Effect of soil amendments on phytoextraction potential of Brassica juncea growing on sewage sludge

A pot experiment was conducted to investigate the influence of elemental sulfur, gypsum and chelating agent (Ethylenediaminetetraacetic acid) on copper, zinc, nickel, cadmium, chromium and lead uptake by Brassica juncea from sewage sludge. Addition of sulphur acidified the sludge, which caused the pH decrease to 5.4 with an initial pH 6.7. The shoot and root biomass were increased with sulfur addition, while decreased with Ethylenediaminetetraacetic acid addition. Applications of Ethylenediaminetetraacetic acid and sulfur resulted in a considerable increase in copper and lead concentrations in the plant. The highest root concentration of copper obtained to be 110?mg/kg?dw at Ethylenediaminetetraacetic acid treatment. For sulfur treatment, lead concentrations in shoots indicated almost high concentrations 77?mg/kg, about twofold increases relative to roots (34?mg/kg). The Transportation Index of all studied metals were quite low (TI?<?0.5), whereas the Bioaccumulation Factor values were much higher, varied from 0.01 to 9.67. Furthermore, the plant showed better Bioaccumulation Factor for copper and lead metals in both shoot and root. The efficiency to remove copper and lead from sludge is high in this plant. As a result, elemental sulfur will be effective amendment for phytoextraction of heavy metals from sewage sludge.     

Heavy metal pollution in the soil surrounding a thermal power plant in Playas de Rosarito,Mexico

The generation of electricity has been identified as one of the main pollutant activities, and some studies have established an increment of heavy metals in soil in the areas surrounding these plants. The aim of this study was to evaluate the soil concentrations of heavy metals in the zone surrounding a thermoelectric power in Mexico. Thirty-two top soil samples (0–5 cm) were collected; additionally, four depth profiles (1 m) were investigated. Median concentrations for chromium, vanadium, nickel, mercury, and cadmium were 47, 47, 73, 0.02, and 0.01 mg/kg, respectively. Higher Cr, Ni, and V concentrations were observed in the soil depth profiles located closer to the plant in comparison with the concentrations found in the soil depth profile located further away from the plant; these results may indicate a possible accumulation of these metals. The geoaccumulation index results indicated that most of the sites were in the classifications of unpolluted and unpolluted to moderately polluted (classes 1 and 2). The statistical results showed that downwind of the plant in relation to the prevailing winds, there was a strong correlation between soil concentrations of chromium, copper, nickel, and vanadium. Based on the results of this study, it can be concluded that the use of fuel oil at the thermoelectric plant contributed to the accumulation of vanadium and nickel in the soil of the surrounding areas, as well as chromium and copper.     

Assessing cadmium risk in wheat grain using soil threshold values

At present, the prior-established threshold values are widely used to classify contaminated agricultural soils with heavy metals under the cultivation of a variety of crops, without considering the different sensitivity of plants to heavy metals. Evaluation of the characteristics of cadmium transfer from a polluted calcareous soil to cultivated wheat crop and assessment of the efficiency of using the threshold values to reflect the soil pollution risk by cadmium in Zanjan Zinc Town area at the northwest of Iran were the goals of this study. Totally, 65 topsoil (0–20 cm) and corresponding wheat samples of an agricultural region in the proximity of a metallurgical factory were collected and analyzed for cadmium concentration. The results revealed that industrial activities strongly control cadmium distribution in the studied soils. Relatively high bioavailable cadmium contents (mean 0.77 mg kg^?1) were found in the soils, notwithstanding their alkalinity. It was observed that just 22.5% of the studied area around the Zinc Town is covered by polluted soils with the cadmium concentration exceeding the maximum permissible concentration of 5 mg kg^?1, whereas cadmium concentration in wheat grains of 19 sampled plants is higher than the threshold value of 0.2 mg kg^?1. Among these polluted plants, a total of eight samples were grown in areas classified as unpolluted soils with cadmium, based on the soil threshold value. It seems that this misclassification of polluted soils is mainly related to the crop sensitivity to heavy metals uptake from the soil which should be considered.     

