Cd Fluxes Research Articles

Seasonal variation, contribution and dynamics of trace elements in the drainage basin and estuary of the Serinhaém river, BA

In the present study a mass balance calculation was used to quantify trace elements (Al, Ba, Cd, Cr, Cu, Fe, Mn, Pb, Ti, V and Zn) fluxes exported from the Serinhaém River estuary to the Atlantic Ocean. The studied elements exportation in the particulate fraction showed higher fluxes in the first sampling campaign and a high export rate to the Atlantic Ocean during this period. The physical-chemical parameters showed the highest values in sampling campaign 1. These variations are probably the cause of the different trace elements behavior in fluvial and estuarine areas, where removal and addition processes between particulate and dissolved phases took place, affecting distribution coefficient and fluxes to the Atlantic Ocean. EPA ecosystems present values in accordance with Brazilian legislation for pristine areas, however, monitoring programs must be carried out in the region, to avoid future environmental problems.

Machine learning method for predicting cadmium concentrations in rice near an active copper smelter based on chemical mass balance

Identification the sources of heavy metals can effectively control and prevent agricultural soil pollution. Here we performed a three-year mass balance study along a gradient of soil pollution near a smelter to quantify the potential contribution and net cadmium (Cd) fluxes and predict Cd concentration in rice grains by multiple regression (MR) and back propagation (BP) neural network. The Cd inputs were mainly from the irrigation water (54.6–60.8%) in the moderately polluted and background sites but from atmospheric deposition (90.9%) in the highly polluted site. The Cd outputs were mainly from the surface runoff (55.8–59.5%) in the moderately polluted and background sites, but from Sedum plumbizincicola phytoextraction (83.6%) in the highly polluted site. The soil Cd concentrations, the annual fluxes of atmospheric deposition, pesticides and fertilizers, irrigation water, surface runoff, and leaching water were selected as the dependent factors to predict Cd concentrations in rice grains. The genetic algorithms (GA)-BP neural network model gives the best prediction accuracy compared to the BP neural network model and multivariate regression analysis. The major implication is that the health risks through the consumption of rice can be rapidly assessed based on the Cd concentrations in rice grains predicted by the model.

Bioactive levels of Zn, Pb, Cu, Cd and Mg, Fe in pollution sensitive and tolerant Scots pines needles – Is survival mineral-dependent?

Pine species are considered worldwide as developing various mechanisms counteracting industrial pollution specifically with Zn, Pb, Cu, and Cd. We assumed that the survival of plants should involve also the active concentrations of plant-born heavy metals as well as the mineral elements (Mg, Fe) crucial for normal photosynthetic activity of needles. The needles were collected from 100 randomly selected trees, which were divided into 50 specimens of sensitive (S) and 50 specimens of tolerant (T) species. In the study, the needles were also separated by age into 1 and 2 year-old needles. Two solutions of pH 3.5 and 6.0, mimicking acid rains (AR) were applied for extracting the bioactive forms of Zn, Pb, Cu, Cd and Mg and Fe. The elaborated mineral photosynthetic indices (12 in total), SPI (Single Phytotoxicity Indices), IPI (Integrated Phytotoxicity Indices) and TIPI (Total Integrated Phytotoxicity Indices) revealed that bioactive concentrations of Mg and Fe should be specifically regulating Zn, Pb, Cu, Cd fluxes in Scots pine needles. Such mechanism appears crucial for the survival of pine needles, both 1 and 2-years old, since Mg and Fe are directly activated in the photosynthesis process. The concentrations of bioactive Mg and Fe fractions were higher in sensitive (S) as compared to tolerant (T) pines, explaining thus the basis of their response - stronger for S and weaker for T - to adverse effects induced by the particular heavy metals. We stipulated that magnesium and iron should emerge promptly and permanently as toxicity mitigation factors, acting as a Mineral Toxicity Fence (MTF), supporting thus the survival mineral-dependent hypothesis.

