Radiat. Phys. Chem. Vol. 28, No. 3, pp. 281-282, 1986 Int. J. Radiat. Appl. Instrum., Part C Printed in Great Britain. All rights reserved

0146-5724/86 $3.00 + 0.00 Copyright © 1986 Pergamon Journals Ltd

OZONE PLUS RADIATION ON AQUEOUS SOLUTION OF D N A - - A SUGGESTION FOR TREATMENT

OF WASTE WATER

GOURI UNNIKRISHNAN, KAMALA GOPAKUMAR and D. KRISHNAN Division of Radiological Protection, Bhabha Atomic Research Centre, Trombay, Bombay-400 085, India

(Received 1 February 1986)

INTRODUCTION

Radiation can be used in sewage (or waste water) treatment for degrading large molecules as well as for significantly reducing pathogens. The doses used are of the order of megarads. Any agent which would potentiate these radiation effects will help in better efficiency of the treatment or in reducing the total radiation dose (and thus the time of irradiation) for the same required effect.

Miyata et al/~) have reported a reduction in total organic carbon (TOC) in model compounds as a result of irradiation. They reported a tenfold increase in TOC reduction when they bubbled O2 containing 3% ozone through aqueous solutions of dimethyl phthalate, azodyes, phenol or chlorophenol, during ~-irradiation. We used aqueous solution of deoxy- ribonucleic acid (DNA) as a model compound in a similar experiment. This note describes the results.

MATERIALS AND METHODS

Calfthymus DNA (Sigma Chemicals) was used in singly distilled water for all experiments (100/~g/ml i.e. 3 x 10 -4 M). Ozone generator was an electrical spark type apparatus using pure oxygen from an oxygen cylinder. Depending on the oxygen gas flow rate, the ozone content of the gas was 1-3%. A smaller portable version was also used.

Experiments were performed in either of the three methods described below:

(i) Singly distilled water was saturated with ozon- ated oxygen for 30 min. This was then mixed with aqueous solution of DNA to get a final concentration of 3 x 10 -4 M DNA. The resultant 03 concentration w a s 2 x 1 0 -SM.

(ii) Ozone-containing oxygen was passed through 3 x 10-4M aqueous solution of DNA for about 30min. The resulting 03 concentration was 6 x 10-5 M.

(iii) Ozone containing oxygen was bubbled through DNA solution before as well as during the irra- diation. The ozone concentration here was about 1.5 x 10 -6 to 4.5 x 10 -6 M. For ozone bubbling dur-

ing irradiation a portable type ozonating apparatus was used which could only generate small amounts of ozone.

The concentrations given in the results are initial concentrations. The effective concentration will be smaller as seen by the ozone decay with time in aqueous solution.

Ozone content in water or other aqueous solutions was determined by neutral potassium iodide method in which iodide is oxidized to iodine which gives optical absorption at 350 nm32> The concentration of ozone was determined assuming a stoichiometric ratio of 1 : 1 of the potassium iodide reaction ~3) with respect to dissolved 12 in water.

Ozone being highly reactive, its decay with time in water was needed for experiment design. It was seen that 03 decays to less than 5% of its initial value in 3 h; the time for reaching half the concentration being 50 min. This gave a rough estimate of the concen- trations of ozone present during irradiations. Irra- diations were finished within the minimum duration possible, starting from the time of ozonation.

Inorganic phosphate (Pi) was estimated by the Berenblum and Chain method described earlier, ~4) but after preprecipitating DNA by 2N H2S 04. The effect of ozone itself (without radiation) on P~ release from DNA was measured and this was treated as blank reading.

RESULTS AND DISCUSSION

The results of the three concentrations are given in Table 1. The sensitizing factor (SF) was defined as,

SF = Pi released in presence of 03

Pi released without 03

For estimating Pi released, the blank reading with- out irradiation (i.e. zero dose) was subtracted. As can be seen from Table 1, SF is of the order of 1.5--4. It is hoped that continuous ozone bubbling during irradiation at higher concentrations may give a much higher sensitization factor. It is further hoped that the SF may not be reduced for the higher doses

281

282 GOURI UNNIKRISHNAN et al.

Table I. Effect of ozone present during irradiation of aqueous solution of DNA, on inorganic phosphate release

Pi released (M) Sensitization

S. No. Ozone concentration in air in 03 factor

1. 1.5×10 6 t o 4 . 5 × 1 0 6M 8 × 1 0 6 1.24×10 5 1.5 2. 2 x 1 0 5M 3 . 2 2 × t 0 6 6 .4×10 ~ 2 3. 6 × 1 0 SM 3.22× 10 ~ 1.26× 10 ~ 4

DNA concentrat ion=3 x 10 4M (100#g/ml); Gamma dose--100krad; In the first experiment ozone was continuously passed during irradiation; In the second experiment DNA was mixed with ozonated solution before irradiation; In the third, ozone was passed through DNA solution before irradiation. P, measurements are within 10% error; duplicate samples were well below 10%.

of radiation and higher concentrations of solute obtained in an actual application viz. sewage irra- diation.

A significant synergistic effect of radiation and ozone has been found in the reduction of TOC (total organic carbon) of water containing lignin, formic acid, ethylene glycol, azo-dye and phenol which are difficult to degrade by activated sludge treatment. Almost complete reduction can be seen in treatment with ozone and 7 radiat ion)5) This synergistic effect is explained by the conversion of HO2 radicals to OH radicals, which are strong oxidizing species to most of the organic compounds.

H O 2 + 0 3 = O H + 2 0 2

The treatment of waste water using this synergistic effect has been studied in a continuous process at the Takasaki Radiation Chemistry Research Establish- ment. (6)

The synergistic effect of 03 on P~ release (which is indicative of degradation of the macromolecule) seen by us suggests that this could be useful in sewage treatment if field technical problems can be over- come. Sensitization by 03 of Pi release which is a measure of strand breaks in DNA eventually leading

to cell death, indicates 03 may also have a synergistic effect with radiation for cell killing.

However, some practical problems relating to the suggestion contained in this paper can be envisaged. They are: (a) cost-benefit estimation of ozone bub- bling; and this again compared to oxygenation or even simple aeration of the sewage; (b) possibility of production and availability of ozone at the work site. Alternatively, the feasibility of internal ozone prod- uction using u.v. lamps inside the irradiation cham- ber may be investigated.

REFERENCES

1. T. Miya ta , M. Ara i and M. Wash ino , 6th Int. Congress of Radiation Research, Tokyo , 1979 (Abs t rac t No. A-25-4).

2. D. H. Byers and B. E. Sa l tzman, Am. Ind. Hyg. Assoc. J. 1958, 19, 251.

3. S. L~ Kopeynsk i and J. Bufalini , Anal. Chem. 1971, 43, 1126.

4. K. G. K u m a r , N. S. Bhandar i , D. K r i s h n a n and G. U. Kr i shnan , Radiat. Eft. Lett. 1980, 50, 111.

5. M. Takeh i sa and A. S a k u m o t o , Proc. Int. Conf. on Ind. Appl. of Radioisotopes Radiat. Technology, p. 217. I A E A , Vienna, 1982.

6. S. Machi , Radiat. Phys. Chem. 1983, 22, 91.