Evaluating the Contribution of Long-Range Transport of Heavy Metals from the Asian Continent to Their Concentrations in Sediment Cores from Lake Shinji,Western Japan

The historical trend of heavy metal pollution recorded in sediment cores from Lake Shinji, western Japan, was investigated to evaluate the contribution of increasing long-range transport of heavy metals from the Asian continent in recent years. The concentrations of Cd, Co, Cr, Cu, Ni, Pb, Sb, and Zn and lead isotope ratios were determined for sediment cores collected at two sites in the lake. Among the metals, Cd, Sb, and Zn showed markedly high concentrations since the 1970s. Moreover, a high Pb concentration and less radiogenic lead isotope ratios have been observed since the 1980s in the core from a site close to the mouth of a major river. Air masses from the Asian continent, including China, Russia, and South Korea, have less radiogenic lead isotope ratios than those from Japan. This suggests that the recent increase in Pb concentration in the sediment core is primarily due to the long-range transport of heavy metals from the Asian continent, followed by their deposition in the catchment area of the river. The concentration ratios of Pb/Cd, Pb/Sb, and Pb/Zn of the sediment around 2000 were calculated on the basis of the metal concentrations in excess of those before 1940. They were then compared with the volume-weighted annual average concentration ratios of Pb/Cd, Pb/Sb, and Pb/Zn of rain samples collected on the shore of the lake for 1999–2001. The result showed that the ratios of the former to the latter are 1.0 for Cd, 0.69 for Sb, and 0.31 for Zn. Thus, it is likely that the long-range transport of Cd and Sb from the Asian continent also contributes significantly to the recent increase in the concentrations of these metals in the sediment core from Lake Shinji. For Zn, however, the contribution from the Asian continent was evaluated to be small, suggesting the importance of local sources such as effluent discharges.     

Distribution of Trace Elements in Sediments and Biota of Songkhla Lake, Southern Thailand

The concentrations of Co, Ni, Cu, Zn, Cd, Pb, As, Fe, Mn, and Al were determined in sediments and biota of Songkhla Lake, a shallow coastal lagoon located in southern Thailand. In June 2006, surface sediments were sampled in 44 stations in the three sections of the lake (inner-, middle-, and outer sections). Sediment cores were also sampled in 13 stations in three cross-sections of the lake. In surface sediments, trace and major elements, organic matter, sediment grain size analysis, and sulfides were determined, and in the sediment cores, redox profiles were made. Soil samples were also collected at garbage dumping sites in the vicinity of the lake. In addition, the metal accumulation in two catfish species (Arius maculatus and Osteogeneiosus militaris) and the crustacean (Apseudes sapensis) was also investigated. Trace element concentrations in sediments of Songkhla Lake show that, especially the Outer section of the lake, in particular the sediments at the mouths of the Phawong, U-Taphao, and Samrong Canals are significantly enriched with trace elements due to municipal, agricultural, and industrial discharges entering the lake through the canals. Aluminum-normalized enrichment factors throughout the lake vary from 0.4 to 1.7 for Ni, 0.3 to 3.3 for Cu, 0.2 to 7 for Zn, 0.1 to 14 for As, 1 to 24 for Cd, 0.7 to 6.8 for Pb, and 0.1 to 7.8 for Mn. Correlations between the elements and sediment characteristics show that Cu, Zn, Cd, and Pb are essentially associated with the sulfide fraction; that Ni and Co are predominantly bound to the clay minerals and iron oxy-hydroxides, and that As is principally bound to iron oxy-hydroxides. The accumulation of trace elements between muscle tissue and liver and eggs of A. maculatus and O. militaris is element-specific, but concentrations of trace elements in fish muscle tissue are well within the limits for human consumption.     

