A method for heavy metal exposure risk assessment to migratory herbivorous birds and identification of priority pollutants/areas in wetlands

Effects of land use/cover change on heavy metal distribution of soils in wetlands and ecological risk assessment

This study aimed to determine the impact of land use/cover changes on the heavy metal content in the Sultan Marshland and surrounding area and assess the pollution status. 54 topsoil samples (0-20 cm) were collected from the Rangeland, Farmland, Scrubland, Southern Marshland, Northern Marshland, and Dry Lake areas. The heavy metal contents of the soil samples (Cr, Pb, Fe, Zn, Cu, Co, Mn, Cd, Mo, As, and Ni) were determined using ICP-MS and ICP-OES devices. The impact of land use/cover change on soil heavy metal content was evaluated using variance analysis, while differences between groups were identified using the Duncan test. Principal Component Analysis (PCA) was conducted to identify potential sources of heavy metals. The contamination status of the soils was evaluated based on land use/cover using the Contamination Factor (Cf), Pollution Load Index (PLI), Ecological Risk Factor (Er), and Potential Ecological Risk Index (PERI). Changes in land use/cover around the Sultan Marshlands affected heavy metal distribution of the soils except for Cd. Among all land use/cover types, Fe concentration was the highest in the soils, while Cd concentration was the lowest. Soils in Southern Marshland exhibited higher average concentrations of Cr, Fe, Zn, Co, Cu, and Ni compared to other land uses/covers. Farmlands and rangelands had higher concentrations of Cd, As and Pb. Land use/cover was ranked based on the total heavy metal load in the following order in terms of average values: Southern Marshland > Scrubland > Farmland > Rangeland > Northern Marshland > Dry Lake. According to Cf, the soils in the Dry Lake were exposed to considerable levels of As contamination. Based on PLI, half of the soil sampling points in the Southern Marshland soils showed a degradation in environmental quality. Er indicated that all land uses moderately polluted with Cd. According to the average PERI, all soils under different land use/cover types were categorized as having a low ecological risk. It was believed that heavy metals originated from both natural and human activities. To ensure the sustainability of the ecosystem and to mitigate the risk of heavy metal pollution entering the food chain, it is recommended to manage farming and mining activities and land use habits.

Potential toxic heavy metals in village rainwater runoff of antimony mining area, China: Distribution, pollution sources, and risk assessment

The potential toxic heavy metal runoff from antimony mining areas poses a serious threat to the water environment and the health of residents in the village. The study found that the average concentrations of As, Sb, Cr, Pb, and Cd in the runoff were 0.1237, 0.1148, 0.0332, 0.0140, and 0.0013 mg/L, which were higher than the normal average concentrations in the water environment of 0.018, 0.0009, 0.05, 0.012, and 0.000013 mg/L, respectively.Sb and As are severely polluted, while Cd, Pb, and Cr have lower pollution levels. The coefficients of variation for As, Sb, Cr, Pb, and Cd range from 0.079 to 1.051, with Sb showing exceptionally high variability. Heavy metal elements Pb, Cd, and Sb accumulate in the southeastern area of the village, with Sb concentrations decreasing from the southeast to the northwest. As is mainly distributed in the northeastern part of the village, while Cr is primarily found in the central-western region. Source analysis indicates that As and Sb originate from mining and industrial activities, dust deposition, and domestic sewage. Cr comes from the natural geological background and metal product industry, Pb from lead-acid batteries, industrial activities, and gasoline additives, and Cd from fertilization in residential green areas and pesticide use. Health risk analysis reveals that the hazard index (HI) values for As and As in the water environment are 1.49 and 2.31, respectively, both exceeding 1, posing a serious threat to the health of village residents. The HI values for Pb, Cr, and Cd elements are all below 1, indicating lower risks. This study identified that Sb in the antimony ore area and its associated metal element As are the main elements leading to potential heavy metal pollution in the runoff of village residential areas, providing direction for subsequent water environment restoration work.

