Toxic Equivalent Quantity Value Research Articles

Spatial distribution, source, and ecological risk of PAHs in the sediment of the Fenhe River Basin, China.

Polycyclic aromatic hydrocarbons (PAHs) are persistent toxic substances that have ubiquitous presence in water, air, soil, and sediment environments. The growth of PAH toxicities and related ecotoxicology risk in sediment has been a serious concern. Present study examined the PAH concentration, sources, and ecological risk from the selected sites in sediment of Fenhe River. The characteristic molecular ratio (CMR) and principal component analysis (PCA) were applied to analyze the sources. The ecological risk assessment was conducted based on the sediment quality guidelines, the mean effects range median quotient, as well as the toxic equivalent quantity values. The results showed that the mean values of total contents of the 16 individual PAHs were 3.66 mg/kg and 3.16 mg/kg in wet and dry seasons, which were relatively high when compared with other rivers worldwide. Their spatial distribution presented the lower contents in the upstream, while higher concentrations in the middle and down streams of the river. The low molecular weight PAHs were major constituents, and 3-ring PAHs have the highest contents. The results of source analysis indicated that PAHs were primarily from the burning of oil, coal, and biomass. The ecological risk evaluations suggested that the possible adverse biological effects, the low to medium comprehensive risks, and the minor carcinogenic risks existed in the study area. This investigation might provide useful baseline data and technical support for policy-makers and researchers.

Seasonal congener survey for polychlorinated biphenyls in sediments of south-western rivers, Nigeria: Occurrence, sources, and ecotoxicological risks

In this work, sediment samples from major rivers within southwestern Nigeria were collected to study the seasonal distribution, transport, and ecological risk assessment of polychlorinated biphenyls (PCB) using gas chromatography coupled with an electron capture detector (GC–ECD). The ΣPCB concentrations ranged from 9.86–77.56 μg/kg and 11.88–80.76 μg/kg in dry and wet seasons respectively. The most predominant PCBs congener in all the sediments was 2,2’,4,5,5’-PeCB(#101) with mean concentrations of 4.35 ± 2.96 and 6.10±3.38μg/kg across all locations in dry and wet seasons respectively. Relevant guidelines including sediments quality guidelines (SQGs) mean effect range-median quotient (m-ERM-Q), and toxic equivalent factor (TEF) were used for risk assessment and to evaluate the ecological risks of PCBs across the rivers. The toxic equivalent quantity (TEQ) ranged from 0.044–0.807 μg-TEQ/kg and 0.055–0.825 μg-TEQ/kg for the dry and wet seasons respectively. The non-ortho PCBs congeners constituted ≥ 99.8% of the ∑TEQ values. The seven indicators PBCs for evaluating non-dioxin-like PCBs ranged from 3.70–32.69 μg/kg across the seasons and accounted for 33.4%, 39.8%, 36.8%, 37.9%, 41.4%, and 40.4% of the ∑PCBs at Asejire, Odo Ona, Ogbese, Ogun, Ikorodu rivers and Third Mainland Bridge Ocean respectively. In two out of six rivers, the ∑PCBs exceeded the Canadian SQG threshold effect level of 21.5 and 34.1μg/kg for fresh and marine sediments respectively. The results of the study call for a concerted effort toward holistic monitoring of PCB residues in rivers in Nigeria to ensure ecological integrity and the protection of human health.

Transformation characteristics of polycyclic aromatic hydrocarbons during hydrothermal liquefaction of sewage sludge

Transformation characteristics of polycyclic aromatic hydrocarbons (PAHs) during hydrothermal liquefaction (HTL) of sewage sludge are explored in this study. PAHs are generated in the range of 7.3–13.8 mg/kg during HTL of sludge. The increase of reaction time (0–60 min) favors the formation of PAHs; however, the reaction temperature and solid–liquid ratio exhibit a critical value (300 °C and 0.1 g/mL, respectively), at which, the amounts of PAHs synthesized are the lowest. Most PAHs (> 89%) are distributed in bio-oil. Compared with those of raw sludge, the total/leachable contents and toxic equivalent quantity (TEQ) of PAHs in biochar are all reduced, suggesting a lower environmental risk for biochar in view of PAH hazard. Notably, the total contents of PAHs in bio-oil reach 55.0–106.6 mg/kg, with high TEQ values of 6.1–8.6 mg/kg. The liquefaction process should be further improved to reduce the content and toxicity of PAHs in bio-oil.

