The authors have declared that no competing interests exist.
This study was conducted to investigate the concentration of three heavy metals; iron, chromium and lead in surface water and plant (
Studies on heavy metal pollution of rivers, lakes, fish and sediments have become a major environmental focus in recent decades because they are one of the most serious pollutants in our natural environment due to their toxicity and persistence
Water pollution occurs when unwanted materials (with potentials to threaten human and other natural systems) find their way into rivers, lakes, wells, streams, boreholes or even reserved fresh water in homes and industries
Rivers are by far the cheapest form of water supply compared to other sources like groundwater and seawater desalination. Meeting water quality expectations for streams and rivers is required to protect drinking water resources, encourage recreational activities and provide a good environment for fish and wildlife
This study was conducted to measure the quality of surface waters of Epie Creek with respect to its total metal concentrations. The Epie creek is located within latitude 5˚23'N, 5˚30'N, and Longitude 6˚58'E, 7˚04'E. It traverses through the stretch of Yenagoa (Igbogene axis) to government house (Okutukutu axis), being one of the major essential surface waters in Bayelsa State. The creek is connected to Ikoli and Taylor creeks. Also, the creek serves as a recipient channel for domestic, commercial and poorly managed industrial wastes, while the water is often used for drinking, bathing, recreational and transportation activities. Heavy metal concentrations in the water were compared with those of
The aim of this study is to evaluate the level of heavy metal contamination of water from Epie creek, especially those emanating at points close to waste dumpsites. The study also aims to determine the level of bioaccumulated trace/heavy metals within different sections (leaves, stems and roots) of
Solutions and reagents used include: distilled water, 37% hydrochloric acid (Sigma-Aldrich Chemicals, USA), 65% nitric acid (Riedel-De Haen, Germany).
Flame atomic absorption spectrophotometer (Model: GBC Avanta Ver. 2.02/AA6600), analytical weighing balance (Model: Mettler AE200), hot plate (Model: Corning PC-351), Soil sieve (Model: Endecotts Ltd - stainless steel with 2mm mesh and brass frame).
Study was conducted along the stretch of Epie Creek, from Igbogene to Okutukutu axis of Yenagoa City. Yenagoa metropolis with latitude 5˚23'N and 5˚30'N, and Longitude 6˚58'E and 7˚04'E is located in Bayelsa State, within the south-south region of the oil-rich Niger Delta zone of Nigeria.
Three replicate water samples were randomly collected from six locations along the Epie Creek. Surface waters were directly collected from the superficial layer into sampling containers. The sites were: up-Igbogene (control) (latitude 05.0386, longitude 06.4033); Igbogene (latitude 05.0255, longitude 06.3996); Akenfa (latitude 05.0019, longitude 06.3787); Agudama (latitude 04.9791, longitude 06.3675); Edepie (latitude 04.9616, longitude 06.3660); and Okutukutu axis (latitude 04.9543, longitude 06.3448). The sampling stations were selected based on their proximity to effluent discharge points in which waste dump sites were used as point sources of pollution along the river, while up-Igbogene axis was sampled as control. The grass species were found sprouting within the water environment but at close proximity to the river embankments. From each of the field locations, three replicate grass samples were collected.
Samples were collected in the dry season month of December 2017. The water samples were collected from the sampling stations in clean, sterilized 250 mL plastic bottles. They were then acidified with 5 mL concentrated nitric acid and transported to the laboratory for heavy metal analysis. In the field, the containers were severally rinsed with habitat water at each sampling point prior to collection.