Occurrence and exposure risk assessment of organochlorine pesticides in two waterbird species from Honghu Lake Wetland, Central China

Monitoring and evaluating bird exposure to hazardous pollutants in wetlands are receiving considerable attention. In this study, the occurrence of 18 organochlorine pesticides (OCPs) in the muscle of bean geese (Anser fabalis) and common teals (Anas crecca) collected from Honghu Lake Wetland (HLW), Central China was studied. Additionally, an exposure risk assessment model was applied to obtain risk levels of OCPs to these birds through three oral routes (food intake, water drinking and soil ingestion). The results suggested that the most abundant OCPs detected in the muscle of waterbirds were DDTs (7.68-602 ng/g lipid weight), followed by HCHs (1.39-89.8 ng/g lipid weight). A significant difference (p < 0.05) existed between two species, but most of OCPs exhibited no statistically relationship with age or gender (p > 0.05). The compositional patterns of OCPs combined with ratios of certain metabolites to their parent compounds indicated that all OCPs in the HLW were largely from historical usage except heptachlor. The exposure risk assessment revealed that common teals with lighter weight had greater exposure risks than bean geese. Of the OCPs analyzed, DDTs could probably cause harm to target birds studied here. Exposure via food intake was identified to be significant while soil ingestion and water drinking contributed least, but they should still be concerned.

Spatial distribution and source analysis of airborne trace metal deposition using moss biomonitoring in Huai'an, China

Terrestrial mosses are tracers for studying atmospheric trace metal deposition and pollution. Here, Al, Fe, Zn, Mn, Ba, Cu, V, Cr, Pb, Ni, Co, and Cd concentrations in mosses from Huai'an, China, were measured to investigate their contamination level, spatial distribution, and sources. The average concentration of all the metals (except Ni) was much higher than those in Albania, a "hotspot" of toxic metal contamination in Europe. The pollution degree of the metals varied significantly: moderate contamination by Al, Fe, Mn, Zn, Cr, V, and Cd; slight contamination by Ba, Cu, Ni, and Pb; and suspected contamination by Co. Based on the Nemerow index (P_N), only 8% of the moss samples were graded as moderate pollution, while the remaining 92% were rated as heavy pollution, with Cd and Zn contributing the most. The potential ecological risk index (RI) indicated a moderate potential ecological risk from the metals in Huai'an, with the atmosphere most heavily polluted by Cd. Further, the positive matrix factorization (PMF) model was applied to confirm the metal contamination sources and allocate their source contributions in Huai'an mosses. The results showed that the source contributions of industrial activities related to metal smelting, textile dyestuff and agricultural activities, mining development, natural source, and coal burning and traffic emission accounted for 28.86%, 20.29%, 19.83%, 17.98%, and 13.04%, respectively.

Heavy metal exposure to a migratory waterfowl, Northern Pintail (Anas acuta), in two peri-urban wetlands

In this study, the heavy metal exposure risk model was employed to assess the exposure risk to a predominantly herbivore waterfowl, Northern Pintail, wintering in two wetland habitats in the Purulia district of West Bengal, located on overlapping Central Asian Flyway (CAF) and East Asian-Australasian Flyway (EAAF). Both wetlands were important staging and roosting grounds for migratory waterfowl for ages. The exposure model was used to quantify the risk of exposure to metals through oral ingestion. Exposure doses of Cu, Zn, Pb, and Cr through food plants ingestion and food-associated sediment consumption pathways were two potent sources of heavy metal exposure in the waterfowl under study. Exposure through water intake was ignored as metals were either of negligible concentrations or below the detection limit in water samples. Heavy metal concentrations showed significant positive correlations between bottom sediment and plant at both sites. At Purulia Sahebbandh (Site 1), the total exposure dose of all four metals was much higher than their conforming tolerable daily intake (TDI), and thereby, the metals might pose threats to the migratory wintering herbivorous waterfowl populations. However, in Adra Sahebbandh (Site 2), total exposure doses of Pb, Zn and Cu were much below their corresponding TDI. The Hazard Quotient (HQ) of Cr was highest followed by nonessential toxic Pb and these two elements could be considered as priority pollutants at Site 1. Prioritize threats were decreased in the following sequence: Cr > Pb > Cu > Zn at Site 1 and Cr > Zn > Pb > Cu at Site 2. Hazard Index was found to be >5 at Site 1 and for much higher metal loads a significant correlation between metal concentrations in plants, bottom sediment and exposure doses were also recorded. Therefore, the peri-urban Purulia Sahebbandh wetland could immediately be considered for risk control and demanded holistic management of important waterfowl habitats.

