Gaseous elemental mercury emissions from informal E-Waste recycling facilities in Pakistan.

Detrimental effects of mercury (Hg) on ecosystems and human health have been well-documented. Whereas emissions of gaseous elemental mercury (GEM) from e-waste recycling have been reported in developed countries, much less is known about the situation in the Global South. Using a total of 132 passive air samplers, seasonally resolved concentrations of GEM in air were measured continuously at 32 informal e-waste recycling facilities and background location in Pakistan for a period of one year between September 2020 and December 2021. Annual average GEM concentrations at the studied locations ranged from 1.8 to 92 ng m-3. Among the studied cities, higher concentrations were measured in Karachi (mean ± s.d: 17 ± 22, range: 4.2-92 ng m-3), Lahore (16 ± 4.2, 8.2-22 ng m-3) and Peshawar (15 ± 17, 4.9-80 ng m-3), while lower levels were measured in Hyderabad (6.9 ± 6.2, 3.1-25 ng m-3), consistent with a higher rate of informal recycling activities in metropolitan areas. Seasonally, higher GEM levels occurred during autumn (15 ± 16: 3.3-92 ng m-3) and summer (13 ± 8.7: 1.8-80 ng m-3) than in winter (12 ± 8.4: 2.5-49 ng m-3) and spring (9.2 ± 7.3: 1.8-80 ng m-3), possibly reflecting enhanced volatilization at higher temperatures and/or varying magnitude of recycling operations in different seasons. Policies and strict regulations related to e-waste management should be developed and implemented urgently in the country.

Streptomyces pactum and Bacillus consortium influenced the bioavailability of toxic metals, soil health, and growth attributes of Symphytum officinale in smelter/mining polluted soil.

Soil microbes influence the uptake of toxic metals (TMs) by changing soil characteristics, bioavailability and translocation of TMs, and soil health indicators in polluted environment. The potential effect of Streptomyces pactum (Act12) and Bacillus consortium (B. subtilis and B. licheniformis; 1:1) on soil enzymes and bacterial abundance, bioavailability and translocation of Zn and Cd by Symphytum officinale, and physiological indicators in soil acquired from Fengxian (FX) mining site. Act12 and Bacillus consortium were applied at 0 (CK), 0.50 (T1), 1.50 (T2), and 2.50 (T3) g kg-1 in a split plot design and three times harvested (H). Results showed that soil pH significantly dropped, whereas, electrical conductivity increased at higher Act12 and Bacillus doses. The extractable Zn lowered and Cd increased at each harvest compared to their controls. Soil ß-glucosidase, alkaline phosphatase, urease and sucrase improved, whereas, dehydrogenase reduced in harvest 2 and 3 (H2 and H3) as compared to harvest 1 (H1) after Act12 and Bacillus treatments. The main soil phyla individually contributed ∼5-55.6%. Soil bacterial communities' distribution was also altered by Act12 and Bacillus amendments. Proteobacteria, Acidobacteria, and Bacteroidetes increased, whereas, the Actinobacteria, Chloroflexi, and Gemmatimonadetes decreased during the one-year trial. The Zn and Cd concentration significantly decreased in shoots at each harvest, whereas, the roots concentration was far higher than the shoots, implicating the rhizoremediation by S. officinale. Accumulation factor (AF) and bioconcentration ratio (BCR) of Zn and Cd in shoots were lower and remained higher in case of roots than the standard level (≥1). BCR values of roots indicated that S. officinale can be used for rhizoremediation of TMs in smelter/mines-polluted soils. Thus, field trials in smelter/mines contaminated soils and the potential role of saponin and tannin exudation in metal translocation by plant will broaden our understanding about the mechanism of rhizoremediation of TMs by S. officinale.

The influences of fly ash on stabilization for Cd in contaminated soils.

