Phosphorus is more effective than nitrogen in restoring plant communities of heavy metals polluted soils

Effect of various phosphorus levels on the extraction of Cd, the transformation of P, and phosphorus-related gene during the phytoremediation of Cd contaminated soil

Phytoremediation has emerged as a common technique for remediating Cd pollution in farmland soil. Moreover, phosphorus, an essential element for plants, can alter the pectin content of plant cell walls and facilitate the accumulation of Cd in plant tissues, thereby enhancing phytoremediation efficiency. Therefore, pot experiments were conducted in order to investigate the effect of phosphorus levels on Cd extraction, phosphorus transformation and phosphorus-related genes during phytoremediation. The results revealed that an optimal application of suitable phosphate fertilizers elevated the soil's pH and electrical conductivity (EC), facilitated the conversion of soil from insoluble phosphorus into available forms, augmented the release of pertinent enzyme activity, and induced the expression of phosphorus cycling-related genes. These enhancements in soil conditions significantly promoted the growth of ryegrass. When applying phosphorus at a rate of 600 mg/kg, ryegrass exhibited plant height, dry weight, and chlorophyll relative content that were 1.27, 1.26, and 1.18 times higher than those in the control group (P0), while the Cd content was 1.12 times greater than that of P0. The potentially toxic elements decline ratio and bioconcentration factor were 42.86% and 1.17 times higher than those of P0, respectively. Consequently, ryegrass demonstrated the highest Cd removal efficiency under these conditions. Results from redundancy analysis (RDA) revealed a significant correlation among pH, total phosphorus, heavy metal content, phosphorus forms, soil enzyme activity, and phosphorus-related genes. In conclusion, this study suggests applying an optimal amount of suitable phosphate fertilizers can enhance restoration efficiency, leading to a reduction in soil Cd content and ultimately improving the safety of crop production in farmlands.

Bio-organic fertilizer facilitated phytoremediation of heavy metal(loid)s-contaminated saline soil by mediating the plant-soil-rhizomicrobiota interactions

Bio-organic fertilizer (BOF) was effective to promote the phytoremediation efficiency of heavy metal(loid)s-contaminated saline soil (HCSS) by improving rhizosphere soil properties, especially microbiome. However, there existed unclear impacts of BOF on plant metabolome and plant-driven manipulation on rhizosphere soil microbiota in HCSS, which were pivotal contributors to stress defense of plants trapped in adverse conditions. Here, a pot experiment was conducted to explore the mechanisms of BOF in improving alfalfa (Medicago sativa)-performing phytoremediation of HCSS. BOF application significantly increased the biomass (150.87-401.58 %) to support the augments of accumulation regarding heavy metal(loid)s (87.50 %-410.54 %) and salts (38.27 %-271.04 %) in alfalfa. BOF promoted nutrients and aggregates stability but declined pH of rhizosphere soil, accompanied by the boosts of rhizomicrobiota including increased activity, reshaped community structure, enriched plant growth promoting rhizobacteria (Blastococcus, Modestobacter, Actinophytocola, Bacillus, and Streptomyces), strengthened mycorrhizal symbiosis (Leohumicola, Funneliformis, and unclassified_f_Ceratobasidiaceae), optimized co-occurrence networks, and beneficial shift of keystones. The conjoint analysis of plant metabolome and physiological indices confirmed that BOF reprogrammed the metabolic processes (synthesis, catabolism, and long-distance transport of amino acid, lipid, carbohydrate, phytohormone, stress-resistant secondary metabolites, etc) and physiological functions (energy supply, photosynthesis, plant immunity, nutrients assimilation, etc) that are associated intimately. The consortium of root metabolome, soil metabolome, and soil microbiome revealed that BOF facilitated the exudation of metabolites correlated with rhizomicrobiota (structure, biomarker, and keystone) and rhizosphere oxidative status, e.g., fatty acyls, phenols, coumarins, phenylpropanoids, highlighting the plant-driven regulation on rhizosphere soil microbes and environment. By compiling various results and omics data, it was concluded that BOF favored the adaptation and phytoremediation efficiency of alfalfa by mediating the plant-soil-rhizomicrobiota interactions. The results would deepen understanding of the mechanisms by which BOF improved phytoremediation of HCSS, and provide theoretical guidance to soil amelioration and BOF application.

