Humic Solution Research Articles

Humic Compound Application Against Soil Quality Improvement and Enhancement of Pepper Plant Growth

[HUMIC COMPOUND APPLICATION FOR SOIL QUALITY IMPROVEMENT AND ENHANCEMENT OF PEPPER GROWTH]. Pepper (Capsicum Annum) is a strategic commodity that contributes to Indonesia's economy. The price of pepper fluctuates due to the instability of pepper production, which is influenced by multiple factors such as decreasing of soil fertility. Soil conditioner can help to improve soil fertility. The purpose of this research was to determine the effect of humic compounds application on pepper cultivation to improve soil fertility and increase the growth and yield of pepper. The research was conducted from February to August 2021 at the IPB Pasir Sarongge Experimental Field in Cianjur, West Java. The study was conducted using a Completely Randomized Group Design (CRGD) with one factor, humic compound solution concentrations of 0, 2.5, 5, 7.5, 10, and 12.5 mL/L, with each level repeated four times. Duncan's Multiple Range Test (DMRT) was used to separate the mean of the data after variance analysis. The result showed that humic compound application can improve soil fertility, growth and yield of pepper plants as indicated by increasing the value of Cation Exchange Capacity (CEC), decreasing potassium leaching rate and increasing all growth and yield characters except the yield per plant character. The application of 12.5 mL/L humic compounds increased CEC, decreased potassium leaching rate to 0%, increased plant height (37.40%), number of branches (56.72%) and number of fruits (57.81%). The application of humic compounds at 10 mL/L increases the weight of 10 fruits (30.78%), yield per plant (27.56%), yield per plot and predicted yield per hectare (47.58%).

Characterization of coagulant-induced ultrafiltration membrane fouling by multi-spectral fusion: DOM properties and model prediction based on machine learning

This study used the ultraviolet-visible (UV–vis), synchronous fluorescence, and excitation-emission matrix (EEM) spectroscopy coupled with zeta potential and particle size to explore the dissolved organic matter (DOM) solutions properties with the addition of two kinds of coagulants, including aluminum chloride and ferric chloride, in humic solutions and surface water. The results of zeta potential and particle size showed the size of aggregates became larger with the addition of coagulant. The binding sequence of coagulant to DOM was followed from aromatic amino acids to fulvic-like and humic-likes fractions. The results of the unified membrane fouling index (UMFI) were showed negatively correlated with the concentrations of coagulant due to the cake layers formed by aggregates being looser and more permeable. Among all the 12 spectral parameters, slope radio (SR) and specific fluorescence intensities (SFI) had the most significant correlation to UMFI. The multi-spectral fusion for predicting UMFI was established via multiple linear regressions and the backpropagation neural network (BPNN) by using the parameters with both SR and SFI with good accuracy and robustness. Sensitivity analyses results showed that SFI was more sensitive than SR in solutions with high protein-like substances, while SR was more sensitive than SFI with high humic-like substances.

Assessing the potential of biochar aged by humic substances to enhance plant growth and soil biological activity

BackgroundSoil carbon-rich organic amendments (biochar, humic substances) may improve the quality and fertility of arable soil. Their co-application can additively enhance the beneficial effect on soil. Hypothetically, the pre-treatment of biochar, by aging via soaking in a solution of commercially available humic substances, could result in synergism, which may exceed the benefit from simple co-application of both amendments to the soil. Therefore, the aim of this study was to investigate the impact of biochar, humic substances, the combination of both, and the impact of biochar aged by humic substances solution on soil microbial activities and plant growth in a short-term pot experiment with lettuce.ResultsThe aging of biochar decreased the C:N ratio as compared to non-activated biochar. The co-application of biochar and humic substances into the soil resulted in the highest microbial biomass carbon and respiration activity. The majority of enzyme activities (β-glucosidase, arylsulfatase, N-acetyl-β-d-glucosaminidase, phosphatase) were the highest in humic substances-amended soil. The application of humic substances and biochar with humic substances seemed to stimulate microbial growth and activity followed by the competition of microflora for nutrients with plants, whereas the aged biochar behaved differently. The plants treated by aged biochar achieved the highest values of dry aboveground and root biomass of all variants. However, the assumed rapid uptake of nutrients by plants resulted in lower nutrient availability for microflora, and a decline in microbial viability.ConclusionsBased on this study, the positive effect of co-applied humic substances and biochar on soil fertility, quality, and health can be concluded. The usability of biochar aging by humic solution requires further study.Graphic abstract