抚仙湖重金属污染强度、历史及来源的沉积记录

This study focused on the concentration change of heavy metals of sediment cores in heavily polluted north area and less polluted middle area of Fuxian Lake in Southwest China.On the basis of the analysis of Cu,Ni,Ti,V,Pb,Cd,and Zn concentration-depth profiles,the pollution history of heavy metals was studied using ¹³⁷cesium (¹³⁷Cs) dating.The sources of heavy metals were distinguished by normalization of their profiles to aluminum and analysis of heavy metal concentrations of potential source materials.Geoaccumulation index (I_geo) was used to quantify their contamination intensity.The results showed that all the heavy metals found in the Fuxian Lake sediments originated naturally before 1980s.Cu,Ni,Ti,and V were still mainly natural in the north lake after 1980s,Cu,Ni,Ti,V,and Pb were mainly natural in the middle lake at all time,but the concentrations of Pb and Zn in the north lake were influenced by industrial wastes from the phosphorus fertilizer factory and cement plants.In all the lake,the contaminations of Cd and Zn were the results of agricultural cultivation using a large amount of fertilizers and the atmospheric fallouts of dusts from cement plants.At present,the geoaccumulation indices showed that the Fuxian Lake sediments were moderately to strongly polluted by Cd in the middle lake,and unpolluted to moderately polluted by Pb and Zn and strongly polluted by Cd in the north lake.Moreover,the pollution intensities of Cd,Zn,and Pb have been increased since 1980s.     

Ozone Sensitivity Differences in Five Tomato Cultivars: Visible Injury and Effects on Biomass and Fruits

A complete record derived from the core from the Daihai Lake in a remote area provides new insights into the changing atmospheric heavy metal deposition associated with historical industrial activities, the Asian monsoon, long-range transport, and the chemical composition of matter derived from weathering of catchment. The fluctuation of lithogenic element concentration in the lake sediments can readily be explained by a particle sorting effect induced by the Asian monsoon. The variation of atmospheric deposition of Cu and Pb shows a similar profile in the lower part of the core sediments, and coincides with environmental change, with high atmospheric deposition coupled with wet, temperate period; while low deposition with dry, cold period, indicating a transport variation of heavy metal pollutants entrained by the Asian summer monsoon. From the beginning of nineteenth century, the atmospheric deposition of Cu and Pb decreased and then slowly increased. This may be associated with the destroyed industry induced by long-term wars in China and the less heavy metal pollutants relative to the weak Asian summer monsoon in this period. Comparison between atmospheric-derived metal and sediment trap metal using Ga as the reference element shows that atmospheric Cu and Pb budgets do not exceed the fluvially-induced Cu and Pb budgets in the indirectly disturbed area. On average, there have been approximately 5.4 mg m^?2 yr^?1 of Cu and 5.1 mg m^?2 yr^?1 of Pb atmospherically deposited in the region.     

南海湖沉积物中生物有效态重金属含量及其空间分布

为判识湖泊沉积物中重金属的地球化学行为特征及其控制因素,以包头市南海湖为研究对象,采用连续提取法,系统开展了沉积物中生物有效态重金属的分布研究。结果表明,表层沉积物中重金属生物有效态（前4态之和）的平均比例序列为Cd〉Pb〉Zn〉Cu;Cu的生物有效态占总量的比例为23%,Pb为75%,Zn为42%,Cd为83%。总体而言,表层沉积物中Cd和Pb的潜在危害性最大。湖心区、西南和东北部湖区为表层沉积物中Cu、Pb和Zn的生物有效态含量高值区,Cd仅在西南湖区表现高值。有机物结合态为沉积物柱芯中Cu和Cd生物有效态的主导形态,铁锰氧化物结合态为Pb和Zn生物有效态的主导形态。强还原性条件下,沉积物中以铁锰氧化物结合态为主导形态的Pb、Zn、Cd有一定的潜在风险,Cu的潜在危害较小。与黄河沉积物重金属形态百分比的对比分析表明,南海湖沉积物对重金属的固定能力更强。     

