Environ. Sci. Technol. 2008, 42, 6817–6822
Sediment Record and Atmospheric Deposition of Brominated Flame Retardants and Organochlorine Compounds in Lake Thun, Switzerland: Lessons from the Past and Evaluation of the Present C H R I S T I A N B O G D A L , * ,†,| PETER SCHMID,† MARTIN KOHLER,‡ ¨ LLER,† SAVERIO IOZZA,† CLAUDIA E. MU THOMAS D. BUCHELI,§ MARTIN SCHERINGER,| AND ¨ HLER| KONRAD HUNGERBU Empa, Swiss Federal Laboratories for Materials Testing and ¨ berlandstrasse 129, CH-8600 Du Research, U ¨bendorf, Switzerland, State Food Law Enforcement Authority, Werkhofstrasse 5, CH-4509 Solothurn, Switzerland, Agroscope Reckenholz-Ta¨nikon Research Station ART, Reckenholzstrasse 191, CH-8046 Zu ¨rich, Switzerland, and Institute for Chemical and Bioengineering, ETH Zurich, Wolfgang-Pauli Strasse 10, CH-8093 Zu ¨rich, Switzerland
Received April 7, 2008. Revised manuscript received June 27, 2008. Accepted July 4, 2008.
Chronology of brominated fame retardants (BFRs), a class of currently widely used chemicals, was compared to the respective historical profiles of legacy organochlorine compounds in three dated sediment cores from a prealpine lake (Lake Thun, Switzerland). Concentrations of polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs) started to increase in the 1980s-1990s. In the more recent sediment layers, PBDEs still had steady or increasing concentrations, whereas for HBCDs one sediment core revealed a decreasing trend. In contrast to the contemporary BFRs, concentrations of legacy organochlorines, such as polychlorinated biphenyls (PCBs),polychlorinatednaphthalenes(PCNs),anddichlorodiphenyl trichloroethane (DDT), peaked in deeper sediment layers deposited some decades ago. Measurements of atmospheric deposition and evaluation of wastewater discharges point toward deposition on the lake surface as a relevant input pathway and wastewater as a minor source of POPs in Lake Thun. The effect of the environmental awareness and the regulations taken in the 1970s to reduce environmental pollution of organochlorines is well reflected in the analyzed sediment cores. The sediment burden closely follows estimated time trends of consumption and emission of PCBs and DDT. The current residues in sediment of BFRs are still lower than the historical peak levels of organochlorines. However, current atmospheric deposition of BFRs is similar to deposition of PCBs. * Corresponding author, phone: +41 44 823 4260, fax: +41 44 823 4614; e-mail:
[email protected]. † Empa, Swiss Federal Laboratories for Materials Testing and Research. ‡ State Food Law Enforcement Authority. § Agroscope Reckenholz-Ta¨nikon Research Station ART. | Institute for Chemical and Bioengineering. 10.1021/es800964z CCC: $40.75
Published on Web 08/19/2008
2008 American Chemical Society
Considering the high amount of BFRs presently stocked in the anthroposphere in flame proofed materials, further measures to reduce emissions during BFRs life cycle are recommended to prevent high environmental pollution as it occurred for the organochlorine compounds.
