Heavy metals in vegetables and their impact on the nutrient quality of vegetables: A review

Vegetables are vital to the human diet, and in particular provide the well-known nutrients to maintain normal physiological functions. The prolonged application of large amount of fertilizers and pesticides has resulted in heavy metal accumulation in vegetable gardens. Exposure to heavy metals by the consumption of contaminated vegetables and its toxicity is a serious concern. This article reviews the presence of heavy metals in different vegetables, their mechanism of absorption, impact of heavy metals on physiology, and nutrient reduction and associated impact on humans with emphasis on pregnant women based on the existing scientific literature. However, a limited number of studies was found in the data base that examined the reduction of nutrients in the vegetables due to heavy metal contamination. The heavy metals were found in 36 vegetables in 61 regions of the world and were above permissible limits in most of the vegetables. Specific study to human toxicity due to the contamination of heavy metals may be conducted with emphasis on pregnant women, children, and elderly people. Furthermore, strategy and policy should be devised to control the heavy metals in vegetables and those vegetables that are hyper-accumulators of heavy metals should be identified for awareness purposes.     

Acidulated activation of phosphate rock enhances release,lateral transport and uptake of phosphorus and trace metals upon direct-soil application

Phosphate rock (PR) was activated via acidulation with HCl, EDTA, and oxalic acid to enhance its reactivity. The release, lateral transport, and uptake of phosphorus (P) along with trace metals from pristine and activated PRs were investigated in a soil micro-block system over a period of 27 days, using wheat (Triticum aestivum L.) plants. Significantly (p < 0.05) higher amounts of available soil P, Fe, Mn, and Zn were released from all the PRs after application to soil within first 9 days of seedling transplantation, while the release of other trace metals (Cd, Co, Cr, Cu, Ni, and Pb) was minimal (<1.2 mg kg^?1). On cumulative basis, APR-O (oxalic acid activated PR) was the most efficient amendment releasing 164% more available P, followed by APR-E (EDTA activated PR) releasing 130% more available P, compared to the pristine PR. Similar results were also observed in the release of available Fe, Mn, Zn, and other trace metals. The highest diffusive mass fluxes for available P, Mn, Fe, and Zn in soil were observed after 3 days of seedling transplantation, which reduced subsequently. The uptake of P, Fe, Mn, and Zn by wheat plants was increased by 394%, 715%, 92%, and 91%, respectively, in APR-O application compared to the pristine PR, while it was increased by 280%, 188%, 16%, and 27%, respectively, in APR-E application compared to the pristine PR. Subsequently, APR-O and APR-E amendments resulted in enhanced shoot lengths, root lengths, shoot dry matter, and root dry matter contents of wheat plants. Hence, it was concluded that activation of PR with oxalic acid and EDTA prior to direct soil application may enhance the reactivity of PR and could serve as a cost-effect fertilization strategy for higher wheat crop production.     

Straw mulching with fertilizer nitrogen: An approach for improving crop yield,soil nutrients and enzyme activities

Field experiments were conducted to study soil properties, soil enzymes activities, water use efficiency (WUE) and crop productivity after six years of soya bean straw mulching in the semi‐arid conditions of China. The experiment included four treatments: CK (Control), N (240 kg N ha^‐1), H (soya bean straw mulching at half rate 700 kg ha^‐1 with 240 kg N ha^‐1) and F (soya bean straw mulching at full rate 1,400 kg ha^‐1 with 240 kg N ha^‐1). Soil organic carbon (SOC), soil labile organic carbon (LOC), soil available N (AN), available P (AP) and enzyme activities were analysed after wheat harvesting in 2016 and 2017. Results show that straw amounts had positive effects on the soil fertility indices being higher for treatment F. The SOC, LOC, AN, AP and enzyme activities (i.e. saccharase, urease and alkaline phosphatase) were in the order of F > H > N > CK. High wheat grain yield and WUE were observed for F treatment. A total of six years mulching along with 240 kg ha^‐1 nitrogen fertilizer application is sufficient for wheat yield stability and improving soil properties except urease activities in the semi‐arid condition of China. However, the straw mulching amount should be further studied with minimum nitrogen fertilizer for an environment‐friendly and effective approach for improving the soil biological properties with adequate crop production on a sustainable basis in the semi‐arid region of China.     

