Direct Atmospheric Fallout Research Articles

Quantifying microplastic stocks and flows in the urban agglomeration based on the mass balance model and source-pathway-receptor framework: Revealing the role of pollution sources, weather patterns, and environmental management practices

Microplastics are widely present in global ecosystems, threatening both marine and freshwater species. Given this problem, it is vital to research where land-based microplastics originate and how they are transmitted to receiving waters in urban agglomerations. Research results should inform systemic mitigation efforts to prevent future contamination. This study established the multi-directional transmission network of a microplastic mass balance system using a source-pathway-receptor framework, and involving annual source stocks and pathway flows with considerable variations under dry and wet weather patterns. Details of a baseline scenario quantifying the occurrence and spread of microplastics in an urban agglomeration were also determined in the context of current environmental management practices. We demonstrated that the total stock of the six major pollution sources amounted to 5317.7 ± 2175.3 and 3320.1 ± 953.6 tons/a in dry and wet weather, respectively; and 2347.8 ± 766.9 and 1991.8 ± 701.8 tons/a flows directly entered the sewer system and receiving water in Shanghai, China, respectively. Prominent microplastic stocks were found in atmospheric fallout, industrial wastewater, and domestic sewage. These stocks were much higher compared to crop farming wastewater, aquacultural wastewater, and livestock and poultry breeding wastewater. Total microplastic flows entering receiving water reached 3207.4 ± 1071.6 tons/a; the largest contributions were from wet weather overflow (23.7%), direct atmospheric fallout (21.7%), wastewater treatment plant effluent (14.2%), industrial wastewater (14.1%), and surface runoff (10.4%). Weather patterns led to divergent microplastic transmission pathways and mass flows, revealing a lagging timeline mode and illustrating the basic spatiotemporal features of microplastic contamination in urban agglomerations. Terminal disposal practices retained about two-fifths of the microplastic flows that would have otherwise been transmitted into receiving water. Of these, land surface sweep contributed half of the retained flow. Improvements in WWTP removal efficiency, storm sewage interception rate, industrial wastewater collection rate, and sewer sediment dredge rate could further enhance the systemic benefits.

210Pb and 137Cs as tracers of recent sedimentary processes in two water reservoirs in Cuba

Hanabanilla and Paso Bonito Reservoirs are the main fresh water sources for about half a million inhabitants in central Cuba. Prior to this investigation precise information about the losses of storage capacity was not available. Sedimentation is the dominant process leading to reduction in water storage capacity. We investigated the sedimentation process in both reservoirs by analyzing environmental radionuclides (e.g. 210Pb, 226Ra and 137Cs) in sediment cores. In the shallow Paso Bonito Reservoir (mean depth of 6.5 m; water volume of 8 × 106 m3), we estimated a mean mass accumulation rate (MAR) of 0.4 ± 0.1 g cm−2y−1 based on 210Pb chronologies. 137Cs was detected in the sediments, but due to the recent construction of this reservoir (1975), it was not possible to use it to validate the 210Pb chronologies. The estimated MAR in this reservoir is higher than the typical values reported in similar shallow fresh water reservoirs worldwide. Our results highlight a significant loss of water storage capacity during the past 30 years. In the deeper and larger Hanabanilla Reservoir (mean depth of 15.5 m; water volume of 292 × 106 m3), the MAR was investigated in three different sites of the reservoir. The mean MARs based on the 210Pb chronologies varied between 0.15 and 0.24 g cm−2y−1. The MARs calculated based on the 137Cs profiles further validated these values. We show that the sediment accumulation did not change significantly over the last 50 years. A simple empirical mixing and sedimentation model that assumes 137Cs in the water originated from both, direct atmospheric fallout and the catchment area, was applied to interpret the 137Cs depth profiles. The model consistently reproduced the measured 137Cs profiles in the three cores (R2 > 0.9). Mean residence times for 137Cs in the water and in the catchment area of 1 y and 35–50 y, respectively were estimated. The model identified areas where the catchment component was higher, zones with higher erosion in the catchment, and sites where the fallout component was quantitatively recorded in the sediments.

