Distribution of Geochemical Species of P, Fe and Mn in Surface Sediments in the Eutrophic Estuary, Northern Taiwan

The Danshuei River Estuary (DRE) in northern Taiwan is a seriously eutrophic estuary due to the domestic effluent discharge. Surface sediment samples were collected from the DRE to study the concentrations and spatial distributions of different fractions of phosphorus through the five-step sequential extraction method which chemically divides the sedimentary P into five fractions: PSORB, PCDB, PCFA, PDET, and PORG. The Fe and Mn contents in the extracted solution were also determined. The total organic carbon (TOC) and grain size in sediment samples were analyzed as well. The sedimentary total P (TP) concentrations ranged within 537–1310 mg/kg and mostly exceeded 800 mg/kg, suggesting that the DRE sediments were moderately polluted by phosphorus. The PCDB was the dominant fraction of P, averagely contributing 58% of TP, followed by PDET 31%. The contributions of the PSORB and PCFA fractions to the TP were relatively minor. Two fractions, FeCDB and FeORG, of sedimentary Fe equally shared approximately 70% of total Fe, followed by FeDET with 22%. The contribution of different fractions of sedimentary Mn followed the sequence: MnCDB (36%) > MnCFA (29%) > MnORG (14.7%) > MnDET (14.5%) > MnSORB (5.3%). The sedimentary P, Fe, and Mn within the DRE are easily mobilized because they were mainly present in the reducible fraction. The concentrations of sedimentary TP positively correlated with the TOC contents and inversely negatively correlated with grain size, suggesting that the TOC and grain size play the crucial roles in influencing the distribution of sedimentary P within the DRE. Finally, the Fe(III) (hydro)oxides seems to play an important carriers to adsorb dissolved P because PCDB positively correlated with FeCDB.

Distribution of Phosphorus Forms Depends on Compost Source Material

Composting is a sustainable method for recovering nutrients from various organic wastes, including food waste. Every input waste has different nutrient contents, in turn, suggesting that every compost has different fertilizer and/or soil improvement values. The phosphorus (P) concentration and relative distribution of P forms is related to the original organic material. The relative distribution of P forms determines how readily plants can absorb P from the compost-amended soil. The aim of this study was to investigate the content and relative share of P forms in composts made from fish waste, sewage sludge, green waste, and horse manure. Six forms of P (labile; bound to reducible metals; bound to non-reducible metals; bound to easily degradable organic material; and bound to calcium) were determined using sequential extraction method. The results indicated that fish waste compost had relatively high proportion of labile P, suggesting good biological availability. In comparison, sewage sludge compost contained the highest overall P concentration per dry weight unit, while labile P constituted only 6% of summary of P forms. The results indicate that the evaluation of composts as alternative P sources in agriculture should rely on the relative distribution of P forms in the compost in addition to the typically recognized value of the total P.

Status of accumulated heavy metals in soils from organic and conventional farms in Akinyele Local Government, Ibadan, Oyo State, Nigeria

The risk associated with the presence of heavy metals in soil is their potential toxicity and ability to enter the ecosystem through the food chain. Total heavy metal content of a soil is inadequate for predicting the toxicity of heavy metals in soil. Therefore, the current study was designed to determine the various forms in which the selected heavy metals: Chromium (Cr), Lead (Pb), Nickel (Ni), and Cadmium (Cd) exist in the soil to ascertain the available forms for plant uptake. Soils samples were randomly collected from selected organic and conventional farms in Akinyele local government, Ibadan, Oyo State, Nigeria, at different depths (0-15, 15-30 and 30-45 cm) using random sampling method. Routine analysis was carried out to determine the textural classes and chemical properties of soil samples. The total heavy metals of the soil samples were determined and their fractions were analysed using sequential extraction method. Cadmium was not detected in most of the soil samples. Residual fraction was predominant in all the analysed heavy metals. In addition, Cr was more associated with the oxidizable fraction having a range of 0.1 mg/kg from Ajibode organic farm (AO) at 30-45 cm depth. Pb and Ni were both more associated with reducible fraction with Pb having a range of 2.7 mg/kg in Ajibode conventional farm (AI) at 0-15 cm depth and 0.1 mg/kg in (AI) at 30-45 cm depth. Reducible values of Ni ranges from 4.3 mg/kg in AI at 0-15 cm to 1.4 mg/kg in AO at 30-45 cm. The apparent mobility and bioavailability for these heavy metals in the studied soils were in the order: Pb>Cr>Ni. The result showed that uptake of heavy metals by the plants would be low as the concentration of the exchangeable form of the heavy metals in the analysed soil sample has the least concentration when compared with the other forms.

