World Health Organization Toxic Equivalency Research Articles

Gasification-MILD combustion technology with ash-sludge recirculation for reducing multi-phase net dioxin discharges from a waste incineration.

This study addresses the challenge of reducing "net" toxic pollutant discharge, specifically dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), while minimizing the energy consumption and costs associated with detoxification. Our research focuses on reintroducing fly ash and scrubber sludge (ASR) into a hazardous waste thermal treatment system equipped with gasification-intense low oxygen dilution (GASMILD) and an advanced air pollution control system (APCS). This approach yielded a remarkable PCDD/F removal efficiency exceeding 99.9% for both mass and toxic equivalent (TEQ), achieving a net destruction of PCDD/Fs within the system. The success can be attributed to the ASR material's richness in ultrafine particles, which act as nucleation cores during combustion, promoting particle growth and enhancing the capture of PCDD/Fs in the APCS. This leads to a significant reduction (over 93%) in both PCDD/F mass and World Health Organization-toxic equivalent (WHO-TEQ) concentration in the flue gas. While a phase transition of gaseous PCDD/Fs within the APCS caused a shift in the particle size distribution towards larger particles, the overall PCDD/F mass concentration in the stack emissions remained lower with ASR. Notably, the reintroduced PCDD/Fs tend to deposit in the nasal region of the respiratory tract, potentially reducing the health risks associated with deeper lung deposition. This research demonstrates the effectiveness of ASR in achieving net PCDD/F destruction within a GASMILD combustion system, offering a promising strategy for cleaner and more sustainable waste management practices. From a managerial perspective, this approach provides a cost-effective solution for PCDD/F mitigation, contributing to reduced emissions and improved public health.

Polychlorinated dibenzo-p-dioxins, dibenzofurans and dioxin-like polychlorinated biphenyls in bivalve molluscs. Risk to Polish consumers?

Concentrations of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (DL-PCBs) were investigated in six species of bivalve mollusc purchased on the Polish retail market. The risk to consumers was calculated as a percentage of the tolerable weekly intake (TWI) (2 pg World Health Organization toxic equivalent (WHO-TEQ) kg-1 body weight (b.w.)). Altogether 32 samples were analysed using an isotope dilution technique with high resolution gas chromatography coupled with high resolution mass spectrometry. Low levels of all analysed compounds were found. The range of PCDD/Fs was 0.08-0.37 pg WHO-TEQ g-1 of wet weight (w.w.) and 0.04-0.41 pg WHO-TEQ g-1 w.w. for DL-PCBs. The highest concentrations of all analysed compounds were found in Pacific oysters, at 0.30 pg WHO-TEQ g-1 w.w. for the sum of PCDD/Fs and 0.19 pg WHO-TEQ g-1 for the sum of DL-PCBs. These concentrations were 2-4 times higher than those detected in the other analysed mollusc species. Different species-dependent congener profiles were observed for PCDD/F concentrations, while PCB congener concentration profiles were species independent. The risk to consumers was assessed relating theoretical intakes of PCDD/Fs and DL-PCBs per 25, 50 and 100 g of consumption of molluscs per week to the TWI. Taking into account the low consumption of molluscs in Poland and low concentrations of analysed compounds, neither adults nor children are likely to exceed the TWI by ingestion of food in this category.

Determination of the relative potencies of brominated dioxins for risk assessment in aquatic environments using the early-life stage of Japanese medaka

