EVALUATION OF BORON IN SELECTED AQUATIC WEEDS AS FEED OR FOOD

Francis Olawale Abulude, Adesanya Wakilu Olarenwaju, Mary Omofolarin Ogunkoya
Department of General Studies, Federal College of Agriculture, Akure, Nigeria

ABSTRACT

The nutritional values of foods especially green leaves vary a great deal, depending on the types or variety of plant and growing condition. The aim of this work was to evaluate the boron content of selected aquatic weeds found in Nigeria. Carmine method was employed in the analysis. From the analytical result, it was observed that there were differences (57–81 mg 100^-1g DM) in the values obtained. Comparing our results with pacific vegetables there were variability which might be due to the analytical method used, the soil and water contents and geographical origin. It could be concluded that these aquatic weeds might be good sources of boron for animals and humans.

Key words: boron, aquatic weeds, food standard agency advice, boron supplement, strogen.

INTRODUCTION

Aquatic weeds have important effects on the utilization of water both for agriculture and recreational purpose. Loss caused by aquatic weeds can be measured in terms of reduced crop yield, diseases that afflict humans, interference with fishing and navigation. Although aquatic weeds cause many economic problems they are known to have many beneficial uses [1].

Boron is one of the elements found in existence. This element are known to be useful for the health development of plants, man and animals.

Boron is a naturally occurring element in the environment, boron is combined with oxygen and other element in compounds called borates. Borates are widely found in nature, and are present in oceans, sedimentary rocks, coal, shale, and some soils [10,11]. It enters the environment mainly from the weathering of boron containing rocks, from in the form of boric acid vapour and from volcanic and other geothermal activities. These include the use of borate – containing fertilizers and herbicides, the burning of plant based products such as wood, coal, or oil and the release of waste from borate mining and processing. Borates also reach the environment due to the use of borates and per borates in the home and industry, through leaching from treated woods or paper, and from sewage and sewage sludge disposal borates dissolved in the water can absorb unto, and desorbs from the many different surfaces which can be found in rivers, and streams. Borates are also absorbed into soil particles. The degree of adsorption depends upon the type of soil. Plant can accumulate boron, which is necessary for plant growth.  Boron occurs at different concentrations in soil, water or air. Boron accumulates to different degrees in aquatic and terrestrial plants and animals, but does not increase in concentration through the food chain. Humans are exposed to boron from their diet, from drinking water, and from consumer products. Ingestion could also be from the soil or air.

There is insufficient toxicity data for humans. A tolerable intake of boron has been established based on animal data [6]. In Nigeria anti-nutritional evaluation such as phytate, phytate phosphorous and valuable minerals have been determined on aquatic weeds by Abulude [1]. But there is a lack information on boron content in the specific weeds.  So it was decided to check a concentrate on the boron content of the weeds. The results of this analysis are published in this work. The result is meant to enrich and supplement previous work on aquatic weeds. It is hoped that it would provide valuable contribution to existing nutrition data.

MATERIALS AND METHODS

The aquatic plant weeds were collected at the Federal College of Agriculture, Akure Ondo State, Nigeria on the shore of the dam in August 2007. The weeds under consideration are depicted in Table 1 and Figures 1 and 2.

No picture
1. Hydrolea palastric	2. Sphenoclea zeylanica	3. Melastomastrum capitatum

4. Eclipta alba	5. Neptunia oleracea	6. Heterotis rotundifolia

7. Nymphaea lotus	8. Polygonum lanigerium	9. Pista stratiotes

10. Pycreus lanceolatus	11. Kyllingia bulbosa	12. Ludwigia hyssopifolia

13. Ludwigia abyssinica	14. Alternanthera pungens	15. Melochia corchonifolia

16. Clappertonia ficifolia	17. Eichhorinia natans	18. Cyperus iria

19. Ipomoea aquatica	20. Diplazium sammatii

Sample collection
In the selected area, twenty-two samples were collected and identified [2]. The plant were cleared to removed dirts and then washed in tap water and distilled water several times. The leaves were separated from the plants, washed again with distilled water and allowed to drain, and then oven dried at 100°C for 24 h. They were then ground in Kenwood blender, sieved (2 mm) and stored in airtight containers prior to analysis.

Sample preparation and determination of boron
A stock solution of standard boric acid was prepared by dissolving 0.5716 g of highly purified boric acid (analytical grade) in 1 l distilled water in a standard flash. Several standards of 5–50 mg 100 g^-1 were prepared by stepwise dilution. 2 ml of each of the standards was diluted by a factor of 20 and 2 ml of each of the diluted sample solution was analyzed for the boron content as follows: 2 ml of the diluted sample was pipetted into separate 25 ml conical flash. Two drops of concentrated HCl was added to each flash (to eliminate interference) followed by the addition of 10 ml conc. H₂SO₄. The flask was swirled and the mixture was then cooled down. After cooling, 2 ml of carmine reagent (0.5 gL^-1) manufactured by BAH (Chemicals Ltd, Poole England) was added to each flask and swirled. They were then left for 45 min for colour development. These were put in cuvettes and their absorbance read in a spectrophotometer Model 634 Varian Sense at wave length of 585 nm.

