Arsenic Concentration of Rice in Bangladesh

　

Hiromi HIRONAKA ¹・Sk.Akhtar Ahmad²

　

Technical Cooperation on Arsenic mitigation programme in Bangladesh

1) Arsenic Concentration of Rice in Bangladesh

　

Hiromi HIRONAKA , Sk.Akhtar Ahmad

　

Summary

　

　

I. Preface

　

In Bangladesh, "Green Revolution" which uses underground water as water for irrigation advanced 20 years before.
The quantity of production of rice increased by leaps and bounds.
Arsenic came to be contained in drink water by change of the oxidization or reduction situation of a ground sewer layer.
The chronic arsenic poisoning by tubewell water has been the national problem.
In the arsenic pollution area, the uneasiness said whether the arsenic concentration of agricultural products is high has surfaced.
Mr. Sk.Akhtar Ahmad visited Fukuoka City Institute for Hygiene and Environment as a study member of JICA for 16 days of 1999/11/15-11/30.

30 sample of rice made-in-Japan was measured as analysis training study. 67 samples which Dr.Sk.Akhtar Ahmad carried was measured as the non-polluting district as control samples of Bangladesh and of arsenic pollution area

II Method

　

1. Sampling Method

1) 21 sample (cleaned rice) collected from the farmhouse of the Jessor prefecture Samta village which is a arsenic pollution ground .

2) 24 samples collected from the producer of the Rajhahi city circumference containing a arsenic pollution area (Threshed rice).

3) 12 samples collected from the kitchen and the market of Dakha and Rajhahi.

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1 1 . Fukuoka City Institute of Hygine and Environmental, Chief Researcher, Trace analysis Section

2　National Institute Physics and Social Medicine, Bangladesh

4) 30 samples that circulates in Fukuoka city collected by annual Inspection by Food Inspector.

1)〜3);sample collected by Akhtar, 4);Collected by food inspector of Fukuoka City.

　

2. Method of Analysis

1. Threshed rice was made rice cleaning with the home rice-cleaning machine for 5 minutes.

5ml of conc. nitric acid and two boil stones are added, it heats at aluminium block heater 130℃ and digested by wet method.

Since it forming, about 1ml of nitric acid is added, and it removes from a block heater, and cools timely at the beginning.

If it stops forming, it will digested at 130℃ for 8 to 16 hours. If liquid is colouring, nitric acid will be added further small quantity and decomposition is continued.

If liquid becomes almost transparent, 1ml of sulphuric acid(conc.) will be added, and it heats several hours to 16 hour at 160 ℃.

It heats until liquid becomes transparent completely and white smoke arises, adding nitric acid a little if needed.
Once, it heats after cooling until white smoke arises again, in order to add 2ml of distilled water and to remove nitric acid completely.

The scalpel rise of the last sample is carried out with distilled water at 10ml, and it is taken as the sample of FIAS-AA.

1) Reagent

60-62% dark nitric-acid: detrimental metal analysis grade(wako)

95+% dark sulfuric-acid:detrimental metal analysis grade(wako)

arsenic Standard Liquid: As1000ppm (JCSS)

NaBH4:Hydrogenation boron sodium: reagent grade

35-37% HCl: Hydrochloric Acid: Arsenic analysis grade

　2)FIAS-AA analysis conditions

　　Instrument :Perkin Elmer AAnalyst-100

　　　　　　　 +FIAS-100

　　HCL: As 193.7 nm,　2nm Width

　　Carrier gas : Nitrogen

　　Expansion : x2

　　 Recorder　500mv/ Fs

　　Carrier A: 10% (V/V) HCl

　　Carrier B: 0.5% NaBH₄ in 0.05% NaOH

　

　　 Sample Rice 1.0g

　　　　|<--- 5ml HNO₃ conc.

　　 Digestion 130℃

　　　　|<--- 1ml H₂SO₄ conc.

　　 Digestion 160℃

　　　　|<--- 2ml H₂O

　　 Digestion 160℃

　 Fill up to 10ml (Sample for AA)

Scheme1. Flow Chart of As Analysis in Rice

　

III Result and Consideration

Arsenic concentration of rice produced in Bangladesh 1999

The analysis result of the total arsenic concentration of 21 rice samples of Samta produced which is a high-concentration arsenic pollution district was shown in Table-1.

The analysis result of the total arsenic concentration of 41 rice samples, such as the market of Rajhahi and Dacca, was shown in Table-2a and Table-2b as a contrast district of Bangladesh.

The result of arsenic analysis of 29 rice samples produced in Japan in 1998 and 1999 and one calfornia produced rice sample was shown in Table-3.

Those histograms were shown in Fig-1 to Fig-3.

One sample of Samta produced rice which is a arsenic pollution ground was comparatively as high as 0.94 ppm. The significant difference was not seen in an average of rice of the pollution ground and the rice made in Japan. The arsenic concentration of rice of the pollution ground was 2 to 2.5 times other local average value of Bangladesh.

In order to guess the form of arsenic in rice, two sample(SM-16 and SM-17) were digested with the 2N-chloride after cooked with water. Arsenic of only a soluble ingredient is measured, and residue was digested by nitric-acid-sulphuric-acid and total Arsenic were measured. This tries judgment to soluble arsenic (inorganic arsenic) of the form which is decomposed by stomach acid and absorbed within the stomach and intestines, and the form or organic arsenic discharged as stool.

40% - 50% of the total arsenic was arsenic of soluble.

　

IV Conclusion

The arsenic concentration of rice produced in polluted area of Bangladesh was about 0.3 2 to 3 times as much as a non-polluting district. There was no difference As concentration of rice observed between produced in Japan and in polluted area of Bangladesh. The arsenic concentration of rice of Bangladesh is not considered to be the concentration out of which influence comes healthily.

Although some rice contains High Arsenic as 1.0ppm, rice of these pollution district needs to be blended and needs to lower arsenic concentration. Or a high-concentration producer's rice is discriminated and it is thought that it needs to remove from circulation.