Lake Sediment Archive Reveals a Distinct Response to Anthropogenic Pb and Zn Deposition with Historical Periods: Pb-Zn Isotope Evidence.

Anthropogenic activities release large quantities of heavy metals into the atmosphere. In China, the input of these heavy metals through local and trans-boundary atmospheric deposition is poorly understood. To assess this issue, herein, we use Pb and Zn isotopes to constrain the sources of Pb and Zn in a 210Pb-dated sediment core collected from the enclosed lake in South China. We observed a progressive shift toward higher 208Pb/206Pb and Pb fluxes (0.79-4.02 µg·cm-2·a-1) from 1850 to 1950 and a consistent decrease in δ66ZnIRMM (as low as -0.097 ± 0.030‰) coupled with an increase in Pb (1.74-3.36 µg·cm-2·a-1) and Zn (8.07-10.44 µg·cm-2·a-1) fluxes after 1980. These distinguished isotopic signals and flux variations reveal the presence of trans-boundary Pb since 1900, with the addition of local industrial Pb and Zn pollution after 1980. Up to 72.3% of Pb deposited at our site can be attributed to long-distance transportation from previously industrialized countries, resulting in a noteworthy legacy of Pb in China since 1900. Despite the phasing out of leaded gasoline, Chinese gasoline still contributes an average of 20.9%. The contribution of China's mining and smelting activities to Pb has increased steadily since 1980 and remained stable at an average of 25.1% since 2000.

Exploring the variation of bacterial community and nitrogen transformation functional genes under the pressure of heavy metals in different coastal mariculture patterns.

Equilibrium in microbial dynamics and nitrogen transformation in the sediment is critical for maintaining healthy mariculture environment. However, our understanding about the impact of heavy metals on the bacterial community and nitrogen transformation functional genes in different mariculture patterns is still limited. Here, we analyzed 30 sediment samples in the vertical distribution from three different mariculture patterns mainly include open mariculture zone (K), closed mariculture pond (F) and pristine marine area (Q). Illumina MiSeq Sequencing was applied to investigate the bacterial community and structure in the sediment. Quantitative polymerase chain reaction (qPCR) was used to determine the effect of heavy metals on nitrogen transformation functional genes. Results showed that bacterial community and structure varied greatly in different mariculture patterns. Chloroflexi, Proteobacteria and Desulfobacterota were predominant phyla in the coastal mariculture area. High concentrations of heavy metals mainly enriched in the up layer (5-40 cm) of the sediment in the mariculture zone. The abundance of functional genes in the closed mariculture pond was much higher than the open mariculture zone and pristine marine area. And the high abundance of nitrification and denitrification functional genes mainly accumulated at the depth from 5 cm to 40 cm. Heavy metals content such as Fe, Cr, Mn, Ni, As, Cd, Pb and nutrient content NH4+-N, NO3--N and NO2--N were highly associated with bacterial community and nitrogen transformation functional genes. This study comprehensively elaborated the effect of heavy metals on the bacterial community and nitrogen transformation functional genes in different coastal mariculture patterns, indicating the possible role of closed mariculture pond in reducing nitrogen transformation efficiency, which will provide useful information for preventing pollution risk in the mariculture area.

Polycyclic aromatic hydrocarbons in remote lakes from the Tibetan Plateau: Concentrations, source, ecological risk, and influencing factors.

