Effects of Cement dust on Vegetation around Sokoto Cement Company

— The heavy metal deposition around Sokoto Cement Company was investigated to the extent of pollution caused by this industry. Eighty eight samples of plants were separately collected from the four directions of the company into polythene bags and brought to the laboratory for further analyses. The sample were digested using Aqua Regia Method, and the Hg, Zn, Cd, Cr, Ni, Pb and Cu contents were determined by (AAS). Data generated were subjected to Analysis of Variance (ANOVA) to depict the differences and the means were separated with the Duncan Multiple Range Test (DMRT), where significant differences occur. It was found that the concentration of each heavy metal decreased with increase in distance from the industry. It was further found that heavy metals contributed differently to the pollution status of the environment with the eastern part impacting most. Mercury was found to be present in high concentrations in all the plant materials. Zn was the least except for the southern part where Pb was the least. Sokoto Cement campany was found to produce the wastes/ dust that pollutes the environment and acacia nilotica can be used as biomonitor.


INTRODUCTION
Air pollutants responsible for vegetation injury and crop yield losses are causing increased concern in the environment (Fuji, 1973). Air pollution has become a major threat to the survival of plants in the industrial areas (Gupta and Mishra, 1994). Rapid industrialization and addition of the toxic substances to the environment are responsible for altering the ecosystem (Mudd and Kozlowski, 1975;Clayton and Clayton, 1982;Niragau and Davidson, 1986).The cement industry also plays a vital role in the imbalances of the environment and produces air pollution hazards (Stern, 1976). In comparison with gaseous air pollutants, many of which are readily recognized as being the cause of injury to various types of vegetation, relatively little is known and limited studies have been carried out on the effects of cement dust pollution on the growth of plants. Reduction 3 18 when they compared dusted and non-dusted forest communities in the vicinity of limestone quarries and processing plants.
Air pollution is a social disease, a disease generated primarily from the activities of man and adversely affecting his health and welfare (Gilette, 1984). Pollution stress can alter plant growth and quality and the effects are often extensive (Sagar et al., 1982). We are facing the fact that in relatively recent times, the total amount and complexity of toxic pollutants in the environment are increasing day by day. Karachi, the most industrialized and largest city in Pakistan, is suffering from heavy cement dust pollution originating from the cement industry. The cement dust is the source of particulate matter deposits on the buildings and plants. Despite these adverse effects, cement is widely used in building and construction works and a key ingredient in concrete products. It is a binding agent that holds sand and other aggregates together in a hard stone like mass.

COLLECTION OF SAMPLES
Eighty eight samples of twigs of Acacia nilotica samples were collected in the vicinity of the factory (between the months of August-October,2011) at interval of 50m from the mill, that is at (11)  Acacia nilotica were choosen as plant sample because the species is found abundant in the study area and is quite tolerant to heat (>50 o C) and air dryness, It is also frost sensitive. These make the plant to withstand different period and accumulate heavy metals. Twigs of A nilotica were collected from different trees in each direction at 50m interval and 1km as control point by using measuring tape, hand glove and stainless steel pen-knife. The plant samples were packed in separately clean polythene bags and were brought to laboratory for analysis.

DIGESTION OF PLANT SAMPLES
Plant samples of A. nilotica were crushed and oven dried at 60 o C. One gram of each crushed sample was weighed into 125ml Erlenmeyer flask, which has been previously sterilized with acid, (Perchloric acid) and thoroughly rinsed with distilled water. The plant samples were subjected to wet digestion as follows; 4ml of perchloric acid, 25ml conc. HNO3 and 2ml conc.H2SO4 were added in a fume hood into each sample contained in the flask. The contents were mixed and heated gently at medium heat on a hot plate under Perchloric acid fume hood until dense white fumes appear. The contents were heated strongly again for a minute and allowed to cool. Then 50ml distilled water was added and allowed to boil for half a minute on the same hot plate at medium heat.
The contents were allowed to cool and each solution was filtered using whatman No 42 filter paper into 100 ml

DETERMINATION OF HEAVY METALS IN PLANT SAMPLES
The digested samples were separately analyzed for Cd, Cr, Pb, Ni, Cu, Zn and Hg by Atomic absorption spectrophotometeric method. The radiation lamp for each heavy metal to be analyzed was placed in a compartment in the AAS and a tiny pipe attached to the machine (Aspirator) was put inside bottle containing the sample and the concentration of the respective heavy metal was read off by the aid of computer system attached to the machine.

