Phytostabilization of fly ash from a coalmine in Botswana and biovalorisation of the recovered Napier grass (Pennisetum purpureum Schumach.).

The disposal of fly ash (FA) from coal power plants polluting the air, soil, and groundwater is a major environmental concern. Phytoremediation to rehabilitate fly ash dumpsites is a promising alternative but has practical concerns about the disposal of harvested biomass. This study investigated the effect of supplementing fly ash with fresh sewage sludge (FSS), aged sewage sludge, food waste, and compost (COM) to enhance the phytoremediation potential of Napier grass and its subsequent utilization for ethanol production. The highest removal of Mn (1196.12 g ha-1) and Ni (128.06 g ha-1) from FA could be obtained when Napier is grown in the presence of FSS and inorganic fertilizer (NPK). In addition, the highest bioethanol yield (19.31 g L-1) was obtained from Napier grown in fly ash with COM + NPK, thus providing additional economic benefits aside from the remediation process. Given the significant levels of heavy metals present in the pulp and bio-slurry after ethanol production, further research is required in this area to determine the best ways to utilize this waste such as converting it into biochar.

Using energy crops as a phytoremediation agent for fly ash dumpsites has the potential to remediate heavy metal contamination and provide additional economic benefits. Napier grass was able to tolerate high concentrations of heavy metals and yield high biomass in fly ash in the presence of organic amendments. The harvested biomass was successfully converted into substrate for bioethanol production using heavy metal-tolerant yeast. This is the first report on the production of ethanol from the phytoremediation biomass of Napier grass.

Microplastic load in the surface water and Tilapia sparrmanii (Smith, 1840) of the river systems of Okavango Delta, Botswana.

Microplastics are 'emerging' contaminants that threatens freshwaters and may have negative impact on the aquatic organisms. However, Botswana has no information on the status of microplastics, including freshwater like the Okavango Delta- the largest, inland wetland hosting wildlife, tourism, and supporting the socio-economic lifestyle of inhabitants. This study assessed the spatial distribution and characterization of microplastics in surface water and in the digestive organs of fish (Tilapia sparrmanii) from the Okavango delta. Surface water samples (156) and whole intact fish (15) were collected and analysed for microplastic contents by wet peroxide oxidation, potassium hydroxide (fish only), density separation, extraction, and stereomicroscope identification. The weight of microplastics for surface water samples varied from 138.18 to 381.67 µg m-3 and abundance ranged from 10.18 to 22.67 items L-1 with significant difference observed between sites in both variables. In tilapia, the highest microplastic abundance were found in the intestines then the stomach and the gills from the fish samples. Most prevailing size ranges of microplastics in fish and water samples were 1-2 mm and 2-3 mm while the most abundant shapes were fragments and fibres, respectively. Translucent microplastics were dominant in all samples. The results indicate the presence of microplastics in the Okavango delta even though they are very low (µg m-3). This baseline information will provide insights on the loads of microplastics in surface water and the quantities ingested by fish in the Okavango delta hence the need for monitoring. It would also guide on the need for effective policies addressing plastic and microplastic pollution.

Enhanced establishment of Colophospermum mopane (Kirk ex Benth.) seedlings for phytoremediation of Cu-Ni mine tailings.

This study was carried out to determine the effect of cow manure amendment and the method of planting on the growth, survival, and heavy metal accumulation of Colophospermum mopane seedling grown on Bamangwato Concessions Limited (BCL) mine tailings. Different planting strategies were employed where the mopane seedlings were planted with bare roots (devoid of potting soil) and without cow manure (T1, - CM - Soil); with the potting soil adhering to the roots but without cow manure (T2, - CM + Soil); with bare roots in the presence of cow manure (T3, + CM - Soil); and with potting soil intact together with cow manure (T4, + CM + Soil). Cow manure increased the pH of the mine tailings enhancing the survival and growth of the mopane seedlings. Seedlings grown under T1 conditions had a higher concentration of the heavy metals As, Cr, Cu, Mn, Ni, Pb, Zn, Sb, and Sr in their shoots compared to those grown under a T4 environment consisting of potting soil with cow manure. Cow manure decreased the availability of these heavy metals in mine tailings through the humic substance which adsorbed the heavy metal while the soil adhering to the roots diluted the concentration of heavy metals in the rhizosphere thus reducing the uptake and toxicity. Overall, the establishment of mopane seedlings in mine tailings could be enhanced by cow manure amendments and with soil adhering to its roots during transplanting.

Heavy metals in soil, plants, and associated risk on grazing ruminants in the vicinity of Cu-Ni mine in Selebi-Phikwe, Botswana.

