保护牙齿更要保护你——《水中氟化物检测和氟化物添加剂产品安全的基本知识》

DOI：10.1002/opfl.1471

 原文作者：Kip Duchon

原文出处：J Opflow

翻译：阮辰旼

Know the Basics of Water Fluoridation Measurement and Additive Products Safety

水中氟化物检测和氟化物添加剂产品安全的基本知识

The process of water fluoridation—adjusting the fluoride level in drinking water to the recommended level of 0.7 mg/L to improve oral health—has been in place for 75 years. According to the Centers for Disease Control and Prevention (CDC), 72.8% of the US population served by public water systems (PWSs) had fluoridated water in 2016 (www.cdc.gov/oral health). Although fluoridation is simple, effective, and safe, water treatment plant operators will get the best results if they know how to measure fluoride in labs and use proper protective gear to safely handle additives.

对饮用水进行氟化处理已有75年的历史，即将饮用水中的氟化物浓度调整到0.7mg/L的推荐水平以帮助改善口腔健康。根据美国疾病控制和预防中心（CDC）的数据，2016年，由公共供水系统（PWSs）提供服务的美国人口中有72.8%的人喝的都是氟化水。尽管加氟是简单、有效和安全的，但如果水厂的操作人员知道如何在实验室中检测氟化物，并使用适当的保护装置安全地处理氟化物添加剂，就能获得最佳效果。

Fluoride in drinking water at the recommended level of 0.7 mg/L is a small amount. Still, it’s essential to know the correct fluoride level. If the level is too low, the public won’t receive the benefit of improved oral health and reduced tooth decay. If the level is too high, it’s more likely that children could develop enamel fluorosis—a staining of the tooth surface. Best results are achieved when the fluoride level is between 0.6 and 1 mg/L. It’s important to measure the amount of naturally occurring fluoride in the source water to ensure the correct amount of fluoride additive is applied to the drinking water, then verify the correct dosage was applied to the finished water.

The ability to detect and accurately measure the fluoride ion in water is essential to ensuring consumers are obtaining the benefits of fluoridation. To obtain the best operational results, a basic operational analysis should be conducted, as shown in Figure 1 and listed here.

拥有分析以及准确检测水中氟化物浓度的能力，对于确保用户得到氟化水的益处至关重要。为了获得最佳的操作效果，应该执行进行基本的分析操作步骤，如图1所示。

1. Sample the raw water source to determine the amount of existing fluoride in the water. This way, the dosage is calculated to bring the fluoride level to 0.7 mg/L.

2. Verify the fluoride additive concentration by either consulting the manufacturer’s assay or directly measuring the fluoride content of the additive using the testing method defined in the standard AWWA publishes for each additive product: ANSI/AWWA B701 Sodium Fluoride, ANSI/AWWA B702 Sodium Fluorosilicate, and ANSI/AWWA B703 Fluorosilicic Acid.

3. Know the desired dosage and concentration of the fluoride additive to calculate the feed rate and determine the feeder rate.

4. Confirm the finished water concentration is correct by measuring.

The colorimetric and ion-specific electrode (ISE) methods are the most common ways to measure fluoride in water.

1、对原水采样，分析检测原水中存在的氟化物浓度。基于此，计算出要添加多少的氟化物才能满足出厂水0.7 mg/L的要求

2、用于投加到饮用水中的氟化物添加剂的浓度，可以通过咨询供应商的产品规格，或通过美国自来水工程师学会为每种类型添加剂产品制定的检测分析标准方法对氟化物添加剂的浓度进行测定。这些标准方法包括ANSI/AWWA B701氟化钠、ANSI/AWWA B702氟硅酸钠，以及ANSI/AWWA B703氟硅酸。

3、确定了所需要的氟化物目标浓度和所投加的氟化物添加剂的浓度后，计算并确定应用于生产的投加率。

4、通过检测，确定出厂水的氟化物浓度是正确的。

Colorimetric Method. The colorimetric method (method 4500-D in Standard Methods for the Examination of Water and Wastewater, available at www. awwa.org/store) is the simplest, relying on an indicator solution called SPADNS (short for “sulfanilic acid azochromotrop”). SPADNS forms a “color lake” in the sample, which is depleted as higher levels of fluoride are measured.