Blanks of the distilled water were carried through the entire analysis. Concentrated sulphuric acid was used to set the spectrophotometer at zero (to take care of any contribution from the acid) [3]. Determination were in triplicate. Statistical analysis was performed using SPSS for windows 10.0.

Each sample (0.5 g) was dry ashed in a muffle furnace with a temperature of 550°C for 2–4 h (depending on the sample). The ashed sample was dissolved in a little quantity of distilled water, filtered and made up to 50 ml using distilled.

RESULTS AND DISCUSSION

The boron contents of aquatic weeds analyzed varied between 57 and 81 mg 100g^-1 DM (Table 2) the values were either the same or surpass the ones (30–90 mg 100 g^-1) recorded for vegetables grown in the Pacific communities [4] and boron in soil, sample, plant materials, composts, manure, irrigation water and nutrient solution [3].

The concentration of boron found in the aquatic weeds might depend on the interaction of many factors, the main ones being environmental or generic. These include the quality of water, type of soil, the plants grown, or species and other factors [3].

The differences in the contents of the aquatic weeds selected and those in the literature may be due to the geographical origin, the soil content of boron and analytical methods employed by different authors. However, since we humans and animals consume a varied diet obtained from many geographical areas in Nigeria, it is unlikely that boron deficiency in the soil and water in a few areas will cause boron deficient in Nigeria diets. Individual intake will vary considerably about the calculated mean, depending on the amount of protein in the diet and in particular on the amount of boron rich foods, which are eaten.

Food sources of boron include green vegetables, fruit and nuts. One should be able to get all the boron needed from one's daily diet. Taking high doses of boron for long periods of time may reduce fertility in man [7]. According to Food Standard Agency [7] it is advisable to eat a varied and balanced diet to get all boron needed. But it is a good idea not to take too much, because it could be harmful. Taking 6 mg or less of boron supplement a day is unlikely to cause any harm. Boron enhances the body’s ability to absorb Ca, Cu and Mg. It may also promote beneficial levels of ostrogen and testosterone in healthy post menopausal woman and help convert vitamin D to its active for, supporting the absorption of calcium. It has also been shown to be beneficial for bone repair and arthritis relief [8].

Boron is used in pyrotechnics and flares to produce green colours. Boron as been used in some rockets as an ignition sources [9]. When humans consume large amounts of boron – containing food, the boron contents in their bodies may rise to levels that can cause health problems. Boron can infect the stomach, liver, kidneys and brains and can eventually lead to death. When exposed to smell amounts of boron takes place, irritation of the nose, throat or eyes may occur. Eating meat or fish will not increase the boron concentrations in one's body as boron does not accumulate with the tissues of animals. Animals are likely to suffer from nose irritation when they breathe in boron. When animals are exposed to boron during pregnancy their off springs may suffer from birth defects or delayed development [5].

CONCLUSIONS

Aquatic weeds have important effects on the utilization of water both for agriculture and recreational purpose.
One of elements founded in these plants is boron. It may be useful for the health development of plants, animals and man. But boron may create also some kinds of threats, mainly for man.
This paper presents data on boron concentration in selected aquatic weeds, which  can be used as feed or food.
The concentration of boron found in aquatic weeds depend on the interaction of many factors.
The boron contents of aquatic weeds analyzed is either the same or surpass the ones recorded for vegetables grown in Pacific communities.
These data can provide valuable contribution to existing nutrition data.

REFERENCES

1. Abulude F.O., 2005. Nutritional evaluation of aquatic weeds in Nigeria. Electr. J. Environ. Agric. Food Chem. 4(1), 835–840.

2. Akobundu I.O., Agyakwa C.W., 1998. A hand book of West African weeds. I.I.T.A, Ibadan,  Nigeria.

3. Asaolu S.S., 1995. Modification of carmine method for the determination of boron in soil, sample, plant materials, composts, manure, irrigation water and nutrient solution. Afric. J. Sci. Technol. Ser. B, 7(2), 4–6.

4. Barley J.M., 1992. The leaves we eat. SPC Handbook.

5. Boron (B) – Chemical properties, healthy and environmental effects. 2007. Lenntech. htm.

6. Boron – Scientific facts in boron. 2007. Green facts. htm.

7. Eat well, be well. 2008. Food Standard Agency. Eat well be well boron. htm.

8. Essence of life LLC. 2002. Boron-Boron. htm.

9. Its elemental – The element boron. 2006.Jefferson Lab. htm.

10. Setten M.J. van, Uijttewaal M.A., de Wijs G.A., de Groot R.A., 2007. Thermodynamic stability of boron: The role of defects and zero point motion. J. Am. Chem. Soc. 129, 2458–2465.

11. The economics of boron. 2006. Roskill Information Services, Ltd.

Accepted for print: 16.02.2010

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed 'Discussions' and hyperlinked to the article.