Mango samples: Stratified random sampling was used for this experiment. Because of the steep slope of the tailings disposal dam where mangoes are growing, the area was stratified in three strata.
The first stratum was on the top of the slope, the second was at middle of the slope and the third was at the bottom of the slope. The strata were divided in meter intervals. Then random sampling was used to collect the mangoes in three strata. Seven ripe mangoes were collected from each stratum and put in polythene bags. A total of 21 mangoes taken for laboratory analysis.
Soil samples: Using the mango collection points, soil samples were collected by digging up to 20 cm in the ground next to the mango trees. An equal number of samples, as in the mangoes, were collected from the tailings dam.
The collected fruit samples were thoroughly washed and rinsed with distilled water. The samples collected from each stratum were treated independently of the samples from the other strata. The dried samples were then ground into powder and stored in fresh plastic polythene bags in readiness for mineral content analysis.
Analysis of fruit tissue followed the wet digestion methods suggested by Cui et al. Then 25 ml of Nitric acid was added to each beaker and left for 24 hours. After digestion with Nitric acid, 15 ml of per chloric acid was added to each of the mixture prepared earlier. The samples in the beakers were then heated until white fumes appeared per chloric acid fumes. After cooling, the solution was thoroughly mixed and diluted using distilled water up to ml per sample using a ml measuring cylinder and then rinsed using filter papers.
The concentration of Copper, Cobalt and Cadmium in the filtrate was determined using a flame atomic absorption spectrophotometer AAS with high resolution continuum source. The Atomic Absorption Spectrometer AAS was set up following the appropriate operating procedure for the particular model and the instrument was calibrated so that the mineral content of Copper, Cobalt and Cadmium in the samples can be ascertained in Figure 2. Soil samples collected from the tailing dams were also taken to the laboratory.
The samples were mixed and then sieved to obtain homogenous samples. Two 2 grams of each of the soil samples collected from the three 3 tailings plus two 2 duplicates for each were put in beakers, in total 9 samples. Then drops of Hydrofluoric acid HF were added to each sample to break the silicate in the soils. Then 30 ml of Nitric acid was added to each sample for decomposition to take place.
The samples were then heated on the hot plate for 15 minutes. The samples for analysis of Copper, Cadmium and Cobalt were then diluted up to ml with distilled water using flasks of ml. The samples in the flasks were then thoroughly shaken thereafter filtered using filter papers. All glassware used during the study were washed with distilled water and immersed in Nitric acid for 24 hours before being used [ 21 ].
Fruit samples were cleaned with distilled water and peeled with a stainless knife and shred into pieces for drying. After drying the pieces were put in an electrical grinder with stainless blades and ground into powder used for heavy metal analysis.
Distilled water was used throughout the sample preparation and analysis. To evaluate the Copper, Cobalt and Cadmium in mangoes and soils from different strata, we used a one way Analysis of Variance.
This was after testing for normality. Mean separation was done using Boniferoni Post Hoc Analysis as this was a planned experiment. The concentration of the copper in the fruits ranged from 16 ppm ppm in stratum one, 8 ppm ppm in stratum two and 8 ppm ppm in stratum three. The study also observed that the concentration of cobalt in the fruits ranged from 1 ppm-8 ppm across all the strata.
The concentrations ranged from ppm ppm in stratum one, ppm ppm in stratum two and ppm ppm in stratum three. The concentration of cobalt in soil samples ranged from 15 ppm ppm in stratum one, 10 ppm ppm in stratum two and 15 ppm to ppm in stratum three. The contents of cadmium ranged from 0.
The results from the study indicate that the soils and fruit samples from the study areas were heavily contaminated with cadmium, copper and cobalt. Our results corroborate the finding of Muchuweti et al. Copper is an essential dietary element whose function as biocatalysts is necessary for body pigmentation and is widely distributed in the environment.
It is always present in food and animals which are exposed to copper sources in the environment. There is a close relationship between climate and the incidence of cobalt deficiency.
While deficiency is generally only seen in areas with a greater than millimetre annual rainfall, it is the winter rainfall in the current year that has the most influence.
Winter rainfall influences cobalt availability in two ways: it leaches the cobalt from the soil but it also influences the pasture growth rate in the spring flush. Cobalt is not an essential nutrient for plants, so high growth rates in spring dilute the amount of cobalt in the plant.