Soaking of Seedlings Roots in Humic Acid as an Effective Practice to Improve Eucalyptus Nutrition and Growth

ABSTRACT Humic acid (HA) improves the growth and nutrition of eucalyptus changing the plant metabolism and soil properties. HA effects on plants and soil are regulated by concentration and mode of application. The aim of this study was to evaluate the nutrient availability in soil and the eucalyptus nutrition and growth as related to concentrations of HA added to soil or used to soak eucalyptus seedlings roots in humic solutions. The HA concentrations added to whole soil ranged from 0 to 100 mg kg−1 C-HA, while 0 to 5 g L−1 C-HA were used in the seedlings root soaking. The shoot growth and P, K, Ca, B, Mn and Fe accumulated in shoot were increased in HA soaking roots, though HA did not alter soil nutrient availability. HA added to the whole soil improved the P, K, Mg, and Fe availability in soil, besides increased the accumulation of P, K, Ca, Mg, B, Fe, Mn, and Zn in the eucalyptus shoot, as well as shoot and root seedlings growth at optimum C-HA concentrations in the range of 37.4–81.8 mg kg−1. Root soaking with HA is an effective practice to increase the shoot growth and eucalyptus nutrition over the use of HA in whole soil in higher rates.

Optimization of productivity and quality of cucumber plants in protected ground

The paper studies the effect of growth stimulants on morphometric indicators of cucumber plant growth and development in the phase of intensive vegetation and transition to fruiting. The study was carried out at LLC Agricultural Enterprise “Teplitsy Belogorya” on the parthenocarpic hybrid of cucumber Tristan F1. Within the scientific and production experiment the grown cucumber plants on cotton-mineral cubes with drip watering were additionally vegetatively treated with a humic fertilizer solution and Azosol 36 microfertilizer. Phenological observations were carried out and morphometric parameters were determined: plant height, stem and leaf weight, leaf area, root system weight. Under the influence of treatments, the leaf area and weight of cucumber leaves increased by an average of 20 and 17%, respectively. It was established that vegetative treatment with the studied solutions allows partially controlling physiological processes and organogenesis of the greenhouse cucumber plant. The vegetative organs of the cucumber plant leaf, stem and root were found to exhibit different abilities to accumulate chemical elements within the two experiments. The series of element distribution in the natural substance of the plant vegetative organs are shown (in a decreasing amount, total nitrogen, phosphorus, potassium for a series: leaf – stem – root; calcium, magnesium, zinc, iron, manganese and copper for the series: root – leaf – stem). The use of the studied fertilizers increased the commercial quality of cucumber fruits. Button contained a higher amount of total sugar and vitamin C, were environmentally safe in terms of the content of nitrates and heavy metals (cadmium, lead, arsenic, mercury). The optimization of productivity and quality improvement of cucumber plants using biological humic fertilizer and chelate microfertilizer increased the average yield by 5.5% and the profitability of ecologically safe greenhouse vegetables by 3.3%.