Each sample was collected by submerging the receiving container into the river at about 100 mm to 300 mm below the surface with the open end aligned against the flow direction of water current. Similarly, the plant (
All laboratory wares were washed with laboratory detergent, soaked in 10% hydrochloric acid solution overnight, thoroughly rinsed in distilled water, and then dried at 85oC. Exactly 100 mL of unfiltered water was strained through whatmann filter paper, transferred into a 150 mL glass beaker, before adding 5 mL of concentrated nitric acid solution. Afterwards, the acidified water was evaporated to near-dryness on a hot plate. A further 5 mL of concentrated nitric acid solution was added before the sample mixture was continuously heated for 15 minutes. Sample was concentrated to about 5 mL before leaving it to cool at room temperature. Thereafter, the acid digest was filtered into 100 mL volumetric flask and the volume made up to mark with distilled water. The filtration step aids in the removal of silicate and other insoluble materials prior to the aspiration of acid extracts for Pb, Cr, and Fe analysis on the atomic absorption spectrophotometer (AAS). Instrument detection limits were 0.02 mg/L, 0.006 mg/L and 0.09 mg/L for Pb, Cr and Fe respectively. The solution was stored in 125 mL polypropylene bottle and aspirated through the nebulizer unit of the instrument. Concentrations of the respective metals were reported in mg/l units
The plant samples were isolated into their leaf, stem and root sections. All the plant parts were washed with distilled water to remove dirt, dust, and other contaminants. Furthermore, the vegetation samples were washed with distilled water and dried at room temperature (22°C to 25°C) before further subjecting them to oven-drying at 60˚C. The dried plant parts were crushed, powdered and homogenized. The powdered samples were stored in polyethylene sampling bags for further processing. Subsequently, a muffle furnace was used to dry-ash the plant samples. Five grams of each dry-ash sample was weighed into a conical flask. Each of the weighed samples was mixed with 10 mL of 1 N hydrochloric acid (HCl) and 10 mL of 1 N nitric acid (HNO3). A mixture of the ash solution was predigested at about 50˚C on a hot plate. Heating continued until white fumes evolved, resulting in a clear brown-colored solution. The heat was further intensified to 120oC for few minutes until sample was adequately concentrated. Afterwards, the cooled ash solution was filtered and made up to mark in 50 mL volumetric flask using distilled water. Filtrates were made through whatmann No. 1 filter paper and collected into clean and sterilized polypropylene vials. Subsequently, the filtered sample (ash) solutions were aspirated into the atomic absorption spectrophotometer (AAS) and the concentrations of test elements such as lead (Pb), iron (Fe), and chromium (Cr) were determined at wavelengths of 217.0, 248.3 and 357.90 nm respectively. Subsequently, concentrations were recorded in mg/kg units
The concentrations of Pb, Cr and Fe in the different sample matrices were determined using FAAS (GBC Avanta PM, A6600, Australia). The operational condition of equipment is provided in
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Pb | 1.00 | 217.0 | 5.0 | 2.0 | 10.0 | 0.5 | 0.02 |
Cr | 0.2 | 357.9 | 6.0 | 2.0 | 10.0 | 0.5 | 0.006 |
Fe | 0.2 | 372.0 | 7.0 | 2.0 | 10.0 | 5.0 | 0.09 |
In order to determine the association and variation between test metals in surface waters and vegetation of Epie Creek, descriptive statistical analysis was carried out using statistical package for social science (SPSS) version 20. Data was expressed as mean ± standard deviation. The range (minimum and maximum) of the values obtained across the sampling points was also presented. One way analysis of variance (ANOVA) was used to show significant variation at P = 0.05. Where significant variation occurred, Waller-Duncan statistics was used to compare mean values of each test parameter under investigation. Heavy metal distribution in water and vegetation was correlated using Spearman’s rho correlation matrix.
The concentrations of chromium (Cr), lead (Pb) and iron (Fe) in the water and plant (cupscale grass) samples from Epie creek (up-Igbogene (control)) and the other five sample locations (Igbogene, Akenfa, Agudama, Edepie and Okutukutu) are presented in
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4.05±0.06b | ND | ND |
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5.06±0.04c | ND | ND |
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3.42±0.06a | ND | ND |
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4.05±0.04b | ND | ND |
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12.06±0.06e | ND | ND |
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5.44±0.05d | ND | ND |
Data is expressed as mean ± standard error; different letters along the column indicate significant variation (p < 0.05) according to Duncan statistics. Also, ND represents non-detection.
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638.07 ± 2.17f | ND | 3.19 ± 0.14h |
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295.13 ± 7.40ab | ND | 0.95 ± 0.10de |
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5,010.43 ± 96.11j | ND | 3.07 ± 0.10h |
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1,012.85 ± 23.83g | ND | 1.59 ± 0.11f |
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492.57 ± 12.37cde | ND | 0.45 ± 0.04bc |
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9,233.13 ± 38.25l | ND | 7.26 ± 0.19j |
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601.37 ± 11.45ef | 0.21 ± 0.02b | 1.11 ± 0.08e |
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408.93 ± 8.58bc | 0.34 ± 0.03c | 0.21 ± 0.03ab |
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2,399.30 ± 29.31h | ND | 4.74 ± 0.25c |
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469.50 ± 22.53cd | ND | 0.25 ± 0.02ab |
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298.13 ± 6.93ab | ND | ND |
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9,423.17 ± 48.55m | ND | 8.83 ± 0.36k |
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365.53 ± 13.33bc | ND | 1.20 ± 0.06e |
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196.63 ± 5.21a | ND | ND |
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7,122.73 ± 76.74k | ND | ND |
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564.90 ± 17.54def | ND | 0.70 ± 0.09cd |
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288.53 ± 16.58ab | ND | ND |
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3,993.87 ± 96.11i | ND | 3.04 ± 0.13g |
Data is expressed as mean ± standard error; different letters along the column indicate significant variation (p < 0.05) according to Duncan statistics. Also, ND represents non-detection.