Study on Surface Characteristic Parameters and Surface Energy Exchange in Eastern Edge of the Tibetan Plateau

Mount Emei is located on the eastern edge of the Tibetan Plateau, on the transition zone between the main body of the Tibetan Plateau and the Sichuan Basin in China. It is not only the necessary place for the eastward movement of the plateau system but also the place where the southwest vortex begins to develop. Its special geographical location makes it particularly important to understand the turbulence characteristics and surface energy balance of this place. Based on the Atmospheric Boundary Layer (ABL) tower data, radiation observation data and surface flux data of Mount Emei station on the eastern edge of the Tibetan Plateau from December 2019 to February 2022, the components of surface equilibrium are estimated by the eddy correlation method and Thermal Diffusion Equation and Correction (TDEC) method, the characteristics of surface energy exchange in the Mount Emei area are analyzed, and the aerodynamic and thermodynamic parameters are estimated. The results show that the annual average value of zero-plane displacement d is 10.45 m, the annual average values of aerodynamic roughness Z0m and aerothermal roughness Z0h are 1.61 and 1.67 m, respectively, and the annual average values of momentum flux transport coefficient CD and sensible heat flux transport coefficient CH are 1.58×10−2 and 3.79×10−3, respectively. The dimensionless vertical wind fluctuation variance in the Mount Emei area under unstable conditions can better conform to the 1/3rd power law of the Monin–Obukhov similarity theory, while the dimensionless horizontal wind fluctuation variance under unstable lamination and the dimensionless 3D wind fluctuation variance under stable condition does not conform to this law. In the near-neutral case, the dimensionless velocity variance in the vertical direction in this area is 1.314. The daytime dominance of sensible and latent heat fluxes varied seasonally, with latent heat fluxes dominating in summer and sensible heat transport dominating in winter. he surface albedo of Mount Emei in four seasons is between 0.04 and 0.08. The surface albedo in summer and autumn is higher than that in Mount Emei. The influence of the underlying surface on surface reflectance is much greater than other factors, such as altitude, longitude and latitude. The non-closure phenomenon is significant in the Mount Emei area. The energy closure rates before and after considering canopy thermal storage are 46% and 48%, respectively. The possible reason for the energy non-closure in this area is that the influence of horizontal advection and vertical advection on the energy closure is not considered.

Comparisons of pollution level and environmental changes from the elemental geochemical records of three lake sediments at different elevations, Central Asia

• Concentrations and EFs of PTEs in the AS sediments in plains of CA are higher than those in the mountain lakes. • Peak fluxes of PTEs in the AS sediments occurred during 1931–2000 AD, while the mountain lakes appeared after 2000 AD. • Recent increases in Na, Sr and Ca concentrations in the AS sediments are due to natural evaporation. • EFs and fluxes of PTEs in the mountain lakes indicated increasing human activity after 2000 AD. Central Asia (CA) is susceptible to arid climates and influences from anthropogenic activities. Due to regional differences among plains and mountainous regions in CA, the analysis and comparison of lake pollution levels and responses are essential for attaining a comprehensive understanding of climate change and the timing and intensity of human activities, as well as sustainable development . Here, the elemental geochemistry of sediment cores from three lakes at different elevations during the past 120 years was studied. The results showed that before 1930 AD, the concentrations of potentially toxic elements (PTEs) in the Aral Sea (AS) were comparatively high, and their enrichment factors (EFs) showed moderate to significant enrichment. In contrast, the EFs of PTEs in the two mountain lakes were lower, suggesting zero or minor enrichment driven mainly by natural processes. During the period 1931–2000 AD, the EFs of metals in the AS displayed a decrease followed by an increase, and they were dominantly controlled by agricultural activities. The EFs and fluxes of metals began to rise in Lake Issyk-Kul (LIK), whereas their values in Lake Son-Kul (LSK) remained relatively stable. After 2000 AD, the PTE concentrations further decreased in the AS, but the concentrations of Na, Sr, and Ca increased due to natural evaporation. However, in the mountain lakes, the increases in As, P, and total organic carbon contents in LIK were influenced by agriculture activities, and the EFs and fluxes of Cd and Pb increased in LSK due to atmospheric deposition .