Isolation and characterization of metal-resistant bacterial strain from wastewater and evaluation of its capacity in metal-ions removal using living and dry bacterial cells

A novel strain of the genus Micrococcus isolated from wastewater was studied for resistance to seven heavy metals and forty antibiotics. Its capacity to accumulate metal ions was also realized at different pH. The strain exhibited high minimal inhibitory concentration values for metal ions tested and resist to 15 antibiotics. The living cells of the bacterial strain show a largest uptake capacity at pH 6–8.5 for copper, nickel, and zinc with values ranging from 51.45 to 83.90 %, 52.59 to 78.81 %, and 59.55 to 78.90 %, respectively. It was also able to absorbed 59.81–80.08 % of chromium and 58.09–79.41 % of cobalt at pH 7.3–8.5. The maximum lead uptake was obtained at pH 5.5–8.5 with an amount of 55.28–91.06 %. The significant absorption of cadmium was shown at pH 6.5 with 38 %. In 25 µg mL-1 zinc, chromium, and nickel solutions, dead cells of the isolate were able to biosorbed 20.46, 22.5, and 23.98 µg mL^?1, respectively, after 30 min of contact. In other solutions with higher concentrations 50 and 100 µg mL^?1, the amount of each metal immobilized was, respectively, as follows: 38.02 and 90.21 µg mL^?1 for zinc, 39.78 and 89.23 µg mL^?1 for chromium, and 47.19 and 86.83 µg mL^?1 for nickel. Due to its high-metal accumulation capacity in aerobic conditions, these Gram-positive bacteria may be potentially applicable in situ bioremediation of heavy metals contaminating aqueous systems.     

Heavy metal distribution in soil and plant in municipal solid waste compost amended plots

A field study was carried out to evaluate long-term heavy metal accumulation in the top 20 cm of a Tunisian clayey loam soil amended for four consecutive years with municipal solid waste compost at three levels (0, 40 and 80 t/ha/y). Heavy metals uptake and translocation within wheat plants grown on these soils were also investigated. Compared to untreated soils, compost-amended soils showed significant increases in the content of all measured metals: cadmium, chromium, copper, nickel, lead and zinc in the last three years, especially for plots amended with municipal solid waste compost at 80 t/ha/y. Wheat plants grown on compost-amended soils showed a general increase in metal uptake and translocation, especially for chromium and nickel. This heavy metal uptake was about three folds greater in plots amended at 80 t/ha/y as compared to plots amended at 40 t/ha/y. At the end of the experimental period, the diluting effect resulting from enhanced growth rates of wheat plants due to successive compost applications resulted in lower concentrations in the plants (grain part) grown on treated plots. On the other hand, chromium and nickel were less mobile in the aerial part of wheat plants and were accumulated essentially in root tissues. Plant/soil transfer coefficients for compost-amended treatments were higher than threshold range reported in the literature, indicating that there was an important load/transfer of metal ions from soils to wheat plants.     

Biotransformation potential of hexavalent chromium by Bacillus pumilus-S4, Pseudomonas doudoroffii-S5 and Exiguobacterium-S8 in association with hydrophytes

Three chromium-resistant bacteria Bacillus pumilus-S4, Pseudomonas doudoroffii-S5 and Exiguobacterium-S8 were isolated from chromium-contaminated wastewater/soil and could resist very high concentrations of potassium chromate in Luria agar (up to 25 mg ml^?1) and acetate minimal medium (2 mg ml^?1). The strains showed growth at diverse pH and temperatures and could resist multiple heavy metals. Pseudomonas doudoroffii-S5 reduced (8.27 mg hexavalent chromium 24 h^?1) at a lower initial potassium chromate concentration (100 μg ml^?1), but overall more chromate (28.4 mg hexavalent chromium 24 h^?1) was reduced at a higher initial concentration (1,000 μg ml^?1). The addition of various heavy metals (zinc sulphate, copper sulphate, and manganese sulphate at 50 μg ml^?1) in the chromium reduction media did not significantly affect the hexavalent chromium reduction potential of these isolates. The chromium removal/detoxification potential of these strains increased when used in conjunction with hydrophytes Eichornia crassipes and Pistia stratiotes. Interestingly, the whole process runs automatically with less energy input, that is, the bacterial strains support the growth of plant while in turn the plant releases exudates that help bacterial growth.     