Activities and geochronology of 137Cs in lake sediments resulting from sediment resuspension

In lakes with a large surface area to watershed ratio 137Cs delivery is primarily by direct atmospheric fallout to the lake surface, where its activity in the sediments has been used to estimate the exposure to organisms and sediment mass deposition rates. Comparison of 137Cs in the historical atmospheric fallout record with 137Cs activity profiles in sediment cores reveals that although the general features of a maxima in the fallout deposition can be matched to activity peaks in the core, the general shape of the 137Cs profile is not an exact replica of the fallout history. Instead, the sediment reflects post-depositional processes such as resuspension, bioturbation, partitioning of 137Cs between the sediment solids and the pore fluids, and molecular diffusion of 137Cs through the pore fluids. Presented here is a model that couples these processes to a system time averaging (STA) model that accounts for the time history of 137Cs fallout and the particle residence time in the water column or in the ‘active’ surface sediment subject to resuspension. Sediment profiles are examined by comparing reasonable ranges of each of the coefficients of each of these major processes and by applying the model to cores collected from two large, shallow lakes, Lake Erie (USA/Canada) and Lake Winnipeg (Canada). The results indicate that the STA model with molecular diffusion and sediment resuspension best describes the data from these large, shallow lakes.

Dual-Core Mass-Balance Approach for Evaluating Mercury and 210Pb Atmospheric Fallout and Focusing to Lakes

Determining atmospheric deposition rates of mercury and other contaminants using lake sediment cores requires a quantitative understanding of sediment focusing. Here we present a novel approach that solves mass-balance equations fortwo cores algebraicallyto estimate contaminant contributions to sediment from direct atmospheric fallout and from watershed and in-lake focusing. The model is applied to excess 210Pb and Hg in coresfrom Hobbs Lake, a high-altitude lake in Wyoming. Model results for excess 210Pb are consistent with estimates of fallout and focusing factors computed using excess 210Pb burdens in lake cores and soil cores from the watershed and model results for Hg fallout are consistent with fallout estimated using the soil-core-based 210Pb focusing factors. The lake cores indicate small increases in mercury deposition beginning in the late 1800s and large increases after 1940, with the maximum at the tops of the cores of 16-20 microg/m2 x year. These results suggest that global Hg emissions and possibly regional emissions in the western United States are affecting the north-central Rocky Mountains. Hg fallout estimates are generally consistent with fallout reported from an ice core from the nearby Upper Fremont Glacier, but with several notable differences. The model might not work for lakes with complex geometries and multiple sediment inputs, but for lakes with simple geometries, like Hobbs, it can provide a quantitative approach for evaluating sediment focusing and estimating contaminant fallout.

10Be variation in surficial sediments of the Central Indian Basin

Distribution of 10Be in systematically collected (degree×degree interval at 10 to 16 °S; 73.5 to 76.5 °E) surficial siliceous ooze, siliceous clay and pelagic clay sediments (top 2cm) from the abyssal Central Indian Basin and the Andaman Sea is used to evaluate sources and to decipher the transport pathways of sediment particles, demarcate sediment depocenters and erosional areas. While 10Be concentrations display a wide variation (0.12–5.56×109atomsg−1) with an average of 3.58×109atomsg−1 in the Central Indian Basin, the values in the Andaman Sea are uniform with an average of 1.49×109atomsg−1. The 10Be/9Be values in the Central Indian Basin sediments range between 0.06 and 2.99×10−8atomsatoms−1 and average to ∼1.56×10−8 atomsatoms−1. Correlation of 10Be data with some selected major (Al, Mn, Ti) and trace (Rb and Ba) elements suggest that large part of the isotope has been supplied through direct atmospheric fallout from the water column and minor part from lithogenic detrital flux. Significantly lower 10Be accumulation rates in the Central Indian Basin and an order of magnitude higher in the Andaman Sea sediments compared to the estimated global average production rates indicate removal of the isotopes at the continental margins. Bottom topography seems to exert control on local 10Be variation, where sediments deposited in valleys or topographic depressions contain higher 10Be concentrations in contrast to the probably erosion-dominated areas at the slopes and troughs.

