Chlorination by-product levels in hot tap water: Significance and variability

Relationship of trihalomethane in drinking water with hypertension and arrhythmia among young and middle-aged adults in Petropavlovsk, Kazakhstan

There are no studies investigating the association of chlorinated drinking water with the risk of cardiovascular diseases (CVDs) among young and middle-aged adults. This study was aimed to assess the associations between trihalomethanes (THMs) in drinking water and the risk of CVDs in in the target group in Petropavlovsk, Kazakhstan. 448 dwellers of Petropavlovsk were asked about their demographic, socioeconomic, lifestyle, behavioural characteristics, and drinking water preferences. THMs exposure was assessed to each participant based on their residence address. We used multivariable logistic regression analysis to assess the risk of CVDs in young and middle-aged adults. The results showed that the risk of hypertension in the adjusted logistic regression model was increased by 68%   and a 2.7-fold   in the second and third THM tertiles, respectively. Participants in the second and third THM exposure tertiles had a 2.3-fold and a 4.8-fold increase in the risk of arrhythmia.

Transformation of Contaminants of Emerging Concern (CECs) during UV-Catalyzed Processes Assisted by Chlorine

Every compound that potentially can be harmful to the environment is called a Contaminant of Emerging Concern (CEC). Compounds classified as CECs may undergo different transformations, especially in the water environment. The intermediates formed in this way are considered to be toxic against living organisms even in trace concentrations. We attempted to identify the intermediates formed during single chlorination and UV-catalyzed processes supported by the action of chlorine and hydrogen peroxide or ozone of selected contaminants of emerging concern. The analysis of post-processing water samples containing benzocaine indicated the formation of seven compound intermediates, while ibuprofen, acridine and β-estradiol samples contained 5, 5, and 3 compound decomposition by-products, respectively. The number and also the concentration of the intermediates decreased with the time of UV irradiation. The toxicity assessment indicated that the UV-catalyzed processes lead to decreased toxicity nature of post-processed water solutions.

Unchartered waters: the unintended impacts of residual chlorine on water quality and biofilms

Disinfection residuals in drinking water protect water quality and public heath by limiting planktonic microbial regrowth during distribution. However, we do not consider the consequences and selective pressures of such residuals on the ubiquitous biofilms that persist on the vast internal surface area of drinking water distribution systems. Using a full scale experimental facility, integrated analyses were applied to determine the physical, chemical and biological impacts of different free chlorine regimes on biofilm characteristics (composition, structure and microbiome) and water quality. Unexpectedly, higher free chlorine concentrations resulted in greater water quality degredation, observable as elevated inorganic loading and greater discolouration (a major cause of water quality complaints and a mask for other failures). High-chlorine concentrations also reduced biofilm cell concentrations but selected for a distinct biofilm bacterial community and inorganic composition, presenting unique risks. The results challenge the assumption that a measurable free chlorine residual necessarily assures drinking water safety.