Polycyclic aromatic hydrocarbons (PAHs) have received worldwide attention due to their potential teratogenic, persistent, and carcinogenic characteristics. In this study, the PAHs concentrations in two dated sediment cores taken from central Tibetan Plateau (TP) were analyzed to study the deposition history, potential sources, ecological risks, and influencing factors. Total concentration of PAHs (∑PAHs) ranged from 50.0 to 195 ng g-1 and 51.9-133 ng g-1 in sediments of Pung Co (PC) and Dagze Co (DZC), respectively. 2-3-ring PAHs were dominant in the two lake sediments, accounting for an average of 77.5% and 80.1%, respectively. The historical trends of ∑PAHs in the two lakes allowed to distinguish three periods, namely, relative stability before the 1950s, a gradual increase between the 1950s and the 1990s, and then a decline to the present-day. In addition, the trend in the concentration level of each PAH composition was consistent with ∑PAHs before the 1990s, while they exhibited different trends since the 1990s, which may be the result of a combination of anthropogenic activities and climate change in recent years, whereas before the 1990s the PAH profile was mainly influenced by atmospheric deposition. The results of source apportionment examined according to diagnostic ratios and positive matrix factorization were consistent and revealed that PAHs were primarily derived from biomass and coal combustion. Significant correlations between PAHs and organic carbon (OC) indicate that OC might be a key factor influencing the concentration of PAHs in sediments. The ecological risk assessment demonstrated that PAHs in TP sediments occurred at a low risk level. Results of this study could be helpful to develop a deeper insight into the deposition history of PAHs in remote lakes of the TP region and explore the response of these variations to climate change and human activities.

Radium and Lead Radioisotopes Composition of Sediment and Its Biogeochemical Implication in Polymetallic Nodule Area of Clario-Clipperton Zone.

Radioactivity levels of 210Pb and 226Ra were detected in a sediment core obtained using a multi-corer from the polymetallic nodule area inside the Clarion-Clipperton Zone (CCZ), a contract area of the China Ocean Mineral Resources Association (COMR) in the eastern Pacific Ocean. The profile of excess 210Pb (210Pbex) shows that the specific activity of 210Pbex has three parts with different distributions at depths of 0-16 cm (I), 17-36 cm (II), and 37-48 cm (III). When the I section of nonlocal mixing was excluded, using a steady-state diffusion mode, the bioturbation coefficients of the core were estimated to be 24.2 cm2/a at 17-36 cm deep and 5.9 cm2/a at 37-48 cm deep, which were greater compared to previously published results. This is most likely owing to bioturbations caused by various organism species in the two sections.

Source apportionment of polycyclic aromatic hydrocarbons (PAHs) in a sediment core from Lake Dagze Co, Tibetan Plateau, China: Comparison of three receptor models.

Receptor models are a useful tool for identifying sources of polycyclic aromatic hydrocarbons (PAHs) in multiple environmental media. In this study, three different receptor models (including the principal component analysis-multiple linear regression (PCA-MLR), positive matrix factorization (PMF), and Unmix models) were used to apportion the sources of 16 priority PAHs in a sediment core of Lake Dagze Co. The ∑PAHs (sum of all 16 measured PAHs) concentrations ranged from 51.89 to 132.82 ng/g with an average of 80.39 ng/g. The ∑PAHs were dominated by 2-3 ring PAHs, accounting for 80.12% on average, thereby indicating that they mainly originated from biomass and coal combustion and/or from long-range atmospheric transportation. The three models produced consistent source apportionment results. The greatest contributor to ∑PAHs was biomass combustion, followed by coal combustion, vehicle emissions, and petrogenic sources. Moreover, the temporal variation of the common sources was well-correlated among models. The multi-method comparison and evaluation results showed that all three models were useful tools for source apportionment of PAHs, with the PMF model providing better results than the PCA-MLR and Unmix models. The temporal trends of factor contributions were verified by PAHs with different ring numbers. Significant correlations were found between the simulated concentrations of each source factor and the PAHs with different ring numbers (P<0.01), except for the petrogenic source identified by the Unmix model (P>0.05). This study can provide useful information for further investigation of source apportionment of PAHs in the sediment cores.

Anthropogenic impact on the historical phytoplankton community of Lake Constance reconstructed by multimarker analysis of sediment-core environmental DNA.