The transport and mass balance of fallout radionuclides in Blelham Tarn, Cumbria (UK)

Although lake sediment archives are widely used for reconstructing historical records of atmospherically delivered pollutants, the quantitative relationship between fallout levels and their record in the sediments is complex and not well known. The original input signal from the atmosphere can be significantly distorted by mediating transport processes in the catchment, through the water column and within the sediments themselves. Since these processes also affect the fallout radionuclide 210Pb commonly used to date sediments, a better understanding of their impact is also important to improving the accuracy and reliability of sediment dating. Blelham Tarn has been the subject of a number of palaeolimnological investigations using radiometric dating techniques since the early 1970s. More recently it was the site of a major study carried out within the EU Transuranics project concerning the long-term fate of fallout radionuclides in catchment/lake systems. This paper reviews the radiometric data from this study and uses the results to determine mass balances for fallout 210Pb, 137Cs and 239+240Pu in Blelham Tarn, and their spatial distribution over the bed of the lake. Atmospheric fluxes were determined by measuring concentrations in rainwater and cumulative inventories in soil cores from non-eroding sites. Sediment records in a grid of 16 cores were used to determine the spatial distribution over the bed of the lake, and net inputs from the catchment. Mass balance calculations indicate that c. 47% of 210Pb in the sediments derives from erosive inputs from the catchment. For 239+240Pu the figure rises to 61%. Reduced amounts of 137Cs in the sediments are attributed to greater losses of this radionuclide from the water column via the outflow due to its greater solubility. Inputs of radionuclides from the catchment are concentrated near one of the major input streams. Away from this part of the lake the sediment record is dominated by direct atmospheric fallout, though the detailed pattern is influenced by sediment focussing. A one parameter catchment/lake transport model is developed that incorporates the assumption that transport rates will decline with time as fallout on the catchment diffuses into the soil and becomes less available for removal. Values of the transport parameter were calculated for 210Pb and 239+240Pu and found to be comparable. The results suggest that it will take c. 11000 years to remove 50% of 239+240Pu from the catchment to the lake.

Input contribution and vertical migration of plutonium, americium and cesium in lake sediments (Belham Tarn, Cumbria, UK)

Summary The record of the global atmospheric fallout could be found in the lake sediments. A mass balance for fallout radionuclides in Blelham Tarn and its catchment is established. The sediment activity contribution is coming from direct atmospheric fallout and from indirect atmospheric fallout via the catchment. The catchement activity is conveyed to the sediment by the rivers and the direct streaming. A comparison of the fallout and the sediment inventory allows the activity estimation of these different contributions and to understand the mobility of these elements on the catchment and in the sediments. The study of activity profile in sediment core allows to characterise the different radioactive events occurred in the past. For the lake Blelham, the results show two cesium activity peaks and only one peak for transuranic activities. The deepest peaks correspond to the atmospheric nuclear test fallout in the sixties (1963) and the second peak to the Chernobyl accident (1986). The activity ratio 239-240Pu/ 137Cs allows estimating the ratio between cesium activities in sediments coming from these two events. Plutonium and cesium diffusion coefficients are calculated with a simple analytical model.

A comparison on the accumulation characteristics of 7Be and 137Cs in lake sediments and surface soils in western Yunnan and central Guizhou, China

