Laboratory- to field-scale investigations to evaluate phosphate amendments and Miscanthus for phytostabilization of lead-contaminated military sites

Doctor of PhilosophyDepartment of AgronomyGanga M. HettiarachchiPotentially toxic substances can contaminate extensive areas of productive land due to military activities. The most common and widespread metal contaminant in military lands is lead (Pb). The main objectives of this study were to evaluate the feasibility of using Miscanthus, a second-generation biofuel crop, for photostabilization of Pb in contaminated military site soils; the effect of soil amendments on Miscanthus growth; and the effects of continual plant growth, nutrient removal and the soil chemical changes induced by Miscanthus growth on soil Pb bioaccessibility. In 2016, we established a field site on a US Army reservation in Fort Riley, KS. Miscanthus was planted in an area with soil total Pb concentration ranging from 900 – 1,500 mg kg⁻¹ and near-neutral soil pH. Five treatments were evaluated: (i) control plots without tillage with existing vegetation, (ii) no-tillage, no additional amendments planted with Miscanthus, (iii) tilled soil, no additional amendments planted with Miscanthus, (iv) tilled soil amended with triple superphosphate (at 5:3 Pb:P molar ratio) planted with Miscanthus, and (v) tilled soil amended with organic P source (class B biosolids applied at 45 Mg/ha ) planted with Miscanthus. Results from three years show that one-time addition of soil amendments to Pb-contaminated soil supports establishing and stabilizing Miscanthus, increasing biomass yield as well as reducing phytoavailability and bioaccessibility of Pb. Plots amended with biosolids had significantly less total Pb uptake, plant tissue Pb concentration, and Pb bioaccessibility, and more soil enzyme activities, organic carbon, and microbial biomass. Controlled-environment greenhouse and laboratory incubation studies were conducted to test selected additional P sources. Additional sources included non-traditional, less soluble types such as struvite and apatite. The greenhouse study aimed to evaluate the effect of Miscanthus growth on bioaccessibility of amended and non-amended soils and the effect of soil amendments on soil-plant transfer of soil Pb over three Miscanthus cuttings. Soil amendments increased dry matter yield in the first cutting. Soils in Miscanthus pots that were amended with biosolids, had significantly lower total Pb uptake, Pb concentration in plant tissues, and Pb bioaccessibility when compared to the control across all cuttings. Overall, the results suggested that Miscanthus can be effectively and safely grown on Pb-contaminated soils amended with biosolids. The incubation study evaluated the effectiveness of various in situ P treatments on reducing Pb bioaccessibility and the effects of different P sources on the speciation of soil Pb over time. X-ray absorption spectroscopy was used to understand treatment-induced changes to soil Pb speciation. Results showed that soil pH decreased slightly for all treatments. Percent of bioaccessible Pb in soils amended with biosolid were significantly (α=0.05) less than the other amendments. The high rate of biosolids (225 Mg ha⁻¹) was the most effective in controlling the bioaccessibility of soil Pb, and the reductions in bioaccessibility ranged from 63 to 76% compared to the control. X-ray absorption spectroscopy results indicated pyromorphite (stable Pb phosphates) phases were the most dominant Pb species in both amended and non-amended soils. The results of these studies suggest that Miscanthus can be grown successfully in Pb-contaminated shooting range soils in combination with organic or inorganic phosphate amendments, while minimizing the associated environmental risks

Efficient Remediation of Cadmium- and Lead-Contaminated Water by Using Fe-Modified Date Palm Waste Biochar-Based Adsorbents