Microplastics and cadmium affect invasion success by altering complementarity and selection effects in native community

The diversity-invasibility hypothesis predicts that native plant communities with high biodiversity should be more resistant to invasion than low biodiversity communities. However, observational studies have found that there is often a positive relationship between native community diversity and invasibility. Pollutants were not tested for their potential to cause this positive relationship. Here, we established native communities with three levels of diversity (1, 2 and 4 species) and introduced an invasive plant [Symphyotrichum subulatum (Michx.) G. L. Nesom] to test the effects of different pollutant treatments (i.e., unpolluted control, microplastics (MPs) alone, cadmium (Cd) alone, and their combination) on the relationship between native community diversity and community invasibility. Our results indicate that different MPs and Cd treatments altered the invasibility of native communities, but this effect may depend on the type of pollutant. MPs single treatment reduced invasion success, and the degree of reduction increased with increasing native community diversity (Diversity 2: - 14.1 %; Diversity 4: - 63.1 %). Cd single treatment increased the aboveground biomass of invasive plants (+ 40.2 %) and invasion success. The presence of MPs inhibited the contribution of Cd to invasion success. Furthermore, we found that the complementarity and selection effects of the native community were negatively correlated with invasion success, and their relative contributions to invasion success also depended on the pollutant type. We found new evidence of how pollutants affect the relationship between native community diversity and habitat invasibility, which provides new perspectives for understanding and managing biological invasions in the context of environmental pollution. This may contribute to promoting the conservation of biodiversity, especially in ecologically sensitive and polluted areas.

Wide Riparian Zones Inhibited Trace Element Loss in Mining Wastelands by Reducing Surface Runoff and Trace Elements in Sediment

The diffusion of trace elements in mining wastelands has attracted widespread attention in recent years. Vegetation restoration is an effective measure for controlling the surface migration of trace elements. However, there is no field evidence of the effective riparian zone width in mining wastelands. Three widths (5 m, 7.5 m, and 10 m) of Rhododendron simsii/Lolium perenne L. riparian zones were constructed in lead-zinc mining wastelands to investigate the loss of soil, cadmium (Cd), copper (Cu), arsenic (As), lead (Pb), and zinc (Zn). Asbestos tiles were used to cut off connections between adjacent plots to avoid hydrological interference. Plastic pipes and containers were used to collect runoff water. Results showed that more than 90% of trace elements were lost in sediment during low coverage and heavy rainfall periods. Compared with the 5 m riparian zone, the total trace element loss was reduced by 69-85% during the whole observation period in the 10 m riparian zone and by 86-99% during heavy rain periods in the 10 m riparian zone, which was due to reduction in runoff and concentrations of sediment and trace elements in the 10 m riparian zone. Indirect negative effects of riparian zone width on trace element loss through runoff and sediment concentration were found. These results indicated that the wide riparian zone promoted water infiltration, filtered soil particles, and reduced soil erosion and trace element loss. Riparian zones can be used as environmental management measures after mining areas are closed to reduce the spread of environmental risks in mining wastelands, although the long-term effects remain to be determined.

Diversity and botanical composition of native species in the Pampa biome in vineyards cultivated on soils with high levels of copper, zinc and manganese and phytoremediation potential

Viticulture allows the preservation of native species inside vineyards in the Pampa biome. However, phytosanitary treatments in these areas can increase the levels of Cu, Zn and Mn. The study aimed to (i) verify the influence of Cu, Zn and Mn contents in Pampa biome soils; (ii) identify variables related to Cu, Zn and Mn that most contribute to the variation in richness, diversity, and dry matter production of native vegetation, (iii) investigate the phytoremediation potential of species present in vineyards. Botanical composition, Cu, Zn, Mn available in the soil, and plant nutritional composition in two vineyards (V1 and V2) and native field (NF) were evaluated. Vineyards showed higher Cu, Zn and Mn contents in the soil, resulting in the lowest biomass, richness, and diversity of native species. Mn in tissue was the most important variable in explaining the variation in dry matter. Zn in the soil helped to explain the difference in species richness and diversity. P concentration in tissue was important in elucidating the variation in species diversity. Paspalum plicatulum and Paspalum notatum have potential for phytostabilization of metals in vineyards.

