COMPARATVE STUDIES ON THE HEAVY METAL CONCENTRATION IN LEAF STEM AND ROOT OF CORCHORUS OLITORIUS L. IRRIGATED WITH SEWAGE WATER AND TAP WATER RESPCTIVELY

ABSTRACT

The   level   of  accumulation   of   heavy   chemicals   in  the   leaves,   stem   and   roots   of Corchorusolitorius  seedlings  irrigated  with  sewage  (Sewage  effluent)  and  tap  water  to maturity  respectively  was  investigated.  Prior  to  irrigation,  water  quality  indicators  and physico-chemical  properties  of the two  water  sources  were analysed.  The experiment,  a completely randomized design was carried out in a screen house in the Botanic Garden of the Department of Plant Science and Biotechnology, University of Nigeria, Nsukka and lasted for four months. The results showed that sewage water had higher values of biochemical oxygen demand  (BOD),  chemical  oxygen  demand  (COD),  and  temperature  than  tap  water.  The results  also  showed  that  tap  water  had  higher  values  of  dissolved  oxygen  (DO)  and transparency than sewage water.  The results further showed that sewage water had higher values of the analysed  physico-chemical  properties  than tap water. Again, it showed  that sewage water  enhanced  better seedling growth than tap water. Cadmium,  Mercury, Zinc, Copper,  Lead  and  Arsenic  accumulation  in  the  leaves,  stem  and  roots  were  higher  in seedlings irrigated with sewage water when compared with those irrigated with tap  water. The results further showed that the accumulation of heavy chemicals in the leaves, stem and roots of the seedlings irrigated with both water sources, (Sewage and tap) were higher than the accepted standard of the Federal Environmental Protection Agency (FEPA). Based on the results obtained, it is recommended that continued production of leaf vegetables off-season using  sewage  water  be avoided,  because  of possible  health  hazards  posed  by continued consumption of such vegetables.

CHAPTER ONE

1.1         Introduction

Globally, water has been a major requirement for the growth and development of biotic life. Water has for long exerted strong influence on the choice of place for  human settlement. Of all human activities, agriculture and industrial activities have been identified as the  highest  consumer  of  water  (Nweze  and  Chimboh,  2003).  With  time,  increase  in population and sophisticated  advancements  in man’s  industrial  sectors have resulted     in drastic scarcity of available natural/clean water. Hence, the use of waste water either in the raw state or purified form in agricultural activities, especially in the off season vegetable crop production and ornamentals became imperative for decades in Europe, North America and Australia  (Dolgenet  al.,  2004).  Following  the  success  of  propagating  vegetable  crops, ornamentals and lawn  maintenance,  using waste water, the practice became recognized  in many other countries like India, China, Middle East etc. (Hampet al., 1976).

In the developing countries like Nigeria, Ghana, Cameroun, Togo, waste water is used in  vegetable  production,   especially  in  the  dry  season/off  season.  Waste   water   used includedomestic  waste water and sewage effluent (Nweze and Chimboh,  2003). In Egypt, acute shortage of natural/clean water has resulted in the development of alternative sources of obtaining water for agricultural production. Bashiret al., (2006) reported that in Egypt, due to increase in population and agricultural activities, the use of waste water and sewage effluent has progressively increased particularly in the urban cities. The authors reported that waste water  is deposited  on the  ground  to  enable  its  reclamation  for  further  reuse.  They also

reported the reclamation of about four million m3  and two million m3  water in Cairo  and Alexandria  respectively  and  the salvaged  water  could  be used  to  irrigate  about  300,000 fadama for vegetable production

Many authors have appraised the use of sewage water in vegetable production but did not emphasize the health hazards posed by consuming such vegetables (Dolgenet al., 2004, Bashir et al., 2006, Singh and Agrawal, 2010, Maryam, 2011). Dolgenet al., 2004 reported the  benefits  of  irrigating  agricultural  crops  with  sewage  water  to  include;  provision  of chemical nutrients like nitrogen, phosphorus, boron, manganese, copper and zinc to the crops. Maryam  (2011)  pointed  out that the effects of these  chemical  mineral  nutrients  in rapid growth of vegetables  have stimulated  interest  in  the use of sewage  effluent  in vegetable production.  The  author  further  reported  that  irrigating  vegetables  with  waste  water  of

whatever origin could pose health hazards due to the absorption and accumulation of heavy metals in the produced crop, particularly vegetables.

In the developed countries, with large-scale sewage treatment plant, water  salvaged from  sewage  is properly treated  before  recycling  for various  uses (Batstone  and  Keller,

2003). In the developing  countries,  Imhoff treatment  equipment  in use for sewage  water extraction  have  facilities  that  were  below  international  standard  because  the  tanks  are exposed to the air, while the drying beds and the oxygenated ponds may not be functioning effectively (Llyod, 2000). The type of vegetables produced during off-season using sewage effluent (Water) for water supply varies from one locality to another because of the level of revenue generated.  In the South Eastern Nigeria,  popular vegetables produced during off- season include:Telfairiaoccidentalis,  AmaranthusviridisandCorchorusolitorius, while in the South Southern Nigeria, the most popular off-season vegetable is Taliniumtriangulare. In the Northern states, off-season  vegetables  include Lactucasativum,  Daucuscarota  andBrassica oleracea. These vegetables often appeal to the eyes due to their freshness. They (vegetables) are variously used in preparing delicious foods eaten in restaurants, various eating spots like motor  parks, market, roadsides (Sold by food vendors), Universitycommunities  and in big national and international hotels. Generally, people are ignorant of the source of water with which  these  vegetables  were irrigated.  Reports that sewage  effluent-  irrigated  vegetables absorb and accumulate heavy metals, becomesnecessary that the extent of the  heavy metal accumulation in the edible parts of the vegetables should be made known, with the view of ascertaining the safety of human health. Of  all  the  vegetables  produced  off-season  using  sewage  and  or  waste   water, CorchorusolitoriusLquickly comes to mind and thus is selected for this study, because of its popularity in most diets, particularly in the South Western states of Nigeria.

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