World Health Organization toxic equivalency factors (WHO-TEFs) are recommended for risk management of brominated dioxins in aquatic environments because limited information is available on their toxicity to fish. To validate this approach, we obtained the relative potencies of polybrominated dibenzo-p-dioxins and polybrominated dibenzofurans and mixed-halogenated furans (PXDF, X = Cl/Br) against 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) based on their toxicity to the early-life stage of Japanese medaka (Oryzias latipes). 2,3,7,8-substituted brominated dibenzofurans caused typical dioxin exposure effects, such as blue-sac disease. The TCDD-relative potency factors (REPs) of test substances were calculated based on the concentrations in water and eggs that caused 20% lethality on day 28 post-fertilization, and were in the order of: 2-chloro-3,7,8-tribromodibenzofuran (REPwater 3.3, REPegg 4.6) > 2,3,7,8-tetrabromodibenzofuran (0.85, 0.92) > 2,3,4,7,8-pentabromodibenzofuran (0.053, 0.55) > 1,2,3,7,8-pentabromodibenzofuran (0.0091, 0.19). The transfer rate from water to eggs was lower for pentabrominated furans than tetrabrominated congeners, and was expected to decrease with the log Kow of the test substance. Although the REPegg value can be used to compare the toxicity potential of brominated dioxins, REPwater may be more suitable for environmental risk assessment because the uptake potential of these compounds from water should be considered. This study is the first to report higher toxicity of a PXDF congener compared with TCDD in vivo, further investigations of the toxicity of mixed-halogenated dioxins and environmental behavior are necessary for environmental risk assessment.

Limited mobility of dioxins near San Jacinto super fund site (waste pit) in the Houston Ship Channel, Texas due to strong sediment sorption

Sediments from a waste pit in Houston Ship Channel (HSC) were characterized using a number of molecular markers of natural organic matter fractions (e.g., pyrogenic carbon residues, PAHs, lignins), in addition to dioxins, in order to test the hypothesis that the dispersal and mobility of dioxins from the waste pit in the San Jacinto River is minimal. Station SG-6, sampled at the site of the submerged waste pit, had the highest dioxin/furan concentrations reported for the Houston Ship Channel/Galveston Bay (HSC/GB) system (10,000–46,000 pg/g), which translated into some of the highest reported World Health Organization Toxic Equivalents (TEQs: 2000–11,000 pg/g) in HSC sediments. Using a multi-tracer approach, this study confirmed our hypothesis that sludges from chlorinated pulps are a very likely source of dioxins/furans to this pit. However, this material also contained large quantities of additional hydrophobic organic contaminants (PAHs) and pyrogenic markers (soot-BC, levoglucosan), pointing to the co-occurrence of petroleum hydrocarbons and combustion byproducts. Comparison of dioxin/furan signatures in the waste pit with those from sediments of the HSC and a control site suggests that the remobilization of contaminated particles did not occur beyond the close vicinity of the pit itself. The dioxins/furans in sediments outside the waste pit within the HSC are rather from other diffuse inputs, entering the sedimentary environment through the air and water, and which are comprised of a mixture of industrial and municipal sources. Fingerprinting of waste pit dioxins indicates that their composition is typical of pulp and paper sources. Measured pore water concentrations were 1 order of magnitude lower than estimated values, calculated from a multiphase sorption model, indicating low mobility of dioxins within the waste pit. This is likely accomplished by co-occurring and strong sorbing pyrogenic and petrogenic residues in the waste pit, which tend to keep dioxins strongly sorbed to particles.

Characteristics, distribution and sources of polychlorinated biphenyls (PCBs) in coastal sediments from the heavily industrialized area of Asalouyeh, Iran.

In this research, the levels of polychlorinated biphenyls (PCBs) were investigated in the marine sediments of Asaluyeh harbor, in the Persian Gulf. The samples were taken from industrial, semi-industrial and urban regions. The mean concentration levels of total (Σ) 18 detected PCBs were 514.32, 144.67 and 31.6 pg/g dw for the industrial, semi-industrial and urban sampling stations, respectively. Based on a multivariate statistical analysis, it was found that high contamination levels of PCBs in sediments collected along the Persian Gulf were associated with releases from local industries. Total organic carbon (TOC) content was significantly and positively correlated with the concentrations of PCB congeners. World Health Organization toxic equivalents (TEQs) for PCBs ranged from 0.04 to 2.66 pg TEQ/g dry weight (dw) in the coastal sediments. The TEQ values in this study were higher than many reported worldwide in the literature for sediments. This suggests that there are high levels of contamination in the area due to industrial and other human activities.