Effects of dissolved organic matter, pH and nutrient on ciprofloxacin bioaccumulation and toxicity in duckweed

Water pollution induced by antibiotics has garnered considerable concern, necessitating urgent and effective removal methods. This study focused on exploring ciprofloxacin (CIP) removal by duckweed and assessing CIP bioaccumulation and toxic effects within duckweed under varying dissolved organic matter categories, pH levels, and nutrient (nitrogen (N) and phosphorus (P)) levels. The results revealed the proficient and rapid elimination of CIP from water by duckweed, resulting in 86.17 % to 92.82 % removal efficiency at the end of the 7-day experiment. Across all exposure groups, varying degrees of CIP bioaccumulation in duckweed were evident, with uptake established as a primary pathway for CIP elimination within this plant. Additionally, five CIP metabolites were identified in duckweed tissues. Interestingly, the presence of humic acid (HA) and fulvic acid (FA) reduced CIP absorption by duckweed, with FA yielding a more pronounced impact. Optimal CIP removal was recorded at a pH of 7.5, while duckweed displayed heightened physiological stress induced by CIP at pH 8.5. Although the influence of N and P concentrations on CIP removal by duckweed was modest, excessive N and P levels intensified the physiological strain of CIP on duckweed.

Phosphorus Plays Key Roles in Regulating Plants' Physiological Responses to Abiotic Stresses

Phosphorus (P), an essential macronutrient, plays a pivotal role in the growth and development of plants. However, the limited availability of phosphorus in soil presents significant challenges for crop productivity, especially when plants are subjected to abiotic stresses such as drought, salinity and extreme temperatures. Unraveling the intricate mechanisms through which phosphorus participates in the physiological responses of plants to abiotic stresses is essential to ensure the sustainability of agricultural production systems. This review aims to analyze the influence of phosphorus supply on various aspects of plant growth and plant development under hostile environmental conditions, with a special emphasis on stomatal development and operation. Furthermore, we discuss recently discovered genes associated with P-dependent stress regulation and evaluate the feasibility of implementing P-based agricultural practices to mitigate the adverse effects of abiotic stress. Our objective is to provide molecular and physiological insights into the role of P in regulating plants' tolerance to abiotic stresses, underscoring the significance of efficient P use strategies for agricultural sustainability. The potential benefits and limitations of P-based strategies and future research directions are also discussed.

Biochar-immobilized Bacillus megaterium enhances Cd immobilization in soil and promotes Brassica chinensis growth

Phosphate solubilizing bacteria (PSB) has been considered an environmental-friendly phosphate fertilizer without cadmium (Cd) input into soils, but its possibility of Cd fixation in soil needs to be explored. Since direct inoculation results in a rapid decline of the population and activity, we immobilized Bacillus megaterium with maize straw biochar (B-PSB) and investigated its feasibility in remediating Cd-contaminated soil. Pot experiments showed that the application of B-PSB significantly ameliorated the growth of Brassica chinensis under Cd stress, with a fresh weight increased by 59.08% compared to the Cd-control. B-PSB reduced Cd accumulation in Brassica chinensis by 61.69%, and promoted the uptake of P and N by 134.97% and 98.71% respectively. Microbial community analysis showed B-PSB recruited more plant growth-promoting bacteria in near-rhizosphere soil, which provides a favorable microenvironment for both PSB and crops. Column leaching experiments verified that B-PSB achieved the dissolution of stable P while fixing Cd. Batch tests further revealed that biochar served as a successful carrier facilitating the growth of B. megaterium and Cd immobilization. Given the widespread Cd contamination in agricultural soils, our results indicate that B-PSB is a promising soil amendment to secure food safety.

Microbial community composition and degradation potential of petroleum-contaminated sites under heavy metal stress

Total petroleum hydrocarbons (n-alkanes), semi-volatile organic compounds, and heavy metals pose major ecological risks at petrochemical-contaminated sites. The efficiency of natural remediation in situ is often unsatisfactory, particularly under heavy metal pollution stress. This study aimed to verify the hypothesis that after long-term contamination and restoration, microbial communities in situ exhibit significantly different biodegradation efficiencies under different concentrations of heavy metals. Moreover, they determine the appropriate microbial community to restore the contaminated soil. Therefore, we investigated the heavy metals in petroleum-contaminated soils and observed that heavy metals effects on distinct ecological clusters varied significantly. Finally, alterations in the native microbial community degradation ability were demonstrated through the occurrence of petroleum pollutant degradation function genes in different communities at the tested sites. Furthermore, structural equation modeling (SEM) was used to explain the influence of all factors on the degradation function of petroleum pollution. These results suggest that heavy metal contamination from petroleum-contaminated sites reduces the efficiency of natural remediation. In addition, it infers that MOD1 microorganisms have greater degradation potential under heavy metal stress. Utilizing appropriate microorganisms in situ may effectively help resist the stress of heavy metals and continuously degrade petroleum pollutants.