A colorimeter uses a light-emitting diode (LED) source, and the detector measures the amount of light absorbed, indicating the amount of fluoride in the sample. The colorimeter is calibrated using a “zero” fluoride blank and a prepared 1-mg/L standard. Then the user measures the fluoride in the water by comparing the measured light absorbance of the sample with the zero and 1-mg/L standards. The fluoride concentration is proportional to the amount of light absorbance in the range of 0 to 1.4 mg/L. Colorimetric measurement isn’t suitable for fluoride concentrations above 1.4 mg/L, according to Standard Methods. Figure 2 shows a commonly used colorimeter and ampules with premeasured reagent.

Although the colorimetric analytical method is the most common way to measure fluoride, it isn’t always the best method. Several interfering substances, plus water color and turbidity, can result in inaccurate measurement. Standard Methods specifies sample preparation using a reflux distillation with sulfuric acid as a distillation reagent. Distillation converts the fluoride to a fluorosilicic acid or hydrogen fluoride, allowing a correct colorimetric measurement without interference.

Operators should take at least one refluxed split sample monthly to compare with no sample preparation. This is a way to confirm that direct measurement of fluoride without reflux preparation yields the same result. However, colorimetric fluoride measurement is often chosen for its simplicity, and many operators who rely on it aren’t willing to include this sample-preparation step. As a result, there’s potential for inaccurate fluoride measurement by relying on the colorimetric method without validating that the water being tested doesn’t have an interfering substance.

The colorimetric method can also have problems obtaining good results because of other issues, such as zero fluoride and reference fluoride standards for test calibration, incorrect calibration of the colorimeter, residue on the testing cuvette or ampule, improper handling of the sample, and temperature variation. True deionized water and a freshly prepared reference standard are needed for instrument calibration. Natural waters have some amount of fluoride; using a blank with a small amount of fluoride will result in an incorrect calibration of the colorimeter.

The best practice is to purchase deionized reagent-grade water for test calibration. Reference standards normally have a shelf life and need to be replaced once the standard expires or the accuracy of the test method is less reliable. Once references for the zero fluoride blank and the 1-mg/L standard are prepared, they can be reused for a week before a new reference will need to be prepared. The colorimeter should be recalibrated at least once a day using the reference standards—preferably once per shift if it’s used multiple times during a day.

Other problems that can interfere with test accuracy involve the sample. The testing cuvette or ampule used for testing must be clean, with no residue, water drops, scratches, or chips. It’s important to ensure the reference standards and the sample to be measured are equilibrated to the same temperature.

比色法。 最简单操作的比色法是《水和废水检验标准方法》中的方法4500-D，依靠磺胺酸偶氮变色剂（SPADNS）作为指示剂。加入的SPADNS会在样品中形成一个“色湖”，当测量氟化物的浓度较高时，“色湖”中的颜色会被耗尽。

色度计是使用发光二极管（LED）光源，通过检测器测量吸收的光量，表征显示样品中的氟化物浓度。色度计使用不含氟化物的“零”空白样品和配置好的1 mg/L氟化物浓度的标准样品进行校准。然后，用户通过将测得的样品的吸光率与空白和1 mg/L的标准样品的吸光率进行比较来计算出水中的氟化物浓度。氟化物浓度与0~1.4 mg/L浓度范围内的光吸收量成正比。根据标准方法，比色法不适合于氟化物浓度超过1.4 mg/L的情况。图2显示了一个常用的比色计和预先配置的试剂的安瓿瓶。