Introduction Halogenated organic chemicals have been widely used since the beginning of the 20th century for various purposes. Industrial production of technical chemicals, such as polychlorinated naphthalenes (PCNs) and polychlorinated biphenyls (PCBs), started in the 1910s and 1930s, respectively. In 1942, the insecticide dichlorodiphenyl trichloroethane (DDT) was introduced to the world market, whereupon it achieved great commercial success. Due to insufficient risk assessment of these highly chlorinated chemicals, their negative properties emerged only after several decades. Starting in the early 1960s, the persistent, bioaccumulative and toxic nature of many organochlorine compounds, like PCBs and DDT was discovered (1). The ubiquity of these compounds in remote regions has provided evidence for their long-range transport potential and atmosphere as a relevant transport media (1, 2). Triggered by scientific evidence, several international agreements and regulations aimed at the restriction of persistent hazardous chemicals have been established. In Switzerland, PCNs and DDT, as well as PCBs in open applications, such as paints and joint sealants, were banned in 1972. A complete ban of PCBs followed in 1986. The Stockholm Convention initiated in 2001 by the United Nations Environment Programme (UNEP) and in force since 2004, lists twelve particularly hazardous compounds as persistent organic pollutants (POPs), including PCBs and DDT (3). One important objective of the Stockholm Convention includes the identification of additional compounds which have properties similar to the original POPs and represent a risk to humans and the environment. With the use of brominated flame retardants (BFRs), additional organohalogen chemicals of concern have emerged in the last decades. These compounds are routinely added to flammable polymers in consumer products, such as furniture, textiles, plastics, or construction materials in an effort to prevent fire (4). Polybrominated diphenyl ethers (PBDEs) and hexabromocyclododecanes (HBCDs) are among the most widely used BFRs (5). Concern for this emerging class of chemicals has risen because of their bioaccumulative properties observed in biota and in humans together with the restricted knowledge about their potential long-term toxic effects (6-8). For the lower brominated diphenyl ethers, endocrine disrupting properties have been observed, as well as interference with neurobehavioral development (8, 9). In the late 1990s, major manufacturers of BFRs established voluntary emission control programs to minimize industrial emissions into the environment (10, 11). Since 2004, technical PentaBDE and OctaBDE mixtures containing lower brominated congeners have been banned in Europe, while the fully brominated DecaBDE is still in use (12). Sediment cores with discrete layers regularly deposited over time represent a valuable historical archive of the input of POPs into an aquatic ecosystem (13, 14). The aim of this study was to compare the sediment record of contemporary brominated substances to formerly used chlorinated species. We first investigated whether the initiatives recently taken to reduce emissions of BFRs, already had an effect on the VOL. 42, NO. 18, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Map of the Lake Thun area with sediment sampling sites (black points) and location of wastewater treatment plants discharging into Lake Thun (hexagons). sediment burden. Second, the available knowledge in organochlorines has enabled us to study the way in which they were dealt with in the past. Sediment fluxes of POPs were calculated and compared with available information on production and emission of these substances. Measurements of atmospheric deposition and evaluation of wastewater discharges were compared to sediment fluxes. Though, individual aspects and parameters presented here were covered in the literature before (13-18), this study is unique as atmospheric deposition rates are directly opposed to sediment fluxes of both the currently used BFRs (PBDEs and HBCDs) and the historical organochlorines (PCBs, PCNs, and DDT). Historical profiles of POPs in three dated sediment cores from a prealpine lake with a well defined hydrology allow also investigating temporal trends, fluxes, input processes, local patterns, as well as variability of the sediment record from three lake sites.
