Concentrations Of Polychlorinated Dibenzofurans Research Articles

Polychlorinated dibenzodioxins, dibenzofurans and non-ortho substituted polychlorinated biphenyls in caribou (Rangifer tarandus) from the Canadian Arctic

The presence of contaminants in the Arctic environment has raised concerns regarding levels in wildlife and possible effects on the health of wildlife populations. In addition, contaminants in wild foods are of particular concern to those people who rely on these foodstuffs for a significant portion of their diet. Among the most toxic contaminants found in the environment are the polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and non-ortho substituted polychlorinated biphenyls (NOPCBs). Few data exist documenting the levels of these compounds in Arctic terrestrial wildlife. In 1993, caribou samples were obtained from three herds in the Yukon Territory (Finlayson, Tay and Bonnet Plume) and from four herds in the Northwest Territories (Bathurst, Southampton Island, Cape Dorset and Lake Harbour). High resolution gas-chromatography/mass spectrometry was used to measure contaminant concentrations. Wet weight concentrations of PCDDs, PCDFs and NOPCBs were greater in fat tissue than in muscle and liver, however, concentrations in all tissues were extremely low. Lipid normalized concentrations were greater in muscle and liver than in fat, indicating that equilibrium partitioning is not the only process regulating tissue concentrations of these contaminants. There were no significant relationships between concentrations of individual congeners and caribou age. Concentrations of the non-ortho substituted PCBs #126 and #169 were greater in caribou from the eastern Arctic, although levels in all herds were low. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxic equivalents were also low in tissues from all herds. The presence of these compounds in the Arctic can likely be attributed to long-range atmospheric transport. The levels documented in this study are some of the lowest ever reported in wildlife and are unlikely to pose a threat to caribou or their human consumers.

Occupational exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans in a magnesium production plant.

The production of magnesium is a well known source of both aliphatic and aromatic chlorinated compounds, among others the polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The aim of this study was to establish whether increased concentrations of PCDDs and PCDFs could be found in the blood of workers in a magnesium plant. Blood plasma from 10 workers, employed at a magnesium plant for 10 to 36 years, and from a control group consisting of nine people who had no direct contact with the production were studied. Isomer specific analyses of PCDDs and PCDFs by means of high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) techniques were performed. A significant increase was found in the concentrations of some of the congeners, mainly PCDFs, in the workers compared with the control group. Octachlorodibenzofuran (OCDF) is the congener that most strongly correlates with occupational exposure in the magnesium plant. Low concentrations of 1,2,3,4,6,8,9-heptachlorodibenzofuran were found in seven of the workers. Such isomers--that is, not 2,3,7,8-substituted--are rarely found in human samples. Due to the long biological half lives and lipid solubility of PCDDs and PCDFs, blood analyses may serve as an index of past cumulative occupational exposure and a means of assessing a person's exposure situation.

PCDD and PCDF in air, soil, vegetation and oily runoff from a tire fire

In early February 1990, vandals set fire to a used tire storage facility near Hagersville, Ontario, Canada, During the fire, the Ontario Ministry of Environment and Energy (MOEE) monitored the site and surrounding impact zone for numerous organic contaminants. Samples of air, soil, vegetation, runoff water, and oily residue were collected and analyzed for polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF). Air samples produced complex incineration patterns with a large number of isomers detected. Total toxicity equivalents (TEQ) at 1 km downwind of the fire were an order of magnitude higher than those at 3 km downwind. Soil samples collected during the fire did not show elevated PCDD or PCDF concentrations, however, low concentrations were detected in vegetation collected at 100 m and 200 m from the site. PCDD and PCDF concentrations in the foliage decreased with time but were still detectable for at least 200 days after the fire started. As the tires burned, water used to extinguish the fire caused runoff of oil and oily water. Unique patterns of PCDDs and PCDFs were detected in these samples.

Formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) during the combustion of impregnated wood

Wood waste and industrial wood residues often contain various preservatives. The waste management can be combustion, deposition or recycling, but combustion seems to be the most efficient way of disposal. To obtain detailed information about emissions of organic compounds with environmental impact, especially polychlorinated dibenzo-p-dioxins (PCDD) and furans (PCDF), different impregnated wood materials were incinerated in two furnaces after mixing with non-treated wood in a ratio of 1:4. It was found that the concentrations of PCDD and PCDF in the exhaust gas can be kept low under good combustion conditions. However, a non-regular incineration process strongly supports increased emissions of PCDD and PCDF.

Dioxin concentrations in the blood of workers at municipal waste incinerators.

Increased concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzo-furans (PCDFs) in pooled blood samples from workers at municipal waste incinerators have been reported. This study was undertaken to confirm these results in individual blood samples from potentially exposed and unexposed workers at municipal waste incinerators compared with matched unexposed controls and compared with concentrations in the slag and fly ash from the municipal waste incinerators. Concentrations of PCDDs and PCDFs were determined in the blood of 10 workers from an old municipal waste incinerator without adequate pollution controls, 11 workers from a newer incinerator with modern pollution controls, and 25 controls from the general population group matched for age (+/- 10 years), sex, and race, and in the slag and fly ash from the older incinerator. Significant increases of certain PCDDs and PCDFs were found in the blood of the workers from the older incinerator compared with the controls as follows: octaCDD (1051 (438) v 637 (344), P < 0.001), hexaCDF (52.3 (28.7) v 30.2 (18.2), P < 0.01), heptaCDF (43.9 (30.4) v 22.7 (12.4), P < 0.001), total PCDDs (1262 (484) v 825 (454), P < 0.001), total PCDFs (133.0 (68.1) v 93.7 (36.7), P < 0.05), and total PCDD/Fs (1395 (537) v 918 (437), P < 0.001). The workers from the older incinerator with the greatest exposure were found to have the most significant increases of the blood PCDDs and PCDFs, and the pattern of increased PCDD and PCDF congeners in the blood corresponded to the pattern in the incinerator slag and ash. No significant differences were found between the blood concentrations of the workers at the newer incinerator and the controls. Occupational exposure to slag and fly ash from municipal waste incinerators may increase the blood concentrations of PCDDs and PCDFs. Modern pollution control technology in new incinerators may be able to minimise potential exposure to slag and fly ash and thus the absorption of PCDDs and PCDFs from this source.

Levels and source of non- ortho coplanar polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans in pond sediments and paddy field soil

Non- ortho chlorine substituted coplanar polychlorinated biphenyl (Co-PCBs), polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in the sediment samples from reservoir and irrigation ponds, and in a soil from paddy field were analyzed isomer specifically using 13C-labeled their respective internal standards and a selected ion monitoring method of high resolution gas chromatograph mass spectrometry (GC/MS). These compounds were found in all samples analyzed. The average concentrations of the total Co-PCBs, PCDDs and PCDFs in the 10 sediment samples taken from reservoir ponds were 83, 3900 and 360 pg/g of dry weight, respectively, those in 7 sediments from irrigation ponds were 96, 3200, and 96 pg/g, those in 10 sediments from an irrigation pond near an incineration facility were 260, 10,000, and 290 pg/g, respectively, and those in the soil from a paddy field near an incineration facility were 120, 96,000, and 4700 pg/g, respectively. The concentrations of Co-PCBs, PCDDs and PCDFs in the sediments of the irrigation pond were higher than those in the sediments of any other ponds. On the other hand, the concentrations of PCDDs in the paddy field soil were much higher than those in any other sediment samples, but the Co-PCB concentration was about one-half of those in the sediments of an irrigation pond near the facility. These findings suggest that one of pollution sources of Co-PCBs as well as PCDDs and PCDFs, was municipal waste incineration, but that Co-PCB pollution was not caused by herbicides applied in the past.

Contamination of local wildlife following a fire at a polychlorinated biphenyls warehouse in St Basile le Grand, Quebec, Canada.

