The current study was designed for the assessment of lead, cadmium and chromium and some physicochemical properties of soils collected from an open dumpsite in Yenagoa, Nigeria. Surface soil samples at two depths (0-10 and 10-20 cm) were randomly collected at the dump field and control site, and were analyzed for physicochemical parameters and contamination by lead, chromium and cadmium using standard analytical methods. The results show that the main dumpsite had higher sand (>80.0%) and lower clay and silt contents than the control site. Soil mean pH varied between 4.89±0.05 in the control and 7.60±0.02 in the dump. Total nitrogen (N) content of the dump soils ranged from 0.06±0.07 to 0.24±0.09% and is slightly higher than that of the control soil. This is reflected in the high value of organic matter (4.71±0.85%) in dump soils. Available P was quite high ranging from 35.00±1.01 to 84.20±1.02 mg/kg. Cation exchange capacity (CEC) varied between 12.98±0.31 and 91.07±0.11 cmol kg −1 . ECEC levels were moderate to high ranging from 14.10±0.10 to 91.47±0.11 cmol/kg. All the soil samples had very high base saturation (>90.0%) and exchangeable Ca, Mg, K and Na, far above the critical levels set by FAO for agricultural soil. Average levels of Pb ranged from 14.75±0.05 to 16.14±0.04 mg/kg in the dump and 8.35±0.05 to 8.78±0.07 mg/kg in the control. Mean concentration of Cr in the dump soil varied between 0.05±0.01 and 0.06±0.01 mg/kg, and is slightly higher than the control (0.005±0.01 mg/kg), while Cd was found in trace amounts (<0.0001±0.01 mg/kg). These values are all far below the maximum tolerable levels set by FAO and WHO for agricultural soil. It is suggested that the dumpsite and the control area with their adequate soil nutrients and low levels of metals should eventually be converted to agricultural farmland. No remediation is needed at this time. Keywords : Dump waste soil, heavy metal, soil fertility.

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Assessment of some heavy metals and physicochemical properties in surface soils of municipal open waste dumpsite in Yenagoa, Nigeria

Assessment of heavy metal contamination in soils at the Kpone landfill site, Ghana: Implication for ecological and health risk assessment.

Limited farmland in urban and semi-urban areas in Nigeria is compelling city dwellers to cultivate crops in poorly reclaimed lands, including refuse filled borrow pits. This research assessed the heavy metal concentration in soil and maize harvested from a partially reclaimed refuse dumpsite ‘borrow-pit’, located at Egbelu-Minita community, East-West Road of Port Harcourt, one of Nigeria’s seven metropolitan cities. Spatial and temporal samples of three media (surface water, soil and maize) from the partially reclaimed section of the borrow pit were analyzed for copper (Cu), zinc (Zn) and lead (Pb). The resulting datasets were analyzed statistically and the means compared. The order of concentration of the metals in soil was Zn>Cu>Pb; 9.8±1.25, 0.23±0.50, 0.04±0.07 mg/kg, respectively. In maize, the highest concentrations of Zn, Cu and Pb were recorded in the root and stalk. The concentrations of Zn, Cu and Pb in the maize grains were within safe limit set by FAO/WHO, but potential human health implications subsist from continuous consumption of crops harvested from the borrow-pit. Innovative and cost-effective waste management practices integrated into the residential waste disposal system are imperative to minimize heavy metals contamination of soil, surface and groundwater and food resources.

Heavy metal concentration in soil and maize (Zea mays L.) in partially reclaimed refuse dumpsite ‘borrow-pit’ in Port Harcourt, Nigeria

This study examined the nutrient status and textural characteristics of soil from solid waste dumpsites in the city of Port Harcourt. The study was carried out in five solid waste dump sites alongside their respective controls located at Iwofe, Eliozu, Choba, Rumuokwuta and Ozuoba within the city of Port Harcourt for two seasons (wet and dry). A systematic sampling technique was employed for field sampling. Soil sample was collected with soil auger and analysis was done using standard methods. Results showed mean pH value (4.86±0.18 – 7.66±0.44) and; cation exchange capacity (2.2±0.3 -18.11±0.8 meq/100g). The mean electrical conductivity indicated higher conductivity in the control sites (125±5.5 - 492±16 μs/cm) than the dump sites (32.06±2.5 – 299.5±1.5μs/cm).There was high nutrient concentrations in the dump site soils of total nitrogen (0.04±0.01 – 0.62±0.13%); phosphorus (0.041±0.01 – 4.07±0.02mg/kg); potassium (9.19±2.5 – 326±51.91mg/kg) than the controls. On the contrary, there was no significant difference between the soil particle size distribution of the dump site soil and their respective controls. The soil particle size distribution indicated an average of 83% sand, 11% clay and 5% silt, while the soil texture was loamy sandy for all the dump sites except the dump site located at Iwofe. Therefore, solid dumps alter the soil nutrient contents with no significant change in the textural nature of soil.  Key words: Solid wastes, Soil, Particle size, Nitrogen, Nutrient, Dump sites

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Physicochemical Characteristics of Soil from Selected Solid Waste Dump Sites in Port Harcourt, Rivers State, Nigeria

The physicochemical properties and distribution of Pb, Cd, Cr and Ni in soils and growing plants around refuse dumpsites in Akure, Southwestern Nigeria were evaluated to ascertain the impact of the wastes on these soil quality indices and edible plants. The soils close to the dumpsites were more acidic (pH, 5.50) compared with the soils away (25.0 m) from the sites. Also there were corresponding increases in the organic carbon and cation exchange capacities of the soil indicating measurable levels of biodegradability of the wastes. Pb, Cd, Cr and Ni have maximum concentrations of 23.00, 2.91, 9.00 and 24.00 mg/kg respectively in the soils. The amount of Cd determined in the soils was consistent with the critical level obtained for agricultural soils. Results obtained from the plant tissues analysed showed that 0.84 mg/kg Pb was detected in the root of Zea mays, while 0.25 mg/kg Ni was obtained in the root of Sorghum vulgare. Talinum triangulare and Amaranthus crucantus did not possess detectable levels of these metals. The present study has justified the need to continually assess the quality of soils, and the concentration of certain heavy/toxic metals in growing plants around refuse dumpsites.

