Heavy Metal Contamination of soils, stream-sediments, natural waters and agricultural plants in Pb-Zn Mining localities in Enyigba, southeastern Nigeria. Smart C. Obiora Department of Geology, University of Nigeria, Nsukka, Nigeria ([email protected]; [email protected]) Anthony Chukwu Department of Geology and Exploration Geophysics, Ebonyi State University, Abakaliki, Nigeria ([email protected]) Theophilus C. Davies Faculty of Natural Sciences, Mangosuthu University of Technology, Umlazi/Durban, South Africa ([email protected]) Abstract. Field and geochemical studies on the soils, stream-sediments, agricultural plants and natural waters in the Pb-Zn mining localities in Enyigba community in southeastern Nigeria reveal that the immediate environment close to the mines have been adversely contaminated by the heavy metals associated with the minerals recovered from the mines. Comparison of the data on the soils and the stream-sediments with the Canadian Environmental quality guideline for agricultural soils and the computation of geoaccumulation indices and enrichment factors indicate they have been contaminated and enriched in various degrees by Pb, Zn, Cd and Fe while the stream-sediments are contaminated and enriched by Pb, Cd, Cu and Mn. All the agricultural plants (food crops and grasses), with the exception of a yam tuber, contain Pb above the WHO guideline. The lemon grasses appear to be excellent accumulators of Pb as they contain 242 to 464 times the guideline of 0.4 mg/kg. Abnormal concentrations of either Zn or Cd were also recorded in a good number of the food crops and grasses, namely: cocoyam tuber, pumpkin leaf (locally, ‘ugu’ leaf, cassava leaves, lemon grasses, and potato tubers. The concentrations of Pb in all the water samples, except one from a borehole, are abnormal. These findings call for immediate remediation plan, as well as enlightenment of the miners and the local community on the dangers of exposure to these contaminants. Keywords. Heavy metals, contamination, Pb-Zn mining, soils/stream-sediments, agricultural plants, natural waters, Enyigba, Nigeria. 1 Introduction Pb-Zn mineralization is prominent in the Enyigba community which is geologically located within the Lower Benue rift, southeastern Nigeria (politically, in Ebonyi State of Nigeria). The Pb-Zn ores occur in veins within slightly metamorphosed Albian sedimentary rocks which are mainly black slates (Obiora and Umeji, 2004) in an essentially NE-SW trending belt within the Benue rift. The ores are often associated with saline groundwater mineralization and igneous rocks in this belt. The mines in Enyigba community are located within Lat. 6° 10´ 40´´N to 6° 11´55´´N and Long. 8° 08´ E to 8° 09´E. The terrain is generally flat-lying with occasional small hills on which the mines are commonly located. The first recorded production of Pb-Zn ore was in 1925. Mining ceased in some of the mines during the civil war period (1966 to 1970) (Umeji, 2000). Local mining had, however, continued intermittently within the ‘’abandoned mines’’ after the civil war. The ore minerals are commonly galena (PbS), sphalerite (ZnS) and rarely, chalcopyrite (CuFeS2) and bornite (Cu5FeS4). Azurite [2CuCO3Cu (OH)2], smithsonite(ZnCO3) and cerussite (PbCO3) are some of the products of supergene enrichment. The gangues include siderite (FeCO3), calcite (CaCO3), pyrite (FeS2), marcasite (FeS2) and quartz (SiO2) (Umeji, 2000; Obiora and Umeji, 2004). Mine wastes had accumulated around the mines since the onset of mining; these are dumped in the nearby soils on which farmlands are located. Mine waters are pumped into these nearby farmlands and natural waters such as streams and rivers occur in the vicinity of the mines. Pb- Zn mines are known to be potential sources of harmful trace-elements such as Pb, Zn, As, Cd, Mn, Fe, Se, Sb, Cu, Bi, as well as Acid Mine Drainage, which contaminate the immediate environment of the mines, namely: soils and surface waters (Nikolaidis et al., 2010; Obiora, 2012).These elements can be toxic to plants, animals, and human beings when they are absorbed in abnormal concentrations. There are scarcely records of detailed studies carried out to ascertain the extent of contamination of the environment by the mining activities in Enyigba community. The purpose of this study was to determine the concentrations of tracemetals, including those that are essential in plant and animal nutrition and the potentially harmful traceelements common around Pb-Zn mines, in soils/tailings, agricultural plants (food crops/grasses), natural waters, and stream-sediments around the major abandoned Pb-Zn mines in the Enyigba community in order to assess the level of contamination of the environment surrounding the mines by the potentially harmful elements/heavy metals. 