Synthesis of Biomass-Derived Activated Carbons and Their Immobilization on Alginate Gels for the Simultaneous Removal of Cr(VI), Cd(II), Pb(II), As(III), and Hg(II) from Water

Low-cost alginate gels of activated carbons were prepared, which were derived from the peels of banana and sweet lime. The synthesized carbon was activated and immobilized on alginate, producing its gel. These gels were categorized according to their methods of drying, in which air drying, freeze drying, and supercritical drying led to the formation of xerogels, cryogels, and aerogels, respectively. The gels were used for adsorption of heavy metals from their aqueous solution. The heavy metals that were targeted for removal were Pb(II), Cd(II), Cr(VI), As(III), and Hg(II). Among all the adsorbents, the alginate cryogel of sweet lime-derived activated carbon (SLACC) showed the highest removal percentage of heavy metals, and thus, it was used for batch study. The adsorption of heavy metals by SLACC was checked at different times, pH values, adsorbent doses, temperatures, and adsorbate concentrations. The study revealed that the pseudo-second-order model best described the kinetic study, while the adsorption followed the Freundlich isotherm. SLACC showed maximum adsorption capacities (q _cal) of 3.71, 4.22, 20.04, 7.31, and 4.37 mg/g for Cr, Cd, Pb, As, and Hg, respectively, when 20 mg of SLACC was used for the removal of 4 ppm concentration of the targeted heavy metals from their 20 mL solution. Based on the thermodynamic study, it was found that the adsorption was spontaneous and exothermic. Furthermore, the adsorbent was also used on real water samples and showed up to 90% removal efficiency for these targeted heavy metals. SLACC was regenerated with 0.1 M ethylenediaminetetraacetic acid (EDTA) solution and reused for five cycles, in which the percentage removal of heavy metals was more than 50% till the fourth cycle. Furthermore, the leaching study showed that no toxic elements had leached from SLACC into water, making it a safe adsorbent.

A spatial prioritization method for identifying potential eco-risk distributions of heavy metals in soil and birds

Geochemical approaches are popular for evaluations based on heavy metal concentrations in sediments or soils for eco-risk assessment. This study proposes a systematic geochemical approach (SymGeo) to explore six heavy metals in topsoils and bird tissues and organs of the target birds. We assume that the proposed approach based on field-collected heavy metals in topsoils and feathers can predict the areas with the potential risk of the heavy metals in birds. Finite mixture distribution modeling (FMDM) was used to identify background values of the heavy metal concentrations in topsoil. A spatial enrichment factor (EF), potential contamination index (PCI), contamination degree (Cod), and potential ecological risk index (PRI) based on FMDM results for topsoil, and a potential risk index (PRI_bird) of heavy metals in the birds, were utilized for systematic prioritization of high eco-risk areas. Using multiple EF, PRI, and Cod results and multiple PRI-based maps of the heavy metals in feathers, we systematically prioritized risk areas where there is a high potential for heavy metal contamination in the birds. Our results indicate that heavy metal concentrations in the feather, liver, and kidney are not spatially cross-autocorrelated but are statistically significantly correlated with some heavy metals in topsoil due to external and internal depositions. Further, multiple EF, Cod, and RI distributions for topsoil, along with the PRI of the feather, showed that adequate coverages for potential risk for birds were greater than 71.05% in the top 30% and 84.69% in the top 20% potential eco-risk priority area of heavy metals in bird liver and kidney. Hence, our proposed approach suggests that assessments of heavy metals in bird feathers and topsoils without bird organs can be utilized to identify spatially high-risk areas. The proposed approach could be improved by incorporating water and sediment samples to enhance the crowdsourcing and the species-specific data.