Surface activity of humic substances depending on their origin

Humic substances are a general category of naturally occurring, biogenic, heterogeneousorganic substances that can be characterised as being yellow to black in colour, of highmolecular weight and refractory. Surface tension measurement defined humic substances assurface active substances. Unless micellar structural model of humic substances has beensuggested, in the same time there are only a few studies about the factors that affect thesurface activity of humic solutions. The objective of this study was to study changes insurface activity depending on the origin and properties of humic substances.The surface tension-pH curves of humic substances featured a minimum for all solutions,declining steeply from higher and lower pH values. The decrease in surface tension withdecreasing pH reflects the gradual neutralization of acidic sites, which created amphiphilicspecies that migrated to the surface. Surface tension of solutions of humic substancesdecreased with increasing concentration, as well as in presence of metal salts. Manyindustrially produced humic materials demonstrated no or insignificant impact on surfacetension of their solutions, but humic substances isolated from natural environments (water,soil, peat, sediments) demonstrated significant impact of surface tension of their solutions.Thus there exist direct links between origin, structure of humic substances and their ability toinfluence surface tension of aquatic solutions.

The Morphology of Si-K-HAs Composite Prepared by Spray Drying

The silica potassium humic substance (Si-K-HAs) composite have been produce by spray drying successfully. In the previous study the preparation of Si-K-HAs gel by precipitation method required the addition of acid so that Si-K-HAs gel product contains acid salts. This study was develope spray drying method in order to eliminate the use of acid. The mixture of potassium silicate, cellulose and humic potassium solution was mixed with varying volume ratios and flowed into a spray dryer to produce Si-K-HAs powder. The used of cellulose (CMC) in this study acts as a homogeneous agent so that silica and humic substance can be completely mixed at controlled viscosity. Si-K-HAs products were characterized by Scanning electron microscopy (SEM), X-ray fluorescence (XRF), X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), and Surface area analytical (SAA). The result showed that the Si-K-HAs composite prepared by spray dryers have spherical particles, SiO2 in the range of 48-50%, K2O in the range of 49-50%. The present of cellulose caused the increasing of Si-K-HAs particle size e.g 17.30 μm prepared without CMC to 41.11 μm prepared with addition of 100g of CMC. The presence of cellulose can also increase the surface area of the spray-dried Si-K-HAs particles from 111.92 m2g-1; 163.241 m2g-1.

Hastening Potassium Release from Mica Waste by Treating Humic Substrate Solution: An Approach to Adopt Mica Waste as Potassium Amendment in Tea-growing Soil

ABSTRACTMuriate of potash (MoP) is generally applied in soil for supplementing potassium (K) in agricultural soil; though MoP has some disadvantages as K-fertilizer especially under humic agro-climatic condition. In this context, mica waste (MW) could be a potential alternative for K supplementing in soil. However, slow K-releasing nature limits its application as K source in agricultural soil. In this study, humic substrates (HS) were externally applied along with MW for hastening its rate of K release in soil. Application of HS and MW combination significantly (P < .05) increased K availability in soil. A pot study revealed that the combination of HS with even half of the recommended K in the form of MW sustained plant growth and recorded at par exchangeable K content in soil as compared to recommended MoP treatment. The scanning electron microscopy and x-ray diffraction revealed the changes in the crystal structure of HS-treated MW, and that might be attributed to the enhanced release of K from MW. Based on the observations, it could be concluded that application of HS at 7.5 kg HS ha−1 hastened K release from MW to support the plant growth even after supplementing half of the recommended amount of K through MW. This controlled experiment established the potential of HS-treated MW as an alternative K source in agricultural soil. However, it also implied that a field experiment is necessary to optimize the combination of MW and MoP as an integrated K management treatment for a specific agroclimatic condition.

Mobilization of Cu and Pb from multi-metal contaminated soils by dissolved humic substances extracted from leonardite and factors affecting the process

