Foliar uptake of arsenic nanoparticles by spinach: an assessment of physiological and human health risk implications

Atmospheric contamination by heavy metal(loid)–enriched particulate matter (metal-PM) is highly topical these days because of its high persistence, toxic nature, and health risks. Globally, foliar uptake of metal(loid)s occurs for vegetables/crops grown in the vicinity of industrial or urban areas with a metal-PM-contaminated atmosphere. The current study evaluated the foliar uptake of arsenic (As), accumulation of As in different plant organs, its toxicity (in terms of ROS generation, chlorophyll degradation, and lipid peroxidation), and its defensive mechanism (antioxidant enzymes) in spinach (Spinacia oleracea) after foliar application of As in the form of nanoparticles (As-NPs). The As-NPs were prepared using a chemical method. Results indicate that spinach can absorb As via foliar pathways (0.50 to 0.73 mg/kg in leaves) and can translocate it towards root tissues (0.35 to 0.68 mg/kg). However, health risk assessment parameters showed that the As level in the edible parts of spinach was below the critical limit (hazard quotient <?1). Despite low tissue level, As-NP exposure caused phytotoxicity in terms of a decrease in plant dry biomass (up to 84%) and pigment contents (up to 38%). Furthermore, several-fold higher activities of antioxidant enzymes were observed under metal stress than control. However, no significant variation was observed in the level of hydrogen peroxide (H₂O₂), which can be its possible transformation to other forms of reactive oxygen species (ROS). It is proposed that As can be absorbed by spinach via foliar pathway and then disturbs the plant metabolism. Therefore, air quality needs to be considered and monitored continuously for the human health risk assessment and quality of vegetables cultivated on polluted soils (roadside and industrial vicinity).

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Immobilized cell augmented activated sludge process for enhanced nitrogen removal from wastewater.

The immobilized cell augmented activated sludge (ICAAS) system combines a cell immobilization technique and an offline enricher-reactor for the bioaugmentation of the activated sludge system to improve treatment performances. In this study, enhanced nitrogen removal using ICAAS was investigated. Laboratory-scale, offline, batch enricher-reactors were used to maintain nitrification and denitrification activities of coimmobilized nitrifiers and denitrifiers used to augment a laboratory-scale completely mixed activated sludge system (CMAS) treating synthetic wastewater. Cellulose triacetate was the media used to entrap nitrifiers and denitrifiers at a 2:1 mass ratio. The ICAAS augmented with the coimmobilized cells between 5 and 20% by volume gained 24 +/- 5% higher nitrogen removal than a control CMAS, which provided nitrogen removal of 28 +/- 7%. The ICAAS scheme is a viable alternative for upgrading existing activated sludge systems to gain better nitrogen removal. .     

Effect of soil on microbial responses to metal contamination

An experiment was conducted to investigate microbial responses to metal inputs in five soils with varying clay and organic contents; one soil had also a higher pH. These soils were treated with a low metal, sewage sludge control or with this sludge contaminated to achieve Cu=112, Ni=58 and Zn=220 mg kg(-1) in medium and Cu=182, Ni=98 and Zn=325 mg kg(-1) in high metal soils. CO(2) evolution rates were measured at 1 week and at 4-5-day intervals thereafter until the end of the incubation (7 weeks). Extractable metals (CaCl(2) and water), biomass C, metabolic quotient, ergosterol, bacterial-fungal phospholipid fatty acid (PLFA-3 weeks only) ratio and mineral N were measured at 3 and 7 weeks. Metal inputs caused a marked increase in metal availability in the slightly acidic sandy loams, a smaller increase in slightly acidic clays and had little effect in the alkaline loam. After an initial increase in CO(2) evolution with metal inputs in all soils, the high metal treatment alone caused a significant decrease at later stages, mainly in sandy loams. Although biomass C and metabolic quotient decreased in all soils with higher metal inputs, the effect was more pronounced in the sandy loams. Metal inputs increased ergosterol and decreased bacterial-fungal PLFA ratios in most soils. Larger mineral N contents were found in all high metal soils at 3 weeks but, after 7 weeks, metals caused a significant decrease in sandy loams. CaCl(2) and water-extractable Cu, Ni and Zn contents were closely correlated with microbial indices in sandy loam but not in clay soils. Overall, the effect of treatments on microbial and extractable metal indices was greater in loams. Within a single series, higher organic soils showed less pronounced responses to metal inputs, although this trend was not always consistent.     

Role of plants, mycorrhizae and phytochelators in heavy metal contaminated land remediation

Phytoremediation is a site remediation strategy, which employs plants to remove non-volatile and immisible soil contents. This sustainable and inexpensive process is emerging as a viable alternative to traditional contaminated land remediation methods. To enhance phytoremediation as a viable strategy, fast growing plants with high metal uptake ability and rapid biomass gain are needed. This paper provides a brief review of studies in the area of phytoaccumulation, most of which have been carried out in Europe and the USA. Particular attention is given to the role of phytochelators in making the heavy metals bio-available to the plant and their symbionts in enhancing the uptake of bio-available heavy metals.     