Materials and Methods Study Site and Sampling. Lake Thun is a prealpine lake situated in the center of Switzerland. The rivers Aare and Kander represent the two main tributaries of Lake Thun (Figure 1). The population in the Lake Thun watershed is 95 000, and there is no heavy industry and no chemical factory producing or processing chemicals such as BFRs in the region. Four small wastewater treatment plants (WWTP) with low operating capacity and treating only municipal wastewater discharge into Lake Thun. Three sediment cores were sampled from Lake Thun in 2005 (sites denoted SED1, SED2, and SED3) and were divided into 1 cm sections. Bulk atmospheric deposition was sampled at the shore of Lake Thun, using a validated passive sampling technique with a funnel-adsorber-cartridge device (19). More details about the Lake Thun catchment area, the hydrology, sediment sampling, atmospheric deposition sampling, and characterization of sediments are provided in the Supporting Information. Sediment Dating. The chronology of the sediment record was determined based on the analysis of 137Cs and confirmed by 210Pb by γ-ray spectrometry. The mass sediment building rates were determined to be 0.45, 0.39, and 0.28 cm/y for SED1, SED2, and SED3, respectively. Details are given in the Supporting Information (Figures S2 and S3). Organic Carbon Determinations. Total organic carbon (TOC) levels were low in all three sediment cores, decreasing from SED1 (1.1-3.2% TOC) to SED2 (0.8-1.8%) and from SED2 to SED3 (0.4-1.2%) confirming that Lake Thun has pristine sediments. Details are given in the Supporting Information (Figure S4). Extraction, Cleanup and Analysis of POPs. The complete extraction, cleanup and analysis method used is described 6818
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in detail in the Supporting Information. Briefly, dry and homogenized sediment and deposition samples were spiked with isotope-labeled internal standards (13C12-PBDEs, 81Br6HBCDs, 13C12-PCBs, 13C10-PCNs, 13C14-DDT) and Soxhlet extracted. Clean-up was performed according to refs 16 and 17. Prior to analysis, recovery standards were added to the extracts (13C12-BDE-126 and 15N3-musk xylene) to check for the recovery of internal standards. Separation and quantification was performed by gas chromatography coupled to electron ionization high resolution mass spectrometry (GC/ EI-HRMS) based on the isotope dilution method. Among PBDEs, the congeners BDE-28, 47, 99, 100, 153, 183, and 209 were quantified individually (presented as Σtri-hepta-BDE for BDE-28 + 47 + 99 + 100 + 153 + 183 and deca-BDE for BDE-209). For HBCDs the GC/EI-HRMS method used allowed quantifying the sum of all stereoisomers (presented as ΣHBCD). For PCBs the indicator congeners CB-28, 52, 101, 138, 153, and 180 were quantified (presented as ΣPCB) and for PCNs all tetra-CN to octa-CN congeners were quantified individually (presented as ΣPCN). For DDT, the two parent DDT isomers (o,p′-DDT and p,p′-DDT) and their main metabolites (for dichlorodiphenyl dichloroethane: o,p′-DDD, p,p′-DDD; for dichlorodiphenyl dichloroethene: o,p′-DDE, p,p′-DDE; and dichlorodiphenyl monochloroethene DDMU) were determined (DDT and metabolites presented as ΣDDT). As organic matter is the dominant sorption matrix for hydrophobic compounds in sediments and to compare concentrations among different cores, the concentrations of the measured compounds were normalized to TOC (concentrations in ng/g TOC denoted from now on as ng/g). Quality Assurance. Quality control for POPs measurements included quadruple analysis of an identical sediment sample (relative standard deviation 4, 12, 18, 11, 8, and 8% for Σtri-hepta-BDE, deca-BDE, ΣHBCD, ΣPCB, ΣPCN, and ΣDDT, respectively), analysis of reference sediment material for PBDEs (accuracy of two sediment samples from QUASIMEME laboratory performance study 108-113% and 86-101% for Σtri-hepta-BDE and deca-BDE), check for recovery of isotope-labeled internal standards (62-105%, 50-103%, 50-86%, 80-99%, 83-102%, and 60-88% for Σtri-heptaBDE, deca-BDE, ΣHBCD, ΣPCB, ΣPCN, and ΣDDT, respectively), check for recovery of native analytes in spiked sediments from preindustrial times (mean recovery 124, 89, 91, 109, 102, and 99% for Σtri-hepta-BDE, deca-BDE, ΣHBCD, ΣPCB, ΣPCN, and ΣDDT, respectively) and analysis of blank samples (consisting of empty Soxhlet thimbles and calculated for a typical sample amount yielding 0.6, 0.6, 96% of the currently used DecaBDE flame retardant.