2 Methods 2.1 Field Survey, Sampling media, methods and procedure The field survey was carried out in a scale of 1: 15,000 around three major mines, namely: Ndinwanu Ishiagu Enyigba/Ikwo, Ishiagu Enyigba and Alibaruhu mines. The first consists of three elongate pits which trend N - S to 20° NNE – 200° SSW, with length of 250 m, width between 3 and 6 m and depth up to 10 m. The second consists of four elongate pits, three of which trend essentially 345° NNW – 165° SSE to 325° NNW – 145° SSE, with the fourth trending 30° NNE–210° SSW; the lengths are between 30 and 90 m, with widths of 5 to 8 m and depths up to 15 m. The third mine consists two elongate pits which trend essentially 310° WNW – 130° ESE and 334° NNW – 154° SSE, with lengths of 20 and 50 m, respectively, with width varying from 3 to 7 m, and depth> 10 m. The sampling area around the mines varied from 500 square metres to 500 m x 300 m. The method and procedure adopted in the sampling were according to the ones recommended by Kribek (2013) for the UNESCO-SIDA-sponsored Abandoned Mines Project in Sub-Saharan African countries. The samples collected include soils, stream-sediments, tailings, agricultural plants (food crops and grasses, namely: sweet potatoes- tuber and leaf; cassava- tuber and leaf; cocoyam- tuber; yam -tuber; pumpkin leaf and lemon grass), and natural/mine waters. The samples of soils and tailings were collected from farmlands in the vicinity of the mines (i.e. cultivated land). The sampling points were located at every one second (approximately 16 m) along the Latitudes and Longitudes. The soil samples were mainly collected from the top soils (within 0 – 25 cm depth). A few samples from the sub-soils (within a depth of 50 to 100 cm) at some locations were collected in order to obtain information about enrichment or depletion processes between soil layers The agricultural plants (food crops and grasses) were collected wherever they were encountered adjacent the sampling points for the soils and tailings. The natural water samples were collected along the stream/river channels around the three major mines at distances of, at least, 50 m as long as the channel was not dried up. Three streams sampled include the Ina stream, very close to the Ndinwanu Ishiagu Enyigba/Ikwo mines, ‘Ngele Odicha’, close to Alibaruhu mines and ‘Nwangele Akpara’ stream, close to the Ishiagu Enyigba mines.The only river samples was the Akpara River which is also close to the Ishiagu Enyigba mines. Also, water samples were collected from a borehole located nearby one of the mines, Alibaruhu. The sample bottles (trace-elements free) were thoroughly cleaned and filled with distilled water acidified with 1.0 ml of concentrated HNO3 for some days before the sampling. Two sets of water samples, namely: unfiltered (for anion analyses) and filtered (for cation analyses) water samples were collected. The filtration of the water samples was done in the field by the use of disposable filters. The filtered samples were acidified right in the field by the addition of 1.0 ml of super pure concentrated HNO3 using a syringe. The water samples were poured in 50 -100 ml sample bottles by the use of beakers (100 to 200 ml). To avoid sample contamination, the beakers were cleaned with distilled water and dilute HNO3. Also at every location, the sample bottle and its lid were rinsed several times with water from the sampling site. Water temperature and pH were also measured; Electrical Conductivity (EC) could not be measured in the field All the water samples were kept in a portable cooler filled with ice right in the field and transferred to the refrigerator at the end of each day’s survey. In order to ascertain the level of awareness of the local community about the likely impacts of mining activities on their environment and health, interviews were conducted using standard questionnaire designed for the purpose. Also, data on health status of the miners was obtained through tests using a Resonance magnetic quantum Analyser (produced by a Chinese Company and adopted by Kedi Healthcare Nigeria Ltd. 2.2 Sample preparation and analyses All the samples