Heavy Metal Levels and Ecological Risk in Crude Oil-Contaminated Soils from Okpare-Olomu, Niger Delta, Nigeria

Crude oil spills have inflicted extensive disruption upon the Niger Delta ecosystem, resulting in crop loss and severe environmental damage. Such spills exacerbate heavy metal concentration within soil due to the presence of metallic ions. The Okpare-Olomu community has borne the brunt of crude oil pollution from illicit bunkering, sabotage, and equipment malfunction. This study targets an evaluation of ecological hazards linked to heavy metals (HMs) in crude oil impacted agriculturally soils within Okpare-Olomu in Ughelli South LGA of Delta State. In this study, 24 topsoil samples were obtained from areas affected by crude oil pollution;the heavy metal content was evaluated through atomic absorption spectrometry. The concentration ranges for HMs (mg/kg) in soil were: 24.1 - 23,174 (Cu);0.54 - 37.1 (Cd);9.05 - 54 (Cr);12 - 174 (Ni);18.5 - 8611 (Pb);and 148 - 9078 (Zn) at a soil depth of 0 - 15 cm. Notably, metal concentrations were recorded to be above permissible World Health Organization limits. Predominantly, Zn and Pb recorded higher heavy metal concentration when compared to other heavy metals analysed, notably at sampling points PT7 through PT24. Zinc and Pb contamination exhibited highly significant contamination factors, and contamination severity was evidenced across all sample points, signifying a grave risk level. Pollution load indices indicated pervasive extreme pollution levels. Geoaccumulation indices signaled moderate to strong pollution, mainly by Pb and Zn. Ecological risk assessments revealed variable levels of heavy metal contamination, from low to very high, with potential ecological risk reflecting markedly elevated levels. This study underscores the imperative for soil remediation to rectify ecological imbalances in agriculturally affected soil constituents.

Soil Contamination by Heavy Metals and Evaluations on Potential Ecological Risks in an Antimony Mine

To study the status of soil quality in an antimony mine, soil samples were collected from different regions and the elements＇ contents of Sb, Cd, Cr, Cu, Zn, Pb, Hg, Ni and As were analyzed using single factor pollution index, Nemerow index and potential ecological risk index. The heavy metal contamination of soils were evaluated. The results showed that Nemerow index for each sampled point was less than 0.7, meaning a clean state. When potential ecological risk assessment was conducted, the sampled point was less than 150, belonging to light pollution.

Pollution hazards of heavy metals in sewage sludge from four wastewater treatment plants in Nanchang, China

The pollution hazards of heavy metals were investigated in sewage sludge collected from four wastewater treatment plantsin Nanchang City,China,including Honggutan(HGT),Chaoyang(CY),Qingshanhu(QSH)and Xianghu(XH).Contamination/riskcharacteristics of heavy metals(Cu,Pb,Zn,Cd,Cr and Ni)were evaluated based on their leachable content,total content andchemical speciation.The sewage sludge from QSH contained higher total contents of heavy metals(except Pb)than those from HGT,XH and CY.The total contents of Cd and Ni were mostly beyond standard.Cu,Cr and Pb were predominantly present in potentialeffect and stable fractions.Zn and Ni showed higher bioavailability.Cd presented roughly uniform distribution into four fractions.The leaching contents of heavy metals almost exceeded the threshold values,especially for Zn and Ni.The potential ecological riskindexes of heavy metals in sewage sludge were4263.34?7480.26,indicating very high risks.Cd contamination is the major concern.