The aim of the research was to determine the potential of dissolved humic substances extracted from leonardite to mobilize Cu and Pb from multi-metal contaminated soils with the scope of finding an efficient washing solution as a possible substitute for conventional washing agents used to extract heavy metals from polluted soils around mining areas. The efficiency of dissolved humic substances extracted from leonardite to extract Cu and Pb from multi-metal contaminated soil collected from “Larga de Sus” mine (Romania) was determined under batch conditions by single-step extraction. All extraction experiments were conducted in a stirrer with orbital rotation-oscillation and thermostat cupola at 100 oscillations/min and oscillation amplitude of 32 mm. The influence of stirring time (120, 240, 360, 720, 1440, 2400 min), concentration of humic solution (2% and 5%), and soil:solution ratio (mass:volume (m/V)) of 1:8, 1:10, and 1:16 on the Cu and Pb removal efficiency was investigated. The heavy metal concentration from soil and extractant solution was determined through atomic absorption spectrometry. The Cu and Pb removal process from soil using dissolved humic substances proceeded relatively quickly. In investigated experimental conditions, the best Cu and Pb removal efficiencies were observed after 360 min of stirring when 60.3% of Cu and 48% of Pb were extracted from soil (2% humic washing solution). The removal efficiency of Cu increased with increasing the soil:solution ratio and humic solution concentration, at shorter stirring times. In the case of Pb, an important improvement of the mobilization with an increasing soil:solution ratio or humic solution concentration was not observed, along with investigated stirring time. A soil:solution ratio of 1:8 was sufficient to reduce the Cu concentration in the studied soil below the intervention threshold established by Romanian legislation, after 360 min of stirring. The mobilization of Cu and Pb from multi-metal contaminated soil using dissolved humic substances is strongly dependent on stirring time, soil:solution ratio, and concentration of humic washing solution. Nevertheless, the results of the present study demonstrate that dissolved humic substances extracted from leonardite are fairly effective washing agents for soils polluted with Cu, Pb, multiple heavy metals, and other pollutants in high concentrations.

Effect of Complexation of Humic Acid with Iron Minerals on Microbial Degradation of Sulfamethoxazole

Microbial Shewanella oneidensis MR-1 can degrade sulfamethoxazole (SMX) and act as a microorganism with strong electron donating properties, which can accelerate the degradation of SMX when it cooperates with electronic shuttle and disproportionated iron. By adding different TOC concentrations, different molecular weight humic acids, and magnetite and hematite suspensions, the optimal system growth conditions, ie, the temperature of 30°C, pH = 7, the TOC concentration, The effect of humic acid with different molecular weights and the addition and synergistic addition of different iron minerals on the degradation of SMX by Shewanella oneidensis MR-1. The study found that humic acid stock solution, small molecule humic acid, iron mineral and both of them will accelerate the degradation of SMX by microbial MR-1. The concentration of small molecule humic acid will degrade SMX by Shewanella oneidensis MR-1. The effect of the humic acid is greater than that of the original solution. The addition of magnetite and hematite suspension to the reactor alone promotes the degradation of SMX by Shewanella oneidensis MR-1, and the addition of humic acid will improve the degradation rate of SMX.

Humic Acid Isolations from Lignite by Ion Exchange Method

The humic liquid is produced from lignite extraction using alkali solution. Conventional humic acid is obtained by acidifying a humic solution using HCl. The purpose of this research is the formation of solid humic acid from lignite by ion exchange method using cation resin. The results showed that the addition of cation resin was able to reduce the pH from 14 to pH 2 as well as the addition of acid (HCl), indicating the exchange of Na + ions with H + ions. The reduction of pH in the humic solution is influenced by the concentration of sodium ions in the humic solution, the weight of the cation resin, and the ion exchange time. The IR spectra results are in good agreement for humic acid from lignite characterization.

INFLUENCE OF PH AND TEMPERATURE ON SURFACE-ACTIVE PROPERTIES OF SOME HUMIC ACIDS

In this study, surface tension measurements were used to study the surface-active properties of olive humic acid (HAO) and commercial humic acid (HA2). The study was performed under different conditions of concentration, temperature, pH and time. The measurements showed that the amphiphilic character of the humic acids solutes at the air/water interface lowers the surface tension () of the solution with an increasing concentrations and temperatures. The critical micelle concentration (CMC) values of both humic acids decreased with an increase in the temperature. Positive values of ∆So and ∆Ho suggested that, their adsorption at air/water interface, is endothermic and entropy driven. The surface tension–pH curve featured a minimum for both humic solutions, declining from higher and lower pH values.

