High dechlorination of PCBs catalysed by carbon under mild conditions

This article reports high dechlorination of toxic polychlorinated biphenyls (PCBs) under mild conditions. PCBs are priority pollutants acting as endocrine disruptors, human carcinogens and environmental estrogens. Previous remediation methods involving high temperature and pressure have drawbacks such as high cost, de novo dioxins synthesis and difficult recovery of vaporized PCBs. On the other hand, dechlorination methods using mild conditions show the problem of catalyst deactivation. Here, activated carbon was used for the first time as catalyst to dechlorinate 2,4,5 trichlorobiphenyl. High dechlorination, of 87%, was achieved under mild conditions. 2,4,5 trichlorobiphenyl was treated at 40–150°C with calcium hydroxide, sodium hydroxide and sulfur in mixed water and organic solvents. Dechlorination products were biphenyl, orthohydroxy biphenyls, 2,4 dihydroxy biphenyls and biphenyl-2-thiol. Dichlorobiphenyl and orthochlorobiphenyls were found in trace quantities. We found that carbon particles catalysed dechlorination by substitution reactions and suppressed further chlorination. Dechlorination at biphenyl ortho position was preceded by substitution reaction by hydroxyl and thiol ions. Moreover, in the absence of carbon, dechlorination was lower and substituted products were not observed. These findings may be applied at industrial scale to remediate PCB-contaminated waste.     

Relative salinity tolerance of warm season turfgrass species

Fresh water, coupled with soil salinization in many areas has resulted in an increased need forscreening of salt tolerant turf grasses. Relative salinity tolerance of eightwarm season turfgrass species were examined in this study in sand culture. Grasses were grown in a glasshouse, irrigated with either distilled water or saline sea water adjusted to 24, 48 or 72 dSm-1. Salt tolerances of the grasses were assessed on the basis of their shoot and root growth, leaf firing and turf quality. Regression analysis indicated that Zoysiajaponica (Japanese lawn grass) (JG), Stenotaphrum secundatum (St. Augustine) (SA), Cynodon dactylon (satiri) (BS), Zoysia teneuifolia (Korean grass) (KG), Digitaria didactyla (Serangoon grass) (SG), Cynodon dactylon (Tifdwarf) (TD), Paspalum notatum (Bahia grass) (BG) and Axonopus compressus(Pearl blue) (PB) suffered a 50% shoot growth reduction at 36.0, 31.8, 30.9, 28.4, 26.4, 25.7, 20.0 and 18.6 dSm1 of salinity, respectively and a root growth reduction at44.9, 43.7, 33.4, 31.0, 29.5 27.5, 21.5 and 21.4 dSm- of salinity, respectively. Leaf firing and turf quality of the selected species, as a whole, were also found to be affected harmoniously with the change in root and shoot growth. On the basis of the experimental results the selected species were ranked for salinity tolerance as JG>SA>BS>KG>SG >TD>BG>PB.     

Groundwater modeling of Saq Aquifer Buraydah Al Qassim for better water management strategies

Saudi Arabia is an arid country. It has limited water supplies. About 80?C90% of water supplies come from groundwater, which is depleting day by day. It needs appropriate management. This paper has investigated groundwater modeling of Saq Aquifer in Buraydah Al Qassim to estimate the impact of its excessive use on depletion of Saq Aquifer. MODFLOW model has been used in this study. Data regarding the aquifer parameters was measured by pumping tests. Groundwater levels and discharge of wells in the area for the year 2008 and previous record of year 1999 have been collected from Municipal Authority of Buraydah. Location of wells was determined by Garmin. The model has been run for different sets of pumping rates to recommend an optimal use of groundwater resources and get prolonged life of aquifer. Simulations have been made for a long future period of 27?years (2008?C2035). Model results concluded that pumping from the Saq Aquifer in Buraydah area will result into significant cones of depression if the existing excessive pumping rates prevail. A drawdown up to 28?m was encountered for model run for 27?years for existing rates of pumping. Aquifer withdrawals and drawdowns will be optimal with the conservation alternative. The management scheme has been recommended to be adopted for the future protection of groundwater resources in Kingdom of Saudi Arabia.     

Localized hyper saline waters in Arabian Gulf from desalination activity��an example from South Kuwait

Desalination is the only means of reliable water supply in most of the Arabian Gulf States including Kuwait, Saudi Arabia, Bahrain, Qatar, and United Arab Emirates. Huge desalination capacities are installed on the western margin of the Arabian Gulf contributing to increased salinity off the coast. This paper presents long term salinity observation made near outfall of Az Zour Power and Desalination Plant in South Kuwait. The salinity values peak at around 50 ppt at observation station located in open gulf around 5 km from the outfall of the power and desalination plant. The observation highlights the stress on the local marine environment continued incremental salinity can impair the marine biodiversity in the area. The study suggests that a stringent post construction and operational offshore water quality assessment can help in early detection of potentially complex environmental issues.     

