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Orthotolidine ban in India?

Is there ban on use of orthotolidine reagent for chlorine estimation in drinking water, in India?

Any documentation is welcome and will be very helpful.



1. Response

Dear Ranaji,
I do not think that it is officially banned till date. We noticed mention of orthotolidine kit in literature published in 2009 (NRDWP framework- Annexure IV-A). But we have decided to shift to DPD technology considering risk involved with it, in PHED, Assam.

With regards

Diponkar Bordoloi
Assistant Engineer
Public Health and Engineering Department (PHED)
Guwahati, Assam

2. BAN ON O.T.

Dear Dipokar ji,

Kindly intimate the DPD kits you are planning to introduce in PHED

Amit Kr. Singh,
Govt. of Haryana,
Public Health Engg. Department,
Water Testing Lab,Karnal-132001(haryana)

3. Response

Dear Member,

Use of Azo dyes having orthotolidine is banned in textile, leather and coir industries.

The following website gives the llist of banned amines in India

I do not think that there is a official ban in India as for as water testing is concerned. Many field test kits, available in India, are still based on this test., although it should be mentioned that E Merck kit does not use this amine, Files on details of E Merck test strip and quantitative methods are attached.

Technical information on o-toludine is also attached.


Leela Iyengar


4. Response


The orthotolidine method for residual chlorine estimation in water is more sensitive to lower concentrations of chlorine and is affected by temperature and contact time. The presence of natural colour, turbidity and nitrate interferes with the colour development. The maximum and minimum concentration of residual chlorine that can be measured by this method is 10 mg/l and 0.01 mg/l respectively. Although its’ use is not banned in India but the fact is orthotolidine has been demonstrated to be carcinogenic it is advised to handle the chemical with caution.


5. Orthotolidine


I do not think that the use Orthotolidine reagent is banned in India, as Delhi Jal board,the largest water agency in India has got no any information about the ban , we are still using this reagent , but we always cautioun citizens about the side effects of this chemical , as this is one of the best reagent for checking residual chlorine for the vast (about 10,000 km ) network of pipeline in Delhi and most of them are prone to contamination .

With Regards

Sudarshan Rawat 

Water Quality Analyst

Delhi Jal Board


6. Totally agree with your comment on ortho toludine

I totally agree with your comment, thanks!


Thanks Leela ji, Ayan & Sudarshan

Amit Kr. Singh,
Govt. of Haryana,
Public Health Engg. Department,
Water Testing Lab,Karnal-132001(haryana)

8. Response to ban on O.T.

Dear Sirs,

As far as water testing is concerned, we have not come across any communication regarding ban on Orthotolidine for Chlorine Testing.

We are manufacturers of Water Testing Kits since 1985 and manufacture following products for testing of Residual Chlorine:

  1. Chlorine Test Kit (based on Orthotolidine)
  2. Chlorine Test Kit (based on DPD Tablets) - Probably the only Indian manufacturer of DPD Tablets / DPD Tablet based Kits in India
  3. On-line Automatic Chlorine Analyser (First time in India)

While on the subject, I would like to mention some other related aspects to Orthotolidine issue:

a)      Orthotolidine is a known carcinogenic chemical.  However, for testing of Chlorine, quantity of Orthotolidine required is only about 0.3 to 0.4 mg. per test. Hence, in view of the minute quantity that is used in each testing (and quantity that the user is likely to be exposed to), it is felt, the issue of it being harmful is a bit far-fetched. Ban on its use in Chlorine testing may not be a correct approach. Caution while using (and not ban) may be the right approach, in view of utility and simplicity of the OT based Chlorine test.

b)      On the flipside, there is another aspect. The simple OT based test that is used all over India, measures Total Residual Chlorine (TRC). The Indian Standard for drinking water IS:10500 specifies limit for Chlorine as 0.2 ppm minimum Free Residual Chlorine (FRC). FRC can be measured conveniently by DPD method only. Hence, if Indian Standard is to be followed to the word, we should use DPD method for testing Chlorine. With DPD method, it is possible to measure both FRC, as well as, TRC easily and quickly.


Ravi Savant,

Prerana Laboratories, Prerana House, Near Chhatrapati Bank, Vishal Nagar, Jagtap Dairy, Aundh-Wakad Road, Pune – 411 027.

Tel: 020 27274958, 9371015199


9. Need water testing kits for medical college in Uttar Pradesh


We need water testing kits for medical college.

Please send literature and quotes and also from where we can get it in Uttar Pradesh.

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