Effectiveness of potassium in mitigating the salt-induced oxidative stress in contrasting tomato genotypes

To check the efficacy of potassium in alleviating oxidative stress under salt stress, salt-tolerant (Indent-1) and salt-sensitive (Red Ball) tomato (Lycopersicon esculentum Mill.) genotypes were exposed to three levels of sodium chloride (NaCl) (0, 75, 150 mM) and two levels of potassium (4.5 and 9 mM) in solution and foliar form. Thirty days of treatments revealed that increasing NaCl stress increased lipid peroxidation (malondialdehyde, MDA) and correspondingly the activity of antioxidant enzymes (superoxide dismutase, SOD; catalase, CAT; and glutathione reductase GR) in both genotypes. However, higher potassium (K) level in solution or foliar spray during the salt-induced stress decreased MDA and antioxidant activity and increased the growth in salt-tolerant genotype than in the salt-sensitive genotype. Decrease in MDA concentration, activity of antioxidant enzymes, and increase in the growth of tomato plants by the application of potassium under salt stress suggest that potassium is an effective ameliorating agent against salt-induced oxidative damage.     

Biochar-induced changes in soil properties affected immobilization/mobilization of metals/metalloids in contaminated soils

Purpose

Remediation of metal contaminated soil with biochar is attracting extensive interest in recent years. Understanding the significance of variable biochar properties and soil types helps elucidating the meticulous roles of biochar in immobilizing/mobilizing metals/metalloids in contaminated soils.

Materials and methods

Six biochars were produced from widely available agricultural wastes (i.e., soybean stover, peanut shells and pine needles) at two pyrolysis temperatures of 300 and 700 °C, respectively. The Pb-, Cu-, and Sb-contaminated shooting range soils and Pb-, Zn-, and As-contaminated agricultural soils were amended with the produced biochars. The mobility of metals/metalloids was assessed by the standard batch leaching test, principal component analysis and speciation modeling.

Results and discussion

The changes in soil properties were correlated to feedstock types and pyrolysis temperatures of biochars based on the principal component analysis. Biochars produced at 300 °C were more efficient in decreasing Pb and Cu mobility (>93 %) in alkaline shooting range soil via surface complexation with carboxyl groups and Fe-/Al-minerals of biochars as well as metal-phosphates precipitation. By contrast, biochars produced at 700 °C outperformed their counterparts in decreasing Pb and Zn mobility (100 %) in acidic agricultural soil by metal-hydroxides precipitation due to biochar-induced pH increase. However, Sb and As mobility in both soils was unfavorably increased by biochar amendment, possibly due to the enhanced electrostatic repulsion and competition with phosphate.

Conclusions

It is noteworthy that the application of biochars is not equally effective in immobilizing metals or mobilizing metalloids in different soils. We should apply biochar to multi-metal contaminated soil with great caution and tailor biochar production for achieving desired outcome and avoiding adverse impact on soil ecosystem.

     

INTERACTIVE EFFECT OF SULFUR AND NITROGEN ON GROWTH AND YIELD ATTRIBUTES OF OILSEED CROPS (BRASSICA CAMPESTRIS L. AND ERUCA SATIVA MILL.) DIFFERING IN YIELD POTENTIAL

Field experiments were conducted to determine the interactive effect of sulfur (S) and nitrogen (N) on growth and yield attributes of oilseed crops [Brassica campestris L. (V₁) and Eruca sativa Mill. (V₂)] differing in yield potential. Two combinations of S and N (in kg ha^?1): 0S + 100N (?S+N;T₁) and 40S + 100N (+S+N;T₂) were used. Biomass accumulation, leaf area index (LAI), leaf area duration (LAD), and photosynthetic rate in the leaves were determined at various phenological stages. The results showed that the combined application of S and N (+S+N) significantly (P<0.05) improved the growth and yield attributes of both the genotypes compared with N applied alone (?S+N). Genetic variability was observed between the two genotypes in response to combined application of S and N (T₂). Genotype V₁ had higher biomass accumulation, photosynthetic rate, seed yield, oil yield, biological yield, and harvest index when compared with genotype V₂. Treatment T₂ resulted in 142, 95, 56, and 349% enhancement in biomass accumulation, leaf-area index (LAI), leaf-area duration (LAD) and photosynthetic rate, respectively in comparison with treatment T₁ in genotype V₁. Seed yield, oil yield, biological yield, and harvest index were improved by 141, 171, 85, and 30%, respectively, by treatment T₂ in comparison with T₁. In the case of genotype V₂, increase in biomass accumulation, LAI, LAD, and photosynthetic rate due to application of treatment T₂ were 156, 137, 125 and 467%, respectively, over the results of T₁. Seed yield, oil yield, biological yield and harvest index improved by 193, 251, 98, and 48%, respectively, with this treatment. On the basis of results obtained in this study, it can be concluded that sulfur must be included in the nutrient management package for optimum growth and yield attributes of oilseed crops. Furthermore, the yield potential of oilseed crops with low seed and oil yield can be improved using this treatment as achieved in our study in case of taramira (Eruca sativa Mill.), a genotype with low seed and oil yield.     