Impact assessment of subsurface drainage on waterlogged and saline lands

Waterlogging and salinity due to seepage from canals have polluted land and environment in various parts of Pakistan. A sustainable environment requires urgent remedial measures for this problem. The research in this paper presents the impacts of the Fourth Drainage Project, Faisalabad on the twin problem of waterlogging and salinity. Monitoring of the project was made on regular basis. The key performance indicators for the project include the lowering of water table, improvement of water quality and soil salinity, increase in area under cultivation, cropping intensity, and socioeconomic status of the project population. Data regarding water levels and discharge from the drain pipes were collected to monitor the impact on waterlogging. Soil samples were tested to evaluate the impact of drainage on land. It has been found that the percentage of the contaminated land in the project area has considerably been decreased, while the cropping intensities have been increased.     

Prevalence of heavy metal resistance in bacteria isolated from tannery effluents and affected soil

In the present study, a total of 198 bacteria were isolated, 88 from the tannery effluents and 110 from agricultural soil irrigated with the tannery effluents. Tannery effluents and soils were analyzed for metal concentrations by atomic absorption spectrophotometer. The tannery effluents and soil samples were found to be contaminated with chromium, nickel, zinc, copper, and cadmium. All isolates were tested for their resistance against Cr^6?+?, Cr^3?+?, Ni^2?+?, Zn^2?+?, Cu^2?+?, Cd^2?+?, and Hg^2?+?. From the total of 198 isolates, maximum bacterial isolates were found to be resistant to Cr^6?+? 178 (89.9%) followed by Cr^3?+? 146 (73.7%), Cd^2?+? 86 (43.4%), Zn^2?+? 83 (41.9%), Ni^2?+? 61 (30.8%), and Cu^2?+? 51 (25.6%). However, most of the isolates were sensitive to Hg^2?+?. Among the isolates from tannery effluents, 97.8% were resistant to Cr^6?+? and 64.8% were resistant to Cr^3?+?. Most of the soil isolates were resistant against Cr^6?+? (83.6%) and Cr^3?+? (81.8%). All isolates were categorized into Gram-positive and Gram-negative bacteria. In a total of 114 Gram-positive isolates, 91.2% were resistant to Cr^6?+? followed by 73.7% to Cr^3?+?, 42.1% to Zn^2?+?, 40.4% to Cd^2?+?, and 32.5% to Ni^2?+?. Among Gram-negative isolates, 88.1% were found showing resistance to Cr^6?+?, 75.0% to Cr^3?+?, and 47.6% were resistant to Cd^2?+?. Majority of these metal-resistant isolates were surprisingly found sensitive to the ten commonly used antibiotics. Out of 198 isolates, 114 were found sensitive to all antibiotics whereas only two isolates were resistant to maximum eight antibiotics at a time. Forty-one and 40 isolates which constitute 20.7% and 20.2% were resistant to methicilin and amoxicillin, respectively.     

Multiple metal tolerance and biosorption of cadmium by Candida tropicalis isolated from industrial effluents: glutathione as detoxifying agent

The ability of cadmium uptake by metal-resistant yeast, Candida tropicalis, from the liquid medium and wastewater was evaluated. The minimum inhibitory concentration of Cd^2?+? against C. tropicalis was 2,500 mg L^???1. The yeast also showed tolerance toward Zn^2?+? (1,400 mg L^???1), Ni^2?+? (1,000 mg L^???1), Hg^2?+? (1,400 mg L^???1), Cu^2?+? (1,000 mg L^???1), Cr^6?+? (1,200 mg L^???1), and Pb^2?+? (1,000 mg L^???1). The yeast isolate showed typical growth curves, but lag and log phases extended in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 8. The metal processing ability of the isolate was determined in a medium containing 100 mg L^???1 of Cd^2?+?. C. tropicalis could decline Cd^2?+? 70%, 85%, and 92% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd^2?+? 40% and 78% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and nonprotein thiol levels by 135% and 134% at 100-mg L^???1 concentration, respectively. An increase in the synthesis of GSH is involved in metal tolerance, and the presence of increasing GSH concentrations may be a marker for high metal stress in C. tropicalis. C. tropicalis, which is resistant to heavy metal ions and is adaptable to the local environmental conditions, may be employed for metal detoxification operations.     

Invasive plants as biosorbents for environmental remediation: a review

Environmental Chemistry Letters - Water contamination is an environmental burden for the next generations, calling for advanced methods such as adsorption to remove pollutants. For instance,...     

Effect of slow release nitrogenous fertilizers and biochar on growth,physiology, yield,and nitrogen use efficiency of sunflower under arid climate

Environmental Science and Pollution Research - Sunflower plants need nitrogen consistently and in higher amount for optimum growth and development. However, nitrogen use efficiency (NUE) of...     

Temporal variation in leachate composition of a newly constructed landfill site in Lahore in context to environmental pollution and risks

Environmental Science and Pollution Research - This study investigated the seasonal and temporal variations in the extent and source of physiochemical and toxic trace elements in the Lakhodair...