Trace Metal Risk Assessment in Vegetable Crops Irrigated With Sewage Water and Sludge Along Kubanni River Drainage Basin in Zaria Metropolis, Nigeria
Chapter One
Aim and Objectives
The aim of this study is to investigate the trace metal health status of vegetable crops grown with sewage water along Kubanni River bank, Zaria, Nigeria. This will be achieved by pursuing the following objectives:
- Determination of the physico-chemical parameters of sewage water and sludge from the study area as well as tube-well water, which is also used by the farmers that are not close to the River to grow vegetables as
- Determination of the physico-chemical parameters of the River bank soil on which the vegetable crops are grown with sewage water as well as the soil on which tube well water is used as control.
- Determination of the concentrations of Zn, Ni, Cu, Pb and Cd in sewage water, sludge, soils and vegetables (spinach and lettuce) in the study
- Determination of the same metals in tube-well water, soils and vegetables (spinach and lettuce) in the control
- Assessment of fertilizer capacity of sewage sludge of the study
- Determination of chemical fractionation of Zn, Ni, Cu, Pb, and Cd in sewage sludge and soils in order to assess the mobility/availability of the metal from soils to
- Determination of water and soil contamination risks based on the individual and global trace metal contamination
- Establishment of trace metals pollution status of sewage water, sludge, soils and vegetables (spinach and lettuce) by comparison of results to international limits for trace metals.
CHAPTER TWO
LITERATURE REVIEW
Trace Metals
The term trace metals, trace elements, toxic metals and heavy metals are used interchangeably and this sometimes causes confusion (Jannett et al., 1980; and Thornton et al., 1981). According to USEPA (1984), the heavy metals are oftentimes referred to as trace elements or trace metals. According to Passow et al. (1991), the term heavy metals is not rigidly defined and is generally held to refer to those metals having a density greater than five, about forty (40) elements in all. However, more precisely, IUPAC (2002) defined trace metals as metals found in low concentration, in mass fractions of ppm or less, in some specified sources, e.g. soil, plant, tissue, ground water, etc. Some of these metals may be important trace elements in the nutrition of plants, animals or humans (e.g Zn, Cu, Mn, Cr, Ni and V), while others are known to have negative nutritional effects (e.g. Cd, Pb and Hg); all of these trace metals may cause toxic effects if they occur excessively (Spiegel, 2002).
Trace Metal Pollution of Sewage Water
Sewage or wastewater is the used water supply of a community. It consists of outflow from domestic and industrial premises and run-off from roads. The sewage water is composed of domestic-borne waste such as human excrement, wash water and industrial water-borne wastes like oils, animal and vegetable wastes. It also consists of ground, surface and atmospheric water (Ojeka, 2007).
There is a lot of literature outlining the benefits and risks of using sewage (Furedy and Chowdhury, 1996). Sewage has provided an invaluable input into development. For instance peri-urban aquaculture alone sustains several thousand jobs (Lewcock, 1995). Using sewage for irrigation enables farmers to produce vegetable crops during dry season. For example, in Kano ( Nigeria ) and Hubli Dharwad ( India ), most sewage-bearing streams carry water all year round, thus enabling farmers to cultivate their plots of land even during dry season and sell them at a higher wholesale price (Lewcock, 1995). However, since the wastewater (sewage) is heavily polluted with faecal matter and trace metals there are some risks attributed to its use (Furedy and Chowdhury, 1996). The application of sewage can contaminate agricultural products, externally and internally with coliform bacteria and other pollutants, putting not only the farmers but also the consumers at risk when the produce is eaten raw.
CHAPTER THREE
MATERIALS AND METHODS
List of Apparatus and Equipment
- Conical flask – 125ml, 250ml
- Beaker – 50ml, 100ml
- Volumetric flask – 50ml, 100ml, 250ml, 500ml, 1000ml
- Measuring cylinder – 10ml, 100ml
- Plastic bottles for samples and digests – 50ml, 120ml
- Plastic jerry can for samples – 0 litres
- Plastic jerry can for distilled and deionized water – 25 litres
- Polythene bags
- Big bowls for washing
- Plastic buckets
- Reagent bottles
- Funnels – small and big ones
- Stainless steel knives
CHAPTER FOUR
RESULTS AND DISCUSSION
QUALITY ASSURANCE
The validity of the digestion procedures used for sample treatment and the precision and accuracy of the AAS analysis were tested by spiking experiment. The mean percentage recoveries of metals used to spike water, sewage sludge, soil and vegetable samples are presented in Table 4.1. For sewage and tube-well water samples, the mean percentage recoveries of metals ranged from 87.1+0.2 – 95.7+0.5 and 79.2+0.2-95.5+0.3, respectively while mean percentage recoveries of meals in soil and sewage sludge samples varied from 86.4+0.2 – 96.2+0.4 and 88.7+0.5 – 96.7+0.4, respectively. For spinach and lettuce, the recovery values ranged from 85.4+0.3 – 92.8+0.2 and 82.4+0.2 – 96.2+0.3, respectively.