Physicochemical characterization of soils around the processing plant of phosphate of Kpémé in Togo

The soils characterization study around phosphate treatment plant of Kpeme in Togo is a set of themes integrated in the environment safeguarding policy advocated by the first authorities of the country. In this context, this study aims at characterizing the soils of Aglome II (S 1 ), Kpeme (S 2 ) and Goumoukope (S 3 ), by various complementary physico-chemical techniques. The granulometric analysis indicates a texture of a fine grained soil muddy not very argillaceous for S 1 and that of an average sand not very muddy not very argillaceous for S 2 and S 3 . Contents of organic matter (respectively 3.67; 6.72 and 4.7%) and of total limestone (respectively 2.33; 3.26 and 3.02%) of the soils are weak. The fractionation of the organic matter of the soils showed the presence of humic solutions which contain respectively 4.928 g/Kg; 10.897 g/Kg and 4.872 g/Kg of humic matter for the soils S 1 ; S 2 and S 3 .Report/ratio AH/AF is very weak and the infrared spectroscopy of the soils reveal the presence of the tapes characteristic of the functional groupings. Mineralogy was done on fine fractions of the samples of soils through the diffraction of x-rays (DRX).The DRX indicates that fluorapatite prevails in S 1 and quartz prevails in S 2 and S 3 .

Decreased solubilization of Pu(IV) polymers by humic acids under anoxic conditions

Pu(IV) polymer has a very low solubility (log[Pu(IV)aq]total=−10.4 at pH 7.2 and I=0). However, some aspects of their environmental fate remain unclear. Humic acids are able to complex with Pu4+ ions and their dissolved species (<10kD) in the groundwater (neutral to alkaline pH) may cause solubilization of the polymers. Also, humic acids have the native reducing capacity and potentially reduce the polymeric Pu(IV) to Pu(III)aq (log[Pu(III)aq]total=−5.3 at pH 7.2 and I=0). Solubilization and reduction of the polymers can enhance their mobility in subsurface environments. Nevertheless, humic acids readily coat the surfaces of metal oxides via electrostatic interaction and ligand exchange mechanisms. The humic coatings are expected to prevent both solubilization and reduction of the polymers. Experiments were conducted under anoxic and slightly alkaline (pH 7.2) conditions in order to study whether humic acids have effects on stability of the polymers. The results show that the polymeric Pu(IV) was almost completely transformed into aqueous Pu(IV) in the presence of EDTA ligands. In contrast, the dissolved humic acids did not solubilize the polymers but in fact decreased their solubility by one order of magnitude. The humic coatings were responsible for the decreased solubilization. Such coatings limited the contact between the polymers and EDTA ligands, especially at the relatively high concentrations of humic acids (>0.57mg/L). Solubilization of the humic–coated polymers was thus inhibited to a significant extent although EDTA, having the great complexation ability, was present in the humic solutions. Reduction of Pu(IV) polymers by the humic acids was also not observed in the absence of EDTA. In the presence of EDTA, the polymers were partially reduced to Pu(III)aq by the humic acids of 0.57mg/L and the percentage of Pu(III)aq accounted for 51.7% of the total aqueous Pu. This demonstrates that the humic acids were able to reduce the aqueous Pu(IV), instead of the polymeric Pu(IV). Such a demonstration is supported by the very positive redox potential of aqueous Pu(IV)-EDTA complex: Eho′(PuL24-/PuL25-)=154.3mV >>Eh(PuO2(am)/Pu3+)=−182.7mV calculated at 10−10mol/L Pu3+ and pH 7.2. At the higher humic concentrations (>0.57mg/L), the polymers were reduced to a lesser extent because the much denser humic coatings resulted in lower concentrations of the aqueous Pu(IV). Consequently, humic acids make Pu(IV) polymers pretty stable unless the artificial ligands such as EDTA are present in the groundwater.