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3.42 – 12.06 | 1.0 | 196.63 – 9,423.17 | 425.0 |
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ND | 0.1 | <0.006 – 8.83 | 0.10 |
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ND | 0.05 | <0.02 – 0.34 | 0.30 |
Note: ND represents non-detection. Chromium ND = 0.006 mg/l, Lead ND = 0.02 mg/l.
The result shows a wide range of concentrations of the selected heavy metals. The concentrations of iron (Fe) in mg/L are: 4.05 ± 0.06, 5.06 ± 0.04, 3.42 ± 0.06, 4.05 ± 0.04, 12.06 ± 0.06 and 5.44 ± 0.05 respectively for up-Igbogene (control), Igbogene, Agudama, Akenfa, Edepie and Okutukutu sampling sites. Iron was the most significant mineral concentration across all sample locations while lead and chromium were below the instrument detection limits of 0.02 and 0.006 mg/L respectively. Iron levels exceeded the stipulated WHO permissible limit of 1.0 mg/L. The result obtained from this study showed an increasing level of iron in the surface water environment as compared to the concentration range of 0.32 to 2.52 mg/L that was previously reported
Results obtained for the metals (Cr, Fe and Pb) in water samples were compared with WHO maximum permissible limits. The permissible limits of Cr, Fe and Pb for water according to WHO are 0.1 mg/L, 1.0 mg/L and 0.05 mg/L respectively
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1.000 | ||
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-0.113 |
1.000 | |
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0.700 |
-0.137 |
1.000 |
Correlation is significant at the 0.01 level (2-tailed).
Correlation is significant at the 0.01 level (2-tailed). N=54 (n=3).
The concentrations of Cr, Pb and Fe in the various plant sections; roots, stem and leaves, obtained from all the sample and control locations are presented in
Results indicate that the concentration of iron in vegetation sample was in the order; root > leaf > stem. The study further shows that the concentrations (mg/kg) of lead (Pb) in most of the sample locations and up-Igbogene (control) were below measurable detection limit of the instrument for various parts of the plant (
Results show that the highest concentrations of iron (Fe) and chromium (Cr) were found in the plant roots, followed by the leaves, and lastly the stem across all sampling sites. There was significant difference in the concentration of iron and chromium in the roots, leaves and stem for all sample sites. The concentration of metals in the plant tissues revealed the trend; roots > leaves > stem. This may have resulted from the embedding of roots in soil and direct absorption of minerals from bottom soil which ultimately leads to elevated concentrations. The absorbed minerals are transported to the leaves where they are used for photosynthesis whilst being accumulated in leaves. The stem only allows transfer of minerals from the roots to leaves, leading to decreasing element concentrations in the stem.
The FAO/WHO maximum permissible limit for Fe, Cr and Pb in leafy vegetable is 425.0 mg/kg, 0.10 mg/kg and 0.3 mg/kg respectively
The data was statistically analyzed using student’s t-test at a 0.05 significance level. There was no basis of statistical correlation for samples where lead and chromium concentrations were reportedly below measurable detection limit of the instrument at 0.02 mg/l and 0.006 mg/l respectively.
Iron concentrations ranged from 291.44 mg/kg to 4,967.55 mg/kg, showing significant variation (p < 0.05) among the various locations apart from stem samples collected from Akenfa axis and leaf samples from Igbogene axis (p > 0.05) (
Lead concentrations ranged from <0.02 mg/kg to 0.34 mg/kg. Akenfa leaf and stem samples of
Chromium concentrations ranged between <0.006 mg/kg to 8.83 mg/kg. Apart from samples of Akenfa stem and Edepie leaf which depicted no significant difference (p > 0.05), all other cupscale grass samples showed marked significant differences (p < 0.05) across the various field locations of Epie creek (
The mean concentrations highlighted in
In comparison to trace/heavy metal values reported for surface water samples, results of this finding revealed comparatively greater heavy metal distribution in