Atmospheric input of trace metals to Lake Michigan

Atmospheric bulk deposition was collected on a monthly basis in the Lake Michigan basin from September 1975 through December 1976 to determine the atmospheric loading of trace elements to Lake Michigan. The sampling network consisted of bulk collectors located at 21 locations in the northern and southern basin. Atmospheric loading rates to Lake Michigan were estimated as (in units of 10⁵ kg yr^?1): Al-50; Fe-28; Mn-6.4; Zn-11; Cu-1.2; Pb-6.4; Cd-0.11; Co- <0.25; Ca-798; Mg-155; Na-110; K-64. Atmospheric deposition of all elements measured was greater in the southern basin than in the northern basin as a result of intense urban/industrial activity in the former. The percentage of total atmospheric deposition falling in the southern basin was: Fe-74%, Al-71%; Mn-75%; Zn-67%; Cu-62%; Pb-78%; Cd-74%; Co- ti 56%; Ca-79%; Mg-62%; Na-65%; K-61 %. Atmospheric loading rates reported are in general agreement with estimates made by others from emission inventories and aerosol concentrations. Atmospheric loadings were estimated to represent 10% or more of the total loadings to Lake Michigan from tributary and erosion sources for the trace elements Mn, Zn, Cu, Cd and Pb. Also, atmospheric deposition may account for recent accumulations of Zn, Cu, Cd, Pb and Co in southern Lake Michigan surficial sediments. The atmospheric Ph flux to southern Lake Michigan was estimated as ～1.7 μg sm^?2 yr^?1 for 1975–1976 which compares favorably with the 1972 anthropogenic Pb flux of 1.3 μg cm^?2 yr^?1 (total ? ～1.5 μg cm^?2 yr^?1) as determined from Pb-210 dating (Edgington and Robbins, 1976). The geographical distribution of trace element loading implicates the southern periphery of Lake Michigan as the principal emission source area.     

Trace metals in precipitation in Sweden

Trace metals (Cd, Cu, Fe, Mn, Pb, and Zn) concentrations in atmospheric precipitation have been routinely monitored in Sweden since the autumn of 1983. Concentrations are highest in southern Sweden and decrease northward. It is postulated that the long range transport of anthropogenic pollutants from the rest of Europe is the major source of Cd, Pb, and Zn in precipitation. Evidence for this hypothesis is that enrichment factors indicate anthropogenic origin, and Swedish atmospheric emissions of Zn and Cd are 2 to 3 times smaller than deposition fluxes. Also, Cd, Pb, and Zn concentrations are correlated in both space and time and are also well correlated with exSO₄ ⁺, a substance known to be of anthropogenic origin transported long distances.     

Atmospheric bulk deposition of trace metals to the Seine river Basin, France: concentrations, sources and evolution from 1988 to 2001 in Paris

Concentrations of Cd, Cu, Ni, Pb and Zn were determined in bulk atmospheric deposition collected at five stations in the Seine River basin (France), to evaluate sources and fluxes of atmospheric trace metals. Bulk deposition (wet + dry) was sampled weekly from March 2001 to February 2002 for 4 sites and from March to December 2001 for the last one. The concentrations of the elements in bulk deposition (dissolved + particulate form) followed the order: Zn > Pb > Cu > Ni > Cd. Concentrations of Zn, Pb and Ni were highly correlated with one another, suggesting a common source, related to the combustion of coal and heavy fuel. Metal concentrations in bulk deposition did not exhibit a high degree of temporal variability over the annual cycle and were not obviously related to meteorological parameters (rainfall, wind). Estimates of the total annual direct atmospheric deposition of metals to the Seine Estuary ranged from 16 kg yr^{? 1} for Cd to 5600 kg yr^{? 1} for Zn. Loadings of Cd, Cu and Ni from direct atmospheric inputs were less than 1% of those contributed by the Seine River and loadings of Pb and Zn represented 1.27% and 1.56% of the Seine contribution. Direct atmospheric inputs are negligible compared to fluvial inputs, but the indirect atmospheric deposition to the estuary was not estimated. Based on these results, trace metal concentrations in Paris have decreased by a factor of 4.6 for Zn and by a factor of 50 for Ni from 1988 to 2001. Of particular interest is the continued decrease in bulk deposition of Pb during this period, underlining the impact of policy initiatives concerning the reduction of lead on emissions in France.     