DATA ANALYSES
Data generated from the quantification of heavy metals were subjected to descriptive and inferential statistics. Their concentrations were compared with respect to location/site with the use of analysis of variance (ANOVA). The means were separated with the use of Duncan multiple range test (DMRT).The data obtained from the chemical analysis were also subjected to statistical treatment using correlation coefficient matrices. This was carried out in order to establish association and probable source of dispersion or pollution         Jacobson and Hill, (1970). Studies of biochemical changes and pollution effects on the plant metabolism, i.e., reduction in chlorophyll and completely clogged stomates (Ahmed and Qadir, 1975) revealed that these parameters are important in regulating the productivity and also the number of flowers and seeds produced.

IV. RESULTS
Cadmium, chromium, copper, mercury, nickel, lead and zinc that are prominent in cement dust were found to be higher in concentration in the samples analyzed. This indicates the extent to which the soil and vegetation were polluted by the cement dust from the Sokoto cement company. The concentrations of heavy metals are higher in eastern and western part followed by north and least was southern part of the company, the higher concentrations of heavy metals in eastern and western parts was attributed due to the loading of Cement and heavy trucks movement in the east and presence of quarry and production activities in western part of the Company. Ade-Ademilua and Umebese (2007) have pointed out that metal to metal association could cause an increase in concentration of other metal (absent in cement dust) in the polluted soil over time. Forstner (1995) also pointed out that 70% of metals contaminated soils involved two or more metals and the possibility of synergistic effects may be of considerable importance at some heavy metals contaminated sites.
The significant reductions in shoot length and total leaf area observed in the polluted plants have also been reported in the works of Singh and Rao (1981);  and Igbal and shafoeg (1998). The reduction may be due to toxicity of heavy metals which Rout etal., (2000) stated that once inside the cells, the aluminium could inhibit root absorption and growth in both aluminium sensitive and tolerant plants. The significant decrease in vegetative growth of polluted plants may be an indication of a reduction in photosynthesis of polluted plants which could be explained on the bases of quantitative as well as qualitative changes in the incident light available for photosynthesis in cement encrusted leaves (Bohne,1963), interruption in gaseous through stomatal clogging (Darley etal.,1966;Lerman, 1972), reduction in transpiration in terms of the absorption of minerals from soil and inhibition of intracellular processes (Singh and Rao,1981).
The cement dust caused the epidermal cells and stomata of the polluted leaves to become modified .The higher stomata frequency and index in the leaves of the polluted plants indicate morphological modification on the leaves. According to , these may be adaptations for gaseous exchange and transpiration since the surfaces are covered by cement dust.
Studies of the effects of cement-kiln dust deposited on the soils also raised questions. Some investigators reported no harmful effects of cement at levels from 1.5 to 7.5 g/m 2 /day, while others reported that concentrations from 1.0 to 48 g/m 2 /day caused shifts in the soil alkalinity which may be favorable to one crop but harmful to others (Lerman and Darley, 1975) thus confirming the result of this study whose reported higher concentrations of heavy metal in soil samples.On the analytical assessment of some trace metals in soils around the major industrial areas of Northwestern Nigeria and Sokoto Cement Company reported higher mean concentrations of heavy metals: Cd (0.10 ug/g); Cr(83.4 ug/g); Pb(486 ug/g) and Ni(22.9 ug/g). This study also showed higher concentration of heavy metals investigated, the mean values are Cd(16.9mg/l), Cr(15.2mg/l), Pb(8.30mg/l) and Ni(9.03mg/l) which are within the range reported by Abubakar etal., (2006); Birnin Yauri and Argungu (2002). Adejumo et al., (1994) showed that some toxic heavy metals like arsenic (AS), lead (Pb,) nickel (Ni), cobalt (Co), zinc (Zn), copper (Cu) and phosphorus (P) were significantly enriched in the neighbourhood of cement factories in Nigeria. This can lead to reduction of soil fertility, Adejumo et al., (1994), it has also been linked to the damage of dwellings (Perfettini et al., 1989. Deposit of cement dust on roofs can cause microbiological and chemical disintegration of the roofs. Wasserbauer etal., (1998) 3 23 On the basis of this study, it could be said that vegetation around Sokoto Cement Company was found to be affected by cement dust, which might be due to the presence of different toxic pollutants in cement dust. The biological behavior of vegetation e.g A nilotica was found to be highly affected due to the present of different heavy metals found in the twig of the plant. It is clear that the cement dust pollution is an operative ecological factor causing deterioration in the quality of our environment (Shah etal., 1989). It is concluded that the presence of toxic pollutants in cement dust might be responsible for the reduction in vegetation and soil fertility. Traces of toxic metals such as chromium and copper are common in some varieties of Portland cement and are harmful to human beings and other living systems (Omar and Jasim, 1990). The heavy metals present in the cement dust can play an important role in disturbing the various metabolic processes of plant. The growth metabolic processes and yield of winter barley were found to be affected by the Duna cement and lime works (Borka, 1986), in an experiment of six kinds of dust which contained heavy metals introduced under the stand canopy. The dust was collected from zinc, cadmium, aluminum, iron plants, electric power station and the cement plant. The dust was introduced in concentrations of 100, 500, 1000, 2000 and 5000 t Km -2 . The experiment proved that the cement dust brought about changes in the ecosystem. A link between the forest ecosystem under the influence of heavy metals in dust and the effect of these changes on the growth of pine stands was also obtained.
The levels at which the toxic elements were found in both plants and soil sample around the factory in this study showed that they have exceeded regulatory standards, Cd (0.005ug g-1 ); Cr (0.02ug g-1 ); Pb (0.05ug g-1 ) and Ni (0.5ug g-1 ) Fell et al., (2003). It showed that the cement plant is seriously polluting the environment and it confirmed the assertion of Bilen (2010) that cement production is of the main sources of environmental pollution. It also showed that control strategies for prevention of dust release by cement plants have not been implemented in the cement company. Fell et al., (2003) said that in advanced countries, control-strategies for the prevention of dust release by machinery enclosure, local exhaust ventilation, work automation and greater diligence in maintenance of machinery have been implemented, presumably leading to less dust exposure.

VI. CONCLUSION
This research has shown that there is a significant emission of cement dust into the environment around Sokoto Cement Company, up to 1000m distances from the mill in the four cardinal directions. This dusts emitted are capable of posing a serious problem to vegetation and soil fertility even at a distance of 1000m away from the mill. This study has established that higher concentrations of heavy metals both in plant and soil samples (Cd, Cr, Cu, Hg, Pb, Ni and Zn) were obtained in different locations. It could be concluded that vegetation and soil around Sokoto Cement Company were found to be affected by cement dust, which might be due to the presence of different toxic pollutants in cement dust. The biological behavior of vegetation (A nilotica) was found to be highly affected due to the presence of different heavy metals found in the twigs of the plant. It was found that the concentrations of heavy metals were highest in eastern part followed by western then the northern part and the least was southern part of the company. It is clear that the cement dust pollution is an operative ecological factor causing deterioration in the quality of our environment (Shah etal., 1989). I therefore recommend that to safeguard the quality of vegetation around the company, the cement factory management should embark on regular/periodic monitoring of cement dust level in and around the factory environment, and should reduce the dust emission by the use of dust filters.