Characteristics of PCDDs/PCDFs in stack gas from medical waste incinerators

Toxic polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in 45 stack gas samples were measured from 19 medical waste incinerators in South Korea using high-resolution gas chromatography equipped with a high-resolution mass spectrometer. The average concentrations of the sum of 17 toxic PCDD/PCDF congeners emitted from the medical waste incinerators ranged from 0.153 to 101.9 ng/Sm3. Based on the World Health Organization toxic equivalency factor, they ranged from 0.007 to 5.437 ng-TEQ/Sm3. The congener patterns of PCDDs/PCDFs were described using principal component analysis and presented four patterns. In the evaluation of annual average total TEQ concentrations, outlying stack gas samples were excluded. In this study, the number of chlorine substitutions was evaluated as an important factor in congener patterns. Coefficient of determination values were employed for evaluation of correlation between PCDDs and PCDFs. 1,2,3,4,6,7,8-HpCDF was measured as the most emitted congener, while 2,3,4,7,8-PeCDF was the greatest TEQ contributor.

Separate screening of brominated and chlorinated dioxins in field samples using in vitro reporter gene assays with rat and mouse hepatoma cell lines

In 2011, a joint World Health Organization (WHO) and United Nations Environment Programme expert panel recommended the use of the WHO toxicity equivalency factor (TEF) scheme for assessment of the human health risks of brominated dioxins which have different sources from chlorinated dioxins. Therefore, WHO toxic equivalents (TEQs) should be determined for both chlorinated and brominated dioxins. As alternative to the conventional but time-consuming dioxin analysis using gas chromatography high-resolution mass spectrometry, we have developed a screening method involving cleanup and separation of brominated dioxins from chlorinated dioxins in field samples and subsequent analysis by CALUX (chemically activated luciferase expression) assays which are in vitro reporter gene assays detecting dioxin-like compounds. Cleanup and separation were accomplished with silica gel columns impregnated with 55% sulfuric acid and with 10% silver nitrate, respectively, and the average recoveries of the major contributors to the WHO-TEQs were approximately 90%. The CALUX 2,3,7,8-TCDD equivalents (CALUX-TEQs) derived from all the dioxin-like compounds in the cleanup fractions of the field samples (n = 24) were measured by means of the CALUX assays, indicating significant positive correlations between the WHO-TEQs and CALUX-TEQs (r ≥ 0.969, P < 0.001). We found that the ratios of the chlorinated dioxin–derived WHO-TEQs to the brominated dioxin–derived WHO-TEQs were strongly positively correlated with the ratios of the CALUX-TEQs derived from the chlorinated dioxin fractions to the CALUX-TEQs derived from the brominated dioxin fractions (r ≥ 0.833, P < 0.001). These results suggest that our method will be useful for estimating the contributions of chlorinated and brominated dioxins to WHO-TEQs.

Dioxins/furans and PCBs in Canadian human milk: 2008–2011

Human milk was collected between 2008 and 2011 as part of the Maternal – Infant Research on Environmental Chemicals (MIREC) study that was initiated to establish Canadian national estimates of maternal and infant exposure to a broad suite of environmental contaminants (e.g., persistent organic pollutants [POPs], trace elements, phthalates, etc.). Among the 1017 human milk samples collected, 298 were analysed for polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs). World Health Organization (WHO) toxic equivalency concentrations (WHO TEQ2005) for PCDD/F+dioxin-like (DL) PCB ranged from 2.2pg TEQ2005 g−1 lipid to 27pg TEQ2005 g−1 lipid. The relative contribution of PCDDs to the overall WHO TEQ2005 (PCDD/F+DL PCB) has decreased from earlier investigations into POP levels in Canadian human milk. Significantly higher PCB concentrations were observed in milk from women born in Europe relative to those born in Canada (p<0.001), in contrast to results for the PCDD/Fs (p=0.496). Age was found to significantly impact milk ∑PCB concentrations (p=0.018), with elevated concentrations observed in milk from women >30years relative to those <30years of age. While this trend was also observed for the PCDD/Fs, this relationship was impacted by parity. WHO TEQ2005 concentrations were significantly higher in milk from primiparous women (p=0.019) and those >30years relative to those <30years of age (p<0.001). No significant differences were associated with education level or pre-pregnancy body mass index. PCB and PCDD/F concentrations have continued to decline in Canadian human milk since the last sampling of human milk was performed.