Soil from an Abandoned Manganese Mining Area (Hunan, China): Significance of Health Risk from Potentially Toxic Element Pollution and Its Spatial Context

This study assessed the significance and potential impact of potentially toxic element (PTE) (i.e., Mn, Pb, Cu, Zn, Cr, Cd, and Ni) pollution in the surface soil from an abandoned manganese mining area in Xiangtan City, Hunan Province, China, on the health of residents. The risks were sequentially evaluated using a series of protocols including: the geo-accumulation index (I_geo), pollution load index (PLI), potential ecological risk index (RI), and implications for human health from external exposures using the hazard quotient (HQ), hazard index (HI) and carcinogenic risk (CR). The results revealed that Mn and Cd were the major pollutants in the soil samples. The ecological risk assessment identified moderate risks, which were mainly derived from Cd (82.91%). The results of the health risk assessment revealed that generally across the area, the non-carcinogenic risk was insignificant, and the carcinogenic risk was at an acceptable level. However, due to local spatial fluctuation, some of the sites presented a non-carcinogenic risk to children. The soil ingestion pathway is the main route of exposure through both non-carcinogenic and carcinogenic risks, with Mn being the major contributor to non-carcinogenic risk, with Cr and Cd the major contributors to carcinogenic risk. In addition, three pollution sources were identified through the Pearson correlation coefficient and principal component analysis (PCA), which included: a. mining activities and emissions from related transportation; b. natural background; c. agricultural management practices and municipal sewage discharge. The study provides information on the effects of spatial variation for the development of the abandoned mining areas and a useful approach to the prioritization of locations for the development and utilization of soil in these areas in China.

Real-Time Identification of Irrigation Water Pollution Sources and Pathways with a Wireless Sensor Network and Blockchain Framework

Real-time identification of irrigation water pollution sources and pathways (PSP) is crucial to ensure both environmental and food safety. This study uses an integrated framework based on the Internet of Things (IoT) and the blockchain technology that incorporates a directed acyclic graph (DAG)-configured wireless sensor network (WSN), and GIS tools for real-time water pollution source tracing. Water quality sensors were installed at monitoring stations in irrigation channel systems within the study area. Irrigation water quality data were delivered to databases via the WSN and IoT technologies. Blockchain and GIS tools were used to trace pollution at mapped irrigation units and to spatially identify upstream polluted units at irrigation intakes. A Water Quality Analysis Simulation Program (WASP) model was then used to simulate water quality by using backward propagation and identify potential pollution sources. We applied a “backward pollution source tracing” (BPST) process to successfully and rapidly identify electrical conductivity (EC) and copper (Cu²⁺) polluted sources and pathways in upstream irrigation water. With the BPST process, the WASP model effectively simulated EC and Cu²⁺ concentration data to identify likely EC and Cu²⁺ pollution sources. The study framework is the first application of blockchain technology for effective real-time water quality monitoring and rapid multiple PSPs identification. The pollution event data associated with the PSP are immutable.

Trace element distribution in tissues and risk of exposure of ruddy shelduck wintering in Nanhaizi Wetland, Baotou, China