During the 20th century, many lakes in the Northern Hemisphere were affected by increasing human population and urbanization along their shorelines and catchment, resulting in aquatic eutrophication. Ecosystem monitoring commenced only after the changes became apparent, precluding any examination of timing and dynamics of initial community change in the past and comparison of pre- and postimpact communities. Peri-Alpine Lake Constance (Germany) underwent a mid-century period of eutrophication followed by re-oligotrophication since the 1980s and is now experiencing warm temperatures. We extended the period for which monitoring data of indicator organisms exist by analysing historical environmental DNA (eDNA) from a sediment core dating back some 110 years. Using three metabarcoding markers-for microbial eukaryotes, diatoms and cyanobacteria-we revealed two major breakpoints of community change, in the 1930s and the mid-1990s. In our core, the latest response was exhibited by diatoms, which are classically used as palaeo-bioindicators for the trophic state of lakes. Following re-oligotrophication, overall diversity values reverted to similar ones of the early 20th century, but multivariate analysis indicated that the present community is substantially dissimilar. Community changes of all three groups were strongly correlated to phosphorus concentration changes, whereas significant relationships to temperature were only observed when we did not account for temporal autocorrelation. Our results indicate that each microbial group analysed exhibited a unique response, highlighting the particular strength of multimarker analysis of eDNA, which is not limited to organisms with visible remains and can therefore discover yet unknown responses and abiotic-biotic relationships.

Relevance of using the non-reactive geochemical signature in sediment core to estimate historical tributary contributions.

Fluvial suspended particulate matter (SPM) fluxes transport large amounts of contaminants that can affect water quality and river ecosystems. To better manage these inputs in river systems, it is essential to identify SPM and sediment sources. Many studies have applied a fingerprinting method based on using metals integrated into a numerical mixing model to estimate source contributions in a watershed. Most fingerprinting studies use contemporary SPM to trace historical inputs, whereas their metal concentrations were modified over time due to anthropogenic inputs. Moreover, total concentrations of these properties are subject to change due to diagenetic processes occurring in stored sediments. The aim of this study was to assess the relevance of using the non-reactive fraction of metals (i.e. metals and metalloids) in fingerprinting studies to estimate the historical contributions of SPM tributary inputs in a sediment core. To assess metal concentrations in the 'conservative' (i.e. non-reactive) fraction, SPM (samples of sources) and sediment core layers (targeted sediments) were subjected to total mineralization and soft extraction, and the non-reactive fraction was obtained by calculating the difference between the two extractions. This approach was applied on a sediment core from the Upper Rhône River (France), using geochemical signature in contemporary SPM of three major tributaries. We showed that the non-reactive fraction retains a higher number of metals in the range test for the deepest layers, which are characterized by significant anthropogenic inputs. Through apportionment modelling using Monte Carlo simulation, we demonstrated that the tributary contributions computed using the non-reactive fraction are more consistent with historical flood and water flow data and have lower uncertainties than with the total fraction. Working with the non-reactive fraction made it possible to decipher historical inputs of SPM using contemporary SPM samples. This approach enables robust identification of sub-catchment areas liable to provide large quantities of SPM. The non-reactive fraction can be used in a variety of environmental conditions and at various spatial and temporal scales to provide a robust quantification of sediment sources.

A 110 Year Sediment Record of Polycyclic Aromatic Hydrocarbons Related to Economic Development and Energy Consumption in Dongping Lake, North China.

A sedimentary record of the 16 polycyclic aromatic hydrocarbon (PAH) pollutants from Dongping Lake, north China, is presented in this study. The influence of regional energy structure changes for 2-6-ring PAHs was investigated, in order to assess their sources and the impact of socioeconomic developments on the observed changes in concentration over time. The concentration of the ΣPAH16 ranged from 77.6 to 628.0 ng/g. Prior to the 1970s, the relatively low concentration of ΣPAH16 and the average presence of 44.4% 2,3-ring PAHs indicated that pyrogenic combustion from grass, wood, and coal was the main source of PAHs. The rapid increase in the concentration of 2,3-ring PAHs between the 1970s and 2006 was attributed to the growth of the urban population and the coal consumption, following the implementation of the Reform and Open Policy in 1978. The source apportionment, which was assessed using a positive matrix factorization model, revealed that coal combustion was the most important regional source of PAHs pollution (>51.0%). The PAHs were mainly transported to the site from the surrounding regions by atmospheric deposition rather than direct discharge.