Comparative study on plant growth-promoting bacterial inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium-contaminated soil

A field study was conducted to compare FM-1 inoculation by irrigation and spraying for promoting Bidens pilosa L. phytoremediation of cadmium (Cd)-contaminated soil. Cascading relationships between bacterial inoculation by irrigation and spraying and soil properties, plant growth-promoting traits, plant biomass and Cd concentrations in Bidens pilosa L. were explored based on the partial least squares path model (PLS-PM). The results indicated that inoculation with FM-1 not only improved the rhizosphere soil environment of B. pilosa L. but also increased the Cd extracted from the soil. Moreover, Fe and P in leaves play vital roles in promoting plant growth when FM-1 is inoculated by irrigation, while Fe in leaves and stems plays a vital role in promoting plant growth when FM-1 is inoculated by spraying. In addition, FM-1 inoculation decreased the soil pH by affecting soil dehydrogenase and oxalic acid in cases with irrigation and Fe in roots in cases with spraying. Thus, the soil bioavailable Cd content increased and promoted Cd uptake by Bidens pilosa L. To address Cd-induced oxidative stress, Fe in leaves helped to convert GSH into PCs, which played a vital role in ROS scavenging when FM-1 was inoculated by irrigation. The soil urease content effectively increased the POD and APX activities in the leaves of Bidens pilosa L., which helped alleviate Cd-induced oxidative stress when FM-1 was inoculated by spraying. This study compares and illustrates the potential mechanism by which FM-1 inoculation can improve the phytoremediation of Cd-contaminated soil by Bidens pilosa L., suggesting that FM-1 inoculation by irrigation and spraying is useful in the phytoremediation of Cd-contaminated sites.

Responses of the root morphology and photosynthetic pigments of ryegrass to fertilizer application under combined petroleum-heavy metal stress

With developments in industry, petroleum and heavy metal pollution are increasingly affecting soil, significantly harming the environment, biosecurity, and human health. Therefore, the remediation of contaminated soil is becoming increasingly important. In this study, ryegrass (Lolium perenne L.) was planted in petroleum-heavy metal co-contaminated soil with the application of nitrogen and phosphorus fertilizers. Three treatments were set up: uncontaminated soil + ryegrass (SH); petroleum-heavy metal co-contaminated soil + ryegrass (SPGH); and petroleum-heavy metal co-contaminated soil + ryegrass + nitrogen and phosphorus fertilizer (SPGH + NP). The results showed that the petroleum-heavy metal co-contamination promoted increases in the root length, surface area, volume, and diameter of ryegrass roots, increasing the below-ground biomass and decreasing the photosynthetic pigment content in the early stages of the experiment. The ratios of chlorophyll a/b and chlorophyll/carotenoid also increased. However, the application of fertilizer reduced the length, surface area, volume, and diameter of ryegrass roots in the co-contaminated soil, and the below-ground biomass decreased while the above-ground biomass increased. Furthermore, the photosynthetic pigment content was significantly higher than that in the unfertilized treatment and the chlorophyll a/b ratio decreased while the chlorophyll/carotenoid ratio increased. Therefore, fertilizers could alleviate the toxic effects of petroleum-heavy metal combined pollution on ryegrass roots and promote the synthesis of chlorophyll and other pigments, thus reducing the inhibitory effect of petroleum-heavy metal combined pollution on ryegrass growth and facilitating the remediation of the polluted soil.

