lake, China

The sediment of Ya-Er Lake had been heavily polluted by polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from the former chloralkali industry. The total amounts of PCDD/Fs and I-TEQ decreased along the water flow direction and also decreased from top to bottom layers of sediment cores. Sediment of Pond 1 was dominated by PCDF. especially TCDF. In contrast, in the other four ponds, PCDD dominated in all layers and octachlorinated dibenzo-p-dioxin (OCDD) predominated in all of the homologues. When homologue profiles from sediments and water samples were compared using principal component analysis (PCA), the first two principal components represented 95.2% of the variance in the data. The first component explained 75.9% of the variance and the second one 19.3%. Two clusters were most distinct, presenting a shift in PCDD/Fs composition from PCDF to heptachlorinated dibenzo-p-dioxin (HpCDD) and OCDD in sediments and water from Pond I to Ponds 2-5. The pattern variation between Pond I and Ponds 2-5 in Ya-Er Lake was most likely due to the change of process in the chemical plant after the dams between the ponds were built. The results of the present study also showed that log Koc of PCDD/Fs calculated from data of sediment and water in the field were comparable with theoretical log Koc. The results also implied that the concentrations of PCDD/Fs in water and sediments could be predicted from each other by log Koc.     

Modelling the long-term fate of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) in the Grenland Fjords, Norway

The development and application of a predictive fate model (DIG--Dioxins in Grenland) for polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) in the marine environment of the Norwegian Grenland Fjords are described. The objective of the modelling study was to predict long-term future changes in PCDD/F concentrations in the fjord following the cessation of point source emissions. To assess the reliability of the model, the model performance was evaluated by comparing model results to field measurements collected between 1989 and 2001. Model bias (defined as the ratio of median predicted concentration and median observed concentration) for prediction of concentrations for three different PCDD/F congeners (2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 1,2,3,6,7,8-hexadibenzofuran (HxCDF) and octachlorodibenzofuran (OCDF)) in the fjord was between 0.53 and 24, which was deemed a satisfactory result for models of this type. The model was run to determine the dynamic change in concentrations between 1950 and 2050 and to examine the key fluxes of PCDD/Fs in the fjord. Between 1990 and 2050 sediment concentrations of TCDD, HxCDF and OCDF were predicted to fall at fairly constant but gradually slowing rates to concentrations 52, 98 and 88 times lower, respectively, of their 1990 values. Losses of PCDD/Fs from the bottom sediments in the Frierfjord were predicted to be a combination of sediment burial and net resuspension to the water column. Sediment burial was shown to be relatively more important in the fjord's deep-water sediments, whereas resuspension was relatively more important in the shallow sediments. For the shallower sediments, a net water-to-sediment flux was predicted for all three congeners up until the mid-1970s, when emission reductions were initiated, and thereafter a net sediment-to-water flux was predicted. The shallow sediments acted as net sources to the deeper sediments and to the fishing areas in the outer fjord.     

Effect of chlorine content in feeding wastes of incineration on the emission of polychlorinated dibenzo-p-dioxins/dibenzofurans

This study attempts to clarify the effects of chlorine content in waste on the formation mechanisms of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in full scale incinerators by proposing and using the principal component analysis (PCA) to compare the congener profiles of PCDD/Fs in the stack flue gases of 17 emission sources, including incinerators and vehicles. Four incinerators, among these 17 emission sources, were sampled and analyzed in this study, and the data for the other 13 emission sources were selected from previous studies. These 17 emission sources can be classified into four categories, including medical waste incinerators (MWIs, H1-H5), municipal solid waste incinerators (MSWIs, M1-M8), vehicle fuel combustion (unleaded gas-fueled vehicles, UGFV; diesel-fueled vehicles, DFV, n = 2) and polyvinylchloride (PVC) facility vent combustors (PVC1 and PVC2, n = 2). PCA was conducted for these emission sources with the fractions of 17 2,3,7,8-congeners in the stack flue gases as variables to clarify the effect of chlorine content in feeding wastes on the emission of PCDD/Fs. From the results of PCA, we extrapolated that the threshold value of the chlorine content was at 0.8-1.1%, and the formation mechanisms of PCDD/Fs are influenced first by whether the chlorine content in the feeding waste is over or below the threshold value then by other factors, which furnaces or APCDs represent. When the chlorine level in the waste is below the threshold value at 0.8-1.1%, the formation of PCDDs dominates, probably because the chlorine is used to chlorinate the non-substituted phenol to produce chlorophenols, which are important precursors for PCDDs. rather than chlorinate the dibenzofuran. While the chlorine level in the waste exceeds this threshold (0.8-1.1%), the rates of formation of PCDFs increase faster than those of PCDDs, probably because the chlorine content in the waste contributes to the deterioration of combustion conditions, and many products of incomplete combustion (PICs) like PAHs, will grow to a substantial level. When PCDD/Fs are formed from PAHs, the formation rates of PCDFs are higher than those of PCDDs.     