This study on wildlife contamination, one to ten months after the polychlorinated biphenyls (PCB) fire in St Basile le Grand, Quebec, shows that the fire increased PCB and polychlorinated dibenzofuran (PCDF) levels in animals. From the data, it was not possible to detect a significant increase in polychlorinated dibenzodioxin (PCDD) levels after the fire. Given the relatively small sample size, the differences in concentrations could not be estimated precisely. However, it can be asserted with a 95% confidence level that mean concentrations of total PCBs were roughly 2 to 6 times higher in the area contaminated by the plume of smoke, concentrations of homologues with 3 chlorine atoms were 1 to 4 times higher, and levels of homologues with 5 to 9 chlorine atoms were 3 to 13 times higher. The relative deviations between concentrations in areas under the plume and those outside it were similar for all animals sampled. With regard to total PCDFs, mean concentrations were significantly higher under the smoke plume than outside it for all species. This observation is linked to homologues with 4, 5 and 7 chlorine atoms for which significant differences were detected between the two areas. The fire had no effect on the pattern of PCB congeners found in the tissue of animals in the region. Congeners Nos. 153, 180, 138 and 118 represent approximately 50% of total PCBs. Although PCB and PCDF concentrations were higher in the tissue of local wildlife species exposed to the fire, they were nonetheless comparable to those found in other urban and agricultural areas in Canada. These concentrations, in 2,3,7,8-TCDD toxic equivalents, were much lower than those observed in the wake of three other major incidents involving PCDDs (Elgin, Florida; Times Beach, Missouri; and Seveso, Italy).(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of polychlorinated dibenzo- p-dioxins and dibenzofurans in tire fire runoff oil

Samples of oily runoff resulting from the accidental combustion of automobile tires were analyzed for polychlorinated dibenzo- p-dioxins (PCDDs)and polychlorinated dibenzofurans (PCDFs). PCDDs and PCDFs were identified in each of the oil samples studied. The total levels of PCDDs and PCDFs were in the low parts per billion (ppb; 10 −9 g of PCDDs or PCDFs per g of oil) range. In all of the samples analyzed, the total PCDD concentration was approximately 10 times greater than the total concentration of PCDFs. The most toxic PCDD, 2,3,7,8-T 4CDD, contributed only a small percentage to the overall level of the PCDDs in the oil samples.

Polychlorinated dibenzo-P-dioxin and dibenzofuran residues in estuarine and coastal north sea sediments: Sources and distribution

Sediments from two depositional zones of the North Sea (the Wadden Sea and Oyster Grounds) and from the estuaries of the rivers Rhine, Meuse, Scheldt, Ems, and Humber were analyzed for polychlorinated dibenzofurans (PCDFs) and dibenzo-p-dioxins (PCDDs) using a congener-specific procedure. A simple grain-size correction procedure was utilized for the comparison of PCDF and PCDD concentrations in sediments from different origin. This procedure, which applies wet sieving of fresh sediment and isolating and analyzing the <63-μm grain-size fraction, was found to be appropriate for comparing levels of PCDFs and PCDDs in different estuarine and coastal sediments. PCDFs were more widely encountered than PCDDs in all sediments, except for the Ems-Dollard and the Humber estuary. The highest concentrations were found in the outflow sediments of the rivers Rhine and Humber. Concentrations up to 2,980 ng/kg PCDFs, principally 1,2,3,4,6,7,8-HpCDF and OCDF, and up to 1,760 ng/kg PCDDs, principally OCDD, were determined in the River Rhine sediments. Principal component analysis was used to visualize the compositional changes of PCDD and PCDF profiles in the sediments. Two-dimensional projections based on sample scores from the principal component models showed a marked influence of the River Rhine on the presence of these compounds in the western Wadden Sea and the Oyster Grounds. Based on a chemo-metric evaluation of chromatographic profiles of these coastal, estuarine and related freshwater sediments, we have deduced that these compounds originate primarily from industrial operation discharges, related to the production of chloroaliphatic compounds and the chloralkali industry along the River Rhine. The atmospheric deposition of combustion-generated PCDDs and PCDFs appeared significant only for remote marine environments.