Nitrogen and Phosphorus Fertilizer Increases the Uptake of Soil Heavy Metal Pollutants by Plant Community

Soil heavy metal pollution is widespread around the world. Compared with hyperaccumulation plants, non-hyperaccumulator plant communities have many advantages in the remediation of heavy metals pollution in soil. The application of nitrogen (N) and phosphorus (P) is inexpensive and convenient, which can promote the growth of plant. N and P fertilizer might increase plant community remediation of heavy metal polluted soils. In our study, the effects of N and P fertilizer on remediation of soil Cd, Cu, Pb pollution by plant community were studied through a greenhouse experiment. Our results indicated that addition of N, P and N + P fertilizer increased plant community aboveground biomass. Simultaneously, addition of N and P fertilizer increased the accumulation of heavy metals in aboveground of the plant community and accelerated plants absorption soil heavy metals. Among them, N fertilizer had the best effect. Our results provide an inexpensive method for remediation heavy metal pollution of contaminated farmland, abandoned land and mine tailings, etc.

Unlocking All-Solid Ion Selective Electrodes: Prospects in Crop Detection

This paper reviews the development of all-solid-state ion-selective electrodes (ASSISEs) for agricultural crop detection. Both nutrient ions and heavy metal ions inside and outside the plant have a significant influence on crop growth. This review begins with the detection principle of ASSISEs. The second section introduces the key characteristics of ASSISE and demonstrates its feasibility in crop detection based on previous research. The third section considers the development of ASSISEs in the detection of corps internally and externally (e.g., crop nutrition, heavy metal pollution, soil salinization, N enrichment, and sensor miniaturization, etc.) and discusses the interference of the test environment. The suggestions and conclusions discussed in this paper may provide the foundation for additional research into ion detection for crops.

The potential of Bacillus subtilis and phosphorus in improving the growth of wheat under chromium stress

AIM

Hexavalent chromium (Cr⁺⁶ ) is one of the most toxic heavy metals that have deteriorating effects on the growth and quality of the end product of wheat. Consequently, this research was designed to evaluate the role of Bacillus subtilis and phosphorus fertilizer on wheat facing Cr⁺⁶ stress.

METHODS AND RESULTS

The soil was incubated with Bacillus subtilis and phosphorus fertilizer before sowing. The statistical analysis of the data showed that the co-application of B. subtilis and phosphorus yielded considerably more significant (p < 0.05) results compared with an individual application of the respective treatments. The co-treatment improved the morphological, physiological and biochemical parameters of plants compared with untreated controls. The increase in shoot length, root length, shoot fresh weight and root fresh weight was 38.17%, 29.31%, 47.89% and 45.85%, respectively, compared with untreated stress-facing plants. The application of B. subtilis and phosphorus enhanced osmolytes content (proline 39.98% and sugar 41.30%), relative water content and stability maintenance of proteins (86.65%) and cell membranes (66.66%). Furthermore, augmented production of antioxidants by 67.71% (superoxide dismutase), 95.39% (ascorbate peroxidase) and 60.88% (catalase), respectively, were observed in the Cr⁺⁶ - stressed plants after co-application of B. subtilis and phosphorus.

CONCLUSION

It was observed that the accumulation of Cr⁺⁶ was reduced by 54.24%, 59.19% and 90.26% in the shoot, root and wheat grains, respectively. Thus, the combined application of B. subtilis and phosphorus has the potential to reduce the heavy metal toxicity in crops.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study explored the usefulness of Bacillus subtilis and phosphorus application on wheat in heavy metal stress. It is a step toward the combinatorial use of plant growth-promoting rhizobacteria with nutrients to improve the ecosystems' health.

Exogenous Methyl Jasmonate Application Improved Physio-Biochemical Attributes, Yield, Quality, and Cadmium Tolerance in Fragrant Rice