Newborn animals have low reserves and a high requirement for cobalt. Colostrum provides vitamin B12 but milk has low levels. Where pastures are likely to be low in cobalt, young animals should be treated at weeks of age with injectable vitamin B Weaner sheep are also more prone to cobalt deficiency than adult animals.
Sheep and goats appear to be more susceptible to cobalt deficiency than cattle. There is a higher incidence of signs of the disease in these species. Young animals with heavy worm burdens will be more susceptible to cobalt deficiency. Avoid weaning young animals onto pastures that are likely to have a high worm burden. The occurrence of cobalt deficiency is highly variable year-on-year, but ill-thrift, weepy eyes and anaemia in sheep in moderate to high rainfall areas after a wet winter and soft spring are highly suggestive of cobalt deficiency.
The most common way of persuading cellular damage by HMs is by inducing oxidative stress by alleviating free radical levels [ 18 ]. Depending upon ROS generating potential, the bioactive metals are categorized into two classes, i. The non-redox active metals are metals Cd, Ni, Hg, Zn and Al that damage the cells and their subcellular vitals by indirectly accruing ROS level via glutathione depletion, inhibiting antioxidant enzymes, binding active sulfhydryl groups of proteins and activating ROS producing enzymes such as NADPH oxidase [ 17 , 20 , 21 ].
This review deals with uptake, accumulation, transport, toxicity and remediating strategies of cobalt from contaminated soils and water bodies. Cobalt Co was discovered by Georg Brandt in [ 22 , 23 ]. It is a heavy metal having atomic number 27 and atomic mass Co is required as a trace element in both plants and animals.
Co is a beneficial element for leguminous plants for the growth, metabolism, and development of root nodules [ 25 ]. Its importance to the rest of the plant species is still equivocal. It plays an important role in the activities of various enzymes and coenzymes like vitamin B 12 cyanocobalamin [ 26 ]. Some plant species are able to grow in soil possessing high concentrations of Co up to —10, ppm.
Co acts as a coenzyme in a number of cellular processes like the fatty acid oxidation and synthesis of DNA. It was found that deficiency of Co in grasses and feedstuffs leads to diseases in ruminants, like scaly skin, loss of appetite, anaemia and bone fragility [ 31 , 32 ]. Toxic concentrations of Co inhibit active transport in plants. Relatively higher concentrations of Co have toxic effects, including leaf fall, inhibition of greening, discoloured veins, premature leaf closure and reduced shoot weight [ 33 ].
High concentration of Co leads to numerous dysfunctions in the plant system. ROS generation under Co stress in plants generally causes disturbance in photosystem II and stimulates disruption in electron transport chain [ 36 ]. Increased Co content in the soil also reduces photosynthetic pigments and nitrogen metabolism in the plants [ 37 ].
Thus, there is a strong need to remediate Co accumulated sites. The distribution of cobalt is species dependent. Generally leguminous plants contain more Co as compared to grasses and grain crops [ 38 , 39 ]. Toxic concentrations of cobalt inhibit active transport in plants. Also application of excess of Co has detrimental effects on plant growth and metabolic functions, including leaf necrosis and interveinal chlorosis, inhibition of cellular mitosis and chromosomal damage [ 40 ].
Co is also known to inhibit seed germination, root and hypocotyl elongation [ 41 ]. Co appears to be toxic when uptake of essential elements like iron and calcium are inhibited [ 42 , 43 ]. Cobalt is well known to be siderophile, lithophile as well as chalcophile element [ 44 ]. In nature, it is found along with iron, nickel, silver, lead, copper, manganese and also found to exist as carbonates [ 45 ].
It also exists in the form of minerals like cobaltite, skutterudite, erythrite, spherocobaltite and heterogenite. It is found abundantly in both sedimentary and igneous rocks. The ultramafic rocks have higher abundance of Co, i. During differentiation of crust from balastic magma, most of the Co combines with ferromagnesian minerals, which is further limited by the number of lattice sites in Fe—Mg. In granite rocks, Co forms tight coherence with magnesium.