Persistent organic pollutants in the Antarctic coastal environment and their bioaccumulation in penguins

Persistent organic pollutants (POPs), including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), polychlorinated biphenyls (PCBs), polybrominated dibenzo-p-dioxins and dibenzofurans (PBDD/Fs), polybrominated biphenyls (PBBs), and polybrominated diphenyl ethers (PBDEs), have been identified in penguins, lichens, soils, and ornithogenic soils in the Antarctic coastal environment in this study. To the best of our knowledge, no previous study has reported PBDD/F and PBB data from Antarctica. The POP mass contents in penguins were in the following order: PCBs >> PBDEs >> PCDD/Fs; PCBs were the dominant pollutants (6310–144,000 pg/g-lipid), with World Health Organization toxic equivalency values being 2–14 times higher than those of PCDD/Fs. Long-range atmospheric transport is the most primary route by which POPs travel to Antarctica; however, local sources, such as research activities and penguin colonies, also influence POP distribution in the local Antarctic environment. In penguins, the biomagnification factor (BMF) of PCBs was 61.3–3760, considerably higher than that for other POPs. According to BMF data in Adélie penguins, hydrophobic PBDE congeners were more biomagnified at log Kow > 6, and levels decreased at log Kow > 7.5 because larger molecular sizes inhibited transfer across cell membranes.

A four-year survey in the farming region of Chile, occurrence and human exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans, and dioxin -like polychlorinated biphenyls in different raw meats

For the first time in South America, a four-year survey (2011–2014) was conducted to assess the occurrence of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs) in different raw meats (bovine, pork, ovine, chicken, and turkey) sampled from ten of the fifteen regions of Chile. When expressed as pg World Health Organization Toxic Equivalent (WHO-TEQ2005)g−1 fat, the highest PCDD/F values for each species were 0.54 (bovine-2012), 0.27 (pork-2013), 0.23 (ovine-2011), 0.61 (chickens-2013), and 0.34 (turkey-2012). The highest mean dl-PCBs levels were 0.18 (bovine-2011), 0.05 (pork-2014), 0.13 (ovine-2011), 0.1 (chicken-2014), and 0.21 (turkey-2013). Penta- and tetra-chlorinated congeners dominated PCDD/F WHO-TEQ2005 profiles during the survey, while PCB 126 dominated dl-PCBs profiles. Statistically significant interspecies differences were found. Dietary intake was also estimated, and the highest total PCDD/F and dl-PCBs values, found in poultry meat, were 0.09pgWHO-TEQ2005kg−1bwd−1 (2013) for adults and 0.36pgWHO-TEQ2005kg−1bwd−1 (2013) for children. The concentrations and dietary intakes for the studied compounds in raw meat were below international and national maximum permitted limits.

Temporal trend of polychlorinated dibenzo-p-dioxin/polychlorinated dibenzofuran and dioxin like-polychlorinated biphenyl concentrations in food from Taiwan markets during 2004–2012