Presence of polycyclic aromatic hydrocarbons in sediments and surface water from Shadegan wetland – Iran: A focus on source apportionment, human and ecological risk assessment and Sediment-Water Exchange

Polycyclic aromatic hydrocarbons (PAHs) contamination in aquatic system is of concern since it may constitute a sink of these contaminants for wetland ecosystem. We investigated pollution characteristics and ecological risks of PAHs by sampling contaminated sediments and water from the Shadegan wetland in Khuzestan province, south-west Iran. Concentrations of total PAHs in water and sediment samples varied from 42 ± 2.3–136 ± 7.5ng/L and 10 ± 0.5–317 ± 14.3µg/kg, respectively. Source apportionment of PAHs by both approaches (Principal component analysis-multiple linear regression (PCA-MLR) and molecular isomeric ratios of specific PAHs), indicated impact of potential anthropogenic PAH sources including oil spill and incomplete combustion, bulrush combustion, vehicular exhaust and fishing boat emissions. Comparing the PAHs concentration with sediments quality guidelines based on the effect range low values/effects range-median values (ERL/ERM) and the threshold effect levels/probable effect levels (TEL/PEL). Also, a risk quotient (RQ) was elaborated for evaluation of potential toxic effects on aquatic ecosystem. Our data showed relatively insignificant adverse impact for most individual compounds. The toxic equivalent quantity (TEQ) was also calculated to estimation the PAHs toxicity. TEQ value of PAHs (1.9µg/kg) was lower than the safe level (600µg/kg). The fugacity fraction approach was applied to explain the trend of the selected PAHs for water–sediment exchange, which showed that the fluxes for most priority PAHs were from water to sediment suggesting no secondary source impact.

Detoxifying PCDD/Fs and heavy metals in fly ash from medical waste incinerators with a DC double arc plasma torch

Medical waste incinerator (MWI) fly ash is regarded as a highly toxic waste because it contains high concentrations of heavy metals and dioxins, including polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Therefore fly ash from MWI must be appropriately treated before being discharged into the environment. A melting process based on a direct current thermal plasma torch has been developed to convert MWI fly ash into harmless slag. The leaching characteristics of heavy metals in fly ash and vitrified slag were investigated using the toxicity characteristic leaching procedure, while the content of PCDD/Fs in the fly ashes and slags was measured using method 1613 of the US EPA. The experimental results show that the decomposition rate of PCDD/Fs is over 99% in toxic equivalent quantity value and the leaching of heavy metals in the slag significantly decreases after the plasma melting process. The produced slag has a compact and homogeneous microstructure with density of up to 2.8 g/cm3.

Characteristics of the abundance of polychlorinated dibenzo- p-dioxin and dibenzofurans, and dioxin-like polychlorinated biphenyls in sediment samples from selected Asian regions in Can Gio, Southern Vietnam and Osaka, Japan

The levels of polychlorinated dibenzo- p-dioxin and dibenzofuran (PCDD/PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs) were determined in sediment samples from Can Gio, South Vietnam, and Osaka, Japan. Can Gio is known for the defoliation of its mangrove forests by aerial spraying with Agent Orange during the Vietnam War, whereas Osaka is renowned for a PCDD/PCDF pollution accident at a municipal solid-waste incinerator. For comparison, we also analyzed PCDD/PCDFs and DL-PCBs in sediment samples from Hue and Hanoi, Vietnam. The toxic equivalent quantity (TEQ) values in Can Gio were as high as those in Hue, Hanoi, and suburban areas of Osaka, but much lower than those in urban areas of Osaka. The proportion of the World Health Organization (WHO)-TEQ value contributed by 2,3,7,8-tetrachlorinated dibenzo- p-dioxin (TCDD) in Can Gio was approximately 30%, higher than the values in the other sample areas. These data suggest that residual sedimentary TCDD that originated from aerial spraying of Agent Orange occur in only low concentrations in Can Gio. The main contributors to WHO-TEQ values in Can Gio are natural sources, as in Hue. In contrast, commercial PCBs are the dominant contributors to WHO-TEQ values in Hanoi. In Osaka, agrochemicals used in rice cultivation, the incineration of solid waste, and commercial PCBs equally contributed to WHO-TEQ values at suburban locations. The dumping of incinerator-related materials and/or the inadequate management of commercial PCBs have resulted in significantly elevated WHO-TEQ values of 240–370 ng kg –1 dw at urban locations in Osaka.

Contamination Levels of PCDDs, PCDFs and Co-PCBs in Commercial Baby Foods in Japan

To examine dioxin contamination in commercial baby foods in Japan, congener analyses of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) were performed on 102 varieties of baby foods obtained from supermarkets in 2001-2002. The toxic equivalent quantity (TEQ) levels for dioxins in samples ranged from < 0.001 to 0.135 pg-TEQ/g wet weight when undetected or trace levels of congeners were taken as zero. Among 102 samples tested, 26 samples exceeded 0.010 pg-TEQ/g. The highest TEQ value was for "sardine, vegetables" (0.135 pg-TEQ/g), followed by "Japanese radish (daikon), sardine" (0.080 pg-TEQ/g). Thus, dioxins were detected at low levels in baby foods containing animal products such as fishes and/or dairy products.

Levels and congener distributions of PCDDs, PCDFs and Co-PCBs in Japanese retail fresh and frozen vegetables.