The impact of BCL Cu-Ni mines on the surrounding environment has indicated high levels of heavy metal contamination in soil and some plant species. A comprehensive assessment of heavy metal concentration in plants, heavy metal concentration and availability in soils, and the estimates of risk associated with grazing animals in the area are presented. Exhaustive quantification of heavy metal contents in 82 plant samples revealed that some plants such as Boscia albitrunca and Boscia foetida are suitable for multi-metal phytoextraction, and others can accumulate one or two of the metals in soils or tolerate high levels of contamination. Current levels of soil contamination were manifested by acidification and high electrical conductivity, high contamination factor, and a pollution index between 8.31 and 10.79. The amount of exchangeable fractions of metals was higher than ordinary soils which is attributed to the high solubility of deposited materials on the soil surfaces. Daily intake estimates showed a possible risk associated with Pb and Cu contamination among grazing animals in the study area. Overall, the information has identified potential plants or combination of plants that could be utilized for the rehabilitation of the study area through phytoremediation. In addition, the estimates of the daily intake of the minerals due to consumption of plants in the vicinity of the BCL mines warrant for evaluation of the actual levels of heavy metals in grazing animals near the study area and in other mining areas in Botswana.

Rhizosphere properties and heavy metal accumulation of plants growing in the fly ash dumpsite, Morupule power plant, Botswana.

Discarding fly ash from a coal power plant into a dumpsite does not only contribute to deforestation and loss of productive land but also leads to contamination of air, soil, and groundwater. Therefore, fly ash should be managed properly to avoid the migration of contaminants. One management option is phytoremediation using adapted plants and as a prerequisite, there is a need to identify suitable plants that can be used for revegetation of fly ash dumpsites. To identify prospective plants, a survey was carried out by assessing the plants growing in Morupule B fly ash dumpsite based on their ability to accumulate heavy metals and their bioconcentration (BAF) and translocation factors (TF). Of the twenty-two-plant species growing in the fly ash dumpsite of Morupule B power plant station, N. glauca is a potential phytoextraction agent for Cu (TFCu = 1.02; BAFCu = 2.16) and Pb (TFPb = 1.38; BAFPb = 1.65); P. burchellii for Pb (TFPb = 1.61, BAFPb = 0.9) and Zn (TFZn = 1.35; BAFZn = 5.74); I. pes-tigridis for Pb (TFPb = 1.35; BAFPb = 1.56) and Zn (TFZn = 1.62; BAFZn = 7.43); A. pungens for Cr (TFCr = 1.22; BAFCr = 0.11), Cu (TFCu = 2.18; BAFCu = 1.14), and Zn (TFZn = 1.04; BAFZn = 1.44); E. hirta for Zn (TFZn = 1.54, BAFZn = 2.44); A. spinosus for Pb (TFPb = 1.29; BAFPb = 1.55); C. dactylon for Cu (TFCu = 1.86; BAFCu = 1.07) and Zn (TFZn = 1.00; BAFZn = 2.46); and D. aegyptium for Pb (TFPb = 1.19; BAFPb = 2.57). Other plants growing in the fly ash dumpsite are potential candidates for phytostabilization as they can tolerate a high concentration of metals and low essential nutrients. Also, different plant groups variably modified the pH, EC, OM, and exchangeable fractions of metals in the rhizosphere wherein grasses can increase the OM at higher rates, and it has a higher capacity to acidify and solubilize heavy metals in the rhizosphere leading to higher EC and available metals compared to other plant groups. Overall, the information presented is useful in identifying plants or their combinations for the phytoremediation of fly ash and other heavy metal-polluted environments.

Influence of mycorrhiza and fly ash on the survival, growth and heavy metal accumulation in three Acacia species grown in Cu-Ni mine soil.

Acacia albida, Acacia luederitzii, and Acacia tortilis are dominant acacia species in Botswana and have the potential to rehabilitate the heavy metal degraded environment. To establish this claim, experiments to assess the influence of mycorrhizal inoculation and fly ash amendments on the survival, growth and heavy metal accumulation of these species in mine tailings were conducted. A two-factor (AM inoculation × fly ash) in CRD was done on each of the three Acacia species consisting of four treatments: control (no mycorrhizal, no fly ash coded as - AM/- FA), with mycorrhizal but no fly ash (+ AM/- FA), no mycorrhizal but with fly ash (- AM/+ FA), and with mycorrhizal and with fly ash (+ AM/+ FA). After 24 weeks, results showed that the survival and dry matter yield of all Acacia species were enhanced by 10% with fly ash amendments. However, mycorrhiza inoculation alone improved the survival of A. albida and A. luederitzii but reduced that of the A. tortilis in mine tailings. Fly ash amendments increased the pH of the mine tailings, reduced the availability of Cu, Ni, Pb, Mn and Zn and consequently reduced the concentration of these metals in shoots. On the other hand, it increased the availability of As in the mine tailings. In addition, mycorrhizal inoculation reduced the concentration of these metals in shoots regardless of fly ash amendments. Overall, combined mycorrhizal inoculation and fly ash amendment enhanced the establishment of A. luederitzii in heavy metal-contaminated soils by reducing the heavy metal availability and metal uptake, thus increasing the survival and dry matter yield of plants.