The levels of polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzofuran (PCDF) or polychlorinated biphenyl (PCB) in foodstuffs have decreased over the past decade in many countries. However, the trend for the levels of these compounds in foodstuffs in Taiwan remains unknown. In this study, we compared the distribution of PCDD/F and PCB in nine foodstuff categories acquired from Taiwan markets from 2004 to 2012. The levels expressed as World Health Organization toxic equivalents (WHO-TEQs) in the different foodstuffs tested were as follows: fish, average 0.463 pg WHO98-TEQ/g sample > seafood, 0.163 pg WHO98-TEQ/g > eggs, 0.150 pg WHO98-TEQ/g > oils, 0.126 pg WHO98-TEQ/g > meats, 0.095 pg WHO98-TEQ/g > dairy products, 0.054 pg WHO98-TEQ/g > cereals, 0.017 pg WHO98-TEQ/g > vegetables, 0.013 pg WHO98-TEQ/g > fruits, 0.009 pg WHO98-TEQ/g. Levels were particularly high in crab (average: 0.6 pg WHO98-TEQ/g sample (1.243 pg WHO98-TEQ/g sample) and large marine fish (0.6). In Taiwan, a decreasing trend of PCDD/Fs or dioxin-like PCBs (dl-PCBs) was observed in meat, dairy, eggs, and vegetables, whereas an elevated trend was observed in cereals or the levels were nearly equal in fruits and oils at alternative time shift. Dl-PCBs contributed to 60–65% toxicity equivalence levels in fish and seafood, but only to 13–40% in meat and cereal samples. The decreasing trend was consistent with the results in other countries; however, the trends in cereals, fruits, and oils were in contrast to previous results reported in other countries. Cereals and fruits are important crops in southern Taiwan, and the local pollution generated by industries or incinerators may seriously affect the distribution of PCDD/Fs and dl-PCBs. To ensure food safety, a risk assessment for residents living in different areas should be adopted for all food categories simultaneously in the future.

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in municipal and industrial effluents

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) were quantified in 45 effluent samples in the Houston Ship Channel (HSC) system in Texas. Total PCDD/F concentrations ranged from 0.16 to 13.23pgL−1 in the dissolved phase and from 0.79 to 682.27pgL−1 in the suspended phase. Generally, industrial facilities contained more PCDD/F contamination than municipal wastewater treatment plants or refuse facilities. World Health Organization Toxic Equivalents (WHO-TEQs) ranged from 0.007 to 0.279pgL−1 in the dissolved phase and 0.021–1.851pgL−1 in the suspended phase. The major TEQ contributor was 2,3,7,8-TCDD and overall, TEQs were greatest in industrial effluents. A correlation between high solids and high PCDD/F concentrations was observed and based on the results obtained in this study, the abundance of suspended solids may have largely contributed to high PCDD/F contamination in the suspended phase. Homolog profiles revealed that PCDD/F contamination increased with increasing chlorination and the highest concentrations were primarily from the octa-chlorinated congeners (OCDD/F) in both the dissolved and suspended phase.

Passive air sampling for determining the levels of ambient PCDD/Fs and their seasonal and spatial variations and inhalation risk in Shanghai, China.

The seasonal and spatial variations, compositional profiles, and possible sources of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) in ambient air samples in Shanghai of China were investigated by passive air samplers, and the potential inhalation risks posed by these chemicals were evaluated. The following results were obtained: (1) The World Health Organization (WHO) toxic equivalency (TEQ) values for PCDD/Fs were in the range of 10.8-259fgm(-3) (mean 63.4fgm(-3)) in summer and 24.1-154fgm(-3) (mean 83.4fgm(-3)) in winter. Atmospheric PCDD/F levels were in the following order: industrial areas > commercial and residential areas > rural areas. (2) 2,3,4,7,8-PeCDF (24%), 2,3,7,8-TeCDD (16%), 1,2,3,7,8-PeCDD (13%), and 2,3,7,8-TeCDF (12%) were the predominant contributors to the TEQ of PCDD/Fs. (3) There was a slight seasonal trend with higher TEQ values in winter than in summer, which could be related to seasonal variations in the dispersion of PCDD/Fs in ambient air. (4) The children's daily intake was at the lower end of the range for the tolerable daily intake of PCDD/Fs recommended by WHO, which indicates that the inhalation risk of PCDD/Fs for local residents in Shanghai is relatively low.

Consensus toxicity factors for polychlorinated dibenzo-p-dioxins, dibenzofurans, and biphenyls combining in silico models and extensive in vitro screening of AhR-mediated effects in human and rodent cells.