It has very little mobility [ 45 , 46 , 47 ]. Cement industries and carbide tool grinding plants are also responsible for Co leaching [ 49 , 50 ]. Industries related to e-waste processing have also been found to release Co above legal threshold levels [ 51 , 52 ]. Polishing disc used in diamond polishing is also made up of fine cobalt. It is also a potential source of generating Co dust [ 53 , 54 ]. Pigment and paint industries also use Co as siccative that speeds up the process of drying [ 55 ].
Incinerators produce bottom ash which contains Co that leaches to the soil and ground water [ 56 ]. Due to mining activities, Co concentration in surrounding soil and water bodies elevates way beyond regional background levels [ 57 ]. Mobile batteries, televisions TVs , liquid crystal display TVs, and computer monitors also contain Co and become potential source of Co contamination [ 58 , 59 , 60 ].
Several cosmetic products are also source of Co as impurities [ 61 ]. Many dietary items like chocolate, butter, fish, etc. Many older medicinal practices use Co preparations to treat anaemia, post-menopausal symptoms in women [ 64 , 65 , 66 ].
Co is a micronutrient which can be accumulated by plants in very less amount. Co ions may get accrued in the plant parts like fruit, grains and seeds. It is essential to all animals and microorganisms [ 67 ]. However, a physiological requirement for Co has not been demonstrated in higher plants.
Although concentration of Co in plants is normally 0. Metal ions do not biodegrade. Thus the removal of excess metal ions from polluted sites and their secure sequestration are important for the production of safe food, and viable environment [ 69 ]. Uptake, transport and distribution of Co are species dependent and are governed by various mechanistics [ 70 , 71 ]. Transport proteins and intracellular affinity binding sites mediate the uptake of Co ions across the plasma membrane. Many classes of proteins have been entailed in heavy metal transport in plants [ 72 ].
These include CPx-type ATPases that are involved in the overall metal-ion homeostasis and tolerance in plants, the natural resistance-associated macrophage protein Nramp , and the cation diffusion facilitator CDF family proteins, zinc—iron permease ZIP family proteins, etc.
They demonstrated AtHMA3 is located in the vacuolar membrane of plant. Studies have demonstrated involvement of CPX motif in Co ion coordination during transport [ 75 ] Moreover, the metal specificity of these ATPases remains unclear.
Studies on Synechocystis sp. It has also been reported that in higher plants Co ions get bind with the roots, and transferred in the body via passive transport. Co ions enter into the cell through plasma membrane and may be translocated to the whole plant with the help of IRT1 transporters [ 77 ].
Due to foolhardy use of fertilizers, wastewater discharge, coal and motor fuel combustion processes, increased mining of the cobalt ore, the concentration of naturally occurring Co has increased [ 78 ]. Cobalt is not relegated as an essential element for plants.
Nevertheless, it is usually distinguished as a beneficial element having role in certain biochemical and physiological processes of plants.
Higher levels of Co in soil causes toxic impacts on plants that are reflected in their morphology as well as physiology [ 79 , 80 , 81 ] Table 2. Studies also suggested that Co ions effect the growth of Lemna minor with increase in concentration [ 82 ]. Chatterjee and Chatterjee [ 83 ] reported that excess Co led to the occurrence of iron Fe deficiency in young leaves.
Higher Co concentration reduced the biomass, chlorophyll content, and catalase activity, while increased the activities of peroxidase, acid phosphatase, ribonuclease enzymes, and carbohydrate, phosphorus fractions in leaves. Co reduces the translocation of P, S and Cu and drops the transpiration rate and water potential in the leaves of cauliflower [ 1 ].
Application of 5 mM Co resulted in reduction in seedling growth due to chlorosis of the younger leaves [ 84 ]. Excess concentrations of the three metals lead to decrease in chlorophyll content, uptake and translocation of Fe in leaves and reduced proline activity [ 86 ]. The cobalt toxicity on growth and metabolism of tomato plants was studied in sand medium at five levels of concentration, i.
Strong effects of cobalt on tomato were observed at 0. The prominent symptoms were appearance of chlorosis on young leaves followed by necrosis and withering. Supererogatory levels of Co significantly affected biomass, concentrations of various minerals like P, S and Fe, and diminished level of chlorophyll a and b , DNA, starch as well as reducing and non-reducing sugar levels.
