The hazards of chloroform are primarily related to its toxicity and potential for causing health problems. Chloroform is a volatile organic compound that can have several adverse effects, especially upon inhalation or dermal contact. Here are some of the hazards associated with chloroform:
- Toxicity: Chloroform is a toxic substance that can affect the human body upon exposure. It can be harmful if inhaled, ingested, or absorbed through the skin.
- Liver and Kidney Damage: Prolonged or high-level exposure to chloroform can lead to liver and kidney damage.
- Respiratory Irritation: Inhalation of chloroform vapor can irritate the respiratory system, potentially causing coughing, shortness of breath, and chest pain.
- Central Nervous System (CNS) Depressant: Chloroform can act as a depressant on the central nervous system, causing dizziness, headache, drowsiness, and in high concentrations, it can lead to loss of consciousness and even death due to respiratory failure.
- Cardiovascular Effects: High levels of exposure can affect the heart, potentially leading to cardiovascular effects such as palpitations and arrhythmias.
- Carcinogenic Potential: Some studies suggest that chloroform may have carcinogenic properties, although the evidence is not conclusive regarding its potential to cause cancer in humans.
- Reproductive and Developmental Toxicity: There is evidence that chloroform can be harmful to the developing fetus if pregnant women are exposed, and it may also affect fertility in males and females.
Due to these hazards, the use of chloroform is heavily regulated, and it is important to handle it with care, using appropriate safety measures such as ventilation, personal protective equipment, and following proper disposal procedures to minimize the risk of exposure.
Why is chlorine added to tap water?
Chlorine and chlorine compounds are added to tap water because natural water, whether from surface sources (rivers, lakes, and reservoirs) or groundwater, contains small amounts of pathogenic microorganisms and various organic substances. Therefore, it needs to be treated and disinfected to meet drinking water standards. Adding chlorine and chlorine-containing compounds to water is one such disinfection method. The practice of chlorinating water has a history of more than a hundred years both domestically and internationally. Chlorine and chlorine compounds have strong bactericidal properties and have made “outstanding” contributions to controlling intestinal infectious diseases such as cholera and dysentery.
Where does the chloroform in tap water come from?
When chlorine and chlorine compounds are added to water, they react chemically with various impurities, especially organic matter, forming derivatives that number more than three hundred. The impact of these substances on human health has naturally drawn attention. In June 1974, trace amounts of suspected carcinogens, haloalkanes, were detected in the tap water of New Orleans, located on the Mississippi River, sparking widespread concern. Subsequently, the question of whether “chlorinated drinking water causes cancer” led to extensive discussions in Japan, Canada, Germany, and the former Soviet Union.
What are haloalkanes?
Let’s break it down. First, methane, also known as marsh gas, with the molecular formula CH4, is the main component of mine gas in coal mines. The term “halo” refers to the halogen family, which is the second-to-last column on the right side of the periodic table. This family has five elements: fluorine, chlorine, bromine, iodine, and astatine. In haloalkanes, the “alkane” part refers to methane where one or more of its four hydrogen atoms are replaced by one or more halogens.
The main haloalkanes in tap water include chloroform (CHCl3), bromodichloromethane (CHCl2Br), dibromochloromethane (CHClBr2), and carbon tetrachloride (CCl4). How are haloalkanes formed? Chlorine, below fluorine and second in the halogen family, shares the common characteristic of having seven valence electrons, making them strongly electrophilic. Fluorine is the most reactive nonmetal, with chlorine a close second in terms of chemical reactivity and strong oxidizing ability. Chlorine added to water readily reacts with humic substances, methyl ethyl ketone, acetone, ethanol, and acetaldehyde to form chloroform. There is also some residual chlorine in the water, and the content of haloalkanes increases with the amount of free residual chlorine.
Due to the increased ground pollution, water sources in some large Chinese cities often require secondary or even tertiary chlorination to meet drinking water standards, with cumulative chlorine dosages reaching up to 10 mg/L, and free residual chlorine levels at 1 mg/L or more. It is inferred, therefore, that the content of haloalkane substances in tap water will not be too low. According to measurements, the chloroform content in tap water in three Chinese cities is 4.6 to 311 micrograms/L in Beijing, 14.5 to 72.0 micrograms/L in Tianjin, and 24.7 micrograms/L in the Yangpu Water Plant in Shanghai.
The US Congress once directed the EPA to investigate the changes in haloalkane substances during the chlorination process of tap water in 80 cities across the country, as well as the content of haloalkane substances in finished water. The results showed that haloalkanes such as chloroform in tap water far exceeded those in untreated river water.
What is the evidence?
Since there are suspected carcinogens like haloalkanes in tap water, and their content increases with the amount of chlorine added, proving whether they cause cancer requires epidemiological evidence. The United States conducted a survey on cancer mortality rates in 83 counties in Ohio. They divided the drinking water in these counties into two categories: surface water and groundwater. Surface water, due to heavier pollution, requires more chlorination; groundwater is the opposite. The survey found that the chloroform content in all surface water was higher than that in groundwater.
Correspondingly, the total cancer mortality rate among men, as well as the mortality rates for stomach and bladder cancer, in counties drinking surface water were all higher than in those drinking groundwater. The total cancer mortality rate was 6% higher; the Gastric Cancer mortality rate was 19% higher in the first survey and 32% higher in the second; the bladder cancer mortality rate was 19% higher in the first survey and 10% higher in the second. Statistical analysis showed significance for all but the bladder cancer results from the second survey.
Among all haloalkane substances, chloroform is the main suspect for potential carcinogenicity. However, animal carcinogenicity tests with chloroform have produced both negative and positive results. Therefore, it is currently not possible to conclude that chlorinating water will produce carcinogens, but this issue deserves attention and further research.
How to reduce the hazards of chlorine?
After treatment, tap water can generally be consumed without boiling. However, it is still better to heat it to boiling before drinking. Heating the water can cause chlorine and chloroform to evaporate. The evaporation temperature of chloroform is 65°C, and after the water has been boiled for 2 minutes, 99% of the chloroform can evaporate into the air.
Therefore, to prevent the hazards of chloroform, it is best not to drink untreated water. After heating the water to a boil, do not turn off the heat immediately; letting it boil for a few more minutes before turning it off will be more effective. As can be seen, due to the evaporation of chloroform when heated, there is no need to worry about this issue.