were air-dried over several days and subsequently homogenized in agate ball mill to analytical fineness (< 0.063 mm). Altogether, 49 samples of soils, 9 of stream-sediments, 7 of tailings, 14 of agricultural plants, including potato,yam, cocoyam and cassava tubers, 12 of agricultural plants, including potato, cassava, pumpkin and lemon grass leaves and 14 samples each of unfiltered and filtered natural/mine waters were analysed geochemically. The analyses were carried out by the Acme Analytical Laboratories (Vancouver) Ltd, Canada, using the Inductively Coupled Plasma, Mass Spectrometer (ICP-MS). Thirty- six (36) trace-metals, including those essential in plant and animal nutrition and the potentially harmful traceelements common around Pb- Zn mines, were analyzed in the samples of soils, stream-sediments and tailings while seventy (70) trace-metals were analyzed in the water samples. Twelve (12) anions, as well as conductivity were also analyzed in the water samples 3 Results and discussion Comparison of the data on the soils, stream-sediments and tailings with international standards such as the Canadian Environmental quality guideline(1999) for agricultural soils indicates that 30 out of 37 soil samples close to the mines have values of Pb (100 to 7075.4 mg/kg) which exceed the guideline of 70 mg/kg while 10 samples have values of Zn (202 to 7379 mg/kg) which is above the guideline of 200 mg/kg; 6 samples contain Cd (1.6 to 20.7 mg/kg) and Cr(104 to 122 mg/kg) exceeding the guidelines of 1.4 mg/kg and 64 mg/kg, respectively; 5 other samples contain S (900 to 19900 mg/kg) and Se (1.2 to 1.3 mg/kg) which are above the guidelines of 500 mg/kg and 1 mg/kg, respectively. For the soil samples away from the mines (12 in number), all, with the exception of one sample contain Pb (88.2 to 4077.4 mg/kg) which is above the guildeline; 5 samples contain Cr (68 to 118 mg/kg) which exceeds the guideline; only one sample each contain Cd (6.1 mg/kg) and Se (1.4 mg/kg) exceeding the guideline. All the 9 samples of the stream-sediments contain Pb (156.2 to > 10,000 mg/kg) far exceeding the 8000 7000 6000 5000 4000 Pb Zn 3000 Cd 2000 1000 Standard (20) 42 TS (19) 41 TS (18) 40 TS (17) 39 TS (16) 38 TS (15) 37 TS (9B) 32 TS (8B) 30 SS (9A) 31 TS (7B) 28 SS (8A) 29 TS (6B) 26 SS (7A) 27 TS (5C) 24 SS (6A) 25 TS (4F) 22 SS (5B) 23 TS (4E) 21 TS (3D) 20 SS (2C) 18 SS (3C) 19 TS (2B) 17 TS (1C) 15 TS (1D) 16 SS 0 Figure 1a. Histogram plot of contaminants in soils close to the Ndinwanu Ishiagu Enyigba/Ikwo mines. 8000 7000 6000 5000 Pb 4000 Zn Cd 3000 2000 1000 0 (12A) 33TS (12B) 34 SS (13) 35 TS (14) 36 TS Standard Figure 1b. Histogram plot of contaminants in soils away from the Ndinwanu Ishiagu Enyigba/Ikwo mines. Note reduction in the concentration of the contaminants when compared with Fig.1a. guideline; 6 contain Zn (326 to 685 mg/kg) which is above the guideline; 4 contain Cd (1.7 to 2.3 mg/kg) also above the guideline; 2 samples contain Cr (110 to 149 mg/kg) while three others have values of Se (1.1 to 1.6 mg/kg), all above the guidelines. For the 7 tailings samples, all contain Pb (188.3 to >10,000 mg/kg), 6 contain Zn (394 to 891 mg/kg), 4 contain Cd (1.8 to 2.8 mg/kg), 3 contain S (800, 800, 4700 mg/kg), all exceeding the guidelines for the respective elements. Geoaccumulation indices computed for the soils closer to the mines indicate they are moderately to extremely contaminated by Pb, Zn, and Cd, and moderately by Fe. Enrichment factor shows significant to extremely high enrichment in Pb and significant enrichment in Zn. Conversely, the geoaccumulation indices for soil samples away from the mines indicate they are moderately to extremely contaminated by only Pb and Cd; there is significant to very high enrichment in Pb. The geoaccumulation indices for the stream-sediments also indicate they are heavily contaminated by Pb, heavily to moderately contaminated by Cu and Mn, and moderately to heavily contaminated by Cd. The enrichment factors extremely high enrichment in Pb and moderate enrichment in Cd. All, except one, of the 26 samples of the agricultural plants (food crops and grasses) contain values of Pb (0.45 to 185.74 mg/kg) which exceed the WHO (2002) guideline of 0.4 mg/kg for agricultural plants. That one sample is a yam tuber containing Pb of 0.24 mg/kg. Of all these samples, the lemon grasses were the most enriched (242 to 464 times). 