Consensus toxicity factors (CTFs) were developed as a novel approach to establish toxicity factors for risk assessment of dioxin-like compounds (DLCs). Eighteen polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/Fs), and biphenyls (PCBs) with assigned World Health Organization toxic equivalency factors (WHO-TEFs) and two additional PCBs were screened in 17 human and rodent bioassays to assess their induction of aryl hydrocarbon receptor-related responses. For each bioassay and compound, relative effect potency values (REPs) compared to 2,3,7,8-tetrachlorodibenzo-p-dioxin were calculated and analyzed. The responses in the human and rodent cell bioassays generally differed. Most notably, the human cell models responded only weakly to PCBs, with 3,3',4,4',5-pentachlorobiphenyl (PCB126) being the only PCB that frequently evoked sufficiently strong responses in human cells to permit us to calculate REP values. Calculated REPs for PCB126 were more than 30 times lower than the WHO-TEF value for PCB126. CTFs were calculated using score and loading vectors from a principal component analysis to establish the ranking of the compounds and, by rescaling, also to provide numerical differences between the different congeners corresponding to the TEF scheme. The CTFs were based on rat and human bioassay data and indicated a significant deviation for PCBs but also for certain PCDD/Fs from the WHO-TEF values. The human CTFs for 2,3,4,7,8-pentachlorodibenzofuran, 1,2,3,4,7,8-hexachlorodibenzofuran, 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin, and 1,2,3,4,7,8,9-heptachlorodibenzofuran were up to 10 times greater than their WHO-TEF values. Quantitative structure-activity relationship models were used to predict CTFs for untested WHO-TEF compounds, suggesting that the WHO-TEF value for 1,2,3,7,8-pentachlorodibenzofuran could be underestimated by an order of magnitude for both human and rodent models. Our results indicate that the CTF approach provides a powerful tool for condensing data from batteries of screening tests using compounds with similar mechanisms of action, which can be used to improve risk assessment of DLCs.

Assessment of dioxins and dioxin-like polychlorinated biphenyls in the palm oil supply chains

Samples of palm oil and palm kernel oil (PKO) products were collected from two palm oil processing premises which were named as premise A and B. These samples were then analysed for dioxins and dioxin-like polychlorinated biphenyls (PCBs) content. The concentration of dioxins in the palm oil and PKO samples from premise A ranged from 0.128 World Health Organization-toxic equivalency (WHO-TEQ) pg/g fat to 0.189 WHO-TEQ pg/g fat while the concentration in samples collected from premise B ranged from 0.149 WHO-TEQ pg/g fat to 0.540 WHO-TEQ pg/g fat. Meanwhile, dioxin-like PCBs concentration ranged from 0.336 WHO-TEQ pg/g fat to 0.546 WHO-TEQ pg/g fat for premise A and 0.345 WHO-TEQ pg/g fat to 0.346 WHO-TEQ pg/g fat for premise B. The total numbers of samples analysed were 35 and the levels exhibited were below the maximum level of 0.75 WHO-TEQ pg/g fat and 1.25 WHO-TEQ pg/g fat imposed by the European Commission for dioxins and the sum of dioxins + dioxin-like PCBs content in vegetable oils.

Polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polybrominated diphenyl ethers in sediments and fish species from the Murchison Bay of Lake Victoria, Uganda

Polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and polybrominated diphenyl ethers (PBDEs) were analyzed in sediments and fish from the Murchison Bay of Lake Victoria by high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS). Average concentrations of total (Σ) PCDD/Fs and ΣPBDEs in sediments ranged from 68.8 to 479pgg−1 dry weight (dw) and 60.8 to 179pgg−1 dw, respectively. Contamination levels of sedimentary PCDD/Fs and PBDEs were low to moderate compared to other urbanized regions worldwide. The concentrations in different fish species (Nile perch; Lates niloticus and Nile tilapia; Oreochromis niloticus) were 5.32 to 49.0pgg−1 wet weight (ww) for PCDD/Fs and 59.3 to 495pgg−1 ww for PBDEs. Higher concentrations of the pollutants were found in L. niloticus than O. niloticus, which could be attributed to species differences in feeding habits and lifestyles. World Health Organization-toxic equivalents (WHO2005-TEQs) for PCDD/Fs ranged from 0.08 to 0.33pgTEQg−1 dw and 0.001–0.14pgTEQg−1 ww in sediments and fish, respectively. The TEQ values were low compared to the data for fresh water fish reported in literature and within a permissible level of 3.5pgg−1 ww recommended by the European Commission. Based on the Commission set value and minimum risk level criteria formulated by the Agency for Toxic Substances and Disease Registry, the fish from the Murchison Bay was fit for human consumption.