Levels of polychlorinated biphenyls and polychlorinated dibenzofurans in the blood, subcutaneous adipose tissue and stool of Yusho patients and normal subjects

An effective therapy which assists the elimination of the residual chlorinated compounds in Yusho patients has still not been established. To determine the behavior of polychlorinated biphenyls (PCBs) and polychlorinated dibenzofurans (PCDFs) in patients 20 years since the occurrence of Yusho disease, the concentrations of PCBs and PCDFs in the blood, subcutaneous adipose tissue and stools were investigated in six patients with typical symptoms of Yusho disease. The daily excretion levels of 2,3,4,7,8‐penta‐chlorodibenzofuran (PnCDF), and 1,2,3,4,7,8‐ and 1,2,3,6,7,8‐hexachlorodibenzofurans (HxCDFs) into the stools of Yusho patients were 200 to 1380pg, and 190 to 1590pg, respectively. Similarly, PCBs were excreted at levels of 320 to 1370 ng per day, into the stools. The amounts of PnCDF and HxCDFs excreted into the stool per day was correlated to the levels of those chemicals in the blood and subcutaneous adipose tissue. The daily levels of PnCDF and HxCDFs excreted into the stool were comparable with th...

Humans are a sensitive species to some of the biochemical effects of structural analogs of dioxin

AbstractIn 1979, rice oil contaminated with polychlorinated dibenzofurans (PCDFs) was ingested in a widespread poisoning episode in Taiwan. The PCDFs are structural analogs of 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD). TCDD and the PCDFs are thought to share the same mechanism of action that involves binding to the Ah receptor. In our studies, we compared the effects of TCDD on rat liver to effects in placentas of women exposed to PCDF‐contaminated rice oil. TCDD is a hepatocarcinogen in female rats. Measured parameters included concentrations of human placental PCDF congeners or rat liver TCDD and induction of cytochrome P‐450 isozymes, epidermal growth factor receptor (EGFR) and glucocorticoid receptor (GCR). Placentas from PCDF‐exposed women contained two PCDFs: 2,3,4,7,8‐penta CDF (100 ppt) and 1,2,3,4,7,8‐hexa CDF (400 ppt). The 2,3,4,7,8‐penta CDF binds the Ah receptor 60% as well as TCDD, and the 1,2,4,7,8‐hexa CDF binds 9% as well as TCDD. Cytochrome P1‐450 was induced approximately 100‐fold in exposed placentas. This induction was considered maximal. Placental PCDF concentrations associated with this induction were compared to the amount of hepatic TCDD required to maximally induce the rat liver homolog of P1‐450. These comparisons, accounting for differences in Ah receptor binding, suggested that humans are more sensitive than rats to the P1‐450 inductive actions of the toxic halogenated aromatics. Several assumptions are made, and their validity is discussed. As with the P1‐450, humans are more sensitive to the effects of the halogenated aromatics on EGFR (EGF‐stimulated autophosphorylation) and GCR (binding capacity) than are rats. Although the relationship of these biochemical changes to the carcinogenic effects of TCDD and its analogs is not clear, our data suggest that it is prudent to retain a conservative risk assessment for the toxic halogenated aromatics.