Growth and yield of lemongrass (Cymbopogon citratus) in fly ash with nutrient amendments and Mycorrhiza for three-ratoon period.

Environmental and health concerns due to fly ash dumpsite could be prevented by phytostabilization using non-food crops that will prevent pollutants' migration and provide additional economic returns. The growth and yield of Cymbopogon citratus in the fly ash dumpsite were evaluated in a pot experiment for a three-ratoon period. Application of compost, mycorrhiza, and NPK fertilizer, singly or the combination compost + mycorrhiza, compost + NPK fertilizer, mycorrhiza + NPK fertilizer, and compost + mycorrhiza + NPK fertilizer had increased the dry matter yield and the total essential oil content compared to the control. NPK fertilization regardless of compost and mycorrhiza resulted in more than 5-fold yield over the control. Compost lowered the available heavy metals from fly ash and supplied some essential nutrients while mycorrhiza could have improved water and nutrients acquisition and uptake. However, the nutrients supplied by the compost cannot sustain the requirements for the three-ratoon period. NPK fertilization, compost, and mycorrhiza reduced the concentrations of Cr, Cu, Ni, and Pb in shoots and in essential oil. Overall, the combined application of compost, mycorrhiza, and NPK fertilization at the rate of 120-90-90 kg NPK/ha could enhance the phytostabilization potential of C. citratus in fly ash and produce a high amount of essential oil with a low concentration of heavy metals that could be safe for human use. Novelty Statement Phytostabilization using aromatic plants is a potential alternative for the on-site pollution mitigation strategy of fly ash dumpsite. In this report, the appropriateness of lemongrass as a phytostabilization agent for fly ash dumpsite of the Morupule Power Plant in Botswana was evaluated for a three-ratoon period. This is the first report from Botswana that considered the effect of soil amendments, mycorrhiza inoculation, and NPK fertilization on the growth and yield of lemongrass in fly ash as well as the heavy metal availability and uptake. The results from this study are very useful for identifying site-specific cultural management strategy of using lemongrass in the phytostabilization of fly ash dumpsite in Botswana and elsewhere.

Health risk assessment of volatile organic compounds exposure near Daegu dyeing industrial complex in South Korea.

BACKGROUND: Studying human health in areas with industrial contamination is a serious and complex issue. In recent years, attention has increasingly focused on the health implications of large industrial complexes. A variety of potential toxic chemicals have been produced during manufacturing processes and activities in industrial complexes in South Korea. A large number of dyeing industries gathered together in Daegu dyeing industrial complex. The residents near the industrial complex could be often exposed to volatile organic compounds. This study aimed to evaluate VOCs levels in the ambient air of DDIC, to assess the impact on human health risks, and to find more convincing evidences to prove these VOCs emitted from DDIC. METHODS: According to deterministic risk assessment, inhalation was the most important route. Residential indoor, outdoor and personal exposure air VOCs were measured by passive samplers in exposed area and controlled area in different seasons. Satisfaction with ambient environments and self-reported diseases were also obtained by questionnaire survey. The VOCs concentrations in exposed area and controlled area was compared by t-test. The relationships among every VOC were tested by correlation. The values of hazard quotient (HQ) and life cancer risk were estimated. RESULTS: The concentrations of measured VOCs were presented, moreover, the variety of concentrations according the distances from the residential settings to the industrial complex site in exposed area. The residential indoor, outdoor, and personal exposure concentrations of toluene, DMF and chloroform in exposed area were significantly higher than the corresponding concentrations in controlled area both in summer and autumn. Toluene, DMF, chloroform and MEK had significantly positive correlations with each other in indoor and outdoor, and even in personal exposure. The HQ for DMF exceeded 1, and the life cancer risk of chloroform was greater than 10- 4 in exposed area. The prevalence of respiratory diseases, anaphylactic diseases and cardiovascular diseases in exposed area were significantly higher than in controlled area. CONCLUSIONS: This study showed that adverse cancer and non-cancer health effects may occur by VOCs emitted from DDIC, and some risk managements are needed. Moreover, this study provides a convenient preliminarily method for pollutants source characteristics.