FIGURE 2. Concentrations of BFRs normalized to TOC [ng/g TOC] in three sediment cores from Lake Thun. Measured concentrations above ten times blank level are given by the filled black points and values above LOD but below 10-times blank level are represented by the open white points. Figure 2 shows coherent time trends between the three sediment cores, with concentrations of Σtri-hepta-BDE and deca-BDE still increasing in SED1 and SED2. In 1986 (SED1) and 1991 (SED2), concentrations exceeded for the first time 10 times the blank level. In SED3, Σtri-hepta-BDE appeared in 1997 and deca-BDE in 1990. Though, the lower levels in SED3 inevitably reduce the precision of the measurements, in SED3 the concentrations of PBDEs are noticeably leveling off since the 1990s. The observed peaking years and maximum concentrations of the investigated compounds in the three sediment cores are summarized in the Supporting Information (Table S1). Deca-BDE is the major PBDE congener present in sediments (85, 73, and 62% in SED1, SED2, and SED3, respectively). ΣHBCD appeared in SED1 in 1986, increased until 1993, remained constant from 1993 to 2000, and then noticeably decreased in the three upper layers. In SED2, ΣHBCD appeared in 1978 and concentrations steadily increased between 1999 and 2004. In SED3, concentrations increased in 1983 and remained lower than in the other cores. An increase of the sediment burden of HBCDs in the 1980-1990s in parallel to the market release as a flame retardant is evident. Within the past few years, in the sediment from the shallow depositional zone near the entrance of the lake (SED1) concentrations have decreased, while increasing concentrations were observed in the middle of the lake in the deep depositional zone (SED2). Concentrations remained constant in the Western area (SED3). The decreasing trend in SED1 could conceivably indicate decreasing emissions of HBCDs into the environment. The observation of a decrease of HBCDs in core SED1 only, could result from faster sedimentation of suspended particulate matter from the water column in SED1, as this core provides from a shallow depositional zone of Lake Thun (see the Supporting Information). The lower sedimentation of particles in the deeper zones of SED2 and SED3 might lead to a delay of the turning point in the HBCD trend. Σtri-hepta-BDE leveling off and deca-BDE rapidly increasing has also been observed in a sediment core from Greifensee, a small shallow lake located close to the city of Zurich (17). In contrast to Swiss lakes, in Western Europe in sediments from Drammenfjord (Norway), the western Wadden Sea (The Netherlands), and Lake Woserin (Germany), concentrations of the lower-brominated PBDEs congeners and deca-BDE have decreased since the early to mid-1990s
FIGURE 3. Concentrations of chlorinated organics normalized to TOC [ng/g TOC] in three sediment cores from Lake Thun. Measured concentrations above 10 times blank level are given by the filled black points and values above LOD but below 10 times blank level are represented by the open white points. The years 1972 and 1986, when regulatory measures regarding PCBs and DDT were taken in Switzerland, are marked. (13). Interestingly, the hepta-BDE congener BDE-183, which is indicative of the formerly used OctaBDE technical mixture, could not be identified in these sediments (13), whereas in Lake Thun and Greifensee, BDE-183 was present. In Lake Thun sediments SED1 and SED2, BDE-183 appeared in the early 1980s, whereas in SED3 it remained below or close to LOD. In SED1 concentration of BDE-183 continuously increased toward the sediment surface to 5.3 ng/g. In SED2, the concentration was stable in the two upper sediment layers from 1991 to 2004 with 2.3 ng/g. This shows that in Switzerland emissions of the OctaBDE flame retardant product are still going on, although in Europe it has been phased out since the 1990s and has been banned since 2004 (12). Investigations in one single sediment core in Greifensee reveal that concentrations of ΣHBCD have continuously increased since the mid 1980s, not indicating a decrease of emissions (17). In Lake Ellasjøen located in the Norwegian Arctic, HBCDs have been analyzed at one site and were only detected in the sediment layer with median age 1980 (21). Hence, the latter study indicates a decrease of HBCDs. Recently, levels of HBCDs in the environment have been reviewed, and it has been shown that time trends in biota are not clear yet (6). Some studies show increasing or inconclusive time trends in biota, leading to the conclusion that no indications are available about decreasing concentrations of HBCDs in the environment on a global scale as a consequence of industry’s measures to limit emissions at production and handling sites (10, 11). Our study supports the latter statement, as clearly decreasing concentrations were not observed in all the three sediment cores from Lake Thun with no specific source of HBCDs in its vicinity. To observe a clear HBCDs trend, environmental concentrations need to be further monitored. Temporal Trends of Chlorinated Organics. Concentrations of the legacy chemicals ΣPCB, ΣPCN, and ΣDDT have decreased in the last decades (Figure 3). For ΣPCB, the maximum levels occurred in 1961 in core SED1 and in 1965 in core SED2 (Figure 3 and Table 1). In core SED3, the concentrations remained clearly lower and reached a maximum in the period 1975-1990. The decrease of ΣPCB in sediment cores occurred concurrently with the growing concerns regarding the usage of PCBs in the 1960s and the regulatory measures taken in Switzerland in 1972. VOL. 42, NO. 18, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Annual Flux into Surface Sediment, Annual Atmospheric Deposition and Total Accumulation of POPs in Lake Thuna annual annual surface atmospheric total accumulation sediment flux deposition in sediment Σtrihepta-BDE deca-BDE ΣHBCD ΣPCB ΣPCN ΣDDT
[g/y] 32 130 32 229 32 177b
[g/y] 22 46 42 53 29 na
[kg] 0.5 2.0 0.7 49.3 8.7 73.0b
a Sediment fluxes and accumulation were calculated with the measured concentrations in the three sediment cores, while one third of the surface area was allocated to each sediment core (only the sediment layers with concentrations above 10 times blank level were considered). na ) not analyzed. b Based on the concentrations measured in core SED2.