Trace metals in core sediments from a deep lake in eastern Turkey: Vertical concentration profiles, eco-environmental risks and possible sources.

The contents of 12 trace metals (Hg, As, Pb, Cd, Ni, Cr, Zn, Cu, Co, Mn, Al and Fe) in two sediment cores (Hz11-P02 and Hz11-P09) from the Lake Hazar, one of the deepest natural lakes in Turkey, were examined to evaluate vertical concentration profiles, possible sources, pollution status and eco-environmental risks of these metals. The highest concentrations of Cd and As were detected in the upper part (0-10 cm depths) of core Hz11-P02, while Hg concentration was at a maximum in the upper part of core Hz11-P09. The concentrations of other metals except Cr were the highest in the bottom layer (depths below 100 cm) of both cores. Among trace metals (TMs), Cr, Ni, Al and Mn in core Hz11-P02 and Mn in core Hz11-P09 showed statistically significant correlations with core depth (p < 0.01). The mean concentrations of Hg, Pb, Cd, Cu, Zn, Co, Mn, Al and Fe in core Hz11-P02 were significantly higher than those in core Hz11-P09 (p < 0.01). Also, the mean enrichment factor, geoaccumulation index and contamination factor values of As, Cu, Cd, Zn, Pb and Hg were higher in core Hz11-P02. The ecological risk index (RI) values for core Hz11-P02 were between 150 and 300 in 40.3% of the samples, indicating "moderate ecological risk", whereas the RI values for core Hz11-P09 were <150 in 100% of the samples, indicating "low ecological risk". Factor, cluster and correlation analyses, and contamination indices indicated that As and Hg in core Hz11-P02 predominantly originated from anthropogenic sources, while 12 trace metals in core Hz11-P09 derived from natural sources.

Historical trends of PCBs and PBDEs as reconstructed in a lake sediment from southern Tibetan Plateau.

High-altitude lake sediment can be used as a natural archive to reconstruct the history of pollutants. In this work, the temporal distribution of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) were determined using a high-resolution gas chromatography coupled with high-resolution mass spectrometer (HRGC/HRMS) in an alpine lake sediment core collected from the southern Tibetan Plateau (TP) to examine whether the expected decreasing trends due to the implementation of the international Conventions could be observed. The concentrations of PCBs and PBDEs in the sediment core were in the range of 11.8-142 pg/g dw and ND-457 pg/g dw, and their fluxes were in the range of 2.51-31.7 ng/(m2·yr) and ND-43.2 ng/(m2·yr), respectively. The prevalence of low-chlorinated (tri-CB) PCBs and low-brominated (tri- to tetra-) PBDEs in most sections of the sediment profiles was observed, suggesting that the light molecular weight PCBs and PBDEs have most likely reached lake sediments by long-range atmospheric transport from distant sources. Despite the restrictions on their applications, the sediment records for the concentrations and fluxes showed no corresponding decreasing trend with restrictions for PCBs, which suggested that these POPs (e.g., PCBs) were still emitted to the environment owing to the influence of primary or secondary emissions. To our knowledge, this is the first report on input history of atmospheric PCBs and PBDEs recorded in TP Lake sediment.

Vertical distributions of mercury in marine sediment cores from central and southern part of Bohai Sea, China.