Transformation products distribution of atrazine in corn plants treated with radiolabelled herbicide

Roots of whole plants at four leaf stage grown in specialized soil treatment vessels were treated with ¹⁴C-atrazine. Plant tissues were exhaustively extracted with methanol and extracts were separated by preparative thin layer chromatography (TLC). The extracted material was separated in two TLC bands at Rf0.00 and Rf0.18 containing 33% and 67% of plant ¹⁴C-residues, respectively. Methanol extracts of these bands subjected to derivatization, hydrolysis and analysis by TLC, revealed the presence of a number of transformation products consisting of hydroxy analogues of atrazine and their dealkylated metabolites. The transformation products had variable distribution patterns amongst leaf, stalk and root tissues. Diaminohydroxyatrazine, hydroxyatrazine, and deethylhydroxyatrazine were the main ¹⁴C-residues. Stalk tissue contained more ¹⁴C-residues which were largely located at and just below the ligule. The significance of ¹⁴C-residue accumulation at the ligule and the transformation product compartmentalization are discussed.     

Prevalent fecal contamination in drinking water resources and potential health risks in Swat, Pakistan

Fecal bacteria contaminate water resources and result in associated waterborne diseases.This study assessed drinking water quality and evaluated their potential health risks in Swat, Pakistan. Ground and surface drinking water were randomly collected from upstream to downstream in the River Swat watershed and analyzed for fecal contamination using fecal indicator bacteria(Escherichia coli) and physiochemical parameters(potential of hydrogen, turbidity, temperature, electrical conductivity, total dissolved solid, color, odor and taste). The physiochemical parameters were within their safe limits except in a few locations, whereas, the fecal contaminations in drinking water resources exceeded the drinking water quality standards of Pakistan Environmental Protection Agency(Pak-EPA),2008 and World Health Organization(WHO), 2011. Multivariate and univariate analyses revealed that downstream urbanization trend, minimum distance between water sources and pit latrines/sewerage systems, raw sewage deep well injection and amplified urban,pastures and agricultural runoffs having human and animal excreta were the possible sources of contamination. The questionnaire survey revealed that majority of the local people using 10–20 years old drinking water supply schemes at the rate of 73% well supply,13% hand pump supply, 11% spring supply and 3% river/streams supply, which spreads high prevalence of water borne diseases including hepatitis, intestinal infections and diarrhea, dysentery, cholera, typhoid fever, jaundice and skin diseases in children followed by older and younger adults.     

Feasibility of relating interferon production by wild voles to types of chemical contamination of their environment

In the fall of 1980, a limited field sampling and laboratory analysis profect was undertaken to explore the feasibility of relating immunological responses of field mice (voles) living wild in an area of environmental concern to the level of chemical contamination of that area. The voles were collected in the vicinity of Love Canal by biological sampling teams already there to collect voles for other purposes.The project helped identify those areas of practical uncertainty that must be clarified before the rate of interferon production in voles can be considered as a possible indicator of chemical contamination. Two lines of research are proposed: developing optimumin vitro interferon bioassays systems for vole leukocytes; and characterizing the interferon production responses of voles following controlled exposures to selected carcinogens and other chemicals.     

Domestic Water Contamination in Rapidly Growing Megacities of Asia: Case of Karachi, Pakistan

The development of essential services including water and sanitation in many megacities of the economically developing countries of Asia cannot keep pace with their rapidly growing population and accompanying urban and industrial development. The inadequate water supply and poor sanitation services lead to contamination of their water supply. It also leads to the input of sewage water into the groundwater. The problem is seriously acute in Karachi, the largest city in Pakistan with a population of over 12 million and growing at 6 percent. This paper examines the problem of water contamination in Karachi. The paper presents the data on water quality from various sources, mainly municipal water supply, vendors and well water; the three major sources of water for domestic use in Karachi. Except municipal water from some areas and during certain periods, water from most other sources contain coliform bacteria, and in many cases faecal coliform, in amounts several magnitudes higher than any standards permit. Many samples have also been found to contain heavy metals including Chromium, Lead, Nickel and Arsenic in amounts excessive of permitted standards. The probable sources of contaminants for the various types of water (piped, vendors, wells) indicate that groundwater may be the main contributor. The very source of this groundwater is predominantly from sewage. The health hazards from consuming such contaminated water are obvious. The paper also evaluates the solutions that are being practiced, proposed or may be feasible, as well as those that are evolving.     

The effect of fly ash on plant growth and yield of tomato

A gradual increase in fly ash concentrations in the normal field soil (0, 10, 20...100% volume/volume) increased the porosity, water holding capacity, pH, conductivity, C.E.C., sulphate, carbonate, bicarbonate, chloride, P, K, Ca, Mg, Mn, Cu, Zn and B. Fly ash additions to soil caused significant reductions in nitrogen content, it being almost nil in 90 and 100%. Tomato plants grown in the ash-soil mixture showed luxuriant growth with bigger and greener leaves. Plant growth, yield, (flowering, fruiting, fruit weight/plant, mean fruit weight), carotenoids and chlorophylls were mostly enhanced in the treatments with 40-80% fly ash, being optimal at 50 or 60%. From 60 or 70% onwards, the measured parameters tended to reduce. At 100% fly ash, yield (weight of fruits/plant) was considerably reduced. The boron content of tomato leaves displayed a gradual increase with fly ash addition from 20% onwards, while response of foliar nitrogen was just the opposite. The most economic level of fly ash incorporation was 40%, which improved the yield and market value of tomato fruits (mean weight) by 81 and 30%, respectively.     

In vitro release of bound (nonextractable) 14C residues from plants by corn leaves bomogenates

Corn leaves homogenates were found to release bound (nonextractable) ¹⁴C residues from the aerial portion of matured corn plants. The 22,000 g pellet and 10,000 g supernatant fractions were the most active in releasing the bound ¹⁴C residues. The released ¹⁴C residues comprised mainly 2-OH analogues of the $\text{N}$-monodealkylated analogues of atrazine. It is suggested that the enzymatic system in plants may cause metabolic conversion of bound residues.