10 of the agricultural plants, namely: cocoyam tuber, pumpkin leaf (locally,’ugu’ leaf), cassava leaves and lemon grasses contain Zn (52.5 to 162.4 mg/kg) which exceed the guideline of 50 mg/kg, with highest value of 162.4 mg/kg recorded in the cassava leaves; 6 samples, including one potato tuber, one pumpkin leaf and 3 lemon grasses contain Cd (0.32 to 0.61 mg/kg) which is above the guideline of 0.2 mg/kg. Values of Pb (0.03 to < 4 ppm) in all the water samples, except the borehole sample (0.003 ppm or 2.9 ppb), exceeded the EU /Canadian guidelines of 0.01ppm or 10µg/l (See Nikolaidis et al, 2010) while four samples from the Ina stream with Pb ( < 4 ppm) exceeded the WHO (2011) guideline of 1.5 ppm or 1.5 mg/l. EC was up to 21900 to 35,600 µS/cm which exceed the EU guideline of 2,500 µS/cm. The water temperature measured in the field was in the range of 28.5 to 39°C while the pH was generally in the range of 4.1 to 6.7. This range of pH is below the EU guideline of 6.5 to 9.5 in Nikolaidis et al (2010) and Canadian guideline (2006) of 6.5 to 8.5. The low pH implies that Acid Mine Drainage has been produced as would be expected. According to the oldest man interviewed (age: 95 years), mining started before he was born. Generally, they said that mining had affected their life style. Government started rehabilitation (filling the pits) in some of the mines when there was quarrel between the local miners. The communities are not involved in rehabilitation activities. Generally, the people have low knowledge of the contamination/pollution of the ecosystem by mining activities. They however, said that crops do not do well close to the mines. They are not aware of human/animal diseases that may be attributed to mining. Figure 2. Histogram plot of contaminants in the streamsediments The test of elemental concentrations in the miners using the Resonance magnetic quantum Analyser revealed elevated concentrations of Pb, Cd and As in the miners. Pb (Food crops) 45 40 35 30 25 20 15 10 5 0 Pb effects of the contamination decrease away from the mines. The stream-sediments have been contaminated and/or enriched by Pb, Cd, Cu and Mn. All the agricultural plants, with the exception of a yam tuber, contain Pb above the WHO guideline. The lemon grasses appear to be excellent accumulators of Pb as they contain 242 to 464 times the guideline of 0.4 mg/kg. A good number of the agricultural plants including cocoyam tuber, pumpkin leaf (locally,’ugu’ leaf), cassava leaves, potato tubers, and lemon grasses contain either Zn or Cd above the recommended limit. Values of Pb (0.03 to < 4 ppm) in all the water samples, except the borehole sample (0.003 ppm or 2.9 ppb), exceeded the EU /Canadian guidelines of 10µg/l or 0.01ppm. Acid Mine Drainage has been produced in the immediate surroundings of the mines. Unfortunately, the miners and the local community are ignorant of the extent of damage to the environment, as well as the health risks posed by the mining activities. The findings in this study call for immediate remediation plan, as well as enlightenment of the miners and the local community on the dangers of exposure to these contaminants. Acknowledgements Figure 3a. Histogram plot of Pb in the agricultural plants References Pb (Plant leaves) 200 180 160 140 120 100 80 60 40 20 0 This study, including the field survey and geochemical analyses, was carried out under the UNESCO-SIDA-sponsored Project on abandoned mines in Sub-Saharan African Countries. Pb Figure 3b. Histogram plot of Pb in agricultural plants showing very high abnormal concentrations in the lemon grasses 4 Conclusions Mining activities which had lasted for over a period of 95 years in Enyigba community has adversely affected the immediate environment surrounding the mines, namely: soils, stream-sediments, agricultural plants (food crops and grasses) and natural waters.The concentrations of Pb, Zn and Cd in the soils are generally above the Canadian guidelines for agricultural soils. Geoaccumulation indices and enrichment factors also indicate that the soils have been contaminated and enriched in various degrees by these heavy metals. The Canadian Environmental Council of Ministers of the Environment (1999) Soil Quality Guidelines for the Protection of Environmental and Human Health, updated 2006. Nikolaidis, C, Zafiriadis, I, Mathioudakis, V, and Constantinids, T, (2010) Heavy metal Pollution Associated with Abandoned Lead-Zinc Mine in the Kirki Region, NE Greece. Bull. Environ. 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