Meeting report—Dioxins revisited

Long-term measurements of atmospheric polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (dl-PCBs) were conducted in six satellite cities of Seoul, the capital of South Korea, from January 2003 to December 2009. Of the six sites, three were located in residential areas (Suwon, Anyang, and Seongnam) and the other three were in industrial areas (Ansan, Bucheon, and Siheung). For the 7 years, the average concentrations of PCDDs/PCDFs and dl-PCBs were higher at industrial sites than those at residential sites, and their lowest and highest concentrations were 0.113 ± 0.073 pg international toxicity equivalency quantity (I-TEQ) m−3 and 0.0071 ± 0.0040 pg World Health Organization (WHO)-TEQ m−3 at Seongnam and 0.625 ± 0.597 pg I-TEQ m−3 and 0.0376 ± 0.0285 pg WHO-TEQ m−3 at Ansan, respectively. The annual averages of these compounds tended to decrease from 2003 to 2009, with the most apparent change in 2006 when the regulation of dioxin emission standard was reinforced for flue gas from incineration facilities. Complying with the reinforced standard, the concentrations of PCDFs were reduced more effectively than those of PCDDs, leading to increase in ratios of PCDDs to PCDFs since 2006. Additionally, a seasonal tendency was observed for PCDDs/PCDFs with higher concentrations in winter than summer, which was opposite for dl-PCBs. This seasonal difference suggests their sources such as combustion processes and volatilization and the influence of synoptic-scale circulation. The congener profiles indicated that 1,2,3,4,6,7,8-HpCDF, OCDF, OCDD, and 1,2,3,4,6,7,8-HpCDD were the most abundant, comprising 65.0% of the 17 toxic 2,3,7,8-substituted PCDDs/PCDFs mass. The three congeners of 2,3′,4,4′,5-PeCB, 2,3,3′,4,4′-PeCB, and 3,3′,4,4′-TeCB comprised 75.9% of the 12 dl-PCBs.

High temperature gasification (HTG) pilot plant studies with different waste materials: Formation of PCDD/F and other organic pollutants

This paper presents the results of test runs with the High Temperature Gasification (HTG), a newly developed technology of a thermal treatment of hazardous waste of the VOEST-ALPINE Industrieanlagenbau. When measuring the emissions special attention was paid to organic pollutants, such as polychlorinated dibenzo-p-dioxins (PCDD), polychlorinated dibenzofurans (PCDF), polychlorinated biphenyls (PCB), chlorobenzenes (CB), chlorophenols (CP), polycyclio aromatic hydrocarbons (PAH) and others. The results of the tests with various waste show that the HTG pilot plant produces a relatively low emission level as far as organic pollutants are concerned. The concentrations of PCDDs and PCDFs in flue gas reaches from not detectable up to 0,04 ng/Nm 3 of 2,3,7,8-TCDD-equivalents (I-TEF), thus remaining remarkably lower than the Austrian limit for municipal waste incinerators of 0,1 ngTE/Nm 3 (I-TEF).

Analysis of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) in soil and digested sewage sludge from Stockholm, Sweden

In this investigation the content of PCDDs and PCDFs in sewage sludge samples and top soil from fields situated in the County of Stockholm has been investigated. Further, the contribution of PCDDs and PCDFs to the fields from sewage sludge is compared with the contribution from two non-point emission sources i.e. road traffic and the urban area of the city of Stockholm. The mean concentration in four analyzed sludge samples is 79 pg TEQ/g (organic weight; o.w.). Soil samples taken close to major roads vary between 13 and 49 pg TEQ/g (o.w.) and soil samples (1b-4b) which were not taken close to major roads vary between 9 and 32 pg TEQ/g (o.w.). The results indicate that both road traffic and outlets from the urban area influence the PCDD and PCDF concentrations in the arable soil. Fertilization with sludge (1 tonne dry weight/hectare and year) raise the initial soil concentrations of PCDD and PCDF in the fields by approx. 2 – 3%.

Formation and emission of PCDDs/PCDFs in the petroleum refining industry

The formation of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) during a variety of combustion and chemical manufacturing processes has been well documented. The petroleum refining industry, previously unrecognized as a source of PCDDs and PCDFs, has recently been found to emit these compounds. The PCDDs and PCDFs are formed during the regeneration of spent catalyst material. In stack emission and wastewater effluent samples collected from different petroleum refineries, a series of chlorinated dioxins and furans were identified. The congener distribution patterns observed in these samples were similar to those previously found in flyash samples collected from various municipal waste incinerators. Low parts-per-quadrillion levels of PCDDs and PCDFs have been identified in internal effluent streams. The concentrations of PCDDs and PCDFs in the stack gas samples are typically in the low ng/m 3.