For ΣPCN, the maximum concentrations in each sediment core occurred earlier than for ΣPCB, reflecting the earlier applications of PCNs as industrial chemicals. In some sense, PCNs were forerunners of PCBs with commercial use starting at the beginning of the 20th century. PCBs were introduced to the market in the 1930s and served as important substitutes for PCNs (22). The occurrence of the maximum PCNs concentration varied among the three sites. In SED2, the maximum occurred in 1928 but in cores SED3 and SED1, ΣPCN peaked only in 1958 and 1961, respectively. A local historical source of PCNs affecting the sediment profiles cannot be completely excluded. Also a slight overestimation of the sedimentation rate in SED2, resulting in an increasing dating flaw toward deeper sediment layers, cannot be ruled out. In the core SED2, DDT and its main metabolites were investigated, as another class of chlorinated organic chemicals with high production volumes and different usage patterns (direct release as an insecticide into the environment) compared to technical products. In Switzerland DDT was prohibited in 1972 and despite its worldwide ban for agricultural use, it continues to be employed to control the transmission of malaria in those affected countries. The measurements of ΣDDT showed a maximum in 1952, some 10 years after its introduction as an insecticide to the market by a Swiss company in 1942. In the last decades, levels of ΣDDT have decreased, indicating that the major input due to the direct usage as an insecticide has ceased. Recently, chlorinated paraffins (CPs), also known as polychlorinated n-alkanes and representing another important class of industrial organochlorines, were measured in sediment core SED1 from Lake Thun (16). CPs were commercialized in the same period as PCBs, have similar applications as PCBs, but are still in use nowadays. For CPs, stagnating concentrations since the 1980s at a level higher than the historical maximum of ΣPCB have been observed (16). This shows the ongoing emissions of this class of unregulated chlorinated organics. Recently, the sediment record of PCBs in Greifensee has been published (14). The study shows that ΣPCB peaked around 1957-1960, which is the same period when concentrations reached their highest level in Lake Thun. PCNs data are available from a semirural lake (Esthwaite Water) in northwest England, where ΣPCN peaked around 1962 (15). As we observed in Lake Thun, in Esthwaite Water ΣPCN peaked some 20 years earlier to ΣPCB, and in the latter study the authors also suggest the earlier usage of PCNs as 6820
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a reason for this peak delay. In Greifensee, ΣDDT peaked in 1955, which coincides with the early peak ca. 1952 in Lake Thun (18). Sediment Fluxes and Atmospheric Deposition of POPs. Table (2) presents the calculated annual sedimentation fluxes of POPs, assuming the surface area of the lake bottom equal to the water surface (47.7 km2) and allocating one-third of the area to each sampling site. The calculated fluxes into sediment layers were also integrated over time to calculate the total burden of POPs in sediment. The mean annual bulk deposition on the surface of Lake Thun is largest for ΣPCB, deca-BDE, and ΣHBCD (Table 1). For Σtri-hepta-BDE, ΣHBCD, and ΣPCN, atmospheric deposition is close to the flux into sediment, pointing toward deposition as the major input pathway into Lake Thun. Zennegg and co-workers also propose atmospheric deposition as the major input pathway for Σtri-hepta-BDE in Swiss lakes based on the high correlation between the contaminant levels in fish from eight lakes and their surface/volume ratio. The sediment flux of deca-BDE and ΣPCB is three to four times higher than atmospheric deposition. This indicates an additional source for these compounds, as for instance input by natural surface waters carrying surface runoff or effluents from WWTP. Concentrations of PBDE in sewage sludge, in particular decaBDE, are known to be very high, although only small differences have been observed regarding the different type of wastewater received by the WWTP (23-25). Input into sewage sludge is mainly expected to result from surface runoff, as well as industrial and domestic wastewater (24). Specific loads of BFR in WWTP in Switzerland with a rural catchment area have been shown to be 1.2, 4.5, and 1.2 mg/ capita/y for Σtri-hepta-BDE, deca-BDE, and ΣHBCD. Knowing that the small WWTP that discharge into Lake Thun