|Monday, 04 April, 2016, 08 : 00 AM [IST]|
|Dr Priti Amritkar, Anuprita Raichurkar|
Chlorite and chlorate concentrations were found to be well within the limits, but the amount of bromate was found to be alarmingly high. The BARC report claims 27% of the analysed samples exceeded the limits set by WHO 2011 and EU 98/83/EC. The International Agency for Research on Cancer, a WHO body in France, has classified bromate in group B-2 which means “probable human carcinogen.” Hence, considering the safety of public and outcome of the study carried out at BARC, Bureau of Indian Standards (BIS), on July 28, 2015, made it mandatory to test bromate in packaged drinking water under, Amendment No. 8 of IS 14543: 2004.
Let us understand where this bromate ions come from? They do not exist naturally in the water. Seawater, salt water lakes, underground brines are common sources of bromide ions, the naturally occurring form of elemental bromine. On its own, bromide is not hazardous in nature. It does not have any toxic effects on humans, this fact has been stated by the WHO too. Thus, no regulatory limits have been set for discharge of bromide in surface water. However, when water containing bromide is subjected to the disinfection processes like ozonation, chlorination and photo-oxidation, bromate ions are produced.
During ozonation, naturally existing bromide ions disintegrate ozone catalytically, forming hypobromite. It is an intermediate which forms only at high pH values, at lower pH values hypobromous acid is formed. Hypobromite reacts with the excess ozone, ultimately forming bromate. Hypobromous acid, however, does not undergo this reaction. Thus, at low pH values bromate ions are not formed.
In presence of organic matter, hypobromite also forms other brominated organic compounds, such as bromopicrin, mono and dibromoacetic acid, bromoform, dibromoacetonitrile, and cyanogen bromide. Drinking water disinfected with concentrated hypochlorite solutions also form bromate ions due to the presence of bromide in the raw materials used in manufacture of sodium hypochlorite. Bromate ions can also be formed in electrolytically generated hypochlorous acid solutions when the brine contains bromide. Textile industries use powerful oxidisers like bromate salts in permanent wave neutralising solutions and dying. Bromate salts are also used in milling, beer making and baking. Effluents released from these industries, if not treated properly, seep into the ground water, making it contaminated. Once formed, bromate ions are stable, non-volatisable and cannot be removed easily, thus its analytical estimation in drinking water is absolutely imperative.
A good correlation exists between bromide and bromate ion concentrations, suggesting that bromide ions are indispensable to the formation of bromate. The average exposure levels and chemical toxicity of bromate ions is high, but limited methods are available currently for its elimination from the drinking water. It has been suggested that we curtail the hazardous effects of bromate ions by either eliminating bromide ions prior disinfection or removing bromate ions post- disinfection. Precipitation, ion exchange and membrane filtration are some of the methods that can be used to eliminate bromide ions. Bromate levels can be curbed by carrying out ozonation process at low pH or by the use of purification techniques such as activated carbon filtration. Parameters such as pH, ozone dosage, and temperature, play a crucial role in the formation of bromate. Manufacturers of packaged drinking water should take these factors into consideration and optimise these parameters for the disinfection procedures used in the manufacturing process.
Let us also know more about Bureau of Indian Standards (BIS). It is the National Standards Body, under ministry of consumer affairs, food & public distribution, GoI, operating since 1947. BIS operates a product certification scheme in which it grants licences to manufacturers of products covering diverse disciplines from drinking water to electronics. If a manufacturer has BIS certification, he is allowed to use the ISI mark on the product and/ or its packaging. ISI mark signifies quality products which meet the requirement of respective standards. BIS certification is usually on a voluntary basis, but for certain products which are critical for the health of the nation, BIS has made it mandatory. As per the Food Safety and Standards Authority of India (FSSAI) norms, packaged drinking water can be sold only if it has the BIS certification mark. IS 14543 for packaged drinking water has been effective since March 29, 2001. With the news of pesticide residues in certain beverages and products, BIS standards for packaged drinking water have been subjected to amendments in the year 2004 and later in 2008. These amendments incorporated the regulatory limits for these new found harmful substances, increasing the stringency and ultimately ensuring safe drinking water to the people.
Envirocare Labs is one of the first laboratories in the country that is recognised by BIS for carrying out bromate analysis in packaged drinking water. The analysis is based on internationally recognised method – ISO 15061: 2001 (Water quality – Determination of dissolved bromate – Method by Liquid Chromatography of Ions). It is carried out using anion exchange chromatography where the ions are separated on the basis of their affinity towards the positively charged matrix. The matrix has bound anions which are exchanged by the bromate ions. Eluting bromate ions are detected using a conductivity detector with chemical suppression. The method used for bromate testing at the approved lab should be validated in terms of parameters like linearity, specificity, precision and accuracy. Proficiency Tests / Inter-Laboratory Studies should be carried out and the performance of the lab should be with the acceptable Z-scores.
(Dr Amritkar is director, labs, and Raichurkar is technical executive, Envirocare Labs, Thane)