Isolation and identification of effective cellulolytic bacteria in composting process from different sources

Cellulolytic bacteria have a bio-activating role in the composting process. A study was carried out to isolate and identify cellulolytic bacteria from various sources. The isolates were cultured in the carboxymethyl cellulose (CMC) agar medium and incubated at 30°C for 3–7 days. Based on morphological characteristics of the isolates, maximum diameter of a clear zone around the colony and maximum cellulolytic activity, eight isolate were selected for further studies regarding composting experiments.

Molecular tests based on PCR amplification and sequencing of 16S rRNA gene of isolates showed the closest phylogenetic similarity with the species of Stenotrophomonas rhizophila DSM14405 (99.8%), Brevibacterium halotolerans DSM8802 (99.6%), Achromobacter marplatensis B2 (99.8%), Bacillus methylotrophicus CBMB205 (100%), Pseudomonas azotoformans IAM 1603 (99.7%), Bacillus sonorensis NBRC 101234 (99.8%), Bacillus subtilis KCTC 13429 (100%) and Ochrobactrum thiophenivorans DSM 7216 (99.3%). The study of the isolates impact on the composting of palm wastes in a randomized complete block design with 11 treatments in 3 replications showed that strain IB (B. methylotrophicus) caused a significant decrease in C:N ratio (58%). The increasing of microbial respiration compared with control after 30 days incubation at 37°C showed that the B. methylotrophicus strain IB with cellulolytic characteristics can be applied to hydrolysis of cellulosic biomass in the composting processes.     

Design and implementation of an electronic mobile poultry production documentation system

Documentation is a major component of any traceability system where traceability is defined in the ISO Regulation 8402:1994 as the ability to trace the history, application and location of what is under consideration. Traceability systems are record keeping systems designed to track the flow of product or product attributes through the production process or supply chain. All international supply chains are forced to comply with traceability requirements. In this paper, we develop and implement an end-to-end mobile application prototype that traces the poultry production. This application consists of front-end and back-end systems. At the front-end, the worker uses a GPRS enabled handheld device (cell phone, PDA, etc.) to capture information on poultry operations collected at a remote chicken farm and transmit it to a back-end server in the main office. Through customized application the back-end server analyses all information received from the front-end and based on a built-in business process and business rules, intelligently updates various stakeholders of any breach of bio-security measures that requires immediate attention. The proposed system administrators can also access this application via Internet for management decision making. The back-end system consists of web server, defined business application logic and database server.     

One-step extraction and cleanup procedure for determination of p,p'-DDT, p,p'-DDD, and p,p'-DDE in fish

A simplified method that combines extraction, partitioning, and cleanup in a single step for measuring p,p'-DDT and its metabolites in fish is described. Minced fish samples are emulsified with disodium hydrogen orthophosphate and trisodium citrate, ground with sodium sulfate, and eluted from a chromatographic column prepacked with alumina and silicic acid. The fats and fatty acids are solubilized and easily extracted from the tissues and retained by the column, while p,p'-DDT and its metabolites are quantitatively eluted with 40 mL n-hexane. The eluate is directly applied to a gas chromatographic column. Average recoveries of p,p'-DDT and its metabolites added to fish in vitro are 81%. The average coefficient of variation for recoveries of p,p'-DDT and its metabolites is less than 6.5% and the detection limit is 0.001 micrograms/g for p,p'-DDE, thus making this method very suitable for residue analysis.     

Effects of Increasing Dosages of Acid Mining Wastes in Metal Uptake by Lygeum spartum and Soil Metal Extractability

Water, Air, & Soil Pollution - A yearlong (December 2003 to February 2005) monitoring program was undertaken for urban roadside measurement of benzene, toluene, ethyl benzene, m- and p-xylene,...