Lipid peroxidation and antioxidant status in workers exposed to PCDD/Fs of metal recovery plants

Secondary copper smelters, which primarily utilize the waste materials that contain organic impurities, and the zinc recovery plant, which handles mostly fly ash and slag from the iron and steel industry, are major emission sources of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in Taiwan. In this study, we compared the levels of erythrocyte glutathione (GSH), erythrocyte superoxide dismutase (SOD) and plasma malondialdehyde (MDA) in workers at a secondary copper smelting plant and a zinc recovery plant who may have been exposed to PCDD/Fs. Though the PCDD/F levels were higher in workers of zinc recovery plant than those of secondary copper smelting plant, no significant difference was found for serum PCDD/F levels between the two kinds of plants. We observed a significant difference in plasma MDA levels between workers at the zinc recovery plant (2.54 microM) and those at the copper smelting plant (1.79 microM). There was and a significant positive correlation between plasma MDA levels and the PCDD/Fs levels. In addition, we observed that the MDA levels were not affected by smoking and exercise status. Therefore, the data suggest that the MDA levels of the metal recovery workers are influenced by their PCDD/F exposure. The erythrocyte SOD activity in workers from the zinc recovery plant was marginally higher than that from the secondary copper plant (196 vs. 146 units/ml, p<0.06). In both plants, large variations in the MDA and SOD levels were found, especially in the high-PCDD/Fs-exposure group, which may be attributed, at least partially, to the differences in smoking status and the number of cigarettes smoked. Overall, our results indicate a higher oxidative stress in workers of the zinc recovery plant than in workers of the secondary copper smelting plant in Taiwan.     

Concentrations of polybrominated diphenyl ethers, polychlorinated dibenzo-p-dioxins and dibenzofurans, and polychlorinated biphenyls in human blood samples from Korea

Analysis of blood samples is an effective way of evaluating contamination by persistent pollutants such as polybrominated diphenyl ethers (PBDEs), polychlorinated dibenzo-p-dioxin/furans (PCDD/Fs), and polychlorinated biphenyls (PCBs) in human population. Concentrations of PBDEs, PCDD/Fs and PCBs were measured in the blood of laborers (n = 13) working full time in two different municipal waste incinerator (MWI) plants and residents from the general population (n = 22) living in areas near MWIs in Korea. The concentrations of PBDEs were found to be slightly higher in the blood of incineration workers (8.61-46.05 ng/g lipid; mean, 19.33 ng/g lipid; median, 15.94 ng/g lipid) in comparison to that of residents from the general population (7.24-28.89 ng/g lipid; mean, 15.06 ng/g lipid; median, 14.34 ng/g lipid). The total average PCDD/Fs and PCB TEQ concentration was 20.11 pg/g lipid, averaged over incineration workers (17.73 pg/g lipid) and the general population (21.52 pg/g lipid). In addition, the average total crude concentration of PCDD/Fs was 7.40 ng/g lipids, which was 4.1 times greater than for PBDEs. Congener specific analysis confirmed that BDE 47 was a predictive indicator for total PBDE concentration (correlation coefficient r = 0.912), and that PCB 153 was a predictive indicator for total PCB concentration (r = 0.967). The PBDE levels in human blood in Korea are much higher than those reported in other countries. The presence of the BDE 183 congener was characteristic in the blood of workers from an electronic dismantling facility in MWIs.     

Profile of PCDD/F levels in serum of general Taiwanese between different gender, age and smoking status

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are persistent organic pollutants that are resistant to environmental and biological degradation and disperse into various environmental compartments throughout the atmosphere, water, soil, sediments, and food. Many factors, such as age, sex, lifestyle, and metabolism, can explain the distribution of serum levels after humans exposed to PCDD/Fs. The aim of our study was therefore to investigate the PCDD/Fs distribution and profile of the general population in northern Taiwan. All selected subjects were between 18 and 65 years old and proportionally chosen from five age groups based on population distribution of each district or county. Higher serum PCDD/F levels were found in the elder than in the young, and in females than in males. In addition, nonsmokers and passive smokers showed higher levels of PCDD/Fs than active smokers. The serum concentrations of 2,3,4,7,8-PeCDF; 1,2,3,7,8-PeCDD; and 1,2,3,6,7,8-HxCDD in some subjects seemed to increase with their age, which might have been caused by the longer half-lives of these substances. In future studies, more information about food consumption, occupational exposure, open-combustion, and other potential factors needs to be collected to clarify the most important factors affecting the distribution of serum PCDD/Fs in the general population in Taiwan.     