To evaluate dioxin contamination in retail vegetables, congener analyses of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) were performed on sixty varieties of fresh vegetables including cereals and mushrooms, obtained from Japanese supermarkets in 2002. The toxic equivalent quantity (TEQ) levels for dioxins in samples ranged from < 0.001 to 0.089 pg-TEQ/g wet weight, when undetected and trace were taken as zero. Among the samples, dioxins were generally detected in green leafy vegetables. The highest TEQ value was for mulukhiya (0.089 pg-TEQ/g), followed by spinach and komatsuna (Japanese mustard spinach) (0.077 and 0.074 pg-TEQ/g, respectively). Additionally, the dioxin levels in seventeen varieties of frozen vegetables were also determined, and showed TEQ values ranging from < 0.001 to 0.080 pg-TEQ/g. The total TEQ in commercial vegetables mainly reflected the levels of 1,2,3,7,8-PeCDD, 2,3,4,7,8-PeCDF and 3,3',4,4',5-PeCB (#126) (the sum of them represented 63% of the total TEQ).

Contamination levels and congener distributions of PCDDs, PCDFs and Co-PCBs in several fast foods in Japan.

We determined the concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and coplanar polychlorinated biphenyls (Co-PCBs) in three types of fast foods [(1) seventeen hamburgers and two hot dogs, (2) six portions of fried potatoes and (3) three chicken products] obtained from fast food shops or convenience stores in Japan. All samples tested showed low toxic equivalent quantity (TEQ) levels of dioxins in the range of 0.001-0.083 pg-TEQ/g wet weight (0.006-0.053 pg-TEQ/g for hamburgers and hot dogs, 0.001-0.083 pg-TEQ/g for fried potatoes and 0.053-0.065 pg-TEQ/g for chicken products). The congener profile in hamburgers and hot dogs suggested that the total TEQ was mainly determined by Co-PCBs, especially by 3,3',4,4',5-PeCB (#126), which accounted for 44% of the total TEQ value. Findings for animal foods such as beef and cheese were consistent with this result. For fried potatoes, PCDD/Fs accounted for 94% of the total TEQ value, and 2,3,4,7,8-PeCDF accounted for 32% of PCDD/Fs. Dioxins in the chicken products consisted of 3,3',4,4',5-PeCB (#126) and 1,2,3,7,8-PeCDD, which accounted for 23% and 21% of the total TEQ, respectively. If an adult (50 kg weight) eats 150 g of hamburger, 100 g of potatoes and 150 g of chicken, the daily intake is estimated to be 0.299 pg-TEQ/kg b.w./day using the average values (0.022, 0.028 and 0.059 pg-TEQ/g, respectively) obtained in this study. This value corresponds to 7.5% of the tolerable daily intake (TDI) for PCDD/Fs and Co-PCBs in Japan.

Convenient substitute indices to toxic equivalent quantity for controlling and monitoring dioxins in stack gas from waste incineration facilities

It is necessary to develop technical systems for controlling and monitoring dioxins in stack gas from waste incineration facilities. However, it required much labor, high technical skill and extreme cost to measure dioxins for obtaining the toxic equivalent quantity (TEQ) values. In this study, the positive correlations of the WHO-TEQ values of PCDDs/PCDFs/Co-PCBs or PCDDs/PCDFs with the conventional I-TEQ values of PCDDs/PCDFs were confirmed beforehand for a large number of incineration facilities in a wide concentration range of a hundred thousand times. The relationships between the TEQ values and the concentrations of total PCDDs/PCDFs, each toxic isomer of PCDDs/PCDFs, total Cl4-6BZs, or each homologue of Cl4-6BZs were investigated for various incineration facilities. And it was found that positive correlations of the TEQ values with the concentrations of total PCDDs/PCDFs, 2,3,4,7,8-P5CDF, or Cl5BZ for a large number of different incineration facilities and in a wide concentration range. Consequently, the concentrations of total PCDDs/PCDFs, 2,3,4,7,8-P5CDF and Cl5BZ, whose measuring methods are much easier than that of obtaining the TEQ values, could be used as convenient substitute indices to the TEQ values for controlling and monitoring dioxins in stack gas from various waste incineration facilities.

A measuring method of chlorobenzenes as a convenient substitute index of dioxins in stack gas from waste incineration facilities

Much labor, high technical skill and extreme cost are required to measure dioxins for obtaining the toxic equivalent quantity (TEQ) values. On one side, it was found that there were high amounts of chlorobenzenes (CBZs) in the flue gas from waste incineration facilities, and they are also thought to be one of the principal precursors for dioxins. The concentrations of CBZs could be used as a convenient substitute index to the TEQ values for controlling and monitoring dioxins in stack gas from waste incineration facilities as shown in another report. In this study, collection efficiencies in the sampling performed by a convenient train which was composed of two bottles containing water and diethylene glycol in a cooling box, recoveries in the evaporation of the extract by an evaporator, proper procedure of the concentration by nitrogen purge were investigated for measuring CBZs. It was found that tetra-, penta-, and hexa-chlorobenzenes (Cl4-6BZs) whose boiling points are higher than ca. 240°C could be sufficiently collected and recovered in the sampling and the evaporation. For sufficient recoveries of Cl4-6BZs in the concentration by the nitrogen purge, the final volume should be larger than 200 μl with a proper receiver of the K-D concentrator at 35°C. However, Cl1-3BZs were lost in each of the procedures.