The Nanhaizi Wetland (NHZW) is a significant part of the Baotou Yellow River National Wetland Park in China, an important migration station and habitat for waterfowl. The Yellow River receives a significant amount of industrial and agricultural wastewater. Therefore, the environmental quality of NHZW directly affects the survival of migratory birds in the Baotou region. We aimed to determine the trace element distribution in tissues and risk of exposure in ruddy shelduck and to provide a scientific basis for bird protection and an environmental quality assessment for the NHZW. In January 2018, we collected water, soil, and 18 dead ruddy shelduck Tadorna ferruginea (nine males and nine females) from the NHZW. We measured concentrations of trace elements (Cd, Pb, Cu, Zn, Hg, and As) in the specimens and modeled the risk of exposure to trace elements. Trace element concentration was greatest in feathers, followed by the kidneys, liver, and muscle, in descending. There was no significant difference in trace element accumulation between sexes. Exposure doses of Hg in water; Cr, Pb, and Cu in soil; and Pb, Cu, and Hg in corn were higher than the tolerable daily intake and may adversely affect ruddy shelduck. The calculated hazard quotients (HQ) for trace elements were ranked as follows: Hg > Cr > Pb > Zn > Cu > As, where Hg and Cr were at high risk levels (HQ > 1).

Metal Exposure Risk Assessment for Tree Sparrows at Different Life Stages via Diet from a Polluted Area in Northwestern China

To estimate the risk of metal (Cu, Zn, Pb, and Cd) exposure of tree sparrows through food at different life stages (including nestling, juvenile, adult in summer, and adult in winter), metal daily intake (MDI), metal daily intake per unit of body weight (MDI_BW ), and exposure risks (hazard quotient and hazard index) of tree sparrows at different life stages from a polluted area, Baiyin, and a control area, Liujiaxia, were assessed. Metal daily intakes and MDI_BW s of tree sparrows from Baiyin were higher than those from Liujiaxia, which can be attributed to higher metal concentrations of food sources in Baiyin than those in Liujiaxia. Metal daily intakes and MDI_BW s of nestlings were higher than those of adults and juveniles. This difference is observed probably because nonphytophagous invertebrates, the predominant food fed to nestlings, possessed the highest metal concentrations. In addition, adults in summer had higher MDIs and MDI_BW s than juveniles and adults in winter. This finding is probably observed because juveniles and adults in winter consumed a higher proportion of maize, which had the lowest metal concentrations. In addition, the biomagnification of 4 metals through the food chain increased the health risks of tree sparrows. Exposure risks of tree sparrows to metals were comparable to those of waterfowl and raptors, even when soil metals were below threshold. Environ Toxicol Chem 2019;38:2785-2796. © 2019 SETAC.

Spatial distribution and ecological risk assessment of heavy metals in soil from the Raoyanghe Wetland, China

Wetlands are recognized as one of the most important natural environments for humans. At the same time, heavy metal pollution has an important impact on wetlands. China's Raoyanghe Wetland is one of the most important natural wild species gene banks in China. Eight heavy metal elements (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in surface layer and deep layer soils were analyzed using statistical-, pollution index-, and Nemerow index-based methods, the Hakanson potential ecological risk index method, and principal component and cluster analyses. The results showed that the maximum concentrations of heavy metals exceeded the background values in the core area and buffer zone of the wetland, but the heavy metal content of the soils was generally low and did not exceed 30%. With the exception of Hg, heavy metal concentrations showed strong spatial differentiation. The differences between the surface layer and deep layer soils of the core area were smaller than in the buffer zone. With the exception of Cd, a clear vertical zonation in the buffer zone soils was observed, showing greater evidence of external influences in this zone than the core. With the exception of partial surface soils, which indicated a safe level of pollution in the core area, all other soils were classified as having a ‘mild’ level of pollution. Thus, the wetland is moderately polluted, with both the core area and the buffer zone presenting a low level of potential ecological risk. According to the results of the present study, heavy metal contaminants in the wetland soils were found to be derived mainly from the natural sources.