The Toxicological Effects of Halogenated Naphthalenes: A Review of Aryl Hydrocarbon Receptor-Mediated (Dioxin-like) Relative Potency Factors

There is no doubt that chloronaphthalenes (PCNs) and their brominated counterparts (PBNs) are dioxin-like compounds, but there is less evidence for mixed bromo/chloronaphthalenes (PXNs). In this article we review information relating to the dioxin-like potency of PCNs and PBNs obtained in vivo, in vitro, and in silico. The aim was to help and improve the quality of data when assessing the contribution of these compounds in the risk analysis of dioxin-like contaminants in foods and other sample types. In vivo and in vitro studies have demonstrated that PCN/PBN congeners are inducers of aryl hydrocarbon hydroxylase, ethoxyresorufin O-deethylase, and luciferase enzymes that are features specifically indicative of planar diaromatic halogenated hydrocarbons such as dioxin and dioxin-like compounds. PCNs in the environment are of multisource origin. The limited data on PBNs in the environment suggest that these also appear to originate from different sources. The toxicological data on these compounds is even scarcer, most of it directed toward explaining the exposure risk from accidental contamination of feed with the commercial PBN containing product, Firemaster BP-6. The occurrence of PBNs and PXNs is possible as ultra-trace environmental and food-chain contaminants produced at least from combustion processes at unknown concentrations. Available toxicological and environmental data enable a focus on PCNs as dioxin analogues to an extent that specific local or regional environmental influences could result in a risk to human health. There is the possibility that they may act synergistically with the better-known classic dioxin and other dioxin-like compounds. PBNs and PXNs are much less studied than the dioxins, but are known to be products of anthropogenic processes that contaminate the environment. A continuously increasing use of bromine for manufacture of brominated flame retardants over the past three decades is anticipated as a stream of “brominated” wastes, that when degraded (combusted), will release PBNs and PXNs. This calls for advanced analytical methods and greater interest toxicologically to understand and control pollution and exposure by PBNs and PXNs. Particular congeners of bromonaphthalene in single studies were found to be much more toxic than their chlorinated counterparts. In addition, brominated/chlorinated naphthalenes also seem to be more potent toxicants than PCNs.About 20% of PCN congeners exhibit a dioxin-like toxicity with relative potencies varying between around 0.003 and 0.000001, but additional and more rigorous data are needed to confirm these figures. Recent food surveys have estimated a small but relevant human exposure to these compounds in foods, giving an additional source of dioxin-like toxicity to those compounds already covered by the World Health Organization–Toxic Equivalency Factors (TEFs) scheme. Given the additivity of response postulated for other dioxin-like compounds, it would seem unwise to ignore this additional contribution. Few data available showed that PBN congeners also exhibit a dioxin-like toxicity and are even more potent than PCN congeners, but the relative potency values were not derived for them until now. There are no toxicological data available for PXNs.

Polychlorinated biphenyls in sediments and fish species from the Murchison Bay of Lake Victoria, Uganda

Polychlorinated biphenyls (PCBs) were determined in sediments and two fish species collected from the Murchison Bay in Lake Victoria, using high resolution gas chromatography coupled to a high resolution mass spectrometer. Total PCB concentrations (Σ18PCBs) varied widely with mean values ranging from 777 to 4325pgg−1 dry weight (dw) for sediments and 80 to 779pgg−1 wet weight (ww) for fish. The PCB levels in the sediments were significantly higher at the station closest to Nakivubo channel, presumably due to effluents discharged by the channel, which may contain domestically produced commercial PCB mixtures. For fish, the concentrations in Nile perch (Lates niloticus) were significantly greater than those in Nile tilapia (Oreochromis niloticus) at all study stations, possibly due to dietary differences among species. World Health Organization-toxic equivalents (WHO2005-TEQs) for the dioxin-like PCBs were 0.04–0.64pgg−1 dw and 0.01–0.39pgg−1 ww for sediments and fish, respectively. The non-ortho PCBs exhibited the highest contribution to the Σ12TEQs (>75%) compared to the mono-ortho PCBs in both fish species. The TEQs in the present study were lower than many reported worldwide in literature for fish and were within the permissible level recommended by the European Commission, implying that the fish did not pose health hazards related to PCBs to the consumers.