Cadmium (Cd) has detrimental effects on crop plants, whereas, jasmonates (JAs) play a vital role in abiotic stress tolerance in plants. The present study investigated the effects of exogenous application of methyl jasmonate (MeJa) on the physio-biochemical attributes, yield, and quality of two fragrant rice cultivars, i.e., Xiangyaxiangzhan and Meixiangzhan-2 under Cd stress. The experiment was comprised of four treatments, i.e., CK, control (normal conditions); Cd: 100 mg Cd kg^-1 of soil; MeJa: exogenous application of MeJa at 20 mM; and Cd + MeJa: 100 mg Cd kg^-1 of soil + exogenous MeJa application at 20 mM. Results depicted that Cd toxicity resulted in a substantial reduction of enzymatic activities and non-enzymatic antioxidants, chlorophyll contents, while enhanced oxidative damage in the terms of lipid peroxidation (higher malondialdehyde (MDA) contents), H₂O₂, and electrolyte leakage. Proline contents were found higher whereas protein and soluble sugars were lower under Cd stress as compared with Ck and Cd + MeJa. Exogenous MeJa application further improved the panicles per pot, spikelets per panicle, seed setting (%), 1,000 grain weight, and yield per pot under Cd stress conditions as compared with non-MeJa applied plant under Cd stress. In addition, exogenous MeJa application enhanced the accumulation of macro (N, P, K, Mg, and Ca) and micronutrients (Mn, Zn, Fe, and Cr) in both cultivars under Cd stress, while reduced the Cd contents in different plant parts. Overall, the contents of Cd in different plant organs were recorded as: root > stem > leaves > grains for all treatments. Comparing both cultivars, the grain Cd contents were higher in Meixiangzhan 2 than Xiangyaxianzhan under Cd contaminated conditions. Conclusively, Cd toxicity impaired growth in rice by affecting physio-biochemical attributes, however, Xiangyaxiangzhan performed better than Meixiangzhan-2 cultivar.

Phytoremediation of heavy metal pollution: Hotspots and future prospects

To clarify the global status and research hotspots of heavy metal pollution phytoremediation, we used Web of Science, Cite Space software, and VOS viewer to analyse 1123 publications from the period of 2000-2020. Literature categories, research hotpots, and the most prolific publications by country, institution, and author were analysed separately. Around 34% of the articles are contributed from five countries: China (29.37%), India (11.00%), Spain (6.29%), Italy (6.20%), and Pakistan (5.67%). The hot research topic keywords were "diversity", "translocation", and "enhanced phytoremediation". Cadmium was the most highly concerned heavy metal in the phytoremediation. Twenty-three articles were highly cited, and they mainly focused on 1) enhancing the remediation ability of plants in heavy metal contaminated soil by microbial and chemical additives; 2) the molecular effect and mechanism of heavy metals on plant growth and development; 3) discovering novel heavy metal hyper-enriched plants which can remediate mixed heavy metal pollution. From the above analysis, we concluded that the future research directions should be 1) strengthening the plant remediation ability by biochemical means; 2) studying the molecular mechanism underlying heavy metal damage to plants; 3) studying the enrichment principle of plants for heavy metals. The present study provides a further understanding of the trends in phytoremediation of heavy metal pollution, and the data analysed can be used as a guide for future research directions.

Plant Diversity and Soil Nutrients in a Tropical Coastal Secondary Forest: Association Ordination and Sampling Year Differences

Studying the patterns of changes in species diversity and soil properties can improve our knowledge of community succession. However, there is still a gap in understanding how soil conditions are related to plant diversity in tropical coastal secondary forests. We sampled plant diversity and soil nutrients spanning two different years (2012 and 2019) to assess the patterns of species diversity and relationships of soil nutrients and species diversity on Hainan Island, southern China. Results showed that the soil pH and total nitrogen (TN) significantly decreased while the soil organic matter (OM) and total phosphorus (TP) significantly increased from 2012 to 2019. Plant species diversity was significantly higher in 2012 than in 2019, and the dominant species significantly changed in two different years. Using multiple regression analysis, we determined that soil TP and TN were significantly related to plant diversity in 2012 and 2019, respectively. Using CCA analysis, TN and OM were the strongest predictors for dominant species in 2012, whereas the soil TP and TN were the strongest predictors for dominant species in 2019. Our findings show a significant change in plant diversity and dominant species after 7 years of development in the tropical coastal secondary forest. The patterns of plant diversity and soil nutrients increase our knowledge of forest restoration in coastal areas.

Analysis of Heavy Metal Pollution in Cultivated Land of Different Quality Grades in Yangtze River Delta of China