Temporal and Spatial Variation Characteristics of Heavy Metal in Atmospheric Deposition in China from 2000 to 2018

Owing to the significant impact of heavy metals in atmospheric deposition on soil, clear knowledge on the present situation and temporal and spatial variation in fluxes of heavy metals in atmospheric deposition all around China is urgently needed. In this study, we collected 99 published papers on deposition fluxes of heavy metals from 2001 to 2021 based on the CNKI and Web of Science database and extracted 718 to 1672 monitoring points from these papers. The Meta-analysis method was used to calculate the weighted average of deposition fluxes of heavy metals, and the spatial-temporal characteristics in different periods from 2000 to 2018 were studied by subgroup analysis, which compared the differences between different types of areas, such as agricultural and rural areas and urban and industrial areas. The results showed that the annual fluxes of heavy metals in atmospheric deposition[mg·(m2·a)-1] in China were as follows:Zn (96.75)>Pb (23.37)>Cu (12.77)>Cr (11.04)>Ni (6.61)>As (2.97)>Cd (0.48)>Hg (0.05). Overall, the estimated value of deposition fluxes in China from 2000 to 2018 was higher than that of rural areas in England from 1995 to 1998. The deposition fluxes in industrial areas and urban areas were much higher than those in the agricultural and rural areas, especially the industrial areas where the heavy metal pollution was more serious. The deposition fluxes of As and Cd in the Changsha-Zhuzhou-Xiangtan area were relatively high, whereas the atmospheric deposition of heavy metals in Northeast China, the Pearl River Delta, and North China Plain was more serious than that in the other areas. In the past 20 years, the annual deposition fluxes of Cd fluctuated around the overall average, without an obviously declining trend, whereas the deposition fluxes of Cd in the urban, agricultural, and rural areas showed a trend of growth. These results suggested that precise and risk control measures of atmospheric emissions should be established based on the characteristics of regional industrial structure, which should cover all levels, all types, and all regions. In addition, more restrictive measures should be taken to solve the current problem caused by the higher deposition flux of Cd in atmospheric deposition.

Meta-analysis of Cd input-output fluxes in agricultural soil.

Heavy metal pollution of agricultural soil, especially Cd, has become a global threat to food safety and human health. Analysis of Cd fluxes through different input/output pathways is widely used to predict the change of Cd content in agricultural soil, identify the critical pathways, and assist in developing effective management strategies to protect the environmental quality of agricultural soils. In the present study, literature recording input/output fluxes of Cd through different pathways in agricultural soils were investigated, with study areas primarily located in China, Japan, and Europe. Fluxes of Cd at the study sites were calculated, and comparative analyses were carried out. Results indicated that the dominant input pathway of Cd was strongly associated with the intensity of local industrial activities. Atmospheric deposition was the predominant input pathway of Cd for 75% of the study cases. Irrigation and livestock manure were also major pathways of Cd input in China. The main output pathways were influenced by the planting structure, precipitation, topography, etc. Crop harvesting and leaching to groundwater played important roles among all Cd output pathways in China, and crop harvesting alone could remove a significant amount of Cd from the soil, with an estimated average flux of 6.27g/ha/yr. Leaching was the dominant Cd output pathway in Europe, accounting for 77%-93% of total outflux. To mitigate the accumulation of Cd in agricultural soil, standards to regulate Cd in the atmospheric environment, irrigation water, and agricultural additives should be tightened, and regulated removal and disposal of crops harvested from the heavily contaminated field should be promoted.

Annual net input fluxes of cadmium in paddy soils in karst and non-karst areas of Guangxi, China

In recent years, the problems of high cadmium content and low Cd mobility in karst areas compared with non-karst areas have attracted extensive attention. Identifying the difference between the net Cd flux in karst and non-karst areas is crucial for sustainable land management. Basically, rock weathering is a natural source of Cd. While Cd accumulation in soil has increased due to both anthropogenic and natural sources, the contributions of anthropogenic input and rock weathering to soil Cd concentration in karst and non-karst areas remain unclear. In this study, the input (e.g., atmospheric deposition, fertilizer and irrigation) and output fluxes (e.g., leaching and early and later rice harvest) of Cd in farmland soils in karst and non-karst areas of Guangxi from 2017 to 2018 were monitored. The results showed no significant difference (P = 0.289) in the contributions of various input pathways between karst area and non-karst area, and atmospheric deposition (64–55 %) played an important role in the input fluxes. Nevertheless, the low soil pH value and high rainfall in non-karst areas increase Cd mobility and plant availability in soil, causing the output flux in non-karst areas (5.30 g/ha/y) to be greater than that in karst areas (3.17 g/ha/y). According to the national standard, the exceedance rate of Cd in rice grains in non-karst area (17 %) was higher than that in karst area (15 %). Therefore, ecological risk assessment in non-karst areas with high Cd bioavailability should be prioritized. Furthermore, the annual increase rate of Cd concentration in topsoil of karst and non-karst areas was −0.27 μg/kg/y and −1.23 μg/kg/y, respectively. However, the soil Cd concentration in karst and some non-karst areas still exceeded the guideline value. Given that the net input flux of Cd was negative, the accumulation of Cd in soil may be determined by rock weathering.