Bioaccumulation in Miscanthus sacchariflorus grown on cadmium-contaminated sediments: a comparative study between submerged and non-submerged environments

Bioaccumulation of heavy metals in aquatic plants is significantly affected by hydrological regime and therefore the accumulation and translocation of cadmium in five organs-panicle, leaf, stem, root, and bud-of an emergent plant (Miscanthus sacchariflorus) were compared between the submerged environment and non-submerged environment. In the submerged condition, the cadmium concentration was higher in the panicle and leaf than in the stem, root, and bud. Cadmium concentration in the root exhibited a positive regression with cadmium concentration in the sediment. However, cadmium concentration in the panicle, leaf, stem, and bud exhibited no significant regression with cadmium concentration in the sediment. In the non-submerged environment, the cadmium concentration was higher in the below-ground organs than in the aboveground organs. The mean bioaccumulation coefficient in the 24 investigated plots in the submerged environment was higher than that in the 20 and 40 mg kg^-1 cadmium treatments in the non-submerged environment. The mean translocation factor in the submerged environment was nine times higher than that in non-submerged environment. These results indicate that submergence enhanced cadmium bioaccumulation in the aboveground organs and that this plant can be used to remove heavy metals from polluted rivers and lakes.

Heavy metal bioaccumulation by Miscanthus sacchariflorus and its potential for removing metals from the Dongting Lake wetlands, China

Bioaccumulation of five heavy metals (Cd, Cu, Mn, Pb, and Zn) in six plant organs (panicle, leaf, stem, root, rhizome, and bud) of the emergent and perennial plant species, Miscanthus sacchariflorus, were investigated to estimate the plant's potential for accumulating heavy metals in the wetlands of Dongting Lake. We found the highest Cd concentrations in the panicles and leaves; while the highest Cu and Mn were observed in the roots, the highest Pb in the panicles, and the highest Zn in the panicles and buds. In contrast, the lowest Cd concentrations were detected in the stem, roots, and buds; the lowest Cu concentrations in the leaves and stems; the lowest Mn concentrations in the panicles, rhizomes, and buds; the lowest Pb concentrations in the stems; and the lowest Zn concentrations in the leaves, stems, and rhizomes. Mean Cu concentration in the plant showed a positive regression coefficient with plot elevation, soil organic matter content, and soil Cu concentration, whereas it showed a negative regression coefficient with soil moisture and electrolyte leakage. Mean Mn concentration showed positive and negative regression coefficients with soil organic matter and soil moisture, respectively. Mean Pb concentration exhibited positive regression coefficient with plot elevation and soil total P concentration, and Zn concentration showed a positive regression coefficient with soil available P and total P concentrations. However, there was no significant regression coefficient between mean Cd concentration in the plant and the investigated environmental parameters. Stems and roots were the main organs involved in heavy metal accumulation from the environment. The mean quantities of heavy metals accumulated in the plant tissues were 2.2 mg Cd, 86.7 mg Cu, 290.3 mg Mn, 15.9 mg Pb, and 307 mg Zn per square meter. In the Dongting Lake wetlands, 0.7 × 10³ kg Cd, 22.9 × 10³ kg Cu, 77.5 × 10³ kg Mn, 3.1 × 10³ kg Pb, and 95.9 × 10³ kg Zn per year were accumulated by aboveground organs and removed from the lake through harvesting for paper manufacture.

Tissue distribution and oral exposure risk assessment of heavy metals in an urban bird: magpie from Central Iran

Direct ingestion of soil and/or soil attached to the food items is a potential rout for wildlife exposure to contaminants. In this study, bioaccumulation of five heavy metals (HMs) in internal tissues of an urban bird (Pica pica) collected from Aran-O-Bidgol City, Central Iran and their related soil were investigated. A total of 15 magpie specimens were collected in autumn 2013 and then their internal tissues were digested using a mixture of HNO₃ and H₂O₂, and finally, concentrations of HMs were detected by ICP-OES. In addition, in order to show level of HM exposure risk to magpie, an exposure risk assessment was modeled. Results indicated that HMs were accumulated as follows: liver > kidney > muscle. Zn and Cu were significantly higher in magpie's tissues collected from agricultural site; on the other hand, Pb and Cd were significantly higher in industrial site (p < 0.05). Level of Cd in male's livers (2.11 μg/g dw) was significantly higher than in females (1.85 μg/g dw) (p < 0.05). Levels of Cd, Pb, and Ni in liver, muscle, and kidney, respectively, were significantly higher in adults than in subadults (p < 0.05). Soil exposure doses of all HMs were lower than tolerable daily intake (Zn 4.35, Cu 1.34, Ni 5.65, Pb 0.35, and Cd 0.53). The calculated hazard quotations (HQs) for HMs were as follows: Pb > Zn > Cu > Ni > Cd and for all HMs were at no risk level (HQ < 1). The amounts of hazard index for three sites were as follows: urban (1.032) > agriculture (0.943) ≥ industry (0.941) and only for urban area was at low risk (1 < HQ < 2). It seemed that birds living in a safe environment and/or HM contaminations in soil separately had no negative effects on magpies. We can also suggest that low levels of HMs in magpie's tissues can be due to low levels of HMs in soil.