Heavy metals pollution of water resources is an emerging concern worldwide and seeks immediate attention. Date palm waste was transformed into biochar (BC), which was further modified through Fe-intercalation for the production of magnetic biochar (Fe-BC) in this study. The produced BC and Fe-BC were analyzed for chemical, proximate, surface, and elemental composition. The efficiency of the produced adsorbents to decontaminate the water from Cd2+ and Pb2+ ions was investigated through kinetics and an isotherm adsorption batch trial. Kinetics adsorption data fit well with the pseudo-second order and power function model, while equilibrium data were described well with the Langmuir and Freundlich isotherms. The maximum adsorption capacity as shown by the Langmuir model was the highest for Fe-BC for both Cd2+ (48.44 mg g−1) and Pb2+ (475.14 mg g−1), compared with that of BC (26.78 mg g−1 Cd2+ and 160.07 mg g−1 Pb2+). Both materials showed higher removal of Pb (36.34% and 99.90% on BC and Fe-BC, respectively) as compared with Cd (5.23% and 12.28% on BC and Fe-BC, respectively) from a binary solution. Overall, Fe-BC was more efficient in adsorbing both of the studied metals from contaminated water. The application of Fe-BC resulted in 89% higher adsorption of Cd2+ and 197% higher adsorption of Pb2+ from aqueous media as compared to BC. Kinetics and isotherm models as well as SEM–EDS analysis of the post-adsorption adsorbents suggested multiple adsorption mechanisms including chemisorption, pore-diffusion, and electrostatic interactions

Fate and Transport of Lead and Copper in Calcareous Soil

Heavy metals transport to groundwater relies on the characteristics of soil, such as carbonate and clay minerals, organic matter content, soil pH, and some other factors. Most of the heavy metals in calcareous soils are precipitated as metal carbonate minerals; consequently, their transport to the groundwater is not anticipated. Therefore, the current study focused on the impacts of calcium carbonate presence on the adsorption and transport of lead (Pb) and copper (Cu) in calcareous soil using batch and column experiments. To elucidate the contaminants removal mechanisms in calcareous soils, extensive laboratory batch investigations were conducted to study the equilibrium kinetic and adsorption isotherm characteristics of the two studied heavy metals. The quick adsorption of Pb2+ and Cu2+ by soil was seen in kinetics trials. In addition, Pb2+ and Cu2+ sorption onto the soil was best described by the pseudo-second order kinetic model (R2 = 0.9979 and 0.9995 for Cu2+ and Pb2+, respectively). To explain the equilibrium sorption data, the Freundlich isotherm showed the best fitness to Pb2+ (R2 = 0.96) and Cu2+ (R2 = 0.98), collectively. The Freundlich parameters revealed that the Pb2+ has favorable adsorption; however, Cu2+ has unfavorable adsorption onto the soil. The results of column experiments showed the higher binding of Pb2+ than Cu2+ to the top surface of the soil column, making the movement of these two metals very slow. In columns, most of the Pb2+ and Cu2+ ions were sorbed at an initial 5 and 10 cm, respectively. The findings of this study will help in understanding the fate of heavy metals in calcareous soils

Pollution Indexing and Health Risk Assessment of Heavy-Metals-Laden Indoor and Outdoor Dust in Elementary School Environments in Riyadh, Saudi Arabia

The prevalence of potentially toxic heavy metals (HMs)-bearing dust in the environment is posing serious health risks to humans. Therefore, the occurrence of HMs in indoor and outdoor dust samples of elementary school’s environment in Riyadh, Saudi Arabia, were reported, and associated potential human health risks were estimated in this study. Dust samples were collected from outdoor and indoor environments from eighteen elementary schools using a soft plastic brush. The mean concentrations of Cd, Co, Cu, Ni, Pb, and Zn in collected indoor dust samples were much higher (0.08, 3.45, 59.20, 15.20, 4.99, and 94.10 mg kg−1, respectively) than that of outdoor dust samples (0.07, 3.07, 42.20, 13.60, 4.57, and 62.40 mg kg−1, respectively), due to fans operation, opened windows, and resuspension of dust by children’s activities. The values of estimated enrichment factor revealed that both the outdoor and indoor dusts were moderately contaminated with Zn and Cu, while highly contaminated with Cd and Pb. However, the estimated potential ecological risks associated with HMs were lower. Health risks (non-carcinogenic and carcinogenic) calculations exhibited no potential risks of HMs in the schools’ dust toward children. However, health risks for children were determined in the following order: up to 6 years > 6–12 years > adults. Therefore, assessing the potential health risks posed by HM-contaminated dust in school environments is necessary to avoid any possible children’s health concerns