Removal of Iron Colloid Substances from Aqueous Solutions Using Pulsed Corona Discharge

Pulsed electric discharge has been used for the removal of iron colloid substances from aqueous solutions. The residual concentration of organic substances in aqueous solution depends on the pulse repetition rate. The maximum decrease in organic substances concentration was observed at the pulse repetition rate of 800 pps. Comparison of the results obtained for iron colloid solutions containing humic substances and solutions of humic subtances with no colloids shows that the highest removal efficiency of organic substances was obtained when no iron and silicon ions were present in the solution. The results of our experiments suggest that pulsed electric discharge treatment for the removal of organic substances from natural waters is more efficient at an after-treatment stage, after precipitation of colloid substances.

Coal characteristics and biomarker investigations of Dombayova coals of Late Miocene–Pliocene age (Afyonkarahisar-Turkey)

In Dombayova graben (Dinar-Afyonkarahisar, western Turkey) a 203-m-thick coal-bearing zone of Late Miocene to Pliocene age was recently drilled. The zone hosts several coal beds with a total thickness of 46m. Coal samples from the Dombayova field were studied by means of standard proximate, ultimate, petrological analyses, micro-FTIR spectroscopy and Rock-Eval pyrolysis, and organic geochemical analyses.Coal proximate analyses and the presence of carbonate minerals and fossil shell fragments point to alkaline surface waters of changing pH-values due to fluctuations of the water level in the paleomire and/or Ca-rich water influx. Low sulfur contents argue for sulfate-limitation of bacterial sulfate reduction. Petrographic observations reveal that the coal is dominantly composed of weakly altered wood fragments and roots. The mean random reflectance values of ulminite (0.33%Ro) indicate lignite rank of the coal.The micro-FTIR data of macerals of huminite group indicate higher contributions of aliphatic hydrogen in textinite, compared to more aromatic levigelinite. The semi-quantitative differences in the ratios of selected functional groups suggest that aromaticity and the extent of oxidation are higher in levigelinite. Aliphatic chains are longest in textinite and ulminite, and shortest in texto-ulminite and levigelinite. We interpret this difference to point to a different origin of levigelinite, probably from colloidal humic solutions that were gelified during diagenesis.The concentrations of n-alkanes and their distribution patterns provide evidence for higher terrestrial plants as the dominant source of organic matter. Decreasing pristane/phytane ratios with depth are interpreted to reflect more reducing conditions during peat formation due to higher (ground)water level. The absence of diasterenes is most probably caused by low clay mineral contents and is consistent with the presence of alkaline waters in the paleomire. The presence of terpenoid hydrocarbons in the lignite indicates a major contribution of angiosperms to peat formation. The positive relationship between the concentrations of perylene and lupane-type triterpenoids suggests an increasing abundances of wood-degrading fungi in the peat-forming vegetation characterized by a high density of Betulaceae.

In-line coagulation with quaternary amine polymer prior to microfiltration of humic-rich water

This work was designed to investigate the feasibility of using a low molecular-weight epichlorohydrin/dimethylamine (epi/DMA) polymer as a primary coagulant for the pretreatment of terrestrial humic-rich water prior to the microfiltration (MF) process, without removal of the flocs produced via the coagulation pretreatment. The main issue explored was the effects of different coagulation conditions on the particle characteristics that would also significantly affect the performance of membranes when filtering coagulated humic-rich water. The size distribution and morphological properties of flocs formed through the coagulation of humic-rich water were characterized and the impact of Ca2+ on these characteristics that were associated with the performance of the MF membrane was also determined. Epi/DMA additions from 50% to 150% of the charge neutralization dose substantially decreased fouling compared to when filtering raw humic-rich water. Short-term fouling was increased when 1mM Ca2+ was added, but the charge neutralization coagulation removed almost all of the fouling tendency that had occurred when filtering Ca–humic solution. The median diameter and the fractal dimension of flocs produced were increased as the zeta potential reached close to zero, which resulted in the formation of a cake layer that was easily removed from the surface of the membrane.