Effect of water cadmium concentration and water level on the growth performance of Salix triandroides cuttings

The growth performance of Salix triandroides cuttings at three water cadmium (Cd) concentrations (0, 20, and 40 mg L^-1) and three water levels (- 40 cm, water level 40 cm below the soil surface; 0 cm, water level even with the soil surface; and 40 cm, water level 40 cm above soil surface) was investigated to evaluate its potential in phytoextraction strategies. Compared to cuttings in the - 40 or 0 cm water levels, cuttings in the 40 cm water level showed significantly lower biomass, height, and adventitious root length and significantly fewer leaves and adventitious roots. However, these growth and morphological parameters were not different among the three water Cd concentrations. Water level decreased stomatal conduction and transpiration rate but showed no significant effects on chlorophyll concentration or photosynthetic rate. Chlorophyll concentration and stomatal conductance were higher at 40 mg L^-1 Cd treatment than at 0 or 20 mg L^-1 Cd treatment; yet, photosynthetic rate and transpiration rate were not different. Cd concentration in the leaves and stems increased as the water level increased, but the highest Cd concentration in the roots occurred in the 0 cm water level. As water Cd concentration increased, Cd concentration in the leaves, stems, and roots increased in all three water levels, except in stems in the - 40 cm water level. Under Cd stress, cuttings in the - 40 or 0 cm water levels were characterized by a higher bioaccumulation coefficient, but a lower translocation factor, than those in the 40 cm water level. However, the bioaccumulation coefficient increased with increasing water Cd concentration in all three water levels, as did the translocation factor in the 40 cm water level. The tolerance index for the cuttings was the same among all water levels and water Cd concentrations. The results clearly indicated that the low water level increased plant growth and Cd accumulation in underground parts, while the high water level decreased plant growth but increased Cd accumulation in aboveground parts.

Heavy metal pollution in immobile and mobile components of lentic ecosystems-a review

With growing population and urbanization, there is an increasing exploitation of natural resources, and this often results to environmental pollution. In this review, the levels of heavy metal in lentic compartments (water, sediment, fishes, and aquatic plants) over the past two decades (1997-2017) have been summarized to evaluate the current pollution status of this ecosystem. In all the compartments, the heavy metals dominated are zinc followed by iron. The major reason could be area mineralogy and lithogenic sources. Enormous quantity of metals like iron in estuarine sediment is a very natural incident due to the permanently reducing condition of organic substances. Contamination of cadmium, lead, and chromium was closely associated with anthropogenic origin. In addition, surrounding land use and atmospheric deposition could have been responsible for substantial pollution. The accumulation of heavy metals in fishes and aquatic plants is the result of time-dependent deposition in lentic ecosystems. Moreover, various potential risk assessment methods for heavy metals were discussed. This review concludes that natural phenomena dominate the accumulation of essential heavy metals in lentic ecosystems compared to anthropogenic sources. Amongst other recent reviews on heavy metals from other parts of the world, the present review is executed in such a way that it explains the presence of heavy metals not only in water environment, but also in the whole of the lentic system comprising sediment, fishes, and aquatic plants.