尽管比色分析法是测量氟化物浓度最常用的方法，但它并不总是最佳的方法。一些干扰物质，加上水本身的颜色和浊度，会导致测量不准确。《水和废水检验标准方法》规定了样品的制备采用回流蒸馏法，以硫酸作为蒸馏试剂。蒸馏将氟化物转化为氟硅酸或氟化氢，使比色法测量不受干扰。

操作人员应每月至少取一个回流蒸馏法的样品，与未经过回流蒸馏的原始样品的情况进行比较。这是确定样品不经回流蒸馏制备就直接测量氟化物浓度，是否会得到相同结果的一种方法。然而，选择比色法测量氟化物的原因通常就是因为其操作简单，许多依赖这个方法的操作者并不愿意包括这个样品回流蒸馏的准备步骤。因此，在没有验证被测的样品水是否存在干扰物质的情况下，依靠比色法有可能导致氟化物浓度测量的不准确。

比色法也可能因为其他因素而无法获得良好的检测结果，这些因素例如用于校准的空白样品和标准氟化物样本、比色计的校准不正确、比色皿或安瓿瓶上有残留物、样品处理不当，以及温度变化等。仪器校准需要真正的去离子水和新制备的标准品样本。天然水中含有一定量的氟化物，如果使用含有少量氟化物的空白水样品会导致色度计的校准不正确。

最好的做法是购买去离子试剂级别的水用于校准。参考标准通常是保质期，一旦标准过期或测试方法的准确性不可靠，就需要更换。一旦配制好零氟化物的空白样品和1 mg/L的标准样品，它们可以被重复使用一周，此后需要再配制新的样品。色度计应该每天至少用标准样品重新校准一次，如果在一天内需要多次使用，最好每个检测班次都要校准一次。

ISE Method. The ISE method (method 4500-C in Standard Methods) was developed in the 1930s and is similar to the pH electrode. As shown in Figure 3, a fluoride electrode employs a lanthanum fluoride crystal selective to fluoride ions, and the meter measures the ion activity across the crystal membrane. As the fluoride ions diffuse across the crystal membrane, the ions are depleted at the surface of the electrode and must be replenished by mixing the solution. The electrode senses free fluoride ions with respect to the background solution’s ionic activity.

Consequently, it’s necessary to add a total ionic buffer to ensure the background ionic activity is sufficiently different from the fluoride ion activity to improve measurement precision. The ISE method has fewer interferences than the colorimeter method. Potentially interfering substances must be substantially higher in concentration and are unlikely to be encountered in test solutions at those much higher concentrations. Color and turbidity of the water don’t influence the results.

The best practice is to purchase deionized reagent-grade water to be used for test calibration. Reference standards normally have a shelf life and need to be replaced once the standard expires or the accuracy of the test method is less reliable. Once references for the zero fluoride blank and the 1-mg/L standard are prepared, they can be reused for a week before a new reference is needed. The ISE should be recalibrated at least once a day using the reference standards and preferably once a shift if it’s used for multiple shifts.

The ISE method depends on the integrity of the electrode, which can deteriorate over time. Generally, an electrode is usable for six to 10 months. As shown in Figure 4, the integrity can be easily tested by checking its potential over a one-magnitude ion concentration. Use a 1-mg/L and a 10-mg/L standard, then set the meter to read electrical potential rather than fluoride concentration. A good electrode will have a 56-mV potential difference between the 1- and 10-mg/L standards. For routine operational testing, an electrode with a potential difference of 51–52 mV is often sufficient, but better tolerance to 56-mV potential will produce more accurate results.