Temporal and spatial trends in metal loads to sediments of Lake Simcoe,Ontario

Metal loads to sediments of Lake Simcoe were partitioned into three components, which were attributable to natural background, accelerated erosion, and point + atmospheric sources. These loads were calculated over time using metal concentration profiles together with pre-settlement sedimentation rates based on sonar and time-variable sedimentation rates based on ²¹⁰Po profiles in cores. Concentrations of metals significantly higher than pre-settlement concentrations were observed in all cores in the case of Pb, back to 80 yr BP on average, and in at least 75% of cores, back to 60 yr BP for Cd and Zn and 30 to 45 yr BP for Cu, Ni, and Cr. Total metal loads increased 3 × for Cu and Ni, 4 × for Zn and Cr, 11 × for Cd and nearly 20 × for Ph from pre-1800 to 0 to 10 yr BP. At present about 90% of the anthropogenic loads of Pb and Cd, and 60 to 70% of the anthropogenic Cu, Ni, Zn, and Cr, are from point + atmospheric sources, the balance being from increased erosion. The direct atmospheric input of Cd is relatively high, approximately 77% of point + atmospheric inputs, while inputs of Cr and Ni are low at 1% and 9%, and inputs of Cu, Zn, and Pb are intermediate at 20 to 40% of point + atmospheric inputs. Two significant findings on spatial distribution of metals were the large increases in metal loads to Cook Bay following the drainage of 33 km² of marshes for agricultural use and the widespread dispersal of Cr from point source(s) in Kempenfelt Bay.     

Long distance transport of anthropogenic lead as measured by lake sediments

Long-term atmospheric deposition of Pb has been measured using lake sediment cores. The average ‘whole-lake’ Pb burden was measured for several lakes in each of four regions located throughout Ontario and Quebec, Canada. Since the regions were remote to any point source of Ph, large scale variation in atmospheric transport could be studied. The results indicate that Pb deposition is highest in South-Central Ontario, where lake burdens ranged from 312 to 432 mg m^?2, and that it decreases in an eastward direction into Quebec. Lowest deposition was at the site farthest north, Schefferville, Quebec, where fallout was 31 to 42 mg m^?2, less than one-tenth of that previously observed in South-Central Ontario. Lead-210 dating of sediment cores from the northern site showed that input to these remote lakes has occurred over the same time period as in the southern sites.     

What fraction of the total metal flux into lakes is retained in the sediments?

The concentrations of, and deposition rates for, the pollutant metals (Pb, Cu, Zn, Ni, and Cd) and the rare earth elements are reported for the sediments and settling particulates in a large, remote lake (Lake Opeongo) in the Algonquin Provincial Park, Ontario. Using a mass conservation model based on the rare earth elements, it is estimated that only 40 to 60% of pollutant metals getting into the lake is retained by the sediments. The low retention anada rate may explain the widely reported intra-basin and intra-lake differences in metal contents of sediments and casts some doubt on the use of pollutant metal profiles in retrospective assessment of the human contribution to the metal flux into many lake basins.     