account for 75 000 people and that PBDE partition strongly (>96%) into sludge (25), the load resulting from WWTP effluents is estimated at 3.6, 13.5, and 3.6 g/y for Σtri-heptaBDE, deca-BDE, and ΣHBCD. This calculation shows that WWTP only contribute to a minor extend to the total load of BFR into Lake Thun. Atmospheric deposition and natural surface waters are probably the major input processes into Lake Thun and result most likely from diffuse sources. Sediment Profiles of POPs Compared to Production and Emission Estimates. Total worldwide production of PCBs was 1.3 million t (26). Global PCNs production is estimated to 10% of PCBs (22), hence, around 130 000 t. For the insecticide DDT, global usage in agriculture between 2.6 million t (27) and 4.5 million t (28) have been estimated. In 2001, the global market demand for technical DecaBDE exceeded 50 000 t/year (5). Assuming a steady production during the last 10 years, the total amount of DecaBDE produced is estimated to 500 000 t. The calculated accumulation of ΣPCB and ΣPCN in the three sediment cores approximately reflects the estimated production ratio of 10:1. DDT has been produced in similar orders of magnitude as PCBs, which is also reflected in the similar sediment accumulation for these two organochlorines. Currently the surface flux of DDT is comparable to ΣPCB flux and is probably due to residues of past usage of DDT. Although the total production amount of DecaBDE is approaching the order of magnitude of PCBs production, the estimated accumulated amount in sediment of this compound is still much lower than for ΣPCB. The calculated sediment burden only includes the six PCBs indicator congeners and thus the effective burden of total PCBs is probably higher. As deca-BDE makes up >96% of the technical DecaBDE flame retardant, the gap between burdens of PCBs and deca-BDE compared to the ratio of their production volumes is probably even larger. However, the current flux into surface sediment, as well as atmospheric deposition, is similar for deca-BDE and ΣPCB (Table 1).
FIGURE 4. Averaged normalized flux of (A) PBDEs (sum of BDE-47, -99, and -153), (B) ΣPCB and (C) ΣDDT into Lake Thun sediment. Consumption and emissions to air of PBDEs in Europe are added to Figure (A). Consumption, emissions, and occurrence in joint sealants (right y-axis) of ΣPCB in Switzerland are added to Figure (B). Usage and emissions of DDT due to agricultural purposes are added to Figure (C). Sediment fluxes of less brominated PBDEs, PCBs, and DDT, with known usage and regulation history, were compared to estimated consumption and modeled emissions (Figure 4). For PBDEs, PCBs, and DDT, modeled consumption and emission data until 2000 have recently been published (26, 28-30) and clear regulations are in place (3). Because units and scales are different for fluxes and emissions, amounts for consumption, emissions and sediment flux are normalized to their respective maximum historical values in Figure 4. To account for the temporal and spatial variability in the sediment record, the fluxes from the three cores were averaged on a five year period. For the congeners BDE-47, 99, and 153, which are indicative for the technical PentaBDE, consumption and emissions to air are estimated to have reached their maxima in 1994 and 1998, respectively (Figure 4A). In the 1980s and 1990s the flux, in line with consumption and emission, increased, reflecting the rising usage of technical PentaBDE. The sediment flux of these congeners was maximal in the recently deposited sediment layers. Thus, for lower brominated PBDEs, our sediment investigations do not yet indicate decreasing or stable levels. To observe such a delayed
decrease of the flux into sediment resulting from the initiated voluntary actions and mandatory regulations taken in Europe, continuing investigations in the future are required. Figure 4B presents the sediment flux together with the consumption and emission data (only available until 2000) (26, 29) and the occurrence of PCBs in joint sealants in Swiss public buildings (31). Usage of PCBs as plasticizer in joint sealants was a typical application for PCBs in an “open system” in the 1960s. Since the 1970s, the usage of PCBs in joint sealants has rapidly decreased. However, joint sealants may still contain significant amounts of PCBs and represent one of the existing long-term diffuse sources. The stock of PCBs in joint sealants still in use in Switzerland is currently about 50-150 t (31). Figure 