Polychlorinated dibenzofurans and polychlorinated dibenzo‐p‐dioxins in great lakes fish: A baseline and interlake comparison

AbstractFish from each of the Great Lakes and Lake St. Clair were analyzed for 10 congeners of polychlorinated dibenzofurans (PCDFs) and 8 congeners of polychlorinated dibenzo‐p‐dioxins (PCDDs). PCDFs and PCDDs were identified above detection limits in samples from each lake. Concentrations of PCDFs, principally 2,3,7,8‐TCDF, were highest (102.4 ng/kg) in Lake Michigan lake trout and lowest in late trout from Lake Superior (20.9 ng/kg). Total PCDD concentrations ranged from 7.2 ng/kg in Lake Superior lake trout in 64.5 ng/kg in Lake Ontario lake trout. Concentrations of 2,3,7,8‐TCDD ranged from 1.0 ng/kg in Lake Superior lake trout to 48.9 ng/kg in lake trout from Lake Ontario.While the upper lakes were somewhat similar in the absolute concentration and composition of PCDFs and PCDDs, principle components analysis identified statistically significant inter‐ and in‐tralake differences in the composition of total PCDF and total PCDD. These differences suggest differences in the sources of these compounds to each of the Great Lakes.

Background concentrations of polychlorinated dibenzofurans (PCDFs) and polychlorinated dibenzo-p-dioxins (PCDDs) in office buildings in Boston, Massachusetts

Two office buildings were tested to determine the background surface and air concentrations of PCDFs and PCDDs. Surface samples showed higher concentrations of PCDDs than PCDFs, increase of PCDD concentration with degree of chlorination, similar concentrations of PCDFs irrespective of degree of chlorination, and significant correlations between concentrations of PCBs, and PCDFs and PCDDs. Air samples generally contained non-detectable concentrations of PCDFs and lower chlorinated PCDDs; and a predominance of higher chlorinated PCDDs. These data define a concentration baseline for PCDFs and PCDDs in these buildings, but may be indicative of the concentrations present in other office buildings.

Polychlorinated Dioxin and Furan Discharge During Carbon Reactivation

Analyses are performed on samples collected from various effluent streams of a fluidized‐bed and infrared furnace during reactivation of granular activated carbon (GAC) used in treatment of drinking water. These analyses show that polychlorinated dibenzodioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are produced during GAC reactivation. No detectable concentrations of PCDD or PCDF are seen in the spent carbon fed to the reactivation furnaces. Although the total amount of organic halogens on the spent GAC ranges from 416–657 mg/kg, only small fractional amounts of PCDDs and PCDFs are formed. The low levels of PCDDs and PCDFs emitted into the atmosphere during GAC reactivation and the resulting cancer risks to the exposed population are minimal and negligible.

Isomer-specific determination of polychlorinated dibenzofurans in Japanese and American polychlorinated biphenyls

Extremely toxic Polychlorinated dibenzofurans (PCDFs) were identified in several Japanese and American commercial PCB preparations. These isomerspecific analyses revealed several toxic PCDFs including 2,3,7,8-tetra-, 1,2,4,7,8-penta-, 1,2,3,7,8-penta-, 2,3,4,7,8-penta- and 1,2,3,6,7,8 hexa-chlorodibenzofurans in commercial PCB preparations. The concentrations (μg/g) of PCDFs in unused Kanechlor 300, 400, 500, 600 were 7.5, 26, 7.2, 5.4 and in Aroclors 1242, 1248, 1254, 1260 were 0.60, 3.7, 4.2, 7.5 respectively. An attempt for the detection of polychlorinated dibenzo- p-dioxins (PCDDs) at <2 ng/g level revealed no detectable dioxins.

PCDDs, PCDFs, and metals in selected danish soils

Topsoil samples from five locations in Denmark were collected and analyzed for polychlorinated dibenzo- p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and selected heavy metals. The upper soil layers contained elevated concentrations of PCDDs, PCDFs, Pb, Zn, and Cu compared to the lower layers. The soil contents of PCDDs plus PCDFs were closely related to Pb contents. Higher concentrations were found near urban areas relative to strictly rural locations. From the presented data the provisional Danish background content of PCDDs plus PCDFs is estimated to be 4–7 μg m −2 in the topsoil of coniferous forests.