Superposition Effects of Zinc Smelting Atmospheric Deposition on Soil Heavy Metal Pollution Under Geochemical Anomaly

Guizhou Province is covered by a large area of carbonate rocks where, with a higher background of heavy metals under the geochemical anomaly, more than 3.6 × 105 ha of heavy metal–contaminated soil in the northwest area is related to historical indigenous zinc smelting. To explore the superposition effect of industrial source atmospheric deposition on soil, two watersheds were selected for study: 1) Maoshui reservoir watershed (MS), where there is a zinc smelting plant, and 2) Haishe lake watershed (HS), which was the control. We collected atmospheric depositions and soil for 3 years and analyzed Cadmium (Cd), lead (Pb), chromium (Cr), copper (Cu), nickel (Ni), and zinc (Zn) content. The results show that the heavy metals in the atmospheric deposition of the pollution watershed in MS were much higher than those in the control site, HS. The deposition fluxes of Cd, Pb, Cr, Ni, and Zn in MS were 27.8, 602, 145, 43.9, and 2,225 mg·m−2·a−1, respectively, and were 1.37–2.01 times higher than in HS. Soil heavy metals in MS were 1.01–5.69 times higher than in HS. The elevated concentrations were found focused from northeast to southwest around the plant but was distributed uniformly in HS. The average concentration of Cd, Pb, and Zn in the soil was 6.54, 67.4, and 264 mg·kg−1, respectively, in HS, which represents a high geochemical background even without pollution. After 13 years of deposition by prediction, the contribution of the atmospheric deposition on the soil in the zinc-smelting area was lowest, at 5.10%, for Ni, and highest, at 17.9%, for Cd. Principal component analysis of atmospheric deposition and soil heavy metals reflected that the pollution sources in MS were more diversification than those in HS. Zinc smelting atmospheric deposition showed superposition effects on the accumulation of heavy metals in soil under the geochemical anomaly in this region.

Wildfires trigger multi-decadal increases in sedimentation rate and metal loading to subarctic montane lakes

We evaluated how two large wildfires affected the sedimentation rate and accumulation of lead (Pb), mercury (Hg), and cadmium (Cd) in sediment of four subarctic montane lakes in the Yukon, Canada. The wildfires occurred 60 and 20 years (1958, 1998) before sediment collection in 2018. Site-specific fire exposure was inferred from the charcoal accumulation histories in the lake sediments and the burned catchment area was determined from historical fire maps. The two major wildfires caused a two to five-fold increase in sedimentation rates and a two to eight-fold increase in sediment metal accumulation rates in Little Fox Lake. The mass accumulation rates of metals in Little Fox Lake sediment increased by a maximum of 2.7–4.7 mg Pb m−2 yr−1, 19–29 μg Hg m−2 yr−1 and 37–114 μg Cd m−2 yr−1 following wildfires. Modelling using elemental ratios of lithogenic sources suggested a large proportion of the Pb and Hg accumulating in post-fire sediment was from remobilized legacy anthropogenic pollution. In contrast, Cd fluxes were consistent with variation in catchment weathering. Impacts of wildfires were visible but more muted in the sediment of Little Braeburn Lake, whereas Fox Lake and Grayling Lake sediments showed little to no wildfire impact and served as a reference for external (long-range) metal deposition. Major changes to lake sediment geochemistry in Little Fox Lake were caused by the lack of vegetation and soil recovery in the catchment following the severe 1998 fire. Wildfire impacts were persistent in the lake more than 20 years after the last fire, with no sign of a return to pre-fire Pb, Hg, and Cd accumulation rates. This study shows that wildfires in northern montane catchments can significantly increase the rate of metal accumulation in affected lakes, thereby impeding recovery from reductions in anthropogenic air emissions of these metals.

Heavy metal characteristics in porewater profiles, their benthic fluxes, and toxicity in cascade reservoirs of the Lancang River, China.