The distribution of heavy metal pollution in cultivated land is closely related to the quality of the cultivated land. In this study, 533 soil samples were collected from cultivated land in the Yangtze River delta region in China for Cd, Pb, and Hg analyses. Spatial statistical analysis was used to study the heavy metal pollution in the cultivated land, and the driving forces of heavy metal distribution in different cultivated land quality subdivisions were analyzed with GeogDetector. The conclusions are as follows: (1) Among the three heavy metals in the study area, the coefficient of variation of Cd is the largest, and that of Pb is the smallest. The proportion of Cd and Hg exceeding the standard value (the standard of level two in GB 15618—2018) is relatively large, both of which are 5%; (2) From the perspective of the spatial distribution of soil heavy metal pollution, only four counties (CX, HN, WY, and LH) were free of heavy metal pollution. Soil heavy metal pollution in AJ, SY, QJ, and DS counties is relatively serious, and the pollution may come from agricultural activities, manufacturing, and prevalent coastal shipping industries in these counties; (3) The heavy metal pollution levels of cultivated land with different quality levels are different. The high-quality cultivated land has no high contamination, while the medium and the general cultivated land both have high contamination. High contamination is related to Cd for medium and general cultivated lands, and to Hg in only general cultivated land; (4) The main driving factors of heavy metal concentration in cultivated soil were GDP, followed by soil organic matter, and pH. These results indicate that the spatial distribution of heavy metal concentration in cultivated soil was affected by the level of economic development, followed by the ecological environment, indicating that human activities had a critical impact on the ecological environment of cultivated land.

Bioaccumulation of heavy metals in Stachys inflata and Scariola orientalis affected by particulate matters of a cement factory in central Iran

Industrial activities can affect accumulation of pollutants (e.g., heavy metals (HMs)) by plants and influence their entrance to the food chain. This research was carried out on accumulation of HMs including chromium (Cr), lead (Pb), and zinc (Zn) by two plants Stachys inflata and Scariola orientalis grown in natural grasslands in vicinity of a national park where they are influenced by dispersion of particulate matter (PM) through Sarooj Cement Factory in central Iran. The PM spatial dispersion of the factory was determined using the AERMOD model. Soil and vegetation samples were collected based on the modeled PM levels to analyze their HM contents. Bioconcentration factor (BCF) and transfer factor (TF) from root to shoot were determined in two widespread plants of the region: Stachys inflata and Scariola orientalis. The mean concentration of HMs in the soil samples was as follows: Zn (145.39 mg/kg) > Pb (78.52 mg/kg) > Cr (32.69 mg/kg) which was significantly correlated with simulated PM concentrations. This indicated the common source and distribution pattern of HMs which affected their accumulation in plants. TF and BCF values of the HMs were higher in Scariola orientalis than those of Stachys inflata, especially for Cr showing potentially higher risk to enter the food chain. The results showed that HM concentration in the soil as well as their accumulation by plants were correlated with the simulated PM deposition and not with linear distance from the factory.

Effect of design and operational parameters on nutrients and heavy metal removal in pilot floating treatment wetlands with Eichhornia Crassipes treating polluted lake water

Though having an economic and ecological impact on Marriott Lake management in Egypt, water hyacinth (Eichhornia crassipes) is an aquatic floating macrophyte with a known phytoremediation potential. In order to assess its remediation potential, pilot floating treatment wetlands (FTWs) with E. crassipes were built in duplicates to evaluate the removal of nutrients and heavy metals from the polluted lake water. The experimental design included units with different water depths (15, 25, and 35 cm; D₁₅, D_25, and D₃₅, respectively) and plant coverage (90, 70, 50, and 0%; P₉₀, P₇₀, P_50, and P₀, respectively). The pilot FTWs were monitored over a 7-day operation cycle to identify the optimum combination of design (plant coverage, water depth) and operation (hydraulic retention time; HRT) parameters needed for maximum BOD₅, TN, NH₄-N, and TP removal. NH₄-N removal reached 97.4% in the D₂₅P₅₀ unit after 3 days, BOD₅ 75% in the D₁₅P₉₀ after 3 days, TN 82% in the D₂₅P₇₀ after 4 days, and TP 84.2% in the D₃₅P₇₀ after 4 days. The open-water evaporation rate was higher than the evapotranspiration rate in the planted units, probably due to the warm climate of the study area. Metals were also sufficiently removed through bioaccumulation in plant tissues in the order of Fe > Pb > Cu > Ni (62.5%, 88.9%, 81.7%, and 80.4% for D₂₅P₅₀, D₂₅P₇₀, D₂₅P₅₀, and D₂₅P₉₀, respectively), while most of the assimilated metal mass was translocated to the plant roots. The biochemical composition of the plant tissue was significantly different between the shoot and root parts. Overall, the FTW with 70% E. crassipes coverage, 25-cm water depth, and an HRT of 3-5 days was identified as the optimum design for effective remediation of the polluted Marriott Lake in Egypt.