In past decades, China has experienced substantial economic growth and industrialization. However, the effects of vast development of China on Hg input to the nearby oceans are still unclear. In this study, four representative 210Pb-dated sediment cores were collected in the central and southern part of Bohai sea to investigate vertical changes of Hg contents and explore the relationship between the Hg deposition and pollution history in this region utilizing a large amount of information available. The results indicated that Hg median concentrations of sediment core B62, B66, JQ17 and HZ24 were 0.043 mg/kg, 0.054 mg/kg, 0.033 mg/kg and 0.018 mg/kg respectively, among which, B66 in Yellow river estuary and B62 in central part of Bohai Sea had higher concentrations and HZ24 in Bohai Strait had a lower concentration. 210Pb profile appeared as a three segments model in the core B62, but as many steps of decay with depth in B66. For HZ24, 210Pb activity only fluctuated with depth without any discernible trend. Sedimentary rates of these cores decreased as follows: B66＞B62＞JQ17＞HZ24. Vertical distributions of Hg concentrations in sediment cores were totally different from each other. Hg concentrations in sediment core B62 experienced an initial fluctuation followed by a decreasing trend, while sediment core HZ24 almost showed the uniform decreasing trends from the surface to the bottom. There were three segments of variation in sediment cores JQ17: initial fluctuation followed by an obviously decreasing tendency and then a converted variation from surface to bottom. Hg contents changes in core B62 might reflect the additive effects from atmospheric deposition at a larger scale and the river-delivered sediment accumulation, while Hg vertical changes in B66 mainly had a close relationship with the input of Yellow river. The converted variation at the bottom section in sediment cores JQ17 was inferred to have some relationship with the Chengbei platform construction in the corresponding periods.

Temporal trends of polybrominated diphenyl ethers in the sediment cores from different areas in China.

This paper presented the historical data on the temporal trends of polybrominated diphenyl ethers (PBDEs) in the sediment cores collected from the Huaihe River, Yellow River and Chaohu Lake, China. Among the 40 targeted PBDE congeners, only 10, 6, and 9 of them were detected respectively in the samples from the Huaihe River, Yellow River and Chaohu Lake. On average, the total PBDEs concentrations in sediments were highest in Chaohu Lake followed by the Huaihe River and the Yellow River. As compared to other PBDE congeners, BDE-209 had higher concentrations and detection rates. The similar down core variation between PBDEs and total organic carbon (TOC) suggests that TOC is an important factor influencing PBDEs distribution in the sediments. The total PBDEs concentrations showed an increasing trend from bottom to upper sediments before a decreasing trend in the topmost sediments. The rapid urbanization and industrialization of these regions in recent decades may cause the historically increasing concentrations of sedimentary PBDEs, especially BDE-209. The decreasing PBDEs concentrations in topmost sediments was probably related to the strict environmental policies at present.

Seasonal and spatial contamination statuses and ecological risk of sediment cores highly contaminated by heavy metals and metalloids in the Xiangjiang River.

To reveal seasonal and spatial variations of heavy metals and metalloids (HMMs) in sediment of the Xiangjiang River, a total of 24 water and 649 sediment samples were collected from six sampling stations in the Songbai section of the river which had been polluted by HMMs for 100 years. Their contamination statuses and ecological risk were determined by enrichment factor (EF), geo-accumulation index (Igeo), pollution load index (PLI), and mean probable effect concentration quotients (mPECQs) analyses. The results revealed a unique seasonal distribution of metals in the sampling stations: The highest concentrations were revealed in the dry seasons (autumn and winter) and the lowest during the wet seasons (spring and summer). It exhibited a greater seasonal variation in the estuary sediment cores (sites ME and MW) than in the cores of other sites. Moreover, the highest concentrations of the tested metals were also found in the estuary sediment cores in the dry seasons (autumn and winter). The highest vertical concentrations of Pb, Zn, Cu, Ni, As, Fe, and Mn were observed at the depths of 16-36 cm in all of the sampled sediment cores. The EF, Igeo, PLI, and mPECQs values of all samples in autumn were higher than in summer. Cd posed the highest ecological risk in all seasons, although its concentrations were lower compared to other studied elements. Our results will benefit to develop feasible sediment quality guidelines for government monitor and remediate the local sediments in the Xiangjiang River.

Contamination assessment and prediction of 27 trace elements in sediment core from an urban lake associated with land use.