The construction of cascade reservoirs on the Lancang River (the upper Mekong) has an important influence on the distribution and accumulation of heavy metals. Heavy metal contents in porewater provide vital information about their bioavailability, studies on this aspect are rare until now. In this study, sediment cores were collected from four adjacent cascade reservoirs in the upper Mekong River to study the distribution, potential sources, diffusive fluxes and toxicity of heavy metals in porewater. The findings indicated that the average contents of Mn, Fe, As, Ni, Cu, Zn, Cd, and Pb in the sediment porewater were 6442, 644, 11.50, 2.62, 1.23, 3.95, 0.031, and 0.24µg/L, respectively; these contents varied as the sediment depth increased. Correlation analysis and principal component analysis showed that Cu, Zn, Cd and Pb were mainly associated with anthropogenic sources, As, Mn and Fe were primarily affected by natural inputs, and Ni was affected by a combination of natural and anthropogenic effects. The diffusive fluxes of Mn, Fe, As, Ni, Cu, Zn, Cd, and Pb in the cascade reservoirs of the Lancang River were 919 - 35,022, 2.12 - 2881, 0.17 - 750, 0.71 - 7.70, 2.30 - 31.18, (-3.35) - 6.40, 0.06 - 0.54, and (-0.52) - 4.08µg/(m2 day), respectively. The results of toxic units suggested that the contamination and toxicity of heavy metals in porewater were not serious. Overall, in the cascade reservoirs, the content and toxicity of heavy metals in porewater of the upstream reservoirs were higher than that of the downstream reservoirs. The operation of the cascade reservoirs enabled greater accumulation of contaminants in sediments of the upstream reservoirs. This research gives strong support for the prevention of heavy metal contamination and the sustainability of water resources under the running condition of cascade reservoirs on such a large international river (the Lancang-Mekong River).

Integrated Assessment of Land-to-River Cd Fluxes and Riverine Cd Loads Using Swat-Hm to Guide Management Strategies

Integrated Assessment of Land-to-River Cd Fluxes and Riverine Cd Loads Using Swat-Hm to Guide Management Strategies

A historical record of trace metal deposition in northeastern Qinghai-Tibetan Plateau for the last two centuries.

Owing to rapid socio-economic development in China, trace metal emissions have increased and lakes even in remote areas have experienced marked changes in the last century. However, there are limited studies revealing long-term trends, anthropogenic fluxes, and spatial characteristics of trace metals in lakes. In this study, we present a geochemical record from Lake Qinghai in the northeastern Qinghai-Tibetan Plateau and reconstruct trace metal pollution history during the last two centuries. The lacustrine sediment core was dated by 137Cs and 210Pb, and sediments deposited prior to the 1850s were selected as the pre-industrial background. Factor analysis and enrichment factor indicated Cr, Cu, and Ni generally originated from natural sources, while Cd, Pb, and Zn have been influenced by human contamination since the mid-1980s. The anthropogenic Cd mainly derived from non-ferrous metal smelting in Gansu Province, and fluxes to Lake Qinghai sharply increased after the mid-1980s. The metal reconstruction is similar to other lake sediment records from China and corresponds well with rapid economic development in China. The spatial pattern of anthropogenic Cd fluxes to lakes is primarily attributed to regional industrial emission, phosphate fertilizers, and manure applied in agriculture.

Effectively reducing the bioavailability of heavy metals in disturbed sediment with biochar: In-situ remediation

The effect of biochar, derived from Phyllostachys pubescens (PP), on the bioavailability and release fluxes of Cd, Cu, and Zn in disturbed sediments was investigated. The content of Cd, Cu, and Zn in overlying water and pore water sharply increased after sediment disturbance. When biochar dose exceeded 2.96 kg/m2, the maximum amount of Cd, Cu, and Zn in the overlying water was significantly decreased, and a 5 cm biochar layer was formed. Release fluxes of Cd2+, Cu2+, and Zn2+ at the new sediment-water interface were negative diffusion fluxes, which reached maximum values of −0.61, −8.31 and −93.57 μg∙(m2d)−1, respectively. The bioavailability of Cd, Cu, and Zn, measured by diffusive gradients in thin film (DGT) probes, reached 0.92, 5.28 and 34.71 μg∙L−1 in sediment when the biochar dose was 14.78 kg∙m−2, which led to a reduction in [Cd]-DGT, [Cu]-DGT, and [Zn]-DGT by 46.51%, 71.54%, and 61.38%, respectively, compared with blank. Bacterial community analysis showed that low dose treatment(2.96–5.91 kg∙m−2) increased the Chao1 and Shannon of bacterial communities, while high dose treatment (8.87–14.78 kg∙m−2) showed negative effect. Overall, the PP biochar can be used to immobilize heavy metals in disturbed sediments as an economically and feasible method in field.