Integrated physicochemical and hydrogeochemical assessment to groundwater quality in Obosi and Onitsha provinces,South-eastern Nigeria

An integrated physicochemical and hydrogeochemical assessment was carried out at an automobile junk market in Obosi and in residential areas in Anambra State, south-eastern Nigeria to examine the concentration of heavy metals in the groundwater and determine the quality of the water for drinking and other domestic purposes. Forty groundwater samples were collected from boreholes and hand-dug wells (three samples from Obosi and the rest from Onitsha). They were subjected to atomic absorption spectrometry using standard field and laboratory techniques and analysed for physicochemical and hydrogeochemical parameters. Results show that the groundwater in the study area is slightly acidic to neutral, soft to moderately hard when compared with the World Health Organization maximum allowable concentration values and the Nigerian Standards for Drinking Water Quality. The electrical conductivity, dissolved oxygen and biochemical oxygen demand ranged from 58 to 1796 μS/cm, 6.78 to 8.76 and 0.17 to 1.50 mg/L, respectively. Heavy metal concentrations measured (in ppm) in the water included nickel, manganese, copper and zinc and varied from 0 to 1.82, 0 to 0.195, 0 to 0.325 and 0 to 0.09, respectively, while heavy metal concentrations in the soil measured (in ppm) included iron, lead and cadmium and varied from 0 to 3.87, 0 to 1.80 and 0 to 7.38 mg/kg, respectively. Statistical results gave significant correlation (at 0.05) between electrical conductivity and total hardness, biochemical oxygen demand and dissolved oxygen, and several others elements. The study helps in the understanding of the chemistry of groundwater for long-term monitoring and management for the local community.     

草本植物间作对空心菜Pb吸收、转运的影响

为了研究不同草本植物间作对空心菜生长状况及对Pb的吸收、转运效果,采用盆栽试验,研究了空心菜在Pb污染土壤中单作及与10种草本植物(高丹草、苏丹草、狼尾草、黑麦草、苦荬菜、菊苣、籽粒苋、三叶草、紫花苜蓿、紫云英)间作对Pb吸收、积累的影响。结果表明：空心菜与黑麦草、苦荬菜、菊苣、籽粒苋、三叶草、紫花苜蓿以及紫云英间作后的茎叶生物量较空心菜单作增加显著(P<0.05),增加了15.79%~84.75%。不同间作方式下的空心菜茎叶Pb含量为7.11~15.36 mg/kg,茎叶Pb富集系数(BCF)为0.024~0.051,根茎叶Pb转运系数(TF)为0.240~0.470。与高丹草、苏丹草、苦荬菜、菊苣以及籽粒苋间作后,空心菜茎叶Pb含量较单作(对照)降低了24.39%~41.46%,茎叶Pb积累量较单作降低了65.36%~75.06%;此外,与上述5种植物间作后空心菜的根际土壤有效态Pb含量降低了4.47%~9.09%,根际土壤pH值则增加了0.32%~2.74%。10种间作植物茎叶Pb含量大小为菊苣>黑麦草>苦荬菜>高丹草>苏丹草>紫云英>紫花苜蓿>狼尾草>三叶草>籽粒苋。不同间作方式下每盆植株Pb总积累量为0.560~2.108 mg/盆,10种间作处理是空心菜单作处理的1.73~3.76倍。研究结果表明,高丹草、苏丹草、苦荬菜、菊苣和籽粒苋与空心菜间作有效降低了空心菜对Pb的吸收积累,同时提高了整个体系对土壤中Pb的总积累量,在间作修复中是较为理想的组合模式。     

Mathematical models to predict soil heavy metal toxicity in the 2012 Olympic site