A sediment core was sampled in an urban lake in southern Brazil, and the presence of 27 trace elements was assessed. The geochronology showed that the core corresponds to the period from 1914 to 2012. Accumulation of metals and the level of pollution was measured by the geoaccumulation index (Igeo) and enrichment factor (EF). According to Igeo and EF, the lake showed a high concentration of Ag, Se, Na, Au, S, Ca, Mg, Ba, Sb, Bi, and Sr with 5 ≤ EF ≤ 45 and Igeo class = 2-6. The EF to Au = 45 and Ag = 40. In contrast, Fe, Al, As, Cr, Ga, La, Sc, and Th do not represent pollution (Igeo ≤ 0 and EF ≤ 1.6). A principal component analysis and Spearman correlation showed a first group composed of Ca, Mg, P, Ba, Sr, Na, K, Ag, Bi, Au, Mo, sand, silt, and total organic carbon with positive correlation ≥ 0.70 and > 0.95 to Sr, Ag, sand, and silt. These were negatively correlated ≥- 0.70 with Fe. The second group: Fe, La, Ga, Ti, V, Cr, As, Al, Th from lithogenic source. Prediction models for the concentration for Mg, Na, P, Sr, Fe, Ga, and total organic carbon to years 2020-2050 were obtained with R2 > 0.65. In the anthropogenic source analyses, a watershed land use map indicates multiple uses of the land, with 53% urban area, 14.6% agriculture, and 14.5% forest.

Record of Hg pollution around outset of colonization in Southern Brazil.

This study presents results of a sediment core located in Coroa de Boi Bay, a not dredged cove within Patos Estuary, Southern Brazil. The distribution of metals (Hg, Cu, Pb) and U in the sediment profile records several contamination events since pre-colonial times to present days. A joint assessment of the distribution of these parameters and the consultation to historical documents allowed us to establish causal links between concentrations anomalies in the sediments and ancient anthropogenic contamination in the area. During the industrial period, sedimentation rates in the bay ranged from 3.4 to 5.5 mm year-1. Applying a sedimentation rate previously calculated for undisturbed sediments in the Patos Estuary, we trace the beginning of Hg contamination as having started in the colonial period in Southern Brazil, soon after a Hispanic-Lusitanian conflict situation in South America. The most probable source of Hg contamination during this period was carroting technology used in fur processing.

n-Alkanes in sediments from the Yellow River Estuary, China: Occurrence, sources and historical sedimentary record.

A total of 21 surface sediments from the Yellow River Estuary (YRE) and a sediment core from the abandoned Old Yellow River Estuary (OYRE) were analyzed for n-alkanes using gas chromatography-mass spectrometry (GC-MS). n-Alkanes in the range C12-C33 and C13-C34 were identified in the surface sediments and the core, respectively. The homologous series were mainly bimodal distribution pattern without odd/even predominance in the YRE and OYRE. The total n-alkanes concentrations in the surface sediments ranged from 0.356 to 0.572mg/kg, with a mean of 0.434mg/kg on dry wt. BASIS: Evaluation of n-alkanes proxies indicated that the aliphatic hydrocarbons in the surface sediments were derived mainly from a petrogenic source with a relatively low contribution of submerged/floating macrophytes, terrestrial and emergent plants. The dated core covered the time period 1925-2012 and the mean sedimentation rate was ca. 0.5cm/yr. The total n-alkanes concentrations in the core ranged from 0.0394 to 0.941mg/kg, with a mean of 0.180mg/kg. The temporal evolution of n-alkanes reflected the historical input of aliphatic hydrocarbons and was consistent with local and regional anthropogenic activity. In general, the investigation on the sediment core revealed a trend of regional environmental change and the role of anthropogenic activity in environmental change.

A cold and organic solvent tolerant lipase produced by Antarctic strain Rhodotorula sp. Y-23.