CHAPTER FIVE
CONCLUSION AND RECOMMENDATIONS
Conclusion
The findings of this study revealed that the physico-chemical parameters of sewage waters were not suitable for irrigation but that those control area waters (tube-well waters) were suitable for irrigation. Trace metal contents were generally more in study areas and thus, it can be concluded that the study areas received more pollution load of trace metals than the control areas. Trace metal contents in the sewage sludge have not accumulated beyond the permissible limits as recommended by EU. The soils from the study area were contaminated with the trace metals. However, there was an increase in the trace metal contents in the vegetables harvested from sewage water-irrigated soils as compared to tube-well water- irrigated ones. The levels of Cd, Pb and Ni in the vegetables of the study area exceeded the permissible limits of metals and are, therefore, not fit for human consumption. The study further showed that growing vegetables in sewage water containing variable amounts of trace metals led to increase in concentration of trace metals in the soils and vegetation. The results show that the distribution profile of the metals in the four environmental compartments studied for study areas was as follows: sewage sludge > soil > vegetation > sewage water. In all of the samples analysed Zn had the highest mean values relative to other metals followed in some cases by Cu and in other cases by Ni, while Cd had the lowest values. Therefore, Zn was the most prevalent metal in the samples while Cd was the least.
Recommendations
Since irrigation with sewage water or wastewater is an attractive solution to the problem of both wastewater disposal and the scarcity of irrigation water, soil, plant and water quality monitoring and evaluation should periodically be carried out in order to prevent potential health hazards to consumers of vegetables from such areas. As such, alternative source of irrigation water should be explored like sinking of enough tube-wells in the area through government and non-governmental aid, so as to minimize the extent of trace metal contamination to the soils and vegetation in turn. The use of sewage sludge as fertilizer should be monitored to ensure that the trace metal content do not pose threat to safety of the vegetables that will be grown with it.
REFERENCES
- Abdel-hady, B. A. (2007). Compare the Effect of Polluted and River Nile Irrigation water on Content of Heavy Metals of some Soil and Plant. Research Journal of Agricultural and Boilogical Science, 3 (4), 287-294.
- Abdullahi, M. S., Uzairu, A., Harrison, G. F. S., Balarabe, M. L., Okunola, O. J. (2008). Comparative study of tomatoes and onions from irrigated farmlands on the bank of River Challawa, Kano, Nigeria. International Journal of Environ.mental Research, 2 (1), 65 – 70.
- Adakole, J. O. (1995). The Effects of Pollution on a Stretch of River Kubanni ,Zaria . MSc. Thesis, Department of Biological sciences, Ahmadu Bello University, Zaria, Nigeria, p. 48.
- Ademoroti, C. M. A. (1979). Studies on Physico-chemical method of waste water treatment. Ph.D. Thesis, University of London, pp. 59 – 84.
- Ademoroti, C.M.A. (1996). Standard Method for Water and Effluents Analysis. 1st Edn.,Mareh prints and Consultancy, Jova Akpobore, Ugbowo, Benin, Nigeria, p. 56.
- Agbenin, J.O. (1995). Laboratory Manual for Soil and Plant Analysis. Department of Soil Science, Ahmadu Bello University, Zaria, Nigeria, pp. 13-29.
- Akan, J. C., Abdulrahaman, F. I., Damari, G. A. and Ogugbuaja, V. O. (2008). Physico- chemical determination of pollutants in wastewater and vegetable samples along the Jakara wastewater channel Kano metropolis, Kano state, Nigeria. European Journal of Scientific Research, 23 (1), 122 – 133.
- Alabaster, J. S. and Lloyd, R. (1980). Water Quality for Fish, 2nd Edn. London, Butterworthn, pp. 56-58.
