Proximate Evaluation of Organic Pollutants in Onion Plants Cultivated Along the Bank of River Jakara Kano State of Nigeria

The paper gave result findings for organic pollutants in onion plants cultivated along the bank of River Jakara Kano State. Samples of onions were purchased and harvested in farms cultivated in the banks of the aforementioned Rivers. Samples of onions were treated and analyzed in National Research and Institute for Chemical Technology (NARICT) Laboratory Zaria, Nigeria. Onion root samples analyzed has six (6) groups of organic pollutantsdetected with various percentage values. They include alkane (decane 10.6%, undecane 9.2%, dimethyl undecane, 2.3%, trimethyldecane 2.2%); alkyne (octadecyne, 1.9%); arene (aromadendrene, 2.3%); alkanol (phytol, 1.0%); fatty acid (hexadecanoic acid, 1.34%, linolenic acid, 1.7%); organosulphur (diphenyl cyclo propyl phenyl sulphoxide, 3.1%). While the onion control samples (collected from river Watari without activity) analyzed, gave one group of organic pollutants that is alkane group, they include docane (9.0%, 20.1%), methyl docane (9.2%, 12.8%), dodecane (4.0%, 8.6%), trimethylundecane (10.4%, 2.6%), octacosane (2.5%, 1.4%) and hexadecane (0.7%, 1.7%). The result of this study indicates that all the samples collected, examined and analyzed for onions (with exception of control samples) have percentage (%) values greater than threshold level recommended by World Health Organization (WHO) and National Environmental Standards and Regulations Enforcement Agency (NESREA), which is unsafe for human consumption.


Introduction
Organic compounds are compounds that contain carbon, usually in combination with elements such as hydrogen, oxygen, nitrogen and sulphur. It is also compounds that consist of long bonds, usually made up of carbon and other elements mostly from living origin. Organic pollution is the term used when large quantity of organic compounds (pollutants) from domestic activities, industrial operations and agricultural processes are discharged into air, soil, water or even plants.
Surface water such as lakes, streams and rivers are important sources of water for various human activities, including agricultural production. These waters are also used as an avenue for dumping wastes which consist of inorganic, organic and microbial pollutants. But, heavy organic concentrations in soil and water are associated with biological and geochemical cycles and are influenced by anthropogenic activities such as agricultural practices, industrial activities and waste disposal methods. Contamination and subsequent pollution of the environment by organic pollutant have become a global concern due to their distribution and effect on the ecosystem.
Researchers like [1] & [2] among others have shown that some common vegetables are capable of accumulating high level of metals and organic compounds from the soil. Certain species of Brassica (cabbage) are hyperaccumulators of organic compounds and heavy metals in the edible tissues [3]. Therefore, people could be at risk of adverse health effects of consuming common vegetable cultivated in contaminated soil and water.
The population mostly affected by organic pollutant toxicity is pregnant women, very young children and aged human [2] & [4]. Neurological disorders, central nervous system destruction and cancers of various body organs are also organic pollutants effects. Low birth weight and mental retardation of newly born children have been reported in some pregnant women ingested with organic chemicals [2] & [5]. Hence, it is important to keep constant monitoring of vegetable plants especially those cultivated and preserved by organic substances.

Justification for the Research
River Jakara got its name from one of the early historic settlements near Dala in the core of Kano city. It geographical characteristics falls between latitudes '8 o 30'N in Wasai village and 8 0 50'N in Yadai village and longitudinally falls between '12 o 5'E and '12 o 19'E. Generally, the entire field along River Jakara is an area used throughout the dry season (over seven months) for cultivation of variety of vegetable crops, which include cabbage, garden egg, carrot, lettuce, spinach, onions, tomatoes, water leaves among others. These vegetables are important part of human food and people eat them raw or cooked. The river receives waste water from industrial, domestic and agricultural activities. Literature research revealed paucity on studies of organic pollutants in vegetables cultivated in this area. That is why this research work is directed to investigate the organic pollutants in plant cultivated in this area using onion as its case study.

Sampling Procedure
Vegetable samples of onion (stem, root and control stem/root samples) are harvested in the morning and evenings for three days consecutively were purchased in farmlands located along River Jakara, Kano State. Consequently, vegetable sample of onions also harvested in River Watari (located Bichi LGA Kano with no industrial and domestic activities but little agricultural activities) in the morning and evening, purchased from farmer along proximate location of the River was used as control.

Sampling Preparation and Extraction Procedure
The sample of vegetables was taken to the laboratory to wash thoroughly with distilled water and later dried. A portion of each sample (previously washed with distilled water and dried) was slashed with knife and pounded in a mortar to paste of its solution by adding de-ionized water. It was soaked for a while before filtering, using whatman0.45 µm filter paper. Each filterate (containing 50cm 3 ) was treated with 50cm 3 of trichloromethane and di-ethylether inside a separatory funnel. Two layers of organic and aqueous solvent were formed after previously shaken for 5 minutes and kept standing on retort stand for 5 minutes to settle. The organic solvent was decanted and concentrated using sodium sulphate to extract the organic compound in each sample, it was then placed in a vial, labeled and refrigerated before proceeding to Gas Chromatography-Mass Spectrometer analysis (GC/MS) [3]. Same procedure was replicated for other samples.

Analysis of the Organic Extracts by GC/MS
The various organic pollutants in labeled vials were taken to NARICT LABORATORY, Zaria, Kaduna State, Nigeria for Gas chromatography/mass spectrometer analysis.
The Gas Chromatography-Mass Spectrometer -QP 2010 Plus Schimadzu Japan Model works on the principle of mixture injected get separated into individual substance when the machine is switched on. The gases are carried through a column with inert gas (such as Helium). As the separated substance emerges from the column opening, they flow into the mass spectrometer. The mass spectrometer identifies the component by mass (Mass/charge ratio) of the analyte molecules [7], [ Table 1; illustrated above depicts mean percentage (%) values of organic pollutants detected in onion root samples, onion shoot samples, onion root control samples, onion shoot control samples. Twenty two (22) organic pollutants were detected with their percentage values of the aforementioned samples. They include decane, undecane, dodecane, dimethyl undecane, trimethyldecane, aromadendrene, paracyclophane, octadecyne, hexadecanoic acid, hexadecane, phytol, linolenic acid, ethyl cycloheptatriene, diphenyl cyclopropyl phenyl sulphoxide, hexyl propyl ester, dimethyl hexanone, bromo octane, ethyl hexyl mercapto acetate, methyl octadecanoate, chlorotetradecane, squalene and octacosane.

Conclusion
The inference reveals that six and five organic groups (onion root and onion shoot samples respectively) of various organic pollutants with their peculiar toxicity were examined and detected while the control samples (onion shoot and onion root samples) gave only a group of organic pollutant (alkane group for control sample of onion root and shoot) whose toxicity is tremendously minimum compared to other group of organic pollutants discovered. The result of this study indicates that all the samples collected, examined and analyzed for onions (with exception of control samples) have percentage (%) values greater than threshold level recommended by World Health Organization (WHO) and National Environmental Standards and Regulations Enforcement Agency (NESREA). This state that human exposure present (for haloalkane, organosulphur among others) at level greater or equal to 0.1% is identified as probable, possible or confirmed human carcinogen by international agency for research on cancer (IARC). Pertaining to control samples predominantly alkane group, the United State Environmental Protection Agency (USEPA) listed alkane as a non-hazardous pollutant with a relatively short half-life, not expected to bioaccumulate [3], [10] & [12].