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Evaluation of physicochemical properties and distribution of Pb, Cd, Cr and Ni in soils and growing plants around refuse dumpsites in Akure, Nigeria.

The levels of soil parameters and selected heavy metals around a solid waste dumpsite receiving untreated wastes from all sources and a control site within Port Harcourt, Nigeria have been examined. Top soil (0–15 cm) and sediment samples were collected and analysed for pH value, particle size, total nitrogen, potassium, available phosphorus, organic matter, effective cation exchange capacity, cadmium, nickel and lead using standard methods. The results showed that the waste dump contributed to the high levels of nutrients and heavy metals. The dry season mean concentrations were: organic matter (5.28 ± 1.34% or 132,422.4 kg ha−1), K (1.60 ± 0.52 meq per 100 g), N (0.09 ± 0.06% or 2257.2 kg ha−1), Av.P (15.11 ± 7.57 μg g−1), Cd (1.34 ± 0.72 μg g−1), Ni (4.10 ± 1.63 μg g−1) and Pb (38.85 ± 22.18 μg g−1) while the wet season mean concentrations were organic matter (5.46 ± 1.39% or 136,936.8 kg ha−1), K (2.79 ± 0.81 meq per 100 g), N (0.10 ± 0.05% or 2508 kg ha−1), Av.P (9.22 ± 2.69 μg g−1), Cd (1.72 ± 1.22 μg g−1), Ni (14.95 ± 14.94 μg g−1) and Pb (53.50 ± 40.09 μg g−1). There was efficient mineralization process in the area. The texture of soil on the main dumpsite was loamy sand, which suggests that the ground water in the area is susceptible to contamination by surface pollutants. The texture of soil at the control site is sandy loam while sediment has the textural class of sand. Decomposed organic materials and agricultural activities influenced the texture of soils. The soils from the main dump and sediment were slightly alkaline while the control soil was moderately acidic. In both seasons, a significant variation exists (P < 0.05) between the metal concentrations in soil at the main dump and those in the sediments with a positive correlation (r = 0.572149) in the wet season and (r = 0.956647) in the dry season. The presence of liming materials and activities of microorganisms on the waste dump increased the pH of the soils. The accumulation of nutrients results in the luxuriant growth of plants/crops on the waste dump.

Resume

Le niveau de divers parametres et le taux de certains metaux lourds ont ete examines autour d'une decharge qui recoit des dechets solides non traites de toutes origines et sur un site de controle dans Port Harcourt. On a recolte des echantillons de la partie superieure du sol (0 a 15 cm) et des sediments et on les a analyses pour connaitre le pH, la taille des particules, l'azote total, le potassium, le phosphore disponible, la matiere organique, la capacite effective d’echange de cations, le cadmium, le nickel et le plomb, en utilisant des methodes standards. Les resultats ont montre que la decharge contribuait aux taux eleves de nutriments et de metaux lourds. Les concentrations moyennes en saison seche etaient: matieres organiques (5,28 ± 1,34% ou 132.422,4 kg ha−1), K (1,60 ± 0,52 meq per 100 g), N (0,09 ± 0,06% ou 2.257,2 kg ha−1), P disp. (15,11 ± 7,57 μg g−1), Cd (1,34 ± 0,72 μg g−1), Ni (4,10 ± 1,63 μg g−1) et Pb (38,85 ± 22,18 μg g−1), tandis qu'en saison des pluies, les concentrations moyennes etaient pour les matieres organiques (5,46 ± 1,39% ou 136.936,8 kg ha−1), K (2,79 ± 0,81 meq/100 gr), N (0,10 ± 0,05% ou 2.508 kg ha−1), P disp. (9,22 ± 2,69 μg g−1), Cd (1,72 ± 1,22 μg g−1), Ni (14,95 ± 14,94 μg g−1) et Pb (53,50 ± 40,09 μg g−1). Il y a un processus efficace de mineralisation dans la zone. La texture du sol de la decharge principale est un sable riche, ce qui suggere que l'eau souterraine est sensible a la contamination des polluants de surface. La texture du sol du site de controle est un terreau sableux alors que les sediments ont une texture de la classe des sables. Les matieres organiques decomposees et les activites agricoles influencaient la texture des sols. Les sols de la decharge principale et des sediments etaient legerement alcalins alors que le sol de controle etait moderement acide. Pendant les deux saisons, il existe une variation significative (P < 0,05) de la concentration du sol en metaux entre la decharge principale et les sediments, avec une correlation positive (r = 0,572149) en saison des pluies et (r = 0,956647) en saison seche. La presence de residus de chaux et l'activite des microorganismes sur la decharge ont augmente le pH des sols. L'accumulation de nutriments a comme consequence la croissance luxuriante des plantes et des cultures sur la decharge.

Victor O. T. Omuaru

Papers

Soil quality around a solid waste dumpsite in Port Harcourt, Nigeria