Some laboratory experimental designs for obtaining dynamic property data on dioxins

The presence of polychlorinated p-dibenzodioxins and polychlorinated dibenzofurans (hereafter PCDD/F) in municipal waste incinerator effluents has sparked a variety of laboratory investigations in the last few years in the hope of learning more about the formation and destruction mechanisms of these compounds. In the course of the investigations a variety of approaches have been employed. It is the purpose of this paper to review these designs and to comment on them in general as well as in specifics. Since under the conditions of interest the quantities of PCDD/Fs are miniscule compared with other products and reactants and because there are nearly 200 congeners, quantitative information is difficult and expensive to obtain. A second aspect concerns the reaction rates involved. No intrinsic kinetic studies have been conducted and no intrinsic values for PCDD/F rates of formation exist. Such information will be necessary, however. As will be shown below, there seems to exist a basic conflict between reaction rates as may be inferred from some laboratory experiments and rates seemingly required by the time/temperature histories of gases and particles in incinerators. The paper is divided into four major parts: homogeneous formation and destruction, heterogeneous formation and destruction, comments on discrepancies, and suggested designs.     

Chemical inhibition of PCDD/F formation in incineration processes

This review summarises results of our pilot-scale experiments to find suitable inhibitors for preventing the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) during waste incineration and to specify the role of the main factors affecting the inhibition process, and is based on doctoral dissertation of Ruokoja?rvi (2002). Results of previous experiments reported by other researchers are also presented and compared with ours. The detailed aims of our experiments were (1) to compare the effects of different inhibitors on PCDD/F formation during incineration in a pilot plant, (2) to investigate the role of the particle size distribution of the flue gas on the inhibition of PCDD/Fs, and (3) to find the main parameters affecting PCDD/F inhibition in waste incineration. Prevention of the formation of PCDD/Fs with chemical inhibitors and the effects of different supply points, feed temperatures and process parameters were studied in a pilot scale incinerator (50 kW) using light heating oil and refuse-derived fuel as test fuels. Various concentrations of the gaseous inhibitors (sulfur dioxide, ammonia, dimethylamine and methyl mercaptan) were sprayed into the flue gases after the furnace, in addition to which urea was dissolved in water and injected in at different concentrations. The residence time of the flue gas between the furnace and the PCDD/F sampling point was varied in the tests. In another set of urea tests, urea-water solutions at three concentrations were mixed with the RDF prior to incineration. PCDD/F and chlorophenol concentrations, together with other flue gas parameters (e.g. temperature, O2, CO, CO2 and NO), were analysed in the cooling flue gases. The gaseous and liquid inhibitors both notably reduced PCDD/F concentrations in the flue gas, the reductions achieved with the gaseous inhibitors varying from 50 to 78%, with dimethyl amine the most effective, while that produced with urea was up to 90%. The PCDD/F reductions were greater at increased inhibitor concentrations and with increased residence time of the flue gas between the furnace and the sampling point. PCDD/F concentrations in the particle phase decreased much more markedly than those in the gas phase. The urea inhibitor did not alter the particle size distribution of the PCDD/Fs when the amount of inhibitor was adequate. Chemical inhibitors seem to offer a very promising technique for preventing the formation of PCDD/Fs in waste incineration. The addition of urea to the fuel before combustion proved to be very effective approach and could be a useful technique even in the full-scale incinerators.     

Secondary exposure to dioxins through exposure to PCP and its derivatives.

This study discusses the potential exposure of occupational workers and general consumers in the European Union (EU) to polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) caused by exposure to pentachlorophenol (PCP) and its derivatives. A synthesis of reported exposure data relating exposure to PCP and its derivatives in an occupational setting has indicated that the PCDD/F intake for exposure in the 1990s averaged over a lifetime is likely to be in the order of 0.02-1 pg I-TEQ kg-1 bw day-1 with actual exposures more likely to occur at the lower end of the range, around the median of 0.16 pg I-TEQ kg-1 bw day-1. Workers who have experienced past exposure to PCP and its derivatives especially in the early to mid 1980s, will have been subjected to higher exposures to PCDD/Fs due to the generally higher concentrations of PCDD/Fs in PCP products at that time. Exposure to PCP and its derivatives via the food chain is judged to be the most significant intake route of PCDD/Fs into consumers. The ingestion of milk and dairy products obtained from cows grazed on pasture dressed with sewage sludge has the potential to raise the average daily intake of PCDD/Fs via the diet by about 40% if all foods consumed derived from sludge amended soil. To the extent quantifiable, exposure to PCP in an occupational setting contributed approximately 16% as a median to the overall background exposure to PCDD/Fs, while for consumers this contribution ranged from 2 to 60% depending on the exposure to sludge amended foods.