Weinberg Howard S, Delcomyn Carrie A, Unnam Vasu
Department of Environmental Sciences and Engineering, University of North Carolina at Chapel Hill, Rose Hall, Chapel Hill, North Carolina 27599-7431, USA.
Environ Sci Technol. 2003 Jul 15;37(14):3104-10. doi: 10.1021/es026400z.
Bromate is a contaminant of commercially produced solutions of sodium hypochlorite used for disinfection of drinking water. However, no methodical approach has been carried out in U.S. drinking waters to determine the impact of such contamination on drinking water quality. This study utilized a recently developed method for quantitation of bromate down to 0.05 microg/L to determine the concentration of bromate present in finished waters that had been chlorinated using hypochlorite. Forty treatment plants throughout the United States using hypochlorite in the disinfection step were selected and the levels of bromate in the water both prior to and following the addition of hypochlorite were measured. The levels of bromate in the hypochlorite feedstock were also measured and together with the dosage information provided by the plants and the amount of free chlorine in the feedstock, it was possible to calculate the theoretical level of bromate that would be imparted to the water. A mass balance was performed to compare the level of bromate in finished drinking water samples to that found in the corresponding hypochlorite solution used for treatment. Additional confirmation of the source of elevated bromate levels was provided by monitoring for an increase in the level of chlorate, a co-contaminant of hypochlorite, atthe same point in the treatment plant where bromate was elevated. This study showed that bromate in hypochlorite-treated finished waters varies across the United States based on the source of the chemical feedstock, which can add as much as 3 microg/L bromate into drinking water. Although this is within the current negotiated industry standard that allows up to 50% of the maximum contaminant level (MCL) for bromate in drinking water to be contributed by hypochlorite, it would be a challenge to meet a tighter standard. Given that distribution costs encourage utilities to purchase chemical feedstocks from local suppliers, utilities in certain regions of the United States may be put at a distinct disadvantage if future lower regulations on bromate levels in finished drinking water are put into place. Moreover, with these contaminant levels it would be almost impossible to lower the maximum permissible contribution to bromate in finished water from hypochlorite to 10% of the MCL, which is the norm for other treatment chemicals. Until this issue is resolved, it will be difficult to justify a lowering of the bromate MCL from its current level of 10 to 5 microg/L or lower.
溴酸盐是商业生产的用于饮用水消毒的次氯酸钠溶液中的一种污染物。然而，美国的饮用水中尚未采用系统的方法来确定这种污染对饮用水质量的影响。本研究采用了一种最近开发的可定量至0.05微克/升溴酸盐的方法，以测定使用次氯酸盐进行氯化处理后的成品水中溴酸盐的浓度。在美国各地选择了40个在消毒步骤中使用次氯酸盐的处理厂，并测量了添加次氯酸盐前后水中溴酸盐的水平。还测量了次氯酸盐原料中溴酸盐的水平，并结合各处理厂提供的投加量信息以及原料中游离氯的含量，就有可能计算出理论上会带入水中的溴酸盐水平。进行了质量平衡分析，以比较成品饮用水样品中溴酸盐的水平与用于处理的相应次氯酸盐溶液中的溴酸盐水平。通过监测在处理厂中溴酸盐含量升高的同一点处次氯酸盐的共污染物氯酸盐含量的增加，进一步证实了溴酸盐含量升高的来源。这项研究表明，在美国，经次氯酸盐处理后的成品水中溴酸盐的含量因化学原料的来源而异，化学原料可向饮用水中添加高达3微克/升的溴酸盐。尽管这在目前行业协商的标准范围内，该标准允许次氯酸盐对饮用水中溴酸盐的最大污染物水平（MCL）贡献高达50%，但要达到更严格的标准将是一项挑战。鉴于配送成本促使公用事业公司从当地供应商购买化学原料，如果未来对成品饮用水中溴酸盐水平实施更严格的规定，美国某些地区的公用事业公司可能会处于明显的劣势。此外，鉴于这些污染物水平，几乎不可能将次氯酸盐对成品水中溴酸盐的最大允许贡献降低至MCL的10%，而这是其他处理化学品的标准。在这个问题得到解决之前，很难证明将溴酸盐的MCL从目前的10微克/升降至5微克/升或更低是合理的。