Soil contaminated with potentially toxic metals (PTMs) has being a global environmental issue, which needs to be addressed on the priority basis. Fly ash (FA) is a kind of low-cost alkaline materials, which has been widely used in remediation of soil contaminated by PTMs, while the effects of FA on the stability for PTMs in contaminated farmland soil are still not clearly evaluated. In this study, cadmium (Cd) contaminated soil samples, collected from Shaanxi (SX), Hubei (HB), and Zhejiang (ZJ) province of China, were amended with FA addition (0, 1%, 2.5%, 5%, and 10% dose), and 1-year changes of Cd availability in soil samples were focused on. In addition, biological assessment method through pot culture was carried out to evaluate the reuse potential of Cd contaminated soils amended by FA. The result indicated that FA had a notable impact on decreasing the Cd mobility of SX soil (sand type), with 18.2~52.1% reduction in the DTPA extractable solution, followed by HB soil with 5.9~16.7% reduction, but no obvious effect of FA on ZJ soil (clay type) was observed. Furthermore, the results of pot experiment revealed that FA application could increase the biomass of Chinese cabbage. However, the DTPA extractable Cd in soils after planation and the Cd accumulation of plant increased. The results revealed that FA was not a promising soil stabilizer to immobilize HMs in Cd contaminated soil, and careful consideration should be given to Cd contaminated soils with FA restoration especially in their using for farmland productive due to the remaining risk of Cd bioavailability. These results also contributed to provide references for similar soil pollution remediation.

Mono-and co-applications of Ca-bentonite with zeolite, Ca-hydroxide, and tobacco biochar affect phytoavailability and uptake of copper and lead in a gold mine-polluted soil.

We assessed the efficacy of Ca-bentonite (CB) alone and combined with Ca-hydroxide (CH), tobacco biochar (TB), and zeolite (ZL) aiming to immobilize Cu and Pb and decrease their bioavailability and uptake by pak choi followed by maize in a mining contaminated soil. The CB alone was able to decrease the availability and uptake of Cu and Pb by pak choi and maize. The mono- and multi-combination of CH, TB, and ZL with CB showed contradictory impact on the availability and uptake of Cu and Pb as compared to the mono-application of CB. The combination of CB with ZL and CH + ZL reduced the uptake of Pb by pak choi and maize, while the combination of CB with TB and ZL reduced the uptake of Cu by pak choi and maize as compared to the mono-application of CB. The co-application of CB with CH increased the phytoextraction of Cu by maize and Pb by pak choi shoots as compared to the mono-application of CB. We conclude that modified clays such as CB alone or combined with ZL, TB, and/or CH might be suitable candidates for phytomanagement of Cu and Pb contaminated soils.

Beneficial effects of tobacco biochar combined with mineral additives on (im)mobilization and (bio)availability of Pb, Cd, Cu and Zn from Pb/Zn smelter contaminated soils.

The efficacy of tobacco biochar (TB) alone and in combined with mineral additives: Ca-hydroxide (CH), Ca-bentonite (CB) and natural zeolite (NZ), on immobilization of Pb, Cd, Cu and Zn, via reduce its (bio) availability to plants were investigated. The soils were collected from Tongguan contaminated (TG-C), Fengxian heavily contaminated (FX-HC) and Fengxian lightly contaminated (FX-LC) fields, Shaanxi province, China. The contaminated top soils were treated with low-cost amendments with an application rate of 1% and cultivated by Chinese cabbage (Brassica campestris L.) under greenhouse condition. Results showed that the all amendments (p < 0.05) potentially maximum reduced the DTPA-extractable Pb 82.53, Cd 31.52 and Cu 75.0% with TB + NZ in FX-LC soil, while in case of Zn 62.21% with TB + CH in FX-HC soil than control. The addition of amendments clearly increased dry biomass of Brassica campestris L. as compared with un-amended treatment (except TB + CH). Furthermore, these amendments markedly increased the uptake by plant shoot viz, Cd 10.51% with TB alone and 11.51% with TB + CB in FX-HC soil, similarly in FX-LC Cd increased 5.15% with TB + CH and 22.19% with TB + NZ, respectively. In same trend the Cu uptake in plant shoot was 19.30% with TB + CH in TG-C, whereas 43.90 TB + CH and 19.24% with TB + NZ in FX-LC soil. On the other hand as compared to control Cu accumulation in plant root was observed by TB, TB + CH and TB + CB treatments, while maximum uptake was 62.41% with TB + CH in TG-C soil. Consequently, except TB + CH treatment the chlorophyll content potentially increased in all amendment than control treatment, because of changes in soil EC, pH but increased CEC values after application of amendments. The results of this pot experiment are promising but they will further need to be confirmed with long-term field experiments.