Origins of Sediment-Associated Contaminants to the Marais Vernier, the Seine Estuary, France

The Marais Vernier is the largest freshwater wetland in the Seine Estuary in northern France. It is in a heavily urbanized and industrialized region and could be affected by atmospheric deposition and by fluvial input of contaminants in water diverted from the Seine River. To evaluate contaminant histories in the wetland and the region, sediment cores were collected from two open-water ponds in the Marais Vernier: the Grand-Mare, which was connected to the Seine by a canal from 1950 to 1996, and the Petite Mare, which has a small rural watershed. Diversions from the Seine to the Grand-Mare increased sedimentation rates but mostly resulted in low contaminant concentrations and loading rates, indicating that the sediment from the Seine was predominantly brought upstream by tidal currents from the estuary and was not from the watershed. Atmospheric sources of metals dominate inputs to the Petite Mare; however, runoff of metals from vehicle-related sources in the watershed might contribute to the upward trends in concentrations of Cr, Cu, and Zn. Estimates of atmospheric deposition using the Petite Mare core are consistent with measured deposition in the region and are mixed (similar for Hg and Pb; larger for Cd, Cu, and Zn) compared with deposition estimated from sediment cores in the northeastern United States. A local source of PAHs in the watershed of the Petite Mare is indicated by higher concentrations, higher accumulation rates, and a different, more petrogenic, PAH assemblage than in the Grand-Mare. The study illustrates how diverse sources and transport pathways can affect wetlands in industrial regions and can be evaluated using sediment cores from the wetland ponds.     

The Effect of River Liming on the Trace Metal Budgets of a Down Stream Lake

Sediment cores from two lakes, connected by a limed river, were analyzed for organic matter, calcium (Ca), iron (Fe), manganese (Mn), zinc (Zn), copper (Cu), lead (Pb), cadmium (Cd), and ion exchange capacity. The distribution of trace metals in the pristine upper lake is governed primarily by changes in the long distance atmospheric transported pollutants. In the lake down stream of the liming station the distribution of trace metals in sediments deposited before liming started (1985) is similar to that in the pristine lake. Liming of the connecting river raises the pH value by about 1.8 units from 5.1 enhancing the accumulation rate of trace metals in the downstream lake. Iron enriched acid insoluble particles are likely to be important carriers of trace metals. The liming agent itself is the most important source for Pb, while increased accumulation of Zn and Cd is caused primarily by enhanced scavenging of dissolved metals. For Cu the two sources are of about equal importance.     

Impact of man's activities on the chemical composition of the sediments of lakes superior and Huron

The concentrations of organic matter, major elements and trace elements were determined at 15 core locations in Lake Superior and Huron. The chemical compositions of the cores are related to sediment particle size, Eh, pH, chronology and location. Concentrations of Si, Al, Ca, Mg, K, Na, and Ti, which represent the major mineral species in the sediments, are generally uniform in each core. Surface enrichments of Hg, Pb, Zn, Cu, Ni, Co, Cd, Cr, Be, V, As, Org-C, and N at many of the locations are attributed to anthropogenic inputs of these elements in recent years. Concentration profiles of Fe, Mn, P, and S are influenced by migration of these elements in the pore waters. High anthropogenic Cu loadings in Lake Superior were related to Cu mining activities in the lake basin, while high anthropogenic inputs of Ni to the Lake Huron sediments were related to Ni contamination from the Sudbury area. Sediment loading calculations show that the anthropogenic inputs of trace and nutrient elements are related to the sedimentation rate, that the inputs are dispersed over wide areas of the lakes and that inputs to Lake Superior have increased significantly since 1955. Evidence is presented that atmospheric inputs are an important source of contaminants.     

historical deposition rates of Cd,Cu, Pb,and Zn in Norway and Sweden estimated by 210Pb dating and measurement of trace elements in cores of peat bogs