Sequential Extraction and Risk Assessment of Potentially Toxic Elements in River Sediments

In this study, the sequential extraction method was applied to extract selected potentially toxic elements (PTEs) (Cd, Cr, Cu, Fe, Ni, Pb and Zn) in river sediments collected from the Blood River situated in Seshego area, Limpopo Province, South Africa. The study aimed to assess a possible trend of mobilisation of these elements from sediment to water. The accuracy of the sequential extraction method was confirmed by analysing sediment-certified reference material, and quantitative percentage recoveries ranging from 86 to 119%, 81 to 111% and 77 to 119% were achieved for exchangeable, reducible and oxidisable fractions, respectively. The potential risk of the PTEs in sediments was evaluated. The calculated values of contamination factor (CF) as well as risk assessment code (RAC) for Cd, Cu, Ni and Pb revealed the mobility of these elements. The PTEs in river sediments are at a high toxicity-risk level and could therefore cause a threat to organisms dwelling in sediments and humans via consumption of crops irrigated with the polluted river water.

Forms of Gold and Arsenic in Surface Sediments at the Novye Peski Gold Deposit and Their Sorption by Humic Acid

Forms of gold and arsenic, as one of the main pathfinders, were researched in the podzolic, illuvial, and parent material horizons of podzol soil at the Novye Peski gold deposit. Forms of gold and arsenic were studied with the sequential extraction method. The results of this study showed that the main forms of gold are water-soluble, bound to organic matter, and “insoluble”; for arsenic: bound to Fe and Mn-(oxy)hydroxides and bound to organic matter. The form bound to organic matter was considered in detail and gold and arsenic were analyzed in humic and fulvic acids solutions extracted from podzol soil. It was determined that gold is mainly bound to humic acid (HA), and arsenic to fulvic acid. Due to the prevalence of the form of gold bound to humic acid, the modelling process of different gold and arsenic (III) contents sorption on solid humic acid were observed and data on quantity of adsorbed ions per unit mass of HA and recovery ratio were obtained. More than 90% gold recovery rate was observed for concentrations less than 10 µg/cm3 and for arsenic it was in a range of 8–15%.

Experimental Investigation into the Effect of Pyrolysis on Chemical Forms of Heavy Metals in Sewage Sludge Biochar (SSB), with Brief Ecological Risk Assessment

Experimental investigations were carried out to study the effect of pyrolysis temperature on the characteristics, structure and total heavy metal contents of sewage sludge biochar (SSB). The changes in chemical forms of the heavy metals (Zn, Cu, Cr, Ni, Pb and Cd) caused by pyrolysis were analyzed, and the potential ecological risk of heavy metals in biochar (SSB) was evaluated. The conversion of sewage sludge into biochar by pyrolysis reduced the H/C and O/C ratios considerably, resulting in stronger carbonization and a higher degree of aromatic condensation in biochar. Measurement results showed that the pH and specific surface area of biochar increased as the pyrolysis temperature increased. It was found that elements Zn, Cu, Cr and Ni were enriched and confined in biochar SSB with increasing pyrolysis temperature from 300–700 °C; however, the residual rates of Pb and Cd in biochar SSB decreased significantly when the temperature was increased from 600 °C to 700 °C. Measurement with the BCR sequential extraction method revealed that the pyrolysis of sewage sludge at a suitable temperature transferred its bioavailable/degradable heavy metals into a more stable oxidizable/residual form in biochar SSB. Toxicity of heavy metals in biochar SSB could be reduced about four times if sewage sludge was pyrolyzed at a proper temperature; heavy metals confined in sludge SSB pyrolyzed at about 600 °C could be assessed as being low in ecological toxicity.

Arsenic in Soils Affected by Mining: Microscopic Studies vs. Sequential Chemical Extraction

Soil samples from three inactive mines, corresponding to different Arsenic-bearing mineralization types, were collected and studied. The aim was to determine the influence of mine wastes mineralogy/geochemistry and texture in As mobility and to compare results from sequential chemical extraction and microscopic techniques (optical and electron) at a grain scale. Arsenic in soils is found mainly associated to the residual fraction, indicating that mechanical As dispersion is mainly responsible for As soil pollution. The use of objective microscopic techniques (i.e., Scanning Electron Microscopy-Energy Dispersive Spectroscopy -SEM-EDS-, High Resolution Transmission Electron Microscopy -HR-TEM) has pointed out that the selected sequential extraction method overestimates the role of Mn amorphous oxy-hydroxides and organic matter in As retention while underestimating the mechanism of As adsorption onto clay particle surfaces.