Potential use of lime combined with additives on (im)mobilization and phytoavailability of heavy metals from Pb/Zn smelter contaminated soils.

This explorative study was aimed to assess the efficiency of lime alone and in combined with additives to immobilize Pb, Cd, Cu and Zn in soil and reduce their phytoavailability for plant. A greenhouse pot experiment was performed by using low and heavily contaminated top soils viz. Tongguan contaminated (TG-C); Fengxian heavily contaminated (FX-HC) and Fengxian low contaminated (FX-LC). The contaminated soils were treated with lime (L) alone and in combined with Ca-bentonite (CB), Tobacco biochar (TB) and Zeolite (Z) at 1% and cultivated by Chinese cabbage (Brassica campestris L). Results revealed that all amendments (p< 0.05) significantly reduced the DTPA-extractable Pb 97.33, Cd 68.06 and Cu 91.11% with L+TB, L+CB, L+Z in FX-LC soil and Zn 87.12% respectively, with L+CB into TG-C soil. Consequently, the application of lime alone and in combined with additives were drastically decreased the dry biomass yield of Brassica campestris L. as compared with control. Thus, these feasible amendments potentially maximum reduced the uptake by plant shoots upto Pb 53.47 and Zn 67.93% with L+Z and L+TB in FX-LC soil, while Cd 68.58 and Cu 60.29% with L+TB, L+CB in TG-C soil but Cu uptake in plant shoot was observed 27.26% and 30.17% amended with L+TB and L+Z in FX-HC and FX-LC soils. On the other hand, these amendments were effectively reduced the potentially toxic metals (PTMs) in roots upto Pb77.77% L alone in FX-HC, Cd 96.76% with L+TB in TG-C, while, Cu 66.70 and Zn 60.18% with L+Z in FX-LC. Meanwhile, all amendments were responsible for increasing soil pH and CEC but decreased soils EC level. Based on this result, these feasible soil amendments were recommended for long term-study under field condition to see the response of another hyper accumulator crop.

Role of Streptomyces pactum in phytoremediation of trace elements by Brassica juncea in mine polluted soils.

The industrial expansion, smelting, mining and agricultural practices have increased the release of toxic trace elements (TEs) in the environment and threaten living organisms. The microbe-assisted phytoremediation is environmentally safe and provide an effective approach to remediate TEs contaminated soils. A pot experiment was conducted to test the potential of an Actinomycete, subspecies Streptomyces pactum (Act12) along with medical stone compost (MSC) by growing Brassica juncea in smelter and mines polluted soils of Feng County (FC) and Tongguan (TG, China), respectively. Results showed that Zn (7, 28%), Pb (54, 21%), Cd (16, 17%) and Cu (8, 10%) uptake in shoot and root of Brassica juncea was pronounced in FC soil. Meanwhile, the Zn (40, 14%) and Pb (82, 15%) uptake in the shoot and root were also increased in TG soil. Shoot Cd uptake remained below detection, while Cu decreased by 52% in TG soil. The Cd and Cu root uptake were increased by 17% and 33%, respectively. Results showed that TEs uptake in shoot increased with increasing Act12 dose. Shoot/root dry biomass, chlorophyll and carotenoid content in Brassica juncea were significantly influenced by the application of Act12 in FC and TG soil. The antioxidant enzymatic activities (POD, PAL, PPO and CAT) in Brassica juncea implicated enhancement in the plant defense mechanism against the TEs induced stress in contaminated soils. The extraction potential of Brasssica was further evaluated by TF (translocation factor) and MEA (metal extraction amount). Based on our findings, further investigation of Act12 assisted phytoremediation of TEs in the smelter and mines polluted soil and hyperaccumulator species are suggested for future studies.