Ethoxyresorufin-O-deethylase (EROD) induction by TCDD, PeCDF and PCB 126 in bobwhite quail hepatocytes

World Health Organization (WHO) toxic equivalency factors are used to calculate toxic equivalent (TEQ) concentrations of complex mixtures of dioxin-like compounds (DLCs), such as polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans and polychlorinated biphenyls (PCBs), for mammals, fish and birds. The TEQ concept assumes that all species of a taxa respond with similar sensitivity to individual DLCs, but several reports do not support this assumption for birds. Our laboratory is conducting research to attempt to uncover the fundamental mechanism(s) underlying the reasons why avian species differ in sensitivity to DLCs. The present study determined concentration-dependent effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF) and 3,3',4,4',5-pentachlorobiphenyl (PCB 126) on ethoxyresorufin-O-deethylase (EROD) activity in primary cultures of northern bobwhite quail (Colinus virginianus) hepatocytes. Bobwhite quail were studied because (1) this species is used in the laboratory for toxicity testing and (2) the amino acids at all locations within the ligand binding domain (LBD) of aryl hydrocarbon receptor 1 (AHR1) in bobwhite quail and ring necked pheasant (Phasianus colchicus) are identical. Because earlier work indicated the importance of the identity of amino acids at key sites within the AHR1 LBD, we hypothesized that bobwhite quail and ring necked pheasant hepatocytes should have similar sensitivity to EROD induction by DLCs. ECthreshold-based relative sensitivity of the bobwhite quail compared to chicken for TCDD, PeCDF and PCB 126 was 0.11, 0.17 and 0.02, respectively. The rank order of potency was PeCDF > TCDD > PCB 126. The results confirm that bobwhite quail and ring-necked pheasant hepatocytes have similar sensitivity to EROD induction by TCDD, PeCDF and PCB 126.

Effect of Carrier Gas Flow Rate in Thermal Desorption Process of PCBs Contaminated Soil

A real PCBs contaminated soil was heated at 500°C using pure nitrogen as carrier gas under different flow rate to investigate the influence of carrier gas flow rate on the thermal desorption process. After 1 hour thermal treatment, the residual PCBs in soil decreased and the removal efficiency (RE) of PCBs is up to 95.1%. The distributions of PCBs in soil under different flow rate were identical. The World Health Organization toxic equivalency quantity (WHO TEQ) of PCBs in soil got its lowest value at 400Nml/min. Tetra-and higher chlorinated PCBs desorbed to carrier gas increased with increased flow rate, while the total amount of PCBs, Tri-and lower chlorinated PCBs first increased then decreased. The distributions of PCBs in carrier gas became more closely to the raw soil with increased flow rate. The TEQ of PCBs in carrier gas increased with increased flow rate. Increased flow rate enhanced the mass transfer of PCBs in the soil but shortened the preheating time of carrier gas and the retention time of carries gas, weakening the mass transfer and degradation process in gas phase. The RE of WHO TEQ of PCDDs in treated soil decreased from 86.7% to 83.2% with increased flow rate while the RE of WHO TEQ of PCDFs decreased from 85.4% to 70.0%. After thermal treatment process, the total amount of PCDD/Fs TEQ in soil and carrier gas increase from 43.8% to 18.6% times of that in raw soil. Considering removal efficiency of PCBs and PCDD/Fs and generation of PCDD/Fs in soil and gas phase, an optimized flow rate should be set at about 400Nml/min.