Prediction of soil solution concentrations and leaching losses of cadmium in agricultural soils.

Cadmium (Cd) leaching is often estimated in Cd balance models using the product of drainage water (precipitation excess) and soil solution Cd concentration. However, Cd concentrations are seldom available but rather predicted using empirical models. Despite the availability of empirical models that estimate soil solution Cd concentrations, they have limitations for use in New Zealand where total Cd in agricultural soils is low and organic matter (OM) high. This study derived a Freundlich-type model from desorption data and a soil-liquid partitioning coefficient (KD ) model based on sorption data to predict soil solution Cd concentrations from commonly measured soil parameters that could be used to calculate Cd leaching fluxes. Independent soil solution Cd concentrations and Cd fluxes measured in drainage water from field trials were used to validate the predictive capacity of the models. It was found that soil pH and OM content were the most important factors controlling soil solution Cd, along with total Cd. Both models explained 83% of the variation in measured soil solution Cd concentrations in an independent dataset. Comparisons between Cd fluxes predicted using the Freundlich-type model and measured fluxes were within 25% of each other at 6 of 19 field sites studied. However, physical and chemical nonequilibrium conditions in soils and uncertainty in measured values likely contributed to differences between predicted and measured Cd fluxes at other sites. To unravel the impact of nonequilibrium and soil physical conditions on Cd concentrations in drainage water, more data are required on Cd concentrations collected under field conditions. This will allow better validation of the approach used in Cd balance models to calculate Cd leaching from soils.

Assessment of the potential for phytoremediation of cadmium polluted soils by various crop rotation patterns based on the annual input and output fluxes

Phytoremediation potential of two oil crop rotations (oilseed sunflower–rape (O+Ra) and peanut–oilseed rape (P+Ra)) was compared with three conventional cropping patterns (rice–rape (R+Ra), rice–rice (R+R), single cropped rice (SR)) in experimental plots with cadmium (Cd)-contaminated soil. A new approach was used to evaluate phytoremediation potential based on the balance between annual input and output fluxes of Cd in farmland soil. In O+Ra and P+Ra rotations, 77.24 and 62.09 g/ha Cd were removed, respectively, whereas in R+Ra, R+R, and SR patterns, 41.79, 46.46, and 23.85 g/ha Cd were removed, respectively. The balance between inputs and outputs of Cd was − 40.72 and − 25.76 g/ha under O+Ra and P+Ra rotations, respectively. Available Cd content in topsoil was reduced by 5.58% and 3.91% under O+Ra and P+Ra rotations, respectively. Based on the balance between Cd inputs and outputs, phytoremediation efficiencies of O+Ra (1.23%) and P+Ra (0.78%) rotations were higher than those of R+R (0.29%), R+Ra (0.13%), and SR (−0.38%) systems. Because crop removal is the main Cd output pathway, selection of a suitable crop is particularly important in remediation of Cd-contaminated farmland.

Release flux of heavy metals from river sediments at different flow rates

Abstract This paper simulates sediment motion under different hydrodynamic conditions, aiming to investigate the release flux of heavy metals in river sediments. During the lab experiments, carried out in a circular rectangular flume device, water velocity in the flume was altered by controlling the gate switch, and the flow rate was controlled from 0 to 1 m/s. Sediment from the Le'an River and chlorine-removed tap water were used as experimental sediment and water, respectively. Through analyses of Cu, Zn, Cd, and Pb concentration in water at different flow rates, the relationship between the release flux (y) of Cu, Zn, Cd, and Pb and the flow rate (x) was established with a fitting error of less than 15%. In order to judge the reliability of the conclusions, experimental results were verified outdoors. The results showed when the sediment particle size is between 0 and 250 μm, within 1 hour, a quadratic polynomial correlation between the release flux of Cu, Cd, and Pb from river sediments and water velocity when the water pH is 5–9 and the flow rate is 0–65 cm/s; when the water pH is 5–9, the flow rate is 0–35 cm/s, the release flux of Zn from river sediments was shown to have a quadratic polynomial relationship with water velocity. The error between the calculated and measured values of heavy metals released from sediment in the Le'an River were within 5–30%. Our results can provide a theoretical reference for the control and treatment of heavy metal pollution in rivers and further improve corresponding water quality models.