Desodification from calcareous saline sodic soil through phytoremediation with Phragmites australis (Cav.) Trin. ex Steud. and gypsum.

The reclamation of saline sodic soils requires sodium removal and the phytoremediation is one of the proven low-cost, low-risk technologies for reclaiming such soils. However, the role of Phragmites australis in reclaiming saline sodic soils has not been evaluated extensively. The comparative reclaiming role of P. australis and gypsum was evaluated in a column experiment on a sandy clay saline sodic soil with ECe 74.7 dS m-1, sodium adsorption ratio (SAR) 63.2, Na+ 361 g kg-1, and pH 8.46. The gypsum at 100% soil requirement, planting common reed (P. australis) alone, P. australis + gypsum at 50% soil gypsum requirements, and leaching (control without plant and gypsum) were four treatments applied. After 11 weeks of incubation, the results showed that all treatments including the control significantly reduced pH, EC, exchangeable Na+, and SAR from the initial values, the control being with least results. The gypsum and P. australis + gypsum were highly effective in salinity (ECe) reduction, while sodicity (SAR) and Na+ reductions were significantly higher in P. australis + gypsum treatment. The reclamation efficiency in terms of Na+ (83.4%) and SAR (86.8%) reduction was the highest in P. australis + gypsum. It is concluded that phytoremediation is an effective tool to reclaim saline sodic soil.

Streptomyces pactum assisted phytoremediation in Zn/Pb smelter contaminated soil of Feng County and its impact on enzymatic activities.

Anthropogenic activities, such as industrial expansion, smelting, mining and agricultural practices, have intensified the discharge of potentially toxic trace elements (PTEs) into the environment, threatening human health and other organisms. To assist phytoremediation by sorghum in soil contaminated by smelters/mines in Feng County (FC), a pot experiment was performed to examine the phytoremediation potential of Streptomyces pactum (Act12) + biochar. The results showed that root uptake of Zn and Cd was reduced by 45 and 22%, respectively, while the uptake of Pb and Cu increased by 17 and 47%, respectively. The shoot and root dry weight and chlorophyll content improved after Act12 inoculation. ß-glucosidase, alkaline phosphatase and urease activities in soil improved and antioxidant activities (POD, PAL, PPO) decreased after application of Act12 + biochar due to a reduction in stress from PTEs. BCF, TF and MEA confirmed the role of Act12 in the amelioration and translocation of PTEs. PCA analysis showed a correlation between different factors that affect the translocation of PTEs. Overall, Act12 promoted the phytoremediation of PTEs. Field experiments on Act12 + biochar may provide new insights into the rehabilitation and restoration of soils contaminated by mines.

Spatial distribution and risk assessment of heavy metals in soil near a Pb/Zn smelter in Feng County, China.

A large scale survey and a small scale continuous monitoring was conducted to evaluate the impact of Pb/Zn smelting on soil heavy metals (HMs) accumulation and potential ecological risk in Feng County, Shaanxi province of China. Soil parameters including pH, texture, CEC, spatial and temporal distribution of HMs (Cd, Cu, Ni, Pb and Zn), and BCR fractionation were monitored accordingly. The results showed the topsoil in the proximity of smelter, especially the smelter area and county seat, were highly polluted by HMs in contrast to the river basins. Fractionation of Cd and Zn in soil samples revealed higher proportion of mobile fractions than other HMs. The soil Cd and Zn contents decreased vertically, but still exceeded the second level limits of Environmental Quality Standard for Soils of China (EQSS) within 80cm. The dominated soil pollutant (Cd) had higher ecological risk than Cu, Ni, Zn and Pb. The potential ecological risk (PER) factor of Cd were 65.7% and 100% in surrounding county and smelter area, respectively. The long-term smelter dust emission mainly contributed to the HMs pollution and posed serious environment risk to living beings.