The uplifting of the Himalayas has resulted in the development of a three-tiered landform in Southern China, the Yunnan–Guizhou Plateau is the middle tier of this landform on the eastern slope of the Himalayas. Lake Hongfeng and Lake Baihua in central Guizhou are about 1000 km away from Lake Erhai in western Yunnan. Sediment cores were collected from Lakes Erhai and Lugu in west Yunnan and Lakes Hongfeng and Baihua in central Guizhou, along with 28 surface soil cores from the watersheds of these lakes. The accumulation characteristics of 7xxxxBe and 137yyyyCs show that: (1) 137Cs activities in the soil cores of central Guizhou were higher than that in the western Yunnan. The activities and maximum penetrative depth of 7Be were similar for the two regions. The activity ratio of 7Be/ 137Cs in surface soil reached 100–1000 in western Yunnan, but only 10–100 for central Guizhou region. (2) 7Be inventories in soil cores at most sampling sites of central Guizhou were low, reflecting severe soil erosion. 7Be inventories in the soil cores of Lake Lugu watershed in summer–autumn were higher than that in Lake Hongfeng/Baihua watershed and also higher than that in Lake Erhai watershed. This could be related to high 7Be precipitation in summer and altitude. (3) 7Be inventories in sediment cores of Lake Erhai, Lake Lugu and Lake Baihua were 237±73, 322±19 and 783±44 Bq m −2, respectively. Based on activity values that were corrected to deposition, prior to 1986, 137Cs inventories in these lakes were 519±26, 937±13 and 3704±56 Bq m −2, respectively. (4) Modeling indicated that 7Be and 137Cs accumulations in Lake Hongfeng and Lake Baihua were dominated by watershed erosion, and controlled by the retention factor in Lake Erhai and Lake Lugu, but the 137Cs inventory ratios obtained in the sediment core and from direct atmospheric fallout were similar, and the ratios were smaller for 7Be. (5) 7Be inventories from direct atmospheric fallout in Lake Erhai, Lake Lugu and Lake Baihua were 0.07±0.02, 0.29±0.02 and 0.08±0.01 Bq m −2, respectively. Prior to 1986, 137Cs inventories were 0.11±0.01, 0.22±0.01 and 0.37±0.01 Bq m −2, respectively, showing that 137Cs deposition has a regional difference. This phenomenon may reflect that uplift of the Himalayas has a screening effect on the fallout of globally distributed atmospheric pollutants in western Yunnan, China.

Distribution and inventories of some artificial and naturally occurring radionuclides in medium to coarse-grained sediments of the channel

Concentrations of artificial ( 60 Co, 137 Cs, 238 Pu and 239,240 Pu ) and naturally occurring radionuclides ( 40 K, 212 Pb and 214 Pb , daughter nuclides of the 232 Th and 238 U series) in bottom sediments of the Channel are reported. They are grain-size modulated but usual grain-size normalisation methods fail due to the strong heterogeneity of the sediment admixture and/or the occurrence of rock debris in the area of concern. When plotted versus distance from Cap La Hague, 60 Co and Pu isotope concentrations display a maximum in the Central Channel, but 137 Cs do not. This is further explained by the contribution of the releases from the La Hague plant relative to other radionuclide inputs, especially Atlantic inflow and direct atmospheric fallout. Apparent transit times from Cap La Hague are derived from Pu isotopic ratios and yield average sediment velocities ranging from some kilometres to some tens of kilometres per year. Sediment inventories of artificial radionuclides show that a significant part of the input of 60 Co and Pu isotopes is immobilised in the Channel seabed while most of the 137 Cs input has been evacuated by water mass circulation.

The post-Chernobyl budget of 137Cs and 90Sr in the Black Sea

Calculations of annual radionuclide budgets in the Black Sea for the period 1986–1995 have been carried out to estimate the contribution of radionuclides of Chernobyl origin to contamination of the Black Sea and to evaluate the various pathways by which 137Cs and 90Sr are introduced into the sea. The scale of radioactive contamination of the Black Sea as a result of the Chernobyl accident is close to that of weapons test contamination. In both cases, the main pathway of 137Cs and 90Sr input to the seawater was direct atmospheric fallout. River runoff brings relatively small amounts of 137Cs into the Black Sea. The river-derived share of 90Sr input reached 25% of its total input for the first 10 years after the accident and continues to grow. Decreases in the inventory of 137Cs and 90Sr in the seawater, caused by radioactive decay and their removal through the Bosporus Strait into the Marmara Sea, have been occurring since 1987. In 1994, the 90Sr inventory approached the pre-accident level. It is estimated that the 137Cs inventory will reach its pre-accident level by 2025–2030.

Land Use and Lake Sedimentation on the New England Tablelands of New South Wales, Australia