From six ombrotrophic mires located far from distinct local sources in Sweden and Norway, a core was sampled in bog hummocks in 1988 and dated by 210_Pb. Ten slices from each core were analyzed for Cd, Cu, Pb, and Zn. Based on the datings, the accumulation rates of Cd, Cu, Pb, and Zn have been estimated for the last 150 years. A reasonable agreement exists in the comparison between the recent deposition in the peat bog and nearby bulk deposition measurements. Highest deposition has been measured in southern Norway and the western part of Sweden. Generally, deposition has increased during the last 150 years, except at a station on the east coast of Sweden. In a study in Sweden where heavy metals have been measured in mosses every five years time since 1970, significant decreases in the concentrations of heavy metals have been found. Similar decreases have not been measured in the present study, although both methods are expected to reflect atmospheric deposition. Several studies have indicated that peat bogs are not suitable for measuring the historical evolution of trace metals. However, despite the disagreement, the recent literature suggests that it can be done with reasonable accuracy when performed with samples from hummocks in the peat bog.     

云南滇池沉积物中重金属的形态分布特征

Fractionation of heavy metals in sediments can help in understanding potential hazards of heavy metals. The present study analyzed total concentrations and fractions of selected heavy metals （Cd, Cr, Cu, Pb, and Zn） in surface sediments from Dianchi Lake, Yunnan Province, China, as well as factors that may affect distributions of the various heavy metal fractions. Total concentrations of the heavy metals decreased in the order Zn 〉 Cu 〉 Pb 〉 Cr 〉 Cd. These heavy metals, except Cr, were much higher than their background levels, indicating that Dianchi Lake was polluted by Cd, Zn, Pb, and Cu. Cadmium occurred mainly as the non-residual fraction （sum of the HOAc-soluble, reducible, and oxidizable fractions） （97.6%）, and Zn （55.7%） was also predominantly found in the non-residual fraction. In contrast, most of the Cr （88.5%）, Pb （81.8%）, and Cu （59.2%） occurred in the residual fraction. Correlation analysis showed that total heavy metal concentrations, organic matter and reducible Fe were the main factors affecting the distributions of the various heavy metal fractions. In the Walhai section of Dianchi Lake （comprising 97% of the lake area）, the concentrations of Cd, Zn, Pb, and Cu in the non-residual fraction were significantly lower （P ≤ 0.01 or 0.05） than those of the Caohal section （3% of the lake area）. This indicated that potential heavy metal hazards in the Caohai section were greater than the Waihai section.     

Trace Metal Levels and Partitioning in Wisconsin Rivers

Trace metal clean-techniques were applied in the determination of the levels and particle partitioning of Al, Cd, Cu, Pb, Zn in 14 rivers in Wisconsin. Nine headwater and five receiving water sites, representing both major river systems and diverse physiographic regions were sampled in the fall of 1991 and 1992, and spring of 1993. Mean filterable concentrations (range) of Cd 9.5 (4.6–26), Cu 620 (110–1800), Pb 76 (20–200), and Zn 460 (160–930) ng L-1 are comparable with recent data from oceanic, Great Lakes, and other river systems determined by researchers using modern ‘clean’ methods. Metal partition coefficients at each site generally followed the trend (pooled mean log Kd): Pb (5.84) > Zn (5.54) > Cd (4.92) > Cu (4.94). Order-of-magnitude differences in Kds were observed between sites, however, a large fraction of this variance could be explained by dissolved organic carbon (DOC) levels and degree of anthropogenic perturbation. Watershed yields of Cd, Pb, and Zn, under baseflow conditions were a very small fraction, typically 1–2%, of atmospheric loading. Copper yields represented a much higher fraction, particularly during spring high flow conditions. Filterable levels and yields of Al, Pb, and Zn are significantly higher in non-calcareous systems than in calcareous ones, which correlates with the higher levels of DOC in non-calcareous, forested systems.     