离子选择电极法（ISE） 。 ISE法（《水和废水检验标准方法》中的4500-C方法）是在20世纪30年代开发的，与pH电极法相似。如图3所示，氟化物电极采用了对氟化物离子有选择性的氟化镧晶体，分析仪测量穿过晶体膜的离子活性。当氟化物离子扩散穿过晶体膜时，离子在电极表面被消耗，必须通过混合溶液来补充。电极即感应自由氟化物离子与背景溶液的离子活性之间的关系。

因此，有必要加入一个总的离子缓冲溶液，以确保背景离子活性与氟化物离子活性之间有足够的差异，从而得以提高测量精度。ISE方法和比色计方法相比干扰更少。因为如果要引发干扰，潜在的干扰物质的浓度必须高得多，但这种浓度高得多的情况在测试溶液中不太可能遇到。而且水的颜色和浊度不影响结果。

最好的做法是购买去离子试剂级的水用于测试校准。参考标准通常有保质期，一旦配制好零氟化物的空白样品和1 mg/L的标准样品，它们可以被重复使用一周，此后需要再配制新的样品。色度计应该每天至少用标准样品重新校准一次，如果在一天内需要多次使用，最好每个检测班次都要校准一次。

Like other additives used at a water treatment facility, water fluoridation additive products require operators to use personal protective equipment (PPE) to reduce the potential for exposure. Hazards related to material handling include acid burns to skin and eyes with fluorosilicic acid and inhalation of dust when handling dry crystalline salts.

The best reference for safe handling practices is the safety data sheet (SDS) provided by each additive product’s manufacturer. Chemical companies must provide an SDS for each product that poses a safety risk for personnel exposure. Each SDS must describe the product and hazards and provide recommended PPE to reduce exposure risk. The SDS must be reviewed and updated by the issuing entity at least once every three years and within one year if it’s recognized that new information about the product is needed.

与水处理过程中使用的其他药剂一样，氟化物添加药剂产品也要求操作人员使用个人防护设备（PPE）以减少与药剂直接接触的可能性。与该药剂本身有关的危害包括氟硅酸对皮肤和眼睛的酸灼伤，以及处理干燥结晶盐时误吸入粉尘。

安全的操作方法的最佳参考来源，是每个化学药剂产品的供应商提供的安全数据表（SDS）。化学品供应商必须为每一种与操作人员接触有安全风险的产品提供安全数据表（SDS）。每个SDS必须描述产品和其危害，并提供建议的个人防护设备以减少暴露风险。安全数据表必须由发布单位至少每三年审查和更新一次，如果确认需要更新关于产品的信息，则必须在一年内进行审查和更新。

Fluorosilicic acid is strong, but it’s diluted in an aqueous solution with a content of approximately 25 percent fluorosilicic acid and 75 percent water. The AWWA standard for fluorosilicic acid specifies a diluted aqueous solution to balance the consideration of having a higher acid content to reduce the cost of transporting water during delivery, with the consideration of a lower acid content to reduce personnel exposure to a strong acid. This solution blend results in an aqueous solution that reduces the potential for acid burns to the body. Having a lower-concentration aqueous solution allows the PPE to be simplified to a rubber apron, long-sleeve gauntlet rubber gloves, rubber boots, safety goggles, and a face shield. Typical cost for these items is less than $100 per operator.

氟硅酸是强酸，但它被稀释在水溶液中，其浓度约为25%的氟硅酸和75%的水。美国自来水工程师协会AWWA的氟硅酸标准规定了其稀释水溶液的规格，以平衡考虑具有较高的酸浓度以减少输送过程中的过多水造成的成本，同时也考虑到了较低的酸浓度以减少人员对强酸的接触。这种稀释后的混合溶液可以减少人体被酸灼伤的可能性。有了低浓度的混合水溶液，个人防护设备就可以简化为橡胶围裙、长袖高筒橡胶手套、橡胶靴、安全护目镜和面罩。这些物品的一般成本是每个操作员不到100美元。

A respirator isn’t required when handling fluorosilicic acid unless a firefighter is actively responding to a fire. Fluorosilicic acid releases a small quantity of hydrogen fluoride gas, which is volatile at room temperature, but the content of hydrogen fluoride gas is less than 1 percent, so the release rate is minimal. Even if there was a massive release of fluorosilicic acid from a tank rupture, the amount of potential hydrogen fluoride to evaporate would result in an exposure below a personnel exposure threshold.