Heavy metal concentrations in samples collected from the London 2012 Olympic Village were determined using a three-step sequential extraction and a rapid extraction method. Metal toxicity was measured by employing the Microtox^? solid phase analysis. Both extraction methods produced comparable results (p?=?0.996), but the rapid method produced higher readings. A number of heavy metals were detected using the two extraction methods, including aluminum, arsenic, cadmium, chromium, copper, iron, nickel, lead and zinc; beryllium, molybdenum, niobium and titanium were also found in low concentration ranging between 0.16 and 27.10?mg/kg in the total acid digestion. The total metal levels in all the soil samples were within the UK Soil Guideline Value (SGV) except for lead which ranged between 62.9 and 776.2?mg/kg. The 30?min EC₅₀ of different soil fractions was 2?C5.8?g/L. In the absence of any of heavy metals in the SGV, the Dutch Guideline values were referred. Mathematical models for a number of metals were generated based on the changes in EC₅₀ values between each (F1, F2 and F3) soil fractions and the initial toxicity in the non-fractionated samples. The resulting models produced good R² values (>96%) for predicting the change in toxicity of lead, cadmium, zinc and copper by measuring their changes in concentrations. These models could substantially reduce the time requires to determine the toxicity in the samples; they would be a useful tool in the clean up process where monitoring of metal toxicity is required.     

Trace metal levels in edible wild fungi

Metal levels (cadmium, cobalt, chromium, copper, iron, nickel, lead and zinc) of seventeen different edible wild fungi species (Agaricus campestris, Calocybe gambosa, Coprinus comatus, Hericium coralloides, Hydnum repandum, H. repandum var. rufescens, Lactarius deliciosus, L. salminocolor, Macrolepiota procera, Pleurotus ostreatus, P. ostreatus var. columbinus, Ramaria aurea, R. stricta, Rhizopogon luteolus, Sparassis crispa, Suillus bovinus, Tricholoma terreum) growing in Bolu-Turkey were measured by inductively coupled plasma optical emission spectrocopy. The obtained data were analyzed with “statistical package for the social sciences” statistics program. In addition, relation between metal concentrations in both soil and fungi samples were investigated. The highest metal concentrations in Bolu District, Turkey were measured in A. campestris (cadmium 0.270, chromium 2.735 and zinc 7.683), C. comatus (iron 160.12), M. procera (copper 15.990, cobalt 0.352 and nickel 3.645), R. luteolus (Pb 4.756) mg/kg dw (dry weight). As a result of the measurements, it was observed that metal uptake is related with the species of fungi and is also affected by pH and organic contents of the soil.     

Chelate-assisted phytoextraction of cadmium from a mine soil by negatively charged sunflower

The effects of some chelating agents and electricity on cadmium phytoextraction from a mine soil were examined in pot culture of sunflower to achieve more remediation efficiency. At the beginning of the flowering stage, ethylene-diamine-tetra-acetic acid (EDTA) as a chemical chelator, cow manure extract (CME) and poultry manure extract (PME) as organic chelators were applied (2 g kg^?1 soil) during irrigation. Seven days later, Helianthus annuus was negatively charged by inserting a stainless steel needle in the lowest part of the stem with 10 and 30 V direct current electricity for 1 h each day for 14 days. Afterward, concentration of cadmium in roots and shoots, cadmium translocation factor (TF), cadmium uptake index (UI) and soil available (diethylene-triamine-penta-acetic acid extractable) cadmium were measured. Results indicated that EDTA reduced roots dry weight while none of the roots and shoots was affected by other chelating agents and by electrical treatment as well. Highest concentration of cadmium in shoots was measured in 10 V-control with no significant differences with 30 V-PME and 30 V-EDTA. Utilization of chelating agents did not increase the cadmium TF and cadmium UI while highest values for cadmium TF and cadmium UI were observed in 10 and 30 V treatments, respectively. Available cadmium in the soil near root system treated with 10 and 30 V was relatively lower compared with the soil far from root system. Results of this experiment indicated that charging the plant with direct current electricity ameliorated the efficiency of cadmium phytoremediation.     

Carcinogenic risk evaluation for human health risk assessment from soils contaminated with heavy metals

Human activities have progressively increased in recent years. Consequently, significant environment deterioration resulted. Soils have a particularly varied vulnerability to heavy metal pollution, especially in the vicinity of industrial areas. Heavy metal contamination of soil may induce risks and hazards to humans and the ecosystem, while toxic metals in soil can severely inhibit the biodegradation of organic contaminants. This paper is focused on human health risk assessment from extremely contaminated soil with heavy metals, mainly with carcinogenic elements. The study refers to an agricultural area in the vicinity of an old metallurgical processing industrial facility. The contaminants evaluated in the present paper are beryllium (Be), cadmium (Cd), chromium (Cr), nickel (Ni) and lead (Pb). Contamination level is pointed out through laboratory analysis results of soil samples taken from 0–0.2 m, 0.2–0.4 m soil layers and up to 2.1 m soil depth. Some heavy metal concentrations (Cd, Cr and Pb) exceed the intervention thresholds for sensitive areas, as they are stipulated in the national regulation in Romania. The identified average concentration levels of Cd, Cr^VI and Pb in the first layer of the investigated land are 23.83, 7.71 and 704.22 mg/kg_d.w, respectively. The results show that the potential risk of human health is relevant (higher than the acceptable one after World Health Organization) and a possible solution for the remediation should become a major concern for the investigated area.     