Phytoextraction of toxic trace elements by Sorghum bicolor inoculated with Streptomyces pactum (Act12) in contaminated soils.

The increasing industrial, mining and agricultural activities have intensified the release of potential toxic trace elements (PTEs), which are of great concern to human health and environment. The alarming increase in PTEs concentration, stress the need for biotechnological remediation approaches. In order to assist phytoextraction of PTEs, different combinations of Streptomyces pactum (Act12) with biochar were applied to mining and industrial polluted soils of Shaanxi and Hunan Provinces of China, respectively. Act12 affected soil physico-chemical properties in both soils. Bioavailable Zn and Pb increased due to microbial activities, while Cd decreased by adsorption on biochar surface. Phytoextraction of Zn and Pb occurred in TG and CZ soil, while Cd uptake decreased in iron rich CZ soil by conflicting effect of siderophores. Cd in sorghum shoot was below detection level, but uptake increased in the roots due to minimum available fraction in TG soil. Biochar reduced the shoot and root uptake of Cd. Sorghum shoot, root dry weight and chlorophyll significantly increased after Act12 and biochar application. ß-glucosidase, alkaline phosphatase and urease activities were significantly enhanced by Act12. Antioxidant enzymatic activities (POD, PAL and PPO) and lipid peroxidation (MDA) were decreased after the application of Act12 and biochar by reduced PTEs stress. Act12 and biochar can be used for different crops to enumerate the transfer rate of PTEs into the food chain.

Impact of CaO, fly ash, sulfur and Na2S on the (im)mobilization and phytoavailability of Cd, Cu and Pb in contaminated soil.

Soil heavy metals pollution is a serious problem worldwide due to its potential human health risks through food chain. Therefore, a sustainable solution is needed to efficiently remediate HMs contaminated soils. Our study aimed to assess the impact of CaO, fly ash, sulfur, and Na2S on the immobilization of Cd, Cu, and Pb and their uptake by Chinese cabbage (Brassica rapa chinensis) in a contaminated soil. The concentration of DTPA-extractable Cd, Cu, and Pb was significantly decreased as compared to control in treated soil. However, the solubility of Cd, Cu, and Pb has increased at greater extent in soil system which favored the uptake of metals in roots and shoots of Chinese cabbage. In general, Cd uptake was significantly increased in shoots followed by roots as compared to control. In addition, Cu has also same trend of increased uptake in shoots as compared to roots. However, the uptake Pb in shoots was considerably increased in Na2S treated samples whereas roots have shown great potential for Pb uptake in CaO treated samples as compared to control. Although, sulfur treatments had efficiently immobilized metals but reduced soil pH to highly acidic level which restricted the growth of Chinese cabbage in sulfur treated samples. We assume that sulfur amendment could be applied for immobilization of metals in alkaline soils rather than acidic soils to achieve better immobilization results. In order to achieve sustainable phytoextraction of Cd, Cu, and Pb using CaO, FA, and Na2S, the non-edible hyperaccumulators species are suggested to be investigated in future studies.

Influence of zeolite and lime as additives on greenhouse gas emissions and maturity evolution during sewage sludge composting.