4B reveals that on average ΣPCB flux into sediment peaked some ten years prior to the modeled consumption and emission maxima and also some 10 years prior to the first regulatory measures taken in Switzerland in 1972. This observation suggests a positive effect of the extension of wastewater facilities in the 1960s in Switzerland. After its peak, the flux into sediment closely followed the trend in joint sealants and decreased fast in the 1970s. Closed applications that contain a large amount of PCBs, such as PCBs in transformer oils, were only banned in 1986. In the following years, PCBs could be recovered with adequate methods. In the period 1980-2000, the sediment flux was almost constant, revealing that under favorable conditions, hazardous chemicals like PCBs in such closed systems can be disposed of safely, avoiding relevant environmental emissions. The present sediment input is probably a combination of ongoing diffuse sources, and the legacy of past emissions of PCBs still circulating in the environment. DDT had its major worldwide usage in agriculture in the 1950s-1970s (27), and global emissions peaked in the 1960s-1970s (28) (Figure 4C). The sediment flux decreased rapidly after its peak in the 1950s, which occurred earlier than the estimated global emissions, as for PCBs. Probably emissions due to agricultural use peaked earlier in Switzerland than the worldwide average, as industrial production started in Switzerland in 1942. Like for PCBs, the sediment flux has remained at a constant level since the 1980s, showing no sign for a relevant input of recently applied DDT for public health usage in tropical regions. Contemporary POPs Compared to Legacy POPs. For the investigated organochlorines regulated several decades ago, consistent decreasing time trends were revealed by the three sediment cores. Concentrations in Lake Thun are 1 order of magnitude lower for PBDEs and HBCDs in recent sediments than for PCBs, PCNs, and DDT during their respective peaking times. However, the present atmospheric deposition and flux into surface sediment are similar for deca-BDE and ΣPCB. The way in which currently hazardous chemicals like BFRs are dealt with has certainly improved compared to the former usage of persistent organochlorines. Nevertheless, it is likely that a large part of BFRs that have been produced so far is still stored in the anthroposphere in flame-proofed materials, such as electronic equipment, building materials, and furniture. This stock of BFRs represents an important reservoir and raises concerns and questions about its future impact on the environment. Environmental contamination by these chemicals should be prevented. The type of applications in use and containing BFRs are of concern, as a specific recuperation of BFRs contained in flame proofed materials is sparse.
Acknowledgments Markus Zeh, Daniel Scheidegger, and the Lake Thun police (Canton of Bern) are acknowledged for their support during sampling. We thank Alois Zwyssig, Erwin Grieder, and Michael Sturm (Eawag) for sediment sampling and dating and Franziska Blum (ART) for the TOC analyses. Helpful laboraVOL. 42, NO. 18, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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tory assistance and comments provided by the entire research team of Empa, Urs Schenker (ETHZ), and Tilman Gocht (University of Tuebingen, Germany) are appreciated. Financial support for this study was provided by the Swiss National Science Foundation, the Swiss Federal Office for the Environment, and Empa.
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Note Added after ASAP Publication There were errors in Table 1 in the version of this paper published ASAP August 19, 2008; the corrected version published ASAP September 11, 2008.
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Supporting Information Available Important characteristics of the Lake Thun catchment area, the hydrology, sampling, relevant sedimentary processes and focusing factors of sediment from Lake Thun are described. 137Cs and unsupported 210Pb activity (Figures S2-S3) and TOC in the three sediment cores are provided (Figure S4). The detailed method employed for sample extraction, cleanup, and analysis of POPs is described. Peaking years and maximum concentrations of POPs in the sediment cores are provided (Table S1). This material is available free of charge via the Internet at http://pubs.acs.org.
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