Atmospheric deposition of mercury and cadmium impacts on topsoil in a typical coal mine city, Lianyuan, China

Mercury (Hg) and cadmium (Cd) in the atmosphere from coal combustion emissions play an important role in soil pollution. Therefore, the purposes of this study were to quantitatively evaluate the atmospheric Hg and Cd deposition and to determine the influence of atmospheric deposition on Hg and Cd contents in surface soil in a typical coal mine city. Atmospheric deposition samples were collected from May 2015 to May 2016 at 17 sites located in industrial, agricultural and forest areas in the Lianyuan city. Atmospheric Hg and Cd deposition fluxes in the different land use types showed high variability. Curvilinear regression analysis suggested that the atmospheric Hg deposition fluxes were positively related with Hg contents in soils (R² = 0.86359, P < 0.001). In addition, atmospheric Cd deposition fluxes were also positively correlated with Cd contents in soils when the site LY02, LY04 and LY05 (all belong to agricultural land) were not included in the fitting (R² = 0.82458, P < 0.001). When they were included, there was no significant relationship between them (R² = 0.2039, P = 0.05). The accumulation of Hg and Cd concentration in topsoil due to the influence of atmospheric deposition will increase rapidly in the next 30 years, and the mean value of the increment will reach 2.6007 and 33.344 mg kg^-1. After 30 years, the Hg and Cd concentration will increase slowly. The present study advocates that much attention should be paid to the potential ecological hazards in soil resulting from the atmospheric Hg and Cd deposition.

Changes in heavy metal mobility and availability from contaminated wetland soil remediated with combined biochar-compost

The combination of biochar and compost has been proven to be effective in heavy metals contaminated wetland soil restoration. However, the influence of different proportions between biochar and compost on immobilization of heavy metals in soil has been less studied up to date. Therefore, we investigated the effect of different ratios of biochar-compost mixtures on availability and speciation distribution of heavy metals (Cd, Zn and Cu) in wetland soil. The results showed that applying all amendment combinations into wetland soil increased gradually the total organic carbon (TOC) and water-extract organic carbon (WEOC) as the compost percentage rose in biochar-composts. The higher pH was obtained in a certain biochar addition (20% and 40%) in combinations due to efficient interaction of biochar with compost. All amendments could significantly decrease availability of Cd and Zn mainly from pH change, but increase available Cu concentration as the result of increased water-extract organic carbon and high total Cu content in compost. Moreover, amendments can decrease easily exchangeable fraction and increase reducible of Cd and Zn greatly with increase of compost content in combinations, while amendments containing compost promote transformation of Cu from Fe/Mn oxide and residual fractions to organic bindings. These results demonstrate that different ratios of biochar and compost have a significant effect on availability and speciation of heavy metals in multi-metal-contaminated wetland soil.

Spatial distribution and source identification of heavy metals in surface soils in a typical coal mine city, Lianyuan, China

In this study, we investigated the pollution degree and spatial distribution of heavy metals and determined their sources in topsoil in a typical coal mine city, Lianyuan, Hunan Province, China. We collected 6078 soil surface samples in different land use types. And the concentrations of Zn, Cd, Cu, Hg, Pb, Sb, As, Mo, V, Mn, Fe and Cr were measured. The average contents of all heavy metals were lower than their corresponding Grade II values of Chinese Soil Quality Standard with the exception of Hg. However, average contents of twelve heavy metals, except for Mn, exceeded their background level in soils in Hunan Province. Based on one-way analysis of variance (ANOVA), the contents of Cu, Zn, Cd, Pb, Hg, Mo and V were related to the anthropogenic source and there were statistically significant differences in their concentrations among different land use patterns. The spatial variation of heavy metal was visualized by GIS. The PMF model was used to ascertain contamination sources of twelve heavy metals and apportion their source contributions in Lianyuan soils. The results showed that the source contributions of the natural source, atmospheric deposition, industrial activities and agricultural activities accounted for 33.6%, 26.05%, 23.44% and 16.91%, respectively.