Improving Cd risk managements of rice cropping system by integrating source-soil-rice-human chain for a typical intensive industrial and agricultural region

Cadmium (Cd) accumulation in rice (Oryza sativa L.) leads to a large number of human health risks. To better understand the critical processes of Cd-related health risks and to inform mitigation policies, an assessment method was integrated by coupling source-soil-rice-human systems with anthropogenic Cd sources historical survey, regional soil Cd concentration surveyed data and an extensive literature review of Cd related human diseases. This method was subsequently applied to a rapid developing industrial and agricultural area in China. Results indicated that Cd emission sources increased fourfold from 1990 to 2007, and remained high value about 140 × 103 kg yr−1 after 2008 in the study region. The Cd fluxes in 1990–2017 varied from 3.93 to 73.49 mg m−2. Raw coal consumption contributed to approximately 50% of total Cd fluxes. During 2003–2013, the annual increasing rate of soil Cd varied from −2.34 μg kg−1yr−1 to 7.94 μg kg−1yr−1 with an average 5.14 μg kg−1yr−1. Under the current industry and agriculture developing trends, farmland soil in 2030 will face significant Cd pollution risks and the average soil Cd concentration will increase to 0.35 mg kg−1 which is 1.75 times higher than that of 2003. Consequently, higher Cd concentrations were predicted in rice grain and human blood. About 3.43% of adults may have obesity and hypertension, and approximately 4.96% of children will also be the risk of physical, cognitive neurobehavioral development. The mitigation strategies of Cd source reduction and phytoremediation technology in rice system can significantly decrease Cd-related health risks. These strategies are far less effective in already heavily polluted soils. This study provides critical information on Cd emission factors, Cd related human diseases, and a novel useful tool for policy-makers on metals pollution management.

Controls on the cadmium isotope composition of modern marine sediments

Continental margin sediments have been identified as the dominant sink in the marine budget of cadmium (Cd). The isotopic composition of this important output flux is, however, unknown. Here we present, with measurements on the Argentine continental margin, the first observational constraints on the isotopic composition of Cd in modern marine oxic and sub-oxic sediments. We identify two main removal mechanisms of Cd; in organic material, and by sulfide formation. Surface margin sediments (0–0.5 cm), with dissolved O2 below detection from ∼0.5 cm, are isotopically lighter than overlying oxygenated waters. A mass balance for these surface sediments indicates that Cd is present dominantly as organically-bound particulate Cd. In sub-surface sediments, Cd concentrations increase in the zone of nitrate reduction, and attain similar isotopic compositions as the water that overlies the sediment (i.e. ∼0.35‰ in deep waters). These observations are consistent with a downward diffusive flux of seawater Cd and redox-driven quantitative removal of that Cd during sulfide precipitation. In combination, these two routes of Cd removal lead to burial of isotopically light organic Cd in margin sub-oxic sediments that enables the global isotopic Cd budget to be balanced.

Cadmium distribution in soils, soil litter and cacao beans: a case study from Colombia

Cadmium is a toxic non-essential metal for almost all living systems. It is one of the biggest challenges for farmlands and the food chain because of its toxic effect on human health. This research aims to determine the Cd content in soils, litter and cacao beans, following the Cd fluxes within each cacao system using the two-dimensional electrical resistivity tomography technique. The study was carried out in four farms located in the Magdalena basin in Antioquia, Colombia. The farms showed a heterogeneity in relation to cacao cultivars, altitude, topography and geology. The soil cation electrical capacity, pH and soil organic matter levels, as well as the Al, Al3+H+, Ca, K, Mg and P contents were measured at different depths. Moreover, the Cd content was correlated to the resistivity values of samples taken in situ using ERT. Soil Al3+H+ and the altitude of the farms fitted as the best predictors of the beans’ Cd content. Furthermore, the Cd content in soils from the assessed farms ranged between 1.22 and 2.03 mg kg−1. The Cd content in cocoa beans ranged from 0.07 to 1.44 mg kg−1, with a value of 0.40 mg kg−1 on average. The resistivity values obtained in field showed a high correlation with the soil Cd content determined (R2 = 0.82). The predictive tomography plots highlighted topsoil Cd dynamics between litter, amendments and fertilizers. Therefore, these results underlie the utility of the combined geophysical techniques and soil chemical properties including the analysis of fertilizer amendments to improve the understanding of Cd dynamic.