Uptake and fixation of Zn, Pb, and Cd by Thlaspi caerulescens: application in the cases of old mines of Mibladen and Zaida (West of Morocco)

Contaminated soils and mine tailings pose major environmental and agricultural problems worldwide. These problems may be partially solved by an emerging new technology: phytoremediation. This technique uses plants to extract soil contaminants from the ground. Thlaspi caerulescens is known to accumulate in their tissues several heavy metals from soil and aerial deposition. This study was conducted to screen plants growing on a contaminated site to determine their potential for metal accumulation. Seeds of T. caerulescens metallicolous have been collected in the vicinity of F.T. Laurent le Minier in the Pb–Zn mining district of les Malines (North of Montpellier, Southern France), and seeds of T. caerulescens non-metallicolous were sampled on Larzac Plateau (North of Montpellier, Southern France). Soil substrates were collected from a mine site of Mibladen and Zaida (West, Morroco). Cultivated plant and surface soil samples were analyzed for zinc, lead, and cadmium concentrations by inductively coupled plasma mass spectrometry. A non-metallicolous (NM) ecotype of T. caerulescens and a metallicolous (M) ecotype are compared for Pb, Cd, and Zn accumulation in shoot and root in five metal-contaminated soils and one uncontaminated soil. The growth of individuals from uncontaminated soil was greater than that of individuals from metal-contaminated soils. The NM populations had markedly higher root/shoot ratio compared to M populations. The results indicate that both ecotypes of T. caerulescens are highly tolerant of zinc and Cd. Ecotype NM had constitutively higher Zn uptake capacity than the M ecotype. T. caerulescens species accumulate higher amount of Zn and Cd in their tissues in polluted soil and, in both of the two ecotypes, the root Pb concentrations were much greater than those of the shoot Pb contents. From both uncontaminated and metal-contaminated soils, we conclude that T. caerulescens are interesting material for phytoremediation of zinc and cadmium.     

Accumulation of lead, cadmium, manganese, copper and zinc by sludge worms; Tubifex tubifex in sewage sludge

Tubifex tubifex has been shown to survive in organic polluted environments, however, not much has been done on its inorganic pollution tolerance. Samples of T. tubifex and their respective sewage sludge were taken from Soche wastewater treatment plant in Blantyre City, Malawi during July 2007 to November 2008. The total number of sludge samples taken was fifty one which was made into seventeen composite samples. A total of seventeen T. Tubifex samples were also collected. The samples were analyzed for copper, lead, manganese, zinc and cadmium using standard methods from American Public Health Association and Association of Official Analytical Chemists. The concentrations of metals in sewage sludge and T. tubifex were on dry weight basis and the metals determined were acid extractable. In general, heavy metals concentration was lower in T. tubifex than in sewage sludge. The range of heavy metals concentrations were (in sludge and (T. tubifex)): zinc 275.3–361.5 mg/kg (45.0–82.2 mg/kg), manganese 293.7–230.1 mg/kg (1.21–3.69 mg/kg), copper 86.5–120.1 mg/kg (1.6–4.7 mg/kg), lead 11.2–22.4 mg/kg (Below detection limit–0.95 ) and cadmium 1.12–2.31 mg/kg (1.08–2.18 mg/kg). The results showed significant differences between the concentrations of manganese, copper, lead and zinc in sewage sludge and T. tubifex (p < 0.05). However there was no significant difference between the concentrations of cadmium in sewage sludge and T. tubifex (p > 0.05). T. tubifex did not show the ability to accumulate heavy metals (attributed to its high defecation and metabolic rate) except for cadmium hence cannot be used as a bioindicator for heavy metal pollution in sludge.     