Citrate-Coated Silver Nanoparticles Interactions with Effluent Organic Matter: Influence of Capping Agent and Solution Conditions.

Fate and transport studies of silver nanoparticles (AgNPs) discharged from urban wastewaters containing effluent organic matter (EfOM) into natural waters represent a key knowledge gap. In this study, EfOM interfacial interactions with AgNPs, and their aggregation kinetics were investigated by atomic force microscopy (AFM) and time-resolved dynamic light scattering (TR-DLS), respectively. Two well-characterized EfOM isolates, i.e., wastewater humic (WW humic) and wastewater colloids (WW colloids, a complex mixture of polysaccharides-proteins-lipids), and a River humic isolate of different characteristics were selected. Citrate-coated AgNPs were selected as representative capped-AgNPs. Citrate-coated AgNPs showed a considerable stability in Na(+) solutions. However, Ca(2+) ions induced aggregation by cation bridging between carboxyl groups on citrate. Although the presence of River humic increased the stability of citrate-coated AgNPs in Na(+) solutions due to electrosteric effects, they aggregated in WW humic-containing solutions, indicating the importance of humics characteristics during interactions. Ca(2+) ions increased citrate-coated AgNPs aggregation rates in both humic solutions, suggesting cation bridging between carboxyl groups on their structures as a dominant interacting mechanism. Aggregation of citrate-coated AgNPs in WW colloids solutions was significantly faster than those in both humic solutions. Control experiments in urea solution indicated hydrogen bonding as the main interacting mechanism. During AFM experiments, citrate-coated AgNPs showed higher adhesion to WW humic than to River humic, evidencing a consistency between TR-DLS and AFM results. Ca(2+) ions increased citrate-coated AgNPs adhesion to both humic isolates. Interestingly, strong WW colloids interactions with citrate caused AFM probe contamination (nanoparticles adsorption) even at low Na(+) concentrations, indicating the impact of hydrogen bonding on adhesion. These results suggest the importance of solution conditions and capping agents on the stability of AgNPs in solution. However, the characteristics of organics would play a crucial role in the fate and transport of these nano contaminants in urban wastewaters and natural water systems.

Temperature Induced Aggregation and Clouding in Humic Acid Solutions

Humic acids in aqueous solution demonstrate inverse temperature-solubility relationships when solution conditions are manipulated to reduce coulombic repulsion among the humic polyanions. These effects were followed by dynamic light scattering (DLS) measurements of the resulting aggregates, as well as the addition of a polarity sensitive fluorescent probe (pyrene). The humic solutions could be primed for temperature induced clouding by carefully lowering the pH to a point where hydration effects became dominant. The exact value of the cloud point (CP) was a function of both pH and humate concentration. The CPs mostly lay in the range 50–90°C, but DLS showed that temperature induced aggregation proceeded from approximately 30°C onward. Similar effects could be achieved by adding multivalent cations at concentrations below those which cause spontaneous precipitation. The declouding of clouded humate solutions could be affected by lowering the temperature combined with mechanical agitation to disentangle the humic polymers.

Transfer of PBDEs from TV Housing Plastics to Aqueous Media

To investigate the transfer of PBDEs from products into the aqueous media, experiments and analysis were carried out by contacting TV housing plastics with distilled and dissolved humic solution (DHS) in brown bottles in the artificial climate box. The leaching test conditions were a liquid-to solid ratio of 100:1, and a contact period of 1, 2, 4, 7, 10, 13, 16 and 20 day (s), with pH of 3, 5, 7, 9 and temperature of 15, 20, 25 °C. The leaching concentrations of PBDE increased with DHS rather than distilled water, and were found to be remarkably enhanced when TOC of DHS increased. Despite no detection of most of the lower BDEs in distilled water, most homologues could be detected in DHS, and their solubility increased according to the contact time; those of highly BDEs increased to 10 times their maximum solubility in distilled water. Temperature had limited influence for the limited range investigated. Lower pH generally resulted in higher transfer of PBDEs to aqueous phase.