Lead-210 methods have been used to establish a chronology of sedimentation extending back almost 80 years in Black Mountain Lagoon near Guyra on the New England Tablelands of north-eastern New South Wales, Australia. Estimates of the direct atmospheric fallout of unsupported 210Pb and historical records of the pattern of phosphorus input to the lake provide support for the 210Pb chronology. The sediments in the lake record an episode of disturbance which took place prior to c .1916, but after c .1790-1860. Since then, however, the site-specific rate of minerogenic sedimentation has been maintained at a relatively low and constant level of 0.93 kg m-2 a-1. [Note: the following symbols are used in this paper: a = year (annum), and d min-1 g-1 = radioactivity (spontaneous nuclear disintegrations per minute per gram of material).] This is despite major shifts in land use and intensification of agriculture, despite the occurrence of significant floods and droughts, and in the absence until recent times of the application of soil conservation practices. These rates may be contrasted with rates of 0.023 kg m-2 a-1 from the period 12.3-5.6 ka. These are at least an order of magnitude lower than those of the twentieth century. The lake sediments preserve evidence of the use of agricultural chemicals on the catchment during the twentieth century. These include phosphorus, zinc, arsenic and lead. Soils and sediments may act as long-term toxic stores for such chemicals, a problem often overlooked in rural areas.

USE OF FALLOUT Pb-210 MEASUREMENTS TO INVESTIGATE LONGER-TERM RATES AND PATTERNS OF OVERBANK SEDIMENT DEPOSITION ON THE FLOODPLAINS OF LOWLAND RIVERS

The potential for using fallout (unsupported) Pb-210 (210Pb) measurements to estimate rates of overbank sediment deposition on the floodplains of lowland rivers is explored. A model which distinguishes the contribution from direct atmospheric fallout and the catchment-derived input associated with the deposition of suspended sediment has been developed to interpret the fallout Pb-210 inventories at floodplain sampling sites and to estimate average sediment accumulation rates over the past 100 years. The approach has been successfully used to estimate rates of overbank sedimentation on the floodplains of the Rivers Culm and Exe in Devon, U.K. A detailed investigation of the pattern of longer-term sedimentation rates within a small reach of the floodplain of the River Culm indicated a range of deposition rates between 0.07 and 0.59 g cm−2 a−1, which was in close agreement with estimates of current sedimentation rates obtained using sedimentation traps.

The transport and fluvial redistribution of Chernobyl-derived radiocaesium within the River Wye basin, UK

Relatively little attention has been given to the long term prospect of fluvial transport processes redistributing Chernobyl-derived radiocaesium within the UK. Work undertaken within the Wye basin, central Wales, demonstrates a complex distribution of fallout at the catchment scale, with the bulk of the deposition concentrated in a narrow north-south band, situated in the west central areas of the basin, which contained in excess of 1500 Bq m −2 of 134Cs. Fluvial transport and redistribution of this material was demonstrated by river sampling during the winter of 1988/89, when the radiocaesium content of suspended sediment transported by the River Wye (≈ 30–50 mBq g −1 of 137Cs) remained 3–5-times higher than pre-Chernobyl levels. Floodplain reaches displayed variable levels of secondary contamination, dependent upon the upstream supply of radiocaesium and local morphological controls. Accordingly, the highest 134Cs inventories within the basin (> 6000 Bq m −2) were associated with rapidly accreting floodplain sites. A number of these sites experienced only limited amounts of direct atmospheric fallout. The importance of fluvial redistribution as a secondary contamination mechanism is thus highlighted.

Sedimentation of Pb-210 in Laurentian Shield Lakes

Abstract The average annual flux of Pb-210 from the atmosphere to lake surfaces and to the bottom sediments was measured in seven small lakes located on the Laurentian Shield. Direct atmospheric fallout of Pb-210 was 136 ± 16 Bq m-2 a-1 Streams from the lakes' catchments input an additional 5 to 473 Bq m-2 a-1. Only 16 to 80 percent of the total input was found in the lake sediments. The fractional rate constant for Pb-210 sedimentation from the water column ranged from 0.25 to 5.3 per annum.

Plutonium and americium export to the north-east Pacific Ocean by Columbia River runoff

Between July 1978 and July 1979, monthly samples of water collected near the mouth of the Columbia River were analyzed for Pu and Am to budget the annual quantity of these radionuclides exported to the adjacent coastal zone. During this period, approximately 70mCi of 239, 240Pu and 17 mCi of 241Am were carried by the river to the ocean. From the depositional history of a fine-grained sediment core raised from within the Columbia River estuary, an estimated 4–8 Ci of 239, 240Pu and 1–2 Ci of 241Am have entered the north-east Pacific Ocean by river transport since the late 1950s. This input would have increased the transuranic inventories in adjacent coastal sediments by at most 2·5 times those expected as a result of direct atmospheric fallout.