Increased concentrations of metal also inhibited the activity of antioxidative enzymes like catalase, peroxidase, ribonuclease and acid phosphatase [ 87 ]. Some studies reported that increased concentration 10, 50, , mM of heavy metals Ni, Co, Fe decreased the rate of seed germination, root length, shoot length, protein and phenolics content in broad beans Vicia faba L.
The workers also inferred that bean is a metal resistant plant which has contrived various mechanisms such as denovo synthesis of anti-stress protein or mitigation of ROS by enhanced phenolic production to combat metal stress [ 89 ].
The preliminary levels of Cu, Cd, Cr, Co and Pb in soil, root and shoot of the grass were: soils: Enrichment coefficient EC and translocation factor TF were calculated to estimate the phytoextraction ability of E. The possible mechanism of actions of cobalt in plants, and proposed way of action of oxidizing and chelating agents is presented in Figs.
Bioremediation is an innovative and inventive biological approach that explores potential of microorganisms and plants to reduce and remediate soil and water bodies from toxic chemicals [ 91 , 92 ]. Bioremediation explores potential of microorganisms to remediate given medium viz. Phytoremediation is the direct use of green plants and their associated microorganisms to decrease or stabilize pollution in soils, sediments, ground water, surface water and sludge [ 94 ].
Here, metal tolerant and hyper-accumulating plant—microbe interactions are also explored for mobilization of metals [ 95 , 96 ]. First used in , it is a natural process used to remediate the contaminants, and has gained a lot of consideration during the last few years, on account of its being cost effective and promising technique [ 97 ]. A number of phytoremediation techniques are available, but in the following section only those are discussed which are involved in remediation of Co.
It is method of establishment of metal tolerant vegetation cover over contaminated area in order to immobilise contaminants within rhizosphere zone of plant. Growth of vegetation on contaminated area restricts dispersion of metal laden soil particles by air or water. Further, the microbes growing in rhizosphere immobilize the contaminants by precipitation or adsorption mechanism [ 98 , 99 ].
Moreover, retention or immobilisation of HMs in soil is also dependent upon pH of soil as most of the adsorption sites are pH dependent. This showed that Co is weakly bound in mineral phase as compared to other HMs [ ]. It involves the removal of contaminants from soil or water body through roots of plants and their accumulation in shoot system.
Thus, contaminant is removed from the medium [ ]. This technique is usually employed when phytostabilization is not possible. The success of phytoextraction is dependent upon two factors, i. There are more than four hundred plants which are reported as hyperaccumulators. A study by Malik et al. Thlapsi caerulescens is another hyperaccumulator of Zn also used for phytoextraction of Co. Lycopersicon esculentum was also shown to act as accumulator of Co with accumulating Co in all above ground plant parts except flowers and fruits [ ].
It is the technique exclusive used in water bodies. It explores potential of plant roots to take up and get rid of contaminants from water body [ ]. The contaminants are absorbed and precipitated in the roots from medium. The plants are first raised hydroponically and then they are transferred to the given contaminated water body [ ]. Epipremnum is successfully used for rhizofiltration of Co.
Plant showed a bioconcentration factor of Prajapati et al. Increased contamination of cobalt in the agricultural fields and water bodies is alarming. A number of remedial procedures are available to remediate our contaminated sites.
But the interaction of metals sometimes, makes one or other metal immobile that limits use of bioremediation strategies. So, new techniques and strategies should be continuously devised to reduce limitations of bioremediation procedures. Environ Chem Lett — Google Scholar. Mol Clin Environ Toxicol — Gen Mol Biol — Ecotoxicol Environ Saf — Met Ion Biol Syst — Ciszewski D, Grygar TM A review of flood-related storage and remobilization of heavy metal pollutants in river systems.
Water Air Soil Pollut — Wuana RA, Okieimen FE Heavy metals in contaminated soils: a review of sources, chemistry, risks and best available strategies for remediation. Int Sch Res Not — Bioremed J — Environ Toxicol Pharmacol — Guo J, Kang Y, Feng Y Bioassessment of heavy metal toxicity and enhancement of heavy metal removal by sulfate-reducing bacteria in the presence of zero valent iron.
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