Psychrotolerant yeast Rhodotorula sp. Y-23 was isolated from the sediment core sub-samples of Nella Lake, East Antarctica. Isolate was screened for lipase production using plate assay method followed by submerged fermentation. Production optimization revealed the maximum lipase production by using palmolein oil (5% v/v), pH 8.0 and inoculum size of 2.5% v/v at 15 °C. The potential inducers for lipase were 1% w/v of galactose and KNO3 , and MnCl2 (0.1% w/v). Final productions with optimized conditions gave 5.47-fold increase in lipase production. Dialyzed product gave a purification fold of 5.63 with specific activity of 26.83 U mg-1 and 15.67% yields. This lipase was more stable at pH 5.0 and -20 °C whereas more activity was found at pH 8.0 and 35 °C. Stability was more in 50 mM Fe3+ , EDTA-Na (20 mM), sodium deoxycholate (20 mM), H2 O2 (1% v/v), and almost all organic solvents (50% v/v). Tolerance capacity at wider range of pH and temperature with having lower Km value i.e., 0.08 mg ml-1 and higher Vmax 385.68 U mg-1 at 15 °C make the studied lipase useful for industrial applications. Besides this, the lipase was compatible with commercially available detergents, and its addition to them increases lipid degradation performances making it a potential candidate in detergent formulation.

Historical trends of organochlorine pesticides (OCPs) recorded in sediments across the Tibetan Plateau.

Sediment cores from four lakes across the Tibetan Plateau were used as natural archives to study the time trends of organochlorine pesticides (OCPs). The total concentrations of dichlorodiphenyltrichloroethane (ΣDDT) and hexachlorocyclohexane isomers (ΣHCH) were in the range of 0.04-1.61 and 0.08-1.88 ng/g based on dry weight (dw), while the input fluxes were in the range of 0.3-236 and 0.7-295 pg/cm2/y in the core sediments, respectively. The input fluxes of ΣDDT and ΣHCH generally peaked in sediment layers corresponding to the 1970s-1990s and peaked in top sediment layers. The ratio of α/γ-HCH decreased in the top layer sediments, implying that the contribution of lindane (pure γ-HCH) has been increasing in recent years. In addition, the ratio of o,p'-DDT/p,p'-DDT increased significantly over the last 15-20 years, suggesting that dicofol (characterized by high ratio of o,p'-DDT/p,p'-DDT about 7.0) has recently become a relatively more important source of DDT compared to technical DDT itself. The time trends of OCPs recorded in lake sediments examined the impact on such remote alpine regions by human activities.

Historical record of anthropogenic polycyclic aromatic hydrocarbons in a lake sediment from the southern Tibetan Plateau.

High-altitude lake sediments can be used as natural archives to reconstruct the history of pollutants. In this work, the temporal distribution of polycyclic aromatic hydrocarbons (PAHs) was determined in a sediment core collected from the southern Tibetan Plateau (TP), which was dated by using the 210Pb dating method and validated with the 137Cs fallout peak. The concentrations of the anthropogenic PAHs (Σ8PAH) in the sediment core ranged from 0.83 to 12 ng/g dw, and the fluxes of the Σ8PAH were in the range of 2.1-27 g/cm2/year. The temporal variations in the concentration and input flux of anthropogenic PAHs were low with little variability before the 1950s, and then gradually increased from the 1950s to the 1980s, and an accelerated increase was observed after the early 1980s. The content of total organic carbon played an insignificant role in affecting the time trends of PAHs in the sediment core. Diagnostic concentration fractions of PAH components indicate PAHs in the lake sediment of the southern TP which are mainly from biomass burning and/or from long-range atmospheric transport.

Ecological Risk Assessment of HCH and DDT Residues in a Sediment Core from the Küçükçekmece Lagoon, Turkey.

The residues of organochlorine pesticides (HCHs and DDTs) in a dated (137Cs and 210Pb) sediment core from the Küçükçekmece Lagoon, an urban lake at the southern entrance of the future Canal Istanbul Project, an artificial watercourse, were analyzed with the gas chromatograph equipped with electron capture detector (GC 63Ni-ECD). Concentrations of ∑HCH and ∑DDT along the core varied between 0.4 and 469.4 (average 51.4) ng g-1 dw, and between 0.5 and 72.0 (average 7.4) ng g-1 dw, respectively. α-HCH was the predominant isomer (98%) and followed by γ-isomer (2%). The highest concentrations of technical HCH were found in the sediments dated 1963-1972, whilst the DDT concentrations had their maximum around 1945. The highest concentrations of γ-HCH and p,p'-DDT exceeded probable-effect level values which can lead to frequently cause adverse effects on aquatic biota.