黄石市绿地土壤重金属污染风险评价及来源解析

  目的  城市绿地土壤健康问题日益受到人们的广泛关注。掌握黄石市绿地土壤重金属污染情况,为当地及同类矿冶城市生态建设与转型发展提供技术支撑。  方法  按照多点混合法选择黄石市道路绿地布设采样点,共采集土壤样品48个,测定其多种金属元素含量。使用地累积指数法、潜在生态危害指数法以及多元统计分析法对其进行污染评价;使用ArcGis10.2进行重金属分布可视化分析;利用相关性分析与主成分分析法对各重金属元素进行来源解析。  结果  土壤铅（Pb）、锌（Zn）、铬（Cr）、砷（As）、镉（Cd）、铜（Cu）的平均含量分别为200.12、424.88、109.96、56.74、4.02、376.81 mg kg?1,分别超出湖北省土壤背景值7.49、5.08、1.28、4.61、23.67、12.27倍,除Cr均未超出背景值外,各金属超出背景值样点占总体的比率分别为Cu 100%、Pb 97.92%、Zn 97.92%、As 93.75%、Cd 100%;地累积指数评价结果为53.06% ~ 87.08%样点处于中重度污染水平,89.58%样点的综合潜在生态危害指数大于150。  结论  土壤Cr含量空间分布较为均匀,但仍存在高值区,高值区位于西塞山区某大型冶钢企业附近。土壤Pb、Zn、As、Cu、Cd含量差异大,高值区均位于黄石港区,极高值点均位于下陆区某大型有色金属冶炼厂附近;6种重金属的地累积指数大小、即污染程度依次为:Cd > Pb > Cu > Zn > As > Cr,潜在生态危害指数为:Cd > Cu > As > Pb > Zn > Cr,可见Cd是该研究区域内最主要的重金属污染元素;多元统计分析表明Pb、Zn、As、Cd、Cu来源于人为源,与有色金属冶炼、交通有关,Cr主要来源于岩石的风化和土壤母质等。     

Atmospheric deposition of trace elements in Norway: Temporal and spatial trends studied by moss analysis

The atmospheric deposition of sixteen trace elements, as inferred by their concentration in moss samples collected in 1985 from 500 sites in Norway, is compared with data from a similar survey in 1977. The deposition patterns of V, Zn, As, Se, Cd, Sb, and Pb are substantially influenced by long-range transport from other parts of Europe, but a general decline is evident from 1977 to 1985, most strongly for Pb. For Cr, Fe, Co, Ni, and Cu the deposition patterns are largely determined by contributions from point sources within Norway and on the Kola peninsula close to the Russian/ Norwegian border. The moss data for Br, I, and partly Se reflect airborne supply from the marine environment, whereas Al and Sc serve as indicators of contributions from soil dust. Contributions to the trace element concentrations in moss from sources other than atmospheric deposition are identified and discussed.     

a new high-pressure squeezing technique for pore fluid extraction from terrestrial soils

A core consisting of minerogenic peat and organic-rich mineral sediments was collected at an altitude of 4275 m in the Ovejuyo valley, 100 km NE of La Paz in Bolivia. Age dating with 210Pb showed that the core represents approximately three centuries of sediment accumulation. None of the peats are ombrotrophic. Despite this, the Cd/Al, Cu/Al, Zn/Al, and Pb/Al ratios are all significantly higher in the surface layers, particularly in the top 6 cm: natural, abiological geochemical processes, therefore, cannot account for these elevated heavy metal/Al ratios. There are two possible explanations for the metal enrichments, relative to Al, in the surface layers: bioaccumulation by living plants, and anthropogenic atmospheric metal deposition. While the living plant layer may be responsible for the Cd, Cu, and Zn enrichments, this is an unlikely explanation for the Pb profile. In contrast to the other metals, the concentration of Pb in the first sample (dating from 1985-1994) is less than that of the second sample (dating from 1970-1985). The Pb/Al profile is consistent with the well documented, rapid increase in atmospheric Pb emissions during the present century (which accelerated following the introduction of leaded gasoline), and the decline in Pb pollution during the past 20 years (as a result of the introduction of unleaded gasoline). Thus, the Ovejuyo Valley mire has provided one of the first records of atmospheric Pb pollution in South America.