覆冰绝缘子串闪络前的泄漏电流特性(英文)

Flashover of ice-covered suspension insulator string is one of the major problems for the transmission lines in power grid.As leakage current is one of the important characteristics to predict the flashover of suspension insulator string,measuring method and analysis of the leakage current are developed for ice-covered XWP_2-160 porcelain suspension insulator string in this paper.The waveform of the leakage current is perfectly recorded from the occurrence of micro-discharge to flashover,in which the process can be divided into four periods according to the evolution of the leakage current.There are different rising rates of the leakage current and various phenomena of arc discharge in different periods with the increase of the applied voltage,and the distortion on the leakage current waveform is detected because of the effect of arc discharge.A characteristic current(I_w)and a critical current(I_(FT))of flashover,two important parameters of the leakage current before ice-covered insulator string flashover,are defined for analysis of the leakage current characteristics of pre-flashover along the polluted insulator string covered with ice.Statistical experimental results show that the average values of I_w and I_(FT) are within the major distribution zones,and both currents can be used for predicting the icing flashover.The values of two important leakage currents are approximately constant at different contamination degrees,while the direct relationships between the critical currents and the contamination degrees are not found in this paper.

Distribution and transformation behaviors of heavy metals during liquefaction process of sewage sludge in ethanol-water mixed solvents

Liquefaction of sewage sludge(SS)in ethanol-water cosolvents is a promising process for the preparation of bio-oil/biochar products.Effect of the combined use of ethanol and water on the distribution/transformation behaviors of heavy metals(HMs)contained in raw SS is a key issue on the safety and cleanness of above liquefaction process,which is explored in this study.The results show that pure ethanol facilitates the migration of HMs into biochar products.Pure water yields lower percentages of HMs in mobile/bioavailable speciation.Compared with sole solvent treatment,ethanol-water cosolvent causes a random/average effect on the distribution/transformation behaviors of HMs.After liquefaction of SS in pure water,the contamination degree of HMs is mitigated from high level(25.8(contamination factor))in raw SS to considerable grade(13.4)in biochar and the ecological risk is mitigated from moderate risk(164.5(risk index))to low risk(78.8).Liquefaction of SS in pure ethanol makes no difference to the pollution characteristics of HMs.The combined use of ethanol and water presents similar immobilization effects on HMs to pure water treatment.The contamination factor and risk index of HMs in biochars obtained in ethanol-water cosolvent treatment are 13.1-14.6(considerable grade)and 79.3-101.0(low risk),respectively.In order to further control the pollution of HMs,it is preferentially suggested to improve the liquefaction process of SS in ethanol-water mixed solvents by introducing conventional lignocellulosic/algal biomass,also known as co-liquefaction treatment.

Theoretical limiting concentration for mineralization of trichloromethane and dichloromethane in aqueous solutions by AOPs

It is widely stated that most organic contaminants could be completely mineralized by Advanced Oxidation Processes(AOPs). This statement means that the concentration of the organic contaminant at equilibrium(limiting concentration,LC)is low enough to be neglected.However,for environmental safety,especially drinking water safety,this statement needs to be verified from chemical engineering thermodynamic analysis.In this paper,trichloromethane(CHCl3)and dichloromethane(CH2Cl2) are selected as the model systems,and the equilibrium concentration(theoretical limiting concentration,TLC)for the mineralization of chlorinated methanes in aqueous solutions at the different initial concentrations of chlorinated methanes,pH values and·OH concentrations by AOPs are investigated by thermodynamic analysis.The results in this paper show that the TLC for the mineralization of CHCl3 and CH2Cl2 with·OH increases with increasing initial concentrations of CHCl3 and CH2Cl2,decreases with increasing concentration of·OH,and the TLC for the mineralization of CHCl3 decreases with increasing pH values except that the pH value changes from 3.0 to 3.5.For the mineralization of CH2Cl2 with·OH,at the concentrations of·OH obtained from the literature,there is no obvious change of the TLC with pH values,while as the concentrations of·OH increase by 10 and 100 times,the TLC decreases with the increasing pH values from 2.0 to 3.0 and from 3.5 to 4.5,and increases with the increasing pH values from 3.0 to 3.5 and from 4.5 to 5.0.The investigations in this paper imply that high concentration of·OH,a bit higher pH values(4.0–5.0)in acid environment and low initial concentrations of the organic contaminants are beneficial for the complete mineralization of chlorinated methanes by AOPs.