操作氟硅酸时不需要佩戴呼吸器，除非是消防员正在处理火灾。氟硅酸会释放少量的氟化氢气体，在室温下容易挥发，但氟化氢气体的浓度不到1%，所以释放率极低。即使储罐破裂导致氟硅酸大量释放，潜在的氟化氢蒸发量也会在操作人员的接触阈值以下。

One question that’s occasionally raised is whether hazmat protection is required for handling fluorosilicic acid. Hazmat protection is necessary only for emergency first responders, and it normally includes a Gore-Tex coat and pants that are certified for fluorosilicic acid, along with acid-safe gloves, boots, goggles, and face shield. The cost for hazmat protection will exceed $800 per person. If a water facility believes the presence of another water additive product warrants hazmat protection, that protection may be suitable for fluorosilicic acid as well, but it would need to be certified for exposure to fluorosilicic acid in addition to the other water additive product.

偶尔会有一个问题被提及，即处理氟硅酸是否需要佩戴防毒面具。危险品保护只有在紧急情况下才有必要，通常包括经认证适用于氟硅酸的Gore-Tex外套和裤子，以及防酸手套、靴子、护目镜和面罩，而上述危险品防护的费用将超过每人800美元。如果供水企业认为操作环境中存在另一种具有危害性的药剂产品，就需要进行危化品保护。这种保护装备可能也适用于氟硅酸，但除了需要满足其他应当防护的药剂外，还需要针对氟硅酸进行暴露认证。

Sodium fluoride and sodium fluorosilicate crystalline salts have a different exposure consideration. Although AWWA standards have a granulation sieve requirement to minimize small particulate content, like with all salt products, a small amount of dusting can be expected. Releasing a small quantity of fine dusting crystals could potentially result in inhalation exposure. The use of an air-purifying respirator with a particulate rating from the National Institute for Occupational Safety is sufficient personnel protection. An air-purifying respirator filters atmospheric air, and the particulate filtering provides sufficient protection for handling fluoride additive salts. A self-contained breathing apparatus respirator relying on a tank or independent air supply from outside the room isn’t necessary for handling dry fluoride additive products unless they’re used for fighting a fire in a room. Each operator using an air-purifying respirator should get an annual medical assessment for respirator use. This standard test is conducted in a medical office to ensure a person’s lungs can inhale through a restricted orifice. In addition to a respirator, safety goggles should be worn to protect the eyes from dust. This is often achieved with a respirator integrated with goggles. Gloves protect the hands from cuts, and protective overalls reduce dust contact with clothing. Equipping an operator with PPE for the dry additive products costs less than $100 per person.

氟化钠和氟硅酸钠结晶盐都应被考虑到有不同的接触可能性。尽管AWWA的标准中有一个关于造粒筛的要求，以尽量减少小颗粒的含量，但与所有的盐类产品一样，可以预见到会有少量的粉尘。少量的细小粉尘晶体就有可能导致吸入性接触。使用具有国家职业安全研究所规定的微粒等级的空气净化呼吸器就可以提供足够的人员保护。空气净化呼吸器可以过滤空气，微粒过滤功能可以为拦截氟化物的粉尘提供足够的保护。在处理干燥的氟化物添加剂产品时，依靠空气罐或来自房间外的独立空气供应的自给式呼吸器是没有必要的，除非它们被用于房间内的灭火。每个使用空气净化呼吸器的操作者都应该每年接受一次使用呼吸器的医疗评估。这个标准测试是在医务室进行的，以确保一个人的肺部能够适用通过受限的孔口进行呼吸。除了呼吸器，还应该佩戴安全护目镜以保护眼睛不受灰尘影响。这通常是通过与护目镜结合的呼吸器实现的。手套可以保护双手不被割伤，保护性工作服并可以减少灰尘与衣服的接触。为操作人员配备针对干式添加剂产品的个人防护设备，每人的费用不到100美元。