This study aimed to evaluate the role of different amount of zeolite with low dosage of lime amendment on the greenhouse gas (GHGs) emission and maturity during the dewatered fresh sewage sludge (DFSS) composting. The evolution of CO2, CH4, NH3 and N2O and maturity indexes were monitored in five composting mixtures prepared from DFSS mixed with wheat straw, while 10%, 15% and 30% zeolite+1% lime were supplemented (dry weight basis of DFSS) into the composting mass and compared with treatment only 1% lime amended and control without any amendment. The results showed that addition of higher dosage of zeolite+1% lime drastically reduce the GHGs emissions and NH3 loss. Comparison of GHGs emissions and compost quality showed that zeolite amended treatments were superior than control and 1% lime amended treatments. Therefore, DFSS composting with 30% zeolite+1% lime as consortium of additives were found to emit very less amount of GHGs and gave the highest maturity than other treatments.

Enhancing phosphate adsorption by Mg/Al layered double hydroxide functionalized biochar with different Mg/Al ratios.

Mg/Al ratio plays a significant role for anion adsorption by Mg/Al-layered double hydroxides (Mg/Al-LDHs) modified biochar. In this study, Mg/Al-LDHs biochar with different Mg/Al ratios (2, 3, 4) were prepared by co-precipitation for phosphate removal from aqueous solution. Factors on phosphate adsorption including Mg/Al ratio, pH, and the presence of other inorganic anions were investigated through batch experiments. Increasing Mg/Al ratio in the Mg/Al-LDHs biochar composites generally enhanced phosphate adsorption with Langmuir adsorption maximum calculated at 81.83mg phosphorous (P) per gram of 4:1Mg/Al-LDHs biochar at pH3.0. The adsorption process was best described by the pseudo-second-order kinetic model. Solution pH had greater effects on the phosphate adsorption by Mg/Al LDHs biochar composites with lower Mg/Al ratios. The presence of other inorganic anions decreased the phosphate adsorption efficiency in the order of F(-) > SO4(2-) > NO2(-) >Cl(-). Phosphate adsorption mechanism involves ion exchange, electrostatic attraction and surface inner-sphere complex formation. Overall, Mg/Al-LDHs biochar composites offer a potential alternative of carbon-based adsorbent for phosphate removal from aqueous solution.

Recovery of phosphate from aqueous solution by magnesium oxide decorated magnetic biochar and its potential as phosphate-based fertilizer substitute.

The present study deals with the preparation of a novel MgO-impregnated magnetic biochar (MMSB) for phosphate recovery from aqueous solution. The MMSB was evaluated against sugarcane harvest residue biochar (SB) and magnetic biochar without Mg (MSB). The results showed that increasing Mg content in MMSB greatly improved the phosphate adsorption compared to SB and MSB, with 20% Mg-impregnated MMSB (20MMSB) recovering more than 99.5% phosphate from aqueous solution. Phosphate adsorption capacity of 20MMSB was 121.25mgP/g at pH 4 and only 37.53% of recovered phosphate was desorbed by 0.01mol/L HCl solutions. XRD and FTIR analysis showed that phosphate sorption mechanisms involved predominately with surface electrostatic attraction and precipitation with impregnated MgO and surface inner-sphere complexation with Fe oxide. The 20MMSB exhibited both maximum phosphate sorption and strong magnetic separation ability. Overall, phosphate-loaded 20MMSB significantly enhanced plant growth and could be used as a potential substitute for phosphate-based fertilizer.

Challenges and opportunities in the phytoremediation of heavy metals contaminated soils: A review.

Mining operations, industrial production and domestic and agricultural use of metal and metal containing compound have resulted in the release of toxic metals into the environment. Metal pollution has serious implications for the human health and the environment. Few heavy metals are toxic and lethal in trace concentrations and can be teratogenic, mutagenic, endocrine disruptors while others can cause behavioral and neurological disorders among infants and children. Therefore, remediation of heavy metals contaminated soil could be the only effective option to reduce the negative effects on ecosystem health. Thus, keeping in view the above facts, an attempt has been made in this article to review the current status, challenges and opportunities in the phytoremediation for remediating heavy metals from contaminated soils. The prime focus is given to phytoextraction and phytostabilization as the most promising and alternative methods for soil reclamation.