Mobility of cadmium,chromium, and nickel through the profile of a calcisol treated with sewage sludge in the southeast of Spain

To study the mobility of polluting agents through the soil, the authors have designed an experiment that attempts to reproduce the behavior of heavy metals in the soil as a part of the non-saturated zone. This work was based on a controlled experiment using soil columns. A calcareous soil was amended with 30,000, 90,000 and 180,000 kg sludge/ha. Chromium, cadmium, and nickel were analyzed in soil samples at intervals of 15 cm depth. Leachates were collected at the bottom of the columns and the metals were analyzed. No important displacements of polluting metals were found in this soil.     

Spatial and seasonal distributions of soil phosphorus in a typical seasonal flooding wetland of the Yellow River Delta,China

Soil samples from 0 to 100 cm depth were collected in four sampling sites (Sites A, B, C and D) along a 250-m length of sampling zone from the Yellow River channel to a tidal creek in a seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total phosphorous (TP) and available phosphorus (AP) and their influencing factors. Our results showed that TP contents in spring and AP contents in both seasons in surface soils increased with increasing distances away from the Yellow River channel. TP contents in surface soils (0–10 cm) followed the order Site A (698.6 mg/kg) > Site B (688.0 mg/kg) > Site C (638.8 mg/kg) > Site D (599.2 mg/kg) in fall, while Site C (699.6 mg/kg) > Site D (651.7 mg/kg) > Site B (593.6 mg/kg) > Site A (577.5 mg/kg) in spring. Generally, lower TP content (630.6 mg/kg) and higher AP level (6.2 mg/kg) in surface soils were observed in spring compared to fall (656.2 mg/kg for TP and 5.2 mg/kg for AP). Both TP and AP exhibited similar profile distribution patterns and decreased with depth along soil profiles with one or two accumulation peaks at the depth of 40–80 cm. Although the mean TP content in soil profiles was slightly higher in spring (635.7 mg/kg) than that in fall (628.0 mg/kg), the mean TP stock was obviously lower in spring (959.9 g/m²) with an obvious accumulation at the 60–80 cm soil depth compared to fall (1124.6 g/m²). Topsoil concentration factors also indicated that TP and AP had shallower distribution in soil profiles. Correlation analysis showed that AP had significant and positive correlation with these soil properties such as soil organic matter, salinity, total nitrogen and Al (p < 0.01), but TP was just significantly correlated with TN and Al (p < 0.05).     

A study on soil physico-chemical, microbial and metal content in Sukinda chromite mine of Odisha, India

Soil samples from chromite mining site and its adjacent overburden dumps and fallow land of Sukinda, Odisha, were analysed for their physico-chemical, microbial and metal contents. Chromite mine soils were heterogenous mixture of clay, mud, minerals and rocks. The pH of the soils ranges between 5.87 and 7.36. The nutrient contents of the mine soils (N, P, K and organic C) were found to be extremely low. Analysis of chromite mine soils revealed accumulation of a number of metals in high concentrations (Fe > Cr > Mn > Ni > Zn > Pb > Sr) which exceeded ecotoxicological limits in soil. Correlation and cluster analysis of metals revealed a strong relation between Cr, Ni, Fe, Mn among the different attributes studied. Assessment of different microbial groups such as fungi, actinomycetes and bacteria (heterotrophic, spore forming, free-living nitrogen fixing, phosphate solubilising and cellulose degrading) from mine soils were found to be either extremely low or absent in some soil samples. Further chromium tolerant bacteria (CTB) were isolated using 100 mg/L Cr(VI) enriched nutrient agar medium and were screened for their tolerance towards increasing concentrations of hexavalent chromium and other toxic metals. Out of 23 CTB isolates, three bacteria tolerated up to 900 mg/L, 6 up to 500 mg/L, 20 up to 200 mg/L of Cr(VI). These bacteria were also found to be sensitive towards Cu > Co > Cd and very few CTB strains could show multiple metal tolerance. These strains have great scope for their application in bioremediation of toxic chromium ions in presence of other metals ions, which needs to be explored for their biotechnological applications.     

Assessment of Zn, Cu, Pb and Ni contamination in wetland soils and plants in the Lake Victoria basin

The impact of waste disposal on trace metal contamination was investigated in eleven wetlands in the Lake Victoria Basin. Samples of soil, water and plants were analysed for total Zn, Cu, Pb and Ni concentrations using flame atomic absorption spectrophotometry. The trace metal concentrations in soil were the highest in Katanga wetland with the highest mean concentrations of 387.5±86.5 mg/kg Zn, 171.5±36.2 mg/kg Pb, 51.20±6.69 mg/kg Cu and 21.33±2.23 mg/kg Ni compared to the lowest levels observed at Butabika (30.7±3.2 mg/kg Zn, 15.3±1.7 mg/kg Pb, 12.77±1.35 mg/kg Cu and 6.97±1.49 mg/kg Ni). Katanga receives waste from multiple industrial sources including a major referral city hospital while Butabika is a former solid waste dumpsite. Wetland soil near a copper smelter had a Cu concentration of 5936.3±56.2 mg/kg. Trace metal concentrations in industrial effluents were above international limits for irrigation water with the highest concentrations of 357,000 μg/L Cu and 1480 μg/L Zn at a Cu smelter and 5600 μg/L Pb at a battery assembling facility compared to the lowest of 50 μg/L Cu and 50 μg/L Zn in water discharged from Wakaliga dumpsite. Uptake of trace metals from soil differed from plant to plant and site to site. Higher levels of trace metals accumulated in the root rather than in the rhizome and the least amount was in the leaf. The study identifies industry as a potential source of trace metal contamination of water and the environment pent-up need for policy intervention in industrial waste management.     

The retention of heavy metals in sewage sludge applied to a freshwater tidal wetland

The hypothesis that freshwater tidal wetlands act as sinks for heavy metals was tested using sewage sludge applied biweekly from March to October 1981 at low treatment (25 g m^?2 wk^?1) and high treatment (100 g m^?1) levels. No differences in aboveground macrophyte standing crop were found except in June when high and low treatment sites had significantly higher (p=0.05) standing crops than control sites. Except for chromium, metal standing stocks in the vegetation on treatment sites did not increase as a result of sludge application. The March litter had significantly higher (p=0.05) concentrations of chromium, copper, lead, and nickel at all sites than the October vegetation, but only high and low treatment litter chromium levels were significantly higher (p=0.05) than control litter. When sludge application terminated in October, the top 5 cm of soil at the high and low treatment sites had retained, respectively, 47 and 43% of the cadmium, 53 and 28% of the chromium, 52 and 0% of the copper, 51 and 0% of the zinc, 31 and 0% of the lead, and 0 and 0% of the nickel applied; only cadmium (15 and 46%, respectively) and chromium (12 and 28%, respectively) were still retained the following March. Thus, freshwater tidal wetlands can retain significant quantities of heavy metals associated with sewage sludge. The vegetation and litter play minor roles while the soil plays a major role in heavy metal retention.     

The “Sea Diamond” shipwreck: environmental impact assessment in the water column and sediments of the wreck area

In the “Sea Diamond” shipwreck, it is estimated that almost 1.7 tons of batteries/accumulators and approximately 150 cathode ray tube technology televisions have gone to the bottom of the sea. Under these circumstances, all the aforementioned materials will eventually undergo severe accelerated corrosion. Consequently, a variety of heavy metals will either be released in seawater or precipitate in the form of salts resulting in contamination of the sea sediments. According to the ship data, and the aforementioned quantities of batteries and televisions, it is estimated that approximately 75–80 g of mercury, 630–1,050 g of cadmium and 1.14–1.26 tons of lead exist in the wreck only due to the electrical and electronic equipment present in the ship, not to mention the significant amount of heavy metals such as copper, nickel, ferrous and chromium that exist in the hulk. Four series of seawater sampling (n = 85) were conducted in different stations surrounding the wreck area in order to assess the overall impact from the release of heavy metals in the surrounding aquatic environment. The analysis indicated that there were stations where lead, zinc and cadmium were present in concentrations higher than the permissible limits set by the Unites States Environmental Protection Agency for seawater. Furthermore, the analysis of three series of sediment sampling (n = 31) from the wreck area showed elevated but expected concentration values for ferrous and manganese, considering the geological